Activity of fosfomycin alone or combined with temocillin in vitro and in a murine model of peritonitis due to KPC-3- or OXA-48-producing Escherichia coli

• Published in: Journal of antimicrobial chemotherapy Vol. 73; no. 11; pp. 3074 - 3080
• Main Authors: Berleur, M, Guérin, F, Massias, L, Chau, F, Poujade, J, Cattoir, V, Fantin, B, de Lastours, V
• Format: Journal Article
• Language: English
• Published: England Oxford University Press (OUP) 01-11-2018
• Subjects: Life Sciences; Microbiology and Parasitology
• ISSN: 0305-7453; 1460-2091
• DOI: 10.1093/jac/dky283

Alternative therapeutic regimens are urgently needed against carbapenemase-producing Enterobacteriaceae. Fosfomycin often remains active against KPC and OXA-48 producers, but emergence of resistance is a major limitation. Our aim was to determine whether the association of temocillin with fosfomycin might be useful to treat KPC- or OXA-48-producing Escherichia coli infections.
Isogenic derivatives of E. coli CFT073 with blaKPC-3- or blaOXA-48-harbouring plasmids (named CFT073-KPC-3 and CFT073-OXA-48, respectively) were used. The addition of temocillin to fosfomycin was tested using the chequerboard method and time-kill curves as well as in a fatal peritonitis murine model. Mice were treated for 24 h with fosfomycin alone or in combination with temocillin. Bacterial loads, before and after treatment, were determined in the peritoneal fluid and fosfomycin-resistant mutants were detected.
Temocillin MICs were 8, 32 and 256 mg/L for CFT073 (WT), CFT073-KPC-3 and CFT073-OXA-48, respectively. Fosfomycin MIC was 0.5 mg/L for all strains. The chequerboard experiments demonstrated synergy for all three strains. In time-kill curves, combining temocillin with fosfomycin was synergistic, bactericidal and prevented emergence of resistance for CFT073-pTOPO and CFT073-KPC-3, but not CFT073-OXA-48. In vivo, for the three strains, bacterial counts were lower in peritoneal fluid with the combination compared with fosfomycin alone (P < 0.001) and inhibited growth of resistant mutants in all cases.
The combination of fosfomycin and temocillin demonstrated a benefit in vitro and in vivo against E. coli strains producing KPC-3 or OXA-48-type carbapenemases. This combination prevented the emergence of fosfomycin resistance and proved to be more bactericidal than fosfomycin alone.