Perfil de resistência a antimicrobianos de Streptococcus suis tipo 2 isolados a partir de tonsilas de suínos de abate Antimicrobial Resistance Profile of Streptococcus suis Type 2 Isolates from Tonsils of Slaughter Pigs

Background: Streptococcus suis is an emerging micro-organism responsible for causing meningitis, septicemia, arthritis, endocarditis and pneumonia, in addition to being an occupational zoonosis. In healthy pigs S. suis is located asymptomatically in the tonsils and may be disseminators sources pigs susceptible to the pathogen. To reduce these losses it is necessary to have effective control and treatment agent, however, it is known that antimicrobial resistance is a risk point for the success of the therapy. Thus, the aim of this study was to determine the resistance profile and the minimum inhibitory concentration of antimicrobial isolates of Streptococcus suis type 2 from tonsils of pigs at slaughter. Materials, Methods & Results: Tonsil samples from 302 slaughtered pigs were from three slaughterhouses, they were isolated and typified 219 S. suis type 2. The antibiogram was performed using the technique of Disk Diffusion and Agar 209 isolates in the following antimicrobials were tested: amoxicillin (10 µg), ampicillin (10 mcg), ceftiofur (30 mcg), ciprofloxacin (5 µg), doxycycline (30 mcg), enrofloxacin (5 mcg), erythromycin (15 µg), florfenicol (30 mcg), norfloxacin (10 µg), penicillin G (10 U) and tetracycline (30 µg). And 117 isolates were subjected to minimum inhibitory concentration (MIC), the following concentrations amoxicillin, doxycycline, enrofloxacin in concentrations of 10, 20 and 30 µg and penicillin/spectinomycin 20, 40 and 60 IU. The antimicrobials that showed higher resistance were tetracycline and erythromycin. Most drugs got low resistance ( 10 µg, 1.7% (2/ 117) MIC >20 µg and 0.85% (1/ 117) MIC >30 µg enrofloxacin and 5.9% (7/117) obtained an MIC >10 µg. Discussion: Antimicrobial resistance is an important factor to be considered in the treatment of bacterial diseases, some pathogens are resistant to a wide range of drugs. This may be due to the inappropriate use of antimicrobials, especially those used as growth promoters, leading to increased incidence of bacterial resistance. The high degree of resistance to tetracycline (90.2%) and erythromycin (76.9%) observed in our study can be explained by its use in the prevention and treatment of disease without an effective control. Errors can easily occur leading to underdosing of antibiotics that lead to selection of resistant strains. However high sensibility to the group of β-lactams, quinolones and florfenicol were found, with amoxicillin and ceftiofur antimicrobials, showing greater sensitivity. These antimicrobial classes are widely used in the prophylaxis and therapy of diseases, however the high sensitivity suggests that not exert high selection pressure to S. suis. In the MIC technique, antimicrobials showed low resistance, suggesting that they are due to the higher concentrations tested in this technique when compared with the antibiogram. These results demonstrate that amoxicillin and ceftiofur are less antimicrobial resistance profile, differing tetracycline and erythromycin which showed increased resistance to antimicrobials tested.