Page Banner

United States Department of Agriculture

Agricultural Research Service

Title: Variation of Lag Time and Specific Growth Rate among 11 Strains of Salmonella Inoculated onto Sterile Ground Chicken Breast Burgers and Incubated at 25 C

item Oscar, Thomas

Submitted to: Journal of Food Safety
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 30, 2000
Publication Date: December 20, 2000

Interpretive Summary: Chicken may contain no or low numbers of Salmonella when consumers purchase it. However, improper refrigeration and thawing of chicken at room temperature can result in rapid multiplication of Salmonella to dangerous levels. If undercooked, improperly handled chicken can result in mild to severe gastroenteritis that is characterized by stomach cramps, vomiting, fever, and diarrhea. The rate at which Salmonella multiply on improperly handled chicken depends, in part, on the type of Salmonella present and on the time and temperature of abuse. A study was conducted to determine how fast different strains of Salmonella grow on cooked chicken at a room temperature of 25 C. The results indicate that it takes about three hours for Salmonella to start to grow, and that once they start to grow, they double in number every 1 hour at 25 C. All 11 strains of Salmonella tested showed similar rates of growth on cooked chicken.

Technical Abstract: Eleven strains of Salmonella, which were isolated from the ceca of broilers, were surveyed for their growth kinetics on sterile ground chicken breast burgers incubated at 25 C to determine the variation of lag time and specific growth rate. Growth curves, four per strain, were fit to a two-phase linear model to determine lag time (h) and specific growth rate (log/h). Repeatability of growth kinetics measurements for individual strains had a mean coefficient of variation of 11.7% for lag time (range: 5.8 to 17.3%) and a mean coefficient of variation of 6.7% for specific growth rate (range: 2.7 to 13.3%). Lag time among strains ranged from 2.2 to 3.1 h with a mean of 2.8 h for all strains, whereas specific growth rate among strains ranged from 0.3 to 0.38 log per h with a mean of 0.35 log per h for all strains. One-way analysis of variance indicated that lag time (P=0.029) and specific growth rate (P=0.025) differed among strains. S. Haardt had a shorter (P<0.05) lag time than S. Agona and S. Brandenburg, whereas the specific growth rate of S. Enteritidis was less than (P<0.05) the specific growth rates of S. Typhimurium and S. Brandenburg. All other strains had similar lag times and specific growth rates. The coefficient of variation among strains was 9.4% for lag time and 5.7% for specific growth rate. These results indicate that there were only minor differences in the lag times and specific growth rates among the strains of Salmonella surveyed.

Last Modified: 4/21/2015
Footer Content Back to Top of Page