Actinomyces hominis sp. nov., isolated from a wound swab

Polymicrobial infections with specific Actinomyces and related organisms, using the current taxonomy

Actinomyces organisms reside on mucosal surfaces of the oropharynx and the genitourinary tract. Polymicrobial infections with Actinomyces organisms are increasingly being reported in the literature. Since these infections differ from classical actinomycosis, lacking of specific clinical and imaging findings, slow-growing Actinomyces organisms can be regarded as contaminants or insignificant findings. In addition, only limited knowledge is available about novel Actinomyces species and their clinical relevance. The recent reclassifications have resulted in the transfer of several Actinomyces species to novel genera Bowdeniella, Gleimia, Pauljensenia, Schaalia, or Winkia. The spectrum of diseases associated with specific members of Actinomyces and these related genera varies. In human infections, the most common species are Actinomyces israelii, Schaalia meyeri, and Schaalia odontolytica, which are typical inhabitants of the mouth, and Gleimia europaea, Schaalia turicensis, and Winkia neuii. In this narrative review, the purpose was to gather information on the emerging role of specific organisms within the Actinomyces and related genera in polymicrobial infections. These include Actinomyces graevenitzii in pulmonary infections, S. meyeri in brain abscesses and infections in the lower respiratory tract, S. turicensis in skin-related infections, G. europaea in necrotizing fasciitis and skin abscesses, and W. neuii in infected tissues around prostheses and devices. Increased understanding of the role of Actinomyces and related species in polymicrobial infections could provide improved outcomes for patient care. Key messages Due to the reclassification of the genus, many former Actinomyces species belong to novel genera Bowdeniella, Gleimia, Pauljensenia, Schaalia, or Winkia.Some of the species play emerging roles in specific infection types in humans.Increasing awareness of their clinical relevance as an established or a putative pathogen in polymicrobial infections brings about improved outcomes for patient care.

Nanchangia anserum gen. nov., sp. nov., isolated from feces of greater white-fronted geese (Anser albifrons)

Two rod-shaped and Gram-stain-positive bacteria (strains C64^T and C62) were isolated in 2020 from faeces of greater white-fronted geese (Anser albifrons) from Poyang Lake, PR China. Their optimal growth conditions were at 37 °C, pH 7.0 and with 0.5 % (w/v) NaCl. The two isolates showed a highest 16S rRNA gene sequence similarity to Bowdeniella nasicola DSM 19116^T (92.1 %). Phylogenetic/phylogenomic analyses indicated that strains C64^T and C62 clustered independently in the vicinity of the genera Varibaculum, Winkia and Mobiluncus within the family Actinomycetaceae, but could not be classified clearly as members of any of these known genera. The average amino acid identity values between our isolates and available genomes of members of the family Actinomycetaceae were around the genus threshold value (45-65 %). The major cellular fatty acids of the strains were C_18 : 1ω9c and C_16 : 0. The predominant polar lipids were phosphatidylinositol, phosphatidylglycerol, phosphatidylcholine, diacylglycerol, triacylglycerol and cardiolipin. The amino acid composition of peptidoglycan contained alanine, glutamic acid and glycine. The major respiratory menaquinones were MK-8(H₄) and MK-9(H₄). The whole cell sugars included galactose, arabinose and glucose. On the basis of the results of the 16S rRNA gene sequences comparison, whole-genome phylogenomic analysis, phenotypic and chemotaxonomic characteristics, we propose that strains C64^T and C62 represent a novel species belonging to a novel genus within the family Actinomycetaceae, for which the name Nanchangia anserum gen. nov., sp. nov. is proposed. The type strain is Nanchangia anserum C64^T (=CGMCC 1.18410^T=GDMCC 1.1969^T=KCTC 49511^T=KACC 22143^T).

