Staphylococcus and Streptococcus Medical Microbiology Spring 2010

Gram positive cocci Subdivided by the presence or absence of catalase activity. Catalase is an enzyme that catabolizes hydrogen peroxide into water and oxygen. If catalase positive, bacterial colony will bubble when a drop of hydrogen peroxide is placed on it. Staphylococcus and related genera are catalase positive Streptococcus and related genera are catalase negative

Staphylococcus GPC that grow in clusters. Non-motile MAY appear singly, in pairs, or short chains but overall will be clustered Non-motile Facultatively anaerobic Bacteria growing in a liquid (broth) culture: 1) Obligate aerobe (Bacillus—later) 2) Obligate anaerobe (Clostridium—later) 3) Facultative anaerobe (Staphylococcus and Streptococcus)

Staphylococcus Can survive in high salt concentrations Temperatures ranging from 18*C to 40*C Present on skin and external surfaces of humans This genus contains 35 species. Some are pathogenic (coagulase positive) Some are not (coagulase negative) Causes an array of life-threatening diseases: Infections of the skin , soft tissues, bone, and urinary tract Many opportunistic infections

Staphylococcus aureus Gold colonies Most virulent and best-known species in this genus.

Physiology and structure of the Staphylococcal cell wall Outermost layer can be covered by a capsule with differing serotypes Aids in virulence and survival because it helps it hold on to tissues and foreign bodies. Half of the cell wall by weight is peptidoglycan-more rigidity and endotoxin-like qualities Teichoic acids are species specific and mediate attachment

Outer surface of some contains clumping factor (coagulase) Important virulence factor When suspended in plasma, clumps will form

Pathogenesis Virulence factors-we have talked abouti several already…can you name any? Capsule Peptidoglycan Teichoic acid coagulase

Additional virulence factors Toxins Cytotoxins: toxic for many cells including leukocytes, erythrocytes, macrophages, and platelets Exfoliative toxins: damage skin Enterotoxins: cause nausea and vomiting Toxic shock syndrome toxin: destruction of endothelial cells Enzymes Coagulase, catalase, and others like penicillinase

Epidemiology of Staphylococci Everyone has coagulase negative staphylococci on their skin also found in the oropharynx, nasopharynx, GI tract, and urogenital tract Transferred through direct contact or through contact with fomites

Clinical Disease Staphylococcus aureus SSSS (staphylococcal scalded skin syndrome), a.k.a. Ritter’s syndrome Infants < 1 month old Characterized by redness and inflammation around the mouth that spreads across the whole body within 2 days Slight pressure can perforate the skin Large blisters form

If the infection is localized to a certain area, it is called impetigo. Impetigo is very common in infants and young children and is highly communicable.

Clinical Disease Staphylococcal food poisoning One of the most common foodborne illnesses Intoxication rather than infection (toxins found in food vs. a direct effect from the bacteria on the patient. Most commonly found in processed meats like ham, potato salad, ice cream (nooooo…) Human contamination

After ingestion of contaminated food, onset of disease is rapid---incubation period is about 4 hours Symptoms last less than 24 hours Vomiting, diarrhea, abdominal pain, nausea Sweating and headache may occur but no fever.

Antibiotics are not recommended since the disease is not caused by growing bacteria Treat dehydration and abdominal discomfort

Clinical Disease TSS Toxic Shock Syndrome First outbreak in 1928 from contaminated vaccines 21 kids infected; 12 died 1980 outbreak reported among menstruating women Bacteria rapidly multiply in certain tampons; toxins produced Presently, 6000 cases of TSS occur in the US annually

Toxin is released into the bloodstream causing hypotension, fever; multiple organ systems are involved. Must be treated with an effective antobiotic or TSS can lead to death

Other cutaneous infections Folliculitis- hair follicles; if it occurs at the base of the eyelid, its called a stye. Furuncles- a.k.a. boils Carbuncles- when several furuncles come together and extend deeper in the skin Chills and fever Wound infections