Species of the E. cloacae complex, especially E. cloacae, E. asburiae and E. hormaechei, are causing severe infections in community and nosocomial outbreaks; therefore it is important to identify them correctly, because incorrect identification could underestimate the infections caused by these microorganisms.
Most clinical laboratories in developed countries routinely identify Enterobacter spp. by phenotypic methods employing commercially available kits or semiautomated systems that are limited to E. cloacae and E. asburiae, while for further identification and discrimination of the other species in this genus, biochemical tests or molecular methods such as 16S rRNA, rpoB and hsp60 gene sequencing should be used.
A high risk of antibiotic failure in treating infections sustained by these microorganisms could exist among patients treated with carbapenem therapy because these species could be VIM producers. For the phenotypic detection of carbapenemase, MIC screening for meropenem could be set at ≥0.5 mg/l. For sporadic carbapenemase producers with low MIC values for meropenem (<0.5 mg/l), carbapenemase is not detected; therefore, ertapenem, even if less specific, remains a valid marker.[70,91,202]
MBL-producing E. cloacae are unusual causes of severe infections in compromised hosts, and empiric therapy with carbapenems may be inappropriate; therefore, colistin, although nephrotoxic, alone or in combination with other antibiotics (cephalosporins, quinolones, aminoglycosides or carbapenems), may represent the only effective therapeutic option against MDR Enterobacter spp..
Members of the E. cloacae complex are part of the endogenous flora of humans and consequently of patients who have become chronically colonized, making it difficult to apply generalized strategies of infection control for these microorganisms that are able to acquire resistance determinants and so becoming MDR.[133,134] Prompt attention should be given to rapid detection of antibiotic-resistant nosocomial pathogens, especially carbapenem-resistant Enterobacteriaceae. The CDC recently proposed a protocol for the detection of carbapenemases in Klebsiella spp. and E. coli in stool samples. Some authors indicate the use of CHROMagar KPC or McConkey agar with carbapenem disks or PCR for blaKPC for KPC-producing Enterobacteriaceae from rectal swabs. Of these three methods, PCR has a higher sensitivity and specificity but is the most expensive; CHROMagar and McConkey agar have the same sensitivity and specificity, but McConkey agar is cheaper.[69,135]
The pathogenetic mechanisms and contributing factors in disease development in the E. cloacae complex are still not well understood; this could be due to the scarcity of information available.
All these observations, together with the awareness of the limited therapeutic options to treat these infections, bring us to the alarming conclusion that we need urgent action to slow down and control the worldwide epidemic spread of these bacteria, especially of the emerging carbapenemase-producing E. cloacae complex strains because they are transmitted by mobile genetic elements.
The authors would like to thank A Bridgewood for the language revision of this manuscript.
Future Microbiol. 2012;7(7):887-902. © 2012 Future Medicine Ltd.