Bacteriophages as Biological Control Agents of Enteric Bacteria Contaminating Edible Oysters

Potential of bacteriophage phT4A as a biocontrol agent against Escherichia coli in food matrices

Escherichia coli is one of the most prevalent foodborne pathogens, frequently found in meat and dairy products. Current decontamination methods are often associated with changes in organoleptic characteristics, nutrient loss, and potentially harmful side effects. Furthermore, despite the array of available methods, foodborne outbreaks still frequently occur. For this reason, bacteriophages (or simply phages) emerged as a natural alternative for the biocontrol of bacterial contamination in food without altering their organoleptic properties. In this study, the potential of phage phT4A was assessed in the biocontrol of E. coli in liquid (milk) and solid (ham) food matrices. Firstly, as foods have different pH and temperature values, the influence of these parameters on phage phT4A viability was also assessed to develop an effective protocol. Phage phT4A proved to be stable for long storage periods at pH 7-8 (56 days) and temperatures of 4-37 °C (21 days). Before application of phages to inactivate pathogenic bacteria in food, previous assays were carried out in Tryptic Soy Broth (TSB) to study the dynamics of phage-bacteria interaction. Then, the antibacterial potential of phage phT4A was evaluated in the two food matrices at different temperatures (4, 10 and 25 °C). This phage was more efficient at 25 °C in all tested matrices (maximum inactivation of 6.6, 3.9 and 1.8 log CFU/mL in TSB, milk and ham, respectively) than at 10 °C (maximum decrease of 4.7, 2.1 and 1.0 log CFU/mL in TSB, milk and ham, respectively) and 4 °C (maximum reduction of 2.6 and 0.7 log CFU/mL in TSB and milk, respectively). However, the decrease of temperature from 25 °C to 10 and 4 °C prevented bacterial regrowth. The results suggest that during phage treatment, a balance between an incubation temperature that provide effective results in terms of bacterial inactivation by the phages and at the same time prevents or delays bacterial regrowth, is needed. The application of phage phT4A at a temperature of 10 °C can be an effective strategy in terms of bacterial inactivation, delaying bacterial regrowth and also reducing energy costs.

Safety Properties of Escherichia coli O157:H7 Specific Bacteriophages: Recent Advances for Food Safety

Shiga-toxin-producing Escherichia coli (STEC) is typically detected on food products mainly due to cross-contamination with faecal matter. The serotype O157:H7 has been of major public health concern due to the severity of illness caused, prevalence, and management. In the food chain, the main methods of controlling contamination by foodborne pathogens often involve the application of antimicrobial agents, which are now becoming less efficient. There is a growing need for the development of new approaches to combat these pathogens, especially those that harbour antimicrobial resistant and virulent determinants. Strategies to also limit their presence on food contact surfaces and food matrices are needed to prevent their transmission. Recent studies have revealed that bacteriophages are useful non-antibiotic options for biocontrol of E. coli O157:H7 in both animals and humans. Phage biocontrol can significantly reduce E. coli O157:H7, thereby improving food safety. However, before being certified as potential biocontrol agents, the safety of the phage candidates must be resolved to satisfy regulatory standards, particularly regarding phage resistance, antigenic properties, and toxigenic properties. In this review, we provide a general description of the main virulence elements of E. coli O157:H7 and present detailed reports that support the proposals that phages infecting E. coli O157:H7 are potential biocontrol agents. This paper also outlines the mechanism of E. coli O157:H7 resistance to phages and the safety concerns associated with the use of phages as a biocontrol.

