Enterobacter cloacae Complex: Clinical Impact and Emerging Antibiotic Resistance

Maria Lina Mezzatesta; Floriana Gona; Stefania Stefani


Future Microbiol. 2012;7(7):887-902. 

In This Article

Epidemiology & Molecular Typing

An increasing number of clonal outbreaks caused by members of the E. cloacae complex is being reported. In recent years, genotypic methods have been developed to increase the discriminatory power of epidemiological investigations. Sensitive and reproducible molecular markers, including those used in ribotyping,[18] small-fragment restriction endonuclease analysis and pulsed-field gel electrophoresis (PFGE)[19] have been applied with success to the E. cloacae complex. PFGE is considered the gold standard, but PCR-based methods, including enterobacterial repetitive intergenic consensus (ERIC) PCR, repetitive extragenic palindromic (REP) PCR and arbitrarily primed PCR[20] belong to a new generation of typing methods in which a single short primer with arbitrarily chosen nucleotide sequences is used in PCR to amplify genomic DNA, and these are cheaper, easier to perform and provide faster results.

When comparing DNA macrorestriction analysis by PFGE with PCR-based DNA fingerprinting techniques, the discriminatory power of PFGE was found to be higher than those of PCR-based techniques.[19]

In the recent study by Stumpf et al., the E. cloacae complex isolates were assigned to their respective genetic cluster by partial hsp60 sequencing; all strains were selected to evaluate the specificity of ERIC and REP PCR for the identification of clonal isolates belonging to the E. cloacae complex.[21] Comparing ERIC PCR with PFGE, a specificity of 14%, considering the detection of 'clonal' isolates, was calculated. REP PCR performed much better, yielding a specificity of 90%. ERIC PCR patterns allowed an accurate classification of the isolates with their respective genomovars, suggesting that ERIC PCR differentiates between genomovars rather than between strains. By contrast, REP PCR differentiates better at the strain level. A proposed diagnostic system for the detection of outbreak strains of the E. cloacae complex is based on an initial REP PCR, which should be confirmed by PFGE in cases of identical patterns, whereas ERIC PCR does not seem to be useful for the detection of outbreak strains when dealing with isolates of the E. cloacae complex. Therefore, both PFGE- and PCR-based fingerprinting are useful for typing of the E. cloacae complex. However, PFGE can detect minor mutations among outbreak strains, and this is important for epidemiological studies of these species in a complex endemic setting.[21]