Category Archives: Antimicrobials

Research – Natural Antimicrobial Agents Utilized in Food Preservation

MDPI

Since the initial transformation of food surpluses, improving food quality and safety are of principal importance to human health. Due to the mass production (eggs, poultry, meat, grains, and pulses) of huge quantities of food, as well as storage and transport, food technologists are faced with challenges of contamination, undesirable microbial growth, the production of toxins, or the deterioration of food (food spoilage). Different food preserving methods (drying, smoking, etc.) have been developed throughout human history to increase the storage time of perishable raw materials or improve diets. For a long time, chemical preservatives used in the prevention of food spoilage or foodborne diseases were considered convenient for consumer protection. Effective in small concentrations and maintaining the sensory properties of food, as well as exhibiting stability at different temperatures or pH values, made their application in the prevention of food spoilage highly applicable. Indeed, they reduce food losses, increase quality, extend shelf life, and enable the development of new formulations as well as food stabilization and standardization [1]. Although consumers still demand safe, fresh-like (minimally processed), nutritionally highly valuable, high-quality foods, attitudes towards chemical conservatives have changed in contemporary nutrition. The continuous intake of chemicals during our (increasingly long-lived) lifetime and the documented adverse activity have changed consumer perceptions and attitudes towards synthetic preservatives in food technology [2]. More natural food production or the application of natural compounds in maintaining food safety have become highly desirable for many consumers in developed countries. Bio-preservatives, naturally occurring compounds from plants, animals, or microorganisms, can be successfully used in extending the shelf life of food, the inhibition/elimination of spoilage and pathogenic microorganisms, and the enhancement of food’s functionality and quality. Natural antimicrobials can be used directly in product formulation, incorporated into packaging material, or surface-coated to prevent spoilage processes or pathogen growth [3].
The most important naturally occurring used compounds in the food industry are essential oils, enzymes, and edible coatings.
Essential oils are highly volatile compounds from herbs and spices such as basil, thyme, oregano, cinnamon, clove, and rosemary, and are used to reduce spoilage microorganisms, increase overall food quality, and to inhibit food-borne pathogens such as SalmonellaListeria monocytogenesEscherichia coliBacillus cereus, and Staphylococcus aureus [4]. Essential oils are effective in inhibiting fungal growth as well as mycotoxin synthesis, reducing fungal damage and health risks [5,6]. Although essential oils are mainly used in the food industry as flavorings, by increasing knowledge of their modes of action and interactions with food matrix components, they can be successfully used in reducing targeted microbes.
Enzymes from animal sources such as lyzozime, lactoferrin, and bacteriocins (natamycin, nisin, pediocin, and reuterin) from bacteria are used in small concentrations in a similar way to prolong shelf life and inhibit pathogen proliferation [7].
Edible coatings, thin layers of naturally occurring polymers, with or without the addition of essential oils or enzymes, used for food coating reduce moisture loss, reduce microbial contamination, and minimize the impact of packaging materials on the environment [8].
Many natural compounds are promising for replacing synthetic food additives while improving overall quality and safety. Through cooperation, food scientists and food technologists can help meet consumer needs for safe and nutritionally valuable food without the adverse effect of synthetic preservatives.
This Special Issue aims to publish quality articles on natural antimicrobials in food preservation, their activity towards pathogens and contaminants, and novel formulations or applications in the production of safe and healthy foods.

Author Contributions

Conceptualization, S.K.-T. and H.P.; writing—original draft preparation, H.P.; writing—review and editing, S.K.-T.; supervision, S.K.-T. All authors have read and agreed to the published version of the manuscript.

Research – Antibacterial Effect of Pomegranate Juice on Listeria innocua and E. coli in Different Media

MDPI

Abstract

The antibacterial effect of pomegranate juice (PJ) at six concentrations (0, 10, 20, 30, 40, and 50%) against Listeria innocua and Escherichia coli was investigated in distilled water (DW) and bacterial culture broth. L. innocua and E. coli at approximately 105 cfu mL−1 were inoculated in PJ samples and incubated at 4, 25, and 37 °C for 0, 6, 24, and 48 h. The bacterial population and pH of culture media were measured at each removal. Results indicated that the antibacterial effect of PJ was dependent upon bacteria species, juice concentration, incubation temperature, and growth medium. Higher juice concentration and incubation temperature resulted in increased antibacterial effects. Bacterial populations were decreased more significantly in DW systems than in the culture broth, while L. innocua was more sensitive to PJ than E. coli in the DW systems. Regardless of PJ concentrations in DW systems, L. innocua, initially inoculated at approximately 105 cfu mL−1, was reduced to undetectable levels at 25 and 37 °C within 24 h. The growth of L. innocua and E. coli was significantly inhibited in bacterial culture broth containing ≥ 20% PJ (p < 0.001). This study provides insight into the potential application of PJ in food and beverage products for food protection.

