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Medical Microbiology Gram Positive Cocci


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 Gram positive
 Facultative anaerobes
 grape like-clusters
 catalase positive
 Major components of normal flora
 skin
 nose
(i) One of commonest opportunistic infections:

⬢ pneumonia
⬢ osteomyelitis
⬢ septic arthritis
⬢ bacteremia: toxic shock syndrome
⬢ endocarditis
⬢ abscesses/boils
⬢ other skin infections: folliculitis
Staphylococcus aureus
 Enterotoxin⬦⬦Superantigen
 Toxic shock syndrome toxin (TSST)
 Exfoliatin⬦⬦⬦Scalded-skin
 Alpha toxins⬦⬦necrosis
 Leucocidins⬦⬦.Kill leukocytes
Lytic exotoxins:

Staphylococcus aureus
 food contaminated from humans
 enterotoxin

 onset and recovery both occur within few hours
 Vomiting
 nausea
 diarrhea
 abdominal pain
Staphylococcus aureus

Food poisoning
 vomiting is more prominent than diarrhea

 ingestion of enterotoxin, which is preformed in foods and hence has a short incubation period (1-8 hours).
Staphylococcus aureus

Food poisoning
Causes vomiting and watery nonbloody diarrhea.
-It acts as a superantigen within the gastrointestinal tract

-It stimulate the release of large amounts of interleukin-1 (IL-1) from macrophages

-It stimulate the release of
Staphylococcus aureus: Enterotoxin
 Causes ____ especially in tampon-using menstruating women or in individuals with wound infections.

 Toxic shock also occurs in patients with ____ used to stop bleeding from the nose.
Staphylococcus aureus:

Toxic shock syndrome toxin (TSST):

Toxic shock
Nasal packing
 fever, hypotension

 diffuse, macular, sunburn-like rash

 Vomiting, diarrhea and desquamation

 three or more of the following organs: liver, kidney, GI tract, central nervous system, muscle, or blood can be i
Staphylococcus aureus:

Toxic shock syndrome
 babies
 scalded skin syndrome
* exfoliatin
S. aureus
 It is the major protein in the cell wall.

 It binds to the Fc portion of IgG at the complement-binding site,

 Preventing the activation of complement.

 No C3b is produced

 The opsonization an
Staphylococcus Protein A
 tissue-degrading enzymes

– lipase
– hyaluronidase
Staphylococcus Spread
– sheep blood agar
• ß hemolytic

• mannitol fermentation

• Golden pigmented (aureus)

• coagulase-positive

• catalase-positive
Staphylococcus aureus: Identification
 All staphylococci produce catalase, catalase degrades H2O2 into O2 and H2O. H2O2 degradation limits the ability of neutrophils to kill

 Coagulase, by clotting plasma, serves to wall off the infected site, thereby retarding the migration
S. aureus produces catalase and coagulase
• major component skin flora

• opportunistic infections
– less common than S.aureus

• nosocomial infections
– heart valves
Staphylococcus epidermidis
 normal human flora on the skin and mucous membranes

 cause infections of intravenous catheters and prosthetic implants, eg, heart valves, vascular grafts, and joints.

 major cause of sepsis in neonates and of peritonitis
Staphylococcus epidermidis: glycocalyx
• Non-hemolytic

– sheep blood agar

• Does not ferment mannitol

• Non-pigmented
⬢ sensitive to novobiocin

Identification: Staphylococcus epidermidis
⬢ non hemolytic
⬢ urinary tract infections
⬢ coagulase-negative
- not differentiated from S. epidermidis
⬢ resistant to novobiocin
Staphylococcus saprophyticus
 Causes urinary tract infections, particularly in sexually active young women.

 Most women with this infection have had sexual intercourse within the previous 24 hours.

 Second to E coli as a cause of community-acquired u
S. saprophyticus:

Urinary Tract Infection
 90% or more of S. _____ strains are resistant to penicillin G.
 Most strains produce b-lactamase.

 Such organisms can be treated with b-lactamase-resistant penicillins, eg, nafcillin, methicillin or cloxacillin
Antibiotic therapy: S.aureus
 Approximately 20% of S. ______ strains are "methicillin-resistant" (MRSA) or "nafcillin-resistant" (NRSA) by virtue of altered penicillin-binding proteins.

 The drug of choice for these staphylococci is ________, to
Antibiotic therapy




 Strains of S aureus with intermediate resistance and with complete resistance to vancomycin (so-called VISA strains) have been isolated from patients.

 These strains are typically methicillin/nafcillin-resistant as well, which makes th
Drugs under investigation:

-Administration of a b-lactamase resistant
penicillin such as nafcillin

-Removal of the tampon or debridement of the
infected site as needed.

- Pooled serum globulins, which contain antibodies agai
The treatment of toxic shock syndrome involves correction of the shock using:

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