staphylococci final
TRANSCRIPT
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Dr Reena Kulshrestha, M.Sc, PhD
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Classification
• Family
• Genus
• Species
Micrococcaceae
Micrococcus and Staphylococcus
S. aureusS. saprophyticusS. epidermidisM. luteusmore
than 20 species
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INTRODUCTIONStaphyloccocci - 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
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Dr Reena Kulshrestha, M.Sc, PhD
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StreptococcusStaphylococcus
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Grouping for Clinical Purposes1. Coagulase positive Staphylococci
Staphylococcus aureus
2. Coagulase negative StaphylococciStaphylococcus epidermidisStaphylococcus saprophyticus
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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 earAll 3 may cause wound infections by penetrating through broken skin• S. saprophyticus – infrequently lives on skin, intestine, vagina; UTI
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A. Staphylococcus aureusMajor human pathogen
Habitat - part of normal flora in some humans and animals
Source of organism - can be infected human host, carrier, fomite or environment
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Grows in large, round, opaque colonies Optimum temperature of 37oC Facultative anaerobe Withstands high salt, extremes in pH, and high temperatures Carried in nasopharynx and skin Produces many virulence factors
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Cultivation of S.aureusTemp. 10-42*C, pH – 7.4 – 7.6Aerobes & facultative anaerobesNutrient Agar – emulsifiable, smooth, shinyColony pigmentation - white, orange &
yellow – at 22*C, aerobic conditins, enhanced with 1% glycerol monoacetate or milk
NA slope – “ oil – paint appearance”Blood Agar – B – hemolysisMac Conkey’s Agar – pink – LF coloniesBroth media – Salt- milk broth, Ludam’s
medium – uniform turbidityDr Reena Kulshrestha, M.Sc, PhD
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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
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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
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•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
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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
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• Protease– Staphylokinase (fibrinolysin)– facilitates adhesion
• Lipases - helps in infecting the skin and sub-
cutaneous tissues• Esterases
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Virulence Factors: Exotoxins•Cytolytic (cytotoxins; cytolysins)- Alpha toxin - hemolysin • Reacts with RBCs, leucocidal, dermonecrotic,
neurotoxic & lethal• Toxic to macrophages, lysosomes, muscle
tissues, renal cortex & circulatory system - Beta toxin• Sphingomyelinase, exhibits ‘ Hot-Cold
phenomenon’- Gamma toxin• Hemolytic activity- Delta toxin• Cytopathic for:• RBCs, Lymphocytes, Neutrophils, Platelets• Enterotoxic activity
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• Leucocidin- ( Panton- Valentine toxin)-2 componenets S & F*Synergohymenotropic toxins (leucocidin+gamma lysin)•Enterotoxin- -Causes Food – poisoning -Nausea, vomiting & diaarhea-IP- 2-6 hrs, Heat stable- 100* for 10- 40 mins-Source of infection – food handler (carrier)-Acts on autonomic nervous system-Potent- ug is toxigenic-Pyrogenic, mitogenic, hypotensive, thrombocytopenic & cytotoxic effects-Diagnosis – Latex agglutination & ELISADr Reena Kulshrestha, M.Sc, PhD
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•Exfoliative toxin (epidermolytic toxin) - ‘ SSSS ’ – exfoliative skin diseases,-– effects new born – ‘Ritter’s disease’ -epidermis gets separated from the underlying tissues-– older patients - Toxic epidermal necrolysis -Milder forms – Pemphigus neonatorum & Bullous impetigo
•Pyrogenic exotoxins- -‘ TSS ’ – fatal multisystem disease – fever, hypotension, myalgia, vomiting, diarhhea, mucosal hyperemia & erythematous rash-Infection of mucosal sites, skin & surgical wounds-Super Ag’s – excessive & dis-regulated Immune Response -activates large no. of T- cells, IL-1 & 2, TNF, INF-y- involves multisystemDr Reena Kulshrestha, M.Sc, PhD
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Natural history of diseaseMany neonates, children, adults -intermittently colonized by S. aureus
Usual sites - skin, nasopharynx, perineum
Breach in mucosal barriers - can enter underlying tissue
Characteristic abscessesDisease due to toxin production
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DISEASESDue to direct effect of organismLocal lesions of skin
Deep abscesses
Systemic infections
Toxin mediatedFood poisoning
toxic shock syndrome
Scalded skin syndrome
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Factors predisposing to S. aureus infections
Host factorsBreach in skinChemotaxis defectsOpsonisation
defectsNeutrophil
functional defectsDiabetes mellitusPresence of foreign
bodies
Pathogen Factors Catalase
(counteracts host defences)
CoagulaseHyaluronidaseLipases (Imp. in
disseminating infection)
