Radiation resistance and virulence of Listeria monocytogenes Scott A following starvation in physiological saline.
The influence of starvation on the resistance of Listeria monocytogenes Scott A to electron beam irradiation in 0.85% (wt/vol) NaCl (saline) and in ground pork was investigated. Exponential- or stationary-phase cells (control) were grown at 35 degrees C in tryptic soy broth supplemented with 0.6% yeast extract. Washed cells were starved for 12 days in saline, and virulence of the pathogen was evaluated at 0, 8, and 12 days during starvation. Samples of saline and irradiation-sterilized ground pork, inoculated with control or starved cells, were irradiated at doses ranging from 0.0 to 2.5 kGy. L. monocytogenes survivors were determined by plating diluted samples of saline or pork on tryptic soy agar supplemented with 0.6% yeast extract and counting bacterial colonies following incubation (35 degrees C, 48 h). Virulence of starved cells and control was not significantly different (P > 0.05). Cells exhibited the highest radiation resistance at 8 days of starvation. Irradiation (0.5 kGy) in saline resulted in approximately 7.14, 5.55, and 2.38 log reduction in exponential, stationary, and starved cells, respectively. Irradiation of ground pork at 2.5 kGy reduced controls by approximately 6.0 log, whereas starved cells were reduced by only 3.8 log. Starved cells consistently exhibited higher irradiation D10-values than controls (P < 0.05). D10-values for exponential, stationary, and starved cells were 0.07, 0.09, and 0.21 kGy and 0.35, 0.42, and 0.66 kGy in saline and ground pork, respectively. These results indicate that starvation cross-protects L. monocytogenes Scott A against radiation inactivation and should be considered when determining this pathogen's irradiation D-value.
Mendonca
A F
AF
Iowa State University, Department of Food Science and Human Nutrition, 2312 Food Sciences Building, Ames, Iowa 50011, USA. amendon@iastate.edu
Romero
M G
MG
Lihono
M A
MA
Nannapaneni
R
R
Johnson
M G
MG
D000222:Adaptation, Physiological; D000818:Animals; D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D003470:Culture Media / Q000737:chemistry; D004307:Dose-Response Relationship, Radiation; D005514:Food Irradiation; D005516:Food Microbiology; D005720:Gamma Rays; D008089:Listeria monocytogenes / Q000254:growth & development / Q000472:pathogenicity* / Q000528:radiation effects*; D008461:Meat Products / Q000382:microbiology*; D013552:Swine; D013997:Time Factors; D014774:Virulence / Q000502:physiology
D003470:Culture Media