Species Identification of a Gram-positive Bacterium, Lactobacillus fermentum, Isolated from Canned Food by Multilocus Sequence Typing

Introduction:  Lactobacillus fermentum is a gram-positive species of bacterium known for the production and preservation of fermented food as an acid-producing starter culture. The primary mission of FDA is to enforce the Food, Drug and Cosmetic Act and regulate food, drug and cosmetic products. FDA employs presence of pathogenic microorganisms in these products including spoilage in canned foods as one of the regulatory action criteria and to ensure that these are safe for human consumption. This surveillance study was carried out to assess the effectiveness of pathogen control in a canned food facility located in the United States.

Purpose: The major objective of this study was genetic identification of Lactobacillus fermentum isolated from canned food by multilocus sequence typing (MLST).

Methods: In this study, a total of nine unopened, recalled canned food jars from the same lot containing Black Bean Corn Poblano Salsa were examined initially by conventional microbiologic protocols by performing two-step enrichment followed by streaking on a selective agar. The recovered bacterial isolates were subsequently sequence characterized at gyrB and 16S rRNA loci at first followed by MLST using ABI 3500 XL Genetic Analyzer.

Results: Of the eight subsamples examined for each sample, all subsamples of one of the containers were found positive for the presence of slow growing rod-shaped, gram-positive facultative anaerobic bacteria. Species identification of these recovered bacterial isolates was done initially by our recently developed DNA sequencing protocol based on gyrB and 16S rRNA loci. Later, 11-loci MLST (clpX, dnaA, dnaK, groEL, murC, murE, pepX, pyrG, recA, rpoB, and uvrC) was performed. A total similarity was observed among the 8 subs at all 13 loci sequenced, and the analysis confirmed these canned food bacterial isolates to be Lactobacillus fermentum.

Significance: The results clearly suggested that the multilocus sequencing protocol with modified PCR conditions can provide species-identification of L. fermentum in the canned food monitoring program of public health importance.