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Updated: Aug 20, 2026

Isolation and Identification of Waterborne Antibiotic-Resistant Bacteria and Molecular Characterization of their Antibiotic Resistance Genes
Published on: March 3, 2023
In vitro antienterococcal activity explains associations between exposures to antimicrobial agents and risk of
Louis B Rice1, Viera Lakticová, Marion S Helfand
1Medical and Research Services, Louis Stokes Cleveland VA Medical Center, Cleveland, Ohio 44106, USA. louis.rice@med.va.gov
Abstract:
We compared ceftriaxone and piperacillin-tazobactam at doses ranging from 0.1 to 2 times the human equivalent daily dose (HEDD), to determine their impact on gastrointestinal colonization by ampicillin- and vancomycin-resistant Enterococcus faecium C68 in a mouse model. Ceftriaxone failed to promote colonization at doses up to 0.25 times the HEDD, whereas piperacillin-tazobactam promoted colonization at doses up to 0.5 times the HEDD. Ceftriaxone promoted colonization at doses at least 0.5 times the HEDD, whereas piperacillin-tazobactam inhibited colonization at doses at least 0.75 times the HEDD. Both piperacillin-tazobactam and ceftriaxone inhibited colonization by an enterococcal strain devoid of low-affinity penicillin-binding protein-5 (significantly increasing its susceptibility to these agents), at doses that promoted colonization by E. faecium C68. These results support a model in which the impact that different beta -lactam agents have on colonization by VRE is related to the level of the beta -lactam agent's intrinsic antienterococcal activity against the colonizing strain.
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