title: Evaluation of agar dilution and broth microdilution methods to determine the disinfectant susceptibility.
abstract: A variety of disinfectants have been widely used in veterinary hygiene, food industries and environments, which could induce the development of bacterial resistance to disinfectants. The methods used to investigate antimicrobial effects of disinfectant vary considerably among studies, making comparisons difficult. In this study, agar dilution and broth microdilution methods were used to compare the antimicrobial activities of four quaternary ammonium compounds (QACs) against foodborne and zoonotic pathogens. The potential relationship between the presence of QACs resistance genes and phenotypic resistance to QACs was also investigated. Our results indicated that the minimum inhibitory concentrations (MICs) determined by two methods might be different depended upon different QACs and bacteria applied. Regardless of the testing methods, Klebsiella pneumoniae was more tolerant among Gram-negative strains to four QACs, followed by Salmonella and Escherichia coli. The agreement between MICs obtained by the two methods was good, for benzalkonium chloride (78.15%), didecyldimethylammonium chloride (DDAC) (82.35%), cetylpyridinium chloride (CTPC) (97.48%) and cetyltrimethylammonium bromide (CTAB) (99.16%), respectively. Among all Gram-negative bacteria, 94.55% (n=52) of qacEΔ1-positive strains showed higher MICs (512 mg l(-1)) to CTAB. The qacEΔ1 gene was highly associated (P<0.05) with the high MICs of QACs (⩾512 mg l(-1)). In addition, DDAC remained as the most effective disinfectant against both Gram-positive and Gram-negative bacteria. This is the first study that compared the agar dilution and broth microdilution methods to assess the antimicrobial activity of QACs. The study demonstrated the need to standardize method that would be used in evaluating QACs antimicrobial properties in the future.
authors.affiliation: College of Resources and Environment, Sichuan Agricultural University, Chengdu, Sichuan, People's Republic of China.|The Laboratory of Microbiology, Dujiangyan Campus of Sichuan Agricultural University, Dujiangyan, Sichuan, People's Republic of China.
authors.forename: Guoyan
authors.initials: G
authors.lastname: Wu
authors.affiliation: Department of Food Science, Louisiana State University Agriculture Center, Baton Rouge, LA, USA.
authors.forename: Qianru
authors.initials: Q
authors.lastname: Yang
authors.affiliation: The Laboratory of Microbiology, Dujiangyan Campus of Sichuan Agricultural University, Dujiangyan, Sichuan, People's Republic of China.
authors.forename: Mei
authors.initials: M
authors.lastname: Long
authors.affiliation: College of Resources and Environment, Sichuan Agricultural University, Chengdu, Sichuan, People's Republic of China.|The Laboratory of Microbiology, Dujiangyan Campus of Sichuan Agricultural University, Dujiangyan, Sichuan, People's Republic of China.
authors.forename: Lijuan
authors.initials: L
authors.lastname: Guo
authors.affiliation: The Laboratory of Microbiology, Dujiangyan Campus of Sichuan Agricultural University, Dujiangyan, Sichuan, People's Republic of China.
authors.forename: Bei
authors.initials: B
authors.lastname: Li
authors.affiliation: The Laboratory of Microbiology, Dujiangyan Campus of Sichuan Agricultural University, Dujiangyan, Sichuan, People's Republic of China.
authors.forename: Yue
authors.initials: Y
authors.lastname: Meng
authors.affiliation: Animal Disease Prevention and Food Safety Key Laboratory of Sichuan Province, School of Life Science, Sichuan University, Chengdu, People's Republic of China.
authors.forename: Anyun
authors.initials: A
authors.lastname: Zhang
authors.affiliation: Animal Disease Prevention and Food Safety Key Laboratory of Sichuan Province, School of Life Science, Sichuan University, Chengdu, People's Republic of China.
authors.forename: Hongning
authors.initials: H
authors.lastname: Wang
authors.affiliation: Department of Food Quality and Safety, College of Food Science, Sichuan Agricultural University, Ya'an, Sichuan, People's Republic of China.
authors.forename: Shuliang
authors.initials: S
authors.lastname: Liu
authors.affiliation: College of Resources and Environment, Sichuan Agricultural University, Chengdu, Sichuan, People's Republic of China.|The Laboratory of Microbiology, Dujiangyan Campus of Sichuan Agricultural University, Dujiangyan, Sichuan, People's Republic of China.
authors.forename: Likou
authors.initials: L
authors.lastname: Zou
mesh_terms: D000362:Agar; D001419:Bacteria / Q000187:drug effects*; D004202:Disinfectants / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D008826:Microbial Sensitivity Tests / Q000379:methods*; D050296:Microbial Viability / Q000187:drug effects; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology
chemical_list: D004202:Disinfectants; D000644:Quaternary Ammonium Compounds; D000362:Agar