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The long-used antibiotic fosfomycin has recently been re-evaluated as a potential regimen for treating extended-spectrum β-lactamases (ESBLs) and carbapenem-resistant Enterobacteriaceae (CRE). Fosfomycin is known for its robust bactericidal effect against ESBL-producing Enterobacteriaceae and CRE. However, fosfomycin-modified genes have been reported in transposon elements and conjugative plasmids, resulting in fosfomycin resistance in parts of East Asia. Here we review reports of fosfomycin-modified (fos) genes in Enterobacteriaceae and assess the efficacy of fosfomycin against multidrug-resistant Enterobacteriaceae infections. At least 10 kinds of fos genes have been identified in the past decade; of these, fosA (and fosA subtypes) and fosC2 are primarily found in Enterobacteriaceae. All fosA subtypes except fosA2 are found in plasmids and transposons, nearby insertion sequence elements, or integrons, indicating that mobilizing elements also play an important role in plasmid-mediated fos genes in Enterobacteriaceae. fosA3, which is prevalent in East Asia, has been transmitted (mostly by animals) within and across continents via IS26 mobile elements. The acquisition of multiple antibiotic resistance genes via plasmids and mobile elements has resulted in a need for combined treatments for Enterobacteriaceae cases. The combination of fosfomycin and carbapenem has been the focus of many in vitro studies, but there is a clear need for additional in vivo investigations involving pharmacokinetics.

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Antibiotic-resistant patterns, a mecA homologue complex, and staphylococcal cassette chromosome mec (SCCmec) were analysed in samples of ready-to-eat (RTE) street food in Taiwan. RTE food samples (270) were collected in three densely populated Taiwanese cities between June and November 2014. Among 14 strains being identified as methicillin-resistant coagulase-negative staphylococci (MRCoNS), genetic diversities was determined by PFGE analysis. SCCmec types IV, V, VIII and TXG-24 were detected in 9, and mecASs (a mecA homologue) detected in 8. The mecASs gene complex from S. sciuri subsp. sciuri TXG-24 was found to be closely related to those found in both S. sciuri subsp. sciuri (ATCC29062) and S. sciuri subsp. rodentium (ATCC700061). SCCmecTXG24 carries a class A mec complex, a ccrA5B3-like gene complex, a heavy metal gene complex, and an IS1216 mobile element carrying tet(S). Matching identity to ccrA5 was 84.5% for ccrA in S. pseudintermedius KM241. Matching identify to ccrB3 was 92.1% for ccrB in S. pseudintermedius AI16. Similar ccrA and SCCmec boundary sequences suggest that SCCmec is easily transmitted to coagulase-negative staphylococci (CoNS). Based on MRCoNS strains identified in this research, Taiwanese RTE food products likely carry multiple antibiotic resistance genes that can be transmitted to hospitals and other clinical settings.

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