Endogenous microbial contamination of melons (Cucumis melo) from international trade: an underestimated risk for the consumer?

BACKGROUND: Fruits and vegetables have increasingly been related to foodborne outbreaks. Besides surface contamination, a possible internalization of microorganisms into edible parts of plants during growth has already been observed. To examine an actual risk for the consumer, microbial contamination of the rind and pulp of 147 muskmelons from international trade was assessed using cultural and biochemical methods, polymerase chain reaction and matrix-assisted laser desorption/ionization-time of flight mass spectrometry. RESULTS: One hundred percent of the rind samples [3.69-8.92 log colony forming units (CFU) g-1 ] and 89.8% of the pulp samples (maximum load 3.66 log CFU g-1 ) were microbiologically contaminated. Among the 432 pulp isolates, opportunistic and potentially pathogenic bacteria were identified, mainly Staphylococcus spp. (48.9%), Clostridium spp. (42.9%) and Enterobacteriaceae (27.9%). Salmonella spp., Escherichia coli and isolates of the Bacillus cereus group were found on the rind (1.4%, 0.7% and 42.9%, respectively) and in the pulp (0.7%, 1.4% and 4.7%). Clostridium perfringens was isolated from the rind of seven melons. CONCLUSION: The present study revealed a regularly occurring internal contamination of melons. Possible health risks for consumers because of an occurrence of microorganisms in melon pulp should be considered in future food safety assessments. © 2018 Society of Chemical Industry.

Identification of Stachybotrys spp. by MALDI-TOF mass spectrometry.

Stachybotrys (S.) spp. are omnipresent cellulolytic molds. Some species are highly toxic owing to their ability to synthesize various secondary metabolites such as macrocyclic trichothecenes or hemolysins. The reliable identification of Stachybotrys at species level is currently limited to genome-based identification. This study aimed to establish a fast and reliable MALDI-TOF MS identification method by optimizing the pre-analytical steps for protein extraction for subsequent generation of high-quality fingerprint mass spectra. Eight reference strains of the American Type Culture Collection and the Technical University of Denmark were cultivated in triplicate (biological repetitions) for 2 days in malt extract broth. The mycelia (1.5 ml) were first washed with 75 % ethanol and an additional washing step with dimethyl sulfoxide (10 %) was added to remove unspecific low weight masses. Furthermore, mycelia were broken with roughened glass beads in formic acid (70 %) and acetonitrile. The method was successfully applied to a total of 45 isolates of Stachybotrys originating from three different habitats (indoor, feed, and food samples; n = 15 each): Twenty-seven isolates of S. chartarum and 18 isolates of S. chlorohalonata could be identified by MALDI-TOF MS. The data obtained exactly matched those obtained by genome-based identification. The mean score values for S. chartarum ranged from 2.509 to 2.739 and from 2.148 to 2.622 for S. chlorohalonata with a very good reproducibility: the relative standard deviations were between 0.3 % and 6.8 %. Thus, MALDI-TOF MS proved to be a fast and reliable alternative to identification of Stachybotrys spp. by nucleotide amplification and sequencing.

Detection of Listeria monocytogenes in pork and beef using the VIDAS® LMO2 automated enzyme linked immunoassay method.

Listeria (L.) monocytogenes, a foodborne pathogen, is known to be a possible contaminant of foods during production and processing. Samples (n=985) of raw meat and by-products obtained from beef and pork were first screened by the VIDAS system for the presence of Listeria spp., followed by testing for the presence of L. monocytogenes. Positive L. monocytogenes results were confirmed by plating on selective agars: 14% of the samples were positive for Listeria and 4% tested positive for L. monocytogenes, of which 3% were confirmed on selective agars. In by-products (17%) the contamination with listeriae was higher than in meat cuts (10%). Only samples strongly positive for Listeria spp. by VIDAS were positive for L. monocytogenes. Overall, the prevalence of L. monocytogenes in beef and pork samples was rather low in comparison to most previous studies. The VIDAS system was shown to be a suitable method for screening out Listeria-negative samples; the main advantage being a markedly reduced assay time.