CENTRAL DOGMA OF MOLECULAR BIOLOGY
Reason : In retroviruses, reverse of central dogma occurs.
| A |
If both the assertion and the reason are true and the reason is a correct explanation of the assertion |
|
| B |
If both assertion and reason are true but the reason is not the correct explanation of the assertion |
|
| C |
If the assertion is true but the reason is false |
|
| D |
If both the assertion and reason are false |
Assertion : Central dogma is the flow of information from DNA to mRNA and then decoding the information present in mRNA in the form of protein.
Reason : In retroviruses, reverse of central dogma occurs.
| A |
If both the assertion and the reason are true and the reason is a correct explanation of the assertion |
|
| B |
If both assertion and reason are true but the reason is not the correct explanation of the assertion |
|
| C |
If the assertion is true but the reason is false |
|
| D |
If both the assertion and reason are false |
Answer: B If both assertion and reason are true but the reason is not the correct explanation of the assertion
- Biosynthesis of protein is under direct control of DNA in most cases or else under the control of genetic RNA where DNA is absent. Sequences of bases in a particular segment of a polynucleotide chain will determine the sequence of amino acids in a particular polypeptide.
- The relationship is popularly known as central dogma. Flow of information is one way i.e., from DNA, information is transferred to RNA (mRNA) and from RNA to protein.
- Temin (1970) reported that retroviruses operate a central dogma reverse or teminism inside host cells. Genomic RNA of these viruses first synthesizes DNA through reverse transcription. DNA then transfers information to messenger RNA which takes part in translation of the coded information to form polypeptide.
→ proteins
MOLECULAR CYTOGENETIC TECHNIQUE- (FISH)
| A |
Transfection |
|
| B |
Electroporation |
|
| C |
FISH |
|
| D |
Recombination |
Which of these is not a method for introducing genes into a cell?
| A |
Transfection |
|
| B |
Electroporation |
|
| C |
FISH |
|
| D |
Recombination |
Methods for introducing genes into a cell include, transfection (chemical based), electroporation (physical), infection (viral mediated) and recombination techniques.
| A |
FISH |
|
| B |
PCR |
|
| C |
SSCP |
|
| D |
Karyotyping |
Rapid method of chromosome identification in intersex is:
| A |
FISH |
|
| B |
PCR |
|
| C |
SSCP |
|
| D |
Karyotyping |
A i.e. FISH
FISH, chromosome painting and spectral karyotyping (SKY) are rapid methods of chromosome identificationQ.
Rapid method of chromosome identification in interphase is –
| A |
FISH |
|
| B |
PCR |
|
| C |
SSCP |
|
| D |
Karyotyping |
Rapid method of chromosome identification in interphase is –
| A |
FISH |
|
| B |
PCR |
|
| C |
SSCP |
|
| D |
Karyotyping |
FISH is a cytogenetic technique that can be used to detect the presence or absence of specific DNA sequences (specific gene locus) on chromosomes.
It uses fluorescent probes that bind to only those parts of the chromosome with which they show a high degree of sequence similarity.
Fluorescence microscopy can then be used to find out where the fluorescent probe bound to the chromosome.
FISH can be used for rapid identification of chromosome during interphase.
FISH can be used in metaphase cells to detect specific microdeletions beyond the resolution of routine cytogenetics or identify extra material of unknown origin.
It can also help in cases where it is difficult to determine from routine cytogenetics if a chromosome has a simple deletion or is involved in a subtle or complex rearrangement.
In addition, metaphase FISH can detect some of the specific chromosome rearrangements seen in certain cancers.
RECOMBINANT DNA TECHNOLOGY
| A |
They always yield blunt ends |
|
| B |
They recognize methylated DNA sequence |
|
| C |
They recognize triplet repeats |
|
| D |
They cleave both strands in duplex DNA |
Which of the following statements describing restriction endonucleases is TRUE?
| A |
They always yield blunt ends |
|
| B |
They recognize methylated DNA sequence |
|
| C |
They recognize triplet repeats |
|
| D |
They cleave both strands in duplex DNA |
Restriction endonucleases are produced by prokaryotes for cleaving both strands of foreign DNA.
The host cell’s DNA is not degraded because the recognition sites are specifically methylated.
The endonucleases recognize specific short symmetrical sequences known as palindromes.
These cleavage sites contain two fold rotational symmetry in that the sequence is identical but antiparallel in the complementary strands.
In some cases, single-stranded cohesive ends on each of the complementary strands are produced, while in other cases double-stranded blunt ends are formed.
Modern analysis of DNA structure is highly dependent upon the use of different restriction endonucleases that permit the specific hydrolysis of DNA into large polynucleotides.
| A |
DNA polymerase |
|
| B |
DNA ligase |
|
| C |
DNA topoisomerase |
|
| D |
DNA gyrase |
After digestion by restriction endonucleases DNA strands can be joined again by which of the following enzymes?
| A |
DNA polymerase |
|
| B |
DNA ligase |
|
| C |
DNA topoisomerase |
|
| D |
DNA gyrase |
DNA is cleaved into fragments by restriction endonucleases. After the fragments of DNA have base paired, the ends are covalently joined by the action of DNA ligase.
| A |
Gel electrophoresis |
|
| B |
Agarose gel eletrophoresis |
|
| C |
Paper Chromatography |
|
| D |
High pressure liquid chromatography |
DNA fragments formed by the action of Restriction Endonucleases, are separated by:
| A |
Gel electrophoresis |
|
| B |
Agarose gel eletrophoresis |
|
| C |
Paper Chromatography |
|
| D |
High pressure liquid chromatography |
B i.e. Agarose gel electrophoresis
– Restriction endonuclease (restriction enzyme) makes 2 incisions through sugar phosphate backbone (phospho diester bond) of each strand of ds DNAQ at specific sequence k/a recognition sequences or restriction site. So RE restricts viral (bacteriophage – DNA) replicationQ and protects bacteria (prokaryote) from infection by virusQ.
