Application of MLST and Pilus Gene Sequence Comparisons to Investigate the Population Structures of Actinomyces naeslundii and Actinomyces oris

Uta Henssge,David Beighton,Steven C Gilbert,David R Radford,Thuy Do,Douglas Clark,Claes Wickström,Steven Cox,A J M Ligtenberg

doi:10.1371/journal.pone.0021430

Uta Henssge, David Beighton + Show 7 more

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https://doi.org/10.1371/journal.pone.0021430

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Abstract

Actinomyces naeslundii and Actinomyces oris are members of the oral biofilm. Their identification using 16S rRNA sequencing is problematic and better achieved by comparison of metG partial sequences. A. oris is more abundant and more frequently isolated than A. naeslundii. We used a multi-locus sequence typing approach to investigate the genotypic diversity of these species and assigned A. naeslundii (n = 37) and A. oris (n = 68) isolates to 32 and 68 sequence types (ST), respectively. Neighbor-joining and ClonalFrame dendrograms derived from the concatenated partial sequences of 7 house-keeping genes identified at least 4 significant subclusters within A. oris and 3 within A. naeslundii. The strain collection we had investigated was an under-representation of the total population since at least 3 STs composed of single strains may represent discrete clusters of strains not well represented in the collection. The integrity of these sub-clusters was supported by the sequence analysis of fimP and fimA, genes coding for the type 1 and 2 fimbriae, respectively. An A. naeslundii subcluster was identified with both fimA and fimP genes and these strains were able to bind to MUC7 and statherin while all other A. naeslundii strains possessed only fimA and did not bind to statherin. An A. oris subcluster harboured a fimA gene similar to that of Actinomyces odontolyticus but no detectable fimP failed to bind significantly to either MUC7 or statherin. These data are evidence of extensive genotypic and phenotypic diversity within the species A. oris and A. naeslundii but the status of the subclusters identified here will require genome comparisons before their phylogenic position can be unequivocally established.

Highlights

Actinomyces naeslundii and Actinomyces oris are part of the commensal oral microbiota [1,2,3], may play a role in pathogenesis of caries [1] and have been isolated from extra-oral infections [4]
A. naeslundii genospecies 2 isolates were demonstrated to bind to N-acetyl-b-D-galactosamine and acidic proline-rich proteins and to exhibit an N-acetyl-b-D-galactosamine binding specificity signified by N-acetyl-b-D-galactosamineinhibitable coaggregation with the specified streptococcal strains
The taxonomy of the Actinomyces ‘‘viscosus-naeslundii’’ group has been the subject of much research in order to find valid and reproducible methods to differentiate between these species which were isolated from both humans and rodents

Summary

Introduction

Actinomyces naeslundii and Actinomyces oris are part of the commensal oral microbiota [1,2,3], may play a role in pathogenesis of caries [1] and have been isolated from extra-oral infections [4] The identification of these species has proven difficult over the years since no reliable phenotypic characteristics are known to distinguish between either species [5] though for a period catalase production was used to distinguish between A. naeslundii and isolates described as human Actinomyces viscosus [6]. A. naeslundii genospecies 2 isolates were demonstrated to bind to N-acetyl-b-D-galactosamine and acidic proline-rich proteins and to exhibit an N-acetyl-b-D-galactosamine binding specificity signified by N-acetyl-b-D-galactosamineinhibitable coaggregation with the specified streptococcal strains. Diversity of fimA sequences within each genotype was apparent and strains

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