Phages as biocontrol agents in dairy products

Colorimetric detection of Staphylococcus aureus with enhanced sensitivity based on phage covalently immobilized Co3O4 nanozyme through synergistic inhibition effect

Staphylococcus aureus (S. aureus) is a common foodborne pathogen, posing a serious threat to public health. Consequently, it is crucial to establish a platform for sensitive and specific determination of S. aureus in food. Herein, phage SapYZUH5, isolated by our lab, was covalently immobilized on Co3O4 to synthesize SapYZUH5@Co3O4. Notably, SapYZUH5@Co3O4 exhibited remarkable oxidase-like activity, enabling the catalysis of dissolved oxygen to generate superoxide anion free radicals and accelerate the TMB chromogenic reaction. Upon introduction of S. aureus, specific capture by SapYZUH5@Co3O4 resulted in inhibiting its oxidase-like activity and decelerating the 3,3',5,5'-tetramethylbenzidine (TMB) chromogenic reaction. Moreover, S. aureus can be lysed to release the reductive bacterial contents, which can further inhibit the TMB chromogenic reaction. Based on this principle, SapYZUH5@Co3O4 + TMB reaction system was employed for detection with enhanced sensitivity of S. aureus, yielding an equation: A =  - 0.092 Log (CSA) + 0.79 (R2 = 0.987), with an ultralow limit of detection (LOD) of 28 CFU mL-1. This system exhibited remarkable specificity and anti-interfere towards S. aureus, owing to the excellent affinity of SapYZUH5 towards S. aureus. In addition, S. aureus in the actual food samples was detected using this system, yielding recoveries ranging from 96.34 to 109.43%, demonstrating its exceptional accuracy. Hence, our proposed covalent immobilization of phage on the nanozyme can realize sensitive and specific colorimetric determination of S. aureus in food samples.

Prevalence and Phage-Based Biocontrol of Methicillin-Resistant Staphylococcus aureus Isolated from Raw Milk of Cows with Subclinical Mastitis in Vietnam

S. aureus, particularly methicillin-resistant S. aureus, has been recognized as a main cause of bovine mastitis and food poisoning. This study investigated the prevalence, antibiotic resistance, and phage-based biocontrol of S. aureus and methicillin-resistant S. aureus isolated from raw milk of cows with subclinical mastitis. The results showed that the prevalence of S. aureus and methicillin-resistant S. aureus was 12% (48/400) and 1.5% (6/400), respectively. The S. aureus isolates were highly resistant to penicillin (72.92%), erythromycin (43.75%), and tetracycline (39.58%). Out of 48 S. aureus isolates, 6 were identified as methicillin-resistant strains. Among them, one isolate was found to harbor the sea gene. A total of 5 phages were recovered from 50 pork and 50 chicken meat samples, 1 from pork and 4 from chicken meat samples. Phage PSA2 capable of lysing all 6 methicillin-resistant isolates was selected for characterization. The use of phage PSA2 completely inactivated methicillin-resistant S. aureus SA33 in raw milk at both 24 °C and 4 °C, indicating its potential as a promising antibacterial agent in controlling methicillin-resistant S. aureus in raw milk and treating bovine mastitis.

Isolation and characterization of two Staphylococcus aureus lytic bacteriophages "Huma" and "Simurgh"

Nowadays finding the new antimicrobials is necessary due to the emerging of multidrug resistant strains. The present study aimed to isolate and characterize bacteriophages against S. aureus. Strains Huma and Simurgh were the two podovirus morphology phages which isolated and then characterized. Huma and Simurgh had a genome size of 16,853 and 17,245 bp, respectively and both were Rosenblumvirus with G + C content of 29%. No lysogeny-related genes, nor virulence genes were identified in their genomes. They were lytic only against two out of four S. aureus strains. They also were able to inhibit S. aureus for 8 h in-vitro. Both showed a rapid adsorption. Huma and Simurgh had the latent period of 80 and 60 m and the burst sizes of 45 and 40 PFU/ml and also, they showed very low cell toxicity of 1.23%-1.79% on HT-29 cells, respectively. Thus, they can be considered potential candidates for biocontrol applications.

