Situation and antimicrobial resistance of Streptococcus suis isolated from pigs in Northern region of Thailand

Abstract

This study aims to investigate antimicrobial resistance phenotype of S. suis, examine genetics underlying antimicrobial resistance (AMR) of S. suis in pigs and pork in Northern Thailand and examine genes encoding virulence factors of S. suis in pigs and pork in Northern Thailand. A total of 59 isolates of S. suis were included. All were obtained from pigs and porks in Northern Thailand including Chiang Mai, Chiang Rai, Nan, Phayao and Mae Hong Son during April 2018 to October 2018. All were tested for their susceptibility to antibiotic and, the presence of resistance and virulence genes. All were resistant to tilmicosin. High resistance rates were observed for chlortetracycline (98.31%), clindamycin (98.31%), tetracycline (96.61%), neomycin (88.14%), erythromycin (86.44%), tylosin (79.66%), trimethroprim (74.58%), gentamicin (69.49%), oxytetracycline (69.49%), tiamulin (55.93%), sulfamethoxazole (54.24%), enrofloxacin (45.76%) and ampicillin (33.9%),. Resistance rates to ceftriofur (18.64%), chloramphenicol (10.17%), florfenicol (1.69%) were lower. All were considered multidrug-resistant (MDR). AMR phenotypes were classified into 47 patterns, of which the most common resistance pattern was CLI-CTC-ERY-GEN-NEO-OTC-TET-TIL-TYL (5.1%). Resistance genes identified were tetM (32.3%), tetO(30.5%) and mefA (8.47%). All the isolates carried arcA, but none were positive to epf. The sly gene was very common (91.5%), followed by mrp (69.5%) and hyl (37.3%). Fifteen virulence gene patterns were obtained. The most commonly identified pattern was mrp, sly, arcA, hyl (33.9%), followed by mrp, sly, arcA (28.8%) and sly, arcA (25.4%). This study confirms the important role of subclinical carrier pigs of MDR S.suis and emphasize the need for AMR monitoring/surveillance in pigs and livestock.