Comparative Analysis of Plasmids in the Genus Listeria

Abstract

BackgroundWe sequenced four plasmids of the genus Listeria, including two novel plasmids from L. monocytogenes serotype 1/2c and 7 strains as well as one from the species L. grayi. A comparative analysis in conjunction with 10 published Listeria plasmids revealed a common evolutionary background.Principal FindingsAll analysed plasmids share a common replicon-type related to theta-replicating plasmid pAMbeta1. Nonetheless plasmids could be broadly divided into two distinct groups based on replicon diversity and the genetic content of the respective plasmid groups. Listeria plasmids are characterized by the presence of a large number of diverse mobile genetic elements and a commonly occurring translesion DNA polymerase both of which have probably contributed to the evolution of these plasmids. We detected small non-coding RNAs on some plasmids that were homologous to those present on the chromosome of L. monocytogenes EGD-e. Multiple genes involved in heavy metal resistance (cadmium, copper, arsenite) as well as multidrug efflux (MDR, SMR, MATE) were detected on all listerial plasmids. These factors promote bacterial growth and survival in the environment and may have been acquired as a result of selective pressure due to the use of disinfectants in food processing environments. MDR efflux pumps have also recently been shown to promote transport of cyclic diadenosine monophosphate (c-di-AMP) as a secreted molecule able to trigger a cytosolic host immune response following infection.ConclusionsThe comparative analysis of 14 plasmids of genus Listeria implied the existence of a common ancestor. Ubiquitously-occurring MDR genes on plasmids and their role in listerial infection now deserve further attention.

Identification of the mechanisms of resistance and potential cross resistance of Listeria monocytogenes upon adaptation to different antimicrobials

“…The bcrABC cassette was first identified on a large plasmid (pLM80) harbored by strains implicated in the 1998-1999 hotdog outbreak of listeriosis, and was subsequently also identified on a similar plasmid from a different strain, responsible for another multistate outbreak. The cassette on these plasmids appears to be part of a composite transposon that also includes genes conferring resistance to cadmium (64,121,156).…”

“…Plasmid based BC resistance mechanisms are reported by the various studies (131,186,187 (64,116,121,156). The prevalence of the resistance to these heavy metals varies among different serotypes of L. monocytogenes (127,128,129,147,155).…”

“…The Cadmium resistance mechanism in L monocytogenes is diverse with four distinct cadAC energy-dependent efflux systems identified to date. The first, cadA1cassette is harbored on plasmids associated with a transposon (Tn5422) (121,127,129).…”

“…monocytogenes plasmids (e.g. pLM80) harboring both bcrABC and cadA2 have been characterized in the course of genome sequencing investigations (64,121,156). Genome sequence data of the non-pathogenic listeriae employed as donors in the current study are currently not available.…”

“…The bcrABC cassette was first identified on a large plasmid (pLM80) harbored by strains implicated in the 1998-1999 hotdog outbreak of listeriosis, and was subsequently also identified on a similar plasmid from a different strain, responsible for another multistate outbreak. The cassette on these plasmids appears to be part of a composite transposon that also includes genes conferring resistance to cadmium (64,121,156).Further evidence for the association between BC resistance and resistance to cadmium was obtained from characterization of L. monocytogenes from turkey processing plants. All BC-resistant strains were found to be also resistant to cadmium (though the reverse was not the case; ca.…”