Emergence of CTX-M-15-producing Klebsiella pneumoniae of multilocus sequence types 1, 11, 14, 17, 20, 35 and 36 as pathogens and colonizers in newborns and adults

Objectives: To characterize the population structure and resistance mechanisms of Klebsiella pneumoniae isolates that are highly resistant to third-generation cephalosporins, collected from five Spanish hospitals. Methods: A total of 162 K. pneumoniae isolates from five hospitals located in three geographical areas of Spain were characterized. The number of isolates from each hospital ranged from 3 to 82. The genetic relationship between isolates was established by PFGE and multilocus sequence typing (MLST). bla(ESBL) types and other antibiotic resistance genes were analysed by PCR and sequencing. Plasmids were classified according to their incompatibility group by a PCR-based replicon-typing scheme. Results: All 162 isolates carried the bla(CTX-15) gene. Fifty-eight isolates (35.8%) caused clinical infections and 104 (64.2%) were colonizers. Sixty-nine (42.6%) isolates were collected from newborns and 93 (57.4%) from adults. Using PGFE, the 162 isolates were grouped into seven clusters that were further identified as members of the MLST types 1, 11, 14, 17, 20, 35 and 36. Two hospitals each had two different clones and the remaining three hospitals had a single CTX-M-15-producing K. pneumoniae clone. All clones carried different antibiotic resistance genes, including bla(OXA-1), aac(3)-IIa, aac(6')-Ib-cr, qnrS1 and qnrB. In four of the seven (57.1%) clones the bla(CTX-M-15) gene was transferred by conjugation; in all cases plasmids of the incompatibility group IncF were identified by PCR. Conclusions: This study shows that multiresistant K. pneumoniae producing CTX-M-15 of MLST types 1, 11, 14, 17, 20, 35 and 36 are spreading as pathogens and colonizers among newborns and adult patients in Spain.