– RE cuts both strands of double stranded (ds) DNA at specific restriction sites with palindromic (inverse repeat) arrangement; thus producing smaller, manageable fragments with short sequenes and sticky/ blunt endsQ. These restriction fragments can be isolated by agarose gel /polyacrylamide – electrophoresisQ or HPLC.
After digestion by restriction endonucleases the DNA ends can be ligated (joined/ annealed) by ‘ DNA-ligaseQ
In DNA transfer the vectors used from smallest to largest is:
| A |
Cosmids, Plasmids, Bacteriophage |
|
| B |
Plasmids, Bacteriophage, Cosmids |
|
| C |
Bacteriophage, Cosmides, Plasmids |
|
| D |
Cosmids, Bacteriophage, Plasmids |
In DNA transfer the vectors used from smallest to largest is:
| A |
Cosmids, Plasmids, Bacteriophage |
|
| B |
Plasmids, Bacteriophage, Cosmids |
|
| C |
Bacteriophage, Cosmides, Plasmids |
|
| D |
Cosmids, Bacteriophage, Plasmids |
B i.e. Plasmid, bacteriophage, cosmid
* Plasmid is smallest & most commonly used vectors
* 1Kb = 1000 nucleotide long base
|
Vector/ Vehicle- DNA |
DNA insert size (i.e. can accept DNA fragment of) |
|
Plasmid (PBR 322) |
0.01 – 10 kb (smallest)(2 |
|
Bacteriophage (Lambda charon 4A) |
10 -20 kb |
|
Cosmids |
35 – 50 kb (largest)2 |
| A |
Synthesis of DNA |
|
| B |
Extrachromosomal molecule of DNA |
|
| C |
Sequence of DNA |
|
| D |
Small nuclear RNA |
Palindrome is associated with:
| A |
Synthesis of DNA |
|
| B |
Extrachromosomal molecule of DNA |
|
| C |
Sequence of DNA |
|
| D |
Small nuclear RNA |
The exact significance of palindromic DNA is not known, although several functions have been suggested.
Short palindromes may function as recognition sites of DNA for proteins which also have a two-fold rotational symmetry, e.g. lac repressor protein, CRP protein and many bacterial restriction enzymes.
Palindromes may also give structural strength to the transcribed RNA by hydrogen bonding in the hairpin loops. If the palindromic sequences are not perfectly symmetrical, imperfect loops may result.
DNA amplification is done in by all, except:
PGI 06
| A |
Polymerase chain reaction |
|
| B |
Nucleic Acid Sequence Based Amplification |
|
| C |
Ligase chain reaction |
|
| D |
DNA sequencing |
DNA amplification is done in by all, except:
PGI 06
| A |
Polymerase chain reaction |
|
| B |
Nucleic Acid Sequence Based Amplification |
|
| C |
Ligase chain reaction |
|
| D |
DNA sequencing |
Ans. DNA sequencing
Nucleic acid amplification techniques are:
| A |
PCR |
|
| B |
Real time PCR |
|
| C |
DNA Cloning |
|
| D |
Next generation DNA sequencing |
Nucleic acid amplification techniques are:
| A |
PCR |
|
| B |
Real time PCR |
|
| C |
DNA Cloning |
|
| D |
Next generation DNA sequencing |
Ans: a. PCR …, b. Real time ….[Ref Harper 30th/458; Robbins 9th/180; Lippincott 6th/479;Harrison 19th/ 150e-7; http://link. springer. corn]
- Real-time PCR automates the laborious process of amplification by quantitating reaction products for each sample in every
- Cycle.
- There are several methods for amplification (copying) of small numbers of molecules of nucleic acid to readily detectable levels.
- These NAATs include PCR, LCR, strand displacement amplification, and self-sustaining sequence replication.
- The amplified nucleic acid can be detected after the reaction is complete or (in real-time detection) as amplification proceeds. The sensitivity of NAATs is far greater than that of traditional assay methods such as culture.
Real Time PCR
| A |
Multiplication of RNA |
|
| B |
Multiplication of specific segments of DNA |
|
| C |
Multiplication of Proteins |
|
| D |
To know how much amplification of DNA has occurred |
Real Time PCR is used for:
| A |
Multiplication of RNA |
|
| B |
Multiplication of specific segments of DNA |
|
| C |
Multiplication of Proteins |
|
| D |
To know how much amplification of DNA has occurred |
Ans. (d) To know how much amplification of DNA has occured P“F 1,m,etz. 25/e 714, 27/e, p 124; Greenwood 18/e 79
Real Time. PCR
- It is the molecular detection technique that discriminates real time amplification from conventional PCR assays.
- The real-time polymerase chain reaction (PCR) uses fluorescent reporter molecules to monitor the production of amplification products during each cycle of the PCR reaction.
- This combines the DNA amplification and detection steps into one homogeneous assay and obviates the requirement for gel electrophoresis to detect amplification products.
- Its simplicity, specificity, and sensitivity, together with its, more reliable instrumentation, and improved protocols, has made realtime oenLhmark technology for lite ocLuLtion of DNA.
