Determination of the microbiological contamination in minced pork by culture dependent and 16S amplicon sequencing analysis

Abstract

Routine evaluation of bacterial contamination in minced pork is still mainly performed by the enumeration of indicator bacteria, including total aerobic colony count and E. coli, using standardized isolation methods. However, the bacterial community structure as well as the effect of the storage time and temperature on the aerobic plate count are largely unknown for this matrix. The aim of the study was to characterize the microbial community in minced pork by 16S rRNA amplicon sequencing compared to classical isolation methods combined with identification by Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI TOF MS) and 16S rRNA gene sequencing. Analysis of 14 unrelated samples showed that total aerobic counts determined at 30 °C and 7 °C showed no significant difference, but the richness was higher on PCA at 30 °C for 7 samples, equal in 5, and higher at 7 °C for 2 samples. Members of the genus Pseudomonas, along with the genera Brochothrix and Carnobacterium were commonly identified among both the mesophilic and psychrotrophic population. Comparing to 16S rRNA amplicon sequencing, some contrasting data were obtained. Except for Brochothrix spp. and Pseudomonas spp., that were abundant and always detected, genera obtained with the two methods in the same sample were not always the same. Comparison of different sample preparation techniques and DNA extraction methods demonstrated also in this matrix that different results on the microbial composition and complexity are obtained. Present data illustrate that the combined isolation and identification of isolates using MALDI TOF MS and 16S gene sequencing and overall community profiling using 16S rRNA amplicon sequencing provides complementary results and yields important insights into the complex relationship between microorganisms in a food.