V. de Lastours

Quinolone-resistant Escherichia coli from the faecal microbiota of healthy volunteers after ciprofloxacin exposure are highly adapted to a commensal lifestyle

OBJECTIVES Quinolone-resistant Escherichia coli (QREC) primarily emerge in commensal bacteria under selective pressure. The aim of this work was to investigate the characteristics of QREC from the faecal microbiota after quinolone exposure, as they remain largely unknown. METHODS Forty-eight healthy volunteers received ciprofloxacin from day 1 to day 14. QREC were detected in stools from 14 subjects at day 42. QREC were compared in terms of genetic background, metabolic properties, stress resistance and intestinal colonization abilities with quinolone-susceptible E. coli (QSEC) from the same 14 individuals and from 29 volunteers who remained QREC-free. RESULTS QREC always belonged to a single clone for a given volunteer and to restricted phylogenetic groups. QREC carried significantly more iron capture systems than QSEC. Maximum growth rates in minimal medium with gluconate, general stress regulator RpoS activity assessed by iodine staining and resistance to oxidative and acid stresses were significantly higher for QREC than for QSEC. In a mouse colonization model, QREC efficiently colonized the intestine microbiota despite the presence of QSEC competitors. At day 42, QREC and QSEC faecal counts from the 14 volunteers were comparable except in three subjects where only QREC could be detected. CONCLUSIONS These results suggest that QREC do not have a fitness cost, probably as a result of genetic co-selection, but are highly adapted to a commensal lifestyle. They may not be eliminated easily from the faecal microbiota from healthy subjects once selected.

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

Background 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. Methods 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. Results 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. Conclusions 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.