- Real time PCR is extremely useful in medical microbiology, with greatest impact on virology.
| A |
RT PCR |
|
| B |
bDNA assay |
|
| C |
NASBA |
|
| D |
P24 detection |
Which of the following is most sensitive for diagnosis of HIV?
| A |
RT PCR |
|
| B |
bDNA assay |
|
| C |
NASBA |
|
| D |
P24 detection |
Ans. a. RT PCR
Which of the following techniques is based on RNA?
| A |
RT PCR |
|
| B |
Sanger’s technique |
|
| C |
Next generation sequencing |
|
| D |
Western blot |
Which of the following techniques is based on RNA?
| A |
RT PCR |
|
| B |
Sanger’s technique |
|
| C |
Next generation sequencing |
|
| D |
Western blot |
Ans: A. RT PCR
Ref: Harper’s illustrated biochemistry,3Oh ed, pg. 29,457 and Tietz Fundamental of clinical chemistry and molecular diagnostics, Vh ed.
RT-PCR:
- Reverse transcription polymerase chain reaction (RT–PCR) is a laboratory technique combining reverse transcription of RNA into DNA (in this context called complementary DNA or cDNA) and amplification of specific DNA targets using polymerase chain reaction (PCR).
- It is primarily used to measure the amount of a specific RNA. This is achieved by monitoring the amplification reaction using fluorescence, a technique called real-time PCR or quantitative PCR (qPCR). Combined RT-PCR and qPCR are routinely used for analysis of gene expression and quantification of viral RNA in research and clinical settings.
- A method used to quantitate mRNA levels that rely upon a first step of cDNA copying of mRNAs catalysed by reverse transcriptase prior to PCR amplifi cation and quantitation.
Sanger sequencing,
- Also known as the chain termination method, is a technique for DNAsequencing based upon the selective incorporation of chain-terminating dideoxynucleotides (ddNTPs) by DNA polymerase during in vitro DNA replication.
In which of the following, viral load done by Real Time PCR is of no role in investigative procedures?
| A |
Person with hepatitis B on tenofovir therapy |
|
| B | HSV causing temporal encephalitis | |
| C |
BK virus in patient of allograft renal transplant |
|
| D |
CMV PCR in blood of patient of liver transplant |
In which of the following, viral load done by Real Time PCR is of no role in investigative procedures?
| A |
Person with hepatitis B on tenofovir therapy |
|
| B |
HSV causing temporal encephalitis |
|
| C |
BK virus in patient of allograft renal transplant |
|
| D |
CMV PCR in blood of patient of liver transplant |
Ans. B. HSV causing temporal encephalitis
Ref: “Diagnosis ofherpesvirus infections ofthe central nervous system.’, Herpes : the journal of the IHMF I1 Suppl 2 2004, pp. 48A-564.
- The question simply asks in which of the given conditions calculation of Viral load is not required. In HSV causing temporal encephalitis the role of PCR is just to detect HSV DNA and make a diagnosis of the disease.
- There is no role of detection of the viral load copies in the management or diagnosis of the disease.
Best assessment of protein binding regions on a DNA molecule can be done by:
| A |
DNA footprinting |
|
| B |
RT PCR |
|
| C |
Microarray |
|
| D |
Western blotting |
Best assessment of protein binding regions on a DNA molecule can be done by:
| A |
DNA footprinting |
|
| B |
RT PCR |
|
| C |
Microarray |
|
| D |
Western blotting |
Answer-(a) DNA footprinting [Ref: www.biotecharticles.com; www.biologyexams4u.com Lippincott 6th/473]
- DNA footprinting- An in-vitro technique to find out protein binding regions on a DNA molecule. The technique is also called as DNAse I footprinting.Thousands of proteins (enzymes) are interacting with DNA in the nucleus for regulating activities like replication, transcription, translation etc.
- DNA Footprinting is a molecular technique used to identify the specific DNA sequence (binding site) that binds to a protein.
- This technique mainly used to identify the transcription factors which bind to promoter, enhancer or silencer region of gene to regulate its expression. Therefore the regulation of transcript ion of a gene can be studied using this method.
True about ZIKA virus:
| A | Belong to flavivirus | |
| B |
First case detected in 1953 in Nigeria |
|
| C |
RT PCR is useful in diagnosis |
|
| D |
Causes macrocephaly |
True about ZIKA virus:
| A |
Belong to flavivirus |
|
| B |
First case detected in 1953 in Nigeria |
|
| C |
RT PCR is useful in diagnosis |
|
| D |
Causes macrocephaly |
Answer: (a) Belong to flavivirus, (c) RT PCR is useful in diagnosis, (e) May presents with conjunctivitis (Ref: Harrison 19th/1314; www. cdc. gov;www. nytimes. corn]
- It is spread mostly by the bite of an infected Aedes species mosquitoes (A. aegptiand A. albopictus). T
- It can be passed to a pregnant woman to her fetus. Infection during pregnancy can cause certain birth defects..
- Real-time reverse transcription-polymerase chain reaction (RT PCR) testing should be performed on serum collected during the first two weeks after symptom onset.
- There’s no vaccine or specific treatment tor tlw disease. Treatment instead focuses on relieving symptoms and includes rest, rehydration and medications for fever and pain.
- A maculopapular rash, conjunctivitis, myalgia, and arthralgia usually accompany or follow those manifestations.
Difference between Meningitis and Encephalitis
March 2007
| A |
Pentostatin |
|
| B |
Amphotericin B |
|
| C |
Zidovudine |
|
| D |
Clotrimazole |
Drug used to treat Cryptococcal meningitis is:
March 2007
| A |
Pentostatin |
|
| B |
Amphotericin B |
|
| C |
Zidovudine |
|
| D |
Clotrimazole |
Ans. B: Amphotericin B
Cryptococcus neoformans is an encapsulated yeast-like fungus. It causes meningitis, especially as a secondary infection in AIDS patients.
