Multidrug-resistant Salmonella enterica serovar Panama carrying class 1 integrons is invasive in Taiwanese children

An increase in group D Salmonella isolates with high antimicrobial resistant rates is being seen in Taiwan. This study aimed to determine the multidrug-resistant (MDR, more than three antibiotics) phenotype, genotype, and the correlation between the presence of class 1 integrons and its invasiveness of Salmonella panama and Salmonella enteritidis isolated from children. Methods: Twenty S. panama and 59 S. enteritidis isolates were examined for minimal inhibitory concentrations of ampicillin, chloramphenicol, streptomycin, sulfonamides, and tetracycline by agar dilution method. The presence of blaPSE-1, floR, aadA2, sul1, and tet(G) resistance genes, class 1 integrons, and Salmonella genomic island 1 (SGI1) was identified by polymerase chain reaction. The adhesion and invasion assays of S. panama to Caco-2 cells were determined using the pour plate method. Results: All S. panama and 15 (25.4%) of the S. enteritidis isolates displayed MDR phenotype. Furthermore, MDR genotype was present in 70.0% of S. panama and 6.8% of S. enteritidis. Class 1 integrons were present in 40.0% of S. panama and 11.9% of S. enteritidis. None contained SGI1 or SGI1 variants. Strains carrying class 1 integrons were more frequently isolated from bacteria with MDR (73.3% vs. 37.5%; odds ratio, 4.6; 95% confidence interval, 1.3-16.0; p=0.01) and isolated from blood and cerebrospinal fluid (46.7% vs. 21.9%; odds ratio, 3.1; 95% confidence interval, 1.0-10.1; p=0.05) than noncarriers. S. panama carrying class 1 integrons were more invasive to Caco-2 cells than those without (p=0.01). Conclusion: S. panama and S. enteritidis with class 1 integrons are significantly related to the presence of MDR phenotype. Moreover, S. panama with class 1 integrons may present more invasiveness than those without