Efflux-Mediated bile Resistance in Gram-Positive Pathogens

Gram-positive pathogens are causing many serious infections that affect humans and result in mild to severe diseases worldwide. In order to survive and initiate infection, enteric pathogens must resist the physiochemical defence factors in the human intestinal tract. One of these defence factors is bile, a potent antibacterial like compound in the intestine. Efflux pumps are the important mechanism by which bacteria resist antibacterial agents such as bile. Efflux of antimicrobial substances outside the bacterial cell is considered as a key factor for intestinal colonization and virulence of enteric pathogens. This paper will review the research conducted on efflux–mediated bile resistance in Staphylococcus aureus, Listeria monocytogenes, Enterococcus faecalis and Clostridium perfringens. These bacteria colonize in the human & animal gastrointestinal tract and they have a multiple mechanism to resist the innate defences in the gut and antibacterial activity of bile. However, bile resistance in these bacteria is not fully understood. The evidence from this review suggests that Gram-positive pathogens have the ability to active transport of bile. Further research is needed to know how these pathogens sense bile and how bile regulates its virulence factor. In general, therefore, it seems that understanding the specific mechanism of bile resistance in enteric bacteria including gram-positive pathogens may involve in the development of novel strategies to control and treatment of gastrointestinal infections.

Aspergillus niger Culture Filtrate (ACF) Mediated Biocontrol of Enteric Pathogens in Wastewater

Robust control of pathogens in sewage facilitates safe reuse of wastewater rich in valuable nutrients for potential valorization through biological means. Aspergillus niger is widely reported in bioremediation of wastewater but studies on control of enteric pathogens in sewage are very sparse. So, this study aimed at exploring the antibacterial and nematicidal activity of A. niger culture filtrate (ACF). Antibacterial activity of ACF on enteric pathogens (Klebsiella pneumoniae, Pseudomonas aeruginosa, Vibrio cholerae, Salmonella enterica, Shigella dysenteriae, Escherichia coli, Staphylococcus aureus, Klebsiella variicola) was determined by spectrophotometric growth analysis, resazurin based viability assay and biofilm formation assay. ACF showed inhibition against all enteric pathogens except Pseudomonas aeruginosa. Nematicidal studies on Caenorhabditis elegans showed 85% egg hatch inhibition and 52% mortality of L1 larvae. Sewage treatment with ACF at 1:1 (v/v) showed 2–3 log reduction in coliforms, Klebsiella, Shigella, Salmonella, S. aureus and Vibrio except Pseudomonas, indicating significant alteration of complex microbial dynamics in wastewater. Application of ACF can potentially be used as a robust biocontrol strategy against infectious microbes in wastewater and subsequent valorization by cultivating beneficial Pseudomonas.

Bacteroides Microbial Source Tracking Markers Perform Poorly in Predicting Enterobacteriaceae and Enteric Pathogen Contamination of Cow Milk Products and Milk-Containing Infant Food

Consumption of microbiologically contaminated food is one of the leading causes of diarrheal diseases. Understanding the source of enteric pathogens in food is important to guide effective interventions. Enterobacteriaceae bacterial assays typically used to assess food safety do not shed light on the source. Source-specific Bacteroides microbial source tracking (MST) markers have been proposed as alternative indicators for water fecal contamination assessment but have not been evaluated as an alternative fecal indicator in animal-derived foods. This study tested various milk products collected from vendors in urban Kenyan communities and infant foods made with the milk (n = 394 pairs) using conventional culture methods and TaqMan qPCR for enteric pathogens and human and bovine-sourced MST markers. Detection profiles of various enteric pathogens and Bacteroides MST markers in milk products differed from that of milk-containing infant foods. MST markers were more frequently detected in infant food prepared by caregivers, indicating recent contamination events were more likely to occur during food preparation at home. However, Bacteroides MST markers had lower sensitivity in detecting enteric pathogens in food than traditional Enterobacteriaceae indicators. Bacteroides MST markers tested in this study were not associated with the detection of culturable Salmonella enterica and Shigella sonnei in milk products or milk-containing infant food. The findings show that while Bacteroides MST markers could provide valuable information about how foods become contaminated, they may not be suitable for predicting the origin of the enteric pathogen contamination sources.

