Identification of epidemic strains of Streptococcus suis by genomic fingerprinting

Abstract

A natural outbreak of Streptococcus suis meningitis in two closed swine herds was studied. DNA fingerprinting, serotyping, and biochemical profiles were assessed. Multiple serotypes were recovered from these herds. In farm A, 50 S. suis strains were isolated from 330 swabs collected. Eighteen strains belonged to serotype 2, and 32 strains belonged to serotypes 3, 5, 6, 8, 9, and 11. In farm B, 16 S. suis strains were recovered from a total of 70 samples. Eight strains belonged to serotype 7, and eight belonged to serotypes 2, 3, 5, and 8. In each epidemiological situation, a single strain characterized by a distinctive restriction fragment pattern predominated among affected penmates. The epidemic serotype 2 strain was detected in farm A in weaned pigs between the ages of 5 and 7 weeks. In contrast, the pathogenic strain in farm B belonged to serotype 7 and was isolated from pigs up to 3 weeks of age. The results from both farms strongly suggest a lateral spread of these organisms. No vertical transmission could be shown in either herd. It was concluded that genomic fingerprinting is an appropriate method to distinguish outbreak isolates of S. suis from nonoutbreak strains, within the same serotype or from epidemiologically unrelated clusters of strains.

Use of Ribotyping and Hemolysin Activity To Identify Highly Virulent Streptococcus suis Type 2 Isolates

“…The restriction endonucleases PvuII, PstI, EcoRI, and HaeIII all digested S. suis DNA in this study. As reported previously (2,22,24), a high degree of genomic heterogeneity occurs among S. suis type 2 isolates. In this study, striking differences in ribotype patterns are immediately apparent between the highly virulent and the avirulent and moderately virulent isolates.…”

“…Two isolates that had been characterized as highly virulent by clinical sign scores did not fall within the unique ribotype groups. One isolate (isolate DH5) was recovered from the brain of a pig with meningitis in Minnesota (22), but in a subsequent challenge study, it did not produce disease (10). In this study, the DH5 isolate was the most virulent isolate tested on the basis of morbidity and mortality.…”

Immunomagnetic Isolation of Streptococcus suis Serotypes 2 and 1/2 from Swine Tonsils

“…Lack of these reliable methods for important S. suis serotypes led researchers to get contradictory results. For example, pathogenic S. suis was first considered to spread only horizontally among nursery pigs, with no evidence of vertical transmission (12). However, vertical transmission of the infection has recently been reported (1,19).…”

Dilemma of the Virulence of Streptococcus suis Strains

“…For example, Okwumabua et al (9) mentioned that a field strain from Minnesota (DH5) was avirulent for pigs, whereas Staats et al (12) considered the same strain as highly virulent for the same animal species. This strain was originally isolated from the brain of a pig during an outbreak of S. suis meningitis in a closed farrow-to-finish herd and was considered as representative of the epidemic strain causing the problem in that herd (8). Controversially, this strain was considered avirulent by Galina et al 3 years later (5).…”