Development and stability of bacteriocin resistance in Campylobacter spp

Intervention Strategies to Control Campylobacter at Different Stages of the Food Chain

Campylobacter is one of the most common bacterial pathogens of food safety concern. Campylobacter jejuni infects chickens by 2-3 weeks of age and colonized chickens carry a high C. jejuni load in their gut without developing clinical disease. Contamination of meat products by gut contents is difficult to prevent because of the high numbers of C. jejuni in the gut, and the large percentage of birds infected. Therefore, effective intervention strategies to limit human infections of C. jejuni should prioritize the control of pathogen transmission along the food supply chain. To this end, there have been ongoing efforts to develop innovative ways to control foodborne pathogens in poultry to meet the growing customers' demand for poultry meat that is free of foodborne pathogens. In this review, we discuss various approaches that are being undertaken to reduce Campylobacter load in live chickens (pre-harvest) and in carcasses (post-harvest). We also provide some insights into optimization of these approaches, which could potentially help improve the pre- and post-harvest practices for better control of Campylobacter.

Campylobacter Biofilms: Potential of Natural Compounds to Disrupt Campylobacter jejuni Transmission

Microbial biofilms occur naturally in many environmental niches and can be a significant reservoir of infectious microbes in zoonotically transmitted diseases such as that caused by Campylobacter jejuni, the leading cause of acute human bacterial gastroenteritis world-wide. The greatest challenge in reducing the disease caused by this organism is reducing transmission of C. jejuni to humans from poultry via the food chain. Biofilms enhance the stress tolerance and antimicrobial resistance of the microorganisms they harbor and are considered to play a crucial role for Campylobacter spp. survival and transmission to humans. Unconventional approaches to control biofilms and to improve the efficacy of currently used antibiotics are urgently needed. This review summarizes the use plant- and microorganism-derived antimicrobial and antibiofilm compounds such as essential oils, antimicrobial peptides (AMPs), polyphenolic extracts, algae extracts, probiotic-derived factors, d-amino acids (DAs) and glycolipid biosurfactants with potential to control biofilms formed by Campylobacter, and the suggested mechanisms of their action. Further investigation and use of such natural compounds could improve preventative and remedial strategies aimed to limit the transmission of campylobacters and other human pathogens via the food chain.

Current Perspectives and Potential of Probiotics to Limit Foodborne Campylobacter in Poultry

Poultry has been one of the major contributors of Campylobacter related human foodborne illness. Numerous interventions have been applied to limit Campylobacter colonization in poultry at the farm level, but other strategies are under investigation to achieve more efficient control. Probiotics are viable microbial cultures that can establish in the gastrointestinal tract (GIT) of the host animal and elicit health and nutrition benefits. In addition, the early establishment of probiotics in the GIT can serve as a barrier to foodborne pathogen colonization. Thus, probiotics are a potential feed additive for reducing and eliminating the colonization of Campylobacter in the GIT of poultry. Screening probiotic candidates is laborious and time-consuming, requiring several tests and validations both in vitro and in vivo. The selected probiotic candidate should possess the desired physiological characteristics and anti-Campylobacter effects. Probiotics that limit Campylobacter colonization in the GIT rely on different mechanistic strategies such as competitive exclusion, antagonism, and immunomodulation. Although numerous research efforts have been made, the application of Campylobacter limiting probiotics used in poultry remains somewhat elusive. This review summarizes current research progress on identifying and developing probiotics against Campylobacter and presenting possible directions for future research efforts.

