Isolation of Streptococcus ruminantium (Streptococcus suis-like) from diseased ruminants in Canada

Streptococcus suis is one of the most important swine bacterial pathogens and it has also been isolated from a large variety of animal species, as well as from humans (1). There are several reports on the isolation of S. suis from ruminants (1,2). Although 35 serotypes for S. suis had originally been described, 6 (serotypes 20, 22, 26, 32, 33, and 34) have been re-classified to other bacterial species. Among these, S. suis serotype 33 has been recently classified as a new species, Streptococcus ruminantium (3). The reference strain of S. suis serotype 33 was originally isolated from a lamb with arthritis (1). Biochemically, S. suis and S. ruminantium are very similar and they are not easily differentiated by biochemical tests routinely performed in a diagnostic laboratory. Many of these S. suis-like strains are also positive for the glutamate dehydrogenase gene using polymerase chain reaction (PCR) (gdh-PCR), which was widely used in the past to identify S. suis (4). To discriminate between S. suis and S. suis-like isolates, a PCR targeting the DNA repair protein gene (recN-PCR) was developed to identify "true" S. suis isolates (4). This PCR does not recognize other S. suis-like isolates, such as those belonging to serotypes 20, 22, 26, 32, 33, and 34. In addition, a PCR specific for S. ruminantium has recently been described (2). In this report, we studied 14 clinical isolates from ruminants from 2 farms in Saskatchewan, 1 farm in Prince Edward Island, and 4 farms in Québec. Ten of these isolates were recovered from diseased cattle, while 4 of the isolates originated from sheep (Table 1). All isolates were originally identified as S. suis using traditional biochemical tests. These isolates were from cases of arthritis (sometimes with septic osteomyelitis lesions), pneumonia, endocarditis, and mastitis or from purulent abscesses. One isolate was recovered from a bulk tank milk sample (Table 1). Matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) identified 9 of the isolates as S. suis, 4 as Streptococcus mitis, and 1 as Streptococcus oralis. Serotyping using a multiplex PCR assay was performed at the reference laboratory for S. suis at the University of Montreal. Five of the isolates were identified as S. suis serotype 33 and all others were considered to be untypable (5). All the isolates were negative with the S. suis-specific recN-PCR, but were positive with the newly described S. ruminantium PCR (Table 1). Isolates were further identified by 16S rRNA and chaperonin-60 (cpn60) gene sequencing (6). The sequence analysis with both genes confirmed that all of the isolates were S. ruminantium (Table 2).