Head-to-head in vitro susceptibility comparison of temocillin with amoxicillin/clavulanate, piperacillin/tazobactam and meropenem among Enterobacterales isolates in a UK district general hospital.

OBJECTIVES

Temocillin is increasingly used as a carbapenem-sparing agent for infections caused by resistant Enterobacterales; however, comparative data with commonly used β-lactams remain limited. We evaluated the in vitro activity of temocillin compared with amoxicillin/clavulanate, piperacillin-tazobactam and meropenem using a head-to-head approach.

METHODS

A retrospective laboratory study was conducted on Enterobacterales isolates from urine, blood and respiratory specimens between January and September 2025. Susceptibility testing was performed using EUCAST disc diffusion. Temocillin susceptibility was compared directly with amoxicillin/clavulanate, piperacillin-tazobactam and meropenem for each isolate. Analyses were stratified by ESBL, AmpC and carbapenemase-producing Enterobacterales (CPE) status.

RESULTS

A total of 1,804 isolates were included, of which 861 (47.7%) had resistance mechanism data available. Temocillin demonstrated high overall in vitro activity, with 96.4% of isolates categorised as susceptible (95% CI 95.4-97.2%). Susceptibility to amoxicillin/clavulanate, piperacillin-tazobactam and meropenem was 54.3% (95% CI 52.0-56.6%), 90.9% (95% CI 89.5-92.2%) and 99.9% (95% CI 99.6-100.0%), respectively. Compared with amoxicillin/clavulanate, 53.2% of isolates were susceptible to both agents, while 43.3% were susceptible to temocillin but not amoxicillin/clavulanate, and 2.5% were resistant to both. Against piperacillin-tazobactam, 88.7% of isolates were susceptible to both agents, with 7.7% susceptible to temocillin only and 1.4% resistant to both. Meropenem showed the highest activity; 3.6% of isolates were susceptible to meropenem but not temocillin, while 0.1% were resistant to both. High temocillin activity (> 94%) was observed in ESBL- and AmpC-positive isolates.

CONCLUSIONS

Temocillin demonstrated high in vitro activity and outperformed amoxicillin/clavulanate while showing comparable activity to piperacillin-tazobactam. Its retained activity in multidrug resistant isolates supports its potential role as a carbapenem-sparing option in antimicrobial stewardship.