Lab No (2) : Genus :Staphylococci

Characteristics :

·  Gram positive non spore forming ,non-motile, spherical cells, usually arranged in grape-like clusters.

·  Single cocci, pairs, tetrads and small chains are seen in liquid cultures.

·  Young cocci stain strongly gram-positive, on aging many cells become gram-negative.

·  The three main species of clinical importance :

·  1-Staphylococcus aureus.

·  2-Staphylococcus epidermidis

·  3-Staphylococcus saprophyticus

·  Can readily grow in ordinary media under aerobic and micro-aerophilic conditions.

·  Grow most rapidly at 37 0 c but form pigment best at room temperature of 20-250 c.

·  Colonies in solid media are round. Smooth, raised and glistening.

·  Some of them are normal flora of the skin and mucus membrane of human, others cause suppuration abscess formation and fatal septicemia.

·  Produce catalase, which differentiate test them from the streptococci.

·  Relatively resistant to drying, heat, and 9%Nacl, but readily inhibited by 3% hexachlorophene.

Fig. (1) Staphylococci

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 within 5days after the onset of menses in young women who use tampons.

.Staphylococcus scalded skin syndrome: caused by exfoliative toxin produced by S.aureus.

.S .saprophyticus: relatively common cause of urinary tract infections 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 ( C.S.F)

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 350 c -370c.

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. Mannitol salt agar is used to screen for nasal carriers of S. aureus .

S. epidermidis : white colonies, non- hemolytic.

S. saprophyticus: may me 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.

a.  Slide test: to detect bound coagulase.

Clumping with in 10 seconds ………….. S.aureus .

No clumping within 10 seconds ……… consl (coagulase negative staphylococci)

b.  Tube test : to detect free coagulase.

Fibrin clot …………… S. aureus .

No fibrin clot ……………..cons.

Sensitivity testing :

Novobiocin sensitive ………….. S. aureus and S. epidermidis .

Novobiocin resistant ……………..S. saprophyticus .

Table(1) : shows differentiation of species

Organism / colony appearance / Ccog catalase / Coagu coagulase
produ / Novobiocin
Sensitive / Bl hemolysin
S.aureus / Golden / + / Po + / S / Po +
S. epidermis / White- white- Gray / Pos + / Neg - / Sen S / Negate -
S.s S.saprophyticus / White -Gray / Pos + / Neg - / Re R / Nega -

Treatment:

Penicillin sensitive staphylococci ………… penicillin, ampicillin.

Penicillin resistant staphylococci …………. Cloxacillin,Nafcillin

Methicillin resistant staphylococci ………… 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 carries with topical antiseptics or rifampin and anti-staphylococcal drug.