Bacteriophages and Their Host Range in Multidrug-Resistant Bacterial Disease Treatment

The rapid emergence of multidrug-resistant (MDR) bacteria in recent times has prompted the search for new and more potent antibiotics. Bacteriophages (commonly known as phages) are viruses that target and infect their bacterial hosts. As such, they are also a potential alternative to antibiotics. These phages can be broadly categorized into monovalent (with a narrow host range spectrum and specific to a single bacterial genus) and polyvalent (with a broad host range and specific to more than two genera). However, there is still much ambiguity in the use of these terms, with researchers often describing their phages differently. There is considerable research on the use of both narrow- and broad-host range phages in the treatment of infections and diseases caused by MDR bacteria, including tuberculosis, cystic fibrosis, and carbapenem-resistant Enterobacterales (CRE) infectious diseases. From this, it is clear that the host range of these phages plays a vital role in determining the effectiveness of any phage therapy, and this factor is usually analyzed based on the advantages and limitations of different host ranges. There have also been efforts to expand phage host ranges via phage cocktail development, phage engineering and combination therapies, in line with current technological advancements. This literature review aims to provide a more in-depth understanding of the role of phage host ranges in the effectiveness of treating MDR-bacterial diseases, by exploring the following: phage biology, the importance of phages in MDR bacteria diseases treatment, the importance of phage host range and its advantages and limitations, current findings and recent developments, and finally, possible future directions for wide host range phages.

Multidrug-resistant enteric bacteria in Nigeria and potential use of bacteriophages as biocontrol

Enteric bacterial pathogens have been implicated in many cases of gastroenteritis in Nigeria, a West African country. This situation is worsened by some reports of the high prevalence of multidrug-resistant enteric bacteria. To better prepare for situations in which even antibiotics of last resort would fail to treat infections caused by these pathogens, attention should be paid to alternative antimicrobial strategies. Here, we summarize existing reports of multidrug-resistant enteric bacterial infections in Nigeria, and importantly present the use of bacteriophages (viruses of bacteria) as an attractive antimicrobial alternative to combat these pathogens. It is hoped that this review will encourage research into the use of lytic bacteriophages against multidrug-resistant enteric bacteria in Nigeria.

Bacteriophages as an Alternative Method for Control of Zoonotic and Foodborne Pathogens

The global increase in multidrug-resistant infections caused by various pathogens has raised concerns in human and veterinary medicine. This has renewed interest in the development of alternative methods to antibiotics, including the use of bacteriophages for controlling bacterial infections. The aim of this review is to present potential uses of bacteriophages as an alternative to antibiotics in the control of bacterial infections caused by multidrug-resistant bacteria posing a risk to humans, with particular emphasis on foodborne and zoonotic pathogens. A varied therapeutic and immunomodulatory (activation or suppression) effect of bacteriophages on humoral and cellular immune response mechanisms has been demonstrated. The antibiotic resistance crisis caused by global antimicrobial resistance among bacteria creates a compelling need for alternative safe and selectively effective antibacterial agents. Bacteriophages have many properties indicating their potential suitability as therapeutic and/or prophylactic agents. In many cases, bacteriophages can also be used in food quality control against microorganisms such as Salmonella, Escherichia coli, Listeria, Campylobacter and others. Future research will provide potential alternative solutions using bacteriophages to treat infections caused by multidrug-resistant bacteria.

Phage therapy as a potential approach in the biocontrol of pathogenic bacteria associated with shellfish consumption

Infectious human diseases acquired from bivalve shellfish consumption constitute a public health threat. These health threats are largely related to the filter-feeding phenomenon, by which bivalve organisms retain and concentrate pathogenic bacteria from their surrounding waters. Even after depuration, bivalve shellfish are still involved in outbreaks caused by pathogenic bacteria, which increases the demand for new and efficient strategies to control transmission of shellfish infection. Bacteriophage (or phage) therapy represents a promising, tailor-made approach to control human pathogens in bivalves, but its success depends on a deep understanding of several factors that include the bacterial communities present in the harvesting waters, the appropriate selection of phage particles, the multiplicity of infection that produces the best bacterial inactivation, chemical and physical factors, the emergence of phage-resistant bacterial mutants and the life cycle of bivalves. This review discusses the need to advance phage therapy research for bivalve decontamination, highlighting their efficiency as an antimicrobial strategy and identifying critical aspects to successfully apply this therapy to control human pathogens associated with bivalve consumption.