On farm interventions to minimise Campylobacter spp. contamination in chicken

1. This review explores current and proposed on-farm interventions and assess the potential of these interventions against Campylobacter spp. 2. Interventions such as vaccination, feed/water-additives and, most importantly, consistent biosecurity, exhibit potential for the effective control of this pathogen and its dissemination within the food chain. 3. Due to the extensive diversity in the Campylobacter spp. genome and surface-expressed proteins, vaccination of poultry is not yet regarded as a completely effective strategy. 4. The acidification of drinking water through the addition of organic acids has been reported to decrease the risk of Campylobacter spp. colonisation in broiler flocks. Whilst this treatment alone will not completely protect birds, use of water acidification in combination with in-feed measures to further reduce the level of Campylobacter spp. colonisation in poultry may be an option meriting further exploration. 5. The use of varied types of feed supplements to reduce the intestinal population and shedding rate of Campylobacter spp. in poultry is an area of growing interest in the poultry industry. Such supplements include pro - and pre-biotics, organic acids, bacteriocins and bacteriophage, which may be added to feed and water. 6. From the literature, it is clear that a distinct, albeit not unexpected, difference between the performance of in-feed interventions exists when examined in vitro compared to those determined in in vivo studies. It is much more likely that pooling some of the discussed approaches in the in-feed tool kit will provide an answer. 7. Whilst on-farm biosecurity is essential to maintain a healthy flock and reduce disease transmission, even the most stringent biosecurity measures may not have sufficient, consistent and predictable effects in controlling Campylobacter spp. Furthermore, the combination of varied dietary approaches and improved biosecurity measures may synergistically improve control.

Strategies and novel technologies to control Campylobacter in the poultry chain: A review

Campylobacteriosis is one of the most common bacterial infections worldwide causing economic costs. The high prevalence of Campylobacter spp. in poultry meat is a result of several contamination and cross-contamination sources through the production chain. Moreover, survival mechanisms, such as biofilm formation, viable but nonculturable state, and antimicrobial resistance, enable its persistence during food processing. Therefore, mitigation strategies are necessary in order to avoid and/or inactivate Campylobacter at farm, abattoir, industry, and retail level. In this review, a number of potential strategies and novel technologies that could reduce the prevalence of Campylobacter in poultry meat have been identified and evaluated to provide a useful overview. At farm level for instance, biosecurity, bacteriocins, probiotics, feed and water additives, bacteriophages, and vaccination could potentially reduce colonization in chicken flocks. However, current technologies used in the chicken slaughter and processing industry may be less effective against this foodborne pathogen. Novel technologies and strategies such as cold plasma, ultraviolet light, high-intensity light pulses, pulsed electric fields, antimicrobials, and modified atmosphere packaging are discussed in this review for reducing Campylobacter contamination. Although these measures have achieved promising results, most have not been integrated within processing operations due to a lack of knowledge or an unwillingness to implement these into existing processing systems. Furthermore, a combination of existing and novel strategies might be required to decrease the prevalence of this pathogen in poultry meat and enhance food safety. Therefore, further research will be essential to assess the effectiveness of all these strategies.

Gut Microbiota and Colonization Resistance against Bacterial Enteric Infection

The gut microbiome is critical in providing resistance against colonization by exogenous microorganisms. The mechanisms via which the gut microbiota provide colonization resistance (CR) have not been fully elucidated, but they include secretion of antimicrobial products, nutrient competition, support of gut barrier integrity, and bacteriophage deployment. However, bacterial enteric infections are an important cause of disease globally, indicating that microbiota-mediated CR can be disturbed and become ineffective. Changes in microbiota composition, and potential subsequent disruption of CR, can be caused by various drugs, such as antibiotics, proton pump inhibitors, antidiabetics, and antipsychotics, thereby providing opportunities for exogenous pathogens to colonize the gut and ultimately cause infection. In addition, the most prevalent bacterial enteropathogens, including Clostridioides difficile, Salmonella enterica serovar Typhimurium, enterohemorrhagic Escherichia coli, Shigella flexneri, Campylobacter jejuni, Vibrio cholerae, Yersinia enterocolitica, and Listeria monocytogenes, can employ a wide array of mechanisms to overcome colonization resistance. This review aims to summarize current knowledge on how the gut microbiota can mediate colonization resistance against bacterial enteric infection and on how bacterial enteropathogens can overcome this resistance.

