Streptococcusmacedonicus ACA-DC 198, a bacteriocin producer isolated from Greek Kasseri cheese, was used in a series of invitro and invivo experiments in order to evaluate its pathogenic potential. The strain was examined invitro for haemolytic activity, antibiotic resistance and presence of pathogenicity genes encountered in Streptococcuspyogenes. Subsequently, the strain was orally administered to mice (8.9 log cfu daily), continuously over a period of 12 weeks, in order to ascertain the effects of its long term consumption on animal health and gastric inflammation. S.macedonicus ACA-DC 198 was found to be non-haemolytic and sensitive to ampicillin, chloramphenicol, ciprofloxacin, erythromycin, streptomycin, tetracycline, and vancomycin, with the only resistance observed against kanamycin. PCR amplification and DNA–DNA hybridization did not reveal the presence of any of the S.pyogenes pathogenicity genes examined, namely emm, scpA, hasA, speB, smez2, speJ, sagAB, hylA, ska, speF, speG, slo, hylP2 and mga. In the mouse study, no detrimental effects were observed in the behaviour, general well being, weight gain and water consumption of the animals receiving S.macedonicus ACA-DC 198. Histologic analysis showed no evidence of inflammation in the stomach of the animals receiving S.macedonicus ACA-DC 198, while faecal microbiological analysis revealed that the strain retained its viability passing through the mouse gastrointestinal tract. Finally, no evidence of translocation to the liver, spleen and mesenteric lymph nodes was observed. In conclusion, none of the examined virulence determinants were detected in S.macedonicus ACA-DC 198 and its long term, high dosage oral administration did not appear to induce any pathogenic effect in mice.