Antibiotic Resistance Profile and Bio-Control of Multidrug-Resistant Escherichia coli Isolated from Raw Milk in Vietnam Using Bacteriophages

E. coli is an important zoonotic pathogen capable of causing foodborne illness and bovine mastitis. Bacteriophages have been increasingly considered a promising tool to control unwanted bacteria. The aim of this study is to determine the antibiotic resistance profile of E. coli isolated from raw milk and the efficacy of phage in controlling multidrug-resistant E. coli in raw milk. Antibiotic susceptibility testing showed the highest resistance rates of E. coli isolates to co-trime (27.34%) and ampicillin (27.34%), followed by streptomycin (25.18%), tetracycline (23.02%), and the lowest resistance rates to ciprofloxacin, gentamycin, and ceftazidime, all at a rate of 2.16%. All isolates were susceptible to meropenem. Of the 139 E. coli isolates, 57 (41.01%) were resistant to at least one antibiotic, and 35 (25.18%) were classified as MDR strains. Molecular characterization indicated that 5 (3.6%) out of the 139 isolates were STEC strains carrying stx1 gene. Seven (5.04%) isolates were phenotypically identified as ESBLEC, and four isolates (2.88%) were resistant to colistin. The results of the genotypic test revealed that four out of seven ESBLEC strains carried both blaTEM and blaCTX-M-1, two harbored blaTEM, and one possessed blaCTX-M-1, while mcr-1 was detected in all four colistin-resistant E. coli isolates. In particular, one isolated E. coli strain (EM148) was determined to be a multidrug-resistant strain simultaneously carrying blaTEM, blaCTX-M-1, and mcr-1. A total of eight phages were successfully recovered from raw milk. The application of phage PEM3 significantly reduced viable counts of multidrug-resistant host EM148 in raw milk by at least 2.31 log CFU/mL at both 24 °C and 4 °C.

Evaluating the efficacy of a phage cocktail against Pseudomonas fluorescens group strains in raw milk: microbiological, physical, and chemical analyses

The objective of this study was to investigate the effectiveness of a phage cocktail against Pseudomonas fluorescens group and its effect on the microbial, physical and chemical properties of raw milk during different storage conditions. A phage cocktail consisting of Pseudomonas fluorescens, Pseudomonas tolaasii, and Pseudomonas libanensis phages was prepared. As a result, reductions in fluorescent Pseudomonas counts of up to 3.44 log units for the storage at 4 °C and 2.38 log units for the storage at 25 °C were achieved. Following the phage application, it is found that there was no significant difference in the total mesophilic aerobic bacteria and Enterobacteriaceae counts. However, it was observed that the number of lactic acid bacteria was higher in phage-treated groups. The results also showed that pH values in the phage added groups were lower than the others and the highest titratable acidity was obtained only in the bacteria-inoculated group. As a future perspective, this study suggests that, while keeping the number of target microorganisms under control in the milk with the use of phages during storage, the microbiota and accordingly the quality parameters of the milk can be affected. This work contributes to the development of effective strategies for maintaining the quality and extending the shelf life of milk and dairy products.

Isolation, characterization, and application of lytic bacteriophages for controlling Enterobacter cloacae complex (ECC) in pasteurized milk and yogurt

Reducing bacterial pathogen contamination not only improves overall global public health but also diminishes food waste and loss. The use of lytic bacteriophages (phages) that infect and kill bacteria could be a beneficial tool for suppressing bacterial growth during dairy products storage time. Four Enterobacter cloacae (E. cloacae) complex isolates which were previously isolated from contaminated dairy products were used to identify lytic phages in wastewater. Phages specific to multi-drug resistant (MDR) E. cloacae complex 6AS1 were isolated from local sewage. Two novel phages vB_EclM-EP1 and vB_EclM-EP2 were identified as myoviral particles and have double-stranded DNA genome. Their host range and lytic capabilities were detected using spot test and efficiency of plating (EOP) against several bacterial isolates. The phages had a latent period of 30 min, and a large burst size of about 100 and 142 PFU/cell for vB_EclM-EP1 and vB_EclM-EP2, respectively. Both phages were viable at pH ranging 5-9 and stable at 70 °C for 60 min. The individual phages and their cocktail preparations (vB_EclM-EP1 and vB_EclM-EP2) reduced and inhibited the growth of E. cloacae complex 6AS1 during challenge test in milk and yogurt samples. These results indicate that the E. cloacae complex-specific phages (vB_EclM-EP1 and vB_EclM-EP2) have a potential application as microbicidal agents in packaged milk and milk derivatives during storage time. In addition, our environment is a rich sources of lytic phages which have potential use in eliminating multidrug-resistant isolates in food industry as well as in biocontrol.

