Category Archives: Technology

Research – Antibacterial activity and mechanism of Litsea cubeba essential oil against food contamination by Escherichia coli and Salmonella enterica

Wiley Online

Litsea cubeba essential oil (LC‐EO) has been reported as antibacterial agents, but there are few studies about its possible antibacterial mechanism. The antibacterial activities and the underlying mechanisms of LC‐EO against Escherichia coli O157: H7 and Salmonella enterica were investigated. The results showed that the LC‐EO was more effective against gram‐negative bacteria. The inhibition zone for E. coli O157: H7 and S. enterica were 3.1 ± 0.8 and 4.5 ± 0.6 mm, respectively. The minimum inhibitory concentration of LC‐EO against both bacteria was 0.9 μg/ml, while the minimum bactericidal concentrations were 4.5 and 9 μg/ml. Gas chromatography–mass spectrometry analysis confirmed that citral (86.8%) was the main component of LC‐EO. The results of a time–kill analysis illustrated that treatment with LC‐EO led to a rapid decrease in viable bacterial cell number. The release of electrolytes and nucleic acids from the bacterial cells increased with the dose of LC‐EO. Propidium iodide uptake revealed that LC‐EO caused cell membrane damage. Scanning electron and transmission electron microscopy showed that LC‐EO caused damage to the cell walls and membranes, resulting in cell deformation, atrophy, and large central voids. Thus, LC‐EO may provide the basis for the development of new natural food preservatives.

Research – Effectiveness and Functional Mechanism of a Multicomponent Sanitizer against Biofilms Formed by Escherichia coli O157:H7 and Five Salmonella Serotypes Prevalent in the Meat Industry

Journal of Food Protection

ABSTRACT

Biofilm formation by Escherichia coli O157:H7 and Salmonella enterica at meat processing plants poses a potential risk of meat product contamination. Many common sanitizers are unable to completely eradicate biofilms formed by these foodborne pathogens because of the three-dimensional biofilm structure and the presence of bacterial extracellular polymeric substances (EPSs). A novel multifaceted approach combining multiple chemical reagents with various functional mechanisms was used to enhance the effectiveness of biofilm control. We tested a multicomponent sanitizer consisting of a quaternary ammonium compound (QAC), hydrogen peroxide, and the accelerator diacetin for its effectiveness in inactivating and removing Escherichia coli O157:H7 and Salmonella enterica biofilms under meat processing conditions. E. coli O157:H7 and Salmonella biofilms on common contact surfaces were treated with 10, 20, or 100% concentrations of the multicomponent sanitizer solution for 10 min, 1 h, or 6 h, and log reductions in biofilm mass were measured. Scanning electron microscopy (SEM) was used to directly observe the effect of sanitizer treatment on biofilm removal and bacterial morphology. After treatment with the multicomponent sanitizer, viable E. coli O157:H7 and Salmonella biofilm cells were below the limit of detection, and the prevalence of both pathogens was low. After treatment with a QAC-based control sanitizer, surviving bacterial cells were countable, and pathogen prevalence was higher. SEM analysis of water-treated control samples revealed the three-dimensional biofilm structure with a strong EPS matrix connecting bacteria and the contact surface. Treatment with 20% multicomponent sanitizer for 10 min significantly reduced biofilm mass and weakened the EPS connection. The majority of the bacterial cells had altered morphology and compromised membrane integrity. Treatment with 100% multicomponent sanitizer for 10 min dissolved the EPS matrix, and no intact biofilm structure was observed; instead, scattered clusters of bacterial aggregates were detected, indicating the loss of cell viability and biofilm removal. These results indicate that the multicomponent sanitizer is effective, even after short exposure with dilute concentrations, against E. coli O157:H7 and S. enterica biofilms.

HIGHLIGHTS
  • No viable biofilm cells were detected after treatment with the multicomponent sanitizer.
  • Prevalence of both pathogens was low after treatment with the multicomponent sanitizer.
  • SEM analysis revealed that treatment dissolved the EPS matrix and destroyed the biofilm.

