Molecular analysis of a prolonged spread of Klebsiella pneumoniae co-producing DHA-1 and SHV-12 ß-lactamases.

The study investigated molecular mechanisms for prolonged nosocomial spread of multidrug-resistant Klebsiella pneumoniae co-producing plasmid-mediated AmpC ß-lactamase DHA-1 and extended-spectrum ß-lactamase SHV-12. Forty-eight clinical isolates of K. pneumonia, resistant to the extended-spectrum cepha-losporins, were collected in a 750-bed university hospital over a year. The isolates were characterized for PCR-based ß-lactamase genotypes, isoelectric focusing and pulsed-field gel electrophoresis (PFGE) profiles. Resistance transfer was performed by plasmid conjugation and confirmed by a duplex-PCR and Southern hybridization. On ß-lactamase typing, the strains producing only the DHA-1 enzyme (n=17) or co-producing DHA-1 and SHV-12 enzymes (n=15) were predominant. Judging from a one year-distribution of PFGE profiles, the co-producer was spread primarily with single clonal expansion of the PFGE-type A with subtypes (n=14), whereas the strains producing only DHA-1 enzyme were spread simultaneously with the PFGE-type A (n=ll) and other PFGE types (n=6). Transconjugants of the co-producers were confirmed to harbor either both bla (DHA-1) and bla (SHV-12) or only the bla (DHA-1). In conclusion, this study indicated that the persistent nosocomial spread of multidrug-resistant K. pneumoniae strains was primarily associated with expansion of a clone harboring both the bla (DHA-1) and bla (SHV-12) or the bla (DHA-1) only, and to a lesser extent with the horizontal transfer of the resistant plasmids. Our observations have clinical implication for the control and prevention of nosocomial dissemination of multidrug-resistant K. pneumoniae strains.

Characteristics of non-typhoidal Salmonella isolates from human and broiler-chickens in southwestern Seoul, Korea.

Non-typhoidal Salmonella (NTS) is an important commensal microorganism. The purpose of this study was to determine the epidemiological relation between NTS isolates from livestock and NTS isolates from human by analyzing antimicrobial susceptibilities and performing molecular typing. We determined the serotypes of 36 human clinical isolates and 64 livestock isolates, performed antimicrobial susceptibility testing against 8 antibiotics, and determined the molecular types of isolated NTS spp. by pulsed field gel electrophoresis (PFGE). In human isolates, S. enteritidis was the most common serotype (17 isolates; 47.2%) and S. typhimurium the second most (8 isolates; 22.2%). In livestock isolates, S. typhimurium was the most common serotype (15 isolates; 23.44%), and S. enteritidis was the second most (14 isolates; 21.88%). Ampicillin and tetracycline resistance were 50% (32/64 isolates) each among broiler-chicken NTS isolates. No human or livestock NTS isolates showed resistance to ciprofloxacin, TMP-SMX, or ceftriaxone. However, 19.4% (7/36) and 46.8% (30/64) of the human and livestock NTS isolates were resistant to nalidixic acid (MIC > or = 16 mg/mL), respectively. The presence of the three identical PFGE molecular types from human and broiler-chicken NTS isolates suggests the possibility of transmission from livestock to humans.