N. Harnett et al., MOLECULAR CHARACTERIZATION OF MULTIRESISTANT STRAINS OF SALMONELLA-TYPHI FROM SOUTH-ASIA ISOLATED IN ONTARIO, CANADA, Canadian journal of microbiology, 44(4), 1998, pp. 356-363
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%), recove
red from individuals who had travelled in South Asia, were multiresist
ant. Forty-four of the 48 isolates were resistant to ampicillin, chlor
amphenicol, tetracycline, streptomycin, sulfamethoxazole, trimethoprim
, cotrimoxazole, ticarcillin, and piperacillin; the other four isolate
s were resistant to four to six agents. Forty-two of the multiresistan
t isolates belonged to Vi phage type El, 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 iso
lates showed a temperature-sensitive mechanism of transfer to Escheric
hia coli K-12 strains, characteristic of HI incompatibility group plas
mids. The majority of plasmids had an estimated molecular weight of 12
0 MDa and encoded both citrate utilization and mercury resistance. Pla
smids from three isolates had an estimated molecular weight of 112-115
MDa; one of these isolates encoded citrate utilization but not mercur
y resistance. Analysis of isolates by pulsed-field gel electrophoresis
after digestion with XbaI and SpeI indicated that the majority of mul
tiresistant isolates shared a common restriction profile, while four i
solates had unique patterns.