2. Classification
• Family
• Genus
• Species
Micrococcaceae
Micrococcus and Staphylococcus
S. aureus
S. saprophyticus
S. epidermidis
M. luteusmore
than 20
species
Dr Reena Kulshrestha, M.Sc, PhD
3. INTRODUCTION
Staphyloccocci - derived from
Greek “stapyle” (bunch of grapes)
Gram positive cocci arranged in
clusters
Hardy organisms surviving many
non -physiologic conditions
Include a major human pathogen
and skin commensals
Dr Reena Kulshrestha, M.Sc, PhD
7. Coagulase-negative staphylococcus;
frequently involved in nosocomial and
opportunistic infections
• S. epidermidis – lives on skin and mucous
membranes; endocarditis, bacteremia, UTI
• S. hominis – lives around apocrine sweat
glands
• S. capitis – live on scalp, face, external ear
All 3 may cause wound infections by
penetrating through broken skin
• S. saprophyticus – infrequently lives on skin,
intestine, vagina; UTIDr Reena Kulshrestha, M.Sc, PhD
8. A. Staphylococcus aureus
Major human pathogen
Habitat - part of normal flora in some
humans and animals
Source of organism - can be infected human
host, carrier, fomite or environment
Dr Reena Kulshrestha, M.Sc, PhD
9. Grows in large, round, opaque
colonies
Optimum temperature of 37o
C
Facultative anaerobe
Withstands high salt, extremes in
pH, and high temperatures
Carried in nasopharynx and skin
Produces many virulence factors
Dr Reena Kulshrestha, M.Sc, PhD
10. Cultivation of S.aureus
Temp. 10-42*C, pH – 7.4 – 7.6
Aerobes & facultative anaerobes
Nutrient Agar – emulsifiable, smooth, shiny
Colony pigmentation - white, orange & yellow – at
22*C, aerobic conditins, enhanced with 1% glycerol
monoacetate or milk
NA slope – “ oil – paint appearance”
Blood Agar – B – hemolysis
Mac Conkey’s Agar – pink – LF colonies
Broth media – Salt- milk broth, Ludam’s medium –
uniform turbidity
Dr Reena Kulshrestha, M.Sc, PhD
16. Cell- associated virulence factors
•Capsule or slime layer (glycocalyx) –
inhibits opsonisation
•Peptidoglycan (PG) – rigidity to cell,
activates complement, induces release of
inflammatory cytokines
•Teichoic acid is covalently linked to PG
and is species specific:
- Facilitataes adhesion, protects from
complement-mediated opsonisation
Dr Reena Kulshrestha, M.Sc, PhD
17. S. aureus- ribitol teichoic acid
(polysaccharide A)
S. epidermidis- glycerol teichoic acid
(polysaccharide B)
•Protein A - is covalently linked to PG
-chemotactic, antiphagocytic,
anticomplementary, induces platelet
damage & hypersensitivity
-Binds to Fc terminal of IgG
Dr Reena Kulshrestha, M.Sc, PhD
18. •Clumping factor ( bound coagulase )
-Surface protein for ‘ Slide Coagulase ’ test
- saline suspension of
S.aureus + Human plasma
Cocci are clumped
- Identification of S.aureus
- Capsulated strain may not show
Dr Reena Kulshrestha, M.Sc, PhD
19. Virulence Factors
Extracellular Enzymes
• Coagulase (free) -
– Antigenic, acts along with ‘CRF’
• Hyaluronidase
– “spreading factor” of S. aureus
(Staphylokinase (fibrinolysin), fatty acid
modifying enzymes & proteases )
– Breaks down the connective tissue
• Nuclease
– Cleaves DNA and RNA in S. aureus
– Heat stable
Dr Reena Kulshrestha, M.Sc, PhD
20. • Protease
– Staphylokinase (fibrinolysin)
– facilitates adhesion
• Lipases
- helps in infecting the skin and sub-
cutaneous tissues
• Esterases
Dr Reena Kulshrestha, M.Sc, PhD
24. Natural history of disease
Many neonates, children, adults
-intermittently colonized by S. aureus
Usual sites - skin, nasopharynx,
perineum
Breach in mucosal barriers - can enter
underlying tissue
Characteristic abscesses
Disease due to toxin production
Dr Reena Kulshrestha, M.Sc, PhD
25. DISEASES
Due to direct effect
of organism
Local lesions of
skin
Deep abscesses
Systemic
infections
Toxin mediated
Food
poisoning
toxic shock
syndrome
Scalded skin
syndrome
Dr Reena Kulshrestha, M.Sc, PhD
26. Factors predisposing to S. aureus
infections
Host factors
Breach in skin
Chemotaxis defects
Opsonisation
defects
Neutrophil
functional defects
Diabetes mellitus
Presence of foreign
bodies
Pathogen Factors
Catalase (counteracts
host defences)
Coagulase
Hyaluronidase
Lipases (Imp. in
disseminating
infection)
B lactasamase(ass.
