title: Genomic characterization of novel Listeria monocytogenes serotype 4b variant strains.
abstract: Over 90% of the human listeriosis cases are caused by Listeria monocytogenes serotypes 1/2a, 1/2b and 4b strains. As an alternative to antigen-antibody based serotyping, a PCR-based method for serogrouping has been developed and validated. In this communication, we report an in-depth analysis of five 4b variant strains, four clinical isolates from Australia and one environmental isolate from USA. Although these five strains were serotype 4b by classical serotyping method, the serogrouping PCR profiles of these strains show the presence of a 1/2a-3a specific amplicon in addition to the standard 4b-4d-4e specific amplicons. These strains were further analyzed by pulsed field gel electrophoresis, binary gene typing, multi-locus variable-number-tandem-repeat analysis and a high density pan-genomic Listeria microarray. Using these sub-typing results, the clinical isolates were grouped into two distinct genomic groups- one of which could be part of an unidentified outbreak. The microarray results when compared with our database of other 4b outbreak isolates indicated that the serotype 4b variant strains represent very different genotypic profiles than the known reported 4b outbreak strains representing major epidemic clones. The acquisition of serotype 1/2a gene clusters by the 4b variant strains appears to be independent in origin, spanning large areas of geographical and temporal space and may indicate predisposition of some 4b strains towards accepting DNA from related organisms.
authors.affiliation: Center for Food Safety and Applied Nutrition, US Food and Drug Administration, Laurel, Maryland, United States of America.
authors.forename: Pongpan
authors.initials: P
authors.lastname: Laksanalamai
authors.affiliation: Public Health Microbiology Laboratory, Queensland Health Forensic and Scientific Services, Queensland, Australia.
authors.forename: Bixing
authors.initials: B
authors.lastname: Huang
authors.affiliation: Center for Veterinary Medicine, US Food and Drug Administration, Laurel, Maryland, United States of America.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Sabo
authors.affiliation: Center for Food Safety and Applied Nutrition, US Food and Drug Administration, Laurel, Maryland, United States of America.
authors.forename: Laurel S
authors.initials: LS
authors.lastname: Burall
authors.affiliation: Center for Veterinary Medicine, US Food and Drug Administration, Laurel, Maryland, United States of America.
authors.forename: Shaohua
authors.initials: S
authors.lastname: Zhao
authors.affiliation: Public Health Microbiology Laboratory, Queensland Health Forensic and Scientific Services, Queensland, Australia.
authors.forename: John
authors.initials: J
authors.lastname: Bates
authors.affiliation: Center for Food Safety and Applied Nutrition, US Food and Drug Administration, Laurel, Maryland, United States of America.
authors.forename: Atin R
authors.initials: AR
authors.lastname: Datta
mesh_terms: D001315:Australia; D015373:Bacterial Typing Techniques; D014644:Genetic Variation; D016680:Genome, Bacterial; D006801:Humans; D008089:Listeria monocytogenes / Q000235:genetics* / Q000302:isolation & purification; D008088:Listeriosis / Q000382:microbiology; D020411:Oligonucleotide Array Sequence Analysis; D010802:Phylogeny; D016133:Polymerase Chain Reaction / Q000379:methods; D065288:Serogroup