Antimicrobial Resistance in Campylobacter spp

Campylobacter is a major foodborne pathogen and has become increasingly resistant to clinically important antimicrobials. To cope with the selection pressure from antimicrobial use in both veterinary and human medicine, Campylobacter has developed multiple mechanisms for antibiotic resistance, including modification or mutation of antimicrobial targets, modification or inactivation of antibiotics, and reduced drug accumulation by drug efflux pumps. Some of these mechanisms confer resistance to a specific class of antimicrobials, while others give rise to multidrug resistance. Notably, new antibiotic resistance mechanisms continuously emerge in Campylobacter, and some examples include the recently discovered multidrug resistance genomic islands harboring multiple genes involved in the resistance to aminoglycosides and macrolides, a novel Cfr(C) conferring resistance to phenicols and other drugs, and a potent multidrug efflux pump CmeABC variant (RE-CmeABC) that shows a significantly enhanced function in multidrug resistance and is associated with exceedingly high-level resistance to fluoroquinolones. These newly emerged resistance mechanisms are horizontally transferable and greatly facilitate the adaptation of Campylobacter in the food-producing environments where antibiotics are frequently used. In this article, we will discuss how Campylobacter resists the action of various classes of antimicrobials, with an emphasis on newly discovered mechanisms.

Current and Potential Treatments for Reducing Campylobacter Colonization in Animal Hosts and Disease in Humans

Campylobacter jejuni is the leading cause of bacteria-derived gastroenteritis worldwide. In the developed world, Campylobacter is usually acquired by consuming under-cooked poultry, while in the developing world it is often obtained through drinking contaminated water. Once consumed, the bacteria adhere to the intestinal epithelium or mucus layer, causing toxin-mediated inhibition of fluid reabsorption from the intestine and invasion-induced inflammation and diarrhea. Traditionally, severe or prolonged cases of campylobacteriosis have been treated with antibiotics; however, overuse of these antibiotics has led to the emergence of antibiotic-resistant strains. As the incidence of antibiotic resistance, emergence of post-infectious diseases, and economic burden associated with Campylobacter increases, it is becoming urgent that novel treatments are developed to reduce Campylobacter numbers in commercial poultry and campylobacteriosis in humans. The purpose of this review is to provide the current status of present and proposed treatments to combat Campylobacter infection in humans and colonization in animal reservoirs. These treatments include anti-Campylobacter compounds, probiotics, bacteriophage, vaccines, and anti-Campylobacter bacteriocins, all of which may be successful at reducing the incidence of campylobacteriosis in humans and/or colonization loads in poultry. In addition to reviewing treatments, we will also address several proposed targets that may be used in future development of novel anti-Campylobacter treatments.

Global Epidemiology of Campylobacter Infection

Campylobacter jejuni infection is one of the most widespread infectious diseases of the last century. The incidence and prevalence of campylobacteriosis have increased in both developed and developing countries over the last 10 years. The dramatic increase in North America, Europe, and Australia is alarming, and data from parts of Africa, Asia, and the Middle East indicate that campylobacteriosis is endemic in these areas, especially in children. In addition to C. jejuni, there is increasing recognition of the clinical importance of emerging Campylobacter species, including Campylobacter concisus and Campylobacter ureolyticus. Poultry is a major reservoir and source of transmission of campylobacteriosis to humans. Other risk factors include consumption of animal products and water, contact with animals, and international travel. Strategic implementation of multifaceted biocontrol measures to reduce the transmission of this group of pathogens is paramount for public health. Overall, campylobacteriosis is still one of the most important infectious diseases that is likely to challenge global health in the years to come. This review provides a comprehensive overview of the global epidemiology, transmission, and clinical relevance of Campylobacter infection.

