Prevalence of Streptococcus suis genotypes in wild boars of Northwestern Germany

Abstract

Invasive serotype 2 (cps2+) strains of Streptococcus suis cause meningitis in pigs and humans. Four case reports of S. suis meningitis in hunters suggest transmission of S. suis through the butchering of wild boars. Therefore, the objective of this study was to investigate the prevalence of potentially human-pathogenic S. suis strains in wild boars. S. suis was isolated from 92% of all tested tonsils (n=200) from wild boars. A total of 244 S. suis isolates were genotyped using PCR assays for the detection of serotype-specific genes, the hemolysin gene sly, and the virulence-associated genes mrp and epf. The prevalence of the cps2+ genotype among strains from wild boars was comparable to that of control strains from domestic pig carriers. Ninety-five percent of the cps2+ wild boar strains were positive for mrp, sly, and epf*, the large variant of epf. Interestingly, epf* was significantly more frequently detected in cps2+ strains from wild boars than in those from domestic pigs; epf* is also typically found in European S. suis isolates from humans, including a meningitis isolate from a German hunter. These results suggest that at least 10% of wild boars in Northwestern Germany carry S. suis strains that are potentially virulent in humans. Additional amplified fragment length polymorphism analysis supported this hypothesis, since homogeneous clustering of the epf* mrp+ sly+ cps2+ strains from wild boars with invasive human and porcine strains was observed.

FIG. 1.

Representative MP-PCR of S. suis strains. Lanes: 1, 100-bp ladder; 2, meningitis isolate from a German hunter (strain 199) (27); 3 to 9, isolates from tonsils of wild boars (W183.1, W168.1, W102.2, W31.3, W162.1, W151.2, and W184.1); 10, water; 11, reference strain P1/7; 12, serotype 1 reference strain DSM 9683; 13, mixture of different reference strains (29).

FIG. 2.

Representative mrp (A) and epf (B) PCR of S. suis strains for differentiation of size variants. (A) Lane 1, 100-bp ladder; lane 2, meningitis isolate from a German hunter (strain 199) (27); lanes 3 to 6, isolates from tonsils of wild boars (W183.1, W123.3, W131.1, and W108.2); lanes 7 to 12, mrp reference strains (V7353/1, 90-2741-7, A5373/4, A3286/94, D282, and A5140/3/96) (29). (B) Lane 1, 100-bp ladder; lane 2, strain 199 (see A); lane 3, isolate from a butcher (MAC 724); lanes 4 and 5, cps2⁺ isolates from tonsils of wild boars (W50.2 and W50.3); lane 6, negative control (A5683/93); lane 7, epf⁺ control strain (P1/7); lanes 8 to 12, epf* reference strains (lane 8, 1890; lane 9, 2840; lane 10, 3921; lane 11, 3988; lane 12, 3995) (29, 31).

FIG. 3.

AFLP dendrogram of 70 S. suis isolates from wild boars (indicated by “W” under isolate), 5 human strains (indicated by “H” under origin), and 9 porcine reference strains (indicated by “R” under origin). The pairwise comparison of band patterns was performed using the Pearson product-moment correlation coefficient. The numbers in the parentheses specifying the epf* variant are equivalent to the names of the reference strains with the same-sized epf* (29, 31), except for the variant found only in wild boars (epf³⁰⁰⁴). The “+” under epf and mrp refers to the variants that encode the 110-kDa EF and 136-kDa MRP, respectively. The numbers under origin refer to the 12 regions of sample collection in Northwestern Germany.