Vibrio parahaemolyticus is a pathogenic marine bacterium that is the main causative agent of bacterial seafood-borne gastroenteritis in the United States. An increase in the frequency of V. parahaemolyticusrelated infections during the last decade has been attributed to the emergence of an O3:K6 pandemic clone in 1995. The diversity of the O3:K6 pandemic clone and its serovariants has been examined using multiple molecular techniques including multilocus sequence analysis, pulsed-field gel electrophoresis, and groupspecific PCR analysis. Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has become a powerful tool for rapidly distinguishing between related bacterial species. In the current study, we demonstrate the development of a whole-cell MALDI-TOF MS method for the distinction of V. parahaemolyticus from other Vibrio spp. We identified 30 peaks that were present only in the spectra of the V. parahaemolyticus strains examined in this study that may be developed as MALDI-TOF MS biomarkers for identification of V. parahaemolyticus. We detected variation in the MALDI-TOF spectra of V. parahaemolyticus strains isolated from different geographical locations and at different times. The MALDI-TOF MS spectra of the V. parahaemolyticus strains examined were distinct from those of the other Vibrio species examined including the closely related V. alginolyticus, V. harveyi, and V. campbellii. The results of this study demonstrate the first use of whole-cell MALDI-TOF MS analysis for the rapid identification of V. parahaemolyticus.Recent food-borne illness outbreaks have emphasized the need for rapid, robust, and low-cost methods for microbial identification. Vibrio parahaemolyticus is one of several Vibrio species that cause human infection and occur in coastal estuarine and marine environments worldwide. V. parahaemolyticus causes gastroenteritis, wound infections, and septicemia upon exposure to contaminated water or contaminated undercooked seafood. In the United States, V. parahaemolyticus is the leading causative agent of bacterial seafood-borne gastroenteritis (8). Gastroenteritis-associated V. parahaemolyticus strains typically possess one or both of the thermostable direct hemolysin genes (tdh and trh); however, recent studies have indicated the presence of additional virulence-associated genes including two type III secretion systems (6,7,26,28,33). Following the emergence of the V. parahaemolyticus O3:K6 pandemic clone in 1995, there has been a rise in the number of reported V. parahaemolyticus-associated infections each year, making this species a pathogen of increasing concern (8, 11). The V. parahaemolyticus pandemic clone was first isolated from outbreaks in Asia in 1995 with the O3:K6 serotype and has since emerged with additional serotypes (30). The worldwide spread of the V. parahaemolyticus O3:K6 clone is a recognized international public health issue that requires the use of standardized methods for global monitoring and surveillance such as pulsed-field gel e...

The presence and antimicrobial susceptibility of foodborne pathogens and indicator organisms in animal feed are not well understood. In this study, a total of 201 feed ingredient samples (animal byproducts, n=122; plant byproducts, n=79) were collected in 2002 and 2003 from representative rendering plants and the oilseed (or cereal grain) industry across the United States. The occurrence and antimicrobial susceptibility of four bacterial genera (Salmonella, Campylobacter, Escherichia coli, and Enterococcus) were determined. Salmonella isolates were further characterized by serotyping and pulsed-field gel electrophoresis (PFGE). None of the samples yielded Campylobacter or E. coli O157:H7, whereas Salmonella, generic E. coli, and Enterococcus were present in 22.9%, 39.3%, and 86.6% of samples, respectively. A large percentage (47.8%) of Salmonella-positive samples harbored two serovars, and the vast majority (88.4%) of Enterococcus isolates were E. faecium. Animal byproducts had a significantly higher Salmonella contamination rate (34.4%) than plant byproducts (5.1%) (p<0.05). Among 74 Salmonella isolates recovered, 27 serovars and 55 PFGE patterns were identified; all were pan-susceptible to 17 antimicrobials tested. E. coli isolates (n=131) demonstrated similar susceptibility to these antimicrobials except for tetracycline (15.3% resistance), sulfamethoxazole (7.6%), streptomycin (4.6%), ampicillin (3.8%), and nalidixic acid (1.5%). Enterococcus isolates (n=362) were also resistant to five of 17 antimicrobials tested, ranging from 1.1% to penicillin to 14.6% to tetracycline. Resistance rates were generally higher among isolates recovered from animal byproducts. Taken together, our findings suggest that diverse populations of Salmonella, E. coli, and Enterococcus are commonly present in animal feed ingredients, but antimicrobial resistance is not common. Future large-scale studies to monitor these pathogenic and indicator organisms in feed commodities is warranted.

The PulseNet USA subtyping network recently established a standardized protocol for multiple-locus variable-number tandem repeat analysis (MLVA) to characterize Shiga toxin-producing Escherichia coli O157. To enable data comparisons from different laboratories in the same database, reproducibility and high quality of the data must be ensured. The aim of this study was to test the robustness and reproducibility of the proposed standardized protocol by subjecting it to a multilaboratory validation process and to address any discrepancies that may have arisen from the study. A set of 50 strains was tested in 10 PulseNet participating laboratories that used capillary electrophoresis instruments from two manufacturers. Six out of the 10 laboratories were able to generate correct MLVA types for 46 (92%) or more strains. The discrepancies in MLVA type assignment were caused mainly by difficulties in optimizing polymerase chain reactions that were attributed to technical inexperience of the staff and suboptimal quality of reagents and instrumentation. It was concluded that proper training of staff must be an integral part of technology transfer. The interlaboratory reproducibility of fragment sizing was excellent when the same capillary electrophoresis platform was used. However, sizing discrepancies of up to six base pairs for the same fragment were detected between the two platforms. These discrepancies were attributed to different dye and polymer chemistries employed by the manufacturers. A novel software script was developed to assign alleles based on two platform-specific (Beckman Coulter CEQ8000 and Applied Biosystems Genetic Analyzer 3130xl) look-up tables containing fragment size ranges for all alleles. The new allele assignment method was validated at the PulseNet central laboratory using a diverse set of 502 Shiga toxin-producing Escherichia coli O157 isolates. The validation confirmed that the script reliably assigned the same allele for the same fragment regardless of the platform used to size the fragment.