Category Archives: Food Microbiology Research

Research – Exploitation of plant extracts and phytochemicals against resistant Salmonella spp. in biofilms

Science Direct

Salmonella is one of the most frequent causes of foodborne outbreaks throughout the world. In the last years, the resistance of this and other pathogenic bacteria to antimicrobials has become a prime concern towards their successful control. In addition, the tolerance and virulence of pathogenic bacteria, such as Salmonella, are commonly related to their ability to form biofilms, which are sessile structures encountered on various surfaces and whose development is considered as a universal stress response mechanism. Indeed, the ability of Salmonella to form a biofilm seems to significantly contribute to its persistence in food production areas and clinical settings. Plant extracts and phytochemicals appear as promising sources of novel antimicrobials due to their cost-effectiveness, eco-friendliness, great structural diversity, and lower possibility of antimicrobial resistance development in comparison to synthetic chemicals. Research on these agents mainly attributes their antimicrobial activity to a diverse array of secondary metabolites. Bacterial cells are usually killed by the rupture of their cell envelope and in parallel the disruption of their energy metabolism when treated with such molecules, while their use at sub-inhibitory concentrations may also disrupt intracellular communication. The purpose of this article is to review the current available knowledge related to antimicrobial resistance of Salmonella in biofilms, together with the antibiofilm properties of plant extracts and phytochemicals against these detrimental bacteria towards their future application to control these in food production and clinical environments.

Research – Inactivation kinetics of inoculated Escherichia coli and Listeria innocua in fresh‐cut Chinese cabbage using sweeping frequency ultrasound

Wiley Online

Abstract

Sweeping frequency ultrasound washing is a recent technology of applying varying ultrasound frequencies in the decontamination of fresh produce. Ultrasound inactivation of Escherichia coli and Listeria innocua inoculated on fresh‐cut Chinese cabbage was investigated at sweeping frequencies of 28 ± 2 to 68 ± 2 kHz for washing time of 5–40 min. The survival ratio of Ecoli and Linnocua decreased with the time of exposure to ultrasound washing and varying frequencies. Ecoli were more sensitive to ultrasound washing than Linnocua, achieving >3.0 log reductions after 10 min of washing with 40 ± 2 kHz. A nonlinear Weibull model was used to describe the experimental data, and the fitness of the model was evaluated by the coefficient of determination (R2) and the root mean square error (RMSE). The model used provided a good fit with R2 ≥ .98 for both bacteria and RMSE values in the range of 0.03–0.21 and 0.02–0.32 for E. coli and L. innocua, respectively.

Practical Application

Ultrasound decontamination is an alternative nonthermal technology that has been applied in recent years to improve the microbial safety of fresh produce. The bacterial inactivation is predominantly attributed to cavitation, an occurrence that interrupts cellular arrangement and function. With the known significance of sanitization in the processing of vegetables, it is imperative to develop and appraise novel approaches that contribute to the microbial safety of these fresh produce. Largely, the results of our study could guide the design of new ultrasonic fresh produce wash systems in addition to current industrial practice related to frequency selection and use of ultrasound during fresh produce sanitation.

Research – Interaction and inactivation of Listeria and Lactobacillus cells in single and mixed species biofilms exposed to different disinfectants

Wiley Online

Abstract

Listeria spp. are ubiquitously found in both the natural and the food processing environment, of which Listeria monocytogenes is of an important health risk. Here, we report on the formation of single and mixed species biofilms of L. monocytogenes/Listeria innocua and Lactobacillus plantarum strains in 24‐well polystyrene microtiter plates and on the inactivation of 24‐hr and 72‐hr biofilms using quaternary ammonium compound‐, tertiary alkyl amine‐, and chlorine‐based disinfectants. Fluorescent in situ hybridization (FISH) and LIVE/DEAD BacLight staining were applied for 72‐hr L. innocuaL. plantarum mixed biofilms in the LabTek system for the species identification and the reaction of biofilm cells to disinfectants, respectively. L. monocytogenes/L. innocua were more resistant to disinfectants in 72‐hr than in 24‐hr biofilms, whereas L. plantarum strains did not show any significant differences between 72‐hr and 24‐hr biofilms. Furthermore, L. innocua when grown with L. plantarum was more resistant to all disinfection treatments, indicating a protective effect from lactobacilli in the mixed species biofilm. The biofilm formation and reaction to disinfectants, microscopically verified using fluorescence in situ hybridization and LIVE/DEAD staining, showed that L. innocua and L. plantarum form a dense mixed biofilm and also suggested the shielding effect of L. plantarum on L. innocua in the mixed species biofilm.