Bacteriophages to control Shiga toxin-producing E. coli - safety and regulatory challenges

Shiga toxin-producing Escherichia coli (STEC) are usually found on food products due to contamination from the fecal origin, as their main environmental reservoir is considered to be the gut of ruminants. While this pathogen is far from the incidence of other well-known foodborne bacteria, the severity of STEC infections in humans has triggered global concerns as far as its incidence and control are concerned. Major control strategies for foodborne pathogens in food-related settings usually involve traditional sterilization/disinfection techniques. However, there is an increasing need for the development of further strategies to enhance the antimicrobial outcome, either on food-contact surfaces or directly in food matrices. Phages are considered to be a good alternative to control foodborne pathogens, with some phage-based products already cleared by the Food and Drug Administration (FDA) to be used in the food industry. In European countries, phage-based food decontaminants have already been used. Nevertheless, its broad use in the European Union is not yet possible due to the lack of specific guidelines for the approval of these products. Furthermore, some safety concerns remain to be addressed so that the regulatory requirements can be met. In this review, we present an overview of the main virulence factors of STEC and introduce phages as promising biocontrol agents for STEC control. We further present the regulatory constraints on the approval of phages for food applications and discuss safety concerns that are still impairing their use.

The use of biological seed coatings based on bacteriophages and polymers against Clavibacter michiganensis subsp. nebraskensis in maize seeds

Biological control of bacteria with bacteriophages is a viable alternative to antibiotics. To be successful, biological control bacteriophages must be stable when exposed to the environment. Stabilization can be achieved through incorporation of bacteriophages into polymers and stabilizers that will be coated onto the seed. For this study, bacteriophages against Clavibacter michiganensis subsp. nebraskensis (Cmn), the causal agent of Goss's wilt, were incorporated into polyvinyl polymers with alcohol, ether and pyrrolidone functional groups and coated onto maize (Zea mays L.) seeds. The objectives of this study were to evaluate polymers and stabilizers that can protect Clavibacter michiganensis subsp. nebraskensis (CN8) bacteriophages against dehydration during storage. Bacteriophages stability when coated on seed depended on the glass transition temperature (Tg), functional groups of the polymer, and the presence of stabilizers such as sugars and proteins. Polyvinyl alcohol (PVOH) provided the greatest stability for CN8 bacteriophages on seed when coatings did not contain a stabilizer. A possible reason for the greater stability of this coating is having a glass transition temperature (Tg) very close to ambient temperature. PVOH combined with whey protein isolate (WPI) maintained CN8 bacteriophage activity in storage for four months at 26 °C and seven months at 10 °C. This coating also significantly reduced bacterial loads in seedlings grown from contaminated seeds, without affecting seed germination. Bacteriophage-polymer coatings which are stable during drying and storage, and are compatible with biological systems, not only provide an alternative to traditional antibiotics in agriculture, but also provide options for food, environmental and medical applications.

Bacteriophages as biocontrol agents in aquaculture

Aquaculture production (inland and marine) has been increasing globally reaching 80.1 million metric tons in 2016. Simultaneously the utilisation of fish food per capita has also been risen reaching 20.0 kg per year in 2016. However, the growing industry also experiences problems including diseases caused by viruses, bacteria, fungi, protozoans, helminths and parasitic crustaceans on valuable seafood products resulting in economic losses. Antimicrobial agents and chemical control strategies used to control such diseases are creating environmentally detrimental effects as well as encouraging development and dissemination of antibiotic resistant bacteria. Vaccine developments are costly and lengthy with application difficulties in farm settings. Accordingly, alternative therapies for controlling bacterial pathogens in aquaculture are gaining importance. One such measure is to use bacteriophages that are specific to disease causing bacteria.

Phages for biocontrol in foods: What opportunities for Salmonella sp. control along the dairy food chain?