Research -Holistic Strategies to Control Salmonella Infantis: An Emerging Challenge in the European Broiler Sector

MDPI

Abstract

Salmonella spp. has been globally recognized as one of the leading causes of acute human bacterial gastroenteritis resulting from the consumption of animal-derived products. Salmonella Enteritidis, S. Typhimurium, and its monophasic variant are the main serovars responsible for human disease. However, a serovar known as S. Infantis has emerged as the fourth most prevalent serovar associated with human disease. A total of 95% of isolated S. Infantis serovars originate from broilers and their derived products. This serovar is strongly associated with an elevated antimicrobial (AMR) and multidrug resistance, a resistance to disinfectants, an increased tolerance to environmental mercury, a heightened virulence, and an enhanced ability to form biofilms and attach to host cells. Furthermore, this serovar harbors genes that confer resistance to colistin, a last-resort antibiotic in human medicine, and it has the potential to acquire additional transferable AMR against other critically important antimicrobials, posing a new and significant challenge to global public health. This review provides an overview of the current status of the S. Infantis serovar in the poultry sector, focusing on its key virulence factors, including its virulence genes, antimicrobial resistance, and biofilm formation. Additionally, novel holistic strategies for controlling S. Infantis along the entire food chain are presented in this review.

Research – Use of Essential Oil Emulsions to Control Escherichia coli O157:H7 in the Postharvest Washing of Lettuce

MDPI

Abstract

Essential oils (EOs) have strong antibacterial properties and can be potential sanitizers to reduce pathogen load and prevent cross-contamination during postharvest washing. The objective of this study was to investigate the efficacy of emulsions containing oregano (OR; Origanum vulgare) and winter savory (WS; Satureja montana) EOs at different concentrations (0.94 and 1.88 µL/mL) and storage times (0 h, 24 h, and 7 days), in reducing Escherichia coli O157:H7 on the surface of three types of lettuce (romaine, crisphead, and butterhead). The EO emulsions were compared with one no-rinse treatment and three rinse treatments using water, 200 ppm chlorine, and 80 ppm peroxyacetic acid (PAA), respectively, in a simulated washing system. The results showed that while the EO emulsions significantly reduced E. coli O157:H7 on crisphead lettuce over time, not all treatments were effective for romaine and butterhead lettuce. The mixture of OR and WS at concentrations of 0.94 and 1.88 µL/mL was found to be the most effective in reducing E. coli O157:H7 on inoculated lettuce, resulting in reductions of 3.52 and 3.41 log CFU/g, respectively. Furthermore, the PAA and the mixture of OR and WS at 1.88 µL/mL effectively limited bacterial cross-contamination close to the detection limit for all lettuce types during all storage times. These results suggest that OR and WS EOs could serve as potential alternatives to chemical sanitizers for postharvest lettuce washing.

Research – Staphylococcus aureus in the Processing Environment of Cured Meat Products

MDPI

Abstract

The presence of Staphylococcus aureus in six dry-cured meat-processing facilities was investigated. S. aureus was detected in 3.8% of surfaces from five facilities. The occurrence was clearly higher during processing (4.8%) than after cleaning and disinfection (1.4%). Thirty-eight isolates were typified by PFGE and MLST. Eleven sequence types (STs) were defined by MLST. ST30 (32%) and ST12 (24%) were the most abundant. Enterotoxin genes were detected in 53% of isolates. The enterotoxin A gene (sea) was present in all ST30 isolates, seb in one ST1 isolate, and sec in two ST45 isolates. Sixteen isolates harbored the enterotoxin gene cluster (egc) with four variations in the sequence. The toxic shock syndrome toxin gene (tst) was detected in 82% of isolates. Regarding antimicrobial resistance, twelve strains were susceptible to all the antibiotics tested (31.6%). However, 15.8% were resistant to three or more antimicrobials and, therefore, multidrug-resistant. Our results showed that in general, efficient cleaning and disinfection procedures were applied. Nonetheless, the presence of S. aureus with virulence determinants and resistance to antimicrobials, particularly multidrug-resistant MRSA ST398 strains, might represent a potential health hazard for consumers.