Research – Identification and genotyping of Listeria monocytogenes in the chicken shredding line

Wiley Online

Abstract

The present research was carried out to determine the presence of Listeria monocytogenes in the equipment, staff, and products in the chicken shredding facilities operating in Samsun, and to serotype and genotype the isolates by PCR and PFGE analysis, respectively. Of the total of 192 samples tested, 25 were found to be L. monocytogenes positive from which 51 isolates were acquired. In serotyping of the 51 isolates; 47 (92.2%) and four isolates (7.8%) were identified as 1/2a (3a) and 1/2c (3c), respectively. Twenty‐six of the 51 isolates (51%) were resistant to at least one antibiotic, and 13 (25.5%) were resistant to more than one antibiotic. In the PFGE evaluation, at least 80% similarity was taken as a basis, and in the dendrogram, it was determined as a result of restricting with the Apal enzyme that the isolates were distributed to 25 different clusters and 45 subsets, and as a result of restricting with the AscI enzyme, they were distributed to 29 different clusters and 36 subsets.

Practical Application

Listeria monocytogenes constitutes a major problem for the food industry due to its widespread availability in nature and its role as an environmental contaminant in food processing plants.

Research – Listeria monocytogenes in dairy plants in Southern Brazil: Occurrence, virulence potential, and genetic diversity

Wiley Online

Abstract

Listeria monocytogenes is a foodborne pathogen widely distributed in nature. The aims of this study were to evaluate the occurrence of Listeria spp. in three dairy plants located in Southern Brazil, and to characterize the Lmonocytogenes isolates according to serotypes, virulence genes, and PFGE. A total of 212 samples were collected, and 15 were positive for Listeria spp., of which seven were LmonocytogenesLmonocytogenes isolates harbored all the 11 virulence genes evaluated and belonged to the main virulent serotypes, indicating potential risks of listeriosis for consumers. The PFGE analysis indicated low genetic diversity among the isolates, and the same pulsotypes were detected in a 2‐month period, indicating persistence of Lmonocytogenes.

Practical applications

The study evaluated the occurrence of Listeria spp. in three dairy plants located in Southern Brazil, as well as characterized the L. monocytogenes isolates according to serotypes, virulence genes and PFGE. The presence of Listeria species indicated postprocessing contamination in the dairy plants and threat to public health. Furthermore, the isolates showed a low genetic diversity, since only two pulsotypes were identified, highlighting the strain’s persistence in the processing environment and/or the presence of clones in this region.

Research – Massachusetts General Hospital publishes new Shigella research

Outbreak News Today

The bacterial pathogen Shigella, often spread through contaminated food or water, is a leading cause of mortality in both children and older adults in the developing world. Although scientists have been studying Shigella for decades, no effective vaccine has been developed, and the pathogen has acquired resistance to many antibiotics. The recent discovery of an early adherence step in the infection cycle by researchers at Massachusetts General Hospital (MGH) could provide a new therapeutic target or even a new method for vaccine development.

As it moves through the digestive system, Shigella traverses the small intestine and subsequently infects the large intestine, causing cramping, diarrhea and dehydration in the disease called shigellosis. “We wanted to determine how Shigella makes its first contact with epithelial cells in the early stages of disease development,” says Dr. Christina Faherty, senior author on the study published in mSphere. “Because of certain gene sequence annotations, and the way that Shigella appeared following growth in standard laboratory media, it was believed that Shigella strains do not produce fimbriae or other adherence factors.” Fimbriae are short hair-like fibers that bacterial cells use to adhere to individual epithelial cells to instigate infection.