Isolation and characterization of novel bacteriophage vB_KpP_HS106 for Klebsiella pneumonia K2 and applications in foods

The detection rate of Klebsiella pneumoniae in food is increasing, and it has emerged as a food pathogen. Global health is threatened due to the emergence of multidrug-resistant (MDR) and hypervirulent (hv) K. pneumoniae. Phages have a promising application as antibacterial agents and have the ability to lyse MDR strains. Hence, phage vB_KpP_HS106 against MDR-hv K. pneumoniae strains was isolated from sewage collected from a hospital. It can maintain stable activity at a pH range of 4-12 and a temperature range of 4°C to 50°C. The maximum adsorption rate of phage HS106 was found to be approximately 84.2% at 6 min. One-step growth curve analysis showed that the latent period of HS106 was 10 min and the burst size was approximately 183 PFU/cell. Furthermore, whole genome analysis indicated that the genome of phage HS106 was a double-stranded linear 76,430-bp long DNA molecule with 44% GC content. A total of 95 open reading frames were annotated in the HS106 genome, which did not contain any virulence genes or antibiotic resistance genes. Phage HS106 reduced MDR K. pneumoniae in milk by approximately 1.6 log10 CFU/mL at 25°C and in chicken by approximately 2 log10 CFU/cm3 at 25°C. Therefore, vB_KpP_HS106 is a promising alternative to antibiotics for biocontrol against multidrug-resistant K. pneumoniae in foods.

Application of BI-EHEC and BI-EPEC bacteriophages to control enterohemorrhagic and enteropathogenic escherichia coli on various food surfaces

OBJECTIVES

The purposes of this study were to determine the Efficiency of Plating (EOP) value of Bacteriophage BI-EHEC and BI-EPEC and to evaluate the application of these bacteriophages in reducing population of EHEC and EPEC on various food samples.

RESULTS

In this study, we used bacteriophage BI-EHEC and BI-EPEC, which were isolated from previous study. Both phages were tested with other multiple pathotypes of intestinal pathogenic E. coli to determine the efficiency of plating. BI-EHEC had high efficiency toward ETEC with an EOP value of 2.95 but low efficiency toward EHEC with an EOP value of 0.10, while BI-EPEC had high efficiency toward EHEC and ETEC with EOP values of 1.10 and 1.21, respectively. As biocontrol agents, both bacteriophages able to reduce CFU of EHEC and EPEC in several food samples using 1 and 6-days incubation times at 4 [Formula: see text]. BI-EHEC reduced the number of EHEC with an overall percentage of bacterial reduction value above 0.13 log₁₀, while BI-EPEC reduced number of EPEC with reduction value above 0.33 log₁₀.

Full-scale industrial phage trial targeting Salmonella on pork carcasses

Phages have been suggested as promising biocontrol agents in food, but trials demonstrating the efficiency of phage treatment under industrial settings are missing. Here we performed a full-scale industrial trial to evaluate the efficacy of a commercial phage product to reduce the prevalence of naturally occurring Salmonella on pork carcasses. A total of 134 carcasses from potentially Salmonella positive finisher herds were chosen to be tested at the slaughterhouse based on the level of antibodies in the blood. During five consecutive runs, carcasses were directed into a cabin spraying phages, resulting in a dosage of approximately 2 × 107 phages per cm2 carcass surface. To evaluate the presence of Salmonella, a predefined area of one half of the carcass was swabbed before phage application and the other half 15 min after. A total of 268 samples were analysed by Real-Time PCR. Under these optimized test conditions, 14 carcasses were found positive before phage application, while only 3 carcasses were positive after. This work shows that phage application allows to achieve approximatively 79% reduction of Salmonella-positive carcasses and demonstrates that implementation of phage application in industrial settings can be used as an additional strategy to control foodborne pathogens.

