Evaluation of 3-week-old layer chicks intratracheally challenged with Salmonella isolates from serogroup c1 (O:6,7) and Salmonella Enteritidis

Nonspecific protection of heat-inactivated Mycobacterium bovis against Salmonella Choleraesuis infection in pigs

Trained immunity is the capacity of innate immune cells to produce an improved response against a secondary infection after a previous unrelated infection. Salmonellosis represents a public health issue and affects the pig farming industry. In general, vaccination against salmonellosis is still facing problems regarding the control of distinct serovars. Therefore, we hypothesized that an immunostimulant based on heat inactivated Mycobacterium bovis (HIMB) could have an immune training effect in pigs challenged with Salmonella enterica serovar Choleraesuis (S. Choleraesuis) and decided to explore the amplitude of this non-specific immune response. For this purpose, twenty-four 10 days-old female piglets were randomly separated in three groups: immunized group (n = 10) received orally two doses of HIMB prior to the intratracheal S. Choleraesuis-challenge, positive control group (n = 9) that was only challenged with S. Choleraesuis, and negative control group (n = 5) that was neither immunized nor infected. All individuals were necropsied 21 days post-challenge. HIMB improved weight gain and reduced respiratory symptoms and pulmonary lesions caused by S. Choleraesuis in pigs. Pigs immunized with HIMB showed higher cytokine production, especially of serum TNFα and lung CCL28, an important mediator of mucosal trained immunity. Moreover, immunized pigs showed lower levels of the biomarker of lipid oxidation malondialdehyde and higher activity of the antioxidant enzyme superoxide dismutase than untreated challenged pigs. However, the excretion and tissue colonization of S. Choleraesuis remained unaffected. This proof-of-concept study suggests beneficial clinical, pathological, and heterologous immunological effects against bacterial pathogens within the concept of trained immunity, opening avenues for further research.

HPMCAS-Coated Alginate Microparticles Loaded with Ctx(Ile21)-Ha as a Promising Antimicrobial Agent against Salmonella Enteritidis in a Chicken Infection Model

Salmonella enterica subsp. enterica serovar Enteritidis (S. Enteritidis) in poultry is most often transmitted by the fecal-oral route, which can be attributed to high population density. Upon encountering the innate immune response in a host, the pathogen triggers a stress response and virulence factors to help it survive in the host. The aim of this study was to evaluate the effect of hypromellose acetate/succinate (HPMCAS)-coated alginate microparticles containing the Ctx(Ile²¹)-Ha antimicrobial peptide (AMP) on both intestinal colonization and systemic infection of laying hens challenged with S. Enteritidis. The applied AMP microsystem reduced the bacterial load of S. Enteritidis in the liver, with a statistical significance between groups A (control, no Ctx(Ile²¹)-Ha peptide) and B (2.5 mg of Ctx(Ile²¹)-Ha/kg) at 2 days postinfection (dpi), potentially indicating the effectiveness of Ctx(Ile²¹)-Ha in the first stage of infection by S. Enteritidis. In addition, the results showed a significant decrease in the S. Enteritidis counts in the spleen and cecal content at 5 dpi; remarkably, no S. Enteritidis counts were observed in livers at 5, 7, and 14 dpi, regardless of the Ctx(Ile²¹)-Ha dosage (p-value <0.0001). Using the Chi-square test, the effect of AMP microparticles on S. Enteritidis fecal excretion was also evaluated, and a significantly lower bacterial excretion was observed over 21 days in groups B and C, in comparison with the untreated control (p-value <0.05). In summary, the use of HPMCAS-Ctx(Ile²¹)-Ha peptide microcapsules in laying hens drastically reduced the systemic infection of S. Enteritidis, mainly in the liver, indicating a potential for application as a feed additive against this pathogen.

Risk factors associated with Salmonella prevalence, its antibiotic resistance, and egg antibiotic residues in the layer farming environment

Background and Aim:

Human salmonellosis with non-typhoidal Salmonella remains a global public health concern related to the consumption of contaminated eggs and egg-based products. This study aimed to examine the prevalence of Salmonella, antimicrobial-resistant Salmonella, and egg antibiotic residues concerning risk factors associated with Salmonella contamination in eggs, the layer farming environment, and laying hens kept in battery-cage closed-housing systems.

Materials and Methods:

This study used a repeated cross-sectional design to collect 488 samples from eggs, laying hens, and the farm environment on one laying farm for Salmonella detection according to ISO 6579:2002/AMD 1:2007. Salmonella-positive samples were further tested for serotype and antimicrobial susceptibility using the disk diffusion test. The layer farm contact person was interviewed at the sampling time to evaluate the risk factors associated with Salmonella contamination using logistic regression analysis. For each month, 24 eggs (144 eggs in total) were also randomly sampled from the collection egg area at the farm for antibiotic residue detection using the European Four Plate Test.