Mechanism of the Gut Microbiota Colonization Resistance and Enteric Pathogen Infection

The mammalian gut microbial community, known as the gut microbiota, comprises trillions of bacteria, which co-evolved with the host and has an important role in a variety of host functions that include nutrient acquisition, metabolism, and immunity development, and more importantly, it plays a critical role in the protection of the host from enteric infections associated with exogenous pathogens or indigenous pathobiont outgrowth that may result from healthy gut microbial community disruption. Microbiota evolves complex mechanisms to restrain pathogen growth, which included nutrient competition, competitive metabolic interactions, niche exclusion, and induction of host immune response, which are collectively termed colonization resistance. On the other hand, pathogens have also developed counterstrategies to expand their population and enhance their virulence to cope with the gut microbiota colonization resistance and cause infection. This review summarizes the available literature on the complex relationship occurring between the intestinal microbiota and enteric pathogens, describing how the gut microbiota can mediate colonization resistance against bacterial enteric infections and how bacterial enteropathogens can overcome this resistance as well as how the understanding of this complex interaction can inform future therapies against infectious diseases.

Short and Medium Chain Fatty Acids and Their Derivatives as a Natural Strategy in the Control of Necrotic Enteritis and Microbial Homeostasis in Broiler Chickens

The use of antibiotic growth promoters (AGPs) has historically been the most important prophylactic strategy for the control of Necrotic Enteritis (NE) caused by some Clostridium perfringens toxin types in poultry. During the last five decades, AGPs have also been supplemented in feed to improve body weight gain and feed efficiency as well as to modulate the microbiome (consisting of microbes and their genes both beneficial and potentially harmful) and reduce enteric pathogens, among other benefits. New regulatory requirements and consumer preferences have led to strong interest in natural alternatives to the AGPs for the prevention and control of illnesses caused by enteric pathogens. This interest is not just focused on the direct removal or inhibition of the causative microorganisms but also the improvement of intestinal health and homeostasis using a range of feed additives. A group of promising feed additives is short- and medium-chain fatty acids (SCFA and MCFA, respectively) and their derivatives. The use of SCFA and MCFA, including butyric, caproic, caprylic, capric, and lauric acids, has shown strong effects against NE in broilers both at experimental and commercial levels. These fatty acids also benefit intestinal health integrity and homeostasis. Other effects have also been documented, including increases in intestinal angiogenesis and gene expression of tight junctions. Chemical modifications to improve stability and point of release in the intestine have been shown to improve the efficacy of SCFA and MCFA and their derivatives. The aim of this review is to give an overview of SCFA, MCFA and their derivatives, as an alternative to replace AGPs to control the incidence and severity of NE in poultry.

Plant Bioactive Compounds as an Intrinsic and Sustainable Tool to Enhance the Microbial Safety of Crops

Outbreaks of produce-associated foodborne illness continue to pose a threat to human health worldwide. New approaches are necessary to improve produce safety. Plant innate immunity has potential as a host-based strategy for the deactivation of enteric pathogens. In response to various biotic and abiotic threats, plants mount defense responses that are governed by signaling pathways. Once activated, these result in the release of reactive oxygen and nitrogen species in addition to secondary metabolites that aim at tempering microbial infection and pest attack. These phytochemicals have been investigated as alternatives to chemical sanitization, as many are effective antimicrobial compounds in vitro. Their antagonistic activity toward enteric pathogens may also provide an intrinsic hurdle to their viability and multiplication in planta. Plants can detect and mount basal defenses against enteric pathogens. Evidence supports the role of plant bioactive compounds in the physiology of Salmonella enterica, Escherichia coli, and Listeria monocytogenes as well as their fitness on plants. Here, we review the current state of knowledge of the effect of phytochemicals on enteric pathogens and their colonization of plants. Further understanding of the interplay between foodborne pathogens and the chemical environment on/in host plants may have lasting impacts on crop management for enhanced microbial safety through translational applications in plant breeding, editing technologies, and defense priming.

Effect of season and geographic location in the United States on detection of potential enteric pathogens or toxin genes in horses ≥6-mo-old

We investigated the effects of season and geographic location on detection of nucleic acids of potential enteric pathogens (PEPs) or their toxins (PEP-Ts) in feces of horses ≥6-mo-old in the United States. Results of 3,343 equine diarrhea PCR panels submitted to Idexx Laboratories for horses >6-mo-old were reviewed. Submission months were grouped into 4 seasons, and states were grouped into 4 geographic regions. Logistic regression was performed to assess effects of season and region on detection rates of PEPs and PEP-Ts. Agresti–Coull CIs were determined. Detection rate of Salmonella enterica was higher in the South in summer compared to all other regions, and was also higher in the South in fall compared to the Midwest and Northeast. The Neorickettsia risticii detection rate was lower during summer in the West and higher in fall in the Midwest. Detection of Cryptosporidium spp. was lower during spring, summer, and winter in the West. Differences were not identified for detection rates of Clostridioides difficile, Clostridium perfringens, Lawsonia intracellularis, Rhodococcus equi, equine rotavirus, and equine coronavirus. Overall, our data support seasonal and regional differences in detection rates of S. enterica, N. risticii, and Cryptosporidium spp. in horses ≥6-mo-old in the United States.