Reducing time in detection of Listeria monocytogenes from food by MALDI-TOF mass spectrometry

In this study, direct detection of L. monocytogenes from liquid culture and enrichment broths containing foods was investigated by using MALDI-TOF MS. For determining the sole effect of food constituents on detection and accuracy of identification in enrichment broths, sterile foods were used before the experiments with food. L. monocytogenes could be detected in BHI broth after 24 h of incubation. Detection period was determined as 18 h for 3 × 10 1  cfu/mL initial bacterial count in BHI broth containing sterile food. The period extended in ONE broth containing sterile garnish, which was 24 and 30 h for 3 × 10 1 and 1 cfu/mL inoculum, respectively. It was found that identification times in UHT milk were longer than that of canned garnish. In the experiments performed with foods having a specific microbiota; White cheese, iceberg lettuce, parsley and watermelon were used. Although no reliable identification was obtained by using White cheese, iceberg lettuce and parsley, L. monocytogenes could be detected in 24 h in the enrichment broth containing watermelon. Detection was achieved during a single step enrichment in a reduced time of 24 h for even 1 cfu/mL initial inoculum.