Characterization of KMSP1, a newly isolated virulent bacteriophage infecting Staphylococcus aureus, and its application to dairy products

Staphylococcus aureus is one of the major pathogens causing foodborne outbreaks and severe infections worldwide. Generally, various physical and chemical treatments have been applied to control S. aureus in the food industry. However, conventional treatments usually affected food quality and often produced toxic compounds. Therefore, bacteriophage (phage), a natural antimicrobial agent, has been suggested as an alternative strategy to control foodborne pathogens including S. aureus. In this study, KMSP1, a bacteriophage infecting S. aureus was isolated from a raw milk sample and characterized. Transmission electron microscopy (TEM) analysis revealed that phage KMSP1 belongs to the Myoviridae family. Phage KMSP1 efficiently inhibited bacterial growth for >28 h post-infection. In addition, phage KMSP1 could infect a broad spectrum of S. aureus strains, including methicillin-resistant S. aureus (MRSA) strains. Whole-genome sequence analysis showed that KMSP1 is a lytic phage with the absence of genes related to lysogen formation, toxin production, and antibiotics resistance, respectively. In the genome of KMSP1, the presence of putative tail lysin containing a cysteine/histidine-dependent amidohydrolase/peptidase (CHAP) domain could be one of the reasons for the effective antimicrobial activity of KMSP1. Furthermore, high stability of phage KMSP1 at temperature ranging from 4 to 55 °C and pH ranging from 5 to 11, suggested its potential use in various food systems. Receptor analysis revealed that KMSP1 utilized cell wall teichoic acid (WTA), one of the major virulence factors of S. aureus, as a host receptor. Application of phage KMSP1 at an MOI of 104 achieved a significant reduction of log 8.8 CFU/mL of viable cell number in pasteurized milk and log 4.3 CFU/cm2 in sliced cheddar cheese after 24 h. Taken together, the strong antimicrobial activity of phage KMSP1 suggested that it could be developed as a biocontrol agent in dairy products to control S. aureus contamination.

CRISPR-Cas engineering in food science and sustainable agriculture: recent advancements and applications

The developments in the food supply chain to support the growing population of the world is one of today's most pressing issues, and to achieve this goal improvements should be performed in both crops and microbes. For this purpose, novel approaches such as genome editing (GE) methods have upgraded the biological sciences for genome manipulation and, among such methods, clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated proteins (Cas) are the main exciting innovations since the Green Revolution. CRISPR/Cas systems can be a potent tool for the food industry, improvement of agricultural crops and even for protecting food-grade bacteria from foreign genetic invasive elements. This review introduces the history and mechanism of the CRISPR-Cas system as a genome editing tool and its applications in the vaccination of starter cultures, production of antimicrobials and bioactive compounds, and genome editing of microorganisms.

High Level of Interaction between Phages and Bacteria in an Artisanal Raw Milk Cheese Microbial Community

Microbial starter cultures are used in the production of many cheeses around the world, such as Parmigiano-Reggiano, in Italy, Époisses, in France, and Canastra, in Brazil, providing many of the unique features of these cheeses. Bacteriophages (phages) are ubiquitous and well known to modulate the structure of bacterial communities, and recent data indicate that cheeses contain a high abundance of naturally occurring phages. Here, we analyze the viral and bacterial metagenomes of Canastra cheese: a traditional artisanal Brazilian cheese produced using an endogenous starter culture and raw milk. Over 1,200 viral operational taxonomic units were recovered using both isolated viral-like particles and complete metagenomic DNA. Common viral families identified included Siphoviridae and Myoviridae, with 40% of putative phage genomes unidentified at the family level of classification. We observed very high phage diversity, which varied greatly across different cheese producers, with 28% of phage genomes detected in only one producer. Several metagenome-assembled genomes were recovered for lactic acid-producing bacteria, as well as nonstarter bacterial species, and we identified several phage-bacterium interactions, at the strain level of resolution, varying across distinct cheese producers. We postulate that at least one bacterial strain detected could be endogenous and unique to the Canastra cheese-producing region in Brazil and that its growth seems to be modulated by autochthonous phages present in this artisanal production system. This phage-host relationship is likely to influence the fermentation dynamics and ultimately the sensorial profile of these cheeses, with implications for other similar cheese production systems around the world. IMPORTANCE Our work demonstrated a dynamic yet stable microbial ecosystem during cheese production using an endogenous starter culture. This was observed across several distinct producers and was marked by genomic evidence of continued phage-bacterium interactions, such as the presence of bacterial defense mechanisms. Furthermore, we provide evidence of unique microbial signatures for each individual cheese producer studied in the region, a fact that may have profound consequences on product traceability. This was the first effort to describe and understand the bacteriophage composition and ecological dynamics within the Brazilian Canastra cheese production system. The study of this prototypical backslopping production system provides a solid background for further mechanistic studies of the production of many cheeses around the world.

