Antimicrobials

• 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.

Colistin:

Background:

Two forms of colistin are commercially available: colistin sulfate (available PO for bowel decontamination) and colistimethate sodium (IV or nebulised). When we refer to "colistin" for the Rx of MDRGNs we mean colistimethate sodium.

Well, we have got another one:

Acinetobacter baumanii (from BAL & CSU):

• Until the early 1970s all strains of H. influenzae were susceptible to antibiotics.

• In 1973 the first isolate resistant to ampicillin and producing β-lactamase was reported. This was rapidly followed by strains resistant to tetracycline, chloramphenicol and trimethoprim or multiresistant to the same antibiotics emerged in all parts of the world.

There are three mechanisms of aminoglycoside resistance: reduced uptake or decreased cell permeability, alterations at the ribosomal binding sites, or production of aminoglycoside modifying enzymes.

Reduced uptake or decreased cell permeability

This organism was recovered from a tunnelled CVC of a haemtaology patient. I have never heard of it, so I thought we could summarise it:

Microbiology:

Microbiology:

• Gram negative
• Motile rod
• Polar multitrichous flagella

Identification:

1. All Gram positive bacteria are resistant to nalidixic acid, while most coliforms are sensitive - there an E. faecium can be distinguished from a coliform.
2. All Proteus spp. are resistant to nitrofurantoin, whereas most other coliforms are sensitive.
3. Klebsiella spp are usually only resistant to ampicillin, unless they are ESBLs of course!

AMH.