Results:

The highest Salmonella prevalence rates were in the samples from the layer pen floors, followed by the egg sizing machine (ESM) and eggshells at 65.5%, 52.5%, and 15%, respectively. Salmonellaenterica serovar Corvallis was the dominant serovar (48.38%), followed by Mbandaka (37.76%), Braenderup (14.29%), and Typhimurium (4.08%). Rodent presence at the farm and the frequency of changing the disinfectant foot dip were significant factors related to Salmonella contamination on the pen floors (odds ratio [OR]=22.5, 95% confidence interval [CI]=2.11-240.48, p=0.01; OR=24, 95% CI=2.78-206.96, p=0.004, respectively). Hand-washing before sorting and cleaning the ESM were the significant factors (OR=13, 95% CI=1.2-140.73, p=0.04). The most resistant Salmonella isolates were resistant to oxytetracycline. One isolate of S. enterica Typhimurium was resistant to cefotaxime, enrofloxacin, and oxytetracycline. The antibiotic residues in the egg yolks were streptomycin, enrofloxacin, and tetracycline at prevalence rates of 36.11%, 11.81%, and 7.64%, respectively. Streptomycin was the most abundant residue in the albumen and yolk, followed by tetracycline.

Conclusion:

Salmonella prevalence in layer farming with a closed-housing system is related to effective biosecurity and hygiene issues, such as rodent control, clean farm equipment, and good worker hygiene. In addition, eggs’ antibiotic residues may be related to treating antimicrobial-resistant Salmonella isolates and medicated feed with inappropriate antibiotic withdrawal time.

Infection dynamics of Salmonella Infantis strains displaying different genetic backgrounds - with or without pESI-like plasmid - vary considerably

Food-borne infections with Salmonella are among the most common causes of human diseases worldwide, and infections with the serovar Infantis are becoming increasingly important. So far, diverse phenotypes and genotypes of S. Infantis have been reported. Therefore, the present study aimed to investigate the infection dynamics of two different S. Infantis strains in broilers. For this purpose, 15 birds were infected on day 2 of life with 108 CFU/ml of a pESI+ or a pESI- S. Infantis strain, respectively. Ten uninfected birds served as in-contact birds to monitor transmission. In both groups, an increase of infection was observed from 7 days of age onwards, reaching its peak at 28 days. However, the pESI+ strain proved significantly more virulent being re-isolated from most cloacal swabs and organs by direct plating. In contrast, the pESI- strain could be re-isolated from cloacal swabs and caeca only when enrichment was applied. Although the excretion of this strain was limited, the transmission level to in-contact birds was similar to the pESI+ strain. Differences in infection dynamics were also reflected in the antibody response: whereas the pESI+ strain provoked a significant increase in antibodies, antibody levels following infection with the pESI- strain remained in the range of negative control birds. The actual findings provide for the first time evidence of S. Infantis strain-specific infectivity in broilers and confirm previous observations in the field regarding differences in persistence on farms and resistance against disinfectants.

Succession patterns of the bacterial community in poultry litter after bird removal and sodium bisulfate application

Sulfate-based acid amendments are used for treating litter between broiler chicken flocks and during grow-out for in-house ammonia abatement. These amendments reduce litter pH and inhibit ammonia volatilization by converting ammonia to nonvolatile ammonium. Research on the effects of acid amendments on litter microbiota is limited and usually done in microcosms, which do not replicate natural environments. In this study, we determined the changes in bacterial populations present in litter during downtime (the period after a flock was removed and before new broiler chicks were placed) and 24 h before and after the application of a sodium bisulfate (NaHSO₄ )-based amendment. We used DNA sequencing technologies to characterize the litter microbiota, elucidating microbial shifts in litter samples with respect to downtime, litter depth, and NaHSO₄ application. During downtime (∼18 d), the litter microbiota was dominated by Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria. Sodium bisulfate affected the microbiota in the top layer (3 cm) of reused litter topdressed with fresh pine shavings and resulted in an increase in Escherichia spp. and Faecalibacterium spp. and a decrease in members of the phylum Acidobacteria. Furthermore, culturable Escherichia coli decreased by 1.5 log units during downtime, but an increase was observed for topdressed litter after NaHSO₄ was applied. Although the effect of acidifiers on ammonia reduction, bird performance, and litter performance are well documented, their effect on litter bacteria is not well understood. Our results suggest that acidifiers may perturb litter bacteria when topdressed with fresh pine shavings and that further research is required.