the gram positive cocci

1. GRAM POSITIVE COCCI
STAPHYLOCOCCI
BY OYOM P. ANTHONY
2013-BMLS-FT-009

3. LINNAEAN
CLASSIFICATION
 Kingdom:Bacteria
 Phylum: Firmicutes
 Class: Bacilli
 Order: Bacillales
 Family: Staphylococcaceae
 Genera: Staphylococcus
 Species:Staphylococcus Aureus
 Staphylococcus epidermidis
 Staphylococcus capitis
 Staphylococcus saprophyticus
 Staphylococcus hominis

4. STAPHYLOCOCCI
 Gram positive aerobic organisms
 Reproduce asexually by binary fission
 Common microorganism in the
environment; present in air, water and
dust
 Common strains are S. aureus, S.
epidermidis and S. saprophyticus
 S. aureus commonly inhabits nasal
passages and axillae.
 S. epidermidis is a normal flora on the
skin.
 S. saprophyticus rare but may inhabit
the female genital tract

5. MORPHOLOGY AND STAINING
 Are gram positive
 Spherical, form clusters due to
division in 3 planes, after which the
bacteria remain attached to each
other.

6. MORPHOLOGY AND STAINING
 Are non-motile
 Non spore forming
 Are non-capsulated except in young
cultures; capsulation is lost with
prolonged culturing

7. CULTURE
CHARACTERISTICS
 Grow aerobically and are facultative
anaerobes.
 Capable of growing at temperature s between
220C – 440C (Ideal temp 350C -370C)
 Grows on ordinary media; nutrient agar &
blood agar
 Colonies are 1 – 3 mm diameter, smooth, low
convex, glittering and opaque on nutrient
agar.
 S. aureus will yield large yellow low convex
colonies with β-haemolysis (esp. fresh
isolates) on blood agar
 S. epidermidis will yield small creamy/ white
colonies with no haemolysis on blood agar

8. CULTURE
CHARACTERISTICS
 Pigmentation in S. aureus may be
enhanced by: aerobic incubation, use
of fatty media (e.g. tween agar), or
prolonged incubation of the plate.
 MacConkey Agar will yield small pink
colonies 0.5 – 1mm diameter (for
lactose fermenting strains)
 Modified MacConkey Agar yields no
growth due to inhibition by crystal
violet

9. CULTURE
CHARACTERISTICS
Staphylococcus species are salt
tolerant, will grow in selective media
such as:
 Cooked meat broth with 10% NaCl –
enrichment of S. aureus
 Milk Agar with 7 – 10 % NaCl – for
primary plating and pigmented
colonies
 Mannitol Salt Agar – for isolation of S.
aureus

10. PATHOGENESIS
 Staphylococcal infections are
common in hospitals & communities.
 S. aureus is the most pathogenic, but
S. epidermidis increasingly associated
with nosocomial infections.
 S. saprophyticus associated with
urinary tract infections, especially in
sexually active young females.

11. PATHOGENESIS: Risk
Factors
 Neonates and breastfeeding mothers
 Chronic skin disorders
 Patients on immunosuppressants
 Chronic broncho-pulmonary disorders
e.g. emphysema
 Patients with implants or prosthetics
 Patients with indwelling catheters
 Patients with surgical incisions
 Patients with diabetes mellitus
 Patients with burns

12. PATHOGENESIS
Diseases resulting from tissue invasion
include:
 Skin infections (cutaneous abscesses,
mastitis, wound and burn infections)
 Neonatal infections (pneumonia,
meningitis, skin lesions)
 Pneumonia (Not common in community
setting)
 Endocarditis (particularly in IV drug users
and patients with prosthetic heart valves)
 Osteomyelitis (especially in children)

13. PATHOGENESIS
Toxin mediated diseases include:
 Toxic Shock Syndrome (via vaginal
tampons, wound and burn infections)
 Scalded skin syndrome (common in
infants)
 Staphylococcal Food Poisoning
(commonly from canned foods,
pastries and salads)

