STAPHYLOCOCCUS
- Anaerobic
- Catalase positive
- Gram positive cocci
- Opportunistic
- From skin to multivisceral infection
- Non motile
- Non sporing
- May have PS capsule
- Grape like clusters
- Usual ENVT growth
- Grow in high [NaCL] (7.5%)
- Golden yellow pigment
- Resist external ENVT
TAXONOMY/ staphelococcaceae -> staphylococcus -> 2 subgroups (based on ability to clot
blood plasma by Enz coagulase):
+ Coagulase positive (CoPS): S. aureus
+ coagulase negative (CoNS): S. saprophyticus, S. epidermidis
- Reservoir: ubiquitous, human (ill or carrier)
- Transmission is direct human to human by hands or indirect by food & instruments
- Favoring factors (poor hygiene, immunodepression)
Ag structure/ Capsule (facilitate adherence to catheters & synthetic material + inhibit
phagocytosis)
- Peptidoglycan (imp in pathogenesis, activates complement & evokes prod of
inflammatory cytokines)
- Teichoic acid (facilitate adhesion to host cell + protect from opsonization)
- Protein A: + major cell wall component
+ responsible for antiphagocytic, anticomplementary effects & induce
hypersensitivity
+ linked to peptidoglycan layer & has a unique affinity for binding to the Fc
receptor of IgG
+ its detection can be used for S. aureus identification
Coagulase & surface Prots/
- Outer surface of most strains of S. aureus contains clumping factor (bound coagulase)
- Coagulase binds fibrinogen & converts it to insoluble fibrin -> S clump or aggregate
Virulence factors/ + extraC toxins
- Haemolysin (α,β,γ,δ): haemolytic dermo-necrotic & leurocidal
- Leucocidin (Panton-valentine factor): kills WBC by sporing the CM
- Enterotoxin: act on the ANS
- TSST: fever, skin rashes, diarrhea, conjunctivitis, death
- Exfoliation toxin: blistering & exfoliating D of the skin
+ extraC Enz
- Free coagulase: clot plasma, acts with CRF, binds to prothrombin & convert fibrinogen
to fibrin
- Staphylokinase: degrade fibrin clots
- Hyaluronidase: hydrolyze acidic mucoPS present in the matrix of conn tissue
- Lipase, phospholipase protease: degrade lipid, phospholipid & proteins
Staphylococcus Enz (coagulase, clumping factor, catalase, hyaluronidase, fibrinolysin,
nuclease, lipases, penicillinase)
Staphylococcus Toxins/
Haemolysins (α, β, γ, δ toxins):
- alpha: + prod only under anaerobic conditions, less active against human RBC
+ leucocidal, cytotoxic, dermonecrotic, neurotoxic & lethal
- Beta: haemolytic for sheep, both anaerobic & aerobic prod, lysis at 37°C, evident only
on cold T°, prop called hot-cold phenomenon
- Gamma: act on human, sheep & rabbits RBC
- Delta: lytic to human, sheep & rabbit RBCs
Leucocidin (Panton-Valentin toxin “PVL”):
- Form pores on memb of leukocytes -> destruction
- 2 subunits: HIgA & HIgB or PVL
2 exfoliative toxins (A, B):
- Epidermolytic toxin, 2 types (A-heat stable, B-heat labile)
- Cause epidermal splitting -> blistering D & generalised desquamation leading to SSSS
- SSSS: staphylococcal scaled skin syndrome
- Ritter’s D is a sever SSSS In newborns
- Pemphigus neonatorum & bullous impetigo are milder forms
8 enterotoxins (A-E, G-I):
- Super antigen, responsible for food poisoning, microgram can cause illness
- Nausea, vomiting, diarrhoea within 2-6 hrs
- 8 types: A, B, C1-3, D, E, H) A the most cases, C & D in milk prod
- B causes staphylococcal pseudomembranous enterocolitis
- Stable at 100°C for 30 min & resistant to hydrolysis & jejunal Enz
- Act directly on ANS
Toxic shock syndrome toxin [1 (TSST-1)]:
