Bacteriology

• Clavulanic acid, ceftazidime, cefoxitin, cefotetan and imipenem are all strong inducers or selectors of Class C β-lactamases in many nosocomial gram negative organisms and have the potential to increase the development of resistant organisms in individual patients and in the hospital flora.  Therefore, these agents should be used only when necessary.

Well, we have got another one:

Acinetobacter baumanii (from BAL & CSU):

Background:

Aerococci are:

1. Cardiobacterium valvarum: look at the large zone of inhibition around the antibiotic disc.

Background:

• Over 2000 antigenic types
• Salmonella enterica subspecies enterica serotype Enteritidis = S. Enteritidis.
• They can cause a mild self limiting GI illness ranging to life threatening systemic disease.
• Relative fall in incidence in the UK, although this is still the highest cause of community-associated diahorrea in the developing world.
• Characteristics:
  • Facultatively anaerobic
  • Gm(-) bacilli
  • Grow on a wide range of simple media
  • Highly motile
• Antigens:
  • 'O' antigen: somatic heat stable LPS, anchored on the outer membrane. There is genetic conservation of the lipid A/LPS core region. These are usually just numbers.
  • 'H' antigen: these are the flagellar protein subunits, and in some microbes two distinct flagellar structures are expressed (Phase I & Phase II genes). These are lower case letters (Phase I) & lower case letters with numbers (Phase II).
  • 'V_i' antigen: the virulence factor is expressed in certain serotypes. This protein may encompass the whole bacterium, making detection of 'O' antigens difficult.
  • Designantion by Kauffmann-White: ['O' Ag] [Phase I 'H'] [Phase II 'H'], e.g. S. Typhi (9, 12, [Vi]: d-). Here only one flagellar phase is expressed.
  • Differentiation by phage typing and AB_x sensitivity (e.g. S. Typhimurium is very resistant).

Microbiology:

• Yellow pigmented
• Non-fermenting
• Non-spore forming
• Gram negative
• Rod shaped
• Single polar flagellum with slow mobility (hence the name)
  • Few cells demonstrate motility in culture
• Commonest species found in human clinical specimens

Distribution:

1) CoNS: in pairs & tetrads (polymorphic)

2) S. aureus: grape like bunches, small, monomorphic.

3) Propionibacterium sp.: "spiders web configuration" & anaerobic.

4) Corynebacterium sp.: "chinese characters" & aerobic.