Chromosomal Integration and Location on IncT Plasmids of the blaCTX-M-2 Gene in Proteus mirabilis Clinical Isolates

Analysis of five CTX-M-2-producing Proteus mirabilis isolates in Japan demonstrated that blaCTX-M-2 was located on the chro-mosome in four isolates and on IncT plasmids in three isolates, including two isolates that also carried the gene on the chromo-some. In all four isolates with chromosomal blaCTX-M-2, ISEcp1was responsible for the integration of the gene into the chromo-some. Three different sites in the P. mirabilis genomic sequence were utilized as integration sites. In the past decade, CTX-M enzymes have become themost prev-alent extended-spectrum -lactamases (ESBLs) produced by members of the Enterobacteriaceae (3). In Japan, Toho-1, now renamed CTX-M-44, was initially identified in 1995 (14), and CTX-Menzymes have been prevalent among ESBLs since. Among Proteus mirabilis strain, all 71 CTX-M-producing clinical isolates collected from 2001 through 2003 in Japan carried blaCTX-M-2 (27). A nationwide surveillance study conducted in 2006 involv-ing 54 health care facilities in Japan reported that 28 of 74 P. mirabilis clinical isolates (37.8%) produced ESBLs and that all of them except one harbored blaCTX-M-2 (16). Clonality of CTX-M-2-producing P. mirabilis isolates in Japan was not investigated i