This presentation cover brief discussion of morphological features, cultural characteristics, virulence factors, pathogenesis, epidemiology and lab diagnosis of staphylococcus aureus . #MedicalMicrobiology

1. PowerPoint presentation on
Staphylococcus aureus
SUBJECT- Medical microbiology
Prepared by-
JAHNVI ARORA
MSC MICROBIOLOGY
11228108

2. INDEX
..
- Introduction
- Morphology
- Cultural characteristics
- Virulence factors
- Pathogenesis
- Epidemiology
- Lab diagnosis
- Question bank

3. ABOUT…
•Staphylococcus aureus is a Gram-positive spherically shaped bacterium.
•It is a member of the Bacillota.
•It is a usual member of the microbiota of the body.
•Found in the upper respiratory tract and on the skin.
•It is a facultative anaerobe.
•It acts as a commensal and opportunistic pathogen in human
microbiota and cause skin infections including abscesses, respiratory
infections such as sinusitis, and food poisoning.
•It can cause a range of illnesses, from minor skin infections, such as
pimples, boils, scalded skin syndrome, and abscesses, to life-threatening
diseases such as pneumonia, meningitis, toxic shock syndrome,
bacteremia, and sepsis.
•It is still one of the five most common causes of hospital-acquired
infections.

4. MORPHOLOGY…
Gram-positive, singly, in pairs, or in a short chain of 3-4 bacteria.
Irregular clusters of cells.
1 um in diameter.
Spherical colonies in clusters in two planes.
Cell wall- very thick peptidoglycan layer.
Non-Flagellated, Non-Motile and Non-Sporing.
They are capsulated.
Grapes like clusters arrangement.

5. CULTURAL
CHARACTERISTI
CS...
1)Staphylococci grow readily on most
bacteriologic media under aerobic or
microaerophilic conditions.
2)Colonies on solid media are round,
smooth, raised, and glistening.
3)S. aureus usually forms gray to deep
golden yellow colonies.
4)Mannitol Salt Agar: circular, 2–3 mm in
diameter, with a smooth, shiny surface;
colonies appear opaque and are often
pigmented golden yellow.
5)Tryptic Soy Agar: circular, convex, and
entire margin.
6) Blood Agar: beta-hemolysis.
7)Brain heart infusion agar: Yellow
pigmented colonies.

6. VIRULENCE
FACTORS...
A. ENZYMES
1)Catalase enzyme: conversion of hydrogen peroxide into water and
oxygen
2)Coagulase enzyme and clumping factor: an enzyme-like protein that
clots oxalated or citrated plasma.
3)Other enzymes: hyaluronidase (spreading factor),
staphylokinase(fibrinolysis), proteinases, lipases, β- lactamases.

7. B.
TOXINS
1) Exotoxins:
It comprises of four toxins α,β,γ,δ: also called hemolysin
–α exotoxins- heterogenous protein acts on a broad spectrum of
eukaryotic cell membranes
– β exotoxins- degrades sphingomyelin
– δ exotoxins- disrupts biological membrane
–γ exotoxins- interact with two proteins to form six potential
two-component toxins.
All six toxins lyse WBC by pore formation in the cellular
membranes that increase cation permeability
2) Enterotoxins:
Altogether 15 enterotoxins(A-E, G-P), heat stable, resistant to gut
enzymes.

8. PATHOGENESIS…
Staphylococcus aureus skin abscesses.
A: Formation of a S. aureus skin
abscess.
B: Representative histopathological
section of a skin abscess at day 14 after
infection.
C: Increased magnification of the boxed
area shown in B.
D and E: Gram stains of histological
sections abscess.
Arrows in D indicate S. aureus.
The dark area is a colony of S. aureus.
Arrows in E indicate S. aureus
associated with leukocytes within the
abscess.

9. EPIDEMIOLOGY…
•Predominant reservoir of organisms = Human beings.
•Approximately 15%-30% of normal people harbor S.
aureus in pharynx at given point ,longitudinal view of
carriage:
-30% prolonged , 50% intermittant , 20% never.
-Vagina carriage in ~ 10% of premenopausal women.
-Rectal and perineal carriage also occur.
•Patients with MRSA infections may have high
prevelance (60%) of GI carriage.
•Usually spread by direct person to person contact.
•Most common cause of endocarditis (38%).
•Most common cause of nosocomial infections (13%).
•Most common cause of SSI (20%).
•Most common cause of cellulities , osteomycities
,septic arthiritis.

10. LAB
DIAGNOSIS...
A.
Microscopy
1)Microscopy is useful for pyogenic
infections but not blood infections or
toxin-mediated infections.
2)A direct smear for Gram staining
may be performed as soon as the
specimen is collected.
3)The Gram stain showing typical
Gram-positive cocci that occur singly
and in pairs, tetrads, short chains,
and irregular grape-like clusters can
be suspected to be S. aureus.

11. B. Presumptive
identification
The presumptive identification of S. aureus rests on the isolation of:
> Large mannitol fermenting colonies on MSA
> Gram-positive cocci in clusters
> Catalase-positive organisms
> Coagulase-positive organisms
C. Confirmatory test
Confirmatory tests include biochemical tests, molecular probes, or
mass spectrometry.
D. BIOCHEMICAL REACTIONS
Tests for clumping factor, coagulase, hemolysins, and thermostable
deoxyribonuclease are routinely used to identify S. aureus.

12. LAB DIAGNOSIS…

13. 1) Staphylococcus aureus can ferment mannitol?
Yes , This creates acid by-product and turns phenol indicator in Mannitol Salt Agar to yellow,
giving yellow colonies.
2) Coagulase is not thought to be an important virulence factor for Staphylococcus aureus?
However useful for discriminating between Staphylococcus aureus and “coagulase negative
staphylococci”
3) Staphylococcus aureus can be intracellular in nasal epithelial cells?
Staphylococcus aureus colonisation can be difficult to eradicate, and the lack of
decolonisation activity of antimicrobials with little intracellular activity, such as
flucloxacillin.
4) Name few commonly used antibiotic in many parts of the world
Essentially historical antibiotic, superseded by flucloxacillin, cloxacillin and dicloxacillin.
5) Most people are colonised with Staphylococcus aureus? T/F
False, most people colonised with coagulase negative staphylococci. Colonisation rate for
Staphylococcus aureus probably 10-20% of the population.
QUESTION
BANK...

14. THANK YOU !