Plasmid transferability of KPC into a virulent K2 serotype Klebsiella pneumoniae.

BACKGROUND: KPC-producing carbapenem-resistant Klebsiella pneumoniae (CRKP) infections are associated with high mortality; however, their virulence determinants are not well defined. METHODS: We investigated the virulence and plasmid transferability among KPC-containing K. pneumoniae isolates. RESULTS: KPC-2 and -3 were successfully conjugated and retained by a virulent K2 K. pneumoniae recipient isolate. Antimicrobial susceptibility testing showed KPC-2 and -3 donor strains were resistant to more than four classes of antibiotics while the K2 isolate was only initially resistant to ampicillin. After conjugation of KPC-2 and -3, the K2 K. pneumoniae transconjugants became resistant to all beta-lactams. Additionally, the KPC K2 K. pneumoniae transconjugants continued to retain its high serum resistance and murine lethality. CONCLUSIONS: Conjugation and retainment of KPC by virulent K2 K. pneumoniae and the ability of the tranconjugants to maintain its high serum resistance and murine lethality after conjugation was demonstrated in this study. These findings are concerning for the potential of KPC-like genes to disseminate among virulent K. pneumoniae isolates.

Molecular typing and characterization of nasal carriage and community-onset infection methicillin-susceptible Staphylococcus aureus isolates in two Taiwan medical centers.

BACKGROUND: Compared to methicillin-resistant Staphylococcus aureus (MRSA), characteristics of nasal carriage and community-onset infection methicillin-susceptible S. aureus (MSSA) are less well known. No characteristics of MSSA in Taiwan have been reported previously. METHODS: We analyzed 100 nasal carriage and 34 community-onset infection MSSA isolates by pulsed-field gel electrophoresis (PFGE), spa typing, multi-locus sequence typing, agr typing, virulence gene detection, growth rate measurement, and antimicrobial susceptibility. RESULTS: In PFGE analysis, most (68%) infection isolates could be grouped in one major cluster using a 70% similarity cutoff. In contrast, only 17% of nasal carriage isolates belonged to this cluster. A similar classification was obtained using Based Upon Repeat Pattern analysis of spa types. The MSSA infection isolates cluster was closely related to the virulent clones of clonal complex 1 (CC1), which includes strains MW2 (USA400) and MSSA476. ST188 of CC1 was the predominant clone detected for community-onset MSSA infections. The only common ST type for MSSA and MRSA in Taiwan was ST59, the community-associated MRSA clone. It is likely, therefore, that MRSA originated from MSSA clones through SCCmec transfer. Compared to nasal carriage isolates, infection isolates less frequently possessed egc, tst and hlg genes, were more commonly susceptible to erythromycin (91% vs. 54%), and had shorter mean doubling times (38 min vs. 55 min). CONCLUSIONS: The clonal lineages of MSSA nasal carriage and infection isolates differed in our sample of Taiwan isolates. Most community-onset MSSA infections resulted from relatively few clonal lineages. Nasal carriage isolates more frequently possessed the egc, tst and hlg genes, were more resistant to erythromycin, and grew more slowly.