Transcript Staphylococcus

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 endotoxinlike 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