An investigation into distribution of serotypes and antimicrobial resistance patterns of Streptococcus suis isolates from clinical cases and healthy carrier pigs
The distribution of Streptococcus suis serotypes and antimicrobial resistance patterns in clinical cases and healthy carrier pigs was investigated. Isolates were confirmed as S. suis by various biochemical techniques and serotyped using multiplex PCR amplification. Antimicrobial susceptibility testing was performed using the disk diffusion method. Recovery of S. suis was more likely in samples from suckling and nursery piglets than from sows and finishers (P <0.001), and more commonly recovered from healthy pigs as opposed to sick pigs (P <0.01). Samples from pigs in a continuous flow system were more likely to be found to be S. suis positive than those from pigs in an all-in/all-out system (P <0.01). Twenty-two different serotypes were identified, with types 5, 9, and 31 being the most common types isolated. Most isolates (94.5%) were resistant to at least one antimicrobial agent. A low prevalence of resistance was seen against ampicillin, ceftiofur, and florfenicol (<1.0%), while a high prevalence of resistance against tetracycline (84.2%), tiamulin (65.2%), and spectinomycin (40.4%) and an intermediate level of resistance to trimethoprim/sulfa (13.2%) was identified.