Actinomyces tangfeifanii sp. nov., isolated from the vulture Aegypius monachus

A novel, Gram-stain-positive, catalase-positive, non-spore-forming, short rod-shaped strain (VUL4_3^T) was isolated from rectal swabs of Old World vultures (Aegypius monachus) from the Tibet-Qinghai Plateau, China. Based on the results of biochemical tests and 16S rRNA gene sequence comparison, strain VUL4_3^T was determined to be a member of the genus Actinomyces that is closely related to the type strains of Actinomyces liubingyangii (97.7 % 16S rRNA gene sequence similarity) and Actinomyces marimammalium (96.5 %). Optimal growth occurred at 37 °C, pH 6-7 and with 1 % (w/v) NaCl. The typical major cellular fatty acids of strain VUL4_3^T were C18 : 1ω9c, C16 : 0 and C18 : 0. The VUL4_3^T genome contained 2 207 832 bp with an average G+C content of 51.9 mol%. DNA-DNA hybridization values between strain VUL4_3^T and the above two species of the genus Actinomyces showed less than 32 % DNA-DNA relatedness, supporting a novel species status of strain VUL4_3^T. Based on the phenotypic data and phylogenetic inference, the novel species Actinomycestangfeifanii sp. nov. is proposed. The type strain is VUL4_3^T (=CGMCC 4.7369^T=DSM 103436^T).

Genome-Based Taxonomic Classification of the Phylum Actinobacteria

The application of phylogenetic taxonomic procedures led to improvements in the classification of bacteria assigned to the phylum Actinobacteria but even so there remains a need to further clarify relationships within a taxon that encompasses organisms of agricultural, biotechnological, clinical, and ecological importance. Classification of the morphologically diverse bacteria belonging to this large phylum based on a limited number of features has proved to be difficult, not least when taxonomic decisions rested heavily on interpretation of poorly resolved 16S rRNA gene trees. Here, draft genome sequences of a large collection of actinobacterial type strains were used to infer phylogenetic trees from genome-scale data using principles drawn from phylogenetic systematics. The majority of taxa were found to be monophyletic but several orders, families, and genera, as well as many species and a few subspecies were shown to be in need of revision leading to proposals for the recognition of 2 orders, 10 families, and 17 genera, as well as the transfer of over 100 species to other genera. In addition, emended descriptions are given for many species mainly involving the addition of data on genome size and DNA G+C content, the former can be considered to be a valuable taxonomic marker in actinobacterial systematics. Many of the incongruities detected when the results of the present study were compared with existing classifications had been recognized from 16S rRNA gene trees though whole-genome phylogenies proved to be much better resolved. The few significant incongruities found between 16S/23S rRNA and whole genome trees underline the pitfalls inherent in phylogenies based upon single gene sequences. Similarly good congruence was found between the discontinuous distribution of phenotypic properties and taxa delineated in the phylogenetic trees though diverse non-monophyletic taxa appeared to be based on the use of plesiomorphic character states as diagnostic features.

Actinomyces gaoshouyii sp. nov., isolated from plateau pika (Ochotona curzoniae)

Two strains (pika_113T and pika_114) of a previously undescribed Actinomyces-like bacterium were recovered from the intestinal contents of plateau pika (Ochotona curzoniae) on the Tibet-Qinghai Plateau, China. Results from biochemical characterization indicated that the two strains were phenotypically homogeneous and distinct from other previously described species of the genus Actinomyces. Based on the comparison of 16S rRNA gene sequences and genome analysis, the bacteria were determined to be a hitherto unknown subline within the genus Actinomyces, being most closely related to type strains of Actinomyces denticolens and Actinomyces timonensis with a respective 97.2 and 97.1 % similarity in their 16S rRNA gene sequences. Phylogenetic analyses confirmed that pika_113T was well separated from any other recognized species of the genus Actinomyces and within the cluster with A. denticolens and A. timonensis. The genome of strain pika_113T displayed less than 42 % relatedness in DNA-DNA hybridization with all the available genomes of existing species of the genus Actinomyces in the NCBI database. Collectively, based on the phenotypic characteristics and phylogenetic analyses results, we propose the novel isolates as representatives of Actinomyces gaoshouyii sp. nov. The type strain of Actinomyces gaoshouyii is pika_113T (=CGMCC 4.7372T=DSM 104049T), with a genomic DNA G+C content of 71 mol%.

