Molecular epidemiology of Escherichia coli O25b-ST131 isolates causing community-acquired UTIs in Mexico.

Escherichia coli is a common uropathogen causing community-acquired urinary tract infections (UTIs). Out of 4735 E. coli community-acquired UTIs, 10.2% were extended spectrum ß-lactamases (ESBL)-producing. The identified ESBL types were CTX-M-15 (96.4%), SHV-2a (3%), and TLA-1 (1%). Of the isolates, 94.6% tested positive for plasmid-mediated quinolone resistance (PMQR) genes (aac(6')-lb-cr [92.1%] and qepA1 [7%] and for qnr-determinants [3.5%]). E. coli O25b-ST131 was identified in 25% of the isolates that harbor a non-conjugative 160-kb plasmid (IncFIA) containing the CTX-M-15, and all of these isolates were found to contain PMQR genes. This work can be useful in modeling the potential impact that may have on community-acquired UTIs in Mexico.

Transfer of quinolone resistance gene qnrA1 to Escherichia coli through a 50 kb conjugative plasmid resulting from the splitting of a 300 kb plasmid.

OBJECTIVES: To analyse the in vitro transfer of the qnrA1 gene by a 50 kb (pSZ50) self-transferable plasmid that derives from a 300 kb plasmid (pSZ300) and to determine the complete nucleotide sequence of plasmid pSZ50. METHODS: Extended-spectrum ß-lactamase (ESBL) and plasmid-mediated quinolone resistance (PMQR) genes of an Escherichia coli clinical isolate were analysed. Plasmid analysis included conjugation and selection on seven antibiotics examined by antimicrobial susceptibility testing, RFLP comparison, Southern hybridization, incompatibility group identification and shotgun sequencing. RESULTS: The E. coli 5509 isolate carries the genes encoding the ESBL CTX-M-15 and the quinolone resistance determinants qnrA1, qnrB2 and aac(6')-Ib-cr on a 300 kb plasmid. Seven transfer resistances were analysed by conjugation under two conditions (30 and 37°C), leading to two distinct transconjugant phenotypes with different resistances. Transconjugants of phenotype A harboured a 300 kb plasmid named pSZ300 that conferred resistance to eight antibiotics and harboured the qnrA1, aac(6')-Ib-cr and bla(CTX-M-15) genes. Transconjugants of phenotype B were resistant to three antibiotics and they harboured the qnrA1 gene on an ≈ 50 kb plasmid named pSZ50. Both plasmids were self-transferable at a frequency of 1 × 10(-3). Plasmid pSZ300 was typed to be both an IncF and IncN plasmid, whereas pSZ50 corresponded only to type IncN. Fingerprinting and Southern hybridization showed that plasmid pSZ50 derived from pSZ300. The complete nucleotide sequence of plasmid pSZ50 was determined (51556 bp) and 55 open reading frames were predicted. The qnrA1 gene was identified in a tandem duplicate inside a sul1-type integron structure. CONCLUSIONS: The plasmid pSZ300 represented a fusion of two replicons (IncF and IncN), and our observations suggest that the plasmid pSZ50 (IncN) may split and transfer antibiotic resistance determinants. This mechanism could be advantageous in the dissemination of antibiotic resistance genes.

In vitro activity of tigecycline against extended-spectrum ß-lactamase-producing Enterobacteriaceae and MRSA clinical isolates from Mexico: a multicentric study.

Extended-spectrum ß-lactamase (ESBL)-producing Enterobacteriaceae and methicillin resistant Staphylococcus aureus (MRSA) are important nosocomial pathogens. This study reports the in vitro activity of tigecycline against 573 and 482 ESBL-producing Enterobacteriaceae and MRSA isolates, respectively. More than 94% of all tested isolates were susceptible to tigecycline; MIC(90) found was 0.25 to 2 mg/L for ESBL-producing Enterobacteriaceae and was 0.125 mg/L for MRSA. Tigecycline demonstrated excellent in vitro activity against a wide spectrum of nosocomial pathogens.

Extended-spectrum ß-lactamase-producing enterobacteriaceae causing nosocomial infections in Mexico. A retrospective and multicenter study.

BACKGROUND AND AIMS: Extended-spectrum ß-lactamase (ESBLs) production is still the most frequent mechanism of resistance to cephalosporins in gram-negative bacteria. The aim of the study was to identify the types of ESBL-producing Enterobacteriaceae clinical isolates causing nosocomial infections in Mexico. METHODS: ESBL production was performed using a disk diffusion method. The MIC for several antibiotics was performed by agar dilution on Mueller-Hinton. PFGE typing was carried out on all enterobacteria assayed. The ß-lactamase pattern was obtained by IEF and bioassay. Genes of ß-lactamases were amplified by PCR with specific primers and products were sequenced and analyzed using informatics programs. Plasmid isolation and conjugation experiments were carried out using standard methodologies. RESULTS: There were 134 isolates of Enterobacteriaceae included from a retrospective and multicenter study that included eight Mexican hospitals from 1999 to 2005. The most prevalent species were K. pneumoniae (56%), Enterobacter cloacae (29%), and Escherichia coli (15%). Molecular analysis identified the underlying endemic and polyclonal spread of enterobacterials in each hospital. The most frequent ESBLs identified were SHV-type (84%), TLA-1 (11%), and CTX-M-15 (5%). Successful matings were detected in 68.4% (71/104) isolates. CONCLUSIONS: ESBL-producer K. pneumoniae remains the most frequent bacterial species obtained in nosocomial infections. The SHV-type and TLA-1 ESBLs were disseminated in most hospitals analyzed and CTX-M-15 was emerging in one of the studied hospitals. This work highlights the proper use of antibiotics to avoid the selection of these types of multiresistant bacteria.

Variability of the bla(IMP-15)-containing integrons, highly related to In95, on an endemic clone of Pseudomonas aeruginosa in Mexico.

The acquisition of ß-lactamases, such as class B metallo-ß-lactamases, in Pseudomonas aeruginosa is detrimental to antimicrobial therapy in hospitalized patients. In Mexico, metallo-ß-lactamase IMP-15 has been found to be encoded on the In95 class 1 integron in a major clone of P. aeruginosa. In this work, we describe the variability of this class 1 integron in an epidemic clone of carbapenem-resistant P. aeruginosa clinical isolates highly related to isolates previously described in Mexico.