Relationship between antibiotic susceptibility and biofilm production in a clinical strain of Burkholderia cepacia complex

Infections caused by Burkholderia cepacia complex in patients with cystic fibrosis (CF) are often related to increased mortality. One of the mechanisms that makes the bacteria more resistant to the action of antibiotics is the ability to produce biofilm. It has been compared the antibiotic resistance of two clinical isolates of a biofilm-producing strain called BTS-2, responsible for chronic pulmonary infection in a CF patient. Bacteria were incubated in both Yeast Extract Mannitol Medium (YEM) and Mueller Hinton Broth (MHB) at 30°C for 24 hours. Biofilm was quantified by spectrophotometer readings (OD570) of the extracted crystal violet. By microdilution broth, we evaluated the minimum concentration of antibiotic inhibiting the growth of the planktonic form (MIC); by the technology “Calgary Biofilm Device” and by Resazurin, we evaluated the susceptibility of sessile forms (BIC). Data demonstrate that the microorganism in the course of time changed its sensitivity to some of the antibiotics tested. The comparison between sessile and planktonic forms of BTS2 pre-incubated in MHB showed that sessile forms increased their resistance to antibiotics in a few cases only. BICs of BTS2 pre-incubated in YEM, where the strain produced an amount of biofilm significantly lower than in MHB, showed a higher susceptibility to 4 of the 10 antibiotics tested. Our data showed that the susceptibility of sessile forms of a strain is not always lower than the susceptibility of its planktonic forms and that culture medium can affect significantly the biofilm production.