O7-2 First analysis of antimicrobial resistance in Brucella strains isolated in Italy

Abstract

Brucellosis is one of the world’s most widespread zoonosis. The disease affects livestock causing significant economic losses and can be acquired by humans through close contact with infected animal material or consumption of raw dairy products. While the treatment in animal brucellosis is not indicated, human brucellosis is generally treated with doxycycline combined with rifampicin or aminoglycosides. The levelsof antimicrobial resistance (AMR) in Brucella strains circulating in European countries have not been estimated. The aim of this study is to evaluate antimicrobial susceptibility of Brucella strains isolated from livestock and humans in Italy from 2019 to 2022. A total of 165 strains were analyzed: 96 B. abortus, 61 B. melitensis, two B. canis and four B. suis. Additionally, two Ochrobactrum anthropi strains, isolated from acattle and a human, were included in the study. The susceptibility to nine antimicrobials: gentamicin, streptomycin, doxycycline, tetracyciline, chloramphenicol, rifampicin, ciprofloxacin, levofloxacin and trimethoprim/sulfamethoxazole were assessed using broth microdiluition method. Minimum inhibitory concentrations (MIC) values were interpreted according to CLSI guidelines for potential bacterial agents of bioterrorism and for slow-growing bacteria. More than a half of the analyzed Brucella strains (86/163) were susceptible to all tested antibiotics. The other strains were shown to be resistant/non-susceptible to two antimicrobials, rifampicin and doxycycline, only. Four strains of B. melitensis were full resistant to rifampicin (with a MIC of 4ug/ml). Intermediate resistant to rifampicin was detected in 73/163 (44.8%) Brucella strains and six of these, identified as B. abortus, were also non-susceptible to doxycycline (with a MIC of 2 ug/ml). The two O. anthropi isolates were resistant to rifampicin and chloramphenicol and non-susceptible to streptomycin. The O. anthropi strain isolated from cattle was additionally non-susceptible to trimethoprim/sulfamethoxazole. Brucella strains isolated from wild animals show higher susceptibility to some of the tested antibiotics than strains isolated from farmed animals. The data obtained indicate that a considerate part of Brucella strains circulating in Italy show a reduced susceptibility to rifampicin, one of the commonly used antimicrobials for human treatment. This suggest that monitoring of Brucella spp. AMR in animal populations could provide indications for most effective empirical treatment regime for locally-acquired human brucellosis.