Detection of integrons and antibiotic-resistance genes in Salmonella enterica serovar Typhimurium isolates with resistance to ampicillin and variable susceptibility to amoxicillin-clavulanate

• Published in: International journal of antimicrobial agents 2004-10, Vol.24 (4), p.327-333
• Main Authors: Güerri, Marı́a Luisa, Aladueña, Ana, Echeı́ta, Aurora, Rotger, Rafael
• Format: Article
• Language: English
• Subjects: Amoxicillin - pharmacology; Ampicillin - pharmacology; Antibiotics. Antiinfectious agents. Antiparasitic agents; Base Sequence; Biological and medical sciences; Clavulanic Acid - pharmacology; DNA Primers; DNA, Bacterial - chemistry; DNA, Bacterial - genetics; Drug Resistance, Bacterial - genetics; DT104; Genotype; Humans; Infant, Newborn; Integrons - genetics; Medical sciences; Microbial Sensitivity Tests; Multiple drug-resistance; PFGE; Pharmacology. Drug treatments; Polymerase Chain Reaction; Salmonella enterica; Salmonella typhi - drug effects; Salmonella typhi - genetics; Salmonella typhi - isolation & purification; SGI-1; U302
• ISSN: 0924-8579; 1872-7913
• DOI: 10.1016/j.ijantimicag.2004.04.009

We characterized 29 antimicrobial-resistant Salmonella enterica serovar Typhimurium strains, including four belonging to the monophasic variant 4,5,12:i:–, mostly isolated from infants. They were selected from 3230 strains isolated in the years 1990–2001 on the basis of resistance to ampicillin and variable susceptibility to the amoxicillin-clavulanate combination. Twenty-three strains were resistant to more than four antibiotics. All the strains carried the bla TEM gene and most were able to transfer this gene by conjugation. Sequencing of the gene from one of the amoxicillin-clavulanate-resistant strains allowed identification of the encoded β-lactamase as TEM-1; all of these strains carried a second gene encoding β-lactamase production, either pse-1 or oxa1. However, the association of bla TEM plus pse-1 genes did not always confer resistance to amoxicillin-clavulanate. The pse-1 gene, found in 17 strains, was located in the Salmonella Genomic Island-1 (SGI1), which carries two integrons and encodes multiple drug-resistance. None of the oxa1-bearing strains had the SGI1, yet this gene was found as part of an integron that also carried the aadA1 gene and was not plasmid-associated. Thirteen of the strains harbouring SGI1 belonged to the definitive phage type (DT) 104, and most of those remaining to DT104b and U302; particularly, strains carrying the oxa1-aadA1 integron belonged to the last two phage types. Pulsed field electrophoresis confirmed the clonal organization of DT104 strains, whereas U302 strains fell into different groups, depending on their resistance determinants.