Enterisol Salmonella T/C® Reduces the Shedding and Lymph Node Colonization of Monophasic Salmonella in Support of Food Safety

Enterisol Salmonella T/C^® Reduces the Shedding and Lymph Node Colonization of Monophasic Salmonella in Support of Food Safety

by Boehringer Ingelheim/September 16, 2022

Monophasic Salmonella I 4,[5],12:i-, a variant of the Typhimurium serotype, has emerged as the predominant Salmonella serotype isolated from clinical cases in the U.S. swine population.¹ Infection can cause clinical disease in pigs as well as pose a public health threat as a foodborne pathogen.²

The need for strategies to reduce Salmonella colonization in pigs, along with the shedding and transmission of the pathogen in pig populations, is more critical than ever, considering two recent developments. Firstly, the monophasic serotype has become the most frequent multi-drug-resistant serotype affecting humans in the United States³; and secondly, the USDA Food Safety and Inspection Service (FSIS) has proposed new performance standards for Salmonella in pork.⁴ Lymph nodes found in the swine carcass at slaughter are particularly important to these standards and food safety, since they can end up in the final pork product.⁵

A previous study shows that vaccination with Enterisol Salmonella T/C^®, the only U.S. commercially available vaccine containing a Typhimurium vaccine strain,⁶ confers protection against the monophasic Salmonella, as measured by decreased clinical signs and intestinal lesions, as well as improved average daily gain.⁷ This study set out to determine whether vaccination with ENTERISOL SALMONELLA T/C would confer protection against the monophasic Salmonella variant, as measured by lymph node colonization and fecal shedding.

Study Key Findings ENTERISOL SALMONELLA T/C

Significantly reduces fecal shedding of Salmonella compared to non-vaccinated pigs.
Significantly reduces lymph node colonization of Salmonella compared to non-vaccinated pigs, supporting pre-harvest control and food safety.
Can be an effective tool to prevent multi-drug-resistant monophasic Salmonella in swine.

Study Design

OVERVIEW

The study was conducted to evaluate the effect of ENTERISOL SALMONELLA T/C on the fecal shedding and colonization of a multi-drug-resistant monophasic Salmonella in a precise and controlled manner.

STUDY DESIGN

The randomized, controlled, blinded study evaluated 60 pigs across three different treatment groups. Each treatment group consisted of 20 pigs, blocked for the effects of litter and weight. Treatment groups were 1) non-vaccinated, non-challenged controls (NVNC); 2) non-vaccinated, challenged pigs (NVC); and 3) pigs vaccinated with ENTERISOL SALMONELLA T/C and challenged (EVC). Pigs were challenged at four weeks post vaccination, or approximately 7 weeks of age. The monophasic Salmonella challenge strain, which was administered at a dose of 2x10⁹ organisms per pig, is resistant to ampicillin, streptomycin, sulfisoxazole and tetracycline. Fecal samples were collected for a period of 14 days post infection (dpi), specifically at days 0, 2, 3, 7, 10 and 14 dpi. All pigs were euthanized at 14 dpi, when ileocecal lymph nodes were collected for Salmonella culture and quantification.

Study Results

RESULTS SUMMARY

Pigs vaccinated with ENTERISOL SALMONELLA T/C had a 35% reduction in positive Salmonella lymph node rate compared to non-vaccinated, challenged pigs, which had a 100% positive Salmonella rate (P < 0.05) [Figure 1]. Additionally, vaccinated pigs had a significantly reduced average lymph node Salmonella level (1.32 log10 CFU/gram) compared to non-vaccinated, challenged pigs (2.5 log10 CFU/gram). This represented a significant reduction of both the level of colonization as well as the number of pigs colonized with Salmonella in the vaccinated group (P < 0.05) [Figure 2].

Vaccination also led to a significant reduction of fecal shedding of Salmonella. By 3 dpi, a significant reduction could already be observed, and by 14 dpi, pigs vaccinated with ENTERISOL SALMONELLA T/C presented a more than 100-fold reduction in shedding level (p<0.05) [Figure 3].

Percentage of pigs with positive lymph nodes. Non-vaccinated, non-challenged controls - 0. Non-vaccinated, challenged controls - 100. Vaccinated, challenged pigs - 65.

Figure 2: Salmonella lymph node colonization level. Non-vaccinated, non-challenged controls - 0. Non-vaccinated, challenged pigs - 2.5. Vaccinated, challenged pigs - 1.32.

Figure 3: Fecal Shedding. Line graph showing data over a two week period between non-vaccinated, non-challenged controls, non-vaccinated, challenged pigs, vaccinated and challenged pigs.

^a,b Different superscripts indicate a significant (P < 0.05) difference.

Conclusion

The results of this study demonstrate that ENTERISOL SALMONELLA T/C vaccination can significantly reduce the lymph node colonization and shedding of multi-drug-resistant monophasic Salmonella in swine. These findings are significant to food safety, given that lymph nodes can end up in pork products,5 highlighting the importance of vaccination as a pre-harvest control strategy.

REFERENCES

¹ Naberhaus SA, Krull AC, Bradner LK, et al., Emergence of Salmonella enterica serovar 4,[5],12:i:- as the primary serovar identified from swine clinical samples and development of a multiplex real-time PCR for improved Salmonella serovar-level identification. J Vet Diagn Invest 2019;31(6):818–827.

² Shippy DC, Bearson BL, Holman DB, et al., Porcine response to a multi-drug-resistant Salmonella enterica serovar I 4,[5],12:i:- outbreak isolate. Foodborne Pathog Dis 2018;15(5):253–261.

³ Trachsel JM, Bearson BL, Brunelle BW, Bearson SMD. Relationship and distribution of Salmonella enterica serovar I 4,[5],12:i:- strain sequences in the NCBI Pathogen Detection database. BMC Genomics. 2022;23(1):268. doi: 10.1186/s12864-022-08458-z.

⁴USDA FSIS. Changes to the Salmonella verification testing program: proposed performance standards for Salmonella in raw comminuted pork and intact or non-intact pork cuts and related agency verification procedures. https://www.fsis.usda.gov/policy/federal-register-rulemaking/federal-register-notices/changes-salmonella-verification-0. Accessed Aug. 10, 2022.

⁵ Miller M, Maher JM, Wiseman B, Gragg SE. Salmonella is present in multiple lymph nodes of market hog carcasses at slaughter. Food Protection Trends 2022;42(2):100–106.

⁶ Leite F. Salmonella enterica serovar I 4,[5],12:i:- update on risk factors and control, in Proceedings. 52nd Annu Meet AASV, 2021;161–163.

⁷ Leite F, Arruda P, Jordan D, Bearson S. An evaluation of Enterisol Salmonella T/C^® vaccine in conferring protection against Salmonella enterica serovar I 4,[5],12:i:-, in Proceedings. Allen D. Leman Swine Conf.

US-POR-0348-2022