Cryptococcosis that does not affect the central nervous system can be treated with fluconazole alone.
Cryptococcal meningitis should be treated for two weeks with intravenous Amphotericin B and oral flucytosine. Main disadvantage of Amphotericin B includes nephrotoxicity.
September 2009
| A |
H.Influenzae |
|
| B |
N.meningitidis |
|
| C |
Staph.aureus |
|
| D |
Streptococcus pneumoniae |
Most common cause for meningitis in adults:
September 2009
| A |
H.Influenzae |
|
| B |
N.meningitidis |
|
| C |
Staph.aureus |
|
| D |
Streptococcus pneumoniae |
Ans. D: Streptococcus pneumoniae
N. meningitidis accounts for nearly 25% of the cases. Staph.aureus and coagulase negative staphylococci are important causes of meningitis that occurs following neurosurgical procedures.
September 2009
| A |
Histoplasmosis |
|
| B |
Cryptococcus |
|
| C |
Candida albicans |
|
| D |
Coccidiomycosis |
Most common causative agent for meningitis in the immunocompromised patient is:
September 2009
| A |
Histoplasmosis |
|
| B |
Cryptococcus |
|
| C |
Candida albicans |
|
| D |
Coccidiomycosis |
Ans. B: Cryptococcus
In immunocompetent patients, cryptococcal infection is usually asymptomatic, self-limited, and confined to the lungs.
In persons with advanced HIV infection (e.g., those with CD4 counts
In HIV-infected patients, Cryptococcus can infect almost all organs in the body, but most commonly causes meningitis or meningoencephalitis.
| A |
5 days |
|
| B |
7 days |
|
| C |
14 days |
|
| D |
21 days |
Drug treatment is given for how many days in pneumococcal meningitis
| A |
5 days |
|
| B |
7 days |
|
| C |
14 days |
|
| D |
21 days |
Ans. is ‘c’ i.e., 14 days
Recommendations for duration of treatment
- Pneumococcal meningitis —> 10-14 days
- Meningococcal meningitis 5-7 days
- Hib meningitis —> 7-14 days
- Listeria meningitis —> 21 days
How long should a child be isolated after being diagnosed with bacterial meningitis to prevent further transmission?
| A | Till 24 hours after starting antibiotics | |
| B |
Till cultures become negative |
|
| C |
Till antibiotic course is complete |
|
| D |
Till l2hrs alter admission |
How long should a child be isolated after being diagnosed with bacterial meningitis to prevent further transmission?
| A |
Till 24 hours after starting antibiotics |
|
| B |
Till cultures become negative |
|
| C |
Till antibiotic course is complete |
|
| D |
Till l2hrs alter admission |
Ans: A. Till 24 hours after starting antibiotics
Ref: Ghai Essentisl Pediatrics, 8’t’ ed,, pg. 565′ https://www.cdc.gov
Prevention of transmission:
- Droplet precautions for the first 24 hours of antimicrobial therapy is sufficient
types of culture- classification
| A |
Salt mannitol media |
|
| B |
Pike’s media |
|
| C |
Stuart’s media |
|
| D |
Cary Blair media |
An outbreak of streptococcal pharyngitis has occured in a remote village. In order to carry out the epidemiological investigations of the outbreak it is necessary to perform the culture of the throat swab of the patients suffering from the disease. The transport media of choice would be –
| A |
Salt mannitol media |
|
| B |
Pike’s media |
|
| C |
Stuart’s media |
|
| D |
Cary Blair media |
Ans. is ‘b’ i.e., Pike’s media
“For cultures, swabs should be collected under vision from the affected site and either plated immediately or sent to the laboratory in Pike’s medium (blood agar containing crystal violet and sodium azide)”.
Selective media for vibrio –
| A |
TCBS |
|
| B |
Stuart |
|
| C |
Skirrows |
|
| D |
MYPA |
Selective media for vibrio –
| A |
TCBS |
|
| B |
Stuart |
|
| C |
Skirrows |
|
| D |
MYPA |
Ans. is ‘a’ i.e., TCBS
Selective media for N. gonorrhoeae –
| A |
Thayer martin media |
|
| B |
Smith noguchi media |
|
| C |
Proskaur and Bech media |
|
| D |
Bordet gongue, media |
Selective media for N. gonorrhoeae –
| A |
Thayer martin media |
|
| B |
Smith noguchi media |
|
| C |
Proskaur and Bech media |
|
| D |
Bordet gongue, media |
Ans. is ‘a’ i.e., Thayer martin media
All selective media are correctly matched except ‑
| A |
V cholerae – TCBS medium |
|
| B |
Pseudomonas – Cetrimide agar |
|
| C |
M tuberculosis – LJ medium |
|
| D |
Campylobacter – BCYE medium |
All selective media are correctly matched except ‑
| A |
V cholerae – TCBS medium |
|
| B |
Pseudomonas – Cetrimide agar |
|
| C |
M tuberculosis – LJ medium |
|
| D |
Campylobacter – BCYE medium |
Ans. is ‘d’ i.e., Campylobacter – BCYE medium
Selective media for Pseudomonas ‑
| A |
EMJH medium |
|
| B |
PALCAM agar |
|
| C |
PLET medium |
|
| D |
Cetrimide agar |
Selective media for Pseudomonas ‑
| A |
EMJH medium |
|
| B |
PALCAM agar |
|
| C |
PLET medium |
|
| D |
Cetrimide agar |
Ans. is ‘d’ i.e., Cetrimide agar
Transport media for the bacteria shown in the photomicrograph below is ?
| A |
Alkaline peptone water. |
|
| B |
Cary – Blair medium. |
|
| C |
TC BS medium. |
|
| D | None of the above. |
Transport media for the bacteria shown in the photomicrograph below is ?
| A |
Alkaline peptone water. |
|
| B |
Cary – Blair medium. |
|
| C |
TC BS medium. |
|
| D | None of the above. |
Ans:B.)Cary-Blair medium.
