High prevalence of carbapenem-resistant Klebsiella pneumoniae ST307 recovered from fecal samples in an Italian hospital

Lay abstract Carbapenem-resistant Klebsiella pneumoniae represents a major antibiotic resistance threat worldwide. These microorganisms are associated with high mortality and difficult-to-treat infections. Of particular interest is the production of carbapenemase, enzymes capable of inactivating life-saving drugs such as carbapenems. In the interaction with humans, K. pneumoniae plays different roles: commensal, opportunistic pathogen or true pathogen. Our study aimed to analyze the population of K. pneumoniae obtained from a fecal screening, since gut-colonizing strains are considered the common source of K. pneumoniae nosocomial infections. There are many differences between clinical and colonizing isolates, but the latter are much less characterized. The careful characterization of colonizing strains is crucial, in order to better understand how K. pneumoniae may change its role from commensal to pathogen. Aim: This study reports the characterization of carbapenem-resistant colonizing strains of K. pneumoniae. Methods: 650 stool samples were screened for carbapenem-resistant K. pneumoniae (CR-Kp). All strains were characterized for antibiotic susceptibility, typing features, main carbapenemases and extended-spectrum ss-lactamases. The carbapenemase transferability was assessed by interspecific conjugation. Results: Eighteen CR-Kp were multidrug resistant, five were KPC producing. A predominance of ST307 isolates, constituting the predominant cluster by PFGE analysis, was identified (50% were KPC-2 producers). Conjugation data showed the co-transfer of blaKPC-2, blaTEM-1, blaOXA-1, blaCTX-M-15 in a single large pKPN3-like plasmid. Conclusion: Our data pointed out the diversity of colonizing K. pneumoniae strains compared with clinical ones. The predominance of ST307 strains suggested an increased spreading, even in our area, of this high-risk clone.