We studied the in-vitro activity of seven antibiotics against 95 strains of Brucella melitensis isolated in blood cultures of 95 patients with brucellosis. The minimum inhibitory concentration (MIC) was measured by the agar dilution method. All strains of B. melitensis were inhibited by doxycycline at 0.25 mg/l, tetracycline at 0.5 mg/l, ciprofloxacin at 0.5 mg/l, streptomycin at 1 mg/l, ceftriaxone at 1 mg/l, rifampicin at 4 mg/l and by co-trimoxazole at 0.5/9.5 mg/l. We did not find strains resistant to any of the antibiotics studied. All antibiotics, including ciprofloxacin and ceftriaxone, showed a good in-vitro activity against B. melitensis.

The in vitro susceptibility of Brucella melitensis was examined vis-a-vis the clinical outcome in 75 patients with brucellosis. The initial MICs for Brucella isolates from patients who relapsed and from those who did not were similar. Furthermore, the MICs for isolates from patients whose infections relapsed were no different from those for original isolates. Our results clearly showed that neither initial nor subsequent antibiotic susceptibility plays a role in the likelihood of relapse of patients with brucellosis.

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The Wonderfonteinspruit, South Africa, is highly impacted by a century of gold mining activities. The aim of this study was to investigate the physico-chemical properties of the Wonderfonteinspruit and the receiving Mooi River system, the levels of antimicrobial (metals and antibiotics) resistance characteristics and heterotrophic bacteria levels in these water systems. Various physico-chemical parameters were determined. R2A agar and R2A agar supplemented with antimicrobials were used to enumerate heterotrophic bacteria. Morphologically distinct antimicrobial-resistant isolates were purified and screened for antibiotic susceptibility by a disc diffusion method. Selected isolates were identified, and minimum inhibitory concentration ranges determined. Among the antimicrobial resistant isolates, 87% were resistant to at least one antibiotic. Of these, almost 50% were resistant to more than 3 antibiotic classes. A large proportion was resistant to all 7 antibiotics tested. Phyla detected were Proteobacteria, Firmicutes and Bacteriodetes. High MIC levels for metals and antibiotics were detected among all the genera. Results demonstrate potential impacts of physico-chemical properties on levels of antimicrobial-resistant bacteria. Metal-resistant bacteria were also resistant to multiple antibiotics, suggesting that metal pollution from mining may be responsible for co-selection and maintenance of antibiotic-resistant bacteria in this aquatic system.