Shuaihua Pu
Publications
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1.96Impact points
Prevalence and antimicrobial susceptibility of major foodborne pathogens in imported seafood.
Journal of food protection. 09/2011; 74(9):1451-61.
Seafood is a leading commodity implicated in foodborne disease outbreaks in the United States. Seafood importation rose dramatically in the past 3 decades and now contributes to more than 80% of the total U.S. seafood supply. However, limited data are available on the microbiological safety of impor... [more] Seafood is a leading commodity implicated in foodborne disease outbreaks in the United States. Seafood importation rose dramatically in the past 3 decades and now contributes to more than 80% of the total U.S. seafood supply. However, limited data are available on the microbiological safety of imported seafood. In this study, we obtained a total of 171 salmon, shrimp, and tilapia samples imported from 12 countries in three retail stores in Baton Rouge, LA. The total microbial population and the prevalence and antimicrobial susceptibilities of six major foodborne-pathogen genera (Campylobacter, Escherichia coli, Listeria, Salmonella, Shigella, and Vibrio) were determined. The aerobic plate counts (APC) for the 171 samples averaged 4.96 log CFU/g, with samples from Chile carrying the highest mean APC of 6.53 log CFU/g and fresh samples having a significantly higher mean APC than frozen ones (P < 0.0001). There were 27 samples (15.8%) with unacceptable microbiological quality (APC > 7 log CFU/g). By culture, no sample tested positive for Campylobacter coli, Shigella, or Vibrio vulnificus. Campylobacter jejuni and Salmonella enterica serovar Typhimurium were each recovered once from farm-raised tilapia from China. By PCR, 17.5 and 32.2% of the samples were positive for Salmonella and Shigella, respectively. The overall prevalence rates of other target bacteria were low, ranging from 4.1% for Listeria monocytogenes to 9.4% for E. coli. All of the Vibrio parahaemolyticus isolates recovered were from shrimp, and 63.3% showed intermediate resistance to ampicillin. Both C. jejuni isolates possessed a rare resistance to gentamicin, while 75% of L. monocytogenes isolates were resistant to nitrofurantoin. Taken together, these findings suggest potential food safety hazards associated with imported seafood and warrant further large-scale studies.
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1.90Impact points
Characterization of toxin genes and antimicrobial susceptibility of Staphylococcus aureus isolates from Louisiana retail meats.
Foodborne pathogens and disease. 10/2010; 8(2):299-306.
Staphylococcus aureus is 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. ... [more] Staphylococcus aureus is 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. aureus isolates, 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. aureus isolates 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 seg and 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 eta or 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. aureus isolates from pork. This study demonstrated that S. aureus isolates 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. aureus contamination.
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1.96Impact points
Effects of Plant Maturity and Growth Media Bacterial Inoculum Level on the Surface Contamination and Internalization of Escherichia coli O157:H7 in Growing Spinach Leaves.
Journal of food protection. 11/2009; 72(11):2313-20.
The incidence of foodborne outbreaks linked to fresh produce has increased in the United States. Particularly noteworthy was the 2006 Escherichia coli O157:H7 outbreak associated with prepackaged baby spinach. This study aimed to determine whether E. coli O157:H7 would be present in the aerial leaf ... [more] The incidence of foodborne outbreaks linked to fresh produce has increased in the United States. Particularly noteworthy was the 2006 Escherichia coli O157:H7 outbreak associated with prepackaged baby spinach. This study aimed to determine whether E. coli O157: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 (10(3) and 10(7) CFU/ml) of an E. coli O157: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. coli O157: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 10(7) CFU/ml level, the E. coli O157:H7 green fluorescent protein strain survived the entire cultivation period, although with gradually reduced levels. The experiments demonstrated that internalization of E. coli O157: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. coli O157:H7.
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1.90Impact points
Characterization of Clinical and Environmental Types of Vibrio vulnificus Isolates from Louisiana Oysters.
Foodborne pathogens and disease. 09/2009;
Abstract Vibrio 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... [more] Abstract Vibrio 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. vulnificus oyster 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. vulnificus strains 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. vulnificus isolates possessing both environmental (type A) and clinical (type B) genotypes of 16S rRNA. Additionally, the presence of the viuB fragment (41%) was significantly associated with clinical genotypes of V. vulnificus (p < 0.0001). An interesting seasonal pattern was observed, with clinical-type V. vulnificus isolates more frequently associated with warmer months. In conclusion, the majority of V. vulnificus isolates present in Louisiana raw oysters were of environmental type. There existed a seasonal variation in the V. vulnificus genotypes 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. vulnificus strains from oysters.
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3.03Impact points
Fitness cost of macrolide resistance in Campylobacter jejuni.
International journal of antimicrobial agents. 09/2009;
Whether the acquisition of macrolide resistance imposes a biological burden on Campylobacter jejuni is unknown. In this study, C. jejuni macrolide-resistant mutants and the susceptible parent were compared by non-competitive growth, pair-wise competitive growth, and the ability to tolerate a chillin... [more] Whether the acquisition of macrolide resistance imposes a biological burden on Campylobacter jejuni is unknown. In this study, C. jejuni macrolide-resistant mutants and the susceptible parent were compared by non-competitive growth, pair-wise competitive growth, and the ability to tolerate a chilling process commonly used in poultry processing plants. Overall, mutants demonstrated slower growth rates (average doubling time of 136min vs. 112min for the parent strain) and a lower survival ratio in the competitive growth experiment. However, mutants were equally competent in tolerating the chilling treatment. Our findings indicate that macrolide resistance incurs an obvious fitness cost in C. jejuni. However, the ability of macrolide-resistant C. jejuni mutants to tolerate the chilling process may render them equally capable of persisting in poultry products.
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1.90Impact points
Prevalence and Antimicrobial Resistance Among Campylobacter spp. in Louisiana Retail Chickens After the Enrofloxacin Ban.
Foodborne pathogens and disease. 12/2008;
Abstract Effective 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 Campylobacter spp. from Louisiana retail conventionally raised (n = 141) and orga... [more] Abstract Effective 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 Campylobacter spp. from Louisiana retail conventionally raised (n = 141) and organic (n = 53) chickens as a comparison to evaluate the postban bacterial resistance to antimicrobials. Campylobacter was present in 43.3% of the chickens; similar rates were observed among conventional and organic chickens. A total of 165 Campylobacter isolates were recovered, with Campylobacter jejuni being 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 Campylobacter isolates 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 Campylobacter isolates 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 Campylobacter in 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.
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3.69Impact points
Isolation and Characterization of Methicillin-Resistant Staphylococcus aureus from Louisiana Retail Meats.
Applied and environmental microbiology. 11/2008;
We investigated the prevalence of Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) in 120 retail meats from 30 grocery stores in Baton Rouge, Louisiana. S. aureus was recovered from 45.6% of pork and 20% of beef, whereas MRSA was isolated from six meats (5 pork and 1 beef). The MRSA ... [more] We investigated the prevalence of Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) in 120 retail meats from 30 grocery stores in Baton Rouge, Louisiana. S. aureus was recovered from 45.6% of pork and 20% of beef, whereas MRSA was isolated from six meats (5 pork and 1 beef). The MRSA isolates were of two strain types (clones), one harboring Panton-Valentine leucocidin and belonging to pulsed-field gel electrophoresis type USA300, and the other one belonging to USA100.
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Fei Wang
University of Maryland
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