Research -Anti‐listeria activity and shelf life extension effects of Lactobacillus along with garlic extract in ground beef

Wiley Online

Abstract

The current study investigates the effect of Lactobacillus reuteri and Lactobacillus plantarum combined with water extract of garlic on microbial growth, chemical changes, and sensory attributes in ground beef samples at refrigeration condition (+4°C) up to 12 days of storage. in vitro study revealed that garlic extract combined with L. reuteri or L. plantarum caused 2.13 and 2.57 log reduction in the Listeria monocytogenes count, respectively. Combination of L. plantarum and 1% garlic extract significantly (p < .05) reduced aerobic mesophilic bacteria (1.64 log cycle) and L. monocytogenes (1.44 log cycle) counts in ground beef. Lipid oxidation was also significantly (p < .05) lower in samples treated with L. plantarum plus garlic extract (1%). Furthermore, higher sensory scores were received by samples treated with Lactobacillus plus garlic extract. In conclusion, the combination of L. plantarum and garlic extract was found to be suitable to use in ground beef by controlling the L. monocytogenes growth and increasing its shelf life.

Practical Applications

Garlic extract not only has an antimicrobial activity but also has a stimulatory effect on the Lactobacillus spp. growth. On the other hand, some Lactobacillus strains can inhibit pathogenic bacteria. Then, the combination of Lactobacillus and garlic extract may be used to produce new bio‐preserved and functional meat products. The current study indicated the potential of Lactobacillus combined with garlic extract to control microbial and chemical changes in ground beef. The combination of Lactobacillus plantarum and garlic extract significantly (p < .05) reduced Listeria monocytogenes counts and lipid oxidation rates and improved the sensory scores in ground beef.

Research – Determination of the effect of ethyl pyruvate on the surface contamination of sausage to Listeria monocytogenes by using Q‐PCR assay

Wiley Online

Abstract

In this study, we examined the effect of ethyl pyruvate on the efficacy of the inactivation of Listeria monocytogenes on the surface of sausage samples by using quantitative PCR (Q‐PCR). Propidium monoazide (PMA) was used for direct quantification of viable and dead cells. The samples inoculated with L. monocytogenes (~3 to 4 log CFU/mL) and uninoculated samples were treated with 0, 42, 105, and 420 mg/L vaporized ethyl pyruvate (EP) in 1 L volume containers. Sausage samples were tested on Days 0, 7, 14, 21, and 28 with regards to changes in microbial, physicochemical, and quality characteristics. As compared with control samples (EP no‐applied), 105 and 420 mg/L concentration of vaporized EP applications were provided 1 and 2 log reduction, respectively. The vaporized EP application was considered to be an alternative preservation method for the modified atmosphere and vacuum packaging and could be easily applied, especially in meat products such as sausages.

Practical application

EP could be used for successful preservation of meat and meat products.

New Zealand – MPI puts consumer health first – directs unregistered raw (unpasteurised) drinking milk producers to stop selling

MPI Raw Milk Food Safety KSW Foodworld

The Ministry for Primary Industries (MPI) has directed unregistered raw (unpasteurised) drinking milk suppliers across the country to stop selling their product until they comply with the legal requirements for sale.

MPI compliance staff yesterday executed search warrants at non-compliant raw drinking milk suppliers in Auckland, Hawkes Bay, Manawatu, Horowhenua, Nelson, and Southland following a year-long operation.

MPI’s manager of food compliance Melinda Sando says the purpose of the coordinated site visits was to gather evidence of the offending and to allow further investigation of non-compliant sales.

“We believe that the suppliers we visited today are operating outside of the regulatory framework. By not adhering to the rules for selling raw drinking milk, they are putting consumer health at risk.

“There have been multiple instances in the past of people getting sick after drinking raw milk from some of these suppliers. We can’t let this continue.

“Raw unpasteurised milk is a risky product as it hasn’t been heat-treated (pasteurised) to remove illness-causing bacteria including E. coli, listeria and Campylobacter.

“These types of bacteria most commonly cause severe diarrhoea and vomiting, but occasionally some have been linked with more serious complications that include miscarriage, paralysis, meningitis, and serious kidney problems in children. Raw milk may also be a source of tuberculosis (Tb).

Cambodia – Two die from food poisoning in detox centre

Khmer Times

Two young men out of more than 100 youths being treated for drug addiction at a detox centre in Banteay Meanchey province’s Serei Sorphoan city died today from food poisoning, a health official said.

Keo Sopheatra, director of Banteay Meanchey provincial Health Department, today said that more than 100 youths at Phnom Bak New Life Center had food poisoning on Sunday, but two of them died.