Analysis of Salmonella enterica Serotype Typhi Pulsed-Field Gel Electrophoresis Patterns Associated with International Travel

Abstract

Typhoid fever is a significant cause of morbidity and mortality worldwide, causing an estimated 16 million cases and 600,000 deaths annually. Although overall rates of the disease have dramatically decreased in the United States, the number of travel-related infections has increased in recent decades. Drug resistance among Salmonella enterica serotype Typhi strains has emerged worldwide, making antimicrobial susceptibility testing an important function in public health laboratories. Pulsed-field gel electrophoresis (PFGE) subtyping of food-borne and waterborne pathogens has proven to be a valuable tool for the detection of outbreaks and laboratory-based surveillance. This retrospective study examined the distribution of PFGE patterns of S. enterica serotype Typhi isolates from patients with a history of international travel. Isolates were collected as part of a passive laboratory-based antimicrobial susceptibility surveillance study. Isolates were PFGE subtyped by using the restriction enzyme XbaI to restrict the total genomic DNA. Isolates indistinguishable with XbaI were further characterized using the restriction enzyme BlnI. A total of 139 isolates were typed, representing travel to 31 countries. Restriction fragment patterns consisted of 14 to 18 fragments ranging in size from 580 to 40 kbp. Seventy-nine unique PFGE patterns were generated using XbaI. Isolates from the same geographic region did not necessarily have similar PFGE patterns. Of the 139 isolates, 46 (33%) were resistant to more than one antimicrobial agent (multidrug resistant [MDR]). Twenty-seven (59%) of 46 MDR isolates had indistinguishable PFGE patterns with both XbaI and BlnI. It appears that MDR S. enterica serotype Typhi has emerged as a predominant clone in Southeast Asia and the Indian subcontinent.

Emergence of plasmid-mediated multidrug resistance in epidemic and non-epidemic strains of Salmonella enterica serotype Typhi from Jordan

“…The PFGE pattern of MDR S. Typhi strains investigated was apparently identical to one of the five XbaI-PFGE-patterns identified as circulating MDR S. Typhi strains in Asia and Middle Eastern countries in previous studies [8,26,27,36]. These findings confirm that MDR strains from Jordan are related to those in other countries and could have been introduced possibly about November 2004 or even before.…”

Clonal Expansion and Microevolution of Quinolone-Resistant Salmonella enterica Serotype Typhi in Vietnam from 1996 to 2004

“…PFGE has successfully been used since 1994 and is currently the method for the subtyping of sporadic or epidemic serotype Typhi isolates (7,11,17,28,37). Until recently, differences in PFGE running conditions precluded accurate comparisons with the profiles of serotype Typhi isolates typed by other laboratories.…”

Epidemiological characteristics and molecular typing ofSalmonella entericaserovar Typhi during a waterborne outbreak in Eastern Anatolia

“…This will facilitate presentation of epidemiological data and take measures to prevent current and future epidemics. Pulsed field gel electrophoresis (PFGE), a molecular method used in typology of microorganisms and investigations of clonal relationships, is a highly valuable method for epidemiological analysis of epidemics caused by food or waterborne pathogens (Kubota et al, 2005).…”