Evaluation of selective and enrichment media for isolation of glycopeptide-resistant enterococci from faecal specimens.
OBJECTIVE
Vancomycin-resistant enterococcus enrichment broth (VEB) and vancomycin-resistant enterococcus selective agar with vancomycin 6 mg/L (VSA) are novel azide-aesculin agar-based media that contain meropenem as an additional selective agent. The media were compared with enterococcosel broth (EB) and enterococcosel agar with vancomycin 6 mg/L (EA) for the isolation of glycopeptide-resistant enterococci (GRE) from routine faecal screening specimens.


METHODS
Two hundred and eighteen routine faecal screening specimens from patients at Addenbrooke's Hospital were examined. The majority were from patients on haematology wards (155) or the intensive therapy unit (ITU) (21). Specimens were inoculated on to VSA and EA directly, and after enrichment in VEB and EB, respectively.


RESULTS
One hundred and twenty-eight GRE isolates were recovered from 93 (43%) specimens with enterococci carrying vanA or vanB genes. There were no statistically significant differences between media (specimens positive; numbers of GRE isolates) on direct plating on VSA (87; 104) or EA (86; 97) or following 24 h enrichment in VEB (89; 103) or EB (86; 98). There was no significant advantage to enrichment compared with direct plating. Incubation of enrichment broth cultures for only 6 h appeared detrimental. Enterococci with vanC were isolated significantly less frequently from VEB and VSA than from EB and EA. Growth of organisms other than GRE was more common on VSA than on EA.


CONCLUSIONS
VEB and VSA were at least as effective as EB and EA for the recovery of GRE from faecal screening specimens, but substantially more non-GRE grew on VSA than on EA. Enrichment culture offered no significant advantages over direct plating.
Brown
Derek F J
DF
Clinical Microbiology and Public Health Laboratory, Addenbrooke's Hospital, Cambridge CB2 2QW, UK. dfjb2@cam.ac.uk
Walpole
Enid
E
D000362:Agar; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics; D019729:Carbon-Oxygen Ligases / Q000235:genetics; D003470:Culture Media; D024881:Drug Resistance, Bacterial; D016983:Enterococcus / Q000187:drug effects* / Q000302:isolation & purification*; D005243:Feces / Q000382:microbiology*; D006801:Humans; D014640:Vancomycin / Q000494:pharmacology; D020713:Vancomycin Resistance
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D003470:Culture Media; C071437:VanA ligase, Bacteria; C079913:VanB protein, Enterococcus; C079914:VanC protein, Bacteria; D014640:Vancomycin; D000362:Agar; D019729:Carbon-Oxygen Ligases