MicrobiologyBytes: Microbiology Notes: S.aueeus & E.coli Updated: October 19, 2004 Search

Staphylococcus aureus and Escherichia coli

Staphylococcus aureus

StaphylococcusGram +ve coccus in clusters

Recognized in association with superficial pus-forming lesions: stye, boils/faruncles, abscesses.


Genus: Staphylococcus
Coagulase +ve:
Coagulase -ve:
S. aureus
e.g. S. epidermidis (CNS)

Early experiments (volunteers):

Route of infection:
Dose:
Skin:
Wound:
Stitch:
Low:
-
-
+
Medium:
-
+
+
High:
+/-
+
+

When S. aureus is isolated from septic lesions or blood it is nearly always acting as a pathogen.

Pathogenesis of deep Staphylococcal infections:

Local minor lesion
   Primary Bacteraemia/septicaemia
     Deep "metastatic"lesion
       Secondary bacteraemia/septicaemia

Diseases Caused by Staphylococcus aureus:

1. Skin and soft tissue:

  1. Stye, Boil. Abscess, (faruncle, carbuncle)
  2. Wound infections
  3. Cellulitis
  4. Impetigo

2. Blood and Cardiovascular system:

  1. Septicaemia (bacteraemia, metastatic abscesses)
  2. Endocarditis

3. Musculoskeletal:

  1. Osteomyelitis
  2. Arthritis

4. Toxin mediated diseases:

  1. Toxic shock syndrome
  2. Food poisoning
  3. Scalded Skin syndrome

5. Metastatic abscesses (almost anywhere): e.g. kidney, brain

6. Pulmonary

 

Some Virulence factors of S. aureus:


Escherichia coli

Gram negative Member of the Enterobactereaceae or "coliform" bacilli.

Serotyping is the primary tool for recognising pathogenic strains.


 

Enterovirulent E. coli:

Subdivided by disease associations and recognised virulence factors.

Examples (there are more groups):

Group / Acronym: Disease: "Classical" virulence factor(s): Serotype:
EnteroPathogenic (EPEC): Infantile diarrhoea Intimin and secreted effectors O26
H111
EnteroToxigenic (ETEC) Secretory diarrhoea Fimbrial adhesisns, LT (heat labile) & ST (heat stable) toxins O6
H-
EnteroHaemorrhagic (EHEC)
Shiga toxin producing (STEC)
Haemorrhagic colitis; Haemolytic uraemic syndrome (HUS) Shiga toxins + some EPEC genes O157
H7

ETEC: Invasive and destructive enteric disease due to E. coli.

Uropathogenic E. coli: Serotypes coincide with those found in the patient's normal flora - ENDOGENOUS INFECTION

Serotype - Disease association not as clear as with enteric pathogens.

~ 20% of women and 10% of men will get one or more Urinary Tract Infections (UTIs)

E. coli Summary:

Non-pathogen, Commensal, Opportunistic pathogen, Pathogen (category 2 and 3)

Why? Mobile genetic elements:

Virulence gene: Encoded on:
Fimbrial adhesin Plasmid
Intimin and secreted effectors Pathogenicity island
LT and ST toxins Plasmid

Shiga toxins

Bacteriophage

 

Multiple lines of evolutionary development produced the range of E. coli strains we have now.

And the process continues!


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