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Objectives Over the last decade, a marked increase in Salmonella enterica serotype 4,[5],12:i:- with a core resistance to ampicillin, streptomycin, sulphonamides and tetracycline (ASSuT) has been observed in Europe. This study describes the emergence and characterization of isolates of multidrug-resistant Salmonella 4,[5],12:i:- in Canada. Methods Human clinical isolates of Salmonella 4,[5],12:i:- were identified by provincial laboratories from 2003 to 2010. Serotyping and phage typing were performed by standardized methodologies. MIC values were determined using broth microdilution. PCR was used to determine the presence of resistance genes. Multilocus sequence typing was performed on a selected number of isolates. Results A total of 26 251 Salmonella were submitted as part of the Canadian Integrated Program on Antibiotic Resistance Surveillance (CIPARS). Of these, Salmonella 4,[5],12:i:- accounted for a total of 766 isolates (2.9%), and the number increased significantly from 42 (1.4%) in 2003 to 164 (4.8%) in 2010. The ASSuT+ phenotype was observed in 11.9% (n = 91) of Salmonella 4,[5],12:i:- isolates and increased from two isolates in 2003 to 35 isolates in 2010. Two sequence types (STs) were observed. ST34 was mainly associated with the ASSuT isolates (n = 24; 38%), which contained blaTEM, strA-strB, tet(B) and sul2. ST19 was more likely to be associated with the ACSSuT phenotype and contained blaTEM, floR, strA-strB, sul2 and tet(A) or blaPSE-1, floR, aadA2, sul1 and tet(G). Conclusions The prevalence of Salmonella 4,[5],12:i:- has significantly increased from 2003 to 2010 and it is now the fifth most common serotype reported in Canada causing human disease. Similar antimicrobial resistance patterns, phage types and STs have been observed in Europe.

The in-vitro susceptibilities of 1658 blood culture isolates to ciprofloxacin and 13 other antimicrobial agents were determined, and compared with the results for isolates obtained before and after the availability of ciprofloxacin in 1989. Only six (0.6%) of 995 Enterobacteriaceae were resistant to the fluoroquinolones tested; all of the ciprofloxacin-resistant strains were isolated after 1989 (P = 0.04). No significant increase in ciprofloxacin resistance was found in Pseudomonas aeruginosa or Acinetobacter spp. No resistance to ciprofloxacin was found in 124 Staphylococcus aureus isolates prior to 1989, but five (2.4%) of 208 S. aureus strains recovered after 1989 were ciprofloxacin-resistant (P = 0.16). Rates of resistance to ciprofloxacin and other antimicrobial agents commonly used to treat bacteraemic infections have remained relatively low in this Canadian teaching hospital over the past 16 years.