In-vitro activity of oral third-generation cephalosporins plus clavulanate against ESBL-producing Enterobacterales isolates from the MERINO trial.

Extended-spectrum-beta-lactamase (ESBL)-producing Enterobacterales as a cause of community-acquired uncomplicated urinary tract infection (UTI) is on the rise. Currently, there are minimal oral treatment options. New combinations of existing oral third-generation cephalosporins paired with clavulanate may overcome resistance mechanisms seen in these emerging uropathogens. Ceftriaxone-resistant Escherichia coli and Klebsiella pneumoniae containing CTX-M-type ESBLs or AmpC, in addition to narrow-spectrum OXA and SHV enzymes, were selected from blood culture isolates obtained from the MERINO trial. Minimum inhibitory concentration (MIC) values of third-generation cephalosporins (cefpodoxime, ceftibuten, cefixime, cefdinir), both with and without clavulanate, were determined. One hundred and one isolates were used with ESBL, AmpC and narrow-spectrum OXA genes (e.g. OXA-1, OXA-10) present in 84, 15 and 35 isolates, respectively. Susceptibility to oral third-generation cephalosporins alone was very poor. Addition of 2 mg/L clavulanate reduced the MIC values (cefpodoxime MIC 2 mg/L, ceftibuten MIC 2 mg/L, cefixime MIC 2 mg/L, cefdinir MIC 4 mg/L) and restored susceptibility (33%, 49%, 40% and 21% susceptible, respectively) in a substantial number of isolates. This finding was less pronounced in isolates co-harbouring AmpC. In-vitro activity of these new combinations may be limited in real-world Enterobacterales isolates co-harbouring multiple antimicrobial resistance genes. Pharmacokinetic/pharmacodynamic data would be useful for further evaluation of their activity.