“…Recently, extendedspectrum beta-lactamase (ESBL)-producing antibioticresistant strains, especially E. coli strains, have been in-creasingly reported in fecal samples, and the proportion of ESBL-producing strains in all E. coli has increased to 8-10 in European, Asian, and North American countries (6)(7)(8). ESBLs are class A beta-lactamases with a plasmid-related resistance mechanism; they are categorized into TEM-and SHV-types derived from the natural narrow-spectrum enzymes (9,10) and a CTX-M-type derived from beta-lactamase on the Kluyvera chromosome (11). Reportedly, ESBL-producing strains, which were TEM-or SHV-type, are increasingly CTX-M-type (12).…”