Characterization of bacterial antimicrobial peptides active against Campylobacter jejuni

Campylobacter jejuni is one of the major causes of food poisoning, often resulting from the consumption of improperly cooked poultry products. The emergence of C. jejuni strains resistant to conventional antibiotics necessitates the evaluation of other possible treatments or preventative measures to minimize the impact and prevalence of infections. Antimicrobial peptides produced by bacteria have begun to emerge as a potential means of decreasing the levels of C. jejuni in poultry, thereby limiting Campylobacter contamination in associated food products. A number of bacteriocins produced by Gram-positive bacteria have unexpectedly been described as having antimicrobial activity against the Gram-negative C. jejuni. Additionally, some nonribosomal lipopeptides produced by Bacillus and Paenibacillus spp. show efficacy against this pathogen. This review will describe the bacterial antimicrobial peptides reported to be active against C. jejuni, with an emphasis on the characterization of their primary structures. However, for many of these peptides, little is known about their amino acid sequences and structures. Furthermore, there are unusual inconsistencies associated with the reported amino acid sequences for several of the more well-studied bacteriocins. Clarifying the chemical nature of these promising antimicrobial peptides is necessary before their potential utility for livestock protection from C. jejuni can be fully explored. Once these peptides are better characterized, they may prove to be strong candidates for minimizing the impact of Campylobacter on human health.

Use of synthetic genes for cloning, production and functional expression of the bacteriocins enterocin A and bacteriocin E 50-52 by Pichia pastoris and Kluyveromyces lactis

The use of synthetic genes may constitute a successful approach for the heterologous production and functional expression of bacterial antimicrobial peptides (bacteriocins) by recombinant yeasts. In this work, synthetic genes with adapted codon usage designed from the mature amino acid sequence of the bacteriocin enterocin A (EntA), produced by Enterococcus faecium T136, and the mature bacteriocin E 50-52 (BacE50-52), produced by E. faecium NRRL B-32746, were synthesized. The synthetic entA and bacE50-52 were cloned into the protein expression vectors pPICZαA and pKLAC2 for transformation of derived vectors into Pichia pastoris X-33 and Kluyveromyces lactis GG799, respectively. The recombinant vectors were linearized and transformed into competent cells selecting for P. pastoris X-33EAS (entA), P. pastoris X-33BE50-52S (bacE50-52), K. lactis GG799EAS (entA), and K. lactis GG799BE50-52S (bacE50-52). P. pastoris X-33EAS and K. lactis GG799EAS, but not P. pastoris X-33BE50-52S and K. lactis GG799BE50-52S, showed antimicrobial activity in their supernatants. However, purification of the supernatants of the producer yeasts permitted recovery of the bacteriocins EntA and BacE50-52. Both purified bacteriocins were active against Gram-positive bacteria such as Listeria monocytogenes but not against Gram-negative bacteria, including Campylobacter jejuni.

Proteomic identification of immunodominant membrane-related antigens in Campylobacter jejuni associated with sheep abortion

Campylobacter jejuni clone SA is the predominant agent inducing sheep abortion and a zoonotic agent causing gastroenteritis in humans in the United States. In an attempt to identify antigens of clone SA that may be useful for vaccine development, immunoproteomic analyses were conducted to characterize the membrane proteome of C. jejuni clone SA. 2-DE of C. jejuni membrane-related proteins was followed by immunoblotting analyses using convalescent sera that were derived from ewes naturally infected by C. jejuni clone SA. Totally 140 immunoreactive spots were identified, 50 of which were shared by all tested convalescent sheep sera. Conserved and immunodominant spots were identified by mass spectrometry. Among the 26 identified immunogenic proteins, there were 8 cytoplasmic proteins, 2 cytoplasmic membrane proteins, 11 periplasmic proteins, 3 outer membrane proteins, and 2 extracellular proteins. Notably, many of the immunodominant antigens were periplasmic proteins including HtrA, ZnuA, CjaA, LivK, CgpA, and others, some of which were previously shown to induce protective immunity. Interestingly, 11 immunoreactive proteins including 9 periplasmic proteins are known N-linked glycosylated proteins. These findings reveal immunogens that may potentially elicit protective immune responses and provide a foundation for developing vaccines against C. jejuni induced sheep abortion.

