Food Pathogens

The safety of irradiated pork packed in 25% CO2:75% N2 and stored at abuse temperature (10 or 15°C) was assessed by inoculation studies involving Salmonella typhimurium, Listeria monocytogenes, Escherichia coli, Yersinia enterocolitica and Clostridium perfringens. Irradiation to a dose of 1.75 kGy reduced pathogen numbers to below the detection limit of 102 cells g-1. When higher inoculum levels were used (106 cells g-1) irradiation at 1.75 kGy reduced pathogen numbers by 1 –>5 log10 cycles depending on strain. Clostridium perfringens was the most resistant, and Y. enterocolitica the most sensitive of the pathogens studied.In all cases when high numbers (106 to 107g-1) of spoilage and/or pathogenic bacteria were present initially on the pork the meat appeared spoiled, and although irradiation reduced the number of microorganisms, the meat was still unacceptable from a sensory viewpoint after treatment.It was concluded that the microbiological safety of irradiated, modified atmosp...

There is a lack of efficient and safe preservatives in the food industry. Massive use of some common food preservation methods has led, over the years, to development of a resistance to different treatments by various food pathogens. Enteric bacteria are especially tolerant to adverse environmental conditions-such as low pH and high salt concentrations-which limits efficiency of some preservation methods. Consumers demand for natural, preservative-free, and minimally processed foods and worldwide concern regarding disease outbreaks caused by food-related pathogens have created a need for development of new classes of antimicrobial (AM) agents. The twentieth century revealed a massive array of new peptide-based antimicrobials. Small ribosomally made compounds are found in practically all living species where they act as important component of host defense. Certain indubitable advantages of peptides-pertaining to simplicity, activity spectra, and bacterial resistance-over known preservative agents advocate their potential for food preservation. Nisin, an AM compound originating from bacteria, is so far the only FDA-approved peptide. However, a growing number of reports describe the potential of animal-derived antimicrobial peptides as food preservatives. These studies have yielded various native compounds and/or derivatives that possess markedly improved antimicrobial properties under a broad range of incubation conditions. The present work reviews the most investigated peptides and accounts for their potential use as alternatives to the preservatives used today. The focus is on research aspects aiming at understanding the mechanism of action of these peptides at extreme environments of various food systems. Collectively, the data accumulated are convincingly indicative of potential applications of these peptides in food safety, namely, with respect to fighting multidrug-resistant pathogens.

Time-temperature data, collected during pasteurization or sterilization of a food product, can be converted to the F-value (or F0-value), received by the heated product.
An F-value is an indication for the safety of the heated food, and for its shelflife.
In the past, calculation of the F-value from food time-temperature data, required tedious work with lethality tables. Excel computer program F-SPOIL.xls converts such time-temperature data (with equal time intervals) directly to lethality factors, and calculates the F-value, the microbial spoilage rate, or the % nutrient retention of the heated food.
4 Worked Examples, attached to the spreadsheet, step-by-step show how to use F-SPOIL.xls: both for liquid foods (Examples 1 and 2) and for solid foods (Examples 4A+B).
The time-temperature input of Worked Example 3 (“Validation”) was taken from a heating process in the literature. Both the lethality factors and the F-value, calculated by F-SPOIL.xls, were exactly equal to those in the literature, calculated with lethality tables. A brief explanation of the concept “lethality factor”, the equation how to calculate it, and a lethality factor example calculation, are included in Worked Example 3.

The effect of combining low-dose irradiation (1.75 kGy) with modified atmosphere packaging (MAP) on the microbiological and sensory quality of pork chops stored at refrigeration temperatures was studied. The microflora of irradiated MAP pork was almost exclusively composed of lactic acid bacteria, predominantly Lactobacillus spp. Modified atmospheres containing either 25 or 50% CO2, balance N2, resulted in the best microbial control in irradiated pork held at 4°C, compared to an unirradiated MAP control, and these atmospheres were subsequently used in sensory studies. The atmosphere containing 25% CO2 75% N2 maintained the uncooked colour and odour of irradiated pork chops more effectively than 50% CO2 50% N2. Therefore packaging in a modified atmosphere containing 25% CO2, balance N2, followed by irradiation to a dose of 1.75 kGy is recommended to improve the microbiological and sensory quality of pork chops.

opgB gene of Salmonella enterica serovar Typhimurium was identified earlier in a genome-wide screen for mice virulence (Valentine et al. in Infect Immun 66:3378-3383, 1998). Although mutation in opgB resulted in avirulent Salmonella strain, how this gene contributes to pathogenesis remains unclear. Based on DNA homology, opgB is predicted to be responsible for adding phosphoglycerate residues to osmoregulated periplasmic glucans (OPGs) giving them anionic characteristics. In Escherichia coli, yet another gene, opgC, is also reported to contribute to anionic characteristics of OPGs by adding succinic acid residues. We constructed opgB, opgC, and opgBC double mutants of S. enterica serovar Typhimurium strain SL1344. As predicted opgBC mutant synthesized neutral OPGs that were devoid of any anionic substituents. However, opgB, opgC, and opgBC mutations had no significant impact on mice virulence as well as on competitive organ colonization. In low osmotic conditions, opgB, opgC, and opgBC mutants exhibited delay in growth initiation in the presence of sodium deoxycholate. Anionic substituents of OPGs from Salmonella although appear to be needed to overcome resistance of deoxycholate in hypoosmotic growth media, no evidence was found for their role in mice virulence.

