Molecular Epidemiological Investigation of a Diffuse Outbreak Caused bySalmonella entericaSerotype Montevideo Isolates in Osaka Prefecture, Japan

Abstract

In Osaka Prefecture, Japan, three foodborne outbreaks were caused by Salmonella enterica serotype Montevideo in rapid succession between September 2007 and May 2008. Further, Salmonella Montevideo was also isolated from several sporadic diarrhea patients and asymptomatic carriers examined during approximately the identical period. To investigate the relatedness of the isolates, we performed antimicrobial susceptibility testing, pulsed-field gel electrophoresis (PFGE) analysis, and multiple-locus variable-number tandem repeat (VNTR) analysis (MLVA) for 29 Salmonella Montevideo isolates obtained in this region between 1991 and 2008. Although antimicrobial susceptibility tests had low discriminatory power, PFGE patterns revealed 17 unique types with <90% similarity in combined analyses involving XbaI and BlnI. Moreover, we detected three VNTR loci that were useful to genotype Salmonella Montevideo isolates, with our method ultimately classifying the isolates into 11 MLVA types based on differences in repeat unit number in each examined locus. Six isolates obtained from patients of two separate foodborne disease outbreaks, one sporadic patient, and three different carriers between 2007 and 2008 had nearly identical PFGE patterns and were classified into the identical MLVA type; further, the isolates with this PFGE and MLVA pattern appeared only at that time between 1991 and 2008. These data strongly suggest that genetically identical Salmonella Montevideo strains may have caused the 2007 and 2008 outbreaks in Osaka Prefecture. Our results demonstrate that PFGE using XbaI and BlnI is useful for discriminating between Salmonella Montevideo isolates, even within a limited area, and reconfirm that continuous epidemiological surveillance for bacterial intestinal infections such as salmonellosis may be useful to not only monitor changes in the genetic diversity of isolates, but to also detect diffuse outbreaks.

Increasing quinolone resistance and multidrug resistant isolates among Salmonella enterica in Hong Kong

“…When using two restriction enzymes, XbaI and BlnI, a group in Japan found them useful to discriminate between S. Montevideo isolates. 33 In conclusion, this study revealed that S. Enteritidis and S. Typhimurium remained the two most common Salmonella serovars isolated in Hong Kong. There was a significant increase in resistance to the fluoroquinolones and multidrug resistance but resistance to the third generation cephalosporins remained low.…”

“…Recently, other typing methods, namely multiple-locus variable-number tandemrepeat analysis (MLVA) and multilocus sequence typing (MLST), have been used to type salmonellae. 33,34 MLST was shown not to be as good as PFGE owing to the lack of diversity of the housekeeping genes. 34 MLVA was also not a desirable method.…”

Molecular Epidemiological Analysis of Five Outbreaks Associated withSalmonella entericaSerovar Enteritidis Between 2008 and 2010 on Jeju Island, Republic of Korea

“…Endemic Salmonella infections have been reported in previous studies in several countries including Japan, Hong Kong, and Malaysia (Bakeri et al, 2003;Harada et al, 2011;Liang et al, 2007;Tassios et al, 1997;Thong et al, 1994;Tsen et al, 2001). In a study by Bakeri et al (2003), a single PFGE pattern, PFP X1, predominated in human SE isolates obtained from different parts of Malaysia from 1995 to 2001, and this particular clone was endemic in Malaysia.…”

“…Among genotypic methods, pulsed-field gel electrophoresis (PFGE) is used by the PulseNet program, a molecular subtyping network for foodborne bacterial disease surveillance at the United States Centers for Disease Control and Prevention, to identify widespread outbreaks of bacterial foodborne illness (Foley et al, 2006;Swaminathan et al, 2006). In addition to PGFE, multiple-locus variable number tandem repeat analysis (MLVA) is also useful for discriminating among isolates that are indistinguishable by PFGE (Malorny et al, 2008;Harada et al, 2011).…”

A Foodborne Outbreak of Gastrointestinal Illness Caused by Enterotoxigenic <i>Escherichia coli</i> Serotype O169:H41 in Osaka, Japan

“…PCR reaction mixtures were prepared using puReTaq Ready-To-Go PCR Beads (GE Healthcare, Piscataway, N.J., USA) containing the primers shown in Table 2 and 2 ml of DNA template in a final volume of 25 ml. The amplification conditions used in this study have been described previously (13). The amplified PCR products were electrophoresed in 2.0z (w/v) agarose gels and visualized by staining with ethidium bromide and viewing under UV light.…”