In vitro activity of ampicillin and ceftriaxone against ampicillin-susceptible Enterococcus faecium.

Abstract

OBJECTIVES:

To assess activity of the combination of ceftriaxone and ampicillin against clinical isolates of ampicillin-susceptible Enterococcus faecium.

METHODS:

Ampicillin-susceptible E. faecium (n = 29) and Enterococcus faecalis (n = 10) collected from locations in the USA and France were used for this analysis. Susceptibility testing was performed by gradient diffusion strip (GDS) and broth microdilution (BMD). Synergy with the combination of ceftriaxone and ampicillin was assessed in all isolates using GDS crossing and double disc diffusion methods. Selected isolates (nine E. faecium and three E. faecalis) were assessed for synergy in time-kill studies using ampicillin alone and in combination with ceftriaxone.

RESULTS:

In isolates of E. faecium, the median (range) ampicillin MIC by BMD was 0.5 (0.25-4) mg/L and by GDS it was 2 (1-8)  mg/L. In E. faecalis, the median (range) ampicillin MIC by BMD was 0.5 (0.5-1) mg/L and by GDS it was 2 (0.75-3) mg/L. A total of 24/29 (82.8%) isolates of E. faecium displayed synergy by GDS and 22/29 (75.9%) by double disc diffusion. Seven of 10 (70%) isolates of E. faecalis displayed synergy by GDS and 4/10 (40%) by double disc diffusion. Time-kill studies found synergy in 3/9 (33.3%) E. faecium and 3/3 (100%) E. faecalis.

CONCLUSIONS:

In contrast to the demonstrated synergy in time-kill models of ceftriaxone and ampicillin for E. faecalis, this combination does not appear to provide uniform synergy in E. faecium. Antagonism was not observed. Clinical correlation is necessary and caution should be used when considering ampicillin and ceftriaxone for the treatment of infections caused by ampicillin-susceptible E. faecium.

• Authors: Michael P Lorenzo, James M Kidd, Stephen G Jenkins, David P Nicolau, Seth T Housman
• Journal: The Journal of antimicrobial chemotherapy (J Antimicrob Chemother) Vol. 74 Issue 8 Pg. 2269-2273 (08 01 2019) ISSN: 1460-2091 [Electronic] England
• PMID: 31050740 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: © The Author(s) 2019. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For permissions, please email: [email protected].

Chemical References

• Anti-Bacterial Agents
• Ceftriaxone
• Ampicillin

Topics

• Ampicillin (pharmacology)
• Anti-Bacterial Agents (pharmacology)
• Ceftriaxone (pharmacology)
• Drug Synergism
• Enterococcus faecalis (drug effects, isolation & purification)
• Enterococcus faecium (drug effects, isolation & purification)
• France
• Gram-Positive Bacterial Infections (microbiology)
• Humans
• Microbial Sensitivity Tests
• Microbial Viability (drug effects)
• Time Factors
• United States