Treatment



Staphylococcus

Bacteria in the genus Staphylococcus are pathogens of man and other mammals. Traditionally they were divided into two groups on the basis of their ability to clot blood plasma (the coagulase reaction). The coagulase-positive staphylococci constitute the most pathogenic species S aureus. The coagulase-negative staphylococci (CNS) are now known to comprise over 30 other species. The CNS are common commensals of skin, although some species can cause infections.

S aureus expresses a variety of extracellular proteins and polysaccharides, some of which are correlated with virulence. Virulence results from the combined effect of many factors expressed during infection. Antibodies will neutralize staphylococcal toxins and enzymes, but vaccines are not available. Both antibiotic treatment and surgical drainage are often necessary to cure abscesses, large boils and wound infections. Staphylococci are common causes of infections associated with indwelling medical devices. These are difficult to treat with antibiotics alone and often require removal of the device. Some strains that infect hospitalized patients are resistant to most of the antibiotics used to treat infections, vancomycin being the only remaining drug to which resistance has not developed.

Staph. aureus :

Distinguished primarily by it's ability to produce coagulase , is notorious as the case of suppurative condition ( pyogenic or pus forming ) , mastitis of women & cow, boil , carbuncles , infantile impetigo , internal abscesses , and food poisoning .

Staph. epidermidis : ( Staph. albus )

Is a lesser pathogen or commensal on the skin and mucous membranes .

Staph. saprophyticus : ( Staph. citrus )

Non-pathogenic bacteria , a lemon-yellow colored colonies on nutrient agar medium

| |

|Diagnostic Laboratory Tests |

|Specimens |

|Surface swab pus, blood, tracheal aspirate, or spinal fluid for culture, depending upon the localization of the process. |

|Smears |

|Typical staphylococci appear as gram positive cocci in clusters in Gram-stained smears of pus or sputum. It is not possible to |

|distinguish saprophytic (S epidermidis) from pathogenic (S aureus) organisms on smears. |

|Culture |

|Specimens planted on blood agar plates give rise to typical colonies in 18 hours at 37 °C, but hemolysis and pigment production |

|may not occur until several days later and are optimal at room temperature. S aureus but not other staphylococci ferment |

|mannitol. Specimens contaminated with a mixed flora can be cultured on media containing 7.5% NaCl; the salt inhibits most other |

|normal flora but not S aureus. Mannitol salt agar or commercially available chromogenic media are used to screen for nasal |

|carriers of S aureus and patients with cystic fibrosis. |

|Catalase Test |

|This test is used to detect the presence of cytochrome oxidase enzymes. A drop of 3% hydrogen peroxide solution is placed on a |

|slide, and a small amount of the bacterial growth is placed in the solution. The formation of bubbles (the release of oxygen) |

|indicates a positive test. |

|Coagulase Test |

|Citrated rabbit (or human) plasma diluted 1:5 is mixed with an equal volume of broth culture( in tube) or growth from colonies |

|on agar (on slide) and incubated at 37 °C. A tube of plasma mixed with sterile broth is included as a control. If clots form in |

|1–4 hours, the test is positive. |

|Coagulase-positive staphylococci are considered pathogenic for humans; however, coagulase-positive staphylococci of dogs |

|(Staphylococcus intermedius) and dolphins (Staphylococcus delphini) rarely cause disease in humans. Infections of prosthetic |

|devices can be caused by organisms of the coagulase-negative S epidermidis group. |

|Susceptibility Testing |

|Broth microdilution or disk diffusion susceptibility testing should be done routinely on staphylococcal isolates from clinically|

|significant infections. Resistance to penicillin G can be predicted by a positive test for B-lactamase; approximately 90% of S |

|aureus produce [pic] |

|Serologic and Typing Tests |

|Serologic tests for diagnosis of S aureus infections have little practical value. |

|The table below show the difference between S.aurse & S.albus |

|species |

|haemolysis |

|catalase |

|coagulase |

|mannitol |

|maltose |

|V.P |

|sucrose |

| |

|S.aurse |

|+ |

|+ |

|+ |

|+ |

|+ |

|+ |

|- |

| |

|S.albus |

|- |

|+ |

|- |

|- |

|- |

|- |

|+ |

| |

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