- Superantigen, trigger cytokine storm -> fever, rash, shoch & systemic symptoms
- TSS: fever, hypotension, vomiting, diarrhoea, erythematous rash with desquamation
& hyperaemia of mucousmemb
- Belong to bacteriophage grp 1
- TSST-1: called pyrogenic exotoxin C & enterotoxin F, heatproteolysis resistant exotoxin
- TSST-1 ability to penetrate mucosal barrier respon for systemic effects of TSS
- TSS death is due to hypovolemic shock -> multiorgan failure
RESISTANCE/
- S. aureus rapidly killed by T° > 60°C
- Most strains can grow at 10% NaCl
- S. aureus: susceptible to common disinfectants & antiseptics
Can survive & stay virulent for long period (2-3 months)
- Killed by crystal violet
S. AUREUS PATHOGENECITY/
- pathogenic for human as well as all domestic & free-living warm-blooded animals
- pyogenic organism & lesion are usually localized unlike that of streptococcal lesion
- S. aureus causes D by prod of toxin or by direct invasion & destruction of tissue
- Cause: cutaneous & deep infections, food poisoning, nosocomial infection, TSS, skin
exfoliative D
Pathogenicity/
- Cutaneous infection: pustules, boils, abscesses, styes, impetigo, wound, carbuncles,
burn infection, pemphigus neonatorum
- Deep infections: osteomyelitis, pharyngitis, sinusitis, pneumonitis, empyema,
meningitis; may cause UTI
- Food poisoning
- Nosocomial infections
- Skin exfoliative D: SSSS
- TSS
DIAG/
- Specimen collection (pus, blood) is cultured on blood agar
- Incubation of plates at 37°C for 24 hrs to allow bacterial growth
- After 24 hrs Blood agar plate -> significant growth (golden yellowish colonies)
- Gram staining: gram positive cocci (grape like arrangement)
- Sub-culture isolated organism onto nutrient agar for further biochem testing
- Specimen (pus: wound & abscess & burns; nasal swab; blood: diag endocarditis &
bacteremia; sputum; milk)
+ Double zone of haemolysis:
+ outer zone: “alpha” incomplete haemolysis
+ inner zone: “beta” complete haemolysis
+ double zone haemolysis (by S. aureus, intermedius, pseudointermedius)
- Culture charac:
- Nutrient agar (large, circular, convex, smooth shiny, opaque colonies – golden
yellowish)
- MacConkey’s agar: small pink colonies
- blood agar: Beta-haemolytic colonies, golden yellowish
- Mannitol salt agar: yellow colonies, useful for selective medium from faeces
- aerobe & facultative anaerobe
- optimum pH growth = 7.4-7.5
+ Biochemical props:
- catalase positive
- oxidase positive
- ferment G, lactose, maltose, sucrose, mannitol, with prod of acis
+COAGULASE:
- Slide method: bound coagulase
- Tube method: free coagulase
Antibiotic resistance/
- Beta lactamase (penicillinase)
- MRSA (methicillin resistant staphylococci)
Coagulase negative staphylococcal spp (CONS)
- S. epidermidis: + most frqtly isolated
+ predilection for plastic material
+ associated with infection of IV lines, catheters, prosthetic heart valve
+ colonizes moist body areas such as axilla, inguinal & perianal areas, & toe webs
+ Imp cause of nosocomial infection
- S. saprophyticus: + skin commensal
+ frequently isolated in rectum and genitourinary tract of young women
+ can be causative agent in UTI
+ 2nd most common Urinary infection in young women
PREVENTION/
- Hand antisepsis
- the proper cleansing of wounds and surgical openings, aseptic use of catheters or
indwelling needles and appropriate use of antiseptics.
- Avoiding the handling of food by carriers in the catering trade
- Detection and elimination of nasal carriage
- Isolation of patients carrying MRSA or GISA
