Types of culture media-I

Types of culture media-I

Q. 1

 A 20 years old male patient presents to the STD clinic with a genital ulcer. The gram stain of the smear from the ulcer shows gram negative coccobacilli. Which of the following is the most appropriate culture medium for diagnosing the organism?
 A Thayer-Martin Medium

 B

Blood agar with X & V factors

 C

Chocolate agar with isovitale X

 D

Tellurite blood agar

Q. 1

 A 20 years old male patient presents to the STD clinic with a genital ulcer. The gram stain of the smear from the ulcer shows gram negative coccobacilli. Which of the following is the most appropriate culture medium for diagnosing the organism?
 A

Thayer-Martin Medium

 B

Blood agar with X & V factors

 C

Chocolate agar with isovitale X

 D

Tellurite blood agar

Ans. C

Explanation:

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


Q. 2

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

Q. 2

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

Ans. A

Explanation:

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.

Listeria monocytogenes causes listeriosis and is not a notable cause of pneumonia.
 
Staphylococcus aureus can cause pneumonia, but is easily cultured on routine media.
Ref: Levinson W. (2012). Chapter 19. Gram-Negative Rods Related to the Respiratory Tract. In W. Levinson (Ed), Review of Medical Microbiology & Immunology, 12e.

Q. 3 Chocolate agar is an example of ?

 A

Enriched medium

 B

Enrichment medium

 C

Selective medium

 D

Transport medium

Q. 3

Chocolate agar is an example of ?

 A

Enriched medium

 B

Enrichment medium

 C

Selective medium

 D

Transport medium

Ans. A

Explanation:

Ans is ‘a’ i.e., Enriched medium

Quiz In Between


Q. 4

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

Q. 4

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. B

Explanation:

Ans. is ‘b’ i.e., Transported in alkaline peptone water medium


Q. 5

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

Q. 5

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. B

Explanation:

Ans. is ‘b’ i.e., Haemophilus influenzae 

.                    The important clues in this question are ‑

  1. The organism is gram negative coccobacilli.
  2. It grows only on chocolate agar and not on blood agar.
  3. 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.


Q. 6 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

Q. 6

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. B

Explanation:

Ans. is ‘b’ i.e., Neisseria gonorrhoeae 

.   Amongst the given options only gonococcus is gram negative cocci.

Quiz In Between


Q. 7 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

Q. 7

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

Explanation:

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.


Q. 8 Enrichment media for cholera

 A

VR medium

 B

TCBS medium

 C

Cary-Blair medium

 D

Alkaline peptone water

Q. 8

Enrichment media for cholera

 A

VR medium

 B

TCBS medium

 C

Cary-Blair medium

 D

Alkaline peptone water

Ans. D

Explanation:

Ans. is ‘d’ i.e., Alkaline peptone water


Q. 9

Chocolate agar is:

 A

Basal medium

 B

Enrichment medium

 C

Enriched medium

 D

Simple medium 

Q. 9

Chocolate agar is:

 A

Basal medium

 B

Enrichment medium

 C

Enriched medium

 D

Simple medium 

Ans. B

Explanation:

Ans. (b) Enrichment medium

Quiz In Between



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