[Evaluation of bacterial contamination in disinfectants for domestic use]

To evaluate disinfectants for domestic use for the presence of bacteria, identify them, and determine their tolerance level to benzalkonium chloride.

Fifty-two samples of commercially available disinfectants for domestic use were acquired at random in the metropolitan area of São Paulo, Brazil, and analyzed to detect the presence of bacterial contaminants. The isolated organisms were identified and their tolerance level to benzalkonium chloride was determined by broth macrodilution method.

Sixteen (30.77%) of fifty-two disinfectants sampled were contaminated by Gram-negative bacteria, with counts varying between 10(4) and 10(6) UFC/ml. Alcaligenes xylosoxidans, Burkholderia cepacia and Serratia marcescens were the predominant organisms found. The minimum inhibitory concentration (MIC: mg/ml) of benzalkonium chloride for these bacteria were 2.48, 1.23 and 0.30 to S. marcescens, A. xylosoxidans and B. cepacia, respectively.

The disinfectant formulation containing quaternary ammonium compounds (QACs) may be exposed to contamination by Gram-negative bacteria. The MICs of benzalkonium chloride against the isolated bacteria were low, indicating that the bacteria grown in culture media without QACs lost their tolerance to this biocide.