Staphylococcus
Staphylococcus are gram positive cocci arrange in grapes like clusters. Staphylococcus is classified into 32 species and 15 subspecies.
1. Staphylococcus Aureus
Morphology
They are gram positive cocci arranged in clusters, spherical and 0.8-1 micrometre in diameter, non-motile, non- sporing.
Staphylococcus aureus; gram stained smear of pus cells.
Characteristics
They are aerobes and facultative anaerobes.
Optimal temperature for growth is 37 degree Celsius range being 10-42 degree Celsius and optimum PH 7.4-7.6
Culture
Grow rapidly on ordinary culture media.
1. Nutrient agar
24 hours incubation, it mostly produces pigmented, golden yellow, colonies with 2-4mm in diameter that emulsify easily.
2. Blood agar
In organism produces beta-hemolysis in this medium containing rabbit or sheep blood.
3. MacConkey's agar
Organism produce pink colonies due to lactose fermentation.
4. Mannitol salt sugar
Yellow colour calories are seen on this medium due to fermentation of mannitol by most strains of staphylococcus aureus.
5. Liquid medium (broth)
In nutrient broth organism produces uniform muddy like.
Toxins and Enzymes
Staphylococcus aureus form number of toxins and enzymes, that factor of organism for producing disease in host.
1. Haemolysins
2. Leucocidin
3. Enterotoxin
4. Toxic shock syndrome (TSS)
5. Exfoliative toxin
6. Coagulase
7. Phosphatase
8. Fibrinolysis
Sources and Modes of Transmission
1. Direct contact
Breaks cuts and abrasions in skin or mucus membrane.
2. Through wound
3. Carrier
4. Through fomites
Towel, cloths, toys, pen
5. Droplets transmission
6. Contaminated food
Pathogenesis
Staphylococcus disease may be classified as cutaneous and deep Infections; food poisioning, Nosocomial Infections, skin exfoliative disease and toxic shock syndrome.
Infections due to staphylococcus aureus
1. Cutaneous infection
Superficial infection include pustules, boils, abscesses, wound and burn infections cause dermatitis.
Irritation or inflammation of skin.
Infection of eyelash follicle.
2. Deep Infection
Include tonsillitis, pharyngitis, sinusitis, pneumonitis, meningitis, bacteriaemia, septicemia.
Infection with sepsis, septic joint, endocarditis
3. Food poisioning
Ingested contaminated food which contain enterotoxin of staphylococcus aureus.
4. Nosocomial infection
Cause of hospital acquired infection.
5. Skin exfoliative
Redness and peeling, disease of skin.
Produce by strains of staphylococcus aureus causes underlying tissue of skin occurs exfoliative syndrome.
6. Toxic shock syndrome (TSS)
Causes by TSS mainly use of tampons by menstruation women, skin wounds, surgery.
Lab Diagnosis
Specimen collection;
Suppurative lesions, Pus, Sputum, Blood, Urine, CSF, food or vomit, Faeces.
Transport
Sterile container under aseptic condition.
Direct microscopy
With gram stained smears of pus or wound where, gram positive cocci in cluster seen.
Blue coloured.
Culture
Optimum temperature 37 degree celcius. Optimum PH; 7.4
Colony morphology and gram staining
On blood agar, colonies are 2-4mm in diameter, circular, produce golden yellow pigment, beta haemolysis is seen around colonies.
On gram staining, they are gram positive cocci (1 micrometre in diameter) arranged in grapes like clusters.
Non- motile cocci in cluster are seen in hanging drop preparation.
Biochemical reactions
To distinguish pathogenic strains of staphylococcus aureus.
Only staphylococcus aureus species can ferment mannitol, useful for identification of staphylococcus aureus.
Serological test
Treatment and Prevention
Infection can be prevented by following hygienic practices;
1. Wash hands with soap
2. Keep food preparing area and utensils clean and sanitized, hygienic food, hygienic living practices.
3. Disinfection of fomites
4. Control Nosocomial Infection
Benzyl penicillin is the most effective antibiotics.
Oxacillin, cloxacillin, flucloxacillin and methicillin are penicillin; staphylococcus aureus resistance.
Infection due to staphylococcus aureus
Staphylococcus
Many strains
1. Localized factors
Local infection abscesses
Surgical wound infection
Otitis
Sinusitis
Bacteriaemia
Disseminated Infection
Endocarditis
Septic thrombophlebitis
Deep localized
Osteomyelitis
Septic arthritis
Other deep abscesses
2. Toxins
Exfoliative; scalded skin
TSS
Food fever
Enterotoxins
Poisoning
Toxin shock syndrome; group of sign of illness.
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