Streptococcus suis is an important pathogen of pigs and occasionally causes serious human disease. However, little is known about the S. suis population structure, the clonal relationships between strains, the potential of particular clones to cause disease, and the relevance of serotype as a marker for epidemiology. Here we describe a multilocus sequence typing (MLST) scheme for S. suis developed in order to begin to address these issues. Seven housekeeping gene fragments from each of 294 S. suis isolates obtained from various S. suis diseases and from asymptomatic carriage representing 28 serotypes and nine distinct countries of origin were sequenced. Between 32 and 46 alleles per locus were identified, giving the ability to distinguish >1.6 × 10 ¹¹ sequence types (STs). However only 92 STs were identified in this study. Of the 92 STs 18 contained multiple isolates, the most common of which, ST1, was identified on 141 occasions from six countries. Assignment of the STs to lineages resulted in 37 being identified as unique and unrelated STs while the remaining 55 were assigned to 10 complexes. ST complexes ST1, ST27, and ST87 dominate the population; while the ST1 complex was strongly associated with isolates from septicemia, meningitis, and arthritis, the ST87 and ST27 complexes were found to contain significantly higher numbers of lung isolates. In agreement with the observed distribution of disease-causing isolates of S. suis , most isolates previously characterized as of high virulence in porcine infection models belong to ST1, while isolates belonging to other STs appear to be less virulent in general. Finally nine STs were found to contain isolates of multiple serotypes, and many isolates belonging to the same serotypes were found to have very disparate genetic backgrounds. As well as highlighting that the serotype can often be a poor indicator of genetic relatedness between S. suis isolates, these findings suggest that capsular genes may be moving horizontally through the S. suis population.

Pulsed-field gel electrophoresis (PFGE) was used to investigate the diversity of Streptococcus suis isolates of various serotypes recovered from swine clinical samples in Spain. Capsular types 9 (64.9%) and 2 (14.8%) were the most frequently isolated serotypes followed by serotype 7 (5.9%) and serotype 8 (4.3%). The PFGE results of this study with 60 different pulsotypes indicate a great genetic diversity among the S. suis isolates, which is consistent with the broad distribution of S. suis in the swine population. Forty-five percent of the pulsotypes corresponded to single isolates, no pulsotype was common to all farms, and at least 3 different pulsotypes were isolated in 56% of herds in which more than 3 clinical isolates were analyzed. These results reveal a great diversity both between and within herds throughout the strains of S. suis studied, demonstrating that different strains of S. suis are associated with infection in pigs. Some pulsotypes were more frequently isolated and exhibited a wider distribution over herds than others, and were the unique or predominant strains in several herds, suggesting the existence of a prevalent or a few prevalent clones responsible for a large proportion of clinical cases. Overall, the great genetic heterogeneity of the clinical strains of S. suis , the isolation of different strains within the same herd, and the predominance of particular strains in some herds are evidence that infection by S. suis is a dynamic process and reinforce the idea that the epidemiology of S. suis infection is very complex.

Streptococcus suis is an economically important pathogen of pigs responsible for a variety of diseases including meningitis, septicemia, arthritis, and pneumonia, although little is known about the mechanisms of pathogenesis or virulence factors associated with this organism. Here, we report on the distribution and genetic diversity of the putative virulence factor suilysin, a member of the thiol-activated toxin family of gram-positive bacteria. On the basis of PCR analysis of over 300 isolates of S. suis , the suilysin-encoding gene, sly , was detected in 69.4% of isolates. However, sly was present in a considerably higher proportion of isolates obtained from cases of meningitis, septicemia, and arthritis (>80%) and isolates obtained from asymptomatic tonsillar carriage (>90%) than lung isolates associated with pneumonia (44%). With the exception of serotypes 1, 14, and 1/14, there was no strong correlation between the presence of suilysin and serotype. Analysis of the genetic diversity of suilysin by restriction fragment length polymorphism and sequence analysis found that the suilysin gene, where present, is highly conserved with a maximum of 1.79% diversity at the nucleotide level seen between sly alleles. Assays of hemolytic activity and hybridization analysis provided no evidence for a second member of the thiol-activated toxin family in S. suis . Inverse PCR was used to characterize regions flanking sly , which in turn allowed the first characterization of the equivalent region in a strain lacking sly . Sequence comparison of these regions from sly -positive (P1/7) and sly -negative (DH5) strains indicated that two alternative arrangements are both flanked by genes with highest similarity to haloacid dehalogenase-like hydrolases (5′ end) and putative N -acetylmannosamine-6-phosphate epimerases (3′ end). However, sly appears to be completely absent from the alternative arrangement, and a gene of unknown function is located in the equivalent position. Finally, PCR analysis of multiple sly -positive and -negative strains indicated that these two alternative genetic arrangements are conserved among many S. suis isolates.

This study reports the susceptibility to antimicrobial agents of staphylococci 4 (n=105) isolated from dogs, and the factors associated with this resistance. The study 5 animals were 23 healthy dogs (group A), 24 with first-time pyoderma (group B), and 27 6 with recurrent pyoderma that had undergone long-term antibiotic treatment (group C). 7 Staphylococci were more commonly isolated from the pyoderma-affected than the 8 healthy dogs (p<0.0001). 9 10 Some 78% of the isolates were resistant to at least one antimicrobial agent. 11 Resistance to amoxicillin-clavulanate,cephalosporins (OR 4.29, 95% CI [1.15, 16.3] 12 respectively), enrofloxacin (OR 9.47, 95% CI [1.53, 58.5]) and ciprofloxacin (OR 79.7 13 95% CI [3.26, 1947.4]) was more common among group C isolates. Some 32% of all 14 the isolates were multiresistant (MR) and 10.4% were methicillin-resistant (MRS). The 15 probability of isolating MRS staphylococci in group C increased by a factor of four 16 (95% CI [1.18, 17.9]) compared to A plus B. Multi-resistant (MR) isolates were 17 obtained more commonly from urban than rural dogs (OR 3.79, 95% CI [1.09, 13.17]). 18 All the MRS staphylococci encountered were obtained from urban dogs and more 19 commonly from male dogs (p= 0.07). 20 21 This study shows that dogs bred in urban habitat, with a history of antibiotic 22 therapy in the past year represents significant risk of being carriers of isolates resistant 23 to methicillin (MRS) and other antimicrobials. These factors should be considered 24 before applying an antimicrobial treatment in veterinary clinics