Isolation and characterization of new bacteriophages active against Clostridium tyrobutyricum and their role in preventing the late blowing defect of cheese

Lytic bacteriophages (phages) offer a great potential as biocontrol agents for spoilage Clostridium tyrobutyricum, responsible for butyric acid fermentation in semi-hard and hard ripened cheeses, resulting in late gas blowing defect. With this aim, we have isolated, identified and characterized new lytic phages of C. tyrobutyricum, and have evaluated their efficacy to control cheese late blowing by adding them to manufacture milk. Silage, soil, milk and cheese from dairy farms were screened for anti-clostridial phages, obtaining 96 isolates active against C. tyrobutyricum. According to host range, source and plaque morphology, we obtained 20 phage profiles, 8 of them (represented by phages FA3, FA21, FA29, FA52, FA58, FA67, FA70 and FA88) showing a wider host range and high quality lysis, which were further characterized. Selected isolates showed a non-contractile tail, belonging to the Siphoviridae family, and were grouped into 3 restriction profiles. Viable phages were detected after storage in sodium-magnesium buffer (SM buffer), skim milk and acidified skim milk (pH 5) for 7 d at 4 °C, 12 °C and 37 °C, although a decline in infectivity was observed in some cases. Good phage survival was also detected during semi-hard cheese manufacture and ripening (60 d), and cheese lactococci counts, pH, dry matter values, and volatile compounds were not affected by phage addition. In semi-hard cheese, phage FA67 impaired the early germination of C. tyrobutyricum spores and caused a significant decrease in clostridial vegetative cells counts at 14 d of ripening, delaying by 2 weeks the consumption of lactic acid, formation of butyric acid and appearance of late blowing symptoms, compared to the spoilt control cheese without the phage. This is the first report on the application of phage to control C. tyrobutyricum in cheese.

Genomic Characterisation of UFJF_PfDIW6: A Novel Lytic Pseudomonas fluorescens-Phage with Potential for Biocontrol in the Dairy Industry

In this study, we have presented the genomic characterisation of UFJF_PfDIW6, a novel lytic Pseudomonas fluorescens-phage with potential for biocontrol in the dairy industry. This phage showed a short linear double-stranded DNA genome (~42 kb) with a GC content of 58.3% and more than 50% of the genes encoding proteins with unknown functions. Nevertheless, UFJF_PfDIW6’s genome was organised into five functional modules: DNA packaging, structural proteins, DNA metabolism, lysogenic, and host lysis. Comparative genome analysis revealed that the UFJF_PfDIW6’s genome is distinct from other viral genomes available at NCBI databases, displaying maximum coverages of 5% among all alignments. Curiously, this phage showed higher sequence coverages (38–49%) when aligned with uncharacterised prophages integrated into Pseudomonas genomes. Phages compared in this study share conserved locally collinear blocks comprising genes of the modules’ DNA packing and structural proteins but were primarily differentiated by the composition of the DNA metabolism and lysogeny modules. Strategies for taxonomy assignment showed that UFJF_PfDIW6 was clustered into an unclassified genus in the Podoviridae clade. Therefore, our findings indicate that this phage could represent a novel genus belonging to the Podoviridae family.

Lytic bacteriophages UFJF_PfDIW6 and UFJF_PfSW6 prevent Pseudomonas fluorescens growth in vitro and the proteolytic-caused spoilage of raw milk during chilled storage

In this study, P. fluorescens-infecting phages were isolated, characterized, and evaluated to their potential to control the bacterial counts and, consequently, the proteolytic spoilage of raw milk during cold storage. The UFJF_PfDIW6 and UFJF_PfSW6 phages showed titers of 9.7 and 7.6 log PFU/ml; latent period of 115 and 25 min, and burst size of 145 and 25 PFU/infected cell, respectively. They also were highly specific to the host bacterium, morphologically classified as the Podoviridae family, stable at pH 5 to 11 and were not inactivated at 63 °C or 72 °C for 30 min. These phages found to be effective against P. fluorescens, reducing bacterial count throughout the entire exponential growth phase in broth formulated with milk at both 4 °C and 10 °C. This effect on bacteria growth led to inhibition by at least 2 days in proteases production, delaying the degradation of milk proteins. When applied together in raw milk stored at 4 °C, they reduced the total bacteria, psychrotrophic, and Pseudomonas by 3 log CFU/ml. This study's findings indicate that these phages have a great potential to prevent the growth of Pseudomonas and, consequently, to retard proteolytic spoilage of raw milk during chilled storage.

