KLEBSIELLA
For the purpose of conforming to current clinical usage, the clinically important species and subspecies will be referred to as K. pneumoniae, K. ozaenae, K. rhinoscleromatis and K. oxytoca in this chapter.
KLEBSIELLA ON MACCONKEY AGAR
LABORATORY DIAGNOSIS
The members of the genus Klebsiella are Gram negative, nonmotile, facultative anaerobic rods ranging from 0.3 to 1.0 μm in width to 0.6-6.0 μm in length. Most strains grown readily on standard media, although occasionally cysteine requiring urinary isolates of K. pneumoniae are encountered. These strains will appear as pinpoint colonies on routine media, and require supplementation of media with cysteine for more adequate growth. The vast majority of Klebsiella spp. are encapsulated - contrary to popular belief it is probably not capsule which primarily contributes to the mucoid appearance that some Klebsiella strains exhibit. The Klebsiella which has been linked to the invasive syndrome presenting as liver abscess have a mucoid appearance.
In practice, K. pneumoniae and K. oxytoca are distinguished by indole production by K. oxytoca but not K. pneumoniae. It should be noted however that K. ornitholytica is also an indole producer. The five clinically important species can be distinguished by tests for indole production, ornithine decarboxylase production, he Voges-Proskauer reaction, malonate utilization and o-nitrophenyl-β-D-galactopyranoside (ONPG) production.
KLEBSIELLA ON BLOOD AGAR
Production of plasmid-mediated extended-spectrum beta-lactamases (ESBLs) by Klebsiella spp. has become a major problem. The nature and characteristics of ESBLs are described in greater detail below. Detection of ESBLs in clinical isolates of Klebsiella spp. is problematic since a significant proportion of ESBL producing isolates appear susceptible to third generation cephalosporins or aztreonam. Yet, poor clinical outcomes have been observed when these same antibiotics have been used to treat serious infections due to apparently susceptible ESBL producers. A single surrogate marker for ESBL production, such as ceftazidime resistance, is insufficient for the detection of ESBLs. Virtually all reliable laboratory tests used for detection of ESBLs rely on the change in in vitro activity of oxyimino containing beta-lactams in the presence of a beta-lactamase inhibitor such as clavulanic acid. Examples of ESBL detection methods include the double disk diffusion test, Etest strips containing ceftazidime or cefotaxime with and without clavulanic acid, the Vitek ESBL detection card and the Microscan ESBL plus detection system. Clinical and Laboratory Standards Institute (CLSI) has also developed screening and confirmatory tests for detection of ESBLs. It should be noted that these are standardized for K. pneumoniae and K. oxytoca only.
In some circumstances there is a need to detect ESBL producing Klebsiella spp. from stool or rectal swabs. Examples of such media include Drigalski agar supplemented with cefotaxime 0.5 mg/L , MacConkey agar supplemented with ceftazimide 4 mg/L and nutrient agar supplemented with ceftazimide 2 mg/L, vancomycin 5 mg/L and amphotericin B 1667 mg/L.
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