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Extended-spectrum beta-lactamases in clinical isolates of enterobacteria in Mexico
J Silva1, C Aguilar, Z Becerra
1Bacterial Genetics Department, Instituto Nacional de Salud Pública, Centro de Investigaciones Sobre Enfermedades Infecciosas, Cuernavaca, Mor., Mexico. jsilva@insp3.insp.mx
Abstract:
Resistance to extended-spectrum cephalosporins within members of the family Enterobacteriaceae occurs virtually world-wide. Nevertheless, nothing was known about this problem among isolates from Mexico. To address this issue, we studied oximino-cephalosporin resistant isolates of Klebsiella pneumoniae (13), Escherichia coli (7), and Enterobacter cloacae (23) recovered from patients in Mexico City hospitals during 1990 to 1992. In the presence of clavulanic acid, these strains increased susceptibility to cefotaxime and ceftazidime (MIC90 64 and >256 microg/ml, respectively). The ability of these isolates to transfer resistance to both antibiotics by conjugation was most successfully demonstrated by K. pneumoniae. In all the clinical isolates tested, the largest plasmid coded for the extended-spectrum beta-lactamases (ESBL). Characteristics of pI, by isoelectric focusing (IEF)/bioassay and DNA hybridization with specific probes of TEM and SHV, indicated that in most of the clinical isolates and all transconjugates, the most frequent beta-lactamase coded were SHV-derived (20 strains as 41% of isolates) and a plasmid-encoded beta-lactamase (12 strains as 25% of isolates) (with a pI of >8.2), which is not related to TEM/SHV. Apparently, isolates from Mexico show characteristics similar to isolates from other geographic areas. The type of beta-lactamases coded in these resistant isolates is documented for the first time in Mexico.
Insights
Extended-spectrum cephalosporin resistance in Enterobacteriaceae is global. This study identifies prevalent extended-spectrum beta-lactamases (ESBLs) in Mexican hospitals, including SHV-derived and novel types, for the first time.
Area of Science:
- Microbiology
- Molecular Biology
- Clinical Science
Background:
- Extended-spectrum cephalosporin resistance is a worldwide issue in Enterobacteriaceae.
- Limited data existed on this resistance phenomenon in Mexico prior to this study.
Purpose of the Study:
- To investigate oximino-cephalosporin resistant Enterobacteriaceae isolates from Mexico City hospitals.
- To characterize the types of extended-spectrum beta-lactamases (ESBLs) present in these resistant strains.
Main Methods:
- Analysis of Klebsiella pneumoniae, Escherichia coli, and Enterobacter cloacae isolates from 1990-1992.
- Determination of antibiotic susceptibility in the presence of clavulanic acid.
- Conjugation experiments to assess resistance transfer.
- Isoelectric focusing (IEF)/bioassay and DNA hybridization to identify beta-lactamase types (TEM, SHV, and others).
Main Results:
- Resistant strains showed increased susceptibility to cefotaxime and ceftazidime with clavulanic acid.
- Resistance transfer via conjugation was most effective in K. pneumoniae.
- SHV-derived ESBLs and a novel plasmid-encoded beta-lactamase (pI >8.2) were the most frequent types identified.
- These findings represent the first documentation of ESBL types in resistant isolates from Mexico.
Conclusions:
- Mexican Enterobacteriaceae isolates exhibit ESBL characteristics similar to those found globally.
- SHV-derived and novel beta-lactamases are significant contributors to cephalosporin resistance in this region.
- This study provides crucial baseline data on antimicrobial resistance in Mexico.