Evaluation of four commercial test systems for identification of actinomyces and some closely related species

Identification and diversity of Actinomyces species in a clinical microbiology laboratory in the MALDI-TOF MS era

Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has emerged as a reliable tool for bacterial identification. This study compared the Bruker MALDI-TOF BioTyper MS (MBT) and 16S rRNA gene sequencing for the identification of Actinomyces and Actinotignum spp. The MBT identified 68/77 (88.3%) of Actinomyces isolates to the genus-level and 44/77 (57.1%) of Actinomyces isolates to the species-level using the manufacturer's identification criteria. The MBT did not yield reliable identification for only 1/77 (1.3%) and generated no identification for 8/77 (10.4%) of the isolates. No misidentifications were found. Discordance at the species level was observed for eight isolates. Overall, the MBT demonstrated good concordance with the 16S rRNA gene sequencing with the exception of the closely related species A. naeslundii, A. viscosus and A. oris. A variety of Actinomyces spp. were isolated from orocervicofacial/dental specimens, but only a limited number of species were isolated from urine or intra-abdominal specimens. This study confirms the utility of MBT in the identification of Actinomyces spp. and describes the diversity and anatomic niche of species in human clinical specimens from various body sites.

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.

Actinomyces urogenitalis bacteremia and tubo-ovarian abscess after an in vitro fertilization (IVF) procedure

We describe the first case of bacteremia due to Actinomyces urogenitalis. Bacteremia was secondary to a tubo-ovarian abscess following transvaginal oocyte retrieval. Identification was established by matrix-assisted desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) and confirmed by 16S rRNA gene sequencing. A. urogenitalis should be considered as a potential causative agent of infection after gynecological procedures.

Evaluation of the Andromas matrix-assisted laser desorption ionization-time of flight mass spectrometry system for identification of aerobically growing Gram-positive bacilli

Matrix-associated laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) is a rapid and simple microbial identification method. Previous reports using the Biotyper system suggested that this technique requires a preliminary extraction step to identify Gram-positive rods (GPRs), a technical issue that may limit the routine use of this technique to identify pathogenic GPRs in the clinical setting. We tested the accuracy of the MALDI-TOF MS Andromas strategy to identify a set of 659 GPR isolates representing 16 bacterial genera and 72 species by the direct colony method. This bacterial collection included 40 C. diphtheriae, 13 C. pseudotuberculosis, 19 C. ulcerans, and 270 other Corynebacterium isolates, 32 L. monocytogenes and 24 other Listeria isolates, 46 Nocardia, 75 Actinomyces, 18 Actinobaculum, 11 Propionibacterium acnes, 18 Propionibacterium avidum, 30 Lactobacillus, 21 Bacillus, 2 Rhodococcus equi, 2 Erysipelothrix rhusiopathiae, and 38 other GPR isolates, all identified by reference techniques. Totals of 98.5% and 1.2% of non-Listeria GPR isolates were identified to the species or genus level, respectively. Except for L. grayi isolates that were identified to the species level, all other Listeria isolates were identified to the genus level because of highly similar spectra. These data demonstrate that rapid identification of pathogenic GPRs can be obtained without an extraction step by MALDI-TOF mass spectrometry.

Comparison of phenotypic methods and matrix-assisted laser desorption ionisation time-of-flight mass spectrometry for the identification of aero-tolerant Actinomyces spp. isolated from soft-tissue infections

Aero-tolerant Actinomyces spp. are an under-recognised cause of cutaneous infections, in part because identification using conventional phenotypic methods is difficult and may be inaccurate. Matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF MS) is a promising new technique for bacterial identification, but with limited data on the identification of aero-tolerant Actinomyces spp. This study evaluated the accuracy of a phenotypic biochemical kit, MALDI-TOF MS and genotypic identification methods for the identification of this problematic group of organisms. Thirty aero-tolerant Actinomyces spp. were isolated from soft-tissue infections over a 2-year period. Species identification was performed by 16 s rRNA sequencing and genotypic results were compared with results obtained by API Coryne and MALDI-TOF MS. There was poor agreement between API Coryne and genotypic identification, with only 33% of isolates correctly identified to the species level. MALDI-TOF MS correctly identified 97% of isolates to the species level, with 33% of identifications achieved with high confidence scores. MALDI-TOF MS is a promising new tool for the identification of aero-tolerant Actinomyces spp., but improvement of the database is required in order to increase the confidence level of identification.

Actinomyces neuii: review of an unusual infectious agent

Actinomyces neuii, a species first described in 1994, has proven to be an exception in this genus on account of its aerobic growth, microscopic morphology (no branching), and the types and location of infections. Abscesses and infected atheromas are the most frequent types of infections, followed by infected skin structures, endophthalmitis, and bacteremias, including endocarditis. They are most likely of endogenous origin. To date, approximately 100 cases have been recorded in the literature. Intra-abdominal and intrathoracic infections, however, have not yet been described, and cases of classical actinomycosis seem to be extremely rare. Prognosis has generally been good with antibiotic and/or surgical treatment. Susceptibility to antibiotics has paralleled that of other Actinomyces spp.