Research – Evaluation of antimicrobial activity and mechanism of Mentha longifolia L. essential oil

Wiley Online

As the interest in “natural” and “safe” products grows, the use of natural products instead of synthetic preservatives to combat food spoilage and poisoning caused by microorganisms during processing and storage has become a prioritized option. The present research evaluated the antibacterial activity of the Mentha longifolia L. essential oil (MLEO) against several pathogenic bacteria, and the mechanism of action against methicillin-resistant Staphylococcus aureus (MRSA). Gas Chromatography Quadrupole Time-of-Flight Mass Spectrometry (GC-Q-TOF MS) analysis suggested that main components of MLEO were carvone (47.39%) and limonene (12.48%). The oil showed considerable antibacterial activity with MIC values of 0.394–1.576 mg/mL, and could be a promising bactericide. Non-targeted metabolomics analysis based on GC-Q-TOF MS identified 66 different metabolites, and Kyoto Encyclopedia of Genes and Genomes enrichment analysis of these metabolites revealed that MLEO achieves the effects by affecting amino acid metabolism in MRSA.

Research – Scientists Discover How Foodborne Vibrio Infects People, Could Lead to New Treatments

Food Safety.Com

Food Illness

Researchers at the University of Texas (UT) Southwestern Medical Center have discovered how foodborne pathogen Vibrio parahaemolyticus infects people after eating raw or undercooked shellfish. The findings could lead to new ways to treat illness caused by the enteric bacteria.

The study provides the first visual evidence of how a gut bacterial pathogen uses an “assembly method” to build syringe-like structures to inject toxins into intestinal cells, giving a new view of how enteric bacteria, when exposed to bile acids, efficiently respond and build a virulence system.

Research – Forgotten but not gone: Yersinia infections in England, 1975 to 2020

Eurosurveillance

Yersiniosis, most often caused by  is one of the most common bacterial food-borne zoonoses in Europe with reported overall incidence of 1.8 cases per 100,000 population in 2020 [1]. There is, however, marked variation among countries, with the highest numbers of cases per 100,000 population reported in Denmark and Finland (7.1 and 7.0, respectively) and the lowest in Romania and Bulgaria (0.03 and 0.06, respectively) [1]. Transmission is primarily faecal–oral via food or water contaminated with animal faeces [2]. Yersiniosis has been associated with the consumption of pork meat (raw or undercooked), occupational exposure to pigs, untreated drinking water, milk, vegetables, juices, ready-to-eat and other foods [36]. The incidence of yersiniosis in Europe is higher in males and in children under 5 years, and no clear seasonal pattern has been reported over the last decade [1,3]. Yersiniosis commonly presents as diarrhoea, abdominal pain and fever, and can manifest as acute mesenteric lymphadenitis and terminal ileitis. Although it is usually self-limiting with a low case fatality rate (0.05%), symptoms often persist for several weeks [3,6].

The reported incidence of  infections in the United Kingdom (UK) is well below the European average (0.2 cases per 100,000 in 2019) [3]. Routine testing for  is not currently recommended in the UK, unless there is a clinical suspicion (e.g. appendicitis, mesenteric lymphadenitis, terminal ileitis or reactive arthritis) [7]. The aim of this study was to describe the changing incidence and epidemiology of diagnosed  infections in England between 1975 and 2020 and to estimate the potential under-ascertainment of  due to the lack of routine testing.

