Carrier status of Streptococcus suis in the palatine tonsils of apparently healthy slaughtered pigs of India

ABSTRACT

Streptococcus suis is an emerging bacterial pathogen of huge economic impact to the swine industry worldwide. The information regarding the carrier status of S. suis in the slaughtered pigs along with its genetic characterization is not available in Indian pig population, which needs to be addressed for the therapeutic and preventive measures. In the present study, 563 palatine tonsils of apparently healthy slaughtered pigs were probed for the prevalence, and genetic characterization of S. suis and prevalence were found to be 15.45% and 32.68% by bacteriological and molecular methods, respectively. In 87 isolates recovered, 6 cps-types were detected showing the predominance of serotype 7 (24.13%) and 5 (18.39%), whereas 11 cps-types were detected in tonsillar DNA involving cps-types 9 (28.26%) and 7 (14.13%) as the major serotypes with arcA⁺/sly⁺/epf⁺/mrp⁻ being the prevalent genotype. The histopathological changes with the immunodetection of S. suis antigen confirmed its persistence in asymptomatic carriers. Of 87 bacterial isolates, 7 isolates (serotypes 7 & 2) were pathogenic to Swiss albino mice showing the classical lesions of meningitis and septicemia. The presence of virulent serotypes of S. suis in healthy slaughtered pigs suggests a great health risk to the people engaged in piggery operations and in-contact pigs.

KEYWORDS:

• Carrier pigs
• immunohistochemistry
• multiplex PCR
• palatine tonsil
• pathology
• S. suis
• serotypes
• virulence genes

Highlights

1. Our study provides the first analysis of diversity of Streptococcus suis from the slaughtered pigs of India.

2. The serotypes 5, 7, and 9 were the major serotypes detected in the palatine tonsils of apparently healthy slaughtered pigs of India.

3. Majority of the serotypes belonged to arcA⁺/sly⁺/epf⁺/mrp⁻ genotype.

4. The histopathological alterations with the immunodetection of S. suis antigen in the palatine tonsils confirm its persistence.

5. Mouse pathogenicity testing confirmed the pathogenic potential of serotype 2 & 7 isolates of S. suis.

Acknowledgments

The authors are thankful to the Director, ICAR-Indian Veterinary Research Institute, Izatnagar, India for providing necessary facilities to carry out this work. We also thank staffs of Central Histopathological Laboratory (CHL) for their laboratory assistance.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The authors are thankful to DST-SERB for carrying out this investigation as a part of project work (Science and Engineering Research Board ECR/2017/000878.