Research – Examination of the Culturable Microbiota from Low-Moisture Foods Imported into Canada for Antibacterial Activity against Listeria monocytogenes

Journal of Food Protection

ABSTRACT

Listeria monocytogenes, a resilient and ubiquitous foodborne pathogen, is associated with a high case-fatality rate in humans. This study investigated the culturable microbiota of low-moisture foods (LMFs) imported into Canada to see how well bacteria isolated from these foods could inhibit or inactivate the growth of L. monocytogenes. Imported LMFs were acquired from various supermarkets in the Greater Toronto Area (Ontario, Canada). The foods included dried apples, bee pollen, cumin seeds, date fruits, fennel seeds, pistachios, raisins, and seaweed. Bacterial strains were isolated from the foods using blood agar and then screened using an in-house-designed growth inhibition plate assay against L. monocytogenes. The inhibitory strains detected were then identified using 16S rRNA sequencing. Diverse bacteria were recovered from the foods; 236 isolates belonging to 122 observed phenotypes were obtained. From the inhibition plate assays, 10 of the 11 imported LMFs harbored inhibitory strains against L. monocytogenes, whereby 48 of the collected isolates (20%) were found to produce a zone of inhibition against this pathogen. The inhibitory strains belonged to six genera (Acinetobacter, Aerococcus, Bacillus, Lysinibacillus, Paenibacillus, and Sporosarcina) and 15 unique species. Among all foods tested, the date fruit microbiota displayed the greatest number and diversity of anti–L. monocytogenes inhibitory strains. Overall, it was found that the culturable microbiota of LMFs, imported into Canada, possess bacterial members that can inhibit the growth of L. monocytogenes. These results could lead to the discovery of either novel antimicrobial metabolites or beneficial anti–L. monocytogenes bacteria that could be added to foods to inactivate and/or control L. monocytogenes.

HIGHLIGHTS
  • Modification to an inhibition plate assay detects anti-Listeria bacteria more rapidly.
  • Unconventional anti-Listeria genera, such as Lysinibacillus, were discovered.
  • Date fruit microbiota warrants further investigation for anti-Listeria applications.
  • Isolated bacteria from low-moisture foods are diverse and can inhibit L. monocytogenes growth.

Research – Effect of Peracetic Acid Solutions and Lactic Acid on Microorganisms in On-Line Reprocessing Systems for Chicken Slaughter Plants

Journal of Food Protection

ABSTRACT

During poultry slaughter and processing, microbial cross-contamination between individual chickens is possible, as well as from one slaughter animal to the next without direct contact. One option for reducing the risk of cross-contamination is to decrease the number of microorganisms on contact surfaces by using disinfectants. The aim is to decontaminate the surfaces coming into direct contact with the carcasses. In the present study, the effectiveness of different disinfectants was investigated in laboratory settings, simulating the conditions in the slaughterhouses and in a chicken slaughterhouse. For this, an artificial residue substance (consisting of yeast extract, albumin, and agar) was developed, tested, and included in the assays. Two disinfectants were tested under laboratory conditions: lactic acid (5 and 6.67%) and peracetic acid (0.33 and 0.5%). At the slaughterhouse, peracetic acid (0.021%) was used. In the laboratory tests, it was found that the peracetic acid solution had the highest disinfection potential with respect to an Escherichia coli strain (reduction >4 log CFU mL−1) at 0.5% without an artificial residue substance. The tested lactic acid solutions also showed the highest disinfection potential against a Pseudomonas aeruginosa strain, without an artificial residue substance. When applying the artificial residue substance, the reduction potential of lactic acid and peracetic acid was decreased to less than 1.4 log CFU mL−1. Application of peracetic acid in the slaughterhouse reduced the number of total aerobic bacteria by more than 4 log CFU mL−1 and the number of Enterobacteriaceae by more than 3 log CFU mL−1, depending on the place of sampling.

HIGHLIGHTS
  • Peracetic acid and lactic acid decreases E. coli and P. aeruginosa numbers in vitro.
  • Sanitation in place reduces the number of bacteria in a chicken slaughterhouse.
  • The number of total aerobic bacteria and Enterobacteriaceae was significantly reduced.

Research – Phage Biocontrol Improves Food Safety by Significantly Reducing the Level and Prevalence of Escherichia coli O157:H7 in Various Foods

Journal of Food Protection

ABSTRACT

Management of Shiga toxin–producing Escherichia coli (STEC), including E. coli O157:H7, in food products is a major challenge for the food industry. Several interventions, such as irradiation, chemical disinfection, and pasteurization, have had variable success controlling STEC contamination. However, these interventions also indiscriminately kill beneficial bacteria in foods, may impact organoleptic properties of foods, and are not always environmentally friendly. Biocontrol using bacteriophage-based products to reduce or eliminate specific foodborne pathogens in food products has been gaining attention due to the specificity, safety, and environmentally friendly properties of lytic bacteriophages. We developed EcoShield PX, a cocktail of lytic bacteriophages, that specifically targets STEC. This study was conducted to examine the efficacy of this bacteriophage cocktail for reducing the levels of E. coli O157:H7 in eight food products: beef chuck roast, ground beef, chicken breast, cooked chicken, salmon, cheese, cantaloupe, and romaine lettuce. The food products were challenged with E. coli O157:H7 at ca. 3.0 log CFU/g and treated with the bacteriophage preparation at ca. 1 × 106, 5 × 106, or 1 × 107 PFU/g. Application of 5 × 106 and 1 × 107 PFU/g resulted in significant reductions (P < 0.05) in E. coli O157:H7 levels of up to 97% in all foods. When bacteriophages (ca. 1 × 106 PFU/g) were used to treat lower levels of E. coli O157:H7 (ca. 1 to 10 CFU/10 g) on beef chuck roast samples, mimicking the levels of STEC found under real-life conditions in food processing plants, the prevalence of STEC in the samples was significantly reduced (P < 0.05) by ≥80%. Our results suggest that this STEC-targeting bacteriophage preparation can result in significant reduction of both the levels and prevalence of STEC in various foods and, therefore, may help improve the safety and reduce the risk of recalls of foods at high risk for STEC contamination.

