Saccharomyces cerevisiae Fermentation Products That Mitigate Foodborne Salmonella in Cattle and Poultry.

Prior studies revealed that yeast fermentation products, specifically XPC™ and related products (Diamond V, Cedar Rapids, IA), serve as viable food safety tools across multiple food animal species including cattle and poultry. Providing this supplement in feed leads to reduced prevalence, load, virulence, and antibiotic resistance of foodborne pathogens such as Salmonella and Escherichia coli O157:H7. These findings are worthy of further study, especially when coupled with the enhanced growth and performance observed with these products. Mechanistically, XPC appears to modulate these effects through the immune system and gut microbiome. Herein we further investigated this product and demonstrate that XPC mediates an enhancement of immunocyte killing of Salmonella in calves fed the product. Additionally, these studies reveal that XPC reduces the lymph node infiltration, invasiveness, and antibiotic resistance of Salmonella in dairy calves fed the product-consistent with findings observed in poultry and adult beef cattle. Furthermore, the reduction in invasiveness does not lead to a rebound hyperinvasive phenotype in Salmonella obtained from XPC-fed animals. In summary, these studies suggest that XPC reduces the invasion of Salmonella and may alter various phenotypic characteristics of the pathogen.

Doxycycline as an inhibitor of p-glycoprotein in the alpaca for the purpose of maintaining avermectins in the CNS during treatment for parelaphostrongylosis.

Meningeal worms (Parelaphostrongylus tenuis) are a common malady of alpacas, often refractory to conventional treatments. Ivermectin is a very effective anthelmintic used against a variety of parasites but this drug is not consistently effective against alpaca meningeal worms once the parasite has gained access to the CNS, even if used in a protracted treatment protocol. Ivermectin is not effective against clinical cases of P. tenuis, raising the possibility that the drug is not sustained at therapeutic concentrations in the central nervous system (CNS). A specific protein (designated as p-glycoprotein (PGP)) effluxes ivermectin from the brain at the blood-brain barrier, thus hampering the maintenance of therapeutic concentrations of the drug in the CNS. Minocycline is a synthetic tetracycline antibiotic with an excellent safety profile in all animals tested to date. Minocycline has three unique characteristics that could be useful for treating meningeal worms in conjunction with ivermectin. First, minocycline is an inhibitor of PGP at the blood-brain barrier and this inhibition could maintain effective concentrations of ivermectin in the brain and meninges. Second, minocycline protects neurons in vivo through a number of different mechanisms and this neuroprotection could alleviate the potential untoward neurologic effects of meningeal worms. Third, minocycline is a highly lipid-soluble drug, thus facilitating efficient brain penetration. We thus hypothesized that minocycline will maintain ivermectin, or a related avermectin approved in ruminants (abamectin, doramectin, or eprinomectin), in the alpaca CNS. To test this hypothesis, we cloned the gene encoding the alpaca PGP, expressed the alpaca PGP in a heterologous expression system involving MDCK cells, and measured the ability of minocycline to inhibit the efflux of avermectins from the MDCK cells; doxycycline was used as a putative negative control (based on studies in other species). Our in vitro studies surprisingly revealed that doxycycline was effective at inhibiting the efflux of ivermectin and doramectin (minocycline had no effect). These two avermectins, in combination with doxycycline, should be considered when treating meningeal worms in alpacas.

Amelioration of salmonellosis in pre-weaned dairy calves fed Saccharomyces cerevisiae fermentation products in feed and milk replacer.

Salmonellosis is an insidious and potentially epidemic problem in pre-weaned dairy calves. Managing this disease, or any other diarrheal disease, is a financial burden to producers. Calf mortalities and medicinal treatments are overt costs of salmonellosis, while hidden costs include hampered weight gains and persistent intestinal colonization of the pathogen. In this study, we examined the anti-Salmonella effects of Saccharomyces cerevisiae fermentation products (SCFP) incorporated into both the milk replacer and the starter grain. In a blinded study, 2-8 day-old calves were fed SCFP (n=20 calves) or an SCFP-free Control (n=20 calves) for two weeks before and three weeks after experimental challenge with Salmonella enterica serotype Typhimurium. Following the challenge, calves were monitored for clinical signs and parameters associated with salmonellosis. Calves were then euthanized and examined for rumen development and intestinal Salmonella colonization. When compared to calves that received milk replacer and feed lacking SCFP, calves fed SCFP had fewer bouts of diarrhea and fever. Rumens from these calves were more developed, as measured by the length of papillae, which is consistent with the enhanced weight gain observed in this treatment group. Additionally, Salmonella intestinal colonization was reduced in SCFP-fed calves and Salmonella fecal shedding disappeared at an earlier stage in these calves. This study revealed that the combination of two proprietary S. cerevisiae fermentation products provide marked benefit for preventing the negative effects of salmonellosis in pre-weaned dairy calves, while also boosting productivity. The mechanism of action needs to be clarified, but it may be related to the observed decrease in colonization by the pathogen and increase in rumen development.

Effects of subtherapeutic concentrations of antimicrobials on gene acquisition events in Yersinia, Proteus, Shigella, and Salmonella recipient organisms in isolated ligated intestinal loops of swine.

