Increase in incidence of resistance to ampicillin, chloramphenicol and trimethoprim in clinical isolates of Salmonella serotype Typhimurium with investigation of molecular epidemiology and mechanisms of resistance

Abstract

Antimicrobial resistance patterns of Salmonella serotype Typhimurium isolates obtained during the period 1987-1994 were examined and the molecular epidemiology and the mechanisms of resistance to ampicillin, chloramphenicol and trimethoprim were investigated in 24 strains isolated during 1994. Resistance to ampicillin increased from 18% to 78%, to chloramphenicol from 15y0 to 78%, to tetracycline from 53% to 89% and to co-trimoxazole from 3% to 37%, whereas resistance to norfloxacin remained at 0%. Of Salmonella serotype Typhimurium strains isolated during 1994, all ampicillinresistant strains had an MIC > 256 mg/L, except one strain in which the MIC was 64 mg/L. Twelve strains (52%) had a TEM-type /3-lactamase, nine (39%) a CARB-type /3-lactamase and two strains (8%) had an OXA-type /3-lactamase. Chloramphenicol acetyl-transferase activity was detected in only nine (47%) of 19 chloramphenicol resistant strains, whereas all eight trimethoprim-resistant strains produced a dihydrofolate reductase type Ia enzyme. Three different epidemiological groups were defined by either low-frequency restriction analysis of chromosomal DNA and pulsed-field gel electrophoresis or repetitive extragenic palindromic-PCR. The latter technique provided an alternative, rapid and powerful genotyping method for S. Typhimurium. Although quinolones provide a good therapeutic alternative, the multiresistance of S. Typhimurium is of public health concern and it is important to continue surveillance of resistance levels and their mechanisms.

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

“…The oxa-1 gene was detected in one strain, whereas a tem-like gene was found in the other seven strains, in one case concomitantly with a carb-2 (pse-1) gene. This result is in agreement with previously developed studies (5,6,29,42). Although in some of these studies, such as that performed by Roy et al (29), the percentage of TEM-like ␤-lactamase-producing strains was higher than in ours, this may be explained by the diversity of the geographical origin of the strains collected in our study.…”

“…The presence of the cmlA and floR genes associated with chloramphenicol resistance was determined by PCR (Table 1) and electrophoresis in 2% agarose gels. A previously described colorimetric assay was performed to determine the presence of chloramphenicol acetyltransferase (CAT) activity (6,11). The detection of genes encoding ␤-lactamases (tem-like, carb-like, shv-like, and oxa-1-like (24) was carried out by PCR ( Table 1).…”

“…display high natural susceptibility levels to the most commonly used antibacterial agents (34). However, the occurrences of isolated Salmonella strains showing resistance to one or more antibacterial agent have steadily increased, probably due to continuous antibiotic pressure (3,6,18,27,35). This is an important public health problem that may be related to therapeutic failure (43).…”

Multidrug Resistance Is Mediated by Large Plasmids Carrying a Class 1 Integron in the Emergent Salmonella enterica Serotype [4,5,12:i:−]

“…The objective of this study was to investigate the molecular basis of the multidrug resistance in serotype [4,5,12:i:Ϫ] and ascertain the relations between resistance genes, integrons, and plasmids. For this, several experimental approaches were made, and the results were compared with those obtained for Typhimurium DT104 LSP14/92 (9), used as the type strain of a pentadrugresistance epidemic clone of concern in many countries (3,7,8,9,11,15).…”

Clonal Dissemination of Yersinia enterocolitica Strains with Various Susceptibilities to Nalidixic Acid

“…The first was analysis of chromosomal DNA by digestion with low-frequency restriction enzymes (ApaI and XhoI) followed by pulsed-field gel electrophoresis (PFGE) under conditions previously described (7,9), although changes were introduced in the original protocol to optimize the technique for Y. enterocolitica. We added 20 mM thiocyanate to the TE-1 buffer to inhibit the powerful DNase of Y. enterocolitica.…”