Antimicrobial susceptibility profile, Adherence and invasion to mammalian cells of Brucella melitensis isolates

Susceptibilities of 66 Brucella isolates were tested in vitro. All isolates were susceptible to doxycycline, gentamic in and streptomycin. In addition, propyl paraben, cresol and benzalkoniumchloride were found to be the most powerful tested preservative, disinfectant and antiseptic, respectively. All isolates adhered to and invaded into Vero cells by variable degrees. Adherence and invasion of most isolates were significantly reduced by: (1) pretreatment of test isolates with trypsin and sodium metaperiodate; (2) pretreatment of Vero cells with lipase, neuraminidase and sodium metaperiodate; (3) presence of Ca++, Mg++ and 200mM mannose in the assay medium and (4) growth of test isolates in half MICs of different antimicrobial agents. On the other hand, pretreatment of Vero cells with trypsin increased the adherence and invasion of most test isolates. No significant change in adhesion and invasion by changing the temperature from 27 degrees C to 42 degrees Cor the pH from 6 to 8. Log phase cultures showed higher adherence and invasion than stationary phase cultures.