Effect of rocket (Eruca sativa) extract on MRSA growth and proteome: Metabolic adjustments in plant-based media

The emergence of methicillin-resistant Staphylococcus aureus (MRSA) in food has provoked a great concern about the presence of MRSA in associated foodstuff. Although MRSA is often detected in various retailed meat products, it seems that food handlers are more strongly associated with this type of food contamination. Thus, it can be easily postulated that any food could be contaminated with this pathogen in an industrial environment or in household and cause food poisoning. To this direction, the effect of rocket (Eruca sativa) extract on MRSA growth and proteome was examined in the present study. This goal was achieved with the comparative study of the MRSA strain COL proteome, cultivated in rocket extract versus the standard Luria-Bertani growth medium. The obtained results showed that MRSA was able to grow in rocket extract. In addition, proteome analysis using 2-DE method showed that MRSA strain COL is taking advantage of the sugar-, lipid-, and vitamin-rich substrate in the liquid rocket extract, although its growth was delayed in rocket extract compared to Luria-Bertani medium. This work could initiate further research about bacterial metabolism in plant-based media and defense mechanisms against plant-derived antibacterials

Detection of Listeria monocytogenes in cut melon fruit using analysis of volatile organic compounds

Ready-to-eat fresh cut fruits and vegetables are increasingly popular, however due to their minimal processing there is a risk of contamination with human pathogens. Listeria monocytogenes is of particular concern as it can multiply even at the low temperatures used to store fresh cut products pre-sale. Current detection methods rely on culturing, which is time consuming and does not provide results in the time frame required. Growth of bacteria on a substrate alters its chemical composition affecting the profile of volatile organic compounds (VOCs) emitted. Use of VOCs as a detection method has been hampered by lack of sensitivity and robust sample collection methods. Here we use thermal desorption gas chromatography time of flight mass spectrometry (TD-GC-TOF-MS) followed by analysis with PerMANOVA to analyse VOC profiles. We can discriminate between fresh cut melon cubes inoculated with 6 log CFU/g of L. monocytogenes and uninoculated controls, as well as melon cubes inoculated with <1 log CFU/g of L. monocytogenes stored for 7 days at 4 °C and following equilibration for 6 h at 37 °C. This is a substantial advance in sensitivity compared to previous studies and additionally the collection method used allows remote sampling and transport of the VOCs, greatly facilitating analyses

Special Issue &lsquo;Food Fermentations: Microorganisms in Food Production and Preservation&rsquo;: Editorial

For centuries, microorganisms have been exploited for the production and preservation of substates intended for human consumption [...

Molecular Targets for Foodborne Pathogenic Bacteria Detection

The detection of foodborne pathogenic bacteria currently relies on their ability to grow on chemically defined liquid and solid media, which is the essence of the classical microbiological approach. Such procedures are time-consuming and the quality of the result is affected by the selectivity of the media employed. Several alternative strategies based on the detection of molecular markers have been proposed. These markers may be cell constituents, may reside on the cell envelope or may be specific metabolites. Each marker provides specific advantages and, at the same time, suffers from specific limitations. The food matrix and chemical composition, as well as the accompanying microbiota, may also severely compromise detection. The aim of the present review article is to present and critically discuss all available information regarding the molecular targets that have been employed as markers for the detection of foodborne pathogens. Their strengths and limitations, as well as the proposed alleviation strategies, are presented, with particular emphasis on their applicability in real food systems and the challenges that are yet to be effectively addressed

Transcriptomic Response of L. monocytogenes to Co-Culture with S. cerevisiae

The aim of the present study was to assess the transcriptomic response of L. monocytogenes during co-culture with three S. cerevisiae strains. For this purpose, BHI broth was inoculated with 7 log CFU·mL−1&nbsp;L. monocytogenes serotype 4b strain LQC 15257, isolated from a strawberry sample and 4 log CFU·mL−1&nbsp;S. cerevisiae strains Y32, Y34 and Y37, isolated from spontaneous olive fermentation. Sampling took place after 24 and 48 h incubation at 5 and 20 °C. RNA was extracted, stabilized and the transcription of virulence associated genes prfA, sigB, hly, plcA, plcB, inlA, inlB, inlC and inlJ, was assessed by RT-qPCR. Co-culture with the yeast strains mostly affected the transcription of sigB and inlJ, the upregulation of which during growth at 5 °C for 24 h, reached 10.13 and 9.76 log2(fold change), respectively. Similarly, the effect that incubation time had on the relative transcription of the genes under study was dependent on the co-cultivating yeast strain. On the other hand, the effect of the yeast strain was less pronounced when the relative transcription of the genes under study was assessed between 20 °C and 5 °C. In that case, incubation temperature seemed to have an important effect since, in the 79.2% of the samples analyzed, upregulation was evident, irrespective of yeast strain presence. These results highlight the complex trophic relationships that take place during co-existence between L. monocytogenes and S. cerevisiae

Food molecular microbiology

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Lactic acid bacteria population dynamics during minced beef storage under aerobic or modified atmosphere packaging conditions

A total of 266 lactic acid bacteria (LAB) have been isolated from minced beef stored at 0, 5, 10 and 15 °C aerobically and under modified atmosphere packaging consisting of 40% CO2–30% O2–30% N2 in the presence MAP (+) and absence MAP (−) of oregano essential oil. Sequencing of their 16S rRNA gene along with presence of the katA gene demonstrated dominance of the LAB microbiota by Leuconostoc spp. during aerobic storage at 5, 10 and 15 °C, as well as during MAP (−) and MAP (+) storage at 10 and 15 °C; Lactobacillus sakei prevailed during aerobic storage at 0 °C, as well as at MAP (−) and MAP (+) storage at 0 and 5 °C. The sporadic presence of other species such as Leuconostoc mesenteroides, Weisella viridescens, Lactobacillus casei and Lactobacillus curvatus has also been determined. Pulsed-Field Gel Electrophoresis of high molecular weight genomic DNA revealed the dynamics of the isolated LAB strains. Prevalence of Leuconostoc spp. was attributed to one strain only. On the other hand, packaging conditions affected Lb. sakei strain spoilage dynamics

Preserving Microbial Biodiversity: The Case of Food-Associated Microorganisms

The preservation of microbial diversity is an issue not properly addressed, considering their role in shaping Earth into a habitable planet and their contribution to human well-being. The disturbance of their natural habitats triggers responses, which are reflected in the modification of microecosystem composition and metabolic activities. This is also the case with food-related microecosystems; changes in the growing environment, recorded as agricultural practices and manufacturing or storage conditions, result in similar alterations in the residing microcommunity. In fact, the principle aim of food microbiology is to favor the growth of health-promoting microorganisms and restrict the development of the ones that may negatively affect the quality of food or even cause infection or intoxication. Therefore, the current perspective is one-sided, disregarding issues of general interest, such as the preservation of actual biodiversity. The aim of the present article is to present the current food microbiology perspective, which is based on the different roles of food-related microbiota and highlight the need to move from an anthropocentric to a microbe-centric perception