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The Genus staphylococci are Gram positive non sporing,non motile and spherical cells usually arranged in grape-like clusters
The 03 main species of clinical importance are :
- Staphylococcus aureus
- Staphylococcus epidermidis
- Staphylococcus saprophyticus
- Staphylococcus lugdenenses
- Staphylococcus hominis
- Staphylococcus warneri
Characteristics of the Genus Staphylococci
- It's can readily grow in Ordinary media under aerobic and micro-aerophiliic conditions
- grow most rapidly at 37 0c but form pigment best at room temperature of 20-25 oc
- Colonies in solid media are round, smooth, raised and glistening.
- Some of them are normal flora of the skin and mucus membrane of human, otrhhers cause suppuration abscess formation and fatal septicemia
- Produce catalase, which differentiate them from the streptococci.
- relatively resistant to drying , heat, and 9% NacI, but readily inhibited by 3 % hexachlorophene
Antigenic Structure
- Peptidoglycan( Mucopeptide): Polysaccharide polymer which provide the rigid exoskeleton of the cell wall. It is important in the pathogenesis of infection like eliciting production of cytokines and opsonic antibodies; chemoattractant for polymorphs and activate complement
- Teichoic acid: Polymer of glycerol or ribitol phosphate
- Protein A: Important in immunologic diagnostic test (coagglutination test).
- Capsule: Anti-phagositic property
Enzymes
- Catalase- Produced by staphylococci Converts Hydrogen Peroxide (H202) into Water (H20) and Oxygen(02)
- Coagulase - Coagulase clots oxidated or citrated plasma. Coagulase may deposit fibrin on the surface of organism and alter ingestion by phagocytic cells.
- Clumping factor: A surface compound that is responsible for adherence of the organism to fibrinogen and fibrin Produced by Staphylococcus aureus Determines Invasive potential of the organism.
- Coagulase test differentiates S.aureus(coagulasepositive) from S.epidermidis (coagulase-negative)
- Hyaluronidase- Spreading factor
- Proteinases and lipases
- Staphylokinase- Fibrinolysin
- β-lactamase-Provides resistance of staphylococcus to β-lactam
- antibiotic like penicillin.
- Dnase: Deoxyribonucleotidase
- Nuclease
Toxins
- Exotoxins(α, β, γ, δ) Enterotoxin-Produced by S.aureus when grown in carbohydrate and protein foods.Multiple (A-E, G-I, K-M) soluble heat-stable, gut enzyme resistant toxins which act on neural receptors in the gut to stimulate vomiting center in the central nervous system. It is super antigen causing staphylococcal food poisoning
- Toxic shock syndrome toxin- Superantigen desquamative toxin Produced by S.aureus and Causes fever, shock, multiple-organ failure and skin rash.
- Exfoliative toxin-Epidermolytic super antigen produced by S.aureus and uses generalized desquamation of the skin (staphylococcal scalded skin syndrome).
- Epidermolytic toxin A: Chromosomal gene product and heat stable
- Epidermolytic toxin B: Plasmid mediated and heat labile
- Leukocidin: S aureus toxin which kills WBCs by forming pores and increasing cation permeability
Clinical features
- Folliculitis: Infection of one hair follicle.
- Curbuncle: Infection of multiple hair follicle and surrounding skin.
- Cellulitis: Infection of skin and subcutaneous tissue.
- Abscess formation: focal suppuration
- Mastitis: Infection of breast, especially in lactating mother
- Bulous impetigo: Crusted superficial skin lesion
- Pneumonia: Infection of lung parenchyma.
- Empyema: Accumulation of pus in pleural space
- Osteomyelitis: Infection of bone
- Endocarditis and meningitis: Infection of heart tissue and leptomeninges respectively.
- Food poisoning: Caused by enterotoxin produced by S.aureus Characterized by violent nausea, vomiting, and diarrhea
- Toxic shock syndrome: Caused by toxic shock syndrome toxin-1 produced by S.aureus Characterized by abrupt onset of high fever, vomiting, diarrhea,myalgia, scarlatiform rash,and hypotension with cardiac and renal failure in the most severe disease Occurs with in 5 days after the onset of menses in young womenwho use tampoons
- Staphylococcal scalded skin syndrome: Caused by exfoliative toxin produced by S.aureus.
- S. saprophyticus: Relatively common cause of urinary tractinfections in young women
- S. epidermidis: occasional cause of infection often associated with implanted appliances and devices
Laboratory Diagnosis
Specimen: Surface swabs, pus, blood, sputum, cerebrospinal fluid
Smear: Gram positive cocci in clusters, singly or in pairs.
Culture: Grow well aerobically and in a CO2 enriched ordinary media at an optimal temperature of 35°c-37°c.
Colony appearance : S.aureus: characteristically golden colonies.
frequently non-pigmented after over-night incubation.
hemolytic on blood agar plate.
7.5% Nacl containing media is used for mixed flora contaminated specimen
Mannnitol salt agar is used to screen for nasal carriers of S. aureus
- S.epidermidis: white colonies, non-hemolytic
- S.saprophyticus: may be white or yellow, non-hemolytic.
Biochemical reaction
1. Catalase test
Active bubbling…………….Catalase producing Bacteria (Staphylococci)
No active bubbling…………Non-catalase producing bacteria (streptococci)
2. Coagulase test
Slide test: To detect bound coagulase
Clumping within 10 seconds………… S.aureus
No clumping within 10 seconds………CONS(Coagulase negative staphylococci)
Tube test: To detect free coagulase
Fibrin clot…………….S.aureus
No fibrin clot…………CONS(Coagulase negative staphylococci)
ANTIBIOTIC SENSITIVITY TESTING
Sensitivity testing:
Novobiocin sensitive……. S.aureus and S.epidermidis
Novobiocin resistant……...S.saprophyticus
Treatment
Penicillin sensitive staphylococci………penicillin, ampicillin
Penicillin resistant staphylococci………cloxacillin, Nafcillin
Methicillin resistant staphylocicci……… Vancomycin
Prevention and control
- Source of infection is shedding human lesions, the human respiratory tract and skin
- Contact spread of infection occur in hospitals
- Treatment of nasal carriers with topical antiseptics or rifampin and anti-staphylococcal drug
