Persistence of Fecal Indicator Bacteria and Bacteroidales Universal Marker on Two Different Texture Surfaces

Introduction:  To reduce the risk of produce contamination, fecal indicator bacteria (FIB) are usually quantified, but the source of contamination is not clarified with this method. Members of Bacteroidales have been recognized as a promising option for microbial source tracking (MST). However, persistence of Bacteroidales has been poorly studied in foods and food surfaces. 

Purpose:  To determine the persistence of Bacteroidales and traditional FIB on two different texture surfaces under two storage conditions.

Methods: Pools of sterile feces were inoculated with Enterococcus faecalis ATCC 19433 (8.84 log CFU/ml), Escherichia coli ATCC 25922 (10.30 log CFU/ml) and Bacteroides thetaiotamicron (5.34 log CFU/ml). Aliquots were placed on 47 mm Millipore filters and 47 mm flat cork circles. Samples were maintained in a bioclimatic chamber at 10°C/95% RH (T1) or 25°C/65% RH (T2) for 25 days. Each five days samples were washed and the rinsate plated onto selective agars (Streptococcus KF and Rapid'E. coli 2) and the presence of Bacteroidales universal AllBac marker was analyzed by qPCR. Assays were done three times and analyzed by SPSS 21.

Results:  Without following any pattern, AllBac marker was present in all rinsates until day 25. The detection levels ranged from 1.16 to 4.71 log CFU/ml, independently of the surface texture, feces or storage conditions. Viability of FIB, were reduced during the treatments, E. coli by 1.48 to 4.26 log CFU/ml and 6.06 to 6.30 log CFU/ml at T1 and T2, respectively, and population of E. faecalis was reduced 0.56 to1.39 log CFU/ml at T1 and 2.3 to 4.0 in T2. At T1 both FIB persisted until the end but at T2 E. coli was not recovered on days 10 to 15. FIB persistence were dependent to humidity and species of bacteria (P<0.05).

Significance: This study shows that AllBac marker could persist onto surfaces longer than some FIB and could be a good alternative for MST.