MYCOBACTERIOSIS IN WILD BOARS: STUDY FOR THE USE OFLIQUID MEDIA AND ANTIBIOTIC RESISTANCE

A retrospective study (2004-2010) on 24 Mycobacterium bovis strains isolated from wild boars (Sus scrofa) (n=18) and cattle (n=6) in Imperia province (Savona province has been included in the study just in 2006) was performed to detect the prevalence and distribution of antibiotic-resistant strains. Actually, in this area cases of M. bovis infections in wild boar were related to cases in cattle herds due to the overlapping of their respective habitat and pasture areas, suggesting the role of these animals as bio-indicator of the presence of M. bovis in the environment and, in consequence, in farm animals. Susceptibility of all M. bovis strains to antituberculous drugs (isoniazid-INH, rifampicin-RIF, ethambutol-EMB and streptomycin-STR) was detected by proportion method on Lowenstein-Jensen (LJ) medium using recommended critical concentration, while the 6 bovine M. bovis strains were tested by Versatrek method on liquid medium, too. The proportion method to assess the M. bovis susceptibility to INH, RIF, EMB and STR is the gold standard, but the use of ancillary liquid culture systems (Versatrek method) should be performed for the rapid and timely detection of drug-resistance in tuberculosis strains. All the western Ligurian isolates in this study were sensitive to INH, RIF, EMB and STR by the proportion method; however, light bacterial growth was pointed out in INH medium (2 samples) and in RIF-medium (1 sample). The GenoType® Mycobaterium tuberculosis- multidrug resistantplus (MTBDRplus) VER 2.0 assay was used to detect mutations in rpoB, katG, and inhA genes associated with resistance to RIF and INH on the 3 cases of light bacterial groth. No mutation in rpoB, katG, and inhA genes was detected. The six M. bovis isolates from cattle also tested by Versatrek myco susceptibility kit, Versatrek myco streptomycin kit and Versatrek myco PZA kit were fully INH, RIF and EMB sensitive, except for natural pyrazinamide resistance. A single strain of bovine origin showed resistance to STR at lower concentration (2 µg/ml), but this result was not confirmed by the proportion method. The absence of any drug resistance in cattle could be likely explained with the compulsory eradication program of bovine tuberculosis by elimination of infected animals and the ban on antituberculous drug treatments in animals. However, there is the very real opportunity for other animals in the same herd -which may be harboring tuberculosis- to receive limited antibacterial therapy for other conditions, such as respiratory disease, mastitis, or other localized infections. This may lead to the insurgence of drug resistance in M. bovis strains despite all measures adopted for their control. On the other side, considering the feeding habits of wild boars, i.e. rooting, the fact that no drug resistance was found in M. bovis strains isolated from wild boars suggests the absence of drug contamination in the environment and confirms their role of bioindicator.