Heteroresistance to Vancomycin in Enterococcus faecium

Abstract

This study presents the first report of vancomycin heteroresistance in an Enterococcus faecium isolate from a patient. The original isolate was susceptible in vitro to vancomycin. E-tests showed growth of subcolonies in a zone of inhibition with a vancomycin MIC of >256 g/ml. Both the susceptible and resistant colonies were from the same strain as determined by PFGE, and both contained the vanA gene as determined by PCR.

Performance of three chromogenic VRE screening agars, two Etest® vancomycin protocols, and different microdilution methods in detecting vanB genotype Enterococcus faecium with varying vancomycin MICs

“…The heteroresistance phenotype has only been described for a clinical vanA VRE and for in vitro-generated descendents of vanA-positive E. faecium strain ATCC 51559 ( Alam et al, 2001 andKhan et al, 2008). Also, teicoplanin heteroresistance in vanA VRE strains was described recently (Qu et al, 2009).…”

Heteroresistance to Cephalosporins and Penicillins in Acinetobacter baumannii

“…Heteroresistance was first demonstrated in S. aureus to methicillin (23) and has been reported in Gram-positive bacteria to daptomycin, vancomycin, or penicillin (1,5,16) and in Gram-negative bacteria to colistin, carbapenems, and piperacillin-tazobactam (12-14, 18-21, 24). The present study investigated the heteroresistance to cephalosporins and penicillins in two A. baumannii isolates.…”

“…Heteroresistance exhibits a resistance phenotype due to the presence of mixed populations of drug-resistant and -susceptible organisms in a genetically homogeneous isolate (1,16,22). These heteroresistant isolates were originally susceptible in vitro to low concentrations of antimicrobial agents and subsequently yielded heteroresistance after exposure to the agents (1).…”

“…Many studies have reported heteroresistance to methicillin, daptomycin, or vancomycin in staphylococci and enterococci (1,5,23), heteroresistance to colistin, carbapenems, or piperacillin-tazobactam in A. baumannii, Klebsiella pneumoniae, and Pseudomonas aeruginosa (12-14, 18-21, 24), and heteroresistance to penicillin in Streptococcus pneumoniae (16). This indicates that this phenomenon is not rare and is considered to be a precursor stage, which may lead to the emergence of a resistant strain (6).…”

Heteroresistance

“…Heteroresistance to glycopeptides is not limited in S. aureus but has been described for Enterococcus faecium (Alam et al, 2001;Qu et al, 2009) and coagulase-negative staphylococci as well, including S. epidermidis, S. auricularis, S. capitis, S. haemolyticus, S. simulans and S.…”