Genetic subtyping of <i>Listeria monocytogenes</i> via multiple-locus sequence typing using <i>iap, sigB</i> and <i>actA</i>

Abstract

Pulse field gel electrophoresis (PFGE) is widely used for listeriosis surveillance. Although this technique is effective for epidemiology, the data among laboratories are inconsistent. We previously reported a method for Listeria monocytogenes subtyping combined with sequence analysis of partial iap and whole genome restriction fragment length polymorphism (RFLP) using XbaI, ClaI (BanIII) and PstI. However, distinguishing subtypes was challenging, because the output comprised complicated fragment patterns. In this study, we aimed to establish a simple genotyping method that does not depend on visual observation, rather it focuses on multi-locus sequence typing (MLST) using three genes, iap, sigB and actA. Sixty-eight strains of L. monocytogenes including EGD-e as a reference strain were investigated to ensure consistency with previous data on the genetic characterization. All strains were grouped into 29 types by both analyses. Although there are some differences in classification, major clades included the same strains. Simpson’s indices of diversity (SID) by MLST and iap-RFLP-based typing were 0.967 (95% confidence interval [CI]: 0.955/0.978) and 0.967 (95% CI: 0.955/0.979), respectively. The discriminatory power of both methods can be considered almost identical. Compared with the results of 38 selected strains, the strains within the MLST clusters in this study coincided with those obtained using PFGE. Thus, the MLST strategy could help differentiate among L. monocytogenes isolates during epidemiological studies.

Sequence-Based Characterization of <i>Listeria monocytogenes</i> Strains Isolated from Domestic Retail Meat in the Tokyo Metropolitan Area of Japan

“…On the basis of the data, both phylogenic trees were divided into two large clades, representing lineage I ( and traditional MLST genes. In a previous study, we reported that two strains, 76P1 (Table 3) and 1E1 (sigB AT 37; derived from the skin of beef cattle), possessed nonsense mutations in the sigB gene (6). According to genetic analysis of the sigB allele, this sequence was found to be relatively conserved in L. monocytogenes (14).…”