title: The Identification of Intrinsic Chloramphenicol and Tetracycline Resistance Genes in Members of theBacillus cereusGroup (sensu lato).
abstract: Bacillus toyonensisstrain BCT-7112T(NCIMB 14858T) has been widely used as an additive in animal nutrition for more than 30 years without reports of adverse toxigenic effects. However, this strain is resistant to chloramphenicol and tetracycline and it is generally considered inadvisable to introduce into the food chain resistance determinants capable of being transferred to other bacterial strains, thereby adding to the pool of such determinants in the gastro-enteric systems of livestock species. We therefore characterized the resistance phenotypes of this strain and its close relatives to determine whether they were of recent origin, and therefore likely to be transmissible. To this end we identified the genes responsible for chloramphenicol (catQ) and tetracycline (tetM) resistance and confirmed the presence of homologs in other members of theB. toyonensistaxonomic unit. Unexpectedly, closely related strains encoding these genes did not exhibit chloramphenicol and tetracycline resistance phenotypes. To understand the differences in the behaviors, we cloned and expressed the genes, together with their upstream regulatory regions, intoBacillus subtilis. The data showed that the genes encoded functional proteins, but were expressed inefficiently from their native promoters.B. toyonensisis a taxonomic unit member of theBacillus cereusgroup (sensu lato). We therefore extended the analysis to determine the extent to which homologous chloramphenicol and tetracycline resistance genes were present in other species within this group. This analysis revealed that homologous genes were present in nearly all representative species within theB. cereusgroup (sensu lato). The absence of known transposition elements and the observations that they are found at the same genomic locations, indicates that these chloramphenicol and tetracycline resistance genes are of ancient origin and intrinsic to this taxonomic group, rather than recent acquisitions. In this context we discuss definitions of what are and are not intrinsic genes, an issue that is of fundamental importance to both Regulatory Authorities, and the animal feed and related industries.
authors.affiliation: Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biology, Newcastle University Newcastle upon Tyne, UK.
authors.forename: Helen
authors.initials: H
authors.lastname: Glenwright
authors.affiliation: Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biology, Newcastle University Newcastle upon Tyne, UK.
authors.forename: Susanne
authors.initials: S
authors.lastname: Pohl
authors.affiliation: Servei de Microbiologia, Hospital de la Santa Creu i Sant Pau, Institut d'Investigació Biomèdica Sant Pau Barcelona, Spain.
authors.forename: Ferran
authors.initials: F
authors.lastname: Navarro
authors.affiliation: Servei de Microbiologia, Hospital de la Santa Creu i Sant Pau, Institut d'Investigació Biomèdica Sant Pau Barcelona, Spain.
authors.forename: Elisenda
authors.initials: E
authors.lastname: Miro
authors.affiliation: Research and Development Department, Rubinum S.A. Rubí, Spain.
authors.forename: Guillermo
authors.initials: G
authors.lastname: Jiménez
authors.affiliation: Department of Microbiology, University of Barcelona Barcelona, Spain.
authors.forename: Anicet R
authors.initials: AR
authors.lastname: Blanch
authors.affiliation: Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biology, Newcastle University Newcastle upon Tyne, UK.
authors.forename: Colin R
authors.initials: CR
authors.lastname: Harwood
keywords: Bacillus cereus; Bacillus toyonensis; gene knockouts; intrinsic antibiotic resistance; quantitative PCR