Parallel increase in community use of fosfomycin and resistance to fosfomycin in extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli.

OBJECTIVES: To document fosfomycin susceptibility of extended-spectrum ß-lactamase-producing Escherichia coli (ESBL-EC), analyse trends in fosfomycin use and investigate fosfomycin resistance in ESBL-EC isolated from urinary tract infections (UTIs). METHODS: Twenty-seven Spanish hospitals participating in the European Antimicrobial Resistance Surveillance Network were requested to collect up to 10 sequential ESBL-EC for centralized susceptibility testing and typing. EUCAST guidelines were followed for antibiotic susceptibility testing, and bla(ESBL) type, phylogroups and O25b serotype were determined by PCR and sequencing. In addition, the trend in fosfomycin resistance among ESBL-EC causing UTIs was determined in 9 of the 27 hospitals. Total fosfomycin use for ambulatory care was established by WHO-recommended methods. RESULTS: A total of 231 ESBL-EC (42.4% CTX-M-15, 34.2% SHV-12 and 23.4% CTX-M-14) were collected. The overall rate of fosfomycin resistance was 9.1%, but varied according to ESBL type (5.6% of CTX-M-14 isolates, 5.1% of SHV-12 and 15.3% of CTX-M-15). Of 67 O25b/B2 isolates, 11 (16.4%) were fosfomycin resistant. Predictors of infection with fosfomycin-resistant ESBL-EC were O25b/phylogroup B2 isolates, female gender and nursing home residence. Among 114 197 UTIs caused by E. coli 4740 (4.2%) were due to ESBL-EC. Fosfomycin resistance increased in these isolates from 4.4% (2005) to 11.4% (2009). The use of fosfomycin grew from 0.05 defined daily doses per 1000 inhabitants per day (1997) to 0.22 (2008), a 340% increase. CONCLUSIONS: Key factors related to increased fosfomycin resistance in ESBL-EC causing UTIs could be the rapid growth in community use of fosfomycin, the widespread distribution of the 025b/B2 E. coli clone and the existence of a susceptible population comprising women residing in nursing home facilities.

Emergence of imipenem resistance in clinical Escherichia coli during therapy.

The molecular epidemiology and the mechanisms of resistance of Escherichia coli isolated from two patients infected by imipenem-resistant strains are reported in this study. From one patient, three closely related consecutive isolates of E. coli were recovered; the first was carbapenem-susceptible but acquired imipenem resistance after treatment with ertapenem, and the third isolate was again imipenem-susceptible. An additional imipenem-resistant isolate was recovered from another patient who received imipenem. The genetic relatedness of the E. coli isolates was determined by pulsed-field gel electrophoresis (PFGE) after digestion with XbaI. Standard polymerase chain reaction (PCR) conditions were used to amplify several beta-lactamase genes coding for carbapenemases, extended-spectrum beta-lactamases (ESBLs) and plasmid-mediated AmpC; the E. coli ampC gene promoter was also amplified and sequenced. Primers OmpF-F/OmpF-R and OmpC-F/OmpC-R were used to amplify the ompF and ompC genes. The outer membrane protein (OMP) profiles were studied by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Imipenem-resistant E. coli isolates did not produce carbapenemases but lacked the two major OMPs OmpF and OmpC and had ampC promoter mutations; in addition, one of the imipenem-resistant isolates produced the CMY-2 cephalosporinase, whilst the other produced the new CTX-M-67 ESBL. Carbapenem resistance in this study was associated with lack of expression of OmpF and OmpC porins. Additional mechanisms of beta-lactam resistance, such as plasmid-mediated AmpC and ESBL production, were also found. Development of carbapenem resistance in a CTX-M-67-producing E. coli is first described in this study.