Citrobacterspp. Simultaneously HarboringblaCTX-M,blaTEM,blaSHV,blaampC, and Insertion Sequences IS26andorf513: an Evolutionary Phenomenon of Recent Concern for Antibiotic Resistance

ABSTRACT A collection of 40 confirmed isolates of Citrobacter spp., obtained from the culture of 5,732 clinical samples during 2006 to 2008, was studied for the presence of bla CTX-M , bla TEM , bla SHV , and bla ampC by monoplex and multiplex PCRs. These isolates were also looked at for the presence of insertion elements IS 26 and orf513 , which play an important role in the resistance gene pool. bla CTX-M , bla TEM , bla SHV , and bla ampC were noticed in 67.5%, 40%, 25%, and 40% of isolates, respectively. Sequencing for the specific CTX-M type revealed the presence of CTX-M-15-type extended-spectrum beta-lactamases (ESBL). sul1 -type integrons were detected in 32.5% (13/40) of isolates, and a single plasmid of ca. ∼22 kb was also noticed in all the isolates harboring bla genes. A total of 48.2% (13/27) of isolates harboring bla CTX-M alleles were found to carry IS 26 elements and 53.4% (7/13) of isolates harboring the sul1 -type integrons were found to carry orf513 . Alarmingly, a few isolates simultaneously carried IS 26 and orf513 , reflecting the occurrence of complex evolution. All the Citrobacter isolates were noticed to produce an amplicon of 400 bp in an IS 26 PCR, similar to that of the predominant UK CTX-M-15-producing Escherichia coli clone (clone A) and suggesting a probable genetic relatedness between the two, which could not be proved with British and Indian E. coli isolates in our earlier studies. Here, a first report is being presented describing the occurrence of bla CTX-M-15 in Indian Citrobacter spp. This is also the first report describing the simultaneous occurrence of bla TEM , bla SHV , and bla ampC along with bla CTX-M in class 1 integrons. The recent findings indicate that the genetic environment of bla CTX-M-15 has changed through the insertion of IS 26 and orf513 , although the consequences of these events remain uncertain. It perhaps also suggests a “turnover” of these mobile elements in the population over time.