Several recent reports in the literature show that some microemulsions and nanoemulsions have interesting antimicrobial properties. However, those studies lacked appropriate controls showing the action of the isolated components at similar concentrations. In this study we demonstrate that the bactericidal effects of two previously studied emulsions are due predominantly to one of their components. In fact, the bioactivity of those compounds, namely tributyl phosphate and n-pentanol, is diminished when incorporated in the dispersed oil phases. Therefore, we suggest that future work regarding the antimicrobial action of emulsions include controls similar to the ones carried out in this research.

Antimicrobial behavior of lactic acid bacteria (LAB) has been explored since many years to assess their ability to produce bacteriocin, a natural preservative, to increase the shelf life of food. This study aims to characterize bacteriocin producing strains of lactic acid bacteria isolated from acidic to slightly acidic raw vegetables including tomato, bell pepper and green chili and to investigate their potential to inhibit food related bacteria. Among twenty nine LAB screened for antimicrobial activity, three exhibited antagonism against closely related bacterial isolates which was influenced by varying temperature and pH. They were identified up to strain level as Lactococcus lactis subsp. lactis TI-4, L. lactis subsp. lactis CE-2 and L. lactis subsp. lactis PI-2 based on 16S rRNA gene sequence. Their spectrum of inhibition was observed against food associated strains of Bacillus subtilis and Staphylococcus aureus. Moreover, L. lactis subsp. lactis PI-2 selected on the basis of higher antimicrobial activity was further evaluated for bacteriocin production which was detected as nisin A and nisin Z. These findings suggest the possible use of L. lactis strains of vegetable origin as protective cultures in slightly acidic as well as slightly alkaline food by the biopreservative action of bacteriocins.

In this work, we fabricated a system of integrated self-assembled layer of organosilane 3-mercaptopropyltrimethoxy silane (MPTS) on the screen printed electrode (SPE) and electrochemically deposited gold nanoparticle for Salmonella typhi detection employing Vi gene as a molecular marker. Thi-olated DNA probe was immobilized on a gold nanoparticle (AuNP) modified SPE for DNA hybridization assay using methylene blue as redox (electroactive) hybridization indicator, and signal was monitored by differential pulse voltammetry (DPV) method. The modified SPE was characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and atomic force microscopy (AFM) method. The DNA biosensor showed excellent performances with high sensitivity and good selectivity. The current response was linear with the target sequence concentrations ranging from 1.0 × 10 −11 to 0.5 × 10 −8 M and the detection limit was found to be 50 (±2.1) pM. The DNA biosensor showed good discrimination ability to the one-base, two-base and three-base mismatched sequences. The fabricated genosensor could also be regenerated easily and reused for three to four times for further hybridization studies.

Introduction: Sarcocystosis is mainly a veterinary problem; however, humans can serve as the definitive host for at least two species (Sarcocystis hominis and Sarcocystis suihominis).
Intestinal infections occur in the definitive host after ingesting the intramuscular cysts (sarcocysts) in the intermediate host, which initiate sexual stages in the intestine that terminate in oocysts excreted in the faeces.
Case presentation: A 19-year-old male presented with diffuse abdominal pain, watery nonbloody diarrhoea, nausea, vomiting and intermittent low-grade fever that lasted for more than
3 weeks. Multiple stool cultures on enriched and selective media gave negative results.
Microscopic examination of wet mounts of stool prepared from formalin/ethyl acetate concentrates, together with permanent staining helped in making a definitive diagnosis and ruling
out other coccidian parasites. Diagnosis of the parasite as S. hominis was made based on the size and morphology of the individual sporocysts that were observed in the wet-mount
preparations. This severe case of intestinal sarcocystosis in a healthy adult after eating undercooked beef shawarma meat is described.
Conclusion: The unusual presentation of intestinal sarcocystis described in this case is very rare. The clinical signs and size and morphology of both oocysts and sarcocysts observed in
concentrated wet mounts of stool helped in the definitive diagnosis. The food ingested prior to the appearance of symptoms was important in making the definitive diagnosis of the parasite as S. hominis, as well as the incubation period and treatment.

The capacity of pathogens to respond to environmental signals, such as iron concentration, is key to bacterial survival and establishment of a successful infection. Bacillus cereus is a widely distributed bacterium with distinct pathogenic properties. Hemolysin II (HlyII) is one of its pore-forming cytotoxins, which has been shown to be involved in bacterial pathogenicity in a number of cell and animal models. Unlike many other B. cereus pathogenicity factors, HlyII is not regulated by pleiotropic transcriptional regulator PlcR but controlled by its own regulator, HlyIIR. Using a combination of in vivo and in vitro techniques, we show that hlyII expression is also negatively regulated by iron by global regulator Fur via direct interaction with the hlyII promoter. DNase I footprinting and in vitro transcription experiments indicate that Fur prevents RNA polymerase binding to hlyII promoter. HlyII expression profiles demonstrate that both HlyIIR and Fur regulate HlyII expression in a concerted fashion, with the effect of Fur being maximal in the early stages of bacterial growth. In sum, these results show that Fur serves as a transcriptional repressor for hlyII expression.