Actinomyces liubingyangii sp. nov. isolated from the vulture Gypaetus barbatus

Two strains (VUL4_1T and VUL4_2) of Gram-staining-positive, catalase-negative, non-spore-forming short rods were isolated from rectal swabs of Old World vultures (Gypaetus barbatus) in the Tibet-Qinghai Plateau, China. Analysis of morphological characteristics and biochemical tests indicated that the two strains closely resembled each other but were distinct from other species of the genus Actinomyces previously described. Based on the results of 16S rRNA gene sequence comparison and genome analysis, strains were determined to be members of the genus Actinomyces, closely related to the type strains of Actinomyces marimammalium (96.4 % 16S rRNA gene sequence similarity), Actinomyceshongkongensis (92.4 %), Actinomyceshordeovulneris (92.3 %) and Actinomycesnasicola (92.2 %), respectively. Optimal growth conditions were 37 °C, pH 6-7, with 1 % (w/v) NaCl. Strain VUL4_1T contained C18 : 1ω9c and C16 : 0 as the major cellular fatty acids and diphosphatidylglycerol as the major component of the polar lipids. The genomic DNA G+C content of VUL4_1T was 54.9 mol%. Strain VUL4_1T showed less than 70 % DNA-DNA relatedness with other species of the genus Actinomyces, further supporting strain VUL4_1T as a representative of a novel species. Based on the phenotypic data and phylogenetic inference, a novel species, Actinomyces liubingyangii sp. nov., is proposed with VUL4_1T (=CGMCC 4.7370T=DSM 104050T) as the type strain.

Actinomyces vulturis sp. nov., isolated from Gyps himalayensis

Two strains of Gram-stain-positive, facultatively anaerobic, non-spore-forming short rods (VUL7T and VUL8) were isolated from rectal swabs of Old World vultures, namely Gyps himalayensis, in Tibet-Qinghai Plateau, China. Optimal growth occurred at 37 °C, pH 6-7, with 1 % (w/v) NaCl. Phylogenetic analysis based on 16S rRNA gene sequences classified the two strains to the genus Actinomyces, with highest 16S rRNA gene sequence similarity (95 %) to type strains of Actinomyces haliotis, Actinomyces radicidentis and Actinomyces urogenitalis. The major cellular fatty acids were C18 : 1ω9c and C16 : 0. MK-10(H4) was the major respiratory quinone. The genomic DNA G+C content of the isolate was 54.4 mol%. DNA-DNA hybridization values with the most closely related species ofthe genusActinomyces was 24.6 %. The two strains can be differentiated from the most closely related species such as A. haliotis, A. radicidentis, A. graevenitzii and A. urogenitalis by a list of carbohydrate fermentations and enzyme activities. On the basis of physiological, biochemical and phylogenetic analysis, strains VUL7T and VUL8 represent novel species of the genus Actinomyces, for which the name Actinomyces vulturis sp. nov. is proposed. The type strain is VUL7T (=CGMCC 4.7366T=DSM 103437T).

Actinomyces and related organisms in human infections

Actinomyces israelii has long been recognized as a causative agent of actinomycosis. During the past 3 decades, a large number of novel Actinomyces species have been described. Their detection and identification in clinical microbiology laboratories and recognition as pathogens in clinical settings can be challenging. With the introduction of advanced molecular methods, knowledge about their clinical relevance is gradually increasing, and the spectrum of diseases associated with Actinomyces and Actinomyces-like organisms is widening accordingly; for example, Actinomyces meyeri, Actinomyces neuii, and Actinomyces turicensis as well as Actinotignum (formerly Actinobaculum) schaalii are emerging as important causes of specific infections at various body sites. In the present review, we have gathered this information to provide a comprehensive and microbiologically consistent overview of the significance of Actinomyces and some closely related taxa in human infections.

