In vitro antibacterial efficacy of 14 commercially available disinfectants against the hospital pathogen Stenotrophomonas maltophilia was tested. The test disinfectants included 5 “pure” quartenary ammonium compounds (QACs) and 9 combination formulations with QACs as the major ingredient. Antibacterial efficacy was expressed as MIC, ED50 and inhibition of the rate of incorporation of radioactive precursors [14C] adenine and [14C] leucine. Based on their activity, the disinfectants were divided into four groups. Group I characterized by high inhibitory activity (MIC 0.045–0.09 µg/ml) comprised benzalconium chloride and Triquart. Group II included formulations with good antibacterial activity (MIC 0.19–0.78 µg/ml) while group III formulations showed MICs between 1.56 and 25 µg/ml. The less active Cetrimid (MIC 50–100 µg/ml) was classified into group IV. When effects on biosynthetic processes expressed as R values (IC50 Ade : IC50 Leu) were tested, R < 1 was only recorded for the following formulations: Hexaquart plus, Diesen forte, Sokrena, Forten, ID 212 and Cetrimid. Lower values of IC50 Ade and IC50 Leu are suggestive of effects on the synthesis of nucleic acids and proteins leading to inhibition of the two precursors. Endogenous respiration was almost 50 % inhibited by Cetrimid and Microbac forte at a concentration of 0.78 µg/ml, and 100 % inhibited by Almyrol, Diesen forte and Microbac forte at a concentration of 6.25 µg/ml and by FD312, Triquart, Hexaquart plus, Hexaquart S, ID 212, TPH 5225 at a concentration of 12.5 µg/ml.

        Key words: disinfectants – incorporation of [14C] precursors – respiration – Stenotrophomonas maltophilia.