Molecular characterization of multiresistant strains ofSalmonella typhifrom South Asia isolated in Ontario, Canada

Abstract

Two hundred and fourteen isolates of Salmonella typhi submitted to our laboratory between 1992 and 1996 were tested for susceptibility to 20 antimicrobial agents. Forty-eight of the 214 isolates (22.4%), recovered from individuals who had travelled in South Asia, were multiresistant. Forty-four of the 48 isolates were resistant to ampicillin, chloramphenicol, tetracycline, streptomycin, sulfamethoxazole, trimethoprim, cotrimoxazole, ticarcillin, and piperacillin; the other four isolates were resistant to four to six agents. Forty-two of the multiresistant isolates belonged to Vi phage type E1, two isolates from the Punjab State belonged to phage type A, another from the Punjab State belonged to phage type E3, one isolate from Pakistan belonged to type M1, and one isolate from India belonged to type J1. Plasmids from 45 of 48 isolates showed a temperature-sensitive mechanism of transfer to Escherichia coli K-12 strains, characteristic of H1 incompatibility group plasmids. The majority of plasmids had an estimated molecular weight of 120 MDa and encoded both citrate utilization and mercury resistance. Plasmids from three isolates had an estimated molecular weight of 112-115 MDa; one of these isolates encoded citrate utilization but not mercury resistance. Analysis of isolates by pulsed-field gel electrophoresis after digestion with XbaI and SpeI indicated that the majority of multiresistant isolates shared a common restriction profile, while four isolates had unique patterns.

Variable Number of Tandem Repeats in Salmonella enterica subsp. enterica for Typing Purposes

“…Genotypic variability within DT104 isolates has already been documented by amplified fragment length polymorphism analysis (12) and PFGE (22). The population of serovar Typhi investigated here appeared to be more diverse than the populations of the other serovars; and this is in accordance with the high degree of heterogeneity observed by others among isolates originating from Asia (13,14), India (32), and Chile (11).…”

“…The capability to trace S. enterica serovar Typhi epidemiologically remains of great importance because of the incidence of typhoid fever (5) and the emergence of MDR strains (12,14). Moreover, S. enterica serovar Typhimurium may be responsible for food-borne acute enterocolitis and the spread of MDR DT104 isolates worldwide.…”

“…For example, it has been demonstrated that the DT104 phage type of multidrug-resistant (MDR) serovar Typhimurium is a single clone that has spread pandemically in Europe (30). Similarly, 42 of 48 isolates of MDR serovar Typhi isolates were assigned to Vi phage type E1 (14). The introduction of molecular typing methods, such as ribotyping (1), randomly amplified polymorphic DNA analysis (9), amplified fragment length polymorphism analysis (12), and pulsed-field gel electrophoresis (PFGE) (33), has greatly improved the ability to discriminate between epidemiologically related and unrelated isolates in outbreaks of typhoid fever (29) and other salmonelloses (26).…”

First Canadian Salmonella enterica Serovar Typhi Isolate Harboring an Integron

“…The emergence of multidrug-resistant S. enterica serovar Typhi poses a serious public health concern, resulting in treatment failures and limiting therapeutic options (11). Multidrug-resistant strains have been isolated in Canada from individuals returning from Asia, primarily from India and Pakistan (2). Recently, an S. enterica serovar Typhi strain was isolated from a 30-year-old male in Ontario, Canada, suffering from bacteremia.…”

Single Nucleotide Polymorphism Typing of Global Salmonella enterica Serovar Typhi Isolates by Use of a Hairpin Primer Real-Time PCR Assay

“…Both of our isolates were from Canada. There was no information on whether these two isolates were imported cases, but multidrug-resistant isolates from travelers to Southeast Asia have been reported in Canada (5).…”