14. PATHOGENESIS: Virulence
Factors
 Protein A: binds to IgG, inhibits phagocytosis
 Leukocidins: specifically acts against PMN
leucocytes, damages membranes
 Catalase: neutralizes some super-oxides in
phagosomes
 Coagulase: causes localized clotting
 Haemolysins: causes destruction of erythrocytes
 Exotoxins: e.g. TSST-1, Enterotoxin, Exfolatins
 Resistance to antimicrobial agents (inherent or
acquired)
 Carotenoids (Antioxidant, resists action of super-
oxides)
 Biofilms: especially S. epidermidis, resist
phagocytosis

15. DIAGNOSIS
Samples collected for diagnosis will
depend on type of staphylococcal
infection e.g. ;
 Scalded skin syndrome – from
abnormal skin, blood or urine
 Food poisoning – stool or suspect food
 Osteomyelitis – bone biopsy (since X-
ray might not show changes for 10-14
days after infection)
 Endocarditis – blood for culture
 Other specimens include pus, sputum

16. DIAGNOSTIC TESTS
 Gram Stain: Will reveal purple cocci
occurring in clusters.
 Culture: MacConkey Agar, Blood
Agar, Mannitol Salt Agar can be used
 Biochemical Tests: Catalase,
Coagulase, DNAse
NOTE: Susceptibility testing
recommended due to increased
incidence of MRSA.

17. DIAGNOSTIC TESTS:
CULTURE
 Blood Agar: S. aureus forms large
cream or yellow low convex colonies
with β-haemolysis, S. epidermidis forms
small white colonies with no
haemolysis.
 MacConkey Agar: small pale pink
colonies observed.
 Mannitol Salt Agar: Large yellow
colonies

18. S. aureus, S. epidermidis (Blood
Agar)

19. DIAGNOSTIC TESTS:
BIOCHEMICAL TESTS
 Catalase Test: Presence of effervescence
will indicate presence of staphylococcus, rule
out streptococcus.
 Coagulase: coagulation observed will
indicate presence of pathogenic strain (S.
aureus)
 DNAse: zone of clearance observed will
indicate S. aureus
 Novobiocin test: growth <12mm or uniform
growth till edge of disk will indicate resistance
(S. saprophyticus) & clearance zone >16mm
will indicate susceptibility (S. epidermidis)

20. Catalase & Coagulase Tests

21. Mannitol Salt Agar, DNAse

22. DNAse, Novobiocin

23. MANAGEMENT/TREATMEN
T
 Drainage of abscesses
 Removal of catheters
 Fluid replacement and electrolyte
balancing
 Patients with MRSA should be
isolated
 Administration of antimicrobials

24. TREATMENT
Choice and dosage of antibiotics depend
on:
 Infection site
 Illness severity
 Probability that resistant strains are
present
Many strains produce β-lactamase &
therefore resist Penicillin G & V.
These can be treated with Methicillin,
Nafcillin or oxacillins.
MRSA strains are resistant to the above,
can be treated with Vancomysin.
VRSA strains have also emerged,

25. PREVENTION AND
CONTROL
 Thoroughly sterilize reusable equipment;
organism is vulnerable to alcohol based
sterilizers and moist heat at 600C.
 Disinfection of hands between patient
examinations
 Isolation of MRSA patients
 Maintenance of proper sanitation and body
hygiene when handling food
 Immediately cleaning and treating skin
scratches, abrasions or puncture wounds
 Use of protective gear when handling
patients

26. EPIDEMIOLOGY
 Staphylococcus, especially S. aureus is a
major cause of nosocomial and community
acquired infections.
 Humans are a natural reservoir for S. aureus
and S. epidermidis.
 Young children will have higher colonization
rates due to frequent contact with respiratory
secretions & other exposures.
 Spread is rapid in crowded areas with poor
sanitation.
 MRSA, originally associated with hospitals is
increasingly acquired in communities.

27. THANKS FOR YOUR
ATTENTION