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AbstractStaphylococcus aureusis a leading cause of food poisoning worldwide due to the production of heat-stable enterotoxins. Recently, the isolation of methicillin-resistant S. aureus(MRSA) from food animals and retail meats raised additional food safety concerns. In this study, we characterized 152 S. aureusisolates, including 22 MRSA recovered from Louisiana retail pork and beef meats, for the prevalence of nine enterotoxin and four other exotoxin genes by polymerase chain reaction and antimicrobial susceptibility testing by broth microdilution. Overall, 85% of S. aureusisolates were positive for at least one of six enterotoxin genes identified and 66% harbored two to four enterotoxin genes. The two most predominant ones were segand sei(66% each), followed by seh(20%), sed(15%), sej(13%), and sea(1%). No isolates harbored enterotoxin genes seb, sec, or see, the toxic shock syndrome toxin 1 gene tst, or the exfoliative toxin genes etaor etb. Three MRSA isolates were the only ones harboring Panton-Valentine leucocidin. Resistances were common to penicillin (71%), ampicillin (68%), and tetracycline (67%), followed by erythromycin (30%), clindamycin (18%), oxacillin with 2% NaCl (14%), ciprofloxacin (13%), levofloxacin (13%), gentamicin (3%), quinupristin/dapfopristin (3%), chloramphenicol (2%), and moxifloxacin (1%). Multidrug resistance was commonly observed among MRSA isolates and S. aureusisolates from pork. This study demonstrated that S. aureusisolates found in Louisiana retail pork and beef meats possessed various enterotoxin genes and antimicrobial resistance profiles. Therefore, vigilant food safety practice needs to be implemented for people who handle raw meat products to prevent foodborne infections and intoxications due to S. aureuscontamination.

AbstractVibrio vulnificus, a naturally occurring estuarine bacterium frequently transmitted to humans via raw oysters, is a leading cause of seafood-related deaths in the United States. Although unique virulence markers have not been identified to date, multiple biomarkers have been used previously to associate strains with clinical or environmental types of V. vulnificus. In this study, we evaluated the usefulness of these biomarkers in characterizing 349 V. vulnificusoyster isolates by the presence/absence of a viuB-associated fragment and genotypes of three biomarkers: the virulence-correlated gene (vcg), 16S rRNA, and the capsular polysaccharide (CPS) operon. Genotyping data indicated that environmental-type V. vulnificusstrains accounted for the majority of oyster isolates, and the percentages ranged from 51.6% for 16S rRNA (type A) to 72.5% for CPS (allele 2 or none). There was also a small percentage (8%) of V. vulnificusisolates possessing both environmental (type A) and clinical (type B) genotypes of 16S rRNA. Additionally, the presence of the viuBfragment (41%) was significantly associated with clinical genotypes of V. vulnificus(p< 0.0001). An interesting seasonal pattern was observed, with clinical-type V. vulnificusisolates more frequently associated with warmer months. In conclusion, the majority of V. vulnificusisolates present in Louisiana raw oysters were of environmental type. There existed a seasonal variation in the V. vulnificusgenotypes identified, which may help guide future control measures to focus more specifically on seasons that tend to accumulate more clinical-type V. vulnificus. The study also highlighted the need to identify unique virulence markers in this organism, which could facilitate future screening of virulent V. vulnificusstrains from oysters.

The incidence of foodborne outbreaks linked to fresh produce has increased in the United States. Particularly noteworthy was the 2006 Escherichia coliO157:H7 outbreak associated with prepackaged baby spinach. This study aimed to determine whether E. coliO157:H7 would be present in the aerial leaf tissue of a growing spinach plant when introduced at various plant maturities and different inoculum levels in a greenhouse setting. Spinach seeds of a commercial variety were sown in 8-in. (20.32-cm) pots. After seed germination, two levels (103and 107CFU/ml) of an E. coliO157:H7 green fluorescent protein–expressing strain were introduced into the plant growth media weekly for a total of five times. Inoculated spinach plants were examined weekly for the presence of E. coliO157:H7 on leaves and in surrounding growth media. Among 120 spinach plant samples examined for internal leaf contamination, only one yielded a positive result. Surface leaf contamination occurred occasionally and clustered between 3 and 5 weeks of age, but not among leaves younger than 3 weeks of age. On the other hand, when inoculated at the 107CFU/ml level, the E. coliO157:H7 green fluorescent protein strain survived the entire cultivation period, although with gradually reduced levels. The experiments demonstrated that internalization of E. coliO157:H7 of growing spinach plant leaves under greenhouse conditions was a rare event, but surface contamination did occur, primarily when the plants reached 3 weeks of age. The study provided important data to further assess the association between spinach age and potential contamination of E. coliO157:H7.

AbstractEffective in September 2005, enrofloxacin, a fluoroquinolone group antimicrobial, was withdrawn from use in the U.S. poultry farms. In this 1-year study initiated in October 2006, we isolated and characterized Campylobacterspp. from Louisiana retail conventionally raised (n= 141) and organic (n= 53) chickens as a comparison to evaluate the postban bacterial resistance to antimicrobials. Campylobacterwas present in 43.3% of the chickens; similar rates were observed among conventional and organic chickens. A total of 165 Campylobacterisolates were recovered, with Campylobacter jejunibeing the predominant species (66.7%). No apparent seasonal trend was deduced from the prevalence data. Further, the two main conventional and one organic chicken brands did not carry significantly different rates of Campylobacter(p> 0.05). The most common resistance observed was to tetracycline (31.5%), followed by erythromycin (20%) and ciprofloxacin (6.1%). No resistance to gentamicin was identified. All Campylobacterisolates recovered from organic chickens (n= 48) were susceptible to ciprofloxacin, compared to 8.5% resistance rate for those from conventional chickens (n= 117). Additionally, the resistance rate to erythromycin was significantly higher in Campylobacterisolates from conventional chickens (23.9%) than those from organic chickens (10.4%; p< 0.05). Our results demonstrated a low prevalence and low ciprofloxacin resistance rate of Campylobacterin Louisiana retail chickens after the enrofloxacin ban. Further studies involving a larger sample size over time are warranted to better assess the effects of banning enrofloxacin use in poultry and the levels of fluoroquinolone-resistant Campylobacter.