Phylogenomics and evolutionary dynamics of the family Actinomycetaceae

The family Actinomycetaceae comprises several important pathogens that impose serious threat to human health and cause substantial infections of economically important animals. However, the phylogeny and evolutionary dynamic of this family are poorly characterized. Here, we provide detailed description of the genome characteristics of Trueperella pyogenes, a prevalent opportunistic bacterium that belongs to the family Actinomycetaceae, and the results of comparative genomics analyses suggested that T. pyogenes was a more versatile pathogen than Arcanobacterium haemolyticum in adapting various environments. We then performed phylogenetic analyses at the genomic level and showed that, on the whole, the established members of the family Actinomycetaceae were clearly separated with high bootstrap values but confused with the dominant genus Actinomyces, because the species of genus Actinomyces were divided into three main groups with different G+C content. Although T. pyogenes and A. haemolyticum were found to share the same branch as previously determined, our results of single nucleotide polymorphism tree and genome clustering as well as predicted intercellular metabolic analyses provide evidence that they are phylogenetic neighbors. Finally, we found that the gene gain/loss events occurring in each species may play an important role during the evolution of Actinomycetaceae from free-living to a specific lifestyle.

Actinomyces haliotis sp. nov., a bacterium isolated from the gut of an abalone, Haliotis discus hannai

A novel, Gram-staining-positive, facultatively anaerobic, non-motile and coccus-shaped bacterium, strain WL80T, was isolated from the gut of an abalone, Haliotis discus hannai, collected from the northern coast of Jeju in Korea. Optimal growth occurred at 30 °C, pH 7–8 and with 1 % (w/v) NaCl. Phylogenetic analyses based on the 16S rRNA gene sequence revealed that strain WL80T fell within the cluster of the genus Actinomyces , with highest sequence similarity to the type strains of Actinomyces radicidentis (98.8 % similarity) and Actinomyces urogenitalis (97.0 % similarity). The major cellular fatty acids were C18 : 1ω9c and C16 : 0. Menaquinone-10 (H4) was the major respiratory quinone. The genomic DNA G+C content of the isolate was 70.4 mol%. DNA–DNA hybridization values with closely related strains indicated less than 7.6 % genomic relatedness. The results of physiological, biochemical, chemotaxonomic and genotypic analyses indicated that strain WL80T represents a novel species of the genus Actinomyces , for which the name Actinomyces haliotis sp. nov. is proposed. The type strain is WL80T ( = KACC 17211T = JCM 18848T).

Actinomyces weissii sp. nov., isolated from dogs

Two Gram-positive, rod-shaped, non-spore-forming bacteria were isolated from the oral cavities of two dogs. On the basis of 16S rRNA gene sequence similarities both strains were shown to belong to the genus Actinomyces and were most closely related to Actinomyces bovis (97.3 % and 97.5 %, respectively). The polyamine profile of the two isolates and Actinomyces bovis DSM 43014T was composed of spermidine and spermine as the major components. Menaquinone MK-9 was the major compound in the quinone system of the two strains and Actinomyces bovis . The polar lipid profiles of strains 2298T and 4321 were almost identical, containing diphosphatidylglycerol as the major compound, and moderate to trace amounts of phosphatidylcholine, phosphatidylinositol, phosphatidylinositol-mannoside, phosphatidylglycerol and several unidentified lipids. A highly similar polar lipid profile was detected in Actinomyces bovis DSM 43014T supporting the affiliation of strains 2298T and 4321 to the genus Actinomyces . The typical major fatty acids were C16 : 0, C18 : 0 and C18 : 1ω9c. Fatty acids C14 : 0 and C18 : 2ω6,9c were found in minor amounts. The results of physiological and biochemical analyses revealed clear differences between both strains and the most closely related species of the genus Actinomyces . Thus, strains 2298T and 4321 represent a novel species, for which the name Actinomyces weissii sp. nov., is proposed, with strain 2298T ( = CIP 110333T = LMG 26472T = CCM 7951T = CCUG 61299T) as the type strain.