TRENDS IN THE RESISTANCE TO ANTIMICROBIAL AGENTS OF STREPTOCOCCUS-SUIS ISOLATES FROM DENMARK AND SWEDEN

This study was conducted to determine the MIC values of historical and contemporary Streptoccocus suis (serotypes 2 and 7) from Denmark and S, suis (serotype 2) from Sweden. A total of 52 isolates originating f rom 1967 through 1981 and 156 isolates from 1992 through 1997 in Denma rk and 13 isolates from Sweden were examined for their MICs against 20 different antimicrobial agents. Most antimicrobials were active again st most isolates, A frequent occurrence of resistance to sulphamethoxa zole was observed, with most resistance among historic isolates of ser otype 7 and least resistance among isolates from Sweden. A large numbe r of the isolates was resistant to macrolides. However, all historic s erotype 2 isolates from Denmark were susceptible, whereas 20.4% of the contemporary isolates were resistant. Among serotype 7 isolates 23.3% of the historic isolates were resistant to macrolides, whereas resist ance was found in 44.8% of the contemporary isolates. All isolates fro m Sweden were susceptible to macrolides, Time-associated frequency of resistance to tetracycline was also found. Only a single historic isol ate of serotype 2 was resistant to tetracycline, whereas 43.9% of the contemporary serotype 2 isolates and 15.5% of the contemporary serotyp e 7 isolates were resistant. Only one (7.7%) of the isolates from Swed en was resistant. The differences in resistance between historic and c ontemporary isolates from Denmark were statistically significant. This study demonstrated a significant serotype-associated difference in th e susceptibility to macrolides and tetracycline and demonstrated that an increase in resistance among S. suis isolates has taken place durin g the last 15 years to the two most commonly used antimicrobial agents (tylosin and tetracycline) in pig production in Denmark. (C) 1998 Els evier Science B.V. All rights reserved.