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Abstract
Bacteria colonizing the human intestine have a relevant role in the spread of antimicrobial resistance. We investigated the faecal carriage of extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae in healthy humans from Portugal and analyzed the distribution of sul genes and class 1 and 2 integrons. Faecal samples (n = 113) were recovered from healthy persons (North/Centre of Portugal, 2001–2004) and plated on MacConkey agar with and without ceftazidime (1 mg/L) or cefotaxime (1 mg/L). Isolates representing different morphotypes/plate and antibiotic susceptibility patterns (n = 201) were selected. Isolates resistant to sulfonamides and/or streptomycin, gentamicin, and trimethoprim were screened (PCR and sequencing) for sul genes (sul1, sul2, sul3) and class 1 and 2 integrons. Presence of ESBLs was inferred using the double disk synergy test (DDST) and further confirmed by PCR and sequencing. ESBL producers were selected for clonal analysis, plasmid characterization and conjugation assays by standard methods. ESBL-producing isolates were found in 1.8% (2/113) of samples, corresponding to Escherichia coli of phylogroups A (n = 1) and B1 (n = 1) carrying transferable blaCTX-M-14 and the new blaTEM-153, respectively. A 80kb IncK plasmid bearing blaCTX-M-14 was found, being highly related to that widely spread among CTX-M-14 producers of humans and animals from Portugal and other European countries. sul genes were found in 88% (22/25; sul2-60%, sul1-48%, sul3-4%) of the sulfonamide resistant isolates. Class 1 integrons were more frequently found than class 2 (7%, 14/201 vs. 3%, 6/201). Interestingly, gene cassette arrangements within these platforms were identical to those commonly observed among Enterobacteriaceae from Portuguese food-producing animals, although aadA13 is here firstly described in Morganella morganii. These results reinforce the relevance of human commensal flora as reservoir of clinically relevant antibiotic resistance genes including blaESBLs, and highly transferable genetic platforms as IncK epidemic plasmids.
Highlights
Antimicrobial resistance has become a global public health problem, compromising the treatment of several infectious diseases
extended-spectrum beta-lactamase (ESBL) CHARACTERIZATION We identified Escherichia coli isolates producing CTX-M-14 or TEM-153, a novel TEM-type enzyme differing from TEM-1 by three amino acid changes (E104K, M182T, and G267V) (GenBank accession number KC149518)
The CTX-M-14-producing E. coli isolate showed a phenotype of resistance against streptomycin, sulfonamides, trimethoprim, tetracyclines, chloramphenicol, nalidixic acid, and ciprofloxacin, while the TEM-153 producer was only resistant to nalidixic acid, ciprofloxacin, and neomycin
Summary
Antimicrobial resistance has become a global public health problem, compromising the treatment of several infectious diseases. The production of extended-spectrum beta-lactamases (ESBLs) constitutes one of the currently most spread and relevant antibiotic resistance mechanisms, compromising the use of several beta-lactams. In Portugal, spread of multidrug resistant bacteria, including ESBL producers, in hospitals, healthy food-producing animals, food products and aquatic settings has been described (Machado et al, 2007, 2008, 2009; Mendonça et al, 2007). Their occurrence and diversity in healthy populations is unknown.
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