Staphylococci spp

Staphylococci

Gram-positive cocci non motile non spore forming non capsulated facultative anaerobic catalase-positive resistant to higher osmotic pressure

There are three practical clinically important species :

Species : S.aureus : main pathogen S.epidermidis (S.albus) : opportunistic S.saprophyticus : UTI

Differentiating Tests

Coagulase test : main test S.aureus : Coagulase positive S. epidermidis and S. saprophyticus : Coagulase negative

Staph. epidermidis : It is frequent inhabitant of human surface tissues, including skin mucous membranes. It is usually not pathogenic mo.but it may cause serious infections, If it has unusual position in humans body, for example cardiac surgery patients or those with takes intra-venous catheters.


Staph. saprophyticus : Has been implicated in a cute urinary tract infections in young women 16 –25 years. It has not been found among the normal flora and is not yet known to cause other types of infection.

Staph. aureus : Strains produce a numbers of toxins and enzymes that can exert harmful effects on the cells of the infected host.
Hemolysin : can destroy red blood cells. Catalase . Coagulase : Coagulate plasma . Leukocidin : destroy leucocytes. Hyaluronidase : act on substrate that is structural component of connecvtive tissue Cytotoxins : Cell lysis .



Penicillinase : break down β-lactam drugs .Protein A : Anti phagocytic prosses.Staphylokinase : can dissolve fibrin clots.Lipase : breaks lipds of cell membrane .DNase : DNA hydrolysis .Enterotoxin : by some strains of Staph. aureus can be response of food poisoning

S. aureus - infections

Pyogenic infections furncles ( boils )wound infections Impetigo(skin lesion with blisters that break and become covered with crusting exudate) Abscesses Septicaemia Osteomyelitis Pneumonia
Intoxication Scalded skin syndrome Toxic shock syndrome High fever, diarrhoea, shock and erythematous skin rash which desquamate Food poisoning heat stable entero toxin acts on gut produces severe vomiting following a very short incubation period Resolves on its own within about 24 hours
Pathogenicity :

SKIN LESIONS

Scalded skin syndrome

Coagulase-negative staphylococciinfections

Urinary tract (S. saprophyticus, S. epider-midis.) Systemic (usually from infected prostheses and implants - S. epidermidis) Peritonitis (S. epidermidis.) Septicaemia (S. epidermidis) Endocarditis (S. epidermidis)

1 normal microflora

1 normal microflora
1 normal microflora
2impetigo
11 respiratory infections
8 meningitis
3 furuncle, carbuncle
4 wound inf., abscesses5 spread via lymphatic and blood ways
6 osteomyelitis
7 endocarditis
10nephritis
9 enteritis food poisoning

Staphylococcal inf. of oral cavity

mucosa and submucosa - S.aureus - Sialadenitis (inflammation of parotic glands) - Cheilitis angularis (inflammation of lips) - S.aureus + Candida spp. - Stomatitis (inflammation of palate and tongue). Dentoalveolar abscesses, periapical abscesses Acute, chronic osteitis. Osteomyelitis (mandibula). Gingivitis, periodontitis.

Isolation and Identification of Staphylococci : The laboratory diagnosis of Staphylococci is made by identifying the organism ( usually Staph. aureus ) in clinical specimen Pus from skin lesion, sputum from pneumonia ( when pneumonia is suspected ) urine, spinal fluid or blood. Special care must be taken, not to contaminate the specimen with normal flora.

Staphylococci - laboratory diagnostic

Microscopy Gram staining

2- Catalase test.

3-Coagulase test

b- hemolysis

4- Cultivation BA, salt agar
On blood agar Staph. aureus usually golden to yellow pigment, Where Staph. epidermidis has a white pigment and Staph. saprophyticus either yellow or white pigment.

5- Reaction to carbohydrate mannitol.

6-Dnase test :

Most coagulase positive staphylococci are produced this enzyme. Procedure: Inoculate DNase medium withStaphylococcus after incubation at 37Co for 24hrs, flood the plate with 1 NHCL . Result : A clear zone around the positive DNase strain, the remain plate will be opaque because of the precipitation of DNA by HCL

Negative

Positive

7- Novobiocin disc test

This test is used to differentiating .two coagulase negative species of staphylococci, the zone of inhibition around Staph. saprophyticus is less than 16 mm(resistant).
sensitivity test
Novobiocin
Note :Staph. aureus is a major cause of nosocomial infections, transmitted from hospital or the environment.

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