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

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

http://www.eyedr4kids.com/images/stye.jpg