Abstract
We aimed to establish a method for the rapid identification of three common Gram-positive bacteria (Bacillus cereus, Listeria monocytogenes, and Micrococcus luteus) associated with foodborne diseases. MALDI-TOF-MS was used to determine the effects of sample pretreatment, culture medium, and culture time on the identification results. Then, MALDI-TOF-TOF-MS was used to establish an optimized method and further explore the effects of culture time on secondary proteins. Among the three sample pretreatment methods, formic acid extraction outperformed direct transfer and extended direct transfer, resulting in more protein peaks and higher peak intensity in B. cereus culture samples. However, with different culture times (1–7 d), ion peaks of all bacterial proteins were relatively stable according to MALDI-TOF-TOF-MS data. The protein peaks of B. cereus (1430 m/z), L. monocytogenes (2100 m/z), and M. luteus (2140 m/z) were split into small ion peaks at 1162, 1465, and 1625 m/z, respectively. After 7 d of culture, the secondary spectra, peak intensities, and peak values of formic acid-treated samples were relatively stable, indicating that secondary protein peaks were less affected by culture time. It provides a new approach for the routine identification and market supervision of food safety in China.
Highlights
Diseases caused by the presence of bacteria in food, is the main food safety concerns of many food manufacturers, consumers, researchers and regulatory agencies around the world.According to data released by WHO in 2020, an estimated 600 million people get sick from eating contaminated food, and 420,000 people die every year, resulting in the loss of 33 million healthy life years (DALYs).In particular, bacterial food poisoning incidents that occur in China every year account for 30%–90% of the total number of food poisoning incidents worldwide (Tang et al, 2011; Shan et al, 2012)
We used B. cereus as an example to evaluate the effects of three different sample pretreatment methods on MALDI-TOF-MS identification of common foodborne bacteria
We found that formic acid extraction was better than direct transfer and extended direct transfer methods
Summary
Diseases caused by the presence of bacteria in food, is the main food safety concerns of many food manufacturers, consumers, researchers and regulatory agencies around the world.According to data released by WHO in 2020, an estimated 600 million people (nearly one-tenth of the world’s people) get sick from eating contaminated food, and 420,000 people die every year, resulting in the loss of 33 million healthy life years (DALYs).In particular, bacterial food poisoning incidents that occur in China every year account for 30%–90% of the total number of food poisoning incidents worldwide (Tang et al, 2011; Shan et al, 2012). There are many types of common foodborne pathogens, including Gram-positive and Gram-negative bacteria. Listeria monocytogenes, and Micrococcus luteus are common Gram-positive bacteria that cause foodborne diseases. B. cereus is a facultative aerobic bacterium belonging to the Bacillaceae family. It is widely found in water, air, and soil, and it is easy to detect in food (Yu et al, 2019; Guo et al, 2020; Jessberger et al, 2020; Yu et al, 2020; Sbhatu et al, 2021; Zhao et al, 2021). B. cereus is a conditional pathogen that can cause foodborne poisoning, in addition to traumatic endophthalmitis, orthopedic wound infections, and multiple tissue infections in people with low immune levels (Gaur et al, 2001; Yagishita et al, 2011; Safri et al, 2014; Lotte et al, 2017; Wang et al, 2017)
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