BIOLOGICAL SIGNIFICANCE

Campylobacter jejuni clone SA is the predominant agent inducing sheep abortion and incurs a significant economic loss to sheep producers. This emergent strain is also a zoonotic agent, causing gastroenteritis in humans. However, the immunogens of C. jejuni induced abortion are largely unknown. Considering the significance of C. jejuni clone SA in causing sheep abortion and foodborne illnesses, protective vaccines are needed to control its transmission and spread. Additionally, immunological markers are required for detection and identification of this highly pathogenic clone. To address these needs, we applied an immunoproteomic approach to identify the membrane-associated antigens of this highly virulent C. jejuni clone associated with sheep abortions in the U.S. The findings reveal immunogens that may potentially elicit protective immune responses and provide a foundation for developing vaccines against C. jejuni induced sheep abortion.

Screening for lactic acid bacteria capable of inhibiting Campylobacter jejuni in in vitro simulations of the broiler chicken caecal environment

Thermotolerant Campylobacter spp., specifically Campylobacter jejuni and Campylobacter coli, are the most common bacterial causes of human gastroenteritis in developed countries. Consumption of improperly prepared poultry products and cross contamination are among the main causes of human campylobacteriosis. The aim of this study was to identify lactic acid bacterial (LAB) strains capable of inhibiting C. jejuni growth in initial in vitro trials ('spot-on-lawn' method), as well as in batch fermentation studies mimicking the broiler caecal environment. These experiments served as an indication for using these strains to decrease the capability of Campylobacter to colonise and grow in the chicken caeca during primary production, with the aim of reducing the number of human campylobacteriosis cases. A total of 1,150 LAB strains were screened for anti-Campylobacter activity. Six strains were selected: members of the species Lactobacillus reuteri, Lactobacillus agilis, Lactobacillus helveticus, Lactobacillus salivarius, Enterococcus faecalis and Enterococcus faecium. After treatment with catalase, proteinase K and a-chymotrypsin, anti-Campylobacter activity of cell-free culture supernatant fluid (CSF) for all six strains was retained, which indicated that activity was probably not exerted by bacteriocin production. Based on the activity found in CSF, the compounds produced by the selected strains are secreted and do not require presence of live bacterial producer cells for activity. During initial in vitro fermentation experiments, the E. faecalis strain exhibited the highest inhibitory activity for C. jejuni and was selected for further fermentation experiments. In these experiments we tested for therapeutic or protective effects of the E. faecalis strain against C. jejuni MB 4185 infection under simulated broiler caecal growth conditions. The best inhibition results were obtained when E. faecalis was inoculated before the C. jejuni strain, lowering C. jejuni counts at least one log compared to a positive control. This effect was already observed 6 h after C. jejuni inoculation.

Inactivation of the LysR regulator Cj1000 of Campylobacter jejuni affects host colonization and respiration

Transcriptional regulation mediates adaptation of pathogens to environmental stimuli and is important for host colonization. The Campylobacter jejuni genome sequence reveals a surprisingly small set of regulators, mostly of unknown function, suggesting an intricate regulatory network. Interestingly, C. jejuni lacks the homologues of ubiquitous regulators involved in stress response found in many other Gram-negative bacteria. Nonetheless, cj1000 is predicted to encode the sole LysR-type regulator in the C. jejuni genome, and thus may be involved in major adaptation pathways. A cj1000 mutant strain was constructed and found to be attenuated in its ability to colonize 1-day-old chicks. Complementation of the cj1000 mutation restored the colonization ability to wild-type levels. The mutant strain was also outcompeted in a competitive colonization assay of the piglet intestine. Oxygraphy was carried out for what is believed to be the first time with the Oroboros Oxygraph-2k on C. jejuni and revealed a role for Cj1000 in controlling O2 consumption. Furthermore, microarray analysis of the cj1000 mutant revealed both direct and indirect regulatory targets, including genes involved in energy metabolism and oxidative stress defences. These results highlight the importance of Cj1000 regulation in host colonization and in major physiological pathways.