Characterization of class 1 integrons with unusual 3' conserved region from Salmonella enterica isolates.

The unusual 3' conserved sequence region of class 1 integrons was characterized in seven Salmonella isolates from swine and poultry. Three types of gene cassette arrays, aadA2-cmlA1-aadA1, sat-psp-aadA2-cm1A1-aadA1 and drfA12-orf-aadA2-cmlA1-aadA1, were found to be linked to a genetic organization qacH-IS440-sul3. All class 1 integrons were located on a conjugative plasmid that could be transferred to Escherichia coli. The results support the notion that the use of an antibiotic can select for resistance not only to that specific agent, but also to other unrelated antimicrobials including those that are no longer approved for use in food animal production.

Functional characterization of MexXY and OpmG in aminoglycoside efflux in Pseudomonas aeruginosa.

MexXY is an active efflux system that contributes to intrinsic resistance to aminoglycosides in Pseudomonas aeruginosa. MexXY can function in combination with OprM in aminoglycoside efflux but may also functionally associate with another as yet unidentified outer membrane channel. The possible role of OpmG as a third component of MexXY in aminoglycoside efflux was investigated by construction of unmarked opmG mutants. Loss of OpmG did not have any impact on minimum inhibitory concentrations for aminoglycosides regardless of the presence of oprM, indicating that MexXY does not interact with OpmG in aminoglycoside efflux. In a clinical isolate PAJ010, (mexXY) enhanced streptomycin susceptibility but neither oprM nor opmG could, suggesting that MexXY functionally associates with an unidentified outer membrane protein for aminoglycoside efflux. Expression of an opmG-lacZ transcriptional fusion revealed that OpmG expression was neither constitutive nor inducible by gentamicin. Growth rates of wildtype P. aeruginosa and opmG mutant derivatives were not different, indicating that expression of opmG is not essential for P. aeruginosa growth.

Occurrence of qacE/qacEDelta1 genes and their correlation with class 1 integrons in salmonella enterica isolates from poultry and swine.

In this study, a total of 122 Salmonella enterica isolates from poultry and swine were assessed for susceptibility to clinically important antibiotics and to benzalkonium chloride (BKC). All isolates were examined for the presence of the antiseptic resistance genes qacE and qacEDelta1 and intl1 (class 1 integrase). The intl1-positive strains were further investigated for the presence of the 3' conserved region. The results demonstrated widespread distribution of qacEDelta1 (27%) but no isolate with qacE was observed. The intl1 gene was identified in 23 isolates (70%) with qacEDelta1. All of the intl1-postive strains carried qacEDelta1 in 3' conserved segment, confirming that the qacEDelta1 gene is linked to the integrons. Increased MIC value to BKC was independent of the presence of qacEDelta1, and multiple antibiotic-resistant bacteria were no more tolerant to BKC than the non-multidrugresistant strains, regardless of the presence of qacEDelta1.