The bacteria marked by a black arrow in the photomicrograph is Vibrio Cholera.
Transport media for vibrio cholerae is Cary-Blair medium.
Transport media for fecal specimens
Media appropriate for the transport of fecal specimens that are suspected to contain Shigella, Vibrio cholerae, or Salmonella (including serotype Typhi) specimens are:
1. Cary-Blair transport medium
- High pH (8.4)
- Medium of choice for transport and preservation of V. cholera
- Cary-Blair transport medium can be used to transport many bacterial enteric pathogens, including Shigella, Salmonella, and Vibrio cholerae
2. Amies’and Staurt’s transport media
- Acceptable for Shigella and Salmonella (including ser. Typhi), but they are inferior to Cary-Blair for transport of V. cholerae.
3. Alkaline peptone water
- This medium may be used to transport V. cholerae, but this medium is inferior to Cary-Blair and should be used only when Cary-Blair medium is not available.
- It should not be used if subculture will be delayed more than 6 hours from the time of collection, because other organisms will overgrow vibrios after 6 hours.
4. Buffered glycerol saline (BGS)
- It’s a liquid medium which can be used for Shigella but this transport medium is unsuitable for transport of V. cholerae.
Selective media for TB bacilli is:
| A |
NNN media |
|
| B |
Dorset media |
|
| C |
LJ media |
|
| D |
Nutrient agar |
Selective media for TB bacilli is:
| A |
NNN media |
|
| B |
Dorset media |
|
| C |
LJ media |
|
| D |
Nutrient agar |
Ans. (b) and (c) Dorset media and LJ media
| Solid |
Liquid |
| Lowenstein Jensen media (most widely used) | Dubos contain Tween 80 |
| Dorset egg media | Middle Brook’s |
| Loeffler’s media | Proskauer and Beck’s |
| Pawlowsky media | Sula’s and Sautan |
- Selective agent inhibiting other bacteria in LJ media is Malachite green.
- Human tubercle bacilli do not grow in presence of para-nitrobenzoic acid.
- Traces of fatty acid is toxic for tubercle bacilli in culture media.
- Optimum pH for M. tuberculosis: 6.4-7.0.
Other Options:
NNN media → For Leishmania donovani
Nutrient agar → Simple media
MacConkey media → Differential as well as indicator media for lactose and non-lactose fermenters.
A patient with acute onset of diarrhea comes to emergency. After culture on enriched media, colonies as shown below were visualized. Identify the causative organism:
| A | Vibrio cholera | |
| B |
Salmonella typhi |
|
| C |
Compylolacter jejuni |
|
| D |
E. coli |
A patient with acute onset of diarrhea comes to emergency. After culture on enriched media, colonies as shown below were visualized. Identify the causative organism:
| A |
Vibrio cholera |
|
| B |
Salmonella typhi |
|
| C |
Compylolacter jejuni |
|
| D |
E. coli |
Ans. is. ‘a’ i. e., Vibrio cholera
Types of culture media-I
| A | Thayer-Martin Medium | |
| B |
Blood agar with X & V factors |
|
| C |
Chocolate agar with isovitale X |
|
| D |
Tellurite blood agar |
| A |
Thayer-Martin Medium |
|
| B |
Blood agar with X & V factors |
|
| C |
Chocolate agar with isovitale X |
|
| D |
Tellurite blood agar |
Patient is suffering from chancroid caused by Hemophilus ducreyi.
Hemophilus ducreyi is a pleomorphic gram negative bacillus that causes chancroid, painful genital ulcers and lymphadenitis.
It is grown best from scrapings of the ulcer base on chocolate agar containing 1% IsoVitaleX and vancomycin.
A painful erythematous papule appears at the site of infection after an incubation period of 4 to 10 days. One to two days later, the lesion becomes eroded, ulcerated, and often pustular.
The ulcers are usually 1 to 2 cm in diameter with sharp, undermined margins and are very painful.
The friable base of the ulcer is covered with yellow-gray necrotic exudates.
Multiple lesions are present in up to 50% of patients and “kissing lesions” are frequent.
Painful inguinal lymphadenopathy develops 1 to 2 weeks after primary infection.
It is treated with intramuscular ceftriaxone, oral trimethoprim-sulfamethoxazole, or oral erythromycin often results in healing in 2 weeks.
