National feed inspection program: Results from 1989 to 2022 for the Salmonella monitoring program for livestock feeds

Background

This random sampling program is part of the National Feed Inspection Program and was implemented for the purposes of monitoring the prevalence of Salmonella bacteria in all feeds and feed ingredients. Data are available from domestic and imported feed samples collected by the Canadian Food Inspection Agency (CFIA) from feed mills, farms and retail establishments, over a period of 33 years from April 1, 1989 to March 31, 2022.

Salmonellosis has a significant impact on society in terms of human illness and economic costs. Human illness most commonly results from eating contaminated foods, which are frequently of animal origin, that is meat, milk and eggs. Meat and milk can become contaminated with Salmonella bacteria when faeces from an infected animal come into contact with meat during slaughter or milk during milking. Eggs may become contaminated by contact with faeces from infected hens during laying, or through Salmonella infection of an infected hen's reproductive tract. Salmonella also cause illness and production losses in animals.

Livestock can become infected with Salmonella through consumption of contaminated feed. Sources of contamination of feeds include both the raw materials used to prepare the feed and environmental contamination from infected insects, birds, rodents and other animals that may come into contact with the feed before or after preparation. Any feeds could be contaminated with Salmonella but certain feeds and feed ingredients, such as rendered products, fish meals, oilseed meals and mash feeds typically are more frequently contaminated with Salmonella than others, so these feed types are sampled more repeatedly by the CFIA.

In this monitoring program, the sample analyses to detect and identify the Salmonella bacteria are conducted by the CFIA at the Ottawa Laboratory Carling. Detection of Salmonella in any feed sample is considered as non-compliant and regulatory actions are taken to mitigate the risk of the contaminated feed.

Sample results by fiscal year (April 1 to March 31)

A total of 15,649 samples were collected for analysis under this program from April 1, 1989 to March 31, 2022. Table 1 presents a summary of the number of feed samples tested and the testing results, by fiscal year. The overall sample compliance level for feed samples collected under this program across all years was 88.1%, with levels ranging from 79.3% to 96.0% per fiscal year. While a trend towards increasing compliance over time appears to be present in these data, this information should not be interpreted as evidence of decreasing Salmonella bacterial prevalence in feeds over the years of this study. Factors such as the number of samples by feed type targeted by this program have changed over the years, making year-by-year result incomparable.

Evaluation of feed sample compliance by CFIA area

Table 2 presents a summary of compliance results for the 15,649 samples collected from April 1, 1989, to March 31, 2022, organized by the CFIA area from which the samples were collected. It should be noted that the area where a feed was sampled is not necessarily the same as the area in which the feed was produced. The number of samples collected was proportional to the number of feed producers in each area. Differences in sample compliance levels observed between areas are likely due to regional differences in the types of feeds sampled in these areas, as the prevalence of Salmonella bacteria may differ significantly between different feed types. Table A-1 of appendix I presents compliance results for feed samples by area for each fiscal year (April 1 to March 31).

Evaluation of feed sample compliance by feed type

Table 3A presents a summary of the number of feed samples collected and the compliance results by feed type. The majority of the 15,649 samples collected from April 1, 1989, to March 31, 2022, were complete feeds, feed supplements, and single ingredient feeds. Trace mineral salt and converter feeds were not represented. Table 2-A of Appendix I presents compliance results for feed samples by feed type for each fiscal year (April 1 to March 31).

Evaluation of feed sample compliance by single ingredient type

The single ingredient category is very diverse and for this report the single ingredients have been classified in the categories shown in Table 3B.

Evaluation of feed sample compliance by target species

Table 4 presents a summary of the number of feed samples collected and the compliance results by the target species of the feed sampled. Multiple species feeds, which are predominantly SIFs, were sampled most frequently, but large numbers of samples from specific feeds for chickens, swine, and cattle (dairy and beef) were also collected. Table 3-A in appendix I presents compliance results for feed samples by target species for each fiscal year (April 1 to March 31).

Evaluation of serotypes of Salmonella isolated from feed samples

Table 5 presents a summary of the Salmonella enterica serotypes isolated from feed samples collected from 1989 - 1990 to 2021 - 2022. The serotyping of these isolates was performed by the Public Health Agency of Canada (PHAC) until the fiscal year 2017 - 2018. Since the fiscal year 2018 - 2019, the serotype has been identified by Whole genome sequencing (WGS) by the CFIA at the Ottawa Laboratory Carling. Salmonella bacteria were detected in 1,860 of the 15,649 feed samples collected during this period. Between 2018 and 2022 there were few feed samples where 2 different serotypes were detected within the same sample. That is the reason of the total number of isolates 1,867 is greater that the total of non-compliant samples (Salmonella detected) 1,860. A total of 121 serotypes were identified in the 1,867 isolates detected (Salmonella species taxonomy and serotype names are reviewed in appendix II). That while 360 isolates were of unknown serotype and 8 isolates were found untypable. The serotype composition within the Salmonella bacteria isolated from feed was highly diverse. This is likely a reflection of the multiple sources of Salmonella contamination in feed.

