Sub-Inhibitory Concentrations of Rifampicin Strongly Stimulated Biofilm Production in S. aureus
Agostinho Alves Lima-e-Silva1, *, Renato Geraldo Silva-Filho1, Henry Marcel Zalona Fernandes2, Carmen Soares Meirelles Saramago1, Alice Slotfeldt Viana1, Maria José Souza3, Eduardo Matos Nogueira4
1 Department of Microbiology and Parasitology Rio de Janeiro, Biomedical Institute, Federal University of the State of Rio de Janeiro (UNIRIO), Rio de Janeiro, Brazil
2 IPPMG, Federal University of Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil
3 Federal Hospital of the State Servers, Rio de Janeiro, Brazil
4 Laboratory of Genomic, Biomedical Institute, Federal University of the State of Rio de Janeiro (UNIRIO), Rio de Janeiro, Brazil
Background and Objectives:
Staphylococcus aureus is an important pathogen and a frequent cause of infections associated with biofilm production in implantable medical devices. Biofilm production can be induced by sub-inhibitory concentrations (sub-MICs) of certain antibiotics, but few studies have researched this occurrence in S. aureus. In this study, we investigated the effect of sub-MICs of rifampicin and minocycline on biofilm production by five clinical and five non-clinical S. aureus isolates.
Microtiter Plate assay and Congo Red Agar Test were used to analyze the biofilm production. The biofilm composition was evaluated by the detachment assay with sodium metaperiodate and proteinase K.
Rifampicin sub-MICs induced very high biofilm formation in seven isolates that were non-producers in Tryptic Soy Broth. In one producer isolate, the biofilm formation level was not affected by sub-MICs of this drug. Sub-MICs of minocycline did not induce biofilm production in all isolates tested and in two producer isolates, instead, MIC/2 and MIC/4 inhibited biofilm production. The results of the drugs in combination were similar to those with rifampicin alone. The biofilm matrix was identified as polysaccharide, except for one producer isolate, classified as proteinaceous. Polysaccharide biofilm producer isolates, when grown on Congo Red Agar without sucrose, but with sub-MICs of rifampicin, showed results in agreement with those obtained in Microtiter Plate Test.
The high biofilm production induced by sub-MICs of rifampicin has potential clinical relevance, because this is one of the drugs commonly used in the impregnation of catheters. In addition, it is used adjunctively to treat certain S. aureus infections.
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* Address correspondence to this author at the Biomedical Institute Federal University of the State of Rio de Janeiro (UNIRIO), IB-DMP, Frei Caneca Street, 94 – Rio de Janeiro – RJ- Brasil; CEP: 20211-040, Tel: +55 21 2531-7890; E-mail: email@example.com