0 compared to a pH of 7.0. In their study, all the Quinolones exhibited very low bactericidal activities against the 21 tested strains, regardless of the pH, with a MBC90s (minimal bactericidal concentration) of ≥8 mg/liter. In addition, Akova et al.20 revealed that only rifampicin and doxycycline retained sufficient activity against Brucella at a pH of 5.0, in contrast to the other tested antibiotics. The authors showed that the rifampicin activity increased two to eightfold at the acidic pH. Antibiotic combination studies have revealed an absence of synergism between Quinolones and other antibiotics against Inhibitors,research,lifescience,medical B. melitensis.22,23 Akova et al.20 studied the combination of ofloxacin-rifampicin
against 20 isolates Inhibitors,research,lifescience,medical at pH 7.0 and 5.0 and found antagonism in 17 isolates and indifference in 3 isolates at pH 7.0. In contrast, at pH 5.0, this combination exhibited antagonism, indifference, additive effects, and synergy in 7, 8, 1, and 4 isolates, respectively. The combination of rifampicin-doxycycline was found to be the most synergistic. On the hand, and in their efforts to evaluate the susceptibility of B. melitensis against several antibiotics,
Qadri et al.24 reported cross-resistance of B. melitensis isolates to all Quinolones noted after therapy with ciprofloxacin. A good activity of ciprofloxacin has been reported in many in vitro studies.25,26 In addition, Inhibitors,research,lifescience,medical Baykam et al.27 in a study performed in Turkey and Dimitrov et al.28 in a study performed in AL Kuwait28 found that all their isolates were susceptible to ciprofloxacin, but 9.6%
and 8% of the isolates were resistant to rifampicin in vitro, respectively. In our study, we detected no differences regarding the individual antibiotic Inhibitors,research,lifescience,medical activity when we tested ciprofloxacin (MICrange: 0.125-8 μg/ml at both pH levels) Inhibitors,research,lifescience,medical or sparfloxacin (MICrange: 0.125-4 μg/ml at pH 7.0, and 0.25-4 μg/ml at pH 5.0) against the Brucella isolates from any Syrian SB203580 in vitro region at either pH value. At pH 5.0, the tetracycline activity was reduced in the Central region isolates and its susceptibility in the Southern region was decreased at pH 5.0 compared with that at pH 7.0 (P<0.0007). The rifampicin activity was very low in the Coastal and the Northern regions at both pH levels (MICrange: 32-64 μg/ml). In addition, rifampicin-resistant isolates were observed in these two regions (18 and 28 resistant isolates, respectively). However, one of the most unexpected results Sitaxentan in this study was the very poor activity of streptomycin against all the Brucella isolates (MICrange>128 μg/ml), which has not been published previously.20,22 We suggest that this resistance to streptomycin could have been developed as a result of the aggressive administration of this antibiotic in the treatment for all causes of bovine udder infection cases in Syria. Moreover, in another study performed in our laboratory, we found that the MICrange was 0.125-16 μg/ml for ofloxacin and 0.