Mechanism of Resistance to Several Antimicrobial Agents in Salmonella Clinical Isolates Causing Traveler's Diarrhea

Abstract

The evolution of antimicrobial resistance in Salmonella isolates causing traveler's diarrhea (TD) and their mechanisms of resistance to several antimicrobial agents were analyzed. From 1995 to 2002, a total of 62 Salmonella strains were isolated from stools of patients with TD. The antimicrobial susceptibility to 12 antibiotics was determined, and the molecular mechanisms of resistance to several of them were detected as well. The highest levels of resistance were found against tetracycline and ampicillin (21 and 19%, respectively), followed by resistance to nalidixic acid (16%), which was mainly detected from 2000 onward. Molecular mechanisms of resistance were analyzed in 16 isolates. In these isolates, which were resistant to ampicillin, two genes encoding ␤-lactamases were detected: oxa-1 (one isolate) and tem-like (seven isolates [in one strain concomitantly with a carb-2]). Resistance to tetracycline was mainly related to tetA (five cases) and to tetB and tetG (one case each). Resistance to chloramphenicol was related to the presence of the floR and cmlA genes and to chloramphenicol acetyltransferase activity in one case each. Different genes encoding dihydrofolate-reductases (dfrA1, dfrA12, dfrA14, and dfrA17) were detected in trimethoprim-resistant isolates. Resistance to nalidixic acid was related to the presence of mutations in the amino acid codons 83 or 87 of the gyrA gene. Further surveillance of the Salmonella spp. causing TD is needed to detect trends in their resistance to antimicrobial agents, as we have shown in our study with nalidixic acid. Moreover, such studies will lead to better treatment and strategies to prevent and limit their spread.

SGI1-K, a Variant of the SGI1 Genomic Island Carrying a Mercury Resistance Region, in Salmonella enterica Serovar Kentucky

“…AB114632 and AY605484) (1,32). It is also present in a Salmonella serovar Haifa strain isolated in Spain from a patient with traveler's diarrhea who had recently returned from Egypt (AY563051) (8) and serovar Kentucky isolates from Slovakia (AM039633). Thus, the aacCA5-aadA7 cassette array, which was only identified recently, has already been found in several countries and multiple species, demonstrating how readily cassette arrays containing new resistance genes can spread.…”

Antimicrobial Susceptibility and Mechanisms of Resistance in Shigella and Salmonella Isolates from Children under Five Years of Age with Diarrhea in Rural Mozambique

“…For those Shigella and Salmonella isolates presenting full resistance to antibiotics, genes encoding ␤-lactamases (tem-like, carb-like, shv-like, oxa-1-like, oxa-2-like, and oxa-5-like) associated with Amp resistance were investigated by PCR, as described previously (22,30). Determination of the presence of the cmlA and floR genes associated with Chl resistance was carried out as described by Cabrera et al (7). The colorimetric method was used to detect the presence of CAT activity (4).…”

“…The colorimetric method was used to detect the presence of CAT activity (4). Detection of the tetA, tetB, and tetG genes associated with Tet resistance was performed as previously described (7,13), and detection of genes associated with Sxt resistance (dfrA1, dfrA5, dfrA6, dfrA7, dfrA8, dfrA12, dfrA13, dfrA14, dfrA15, dfrA15b, dfrA16, dfrA16b, and dfrA17) was carried out as described previously (23). Briefly, one colony of the strain was boiled in 25 l sterile distilled water for 10 min, and 25 l of a mixture containing 1.0 mM of each primer, 0.4 mM dNTPs, 2ϫ PCR buffer with Mg, and 2.5 units of Taq polymerase was added.…”

“…A wide range of molecular mechanisms, such as the presence of ␤-lactamases, dihydrofolate reductase, Chl acetyltransferase (CAT) enzymes and many others (7,10,11,22,27), have been described. However, few studies have investigated molecular mechanisms of antimicrobial resistance among isolates from sub-Saharan Africa, due mainly to the limited number of laboratories and research facilities with an adequate infrastructure available on the continent (10,21).…”

A Plasmidic Class 1 Integron from Five Pseudomonas aeruginosa Clinical Strains Harbored aacA4 and Nonsense-mutated cmlA1 Gene Cassettes

“…2,3) For example, the resistance to β-lactams, tetracycline, chloramphenicol, sulfamethoxazole/trimethoprim, or aminoglycosides has been reported. [4][5][6] Multidrug resistance is frequently caused by the enzymatic inactivation of antibiotics; however, enzyme-independent resistance such as accumulation of or defect in uptake of an antimicrobial agent is also common. 6) Transfer of the antibiotic-resistance genes is very likely because the genes are often located on plasmids, transposons, or integrons.…”