HIGHLIGHTS
  • Shiga toxin–producing E. coli is a major food safety challenge for the food industry.
  • EcoShield PX bacteriophage cocktail reduced E. coli O157:H7 levels in foods by up to 97%.
  • The bacteriophage cocktail reduced the prevalence of E. coli O157:H7 in foods by ≥80%.

Research – Evaluation of eight essential oils for postharvest control of Aspergillus carbonarius in grapes

Journal of Food Protection

A wide range of fungal species is associated with post-harvest spoilage of grapes. However, Aspergillus carbonarius is the primary fungus responsible for the contamination of grapes with ochratoxin A, a mycotoxin causing several confirmed health effects to humans and animals. Aiming to find a method, safe for the consumers, to prevent post-harvest decay and ochratoxin A contamination of grapes, the potential use of essential oils as preservatives was investigated. Essential oils of Origanum dictamnus (dittany) , Origanum onites (oregano) , Origanum microphyllum (marjoram) , Thymbra capitata (thyme) , Satureja thymbra (savory) , Rosmarinus officinalis (rosemary) , Laurus nobilis (laurel) and Salvia officinalis (sage) were tested. The essential oil components were identified by GC/MS analysis. A first evaluation of the effectiveness of essential oils was performed in vitro , at a range of concentrations up to 300 μL L -1 . Based on the results of the in vitro tests, the four most effective essential oils ( O. dictamnus , O. onites , T. capitata and S. thymbra ) were tested on Sultana grapes, during post-harvest storage. The four essential oils tested, having the carvacrol and/or thymol as a common component, at a high concentration, significantly reduced, or even completely inhibited the growth of the fungus, in all treatments. As revealed from the results, the essential oils of O. dictamnus , O. onites and S. thymbra were the most effective, causing total inhibition on the growth of the fungus with a minimum concentration of 100 μL L -1 , followed by the essential oil of T. capitata , total effective with a minimum concentration of 200 μL L -1 . Essential oils of O. microphyllum , L. nobilis , S. officinalis and R. officinalis , although they had a significant effect on the growth of A. carbonarius , failed to inhibit its growth completely at any of the concentrations tested.

Research – Comparison of stomaching versus rinsing, for recovering bacterial communities from rainbow trout (Oncorhynchus mykiss) fillets.

Journal of Food Protection

The use of high-throughput methods allows a better characterization of food-related bacterial communities. However, such methods require large amounts of high quality bacterial DNA, which may be a challenge when dealing with a complex matrix that has a low concentration of bacteria like fresh fish fillets. Therefore, the choice of method used to recover bacteria from a food matrix in a cost-effective way is critical, yet little information is available on the performance of commonly used methods. We assessed the recovery capacity of two such methods: stomaching and mechanical rinsing. The efficiency of the methods was evaluated through the quantitative recovery and compatibility with end-point qPCR. Fresh rainbow trout ( Oncorhynchus mykiss ) fillets were inoculated with a bacterial marker, Brochothrix thermosphacta , at different concentrations (7.52 to 1.52 log CFU/g). The fillets were processed by one of the two methods and the recovery of the marker in the suspensions was assessed by plate counting and qPCR targeting B. thermosphacta – rpoC . The same analyses were performed on 6 non-inoculated fresh fillets. Stomaching and mechanical rinsing allowed an efficient and repeatable recovery of the bacterial communities from the 42 inoculated fillets. No significant differences of Recovery Ratios were observed between the marker enumerated in the inoculation suspensions and in the corresponding recovery suspensions after rinsing and stomaching. However, the stomaching method allowed too many particles to pass through the filters bag, making necessary a limiting supplementary filtration step. As a consequence, only the rinsing recovery method allowed a proper PCR quantification of the inoculated B. thermosphacta. The mean recovered bacterial level of the fillets was around 3 log CFU/g. It seems more relevant and cost-effective to recover the endogenous bacterial microbiota of a fish fillet structure using the rinsing method rather than the stomaching method.