Staphylococcus aureus: Morphology,Culture and Biochemical reaction

Staphylococcus aureus: Morphology,Culture and Biochemical reaction

Q. 1

All of the following statements about staphylococcus aureus are true, EXCEPT:

 A

Most common source of infection is cross infection from infected people

 B

About 30% of general population are healthy nasal carriers

 C

Epidermolysin and TSS toxin are superantigens

 D

Methicillin Resistance is chromosome mediated.

Q. 1

All of the following statements about staphylococcus aureus are true, EXCEPT:

 A

Most common source of infection is cross infection from infected people

 B

About 30% of general population are healthy nasal carriers

 C

Epidermolysin and TSS toxin are superantigens

 D

Methicillin Resistance is chromosome mediated.

Ans. A

Explanation:

Carriers of staphylococcus aureus are the primary source for cross infection to individuals who do not normally have this bacterium in their commensal microflora.

Individuals normally free from s.aureus may have less immunity against the lethal consequence of S.aureus infection compared with those who are persistent carrier of the species and suffer from endogenous infection.
 
Most individuals who develop staphylococcus aureus infections are infected with their own colonizing strains.

However, S. aureus may also be acquired from other people or from environmental exposures.
Ref: Jawetz, Melnick and Adelberg’s Medical Microbiology, 23rd Edition, Pages 224 – 228; Staphylococci in Human Disease By Kent B. Crossley, Page 265; Microbiology and Immunology By Monica Gandhi, Page 4; Harrison’s Principles of Internal Medicine, 17th edition, Pages 873 – 879.

Q. 2

Catalase positive, beta-hemolytic staphylococcus –

 A

S. aureus

 B

S. epidermidis

 C

S. saprophyticus

 D

None

Q. 2

Catalase positive, beta-hemolytic staphylococcus –

 A

S. aureus

 B

S. epidermidis

 C

S. saprophyticus

 D

None

Ans. A

Explanation:

Ans. is ‘a’ i.e., S. aureus

  • All staphylococci are catalase positive.
  • Amongst staphylococci, staph. aureus is beta hemolytic.
  • Most species of coagulase negative staphylococcus species are non-hemolytic.

Q. 3

Transient colonization is caused by –

 A

HSV

 B

Trichomonas vaginalis

 C

Staphylococcus aureus

 D

All

Q. 3

Transient colonization is caused by –

 A

HSV

 B

Trichomonas vaginalis

 C

Staphylococcus aureus

 D

All

Ans. D

Explanation:

Ans. is ‘a’ i.e., HSV; ‘b’ i.e., Trichomonas vaginalis; `c’ i.e., Staphylococcus aureus

  • Colonization is the multiplication of microorganism on or within the host that does not result in cellular injury.
  • However, microorganisms that are colonized on a host may be potential source of infection especially if host susceptibility declines or microorganisms virulence increases.
  • Microorganisms residing on human body as normal flora are of two types : ‑

1)    Resident flora

– Resident flora are the microorganisms that are always present, usually without altering the client’s health.

2)    Transient flora

– Transient flora are episodic organisms, they present for a brief period but do not continually live on/in human body.

Common natural flora at various site of body

 

Resident

Transient flora

Skin

Corynebacterium, Micrococcus, Coagulase

Staph aureus, viridans streptococci

 

negative staphylococci, Propionobacterium,

Pityrosporrum, Demodex follicularum

group A streptococci, Enterococcus

Malassezia, E.coli, Proteus, Klebsiella,

Candida, Trichophyton.

Mouth &

Str. viridans, Coagulase negative staph.,

Hemophillus, Peptostreptococci, Bacteriodes,

Prevotella, Vellionella, non-meningococcal

neisseria, Fusobacterium, Actinomyces

Group A Streptococcus, Lactobacillus

N. meningitidis, Candida, CMV, HSV,

Moraxella, Eikenella corrodens.

oropharvnx

 

Nose &

Coagulase negative staph.. Corynebacterium,

Non-meningococcal & Meningococcal

Nasopharynx

Strep. viridans

neisseria, Staph aureus, Str.

pneumoniae, Morexclla

 

Vagina

Lactobacillus, Streptococcus, Prevotella,

Coagulase negative staphylococci,

Gard. vaginalis, Actinomyces

Candida, Trichomonas vaginalis,

Group B streptococci, Enterococcus.

 

Eve

Coagulase negative staph, Micrococci,

Hemophillus, Corynebacterium

Bacillus, Strep viridans, Propionobac‑

terium, Staph aureus, str. pneumoniae

Stomach

 

Streptococci, Lactobacillus,

H. Pylori

 

Small intestine

Lactobacillus, Streptococcus, Vellionella,

Prevotella, Porphyromonas, Bifidobacter

Bacteroides, Clostridium, Enterobacteriacease

Candida, Entamoeba coli, E.Nana,

Trichomonas Hominis,

Blastocystis hominis

 

Large intestine

Bifidobactor, Peptostreptococci, Enterococcus

Candida, Corynebacterium, Pseudo‑

 

Lactobacillus, Vellionella, Eubacterium,

Fusobacterium, Prevotella, Porphyromonas,

Bacteroides, Clostridium, Enterobacteriaceae

monas, MAC, Entamoeba coli,

E.nana, Trichomonas Hominis,

Enterovirus, Blastocystis hominis

Urethra

Corynebacteriurn, Strept viridans, Coagulase

negative staph, Lactobacillus

M. smegmetis, Enterococcus,

Mycoplasma, Neoplasma,

Bacteroides, Fusobacterium


Q. 4

Causative organism in acute bacterial endocarditis is –

 A

Staphylococcus aureus

 B

Streptococcus viridans

 C

Pneumococcus

 D

Streptococcus pyogenes

Q. 4

Causative organism in acute bacterial endocarditis is –

 A

Staphylococcus aureus

 B

Streptococcus viridans

 C

Pneumococcus

 D

Streptococcus pyogenes

Ans. A

Explanation:

Ans. is ‘a’ i.e., Staphylococcus aureus

Streptococcus viridans infects the demaged valve i.e., it causes sabacute endocarditis not acute.


Q. 5

Staphylococcus aureus is a normal inhabitant of:

March 2005

 A

Throat

 B

Nose

 C

Skin

 D

GIT

Q. 5

Staphylococcus aureus is a normal inhabitant of:

March 2005

 A

Throat

 B

Nose

 C

Skin

 D

GIT

Ans. B

Explanation:

Ans. B: Nose

Staphylococci are Gram-positive spherical bacteria.

S. aureus colonizes mainly the nasal passages(especially anterior pares), but it may be found regularly in most other anatomical locales.

S. epidermidis is an inhabitant of the skin.


Q. 6

For phage typing, how many phages of staphylococcus aureus are used ‑

 A

12

 B

15

 C

20

 D

23

Q. 6

For phage typing, how many phages of staphylococcus aureus are used ‑

 A

12

 B

15

 C

20

 D

23

Ans. D

Explanation:

Ans. is ‘d’ i.e., 23

  • Bacteriophage typing of staphylococcus is based on susceptibility of cocci to bacteriphages.
  • This is carried out by pattern method where a set of 23 standard typing phages of S. aureus is used to type staphylococcal isolates and distinguish them from one another by their patterns of susceptibility to lysis. o The phage type of a strain is known by designation of the phages that lyse it.
  • For example, if a strain is lysed by phages 83A, 84 and 85, it is called type 83A/84/85.


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