Recovery of Foodborne Pathogens from Stainless Steel Coupons When Co-inoculated with a Flourescent Compound

Introduction: GloGerm^TMand similar fluorescent compounds have been used to visualize potential spread of microorganisms in a variety of settings (hospitals, labs, and food service environments). However, the quantification of a fluorescent compound alone may not correlate to concentrations of pathogens.  Inoculation of surfaces with a fluorescent compound pathogen cocktail may be beneficial; the fluorescence would help guide sampling locations for subsequent pathogen quantification. 

Purpose: The purpose of this study was to determine if fluorescent compound and foodborne pathogens could be co-inoculated on to stainless steel and result in recoverable populations similar to when a pathogen is inoculated alone.

Methods: Escherichia coli O157:H7, Salmonella Enteritidis, Listeria monocytogenes, and Listeria innocua were inoculated (approximately 8 log CFU/ml) on 2” by 2” stainless steel coupons alone and in combination with the compound (2:1, inoculum:compound). Inoculated coupons were allowed to dry for 20 minutes and then sampled using polyester tipped swabs. The swabs were then placed in phosphate buffered saline, serially diluted, and plated on selective media. The experiment was replicated 3 times, sampling 3 coupons each trial, for a total of 9 samples per treatment/bacteria. The recovery rates of the compound/bacteria cocktail were compared to recovery rates of bacteria alone.

Results: 6.86, 7.01, 6.88, and 6.42 log CFU/ml of L. innocua, L. monocytogenes, S. Enteritidis, and E. coli O157:H7, respectively, were recovered from the stainless steel coupons when bacteria was inoculated alone.  When co-inoculated with the compound 6.75, 7.05, 6.73 and 6.42 log CFU/ml were recovered.  There was no significant difference (P > 0.05) between bacteria recovered from the control coupons and from the compound/bacteria cocktail coupons for all 4 bacteria. 

Significance: Co-inoculating surfaces with fluorescent compound/bacteria cocktails does not affect the recoverability of microorganism which may allow researchers to visually track bacteria through an environment using the fluorescence as a guide where to sample.