Staphylococci&Micrococcii

Staphylococci are gram + positive cocci.They are arranged in characteristic grap – like clusters.They are more than 15 different species.The most importance medical species are: Staph. aureusStaph. epidermidisStaph. saprophyticus Staphylococci

Staphylococci cause a variety of both common and uncommon infection such as: Abscesses of many organs. Endocarditis. Gastroenteritis (food poisoning)caused by an enterotoxin. Toxic shock syndrome(caused by an enterotoxin).

They are infrequently isolated from oral cavity. Higher proportion of Staph. aureus are found in the saliva of healthy subjects older than 70 years.
Note:

Staph. aureus: Habitat and Transmission The habitat is the human skin especially the anterior naris and the perineum. Domesticated animals also carry Staphylococci. Hospital pts. &staff (higher carriage rates) These bacteria are disseminated through air and dust and always present in the hospital environment. The usual transmission rout is via the hands.

Characteristics: G+ cocci in cluster. Non sporing. Non motile. Some strains are capsulate.

Grows aerobically as yellow or gold colonies on blood agar. Catalase positive. Coagulase positive. Protein A. synthesized by almost all strains of Staph. aureus DNAase test. Mannitol fermentation test
Culture and Identification:

Protein A – Latex agglutination test:Protein A of Staph. aureus has a special affinity for IgG. Hence when Latex particles coated IgG are mixed with a suspension of microorganisms on a glass slide, visible agglutination of Latex particles occurs.No such reaction is seen with Staph. epidermidis

Typing is important to determine the source of an outbreak of infection. This is commonly done by the pattern of susceptibility to a set of more than 20 bacteriophages – phage typing Typing of Staphylococcus aureus:

Some of the disease caused by Staph. aureus are: 1-Superficial infections: common agent of boils, carbuncles, pustules, abscesses, conjunctivitis and wound infection, rarely caused oral infections, may cause angular chelitis (together with the yeast Candida). Food poisoning (vomiting and diarrhea) caused by enetrotoxins. 2-Deep infections; Osteomylitis, endocarditis, septicemia and pneumonia.
Pathogenicity:


#Minor and major breaks in the skin. #Foreign bodies such as sutures. #Low neutrophil levels. #Injecting drug abuse.
Predisposing factors for infection are:

(80%) are resistant to β- Lactam drugs and some to a number of antibioticsStrains isolated from hospital ,thes cause hospital infection(nosocomial) multi resistance. Antibiotic active against Staph. aureus include:penicillin for sensitive isolate, flucloxacillin (stable against β- Lactamase), erythromycin, fusidic acid (useful for skin infections), cephalosporins and vancomycin.Hand – washing and aseptic management of lesions reduce Staphylococci spreading. Treatment and prevention:

There are 5 enterotoxin(A-E) elaborated by some strains of Staph. aureus, different antigenically from one to another.*It's a protein . *It resist boiling for 30 minutes.*An important cause of food poisoning.*Ingestion of 25 μg of entrotoxin B results in vomiting and diarrhea in humans.*The emetic effect of entrotoxin is probably the result of central nervous system stimulation after the toxin acts on neural receptor in the gut. Enterotoxin:

Hemolysins: can destroy R.B.C. Coagulase: coagulate plasma. Catalase: Leucocidin: destroy leucocytes. Hyaluronidase: act on substrate that is structural component of connective tissue (break down the tissue and permits the Staph. to penetrate more deeply. Hens it's called spreading factor.
Pathogenizing factors:

DNase: DNA hydrolysis.Cytotoxins: cell lysis.Penicillinase: break down B lactam drugs.Protein A: antiphagocytic.Staphylokinase: can dissolve fibrin clots.Toxic shock syndrome toxin(TSST) Epidemolytic toxin: exfoliation and splitting of epidermis.Enterotoxin (A – E): induce vomiting and diarrhea.Lipase: breaks lipids of cell membrane.

This species is found on the skin surface and is spread by contact.

Staphylococcus epidermidis Habitat and Transmission:

Grows as white colonies on blood agar. Catalase positive. Coagulase negative. Earlier name Staph. albus.
Culture and Identification:

Normal commensal of the skin. (it's opportunistic pathogen).Common examples are catheter – related sepsis,urinary tract infections. Pathogeincity:

Staph. epidermidis exhibits resistance to a number of drugs (multiresistance) including penicillin and methicillin. Sensitive to vancomycin. Staphylococcus saprophyticus: # Urinary tract infections in women. # It has the ability to colonize the periurethral skin and the mucosa. # Grow as white colonies on blood agar.
Treatment:


Stomatococcus
Micrococcus
Staphylococcus
Property
+
-
+
Anaerobic growth
F
O
F
C.H.O. Utilization
Weak
+
+
Catalase
-
+
-
Oxidase
S
S
R
Bacitracin
+
-
-
Adherent to agar


Are catalase positive organisms similar to styphylococci.Coagulase negative.Grow usually as white colonies on blood agar, although some species are brightly pigmented – pink, orange or yellow. Micrococci:

Formerly classified in the genus micrococcus. This species has the ability to form extracellular slime which correlates with its predilection for the lingual surface.
Stomatococcus mucilagenosus