Abstract:

Objective To evaluate the feasibility of ampicillin to predict the imipenem susceptibilities of Enterococcus faecalis and Enterococcus faecium. Methods Totally,127 non-duplicated isolates of Enterococcus faecalis and 124 isolates of Enterococcus faecium were collected from 23 hospitals. The susceptibilities of Enterococcus faecalis and Enterococcus faecium to penicillin,ampicillin and imipenem were determined by broth microdilution and disk diffusion methods. Results For Enterococcus faecalis,which were both sensitive or resistant to penicillin and ampicillin,the categorical agreement（CA） of ampicillin-imipenem by broth microdilution was 100.0%,and there was no very major error（VME） and major error（ME）. For Enterococcus faecalis,which were resistant to both penicillin and ampicillin,the CA of ampicillin-imipenem by disk diffusion was 77.8%,and the ME accounted for 22.2%. For penicillin-resistant but ampicillin-sensitive Enterococcus faecalis,the CA of ampicillin-imipenem were 57.1% and 81.8% by broth microdilution and disk diffusion. Conclusions Ampicillin is better than penicillin to predict the susceptibilities of Enterococcus faecalis and Enterococcus faecium to imipenem. The susceptibilities to ampicillin can not be used to predict the susceptibilities of penicillin-resistant but ampicillin-sensitive Enterococcus faecalis and Enterococcus faecium to imipenem. Enterococcus faecalis and Enterococcus faecium isolates being sensitive to penicillin are predictably susceptible to ampicillin.

Key words: Enterococcus faecalis, Enterococcus faecium, Categorical agreement, Very major error, Major error, Broth microdilution, Disk diffusion