Appendix I: Salmonella testing of feed samples by fiscal year and CFIA area

Salmonella testing of feed samples by fiscal year and feed type

Salmonella testing of feed samples by fiscal year and target species

Appendix II: Review of Salmonella Taxonomy and Serotypes

Species and subspecies

The genus Salmonella currently contains 2 species; bongori and enterica. These species were determined on the basis of genetic relatedness, as determined by DNA hybridization experiments. Salmonella enterica is further divided into 6 subspecies that are designated by names and by Roman numerals: I enterica, II salamae, IIIa arizonae, IIIb diarizonae, IV houtenae and VI indica. These subspecies are differentiated by their biochemical reactions. Salmonella strains from all Salmonella subspecies can be found in cold-blooded animals but only strains from Salmonella enterica subspecies enterica (I) are found in warm-blooded animals. Salmonella subspecies I enterica is therefore of greatest interest to human and animal health.

• Salmonella bongori
• Salmonella enterica subspecies I enterica
• Salmonella enterica subspecies II salamae
• Salmonella enterica subspecies IIIa arizonae
• Salmonella enterica subspecies IIIb diarizonae
• Salmonella enterica subspecies IV houtenae
• Salmonella enterica subspecies VI indica

Serotypes (Serovars)

Serotyping is a serological procedure based on the Kauffmann-White scheme which classifies strains of microorganisms into different groups based on their antigenic composition. The Kauffmann-White scheme is maintained by the World Health Organization at the Institut Pasteur in Paris and strain serotyping is performed only at specialized serotyping laboratories.

Serotyping or antigenic classification of Salmonella is based on antibody reaction with 2 types of surface antigens: somatic O antigens and flagellar H antigens (phase 1 and phase 2). O antigens are polysaccharides present on the outer membrane of gram negative bacteria. H antigens are proteins present on the bacterial flagella. Salmonella serotypes may express either 1 type of H antigen (monophasic), or 2 types of H antigen (diphasic).

A Salmonella serotype is represented by an antigenic formula which is determined by a unique combination of reactions of cell surface antigens (immunologic characterization). For example, the antigenic formula for Salmonella enterica subspecies enterica serotype Typhimurium is 1,4,[5],12:i:1,2 where "1" indicates the subspecies, "4,[5],12" indicates the reaction to O-antigen antisera, "i" indicates the reaction to Phase 1 antisera of the H-antigen and "1,2" indicates the reaction to Phase 2 antisera of the H-antigen.

The serotype name usually refers to the geographic location where the specific Salmonella strain was first isolated, although older names sometimes indicated the animal species from which it was isolated or the clinical syndrome that it caused. To emphasize that these serotype names do not represent separate species, the serotype name is not italicized and the first letter is capitalized (for example. Salmonella enterica subspecies enterica serovar Typhimurium). For convenience, this designation is commonly shortened to include only the genus and serotype name (for example, Salmonella Typhimurium or S. Typhimurium).

Within the Salmonella enterica species, there are over 2,500 Salmonella serotypes of which approximately 60% belong to subspecies I (enterica, found in warm-blooded animals) and these account for about 99% of human infections.

List of references

• Brenner, F. W., Villar, R. G., Angulo, F. J., Tauxe, R., and Swaminathan, B., 2000. Salmonella nomenclature. J Clin Microbiol 38:2465-7.
• Grimont, P. A. D., and Weill, F. X., 2007. Antigenic Formulae of the Salmonella Serovars. 9th Edition. WHO Collaborating Centre for Reference and Research on Salmonella, Paris.
• Ryan, M., O'Dwyer, J., and Adley, C. C., 2017. Evaluation of the Complex Nomenclature of the Clinically and Veterinary Significant Pathogen Salmonella. BioMed Research International, vol. 2017, Article ID 3782182, 6 pages.
• Tindall, B. J., Grimont, P. A., Garrity, G. M., and Euzeby, J. P., 2005. Nomenclature and taxonomy of the genus Salmonella. Int J Syst Evol Microbiol 55:521
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