title: Influence of growth media on the sensitivity of Staphylococcus aureus and Pseudomonas aeruginosa to cationic biocides.
abstract: In this study, the influence of culturing Staphylococcus aureus and Pseudomonas aeruginosa under different growth conditions on their inactivation by the cationic active compounds benzalkonium chloride, chlorhexidine digluconate and octenidine dihydrochloride was investigated. Cells were grown in non-agitated tryptone soya broth as well as on tryptone soya agar according to national and international standards for evaluating chemical disinfectants. In quantitative suspension tests, cells of both test organisms grown on agar were significantly more sensitive to all three biocides than cells grown in broth. The differences in antimicrobial activity were greater in the case of S. aureus than in the case of P. aeruginosa. With S. aureus cultures, differences in the reduction factor of up to 5 log steps were found, with P. aeruginosa up to 2.5 log steps. The results of our uptake tests performed with S. aureus and octenidine dihydrochloride indicated that the growth conditions and the associated different stress factors either had an influence on the composition of the cell surface of this test organism or induced the formation of an efflux system. Cells of S. aureus cultured in broth took up only one-fifth of the amount of biocide molecules compared to cells from agar cultures. These data correlated with the results of the suspension tests. A low uptake of biocides apparently led to a reduced killing rate. In contrast to S. aureus, no significant differences in the uptake of octenidine dihydrochloride by cells of P. aeruginosa could be observed. These cells took up the same amount of the antimicrobial substance, whether on agar or in broth. In view of these results, possible consequences should be considered prior to changing test regulations.
authors.affiliation: Microbiology Department, University of Hamburg, Biocentre Klein Flottbek and Botanical Garden, Ohnhorststrasse 18, 22609 Hamburg, Germany. brill@mikrobiologie.uni-hamburg.de
authors.forename: Florian
authors.initials: F
authors.lastname: Brill
authors.forename: Peter
authors.initials: P
authors.lastname: Goroncy-Bermes
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Sand
mesh_terms: D000891:Anti-Infective Agents, Local / Q000494:pharmacology*; D001548:Benzalkonium Compounds / Q000494:pharmacology; D002710:Chlorhexidine / Q000031:analogs & derivatives / Q000494:pharmacology; D003470:Culture Media; D004202:Disinfectants; D007097:Imines; D008826:Microbial Sensitivity Tests; D011550:Pseudomonas aeruginosa / Q000187:drug effects*; D011725:Pyridines / Q000494:pharmacology; D013211:Staphylococcus aureus / Q000187:drug effects*
chemical_list: D000891:Anti-Infective Agents, Local; D001548:Benzalkonium Compounds; D003470:Culture Media; D004202:Disinfectants; D007097:Imines; D011725:Pyridines; C010882:chlorhexidine gluconate; C034213:octenidine; D002710:Chlorhexidine