Plasmid-mediated quinolone resistance in Salmonella isolates from different sources of Portugal

Abstract number: P1469

Antunes P., Matias R., Peixe L.

Objectives: Plasmid-mediated quinolone resistance is emerging worldwide in Enterobacteriaceae, including Salmonella. Given the importance of fluoroquinolones in therapeutics, we evaluated the incidence of qnr genes and characterised their associated plasmids among a collection of nontyphoidal Salmonella isolates with decreased susceptibility to ciprofloxacin (CipR) obtained from different sources in Portugal.

Methods: We studied all CipR isolates (n = 300; MIC 0.25–1 mg/L) obtained from a collection of 1511 Portuguese Salmonella isolates (2002–2004). They were identified in human clinical sources (n = 214), food products (n = 82), predominantly poultry (n = 53), and environment (n = 4). Antibiotic susceptibility was determined for streptomycin, kanamycin, gentamicin, ampicillin, nalidixic acid, ciprofloxacin, chloramphenicol, tetracycline, sulfamethoxazole and trimethoprim, by the agar dilution method (CLSI). Qnr resistance genes (qnrA, qnrB and qnrS) were sought by PCR according to Cattoir's method and confirmed by sequencing. Plasmid analysis included conjugation assays, determination of size (S1-PFGE) and content (incompatibility groups by rep-PCR typing method, hybridisation and sequencing). Location of qnr and intI1 genes was done by hybridisation of I-CeuI/S1-PFGE.

Results: Twenty per cent of the isolates of our collection exhibited CipR, being the serotype Enteritidis, isolated from humans and poultry products, the main contributor to this phenotype. None of the isolates was found to be positive for qnrA or qnrB. The qnrS1 gene was detected in a single clinical isolate of the serotype Enteritdis from 2003, which was susceptible to all antimicrobial agents, except ciprofloxacin (1 mg/L), nalidixic acid (32 mg/L) and trimethoprim (>16 mg/L). We identified a conjugative IncN plasmid of ca.30Kb carrying the qnrS1 gene and the intI1 gene. Remarkably, this isolate also harboured a non-conjugative plasmid (50Kb) of the FIIA type which is a common replicon found among Salmonella virulence plasmids.

Conclusion: We firstly describe the qnrS1 gene on an IncN plasmid of a Salmonella Enteritidis strain, a serotype commonly implicated in human infections. Despite the presence of this gene on a conjugative plasmid, a low prevalence of qnr genes was observed in Portugal.

Session Details

Date: 16/05/2009
Time: 00:00-00:00
Session name: 19th European Congress of Clinical Microbiology and Infectious Diseases
Location: Helsinki, Finland, 16 - 19 May 2009
Presentation type:
Back to top