Actinomyces timonensis sp. nov., isolated from a human clinical osteo-articular sample

Gram-positive, non-spore-forming rods were isolated from a human osteo-articular sample (strain 7400942(T)). Based on cellular morphology and the results of biochemical analysis, this strain was tentatively identified as a novel species of the genus Actinomyces. Phylogenetic analysis based on 16S rRNA gene sequence comparisons showed that the bacterium was closely related to the type strain of Actinomyces denticolens (96.9 % 16S rRNA gene sequence similarity). A comparison of biochemical traits showed that strain 7400942(T) was distinct from A. denticolens in a number of characteristics, i.e. in contrast with A. denticolens, strain 7400942(T) was negative for nitrate reduction and for beta-galactosidase, alpha-glucosidase and alanine arylamidase activities, it was positive for acid production from N-acetylglucosamine, melezitose and glycogen, and it was negative for acid production from turanose. Matrix-assisted laser-desorption/ionization time-of-flight MS protein analysis confirmed that strain 7400942(T) represents a novel species, as scores obtained for its spectra were significant (>2.2) only with strain 7400942(T). On the basis of phenotypic data and phylogenetic inference, it is proposed that this strain should be designated Actinomyces timonensis sp. nov.; the type strain is strain 7400942(T) (=CSUR P35(T)=CCUG 55928(T)).

Actinomyces massiliensis sp. nov., isolated from a patient blood culture

Gram-positive, non-spore-forming rods (strain 4401292(T)) were isolated from a human blood sample. Based on cellular morphology and the results of biochemical tests, this strain was tentatively identified as belonging to an undescribed species of the genus Actinomyces. Phylogenetic analysis based on 16S rRNA gene sequence comparison showed that the bacterium was related closely to Actinomyces gerencseriae (95.1 % 16S rRNA gene sequence similarity), Actinomyces israelii (95.2 %), Actinomyces oricola (95.2 %), Actinomyces ruminicola (93.3 %) and Actinomyces dentalis (91.4 %). The predominant fatty acids were C18 : 1omega9c and C16 : 0. On the basis of phenotypic data and phylogenetic inference, the novel species Actinomyces massiliensis sp. nov. is proposed; the type strain is 4401292(T) (=CSUR P18(T)=CCUG 53522(T)).

Intrauterine contraceptive device-associated pelvic actinomycosis caused by Actinomyces urogenitalis

We report a case of intrauterine contraceptive device (IUD) associated pelvic actinomycosis due to Actinomyces urogenitalis in a previously healthy young adult woman. Diagnosis was confirmed by 16S ribosomal RNA gene sequencing of bacterial colonies growing from the extracted device. This is the first documented report of human infection caused by this micro-organism.

Microarrays complement culture methods for identification of bacteria in endodontic infections

The aim of this study was to investigate the microbial composition of necrotic root canals using culture methods and microarray technology. Twenty uniradicular teeth with radiographic evidence of periapical bone loss and with no previous endodontic treatment were selected for this study. For molecular diagnosis a DNA chip with 20 different species-specific, 16S-rDNA-directed catcher probes was used. The microorganisms most frequently detected by the DNA chip were: Micromonas micros, Fusobacterium nucleatum ssp., Tannerella forsythia, Treponema denticola, Veillonella parvula, Eubacterium nodatum, Porphyromonas gingivalis, Actinomyces odontolyticus, and Streptococcus constellatus. As expected, additional important bacterial taxa were found by culture analysis, but microorganisms such as T. forsythia and T. denticola could not be identified. In conclusion, microarrays may provide significant additional information regarding the endodontic microbiota by detecting bacterial species that are otherwise difficult or impossible to culture.

Enzymatic/biochemical analysis of Actinomyces with commercial test kits with an emphasis on newly described species

In clinical microbiology laboratories, the identification of Actinomyces-like bacteria can be very laborious and problematic. In the present study, we focused on reactivity patterns of 4 commercial test kits, RapID ANA II, RapID 32A, RapID CB Plus, and BBL Crystal ANR ID, that could be used for rapid preliminary identification of Actinomyces isolates belonging to newly described Actinomyces and closely related species. Out of the 54 strains tested, 25 strains (46%) were correctly identified to the genus/group level by BBL Crystal ANR ID system, 16 strains (30%) by RapID 32 A, 11 strains (20%) by RapID CB Plus, and 7 strains (13%) by RapID ANA II. The main problems with these kits were due to occasional weak enzymatic and sugar fermentation reactions. In conclusion, chromogenic substrate sensitivity and specificity need to be enhanced in order to improve the reliability of the test results of these kits, and the present database updated in order to more precisely identify newly described Actinomyces and closely related species.