Controlling the presence of pathogenic bacteria, such as Salmonella sp., in dairy products production is a burning issue since contamination with Salmonella can occur at any stage of the production chain. The use of Salmonella-phages applied as control agents has gained considerable interest. Nonetheless, Salmonella-phage applications specifically intended for ensuring the safety of dairy products are scarce. This review identifies recent advances in the use of Salmonella-phages that are or could be applied along the dairy food chain, in a farm-to-fork approach. Salmonella-phages can be promising tools to reduce the shedding of Salmonella in cattle, and to reduce and control Salmonella occurrence in postharvest food (such as food additives), and in food processing facilities (such as biosanitizing agents). These control measures, combined with existing methods and other biocontrol agents, constitute new opportunities to reduce Salmonella occurrence along the dairy food production, and consequently to alleviate the risk of Salmonella contamination in dairy products.

Assessment of the Detrimental Impact of Polyvalent Streptophages Intended to be Used as Biological Control Agents on Beneficial Soil Streptoflora

Streptophages are currently being investigated to control potato common scab, however, since a majority of streptophages are reported to be polyvalent, their potential to infect beneficial soil streptomycetes during the application process may have unintended consequences. To test this hypothesis, two phytopathogenic fungi, namely Fusarium solani and Rhizoctonia solani, were tested for their detrimental effect on the test crop wheat (Triticum aestivum cv. Gutha). F. solani caused a significant root weight reduction (34%) in the wheat plant and therefore was tested further in the pot trials with actinomycetes present. Sixty-seven streptomycete isolates from a Tasmanian potato farm were screened for their antifungal abilities against the two phytopathogenic fungi. Four actinomycetes found to be strongly antifungal were then tested for their disease-protective abilities against F. solani in pot trials again using wheat. Addition of the streptomycetes into the container media protected the plants against F. solani, indicating that streptomycetes have a disease-suppressive effect. A further pot trial was conducted to evaluate whether these beneficial streptomycete species would be affected by streptophage treatment and subsequently result in an increased risk of fungal infections. When streptophages were added to the pots, the shoot and root growth of wheat declined by 23.6% and 8.0%, respectively, in the pots with the pathogenic fungus compared to the control pots. These differences might suggest that removal of antifungal streptomycetes by polyvalent phages from plant rhizosphere when biocontrol of plant pathogenic streptomycetes (e.g. Streptomyces scabiei) is targeted might encourage secondary fungal infections in the farm environment. The presented data provide preliminary evidence that streptophage treatment of pathogenic streptomycetes may lead to an aggravated disease risk by soil-borne fungal pathogens when naturally present antagonists are removed. As a result, extensive farm site trials are required to determine the long-term detrimental impact of polyvalent streptophage treatments on beneficial soil streptoflora.

Protective Effects of Bacteriophages against Aeromonas hydrophila Species Causing Motile Aeromonas Septicemia (MAS) in Striped Catfish

To determine the effectivity of bacteriophages in controlling the mass mortality of striped catfish (Pangasianodon hypophthalmus) due to infections caused by Aeromonas spp. in Vietnamese fish farms, bacteriophages against pathogenic Aeromonas hydrophila were isolated. A. hydrophila-phage 2 and A. hydrophila-phage 5 were successfully isolated from water samples from the Saigon River of Ho Chi Minh City, Vietnam. These phages, belonging to the Myoviridae family, were found to have broad activity spectra, even against the tested multiple-antibiotic-resistant Aeromonas isolates. The latent periods and burst size of phage 2 were 10 min and 213 PFU per infected host cell, respectively. The bacteriophages proved to be effective in inhibiting the growth of the Aeromonas spp. under laboratory conditions. Phage treatments applied to the pathogenic strains during infestation of catfish resulted in a significant improvement in the survival rates of the tested fishes, with up to 100% survival with MOI 100, compared to 18.3% survival observed in control experiments. These findings illustrate the potential for using phages as an effective bio-treatment method to control Motile Aeromonas Septicemia (MAS) in fish farms. This study provides further evidence towards the use of bacteriophages to effectively control disease in aquaculture operations.