B lactasamase(ass. With antibiotic resistance)
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Pathogenesis•Pass skin – first line of
defense– Benign infection
•Phagocytosis•Antibody•Inflammatory response
– Chronic infections•Delayed hypersensitivity
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SKIN LESIONSBoilsStyesFuruncles(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)
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DEEP ABSCESSSESCan be single or multipleBreast 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
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Systemic Infections1. With obvious focus
Osteomyelitis, septic arthritis2. No obvious focus
heart (infective endocarditis)Brain(brain abscesses)
3. Ass. With predisposing factors multiple abscesses, septicaemia(IV drug users)
Staphylococcal pneumonia (Post viral)
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B. TOXIN MEDIATED DISEASES1. Staphylococcal food poisoning
Due to production of entero toxinsheat stable entero toxin acts on gutproduces severe vomiting following a very short incubation period
Resolves on its own within about 24 hours
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2. Toxic shock syndromeHigh fever, diarrhoea, shock and erythematous skin rash which desquamate
Mediated via ‘toxic shock syndrome toxin’10% mortality rateDescribed in two groups of patients
Asso. with young women using tampones during menstruation
Described in young children and men
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3. Scalded skin syndromeDisease of young childrenMediated 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
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Antibiotic sensitivity patternVery variable and not predictableVery imp. In Pt. ManagementMechanisms
1.B lactamase production - plasmid mediatedHas made S. aureus resistant to penicillin
group of antibiotics - 90% of S. aureus (Gp A)B lactamase stable penicillins (cloxacillin,
oxacillin, methicillin) used2. Alteration of penicillin binding proteins
(Chromosomal mediated)Has made S. aureus resistant to B lactamase
stable penicillins10-20% S. aureus Gp (B) resistant to all
Penicillins and Cephalasporins)Vancomycin is the drug of choiceDr Reena Kulshrestha, M.Sc, PhD
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Tested in lab using methicillinReferred to as methicillin resistant S.
aureus (MRSA)Emerging problem in the worldIn Sri Lanka prevalence varies from 20-
40% in hospitalsDrug of choice - vancomycinIn Japan emergence of
VIRSA(vancomycin intermediate resistant S. aureus)
No effective antibiotics discovered -We might have to discover
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DIAGNOSIS1. In all pus forming lesions
Gram stain and culture of pus2. In all systemic infections
Blood culture3. In infections of other tissues
Culture of relevant tissue or exudate
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Identification of Staphylococcus in Samples
•Frequently isolated from pus, tissue exudates, sputum, urine, and blood
•Cultivation, catalase, biochemical testing, coagulase
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Mannitol Salts Agar (MSA)
Staphylococcus aureus
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Catalase2H2O2 O2 + 2H2O
Streptococci vs. Staphylococci
Differential Characteristics
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Catalase POS
StaphylococcusCatalase NEG
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S. aureus
Coagulase
Fibrinogen Fibrin
Differential Characteristics
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Treatment
• Drain infected area• Deep/metastatic infections
– semi-synthetic penicllins– cephalosporins– erythromycin– clindamycin
• Endocarditis– semi-synthetic penicillin + an
aminoglycoside
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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
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2. Staphylococcus epidermidisSkin commensalHas predilection for plastic materialAss. With infection of IV lines,
prosthetic heart valves, shuntsCauses urinary tract infection in
cathetarised patientsHas variable ABS pattern Treatment should be aided with ABST
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S. epidermidisLocation
Normal skin flora opportunistic pathogen
Skin/wound infections Endocarditis UTI
Exposure Direct contact
Newborns Elderly
Fomites Catheters Shunts IV needles Prosthetics
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S. saprophyticusPathogenesis
FimbriaAdhesion proteinsAutolysins
DiseasesUTI/cystitisPeritonitisEnopthalmitisEndocaritisSeptic arthritis
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S. xylosusCommensalIndustry
Ferment meatRed color of sausageFerment milkOrange color of cheese
PathogenicityBiofilmsEnterotoxins
DiseaseNosocomialUTIFood poisoning (raw)
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S. capitisEpidemiology
Skin microbioticaHead predominantly
PathogenicityCoagulase (-)AB resistance
DiseasesValvular endocarditisNeonatal septicemiaOsteomyelitis
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S. pseudointermediusAnimal
microbioticaEpidemiology
ZoonoticEnterotoxins+/- coagulase
DiseasesPyoderma (animals)Food poisoning
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