Ref: Tintinalli’s Emergency Medicine, Chapter 44 ; Jawetz, Melnick and Adelberg’s Medical Microbiology, Chapter 18 ; Microbiology By Richard A. Harvey, Page 104 ; District Laboratory Practice in Tropical Countries, Volume 2 By Monica Cheesbrough, Page 202 ; Textbook of Microbiology and Immunology By Parija, Page 222
A 60-year-old alcoholic smoker abruptly develops high fever, shakes, a severe headache, and muscle pain. He initially has a dry, insignificant cough, but over the next few days he develops marked shortness of breath requiring assisted ventilation. Chest x-ray demonstrates homogeneous radiographic shadowing that initially involves the left lower lobe but continues to spread until both lungs are extensively involved. Culture of bronchoalveolar lavage fluid on buffered charcoal yeast extract (BCYE) demonstrates a coccobacillary pathogen. Which of the following is the most likely causative organism?
| A |
Legionella pneumophila |
|
| B |
Listeria monocytogenes |
|
| C |
Streptococcus pneumoniae |
|
| D |
Staphylococcus aureus |
A 60-year-old alcoholic smoker abruptly develops high fever, shakes, a severe headache, and muscle pain. He initially has a dry, insignificant cough, but over the next few days he develops marked shortness of breath requiring assisted ventilation. Chest x-ray demonstrates homogeneous radiographic shadowing that initially involves the left lower lobe but continues to spread until both lungs are extensively involved. Culture of bronchoalveolar lavage fluid on buffered charcoal yeast extract (BCYE) demonstrates a coccobacillary pathogen. Which of the following is the most likely causative organism?
| A |
Legionella pneumophila |
|
| B |
Listeria monocytogenes |
|
| C |
Streptococcus pneumoniae |
|
| D |
Staphylococcus aureus |
The patient has a severe, potentially fatal, pneumonia with prominent systemic symptoms. Culture on BCYE is the specific clue that the organism is Legionella pneumophila.
The disease is respiratory Legionellosis, also known as Legionnaire’s disease, because the disease was first described when it occurred in epidemic form following an American Legion convention at a Philadelphia hotel.
Patients tend to be older (40-70 years old) and may have risk factors including cigarette use, alcoholism, diabetes, chronic illness, or immunosuppressive therapy.
| A |
Enriched medium |
|
| B |
Enrichment medium |
|
| C |
Selective medium |
|
| D |
Transport medium |
Chocolate agar is an example of ?
| A |
Enriched medium |
|
| B |
Enrichment medium |
|
| C |
Selective medium |
|
| D |
Transport medium |
Ans is ‘a’ i.e., Enriched medium
Which of the following statement is true about vibrio cholerae –
| A |
There is no natural reservoir |
|
| B |
Transported in alkaline peptone water medium |
|
| C |
Halophilic |
|
| D |
Oxidase negative |
Which of the following statement is true about vibrio cholerae –
| A |
There is no natural reservoir |
|
| B |
Transported in alkaline peptone water medium |
|
| C |
Halophilic |
|
| D |
Oxidase negative |
Ans. is ‘b’ i.e., Transported in alkaline peptone water medium
A 2 years old child is brought to the emergency with history of fever and vomiting. On examination he has neck rigidity. The CSF examination shows polymorphs more that 2000/m1 protein 100 mg/dl and glucose 10mg/d1. The Gram stain shows the presence of Gram negative coccobacilli. The culture shows growth of bacteria only on chocolate agar and not on blood agar. The caustive agent is ‑
| A |
Neisseria meningitides |
|
| B |
Haemophilus influenzae |
|
| C |
Branhamella catarrhalis |
|
| D |
Legionella pneumophila |
A 2 years old child is brought to the emergency with history of fever and vomiting. On examination he has neck rigidity. The CSF examination shows polymorphs more that 2000/m1 protein 100 mg/dl and glucose 10mg/d1. The Gram stain shows the presence of Gram negative coccobacilli. The culture shows growth of bacteria only on chocolate agar and not on blood agar. The caustive agent is ‑
| A |
Neisseria meningitides |
|
| B |
Haemophilus influenzae |
|
| C |
Branhamella catarrhalis |
|
| D |
Legionella pneumophila |
Ans. is ‘b’ i.e., Haemophilus influenzae
. The important clues in this question are ‑
- The organism is gram negative coccobacilli.
- It grows only on chocolate agar and not on blood agar.
- Causing meningitis in children.
. Haemophilus influenzae :
– Gram negative Coccobacilli
– Can not grow in blood agar because utilization of V factor (NAD or NADP) is limited by the presence of serum NADase.
– Grows well on chocolate agar (blood agar which is heated up to 70-80°C) because, on heating extra X and V factors are liberated from the lysed red cells.
– Is a common cause of meningitis in children.
About other options
– N. Meningitis
. It occur as diplococci (not coccobacilli)
. It can grow on blood agar.
– Legionella pneumophilia
. Does not cause meningitis.
– Bramanhella catarrhalis
. It occur as diplococci (not coccobacilli)
. It can grow on blood agar.
| A |
H. ducreyi |
|
| B |
Neisseria gonorrhoeae |
|
| C |
Str. pyogenes |
|
| D |
Str. pneumoniae |
A pus culture on chocolate agar shows gram negative cocci most likely organism is –
| A |
H. ducreyi |
|
| B |
Neisseria gonorrhoeae |
|
| C |
Str. pyogenes |
|
| D |
Str. pneumoniae |
Ans. is ‘b’ i.e., Neisseria gonorrhoeae
. Amongst the given options only gonococcus is gram negative cocci.
September 2009
| A |
Alkaline peptone water |
|
| B |
Monsour’s taurocholate Tellurite peptone water |
|
| C |
Selenite F broth |
|
| D |
All of the above |
Which of the following is an enrichment media:
September 2009
| A |
Alkaline peptone water |
|
| B |
Monsour’s taurocholate Tellurite peptone water |
|
| C |
Selenite F broth |
|
| D |
All of the above |
Ans. D: All of the above
Culture media may be classified into several categories depending on their composition or use.
A chemically-defined (synthetic) medium is one in which the exact chemical composition is known.
A complex (undefined) medium is one in which the exact chemical constitution of the medium is not known.
