Development of a New Device for the Rapid Detection of Heterofermentative and Homofermentative Lactic Acid Bacteria

Introduction: A new Soleris® vial was developed to rapidly detect heterofermentative and homofermentative lactic acid bacteria contamination in dressings, condiments, and deli and packaged meats.  The vial, based on detection of carbon dioxide produced from the metabolism of the organisms, consists of a detection chamber containing carbon dioxide indicators separated by a barrier layer from a chamber containing a growth medium and test sample.  The majority of lactic acid-producing microorganisms can be detected within 72 hours using the Soleris instrument system. 

Purpose: The purpose of this study was to develop and assess the performance of a device for the rapid detection of lactic acid-producing bacteria in the dressing, condiment, and deli and packaged meat industries.

Methods: Experiments were performed to select the optimal growth medium and indicator chemistries for the most rapid detection of lactic acid bacteria. Inclusivity studies used a panel of the target organisms at levels of <100 CFU/ml.  In addition, the detection time in the instrument and growth of low inoculum levels of the organisms in food matrices was examined.

Results: The inclusivity/exclusivity test panel of ATCC organisms included Lactobacillus, Leuconostoc, Pediococcus, yeast, and mold.  The Soleris instrument detection times were as low as 16.2 hours for an inoculum level of 55 CFU/mL for Lactobacillus fermentum ATCC 9338, and as high as 77.6 hours for 85 CFU/ml of Lactobacillus fructivorans ATCC 8288.  Naturally contaminated deli meats (10² to 10⁴CFU/g) produced a range of detection times between 9.7 and 16.8 hours.  The food matrices tested did not interfere with the vial test.   

Significance: The new Soleris Direct Lactic Acid vial provides a system for the rapid detection of lactic-acid producing microorganisms in <50 hours, with the exception of Lactobacillus fructivorans ATCC 8288, compared to the standard incubation time of 5 days for agar plates.