Genome Mining of Three Plant Growth-Promoting Bacillus Species from Maize Rhizosphere

Bacillus species genomes are rich in plant growth-promoting genetic elements. Bacillus subtilis and Bacillus velezensis are important plant growth promoters; hence, to further improve their abilities, the genetic elements responsible for these traits were characterized and reported. Genetic elements reported include those of auxin, nitrogen fixation, siderophore production, iron acquisition, volatile organic compounds, and antibiotics. Furthermore, the presence of phages and antibiotic-resistant genes in the genomes are reported. Pan-genome analysis was conducted using ten Bacillus species. From the analysis, pan-genome of Bacillus subtilis and Bacillus velezensis are still open. Ultimately, this study brings an insight into the genetic components of the plant growth-promoting abilities of these strains and shows their potential biotechnological applications in agriculture and other relevant sectors.

Investigating dairy microbiome: an opportunity to ensure quality, safety and typicity

A detailed understanding of the microbiome of cheese and dairy products is key to the optimization of flavour, appearance, overall quality and safety. Microorganisms (including bacteria, yeasts, moulds and viruses, especially bacteriophages) from the environment can enter the dairy supply chain at multiple stages with several implications. The ability to track these microorganisms and to understand their function and interaction can be greatly enhanced by the use of high-throughput sequencing. Depending on the specific production technology, dairy products can harbor several strains and antibiotic-resistance genes that can potentially interact with the gut microbiome, once the product is ingested. Milk-associated or cheese-associated microbial communities with their interaction, function and diversity are a key factor for the dairy industry. Multi-omics approaches have been seldom utilized in literature and they need to be further considered. Studying the role, origin, diversity and function of the microbial species involved in the complex system of dairy production can help improve processes in several fields of application. Integrating an extensive sampling procedure with an extensive culture based methodology is necessary. To this end, local producers, and in general stakeholders, should be guided to discover and maintain their microbial diversity. A better management of microbial resources through precision fermentation processes will in turn reduce overall food losses and increase the possibility to use the microbiome in order to increase the local producers' income.

How to Train Your Phage: The Recent Efforts in Phage Training

Control of pathogenic bacteria by deliberate application of predatory phages has potential as a powerful therapy against antibiotic-resistant bacteria. The key advantages of phage biocontrol over antibacterial chemotherapy are: (1) an ability to self-propagate inside host bacteria, (2) targeted predation of specific species or strains of bacteria, (3) adaptive molecular machinery to overcome resistance in target bacteria. However, realizing the potential of phage biocontrol is dependent on harnessing or adapting these responses, as many phage species switch between lytic infection cycles (resulting in lysis) and lysogenic infection cycles (resulting in genomic integration) that increase the likelihood of survival of the phage in response to external stress or host depletion. Similarly, host range will need to be optimized to make phage therapy medically viable whilst avoiding the potential for deleteriously disturbing the commensal microbiota. Phage training is a new approach to produce efficient phages by capitalizing on the evolved response of wild-type phages to bacterial resistance. Here we will review recent studies reporting successful trials of training different strains of phages to switch into lytic replication mode, overcome bacterial resistance, and increase their host range. This review will also highlight the current knowledge of phage training and future implications in phage applications and phage therapy and summarize the recent pipeline of the magistral preparation to produce a customized phage for clinical trials and medical applications.

Isolation and Characterization of a Novel Salmonella Phage vB_SalP_TR2

Salmonella is a widely distributed foodborne pathogen. The use of Salmonella phages as biocontrol agents has recently gained significant interest. Because the Salmonella genus has high diversity, efforts are necessary to identify lytic Salmonella phages focusing on different serovars. Here, five Salmonella phages were isolated from soil samples, and vB_SalP_TR2 was selected as a novel phage with high lytic potential against the host Salmonella serovar Albany, as well as other tested serovars, including Corvallis, Newport, Kottbus, and Istanbul. Morphological analyses demonstrated that phage vB_SalP_TR2 belongs to the Podoviridae family, with an icosahedral head (62 ± 0.5 nm in diameter and 60 ± 1 nm in length) and a short tail (35 ± 1 nm in length). The latent period and burst size of phage vB_SalP_TR2 was 15 min and 211 PFU/cell, respectively. It contained a linear dsDNA of 71,453 bp, and G + C content was 40.64%. Among 96 putative open reading frames detected, only 35 gene products were found in database searches, with no virulence or antibiotic resistance genes being identified. As a biological control agent, phage vB_SalP_TR2 exhibited a high temperature and pH tolerance. In vitro, it lysed most S. Albany after 24 h at 37°C with multiplicities of infection of 0.0001, 0.001, 0.01, 0.1, 1, 10, and 100. In food matrices (milk and chicken meat), treatment with phage vB_SalP_TR2 also reduced the number of S. Albany compared with that in controls. These findings highlighted phage vB_SalP_TR2 as a potential antibacterial agent for the control of Salmonella in food samples.

