The Listeria monocytogenes transposon Tn6188 provides increased tolerance to various quaternary ammonium compounds and ethidium bromide.

Tolerance of the foodborne pathogen Listeria monocytogenes to sublethal concentrations of disinfectants has been frequently reported. Particularly, quaternary ammonium compounds (QACs) such as benzalkonium chloride (BC) are often used in disinfectants and also as antiseptics in food industry and hospitals. Recently, we described Tn6188, a novel transposon in L. monocytogenes harbouring the transporter QacH, a molecular mechanism leading to increased tolerance to BC. In this study, we investigated the presence of Tn6188 within the genus Listeria spp. Our screening indicates that the distribution of Tn6188 may be limited to L. monocytogenes. We confirm that QacH is responsible for the observed increase in tolerance by complementation of a qacH deletion mutant and introducing qacH in a Tn6188 negative strain. We investigated the transporter's substrate spectrum by determining minimal inhibitory concentrations (MICs) and showed that QacH also confers higher tolerance towards other QACs and ethidium bromide (EtBr). This result was supported by increased expression of qacH in the presence of the various substrates as determined by quantitative reverse transcriptase PCR (qRT-PCR). In addition, we detected expression of a Tn6188 transposase gene and circular forms of Tn6188, suggesting activity and possible transfer of this transposon.

Candidimonas bauzanensis sp. nov., isolated from soil, and emended description of the genus Candidimonas Vaz-Moreira et al. 2011.

A Gram-negative, facultatively anaerobic, psychrophilic, motile rod, designated BZ59(T), was isolated from hydrocarbon-contaminated soil. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain BZ59(T) belonged to the genus Candidimonas and had highest 16S rRNA gene sequence similarity with Candidimonas nitroreducens SC-089(T) (97.7 %) and Candidimonas humi SC-092(T) (97.6 %). The ubiquinone was Q-8 and the major fatty acids were C(16 : 0), C(17 : 0) cyclo and summed feature 3 (C(16 : 1)ω7c and/or iso-C(15 : 0) 2-OH). The polar lipid profile contained the major compounds phosphatidylethanolamine, phosphatidylglycerol, phosphatidylmonomethylethanolamine and diphosphatidylglycerol. The major polyamines were putrescine and spermidine; a minor amount of 2-hydroxyputrescine was present. The DNA G+C content of strain BZ59(T) was 61.6 mol%. Combined data from phenotypic, phylogenetic and DNA-DNA relatedness studies demonstrated that strain BZ59(T) represents a novel species of the genus Candidimonas, for which the name Candidimonas bauzanensis sp. nov. is proposed. The type strain is BZ59(T) (= DSM 22805(T) = LMG 26046(T) = CGMCC 1.10190(T)). The description of the genus Candidimonas is emended.