Extended-spectrum β-lactamases (ESBLs) represent a major threat among multidrug-resistant bacterial isolates. They have been increasingly described worldwide since their description in the early 1980s and have risen to prominence among Enterobacteriaceae isolates in nearly all European countries, now not only in the nosocomial but also in the community setting [ 1 x 1 Paterson, DL and Bonomo, RA. Extended-spectrum β-lactamases: a clinical update. Clin Microbiol Rev. 2005; 18: 657–686 Crossref | PubMed | Scopus (1833) | Google Scholar See all References , 2 x 2 Cantón, R and Coque, TM. The CTX-M β-lactamase pandemic. Curr Opin Microbiol. 2006; 9: 466–475 Crossref | PubMed | Scopus (665) | Google Scholar See all References , 3 x 3 Livermore, DM, Canton, R, Gniadkowski, M et al. CTX-M: changing the face of ESBLs in Europe. J Antimicrob Chemother. 2007; 59: 165–174 Crossref | PubMed | Scopus (614) | Google Scholar See all References ]. This review focuses on current European ESBL epidemiology. The population structure of ESBL-producing isolates and the nature of mobile genetic elements carrying bla_ESBL genes are analysed.

The contribution of integrons to the dissemination of extended-spectrum β-lactamases (ESBL) was analyzed on all ESBL-producing Escherichia coli isolates from 1988 to 2000 at Ramón y Cajal Hospital. We studied 133 E. coli pulsed-field gel electrophoresis types: (i) 52 ESBL-producing clinical strains (C-ESBL) (16 TEM, 9 SHV, 21 CTX-M-9, 1 CTX-M-14, and 5 CTX-M-10); (ii) 43 non-ESBL blood clinical strains (C-nESBL); and (iii) 38 non-ESBL fecal isolates from healthy volunteers (V-nESBL). Class 1 integrons were more common among C-ESBL (67%) than among C-nESBL (40%) or V-nESBL (26%) ( P < 0.001) due to the high number of strains with bla _{CTX - M - 9} , which is linked to an In6-like class 1 integron. Without this bias, class 1 integron occurrence would be similar in C-ESBL and C-nESBL groups (47% versus 40%). Occurrence of class 2 integrons was similar among clinical and community isolates (13 to 18%). No isolates contained class 3 integrons. The relatively low rate of class 1 integrons within transferable elements carrying bla _TEM (23%) or bla _SHV (33%) and the absence of class 2 integrons in all ESBL transconjugants mirror the assembly of translocative pieces containing bla _TEM or bla _SHV on local available transferable elements lacking integrons. The low diversity of class 1 integrons (seven types recovered in all groups) might indicate a wide dissemination of specific genetic elements in which they are located. In our environment, the spread of genetic elements encoding ESBL has no major impact on the dispersion of integrons, nor do integrons have a major impact on the spread of ESBL, except when bla _ESBL genes are within an integron platform such as bla _{CTX - M - 9} .

To investigate the diversity of integrons and extended-spectrum β-lactamases (ESBLs) among Enterobacteriaceae from chickens and swine in Portugal and analyse the clonal relationships between Portuguese ESBL-producing isolates of animal and human origin. We analysed samples from faeces of healthy swine (HSF, n = 35), from uncooked chicken carcasses (CM, n = 20) and from faeces of healthy chickens (HCF, n = 20). Samples were plated on MacConkey agar with and without ceftazidime (1 mg/L) or cefotaxime (1 mg/L). ESBLs were characterized by PCR and DNA sequencing. Bacterial identification, antibiotic susceptibility and conjugation assays were performed by standard procedures. Isolate clonal relatedness was established by PFGE and by RAPD for PFGE non-typeable isolates. Escherichia coli phylogenetic groups were identified by a multiplex PCR. Integron analysis was accomplished by PCR-RFLP and sequencing. ESBL-producing Enterobacteriaceae were identified in 60% of CM, 10% of HCF and 5.7% of HSF samples, respectively, mostly corresponding to E. coli (phylogroups A, D and B1). TEM-52, SHV-2 and CTX-M-1 were detected from chicken and SHV-12 from swine samples. High clonal diversity was observed and most bla_ESBL genes were transferable (67%). Class 1 and/or class 2 integrons were identified in 80% of CM, 10% of HCF and 63% of HSF samples, with class 1 integrons more common than class 2 integrons (36% versus 12% of the isolates recovered, respectively). Ten class 1 integron types are described, aadA1 and dfrA1-aadA1 being the most frequently found. Two class 1 integron types (aadA13-estX and dfrA14-aadA1-catB2) and one class 2 integron (aadA1) are first reported here. This study is the first report of ESBLs and integrons from chickens and swine in Portugal and highlights the antibiotic-resistant bacteria and/or resistance genes that might be acquired by humans through the food chain.

This study analyzes the diversity of In60, a class 1 integron bearing CR1 and containing bla _CTX-M-9 , and its association with Tn 402 , Tn 21 , and classical conjugative plasmids among 45 CTX-M-9-producing clinical strains (41 Escherichia coli strains, 2 Klebsiella pneumoniae strains, 1 Salmonella enterica strain, and 1 Enterobacter cloacae strain). Forty-five patients in a Spanish tertiary care hospital were studied (1996 to 2003). The diversity of In60 and association of In60 with Tn 402 or mercury resistance transposons were investigated by overlapping PCR assays and/or hybridization. Plasmid characterization included comparison of restriction fragment length polymorphism patterns and determination of incompatibility group by PCR-based replicon typing, sequencing, and hybridization. CTX-M-9 plasmids belonged to IncHI2 ( n = 26), IncP-1α ( n = 10), IncFI ( n = 4), and IncI ( n = 1) groups. Genetic platforms containing bla _CTX-M-9 were classified in six types in relation to the In60 backbone and in eight subtypes in relation to Tn 402 derivatives. They were associated with Tn 21 sequences when located in IncP-1α or IncHI2 plasmids. Our study identified bla _CTX-M-9 in a high diversity of CR1-bearing class 1 integrons linked to different Tn 402 derivatives, often to Tn 21 , highlighting the role of recombination events in the evolution of antibiotic resistance plasmids. The presence of bla _CTX-M-9 on broad-host-range IncP-1α plasmids might contribute to its dissemination to hosts that were not members of the family Enterobacteriaceae .

CTX-M-15, recently detected in Portugal, is an extended-spectrum β-lactamase (ESBL) that has spread worldwide ([3][1], [4][2], [9][3], [10][4], [15][5]). The basis for the successful dissemination of bla CTX-M-15 is unknown, although the spread of epidemic Escherichia coli strains and/or