Defined media are usually composed of pure biochemicals off the shelf; complex media usually contain complex materials of biological origin such as blood or milk or yeast extract or beef extract, the exact chemical composition of which is obviously undetermined.
A defined medium is a minimal medium if it provides. only the exact nutrients (including any growth factors) needed by the organism for growth.
A selective medium is one which has a component(s) added to it which will inhibit or prevent the growth of certain types or species of bacteria and/or promote the growth of desired species.
A culture medium may also be a differential medium if allows to distinguish between different types of bacteria based on some observable trait in their pattern of growth on the medium. Thus a selective, differential medium for the isolation of Staphylococcus aureus, contains a very high concentration of salt (which the staph will tolerate) that inhibits most other bacteria, mannitol as a source of fermentable sugar, and a pH indicator dye. From clinical specimens, only staph will grow. S. aureus is differentiated from S. epidermidis (a nonpathogenic component of the normal flora) on the basis of its ability to ferment mannitol. Mannitol-fermenting colonies (S. aureus) produce acid which reacts with the indicator dye forming a colored halo around the colonies; mannitol non-fermenters (S. epidermidis) use other non-fermentative substrates in the medium for growth and do not form a halo around their colonies. MacConkey’s medium shows up lactose fermenters as pink colonies
An enrichment medium contains some component that permits the growth of specific types or species of bacteria, usually because they alone can utilize the component from their environment. For example, Alkaline peptone water and Monsour’s taurocholate Tellurite peptone water for vibrio cholera and Selenite F broth for dysentery bacilli.
| A |
VR medium |
|
| B |
TCBS medium |
|
| C |
Cary-Blair medium |
|
| D |
Alkaline peptone water |
Enrichment media for cholera ‑
| A |
VR medium |
|
| B |
TCBS medium |
|
| C |
Cary-Blair medium |
|
| D |
Alkaline peptone water |
Ans. is ‘d’ i.e., Alkaline peptone water
Chocolate agar is:
| A |
Basal medium |
|
| B |
Enrichment medium |
|
| C |
Enriched medium |
|
| D |
Simple medium |
Chocolate agar is:
| A |
Basal medium |
|
| B |
Enrichment medium |
|
| C |
Enriched medium |
|
| D |
Simple medium |
Ans. (b) Enrichment medium
TYPES OF CULTURE MEDIA-II
Loeffler’s syndrome is seen with all except :
| A | >Toxocara | |
| B | >Strongyloides stercoralisL. tryptophan | |
| C | >Giardiasis | |
| D | Giardiasis |
Loeffler’s syndrome is seen with all except :
| A | >Toxocara | |
| B | >Strongyloides stercoralisL. tryptophan | |
| C | >Giardiasis | |
| D | Giardiasis |
Giardiasis [Ref. Harrison 161h/e p 1520]
- Pulmonary diseases associated with tissue or blood eosinophilia are a heterogenous group of disorders.
- They are classified as :
Loeffler’s syndrome
- It is a benign acute eosinophilic pneumonia of unknown cause characterized by migrating pulmonary infiltrates and minimal clinical manifestations.
- These are usually secondary to parasites or drugs.
- Loeffler’s syndrome reflects a hypersensitive response to an ingested or inhaled antigen from food, medication or an infectious agent. Causes of Loeffler’s syndrome
Parasitic infections
- Ascaris
- Schistosomiasis
- Strongyloides
- Ancyclostomiasis
- Trichomoniasis
- Clonorchiasis
- Visceral larva migrans
- Tapeworm
- Paragonimiasis
| A |
Loeffler medium |
|
| B |
LJ medium |
|
| C |
Blood agar |
|
| D |
Tellurite medium |
A child presents with a white patch over the tonsils; diagnosis is best made by culture in:
| A |
Loeffler medium |
|
| B |
LJ medium |
|
| C |
Blood agar |
|
| D |
Tellurite medium |
Culture medium for cultivation of mycobacterium is:
September 2005 & 2011
| A |
Ludlam’s medium |
|
| B |
Loeffler’s serum |
|
| C |
Thayer-Martin medium |
|
| D |
LJ medium |
Culture medium for cultivation of mycobacterium is:
September 2005 & 2011
| A |
Ludlam’s medium |
|
| B |
Loeffler’s serum |
|
| C |
Thayer-Martin medium |
|
| D |
LJ medium |
Ans. D: LJ medium
Diagnosis of tuberculosis
Microscopy
– Rapid diagnosis
– Low sensitivity. Concentration may increase sensitivity up to hundred folds
– Can not differentiate tuberculosis and non-tuberculosis mycobacteria
– False positive results
– Samples must always be studied with one positive and one negative control
Culture
– The gold standard method for tb diagnosis
Culture in LJ media takes 3 to 6 weeks
– Commonly used rapid culture systems have disadvantages:
- Radioactive, expensive, blood containing samples give false results
- All culture methods require decontamination
When grown on LJ medium, M. tuberculosis appears as brown, granular colonies (sometimes called “buff, rough and tough”). The media must be incubated for a significant length of time, usually four weeks, due to the slow doubling time of M. tuberculosis compared with other bacteria (15-20 hours).
Lowenstein-Jensen (g) medium is most widely used for tuberculosis culture.
LJ medium containing glycerol favours the growth of M. tuberculosis while LJ medium without glycerol but containing pyruvate encourages the growth of M. bovis. Both should be used in countries or regions where patients may be infected with either organism.
