Effect of acid adaptation on growth during storage at 10 degrees C and resistance to simulated gastric fluid of Listeria monocytogenes inoculated onto bologna formulated with or without antimicrobials.
The fate of acid-adapted and nonadapted Listeria monocytogenes inoculated onto bologna slices (formulated with or without antimicrobials) was examined during storage and after exposure to in vitro gastric challenge. Bologna slices formulated with no antimicrobials (control), 3% sodium lactate (SL), or 1.8% SL plus 0.25% sodium diacetate (SD) were inoculated (2 log CFU/cm2) with a 10-strain composite of acid-adapted or nonadapted L. monocytogenes strains. Growth or survival of the two inocula on bologna was evaluated during vacuum-packaged storage (10 degrees C) for up to 36 days. Survival of previously acid-adapted or nonadapted L. monocytogenes on stored bologna exposed to simulated gastric fluid (adjusted to pH 1.0 with HCl) for 20, 40, and 60 min also was determined. As expected, inclusion of antimicrobials in the product formulation inhibited growth of L. monocytogenes during storage of vacuum-packaged bologna compared with growth on control samples. Acid adaptation of L. monocytogenes prior to product inoculation did not affect subsequent survival or growth on bologna or resistance to simulated gastric fluid (P > 0.05). Survival of L. monocytogenes exposed to simulated gastric fluid during storage increased with product age, growth phase of the cells, and possibly age of the cells, particularly for control samples (no antimicrobials), in which the pathogen grew uninhibited to approximately 6 log CFU/cm2 by day 8 of storage. Inhibition of L. monocytogenes growth on product formulated with antimicrobials was associated with only sporadic and small numbers of survivors following exposure of these samples to simulated gastric fluid, especially in samples stored longer. However, cell numbers in these treatment groups before the gastric challenge did not exceed 3.8 log CFU/cm2. Inhibition of growth on product with antimicrobials precluded detection of survivors resistant to the effects of simulated gastric fluid.
Formato
Giovanni
G
Center for Red Meat Safety, Department of Animal Sciences, Colorado State University, Fort Collins, Colorado 80523, USA.
Geornaras
Ifigenia
I
Barmpalia
Ioanna M
IM
Skandamis
Panagiotis N
PN
Belk
Keith E
KE
Scanga
John A
JA
Kendall
Patricia A
PA
Smith
Gary C
GC
Sofos
John N
JN
D000222:Adaptation, Physiological; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002417:Cattle; D015169:Colony Count, Microbial; D018857:Food Packaging / Q000379:methods*; D005519:Food Preservation / Q000379:methods*; D005520:Food Preservatives / Q000494:pharmacology*; D005744:Gastric Acid; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008089:Listeria monocytogenes / Q000187:drug effects / Q000254:growth & development*; D008461:Meat Products / Q000382:microbiology*; D013696:Temperature; D013997:Time Factors; D014618:Vacuum
D000900:Anti-Bacterial Agents; D005520:Food Preservatives