OBJECTIVE: To assess antimicrobial resistance and transfer of virulence genes facilitated by subtherapeutic concentrations of antimicrobials in swine intestines. ANIMALS: 20 anesthetized pigs experimentally inoculated with donor and recipient bacteria. PROCEDURES: 4 recipient pathogenic bacteria (Salmonella enterica serotype Typhimurium, Yersinia enterocolitica, Shigella flexneri, or Proteus mirabilis) were incubated with donor bacteria in the presence of subinhibitory concentrations of 1 of 16 antimicrobials in isolated ligated intestinal loops in swine. Donor Escherichia coli contained transferrable antimicrobial resistance or virulence genes. After coincubations, intestinal contents were removed and assessed for pathogens that acquired new antimicrobial resistance or virulence genes following exposure to the subtherapeutic concentrations of antimicrobials. RESULTS: 3 antimicrobials (apramycin, lincomycin, and neomycin) enhanced transfer of an antimicrobial resistance plasmid from commensal E coli organisms to Yersinia and Proteus organisms, whereas 7 antimicrobials (florfenicol, hygromycin, penicillin G, roxarsone, sulfamethazine, tetracycline, and tylosin) exacerbated transfer of an integron (Salmonella genomic island 1) from Salmonella organisms to Yersinia organisms. Sulfamethazine induced the transfer of Salmonella pathogenicity island 1 from pathogenic to nonpathogenic Salmonella organisms. Six antimicrobials (bacitracin, carbadox, erythromycin, sulfathiazole, tiamulin, and virginiamycin) did not mediate any transfer events. Sulfamethazine was the only antimicrobial implicated in 2 types of transfer events. CONCLUSIONS AND CLINICAL RELEVANCE: 10 of 16 antimicrobials at subinhibitory or subtherapeutic concentrations augmented specific antimicrobial resistance or transfer of virulence genes into pathogenic bacteria in isolated intestinal loops in swine. Use of subtherapeutic antimicrobials in animal feed may be associated with unwanted collateral effects.

Beta-lactam antibiotics prevent Salmonella-mediated bovine encephalopathy regardless of the ß-lactam resistance status of the bacteria.

This study assessed the capacity of ß-lactam antibiotics to prevent salmonella-mediated encephalopathy in calves given the putative neuroprotective effects of these drugs of increasing glutamate export from the brain. Both ampicillin and ceftiofur prevented the development of encephalopathy despite resistance of the inoculated Salmonella enterica serovar Saint-Paul isolate to both drugs. A glutamate receptor antagonist also prevented this salmonella-mediated encephalopathy. Glutamate exporters were hyper-expressed in the presence of ß-lactam antibiotics while a glutamate export inhibitor obviated the effects of these antibiotics, demonstrating a neuroprotective effect through glutamate export from the brain. The findings indicate that ß-lactam antibiotics remain an important treatment option for this atypical form of bovine salmonellosis.

Expression of a collagenase that enables blood-brain barrier penetration for Salmonella implicated in bovine encephalopathies.

Recent studies identified strains of Salmonella that induce encephalopathies in calves exposed to stressful situations. In order to cause neurologic signs (such as ataxia, head tilt, and partial blindness), the strain must be able to cross the blood-brain barrier (BBB). One possible way is through the break down of tight junctions, which regulate the permeability of the BBB and can be weakened by enzymes such as collagenases. Salmonella and other Gram-negative bacteria contain a collagenase gene (clg) that is silenced in vitro but inducibly expressed in vivo. We hypothesized that the neuropathic strains of Salmonella express clg in response to neuroendocrine factors in the host and that the expressed collagenase perturbs the BBB allowing for CNS invasion by Salmonella. Our in vitro results revealed that clg is derepressed in serum obtained from stressed cattle. Derepression is relegated to the neuropathic Salmonella strains. In vivo studies indicated that clg expression is required for neuropathogenicity and that pharmacologic maintenance of the BBB prevents both the Salmonella invasion into the brain and the resulting neurologic signs. These studies identify a host-induced Salmonella collagenase that facilitates neuropathogenicity at the level of the BBB.

Comparisons of Salmonella conjugation and virulence gene hyperexpression mediated by rumen protozoa from domestic and exotic ruminants.

Recent studies have identified a phenomenon in which ciliated protozoa engulf Salmonella and the intra-protozoal environment hyperactivates virulence gene expression and provides a venue for conjugal transfer of antibiotic resistance plasmids. The former observation is relegated to Salmonella bearing the SGI1 multiresistance integron while the latter phenomenon appears to be a more generalized event for recipient Salmonella. Our previous studies have assessed virulence gene hyperexpression only with protozoa from the bovine rumen while conjugal transfer has been demonstrated in rumen protozoa from cattle and goats. The present study examined virulence gene hyperexpression for Salmonella exposed to rumen protozoa obtained from cattle, sheep, goats, or two African ruminants (giraffe and bongo). Conjugal transfer was also assessed in these protozoa using Salmonella as the recipient. Virulence gene hyperexpression was only observed following exposure to the rumen protozoa from cattle and sheep while elevated virulence was also observed in these animals. Conjugal transfer events were, however, observed in all protozoa evaluated. It therefore appears that the protozoa-based hypervirulence is not universal to all ruminants while conjugal transfer is more ubiquitous.