Objectives:

The purpose of this study was to determine the distribution of sulphonamide resistance genes sul1, sul2 and sul3 and class 1 integrons in Portuguese Salmonella isolates collected during 2002–2003, from human and nonhuman sources.

Methods:

Eight hundred and seventy-five isolates were tested for resistance to 10 antimicrobial agents by the agar dilution method. Sulphonamide resistant isolates were screened for resistance genes sul1, sul2, and sul3 and class 1 integrons by PCR assays.

Results:

Resistance was found in 54% and multiresistance in 21% of the isolates. In 151 (17%) sulphonamide-resistant isolates (MICs 512 mg/L), 118 (78%) sul1 genes, 57 (38%) sul2 genes and nine (6%) sul3 genes were detected. In 29 isolates, more than one gene encoding sulphonamide resistance was present: sul1 and sul2 in 22, sul1 and sul3 in three and sul1, sul2 and sul3 in four. Class 1 integrons were found in 77% of those isolates. Among the 116 isolates carrying class 1 integrons, 114 presented sul1 gene, found alone (87 isolates) or simultaneously with sul2 (20) or sul3 (3) and with sul2 and sul3 (4). The two strains with class 1 integrons, which lacked the qacED1 and sul1 genes, carried a sul3 gene. Of the 118 sul1-positive isolates, 114 harboured class 1 integrons.

Conclusion:

Class 1 integrons and sulphonamide resistance genes are widespread among Salmonella. The newly described sul3 gene has now been identified in nine Salmonella isolates collected from human and nonhuman sources in Portugal.