1. Staphylococcus and Streptococcus
Medical Microbiology
Spring 2010

2. 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

3. 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)

4. 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

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

6. 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

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

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

9. 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

10. 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

11. 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

13. 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.

14. 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

15. 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.

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

17. 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

18. 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

19. 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