Ingredients
Mineral salt solution
Potassium dihydrogen phosphate anhydrous (1(1-12PO4) 2.4g Magnesium sulphate (MgSO4. 7H20) 0.24g
Magnesium citrate 0.6g
Asparagine 3.6g
Glycerol (reagent grade) 12m1
Distilled water 600m1
| A |
Increase growth of M. tuberculosis |
|
| B |
Inhibits growth of other bacteria |
|
| C |
Nutritive value |
|
| D |
As an indicator |
Role of Malachite green in LJ medium ‑
| A |
Increase growth of M. tuberculosis |
|
| B |
Inhibits growth of other bacteria |
|
| C |
Nutritive value |
|
| D |
As an indicator |
Ans. is ‘b’ i.e., Inhibits growth of other bacteria
Lowenstein-Jensen Medium (LJ medium)
LJ medium consists of mineral salts, asparagine, glycerol, malachite green and hen’s egg.
The malachite green prevents the growth of other microorganism on medium.
It is used as a primary isolation medium for mycobacteria.
Example of selective medium is:
| A | LJ medium | |
| B |
Blood agar |
|
| C |
Selenite F broth |
|
| D |
Chocolate agar |
Example of selective medium is:
| A |
LJ medium |
|
| B |
Blood agar |
|
| C |
Selenite F broth |
|
| D |
Chocolate agar |
Ans. is. ‘a’ i. e., LJ medium
Which of following Culture media combination is/are true except:
| A |
Thayer-Martin media: Gonorrhoea |
|
| B |
Chocolate agar-: enriched media |
|
| C |
Lowenstein-Jensen Medium: Mycobacterium tuberculosis |
|
| D |
Muller-Hinton agar: Corynebacterium diphtheriae |
Which of following Culture media combination is/are true except:
| A |
Thayer-Martin media: Gonorrhoea |
|
| B |
Chocolate agar-: enriched media |
|
| C |
Lowenstein-Jensen Medium: Mycobacterium tuberculosis |
|
| D |
Muller-Hinton agar: Corynebacterium diphtheriae |
Ans: d. Muller-Hinton…[Ref Ananthanarayan 8th/39-43, 229]
- Thayer-Martin is a useful selective media for Neisseria gonorrhoeae”.
- Mueller-Hinton is enriched media for Neisseria.
- C diphtheriae and other corynebacteria grow aerobically on most ordinary laboratory media. On Loeffler’s serum medium, corynebacteria grow much more readily than other respiratory organisms, and the morphology of organisms is typical in smears.
- Lowenstein-Jensen Medium. It is used to culture tubercle bacilli. It contains egg, malachite green and glycerol.
- Chocolate Agar or Heated Blood agar: Prepared by heating blood agar. It is used for culture of pneumococcus, gonococcus, meningococcus and Haemophilus. Heating the blood inactivates inhibitor of growths.
Degradation of Purine Nucleotides
Uric acid is formed in humans in
| A |
Liver |
|
| B |
Kidney |
|
| C |
GIT mucosa |
|
| D |
Joints |
Uric acid is formed in humans in
| A |
Liver |
|
| B |
Kidney |
|
| C |
GIT mucosa |
|
| D |
Joints |
GIT mucosa
Most of the dietary purines are converted to uric acid in lhe intestinal’mucosal cell only. Intestinal bacterialJlora is intolved in degradation of the rest of dietary purines that remain unabsorbed.
A patient with increased Hypoxanthine and Xanthine in blood with hypouricemia which enzyme is deficient?
| A |
HGPRTase |
|
| B |
Xanthine oxidase |
|
| C |
Adenosine deaminase |
|
| D |
APRtase |
A patient with increased Hypoxanthine and Xanthine in blood with hypouricemia which enzyme is deficient?
| A |
HGPRTase |
|
| B |
Xanthine oxidase |
|
| C |
Adenosine deaminase |
|
| D |
APRtase |
- Hypouricemia- Hypouricemia and increased excretion of hypoxanthine and xanthine are associated with xanthine oxidase deficiency.
- Lesch-Nyhan Syndrome- The Lesch-Nyhan syndrome, an overproduction hyperuricemia characterized by frequent episodes of uric acid lithiasis and a bizarre syndrome of selfmutilation reflects a defect in hypoxanthine-guanine phosphoribosyltransferase, an enzyme of purine salvage.
- Adenosine Deaminase Deficiency- Adenosine deaminase deficiency is associated with an immunodeficiency disease in which both thymus-derived lymphocytes (T cells) and bone marrow-derived lymphocytes (B cells) are sparse and dysfunctional. Patients suffer from severe immunodeficiency.
- Purine Nucleoside Phosphorylase Deficiency- Purine nucleoside phosphorylase deficiency is associated with a severe deficiency of T cells but apparently normal B cell function
Degradation of Pyrimidine Nucleotides
What is the end product of catabolism of pyrimidine?
| A |
NH3 |
|
| B |
CO2 & H2O |
|
| C |
Both |
|
| D |
None |
What is the end product of catabolism of pyrimidine?
| A |
NH3 |
|
| B |
CO2 & H2O |
|
| C |
Both |
|
| D |
None |
The end products of pyrimidine catabolism is CO2 and H2O.
Which is the product excreted unchanged in catabolism of pyrimidine?
| A |
Uric acid |
|
| B |
NH3 |
|
| C |
Pseudouridine |
|
| D |
Beta alanine |
Which is the product excreted unchanged in catabolism of pyrimidine?
| A |
Uric acid |
|
| B |
NH3 |
|
| C |
Pseudouridine |
|
| D |
Beta alanine |
Pseudouridine is excreted unchanged as it cannot be catabolized in human.
