Study of the relationship between untypable and typable isolates of Streptococcus suis recovered from clinically ill and healthy nursery pigs.

Streptococcus suis naturally colonizes the upper respiratory tract of pigs and can lead to severe disease conditions. Although there are several serotypes associated with disease, untypable isolates have also been observed. The objective of this study was to investigate the relatedness of untypable S. suis isolates detected in clinical cases and healthy pigs in Ontario, Canada, and their relation to typing serotypes. One hundred fifty-six isolates obtained from 33 cases and 26 farm-and-pen-matched control pigs were sequenced using Illumina HiSeq sequencing. Protein sequences of the capsular polysaccharide genes (cps) were identified and analyzed using a maximum likelihood tree. Among the 27 untypable isolates, 3 were from systemic sites of cases and 13 and 11 were from upper respiratory sites of cases and controls, respectively. One hundred fifty-six isolates were grouped into 17 distinct groups based on the cps gene tree. Isolates from these 17 distinct individual cps groups were distributed among a minimum of one farm and maximum of eight farms. Untypable isolates were detected in 12 of those groups and each cps group had untypable isolates present amongst multiple farms. Interestingly, the three systemic untypable isolates not only coexisted with other serotypes found in the same location of the same pigs but were also found among different cps groups. These isolates are of interest and warrant further investigation. Overall, a wide diversity of S. suis among untypable isolates was observed in this study.

A Case-Control Study to Investigate the Serotypes of S. suis Isolates by Multiplex PCR in Nursery Pigs in Ontario, Canada.

: Streptococcus suis naturally inhabits the tonsils and nasal cavities of pigs. Some strains can cause systemic infection, leading to a wide range of diseases. A case-control study was conducted to (i) examine serotypes isolated from systemic sites (blood/meninges/spleen) in cases, (ii) determine whether serotypes in systemic sites were found in upper respiratory sites (tonsil/nasal cavity) of the same cases, and (iii) determine the serotypes in upper respiratory sites of case and farm and pen- matched controls. In total, 606 samples from 128 pigs were cultured for S. suis. The isolates were examined for presence of gdh and recN genes by polymerase chain reaction (PCR) and were identified as S. suis if both genes were present. The S. suis isolates were then serotyped using a two step-multiplex PCR. Serotypes 9 (n = 9), (2,1/2) (n = 7) and untypable isolates (n = 7) were most commonly found in systemic sites. Detection of serotypes 9 (p = 0.03) in upper respiratory sites were positively associated with their detection in systemic sites of cases, while a trend was seen with serotype (2,1/2) (p = 0.07). Last, no association between serotypes recovered from upper respiratory sites of cases and controls could be detected. Untypable isolates were detected in high frequency, which warrants further investigation. This study confirms that a variety of serotypes can be found in commercial swine production and shows a difference in serotypes recovered from systemic sites in pigs with clinical signs of S. suis infections.

Antimicrobial resistance of Streptococcus suis isolates recovered from clinically ill nursery pigs and from healthy pigs at different stages of production.

Streptococcus suis isolates (N = 379) from clinically ill pigs and from healthy pigs were tested for antimicrobial susceptibility using a disk diffusion method. Isolates from clinical cases had a higher prevalence of resistance compared with isolates from healthy pigs. There was a high to moderate prevalence of resistance to antibiotics commonly used in nursery pig diets such as tetracycline (84.2%), tiamulin (65.2%), and spectinomycin (40.4%). There was a low prevalence of resistance, however, to antimicrobials that are only used as parenteral treatments and not added to feed (e.g., ceftiofur, florfenicol). These findings should help practitioners in choosing appropriate drugs for use on Ontario swine farms.

Résistance antimicrobienne des isolats de Streptococcus suis récupérés de porcs en santé à différents stades de production et de porcelets de pouponnière cliniquement malades. Des isolats de Streptococcus suis (N = 379) provenant de porcs cliniquement malades et de porcs en santé ont été testés pour la susceptibilité antimicrobienne en utilisant une méthode de diffusion par disque. Les isolats des cas cliniques avaient une prévalence accrue de résistance comparativement aux isolats de porcs en santé. Il y avait une prévalence élevée à modérée de résistance aux antibiotiques communément utilisés dans les diètes des porcelets de pouponnière, dont la tétracycline (84,2 %), la tiamuline (65,2 %) et la spectinomycine (40,4 %). Par contre, il y avait une faible prévalence de la résistance aux antimicrobiens qui étaient seulement utilisés comme traitements parentéraux et non ajoutés aux aliments (p. ex., ceftiofur, florfénicol). Ces constatations devraient aider les praticiens à choisir les médicaments appropriés pour utilisation dans les fermes porcines de l'Ontario.(Traduit par Isabelle Vallières).

An epidemiological study of Streptococcus suis serotypes of pigs in Ontario determined by a multiplex polymerase chain reaction.

The purpose of the study was to identify the serotypes of Streptococcus suis from tonsil swabs in clinically ill and healthy pigs in Ontario using a multiplex polymerase chain reaction (PCR) method. Although 22 different serotypes were identified, most isolates were S. suis-like bacteria or untypable.

Étude épidémiologique des sérotypes Streptococcus suisdes porcs en Ontario déterminés par amplification en chaîne par polymérase multiplexe. Le but de cette étude consistait à identifier les sérotypes de Streptococcus suis provenant d'écouvillons des amygdales chez des porcs cliniquement malades et en santé en Ontario en utilisant une méthode multiplexe d'amplification en chaîne par polymérase (PCR). Même si 22 sérotypes différents ont été identifiés, la plupart des isolats étaient des bactéries de type S. suis ou non typables.(Traduit par Isabelle Vallières).