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Assessment of pig saliva as a Streptococcus suis reservoir and potential source of infection on farms by use of a novel quantitative polymerase chain reaction assay

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  • 1 Research Center for Food Safety, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan.
  • | 2 Research Center for Food Safety, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan.
  • | 3 Research Center for Food Safety, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan.
  • | 4 Research Center for Food Safety, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan.
  • | 5 Research Center for Food Safety, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan.
  • | 6 Research Center for Food Safety, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan.
  • | 7 Department of Microbiology, Graduate School of Medicine, Kyoto University, Yoshida-Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan.
  • | 8 Department of Microbiology, Graduate School of Medicine, Kyoto University, Yoshida-Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan.
  • | 9 Department of Microbiology, Graduate School of Medicine, Kyoto University, Yoshida-Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan.
  • | 10 Research Center for Food Safety, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan.

Abstract

OBJECTIVE To evaluate colonization of Streptococcus suis and Streptococcus parasuis on pig farms in Japan and to identify sources of infections.

SAMPLE Saliva, feces, and vaginal swab samples from 84 healthy pigs of several growth stages on 4 farms and swab samples of feed troughs and water dispensers at those farms.

PROCEDURES Samples were collected from August 2015 to June 2016. Two quantitative PCR (qPCR) assays (one for S suis and the other for S parasuis) were designed for use in the study. The novel qPCR assays were used in combination with previously described qPCR assays for S suis serotype 2 or 1/2 and total bacteria. Relative abundance of bacteria in each sample was evaluated.

RESULTS Streptococcus suis was detected in all saliva samples and some of the other samples, whereas S parasuis was not detected in any of the samples, including saliva samples, which indicated a difference in colonization preference. The ratio of S suis to total bacteria in saliva appeared to increase with age of pigs. Streptococcus suis serotype 2 or 1/2 was detected in a few saliva samples and feed trough swab samples at 2 farms where S suis infections were prevalent.

CONCLUSIONS AND CLINICAL RELEVANCE Saliva, especially that of sows, appeared to be a reservoir and source of S suis infection for pigs. The qPCR assay described here may provide an effective way to monitor for S suis in live pigs, which could lead to effective disease control on pig farms.

Abstract

OBJECTIVE To evaluate colonization of Streptococcus suis and Streptococcus parasuis on pig farms in Japan and to identify sources of infections.

SAMPLE Saliva, feces, and vaginal swab samples from 84 healthy pigs of several growth stages on 4 farms and swab samples of feed troughs and water dispensers at those farms.

PROCEDURES Samples were collected from August 2015 to June 2016. Two quantitative PCR (qPCR) assays (one for S suis and the other for S parasuis) were designed for use in the study. The novel qPCR assays were used in combination with previously described qPCR assays for S suis serotype 2 or 1/2 and total bacteria. Relative abundance of bacteria in each sample was evaluated.

RESULTS Streptococcus suis was detected in all saliva samples and some of the other samples, whereas S parasuis was not detected in any of the samples, including saliva samples, which indicated a difference in colonization preference. The ratio of S suis to total bacteria in saliva appeared to increase with age of pigs. Streptococcus suis serotype 2 or 1/2 was detected in a few saliva samples and feed trough swab samples at 2 farms where S suis infections were prevalent.

CONCLUSIONS AND CLINICAL RELEVANCE Saliva, especially that of sows, appeared to be a reservoir and source of S suis infection for pigs. The qPCR assay described here may provide an effective way to monitor for S suis in live pigs, which could lead to effective disease control on pig farms.

Supplementary Materials

    • Supplementary Figure S1 (PDF 55 kb)
    • Supplementary Figure S2 (PDF 56 kb)
    • Supplementary Table S1 (PDF 91 kb)
    • Supplementary Table S2 (PDF 71 kb)
    • Supplementary Table S3 (PDF 72 kb)

Contributor Notes

Dr. Arai's present address is Division of Microbiology, National Institute of Health Sciences, Tonomachi 3-25-26, Kawasaki-ku, Kawasaki, Kanagawa 210-9501, Japan.

Dr. Watanabe's present address is Department of Chemistry, School of Dentistry, Nihon University, Chiyoda-ku, Tokyo 101-8310, Japan.

Dr. Tohya's present address is Pathogenic Microbe Laboratory, Research Institute, National Center for Global Health and Medicine, Toyama 1-21-1, Shinjuku-ku, Tokyo 162-8655, Japan.

Dr. Murase's present address is Parasitic Diseases Unit, Department of Infectious Diseases, Faculty of Medicine, University of Miyazaki, Kiyotake-cho, Miyazaki 889-1692, Japan.

Address correspondence to Dr. Watanabe (watanabe.takayasu@nihon-u.ac.jp).