The occurrence, growth, and biocontrol of Listeria monocytogenes in fresh and surface-ripened soft and semisoft cheeses

Listeria monocytogenes continues to pose a food safety risk in ready-to-eat foods, including fresh and soft/semisoft cheeses. Despite L. monocytogenes being detected regularly along the cheese production continuum, variations in cheese style and intrinsic/extrinsic factors throughout the production process (e.g., pH, water activity, and temperature) affect the potential for L. monocytogenes survival and growth. As novel preservation strategies against the growth of L. monocytogenes in susceptible cheeses, researchers have investigated the use of various biocontrol strategies, including bacteriocins and bacteriocin-producing cultures, bacteriophages, and competition with native microbiota. Bacteriocins produced by lactic acid bacteria (LAB) are of particular interest to the dairy industry since they are often effective against Gram-positive organisms such as L. monocytogenes, and because many LAB are granted Generally Regarded as Safe (GRAS) status by global food safety authorities. Similarly, bacteriophages are also considered a safe form of biocontrol since they have high specificity for their target bacterium. Both bacteriocins and bacteriophages have shown success in reducing L. monocytogenes populations in cheeses in the short term, but regrowth of surviving cells can commonly occur in the finished cheeses. Competition with native microbiota, not mediated by bacteriocin production, has also shown potential to inhibit the growth of L. monocytogenes in cheeses, but the mechanisms are still unclear. Here, we have reviewed the current knowledge on the growth of L. monocytogenes in fresh and surface-ripened soft and semisoft cheeses, as well as the various methods used for biocontrol of this common foodborne pathogen.

Characterization of vB_VpaP_MGD2, a newly isolated bacteriophage with biocontrol potential against multidrug-resistant Vibrio parahaemolyticus

Vibrio parahaemolyticus is a major foodborne pathogen and is also pathogenic to shrimp. Due to the emergence of multidrug-resistant V. parahaemolyticus strains, bacteriophages have shown promise as antimicrobial agents that could be used for controlling antibiotic-resistant strains. Here, a V. parahaemolyticus phage, vB_VpaP_MGD2, was isolated from a clam (Meretrix meretrix) and further characterized to evaluate its potential capability for biocontrol. Podophage vB_VpaP_MGD2 had a wide host range and was able to lyse 27 antibiotic-resistant V. parahaemolyticus strains. A one-step growth curve showed that vB_VpaP_MGD2 has a short latent period of 10 min and a large burst size of 244 phages per cell. Phage vB_VpaP_MGD2 was able to tolerate a wide range of temperature (30 °C-50 °C) and pH (pH 3-pH 10). Two multidrug-resistant strains (SH06 and SA411) were suppressed by treatment with phage vB_VpaP_MGD2 at a multiplicity of infection of 100 for 24 h without apparent regrowth of bacterial populations. The frequency of mutations causing bacteriophage resistance was relatively low (3.1 × 10^-6). Phage vB_VpaP_MGD2 has a double-stranded DNA with a genome size of 45,105 bp. Among the 48 open reading frames annotated in the genome, no lysogenic genes or virulence genes were detected. Sequence comparisons suggested that vB_VpaP_MGD2 is a member of a new species in the genus Zindervirus within the subfamily Autographivirinae. This is the first report of a member of the genus Zindervirus that can infect V. parahaemolyticus. These findings suggest that vB_VpaP_MGD2 may be a candidate biocontrol agent against early mortality syndrome/acute hepatopancreatic necrosis disease (EMS/AHPND) caused by multidrug-resistant V. parahaemolyticus in shrimp production.