Research -Antimicrobial-Resistant Listeria monocytogenes in Ready-to-Eat Foods: Implications for Food Safety and Risk Assessment

MDPI

Abstract

Antimicrobial resistance is an existential threat to the health sector, with far-reaching consequences in managing microbial infections. In this study, one hundred and ninety-four Listeria monocytogenes isolates were profiled for susceptibility using disc diffusion techniques. Possible foodborne listeriosis risk associated with ready-to-eat (RTE) foods (RTEF) and the risk of empirical treatment (EMPT) of L. monocytogenes infections, using multiple antimicrobial resistance indices (MARI) and antimicrobial resistance indices (ARI), respectively, were investigated. Twelve European Committee on Antimicrobial Susceptibility Testing (EUCAST) prescribed/recommended antimicrobials (EPAS) for the treatment of listeriosis and ten non-prescribed antimicrobials (non-PAS)] were evaluated. Antimicrobial resistance > 50% against PAs including sulfamethoxazole (61.86%), trimethoprim (56.19%), amoxicillin (42.27%), penicillin (41.24%), and erythromycin (40.21%) was observed. Resistance > 50% against non-PAS, including oxytetracycline (60.89%), cefotetan (59.28%), ceftriaxone (53.09%), and streptomycin (40.21%) was also observed. About 55.67% and 65.46% of the isolates had MARI scores ranging from 0.25–0.92 and 0.30–0.70 for EPAs and non-PAs, respectively. There was a significant difference (p < 0.01) between the MARI scores of the isolates for EPAs and non-PAs (means of 0.27 ± 0.21 and 0.31 ± 0.14, respectively). MARI/ARI scores above the Krumperman permissible threshold (>0.2) suggested a high risk/level of antimicrobial-resistant L. monocytogenes. The MARI risks of the non-success of empirical treatment (EMPT) attributed to EPAs and non-PAs were generally high (55.67% and 65.463%, respectively) due to the antimicrobial resistance of the isolates. MARI-based estimated success and non-success of EMPT if EUCAST-prescribed antimicrobials were administered for the treatment of listeriosis were 44.329% and 55.67%, respectively. The EMPT if non-prescribed antimicrobials were administered for the treatment of listeriosis was 34.53% and 65.46%, respectively. This indicates a potentially high risk with PAs and non-PAs for the treatment of L. monocytogenes infection. Furthermore, ARI scores ≤ 0.2 for EPAs were observed in polony, potato chips, muffins, and assorted sandwiches, whereas ARI scores for non-PAs were >0.2 across all the RTE food types. The ARI-based estimate identified potential risks associated with some RTE foods, including fried fish, red Vienna sausage, Russian sausage, fruit salad, bread, meat pies, fried chicken, cupcakes, and vetkoek. This investigation identified a high risk of EMPT due to the presence of antimicrobial-resistant L. monocytogenes in RTE foods, which could result in severe health consequences.

Research – Mānuka Oil vs. Rosemary Oil: Antimicrobial Efficacies in Wagyu and Commercial Beef against Selected Pathogenic Microbes

MDPI

Abstract

Essential oils possessing antimicrobial characteristics have acquired considerable interest as an alternative to chemical preservatives in food products. This research hypothesizes that mānuka (MO) and kānuka (KO) oils may possess antimicrobial characteristics and have the potential to be used as natural preservatives for food applications. Initial experimentation was conducted to characterize MOs (with 5, 25, and 40% triketone contents), rosemary oil (RO) along with kanuka oil (KO) for their antibacterial efficacy against selected Gram-negative (Salmonella spp. and Escherichia coli), and Gram-positive (Listeria monocytogenes and Staphylococcus aureus) bacteria through disc diffusion and broth dilution assays. All MOs showed a higher antimicrobial effect against L. monocytogenes and S. aureus with a minimum inhibitory concentration below 0.04%, compared with KO (0.63%) and RO (2.5%). In chemical composition, α-pinene in KO, 1, 8 cineole in RO, calamenene, and leptospermone in MO were the major compounds, confirmed through Gas-chromatography-mass spectrometry analysis. Further, the antimicrobial effect of MO and RO in vacuum-packed beef pastes prepared from New Zealand commercial breed (3% fat) and wagyu (12% fat) beef tenderloins during 16 days of refrigerated storage was compared with sodium nitrate (SN) and control (without added oil). In both meat types, compared with the SN-treated and control samples, lower growth of L. monocytogenes and S. aureus in MO- and RO- treated samples was observed. However, for Salmonella and E. coli, RO treatment inhibited microbial growth most effectively. The results suggest the potential use of MO as a partial replacement for synthetic preservatives like sodium nitrate in meats, especially against L. monocytogenes and S. aureus.