With antibiotic
resistance)
Dr Reena Kulshrestha, M.Sc, PhD
28. Pathogenesis
• Pass skin – first line of defense
– Benign infection
• Phagocytosis
• Antibody
• Inflammatory response
– Chronic infections
• Delayed hypersensitivity
Dr Reena Kulshrestha, M.Sc, PhD
29. SKIN LESIONS
Boils
Styes
Furuncles(infection of hair follicle)
Carbuncles (infection of several hair follicles)
Wound infections(progressive appearance of
swelling and pain in a surgical wound after
about 2 days from the surgery)
Impetigo(skin lesion with blisters that break
and become covered with crusting exudate)
Dr Reena Kulshrestha, M.Sc, PhD
32. DEEP ABSCESSSES
Can be single or multiple
Breast abscess can occur in 1-3% of
nursing mothers in puerperiem
Can produce mild to severe disease
Other sites - kidney, brain from
septic foci in blood
Dr Reena Kulshrestha, M.Sc, PhD
33. Systemic Infections
1. With obvious focus
Osteomyelitis, septic arthritis
2. No obvious focus
heart (infective endocarditis)
Brain(brain abscesses)
3. Ass. With predisposing factors
multiple abscesses, septicaemia(IV drug
users)
Staphylococcal pneumonia (Post viral)
Dr Reena Kulshrestha, M.Sc, PhD
35. B. TOXIN MEDIATED DISEASES
1. Staphylococcal food poisoning
Due to production of entero toxins
heat stable entero toxin acts on gut
produces severe vomiting following a
very short incubation period
Resolves on its own within about 24
hours
Dr Reena Kulshrestha, M.Sc, PhD
36. 2. Toxic shock syndrome
High fever, diarrhoea, shock and
erythematous skin rash which desquamate
Mediated via ‘toxic shock syndrome toxin’
10% mortality rate
Described in two groups of patients
Asso. with young women using tampones during
menstruation
Described in young children and men
Dr Reena Kulshrestha, M.Sc, PhD
38. 3. Scalded skin syndrome
Disease of young children
Mediated through minor Staphylococcal
infection by ‘epidermolytic toxin’
producing strains
Mild erythema and blistering of skin
followed by shedding of sheets of
epidermis
Children are otherwise healthy and most
eventually recover
Dr Reena Kulshrestha, M.Sc, PhD
39. Antibiotic sensitivity pattern
Very variable and not predictable
Very imp. In Pt. Management
Mechanisms
1.B lactamase production - plasmid mediated
Has made S. aureus resistant to penicillin group of
antibiotics - 90% of S. aureus (Gp A)
B lactamase stable penicillins (cloxacillin, oxacillin,
methicillin) used
2. Alteration of penicillin binding proteins
(Chromosomal mediated)
Has made S. aureus resistant to B lactamase stable
penicillins
10-20% S. aureus Gp (B) resistant to all Penicillins
and Cephalasporins)
Vancomycin is the drug of choiceDr Reena Kulshrestha, M.Sc, PhD
40. Tested in lab using methicillin
Referred to as methicillin resistant S. aureus
(MRSA)
Emerging problem in the world
In Sri Lanka prevalence varies from 20- 40% in
hospitals
Drug of choice - vancomycin
In Japan emergence of VIRSA(vancomycin
intermediate resistant S. aureus)
No effective antibiotics discovered -We might
have to discover
Dr Reena Kulshrestha, M.Sc, PhD
41. DIAGNOSIS
1. In all pus forming lesions
Gram stain and culture of pus
2. In all systemic infections
Blood culture
3. In infections of other tissues
Culture of relevant tissue or
exudate
Dr Reena Kulshrestha, M.Sc, PhD
42. Identification of Staphylococcus in
Samples
• Frequently isolated from pus,
tissue exudates, sputum, urine,
and blood
• Cultivation, catalase,
biochemical testing, coagulase
Dr Reena Kulshrestha, M.Sc, PhD
43. Mannitol Salts Agar (MSA)
Staphylococcus aureus
Dr Reena Kulshrestha, M.Sc, PhD
44. Catalase
2H2O2 O2 + 2H2O
Streptococci vs. Staphylococci
Differential Characteristics
Dr Reena Kulshrestha, M.Sc, PhD
49. Prevention
• Carrier status prevents complete
control
• Proper hygiene, segregation of carrier
from highly susceptible individuals
• Good aseptic techniques when
handling surgical instruments
• Control of nosocomial infections
Dr Reena Kulshrestha, M.Sc, PhD
50. 2. Staphylococcus
epidermidis
Skin commensal
Has predilection for plastic material
Ass. With infection of IV lines, prosthetic heart
valves, shunts
Causes urinary tract infection in cathetarised
patients
Has variable ABS pattern
Treatment should be aided with ABST
Dr Reena Kulshrestha, M.Sc, PhD
51. S. epidermidis
Location
Normal skin flora
opportunistic pathogen
Skin/wound infections
Endocarditis
UTI
Exposure
Direct contact
Newborns
Elderly
Fomites
Catheters
Shunts
IV needles
Prosthetics
Dr Reena Kulshrestha, M.Sc, PhD
