staphylococcus aureus a applied microbiology exercise

8/4/2019 Staphylococcus aureus A applied Microbiology Exercise

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Staphylococcus aureus

Basic Identification in Applied MicrobiologyExercise

Dr.T.V.Rao MD

Dr.T.V.Rao MD Travancore Medical College,Kollam Kerala

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Patient presented with

• A 30 years malepatient

presented withan abscess leftmandibular

region since 3days, with onsetof fever.


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What are bacteriological agents

can produce this pyogenic

condition ?


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Most important bacteria are

Most abscesses are due to

infection by

Staphylococcus (as in

the boil abscess), butother bacteria are

sometimes associated

Streptococci, Hemophilus

spp. E.Coli Klebsiella sppPseudomonas spp and

many others.


4



How you proceed to identify the

etiological agent


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How to make a Definitive Diagnosis

• To make a definitive diagnosis and to confirmthat Staphylococcus is the bacteria causingthe infection, Microscopic observation of the

given specimen and a culture can be done.Once a bacteria is identified on a culture, thepattern on sensitivities to antibiotics canhelp to tell whether or not it is actuallyMRSA, routine staph aureus, or anotherbacteria.


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Gram staining showing Gram positive Cocci in clusters

– Probably Staphylococcus spp


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What are Staphylococci:

Gram positive cocci ( from Greekstaphyle, means bunch of grapes ) that

occur singly and in pairs, short chains

and irregular grape-like clusters.


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• Gram-positive cocci, nonmotile, facultativeanaerobes

• Cells occur in grapelike clusters because cells

division occurs along different planes and thedaughter cells remain attached to one another

• Salt-tolerant: allows them to tolerate the saltpresent on human skin

• Tolerant of desiccation: allows survival onenvironmental surfaces (fomites)

Structure and Physiology of

Staphylococcus


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Staphylocoous appear as

• Gram stained

smear showing

Gram positivecocci with cluster

formation

indicates presenceof Staphylococci


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III.

Virulence factors of Staphylococcus aureus


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Staphylococcus aureus grown on Nutrient agar


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General Cultural Characteristics

• Some Staphylococcus

species, most notablyS. aureus, produce ahemolysin that

completely lyses redblood cells of humansand some othermammals (sheep

blood). This is referredto as “beta” hemolysis.

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What are your observation on

Blood Agar


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What are the commonly performed

in vitro pathogenicity tests?


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Staphylococcus aureus: is the

staphylococcus which has the ability toclot plasma, which is coagulase

positive. More than 80% of

Staphylococcus aureus strains producebeta-lactamases.



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Other S. aureus Characteristics

Mannitol fermentation is another usefulcharacteristic – it is unique to, and consistent

among S. aureus strains. Virtually all strains of

S. aureus ferment mannitol.

Bright yellow colonies on a yellow background

indicates mannitol fermentation on mannitol

salt agar.



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Coagulase test for Identification of Staphylococcus

Staphylococcus aureus coagulation of plasma*

“Free” staphylocoagulase

Fibrinogen + CRF Fibrin

Normal coagulation of plasma

Thrombin

Fibrinogen Fibrin

(soluble ) (insoluble)

*EDTA Rabbit plasma is preferred for the “free” or tube coagulase

test because it contains a large amount of CRF



Slide Coagulase Test

• The most important distinctionamong staphylococci is whetheror not they produce the enzymecoagulase. S. aureus the mostcommon pathogen among the

catalase positive gram positivecocci and is differentiated fromother staphylococci by thecoagulase test. Here the bacterialcells have been suspended in adrop of rabbit plasma. Coagulasebound to the cell wall acts on

fibrinogen and causes theclumping of the bacteria (right).Coagulase is an importantvirulence factor of S. aureus


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Tube Coagulase Test

• The tube coagulase testdetects both free and cellbound coagulase of S.aureus. Bacteria are

incubated in plasma for 2-4hours and the tubes turnedon their sides as illustrated.Free coagulase acts onprothrombin and fibrinogenin plasma and forms a fibrin

clot (left). Inmanylaboratoriesstaphylococci are simplydifferentiated as coagulasepositive or coagulase

negative without speciationDr.T.V.Rao MD Travancore Medical College,Kollam Kerala

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Mention commonly used Antibiotic

agents for Staphylococcus aureus• Penicillins

• However Penicillindeveloped early resistance

• Other Beta lactamantibiotics like Ampicillin

• Macrolide group

• Vancomycin, Linezolid( Only in MRSA strains ).

• Commonly used oral anti

staphylococcal antibioticsinclude the first-generationcephalosporins likecephalexin and cefadroxil.


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Plate 1a: Staphylococcus aureus resistant to penicillin (P0.5) only. Note the annular radius of

the zone of inhibition of 9.5 mm around the cefoxitin (FOX 10) disc.



What is the importance of Drug resistance

in this isolate?

• MRSA is an acronym

for Methicillin ResistantStaphylococcus aureus,a bacteria that hasbecome resistant tomany antibiotics,including methicillin,penicillin, amoxicillin,

and cephalosporins. It isroutinely pronounced

M.R.S.A.


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What are the Other Diseases

produced by Staphylococcus aureus


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–

Systemic Diseases• Toxic shock syndrome-TSS toxin is absorbed into the

blood and causes shock

• Bacteremia-presence of bacteria in the blood

• Endocarditis-occurs when bacteria attack the lining of

the heart

• Pneumonia-inflammation of the lungs in which the

alveoli and bronchioles become filled with fluid

• Osteomyelitis-inflammation of the bone marrow and

the surrounding bone

Other Staphylococcal Diseases


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How you Prevent Staphylococcal

Infections

• Prevention

• Staphylococcus is aimportant cause of Hospital infection – Hand antisepsis is the most

important measure inpreventing nosocomialinfections

– Also important is the propercleansing of wounds andsurgical openings, aseptic useof catheters or indwellingneedles, an appropriate useof antiseptics


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• The programme is created for

Undergraduate students in MedicalColleges as a part of Applied

Microbiology exercises

[email protected]


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staphylococcus aureus a applied microbiology exercise

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