Inoculation onto solid surfaces protects Salmonella spp. during acid challenge: a model study using polyethersulfone membranes.
Salmonellae are the most frequently reported cause of outbreaks of food-borne gastroenteritis in the United States. In clinical trials, the oral infective dose (ID) for healthy volunteers was estimated to be approximately 1 million cells. However, in reports from various outbreaks, the ID of Salmonella species associated with solid foods was estimated to be as few as 100 cells. We found that fresh-cut produce surfaces not only provided suitable solid support for pathogen attachment but also played a critical role in increasing the acid tolerance of the pathogen. However the acidic nature of certain produce played no role in making salmonellae resistant to stomach acidity. Inoculation onto fresh-cut produce surfaces, as well as onto inert surfaces, such as polyethersulfone membranes and tissue paper, increased the survival of salmonellae during acid challenge (50 mM Na-citrate, pH 3.0; 37 degrees C; 2 h) by 4 to 5 log units. Acid challenge experiments using cells inoculated onto polyethersulfone membranes provided a model system suitable for studying the underlying fundamentals of the protection that occurs when Salmonella strains are associated with solid foods. The surface-associated acid protection, which was observed in several Salmonella strains, required de novo protein synthesis and was independent of stationary-phase sigma transcription factor.
Gawande
Purushottam V
PV
Produce Quality and Safety Laboratory, Henry A. Wallace Beltsville Agricultural Research Center, Agricultural Research Service, USDA, Beltsville, Maryland 20705-2350, USA.
Bhagwat
Arvind A
AA
D002633:Chemotaxis; D003470:Culture Media; D005516:Food Microbiology; D006863:Hydrogen-Ion Concentration; D027845:Malus / Q000382:microbiology*; D008567:Membranes, Artificial; D010209:Paper; D011108:Polymers; D012475:Salmonella / Q000235:genetics / Q000254:growth & development*; D012486:Salmonella typhimurium / Q000235:genetics / Q000254:growth & development; D013450:Sulfones; D013499:Surface Properties; D014675:Vegetables / Q000382:microbiology*
D003470:Culture Media; D008567:Membranes, Artificial; D011108:Polymers; D013450:Sulfones; C022840:polyether sulfone