Susceptibility of different phases of biofilm of Klebsiella pneumoniae to three different antibiotics.

The existence of majority of bacteria in biofilm mode makes it difficult to eradicate them as antibiotics at much higher concentrations than the MICs are required to destroy these bacteria. This study investigated the effect of different classes of antibiotics on different phases of biofilm formed by Klebsiella pneumoniae. The organism was grown in different phases relevant to biofilm formation: planktonic cells at mid-log phase, planktonic cells at stationary phase, adherent monolayers and mature biofilms and their susceptibility to different classes of antibiotics was assessed. The results showed that planktonic organisms were susceptible to ciprofloxacin, amikacin and piperacillin, and their MBC values were same or eight times higher than their corresponding MICs. MBC of ciprofloxacin and amikacin was found to be four and eight times higher for monolayer than planktonic cells. On the other hand, MBC of piperacillin was >1024 μg ml(-1). K. pneumoniae in a biofilm growth mode was more resistant to antibiotics than all other modes. The effect of amikacin and ciprofloxacin on young and older biofilms, at the highest achievable serum concentrations, was also examined. It was observed that amikacin at a concentration of 40 μg ml(-1) was able to eradicate the young biofilms; however, with increase in the age of the biofilm, it became completely ineffective. Calcofluor staining suggested increased production of exopolysaccharide in older biofilm compared with younger biofim that might be responsible for the increased resistance of older biofilm of K. pneumoniae to antibiotics.