Establishment of a method for evaluating intracellular antibiotic efficacy in Brucella abortus-infected Mono Mac 6 monocytes

Abstract

Background: Brucellae produce chronic and often lifelong infections in natural hosts. The persistent nature of these infections is predominantly due to the capacity of these bacteria to maintain intracellular residence in host macrophages. Successful antimicrobial therapy requires eradication of brucellae from this intracellular niche. It is important to seek new and improved antimicrobials for brucellosis therapy as well as a method to efficiently evaluate their intracellular efficacy.

Objectives: For that reason, we have developed a method to evaluate intracellular drug efficacy for new and improved antimicrobials that show initial in vitro activity against Brucella species during drug screening.

Methods: Mono Mac 6 monocytes (MM6) were used because they are the only human cell line that constitutively expresses the phenotypic and functional characteristics of mature monocytes. This cell line has not previously been used with Brucella, therefore parallel studies were performed with J774 murine macrophages. Both cell lines were infected with Brucella abortus 2308 and antibiotics used clinically for treatment of brucellosis were used to determine intracellular efficacy.

Results: Significant differences in bacterial burden were observed at or above the MIC in both cell lines. Drug concentrations that fell below the MIC were found to significantly reduce intracellular brucellae only in MM6.

Conclusions: The MM6 intracellular efficacy model will provide a useful method to examine the effect of novel antimicrobials for the treatment of human brucellosis.