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.– 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
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