Efficacy of novel phages for control of multi-drug resistant Escherichia coli O177 on artificially contaminated beef and their potential to disrupt biofilm formation

Contaminated beef is a prominent source of foodborne pathogens such as Escherichia coli O177. Susceptibility of nine multi-drug resistant E. coli O177 strains against eight individual phages and six phage cocktails was assessed using polystyrene microplate titer plate. Further, 180 beef samples were independently inoculated with E. coli O177 cells in triplicates and treated with eight individual phages and six phage cocktails to determine their efficacy in inhibiting bacteria growth at 4 °C over a 7-day incubation period. Results revealed that all E. coli O177 strains were susceptible to the phages. A significant log reduction in viable E. coli O177 cell counts was observed on beef samples upon phage treatment over the 7-day incubation period. Two individual phages and three phage cocktails reduced E. coli cell counts to levels below the detection limit (1.0 log₁₀ CFU/g). Log reduction of viable E. coli cell counts ranged from 2.10 to 7.81 CFU/g for individual phages and from 2.86 to 7.81 CFU/g for cocktails. Individual phages and phage cocktails inhibited E. coli O177 biofilm formation with phage cocktails showing high efficacy. Furthermore, phage cocktails showed greater efficacy in destroying pre-formed biofilm than individual phages. Based on these findings, we concluded that phage cocktails developed in this study could be used to reduce E. coli O177 contamination and extend the shelf-life of stored raw beef.

Bacteriophage biocontrol of Shiga toxigenic Escherichia coli (STEC) O145 biofilms on stainless steel reduces the contamination of beef

Shiga toxigenic Escherichia coli (STEC) can form biofilms and frequently cause serious foodborne illnesses. A strain of STEC O145:H25 (EC19990166) known to be a strong biofilm former was used to evaluate the efficacy of bacteriophage AZO145A against biofilms formed on stainless steel (SS) coupons. Exposure of STEC O145:H25 to phage AZO145A (10¹⁰ PFU/mL) for 2 h resulted in a 4.0 log₁₀ reduction (P < 0.01) of planktonic cells grown in M9 broth at 24 °C for 24 h, while reductions were 2.0 log₁₀ CFU/mL if these cells were grown for 48 h or 72 h prior to phage treatment. STEC O145 biofilms formed on SS coupons for 24, 48 and 72 h were reduced (P < 0.01) 2.9, 1.9 and 1.9 log₁₀ CFU/coupon by phages. STEC O145 cells in biofilms were readily transferred from the surface of the SS coupon to beef (3.6 log₁₀ CFU/coupon) even with as little as 10 s of contact with the meat surface. However, transfer of STEC O145 cells from biofilms that formed on SS coupons for 48 h to beef was reduced (P < 0.01) by 3.1 log₁₀ CFU by phage (2 × 10¹⁰ PFU/mL) at 24 °C. Scanning electron microscopy revealed that bacterial cells within indentations on the surface of SS coupons were reduced by phage. These results suggest that bacteriophage AZO145A could be effective in reducing the viability of biofilm-adherent STEC O145 on stainless steel in food industry environments.

Microbial Contamination, an Increasing Threat to the Consumption of Fresh Fruits and Vegetables in Today's World

Microbes are found all over the globe with some few exceptions, including sterilized surfaces. They include normal flora that is nonpathogenic, which contribute to the larger percentage, and pathogenic species which are few. Hence, the activities of humans cannot be completely separated from microbes. Thus, many pathogenic microbes have found their way into fresh fruits and vegetables which are a great source of a healthy diet for humans. The growing demand for fresh fruits and vegetables has necessitated larger production. The larger production of vegetables within the shortest possible time to meet the growing demand has placed them at a higher risk of contamination with the pathogenic microbes, making the safety of consumers uncertain. Study of sources of contamination and type of pathogenic etiological agents isolated from fresh fruits and vegetables includes Bacillus cereus, Campylobacter jejuni, Clostridium botulinum, E. coli O157: H7, Listeria monocytogenes, Salmonella spp., Shigella, Staphylococcus, and Vibrio cholera. Several measures have proven to be effective in controlling contamination of microbes and they include the establishment of surveillance systems to monitor the production chain and thoroughly washing vegetables with vinegar water. Saltwater and other washing techniques are effective but caution should be taken to make sure one does not use one cycle of water for washing all vegetables. The consumption of fresh fruits and vegetables is still encouraged by this review but significant measures must be taken to check the safety of these products before consumption.