Staphylococci final

Dr Reena Kulshrestha, M.Sc, PhD

Classification

• Family

• Genus

• Species

Micrococcaceae

Micrococcus and Staphylococcus

S. aureusS. saprophyticusS. epidermidisM. luteusmore

than 20 species

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

StreptococcusStaphylococcus

Grouping for Clinical Purposes1. Coagulase positive Staphylococci

Staphylococcus aureus

2. Coagulase negative StaphylococciStaphylococcus epidermidisStaphylococcus saprophyticus

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

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

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

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

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

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

•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

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

• Protease– Staphylokinase (fibrinolysin)– facilitates adhesion

• Lipases - helps in infecting the skin and sub-

cutaneous tissues• Esterases

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

• 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

•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

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

DISEASESDue to direct effect of organismLocal lesions of skin

Deep abscesses

Systemic infections

Toxin mediatedFood poisoning

toxic shock syndrome

Scalded skin syndrome

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)

Pathogenesis•Pass skin – first line of

defense– Benign infection

•Phagocytosis•Antibody•Inflammatory response

– Chronic infections•Delayed hypersensitivity

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)

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

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)

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

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

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

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

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

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

Identification of Staphylococcus in Samples

•Frequently isolated from pus, tissue exudates, sputum, urine, and blood

•Cultivation, catalase, biochemical testing, coagulase

Mannitol Salts Agar (MSA)

Staphylococcus aureus

Catalase2H2O2 O2 + 2H2O

Streptococci vs. Staphylococci

Differential Characteristics

Catalase POS

StaphylococcusCatalase NEG

S. aureus

Coagulase

Fibrinogen Fibrin

Differential Characteristics

Treatment

• Drain infected area• Deep/metastatic infections

– semi-synthetic penicllins– cephalosporins– erythromycin– clindamycin

• Endocarditis– semi-synthetic penicillin + an

aminoglycoside

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

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

S. epidermidisLocation

Normal skin flora opportunistic pathogen

Skin/wound infections Endocarditis UTI

Exposure Direct contact

Newborns Elderly

Fomites Catheters Shunts IV needles Prosthetics

S. saprophyticusPathogenesis

FimbriaAdhesion proteinsAutolysins

DiseasesUTI/cystitisPeritonitisEnopthalmitisEndocaritisSeptic arthritis

S. xylosusCommensalIndustry

Ferment meatRed color of sausageFerment milkOrange color of cheese

PathogenicityBiofilmsEnterotoxins

DiseaseNosocomialUTIFood poisoning (raw)

S. capitisEpidemiology

Skin microbioticaHead predominantly

PathogenicityCoagulase (-)AB resistance

DiseasesValvular endocarditisNeonatal septicemiaOsteomyelitis

S. pseudointermediusAnimal

microbioticaEpidemiology

ZoonoticEnterotoxins+/- coagulase

DiseasesPyoderma (animals)Food poisoning

Staphylococci final

Health & Medicine

Transcript of Staphylococci final

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