Gordonia hongkongensis sp. nov., isolated from blood culture and peritoneal dialysis effluent of patients in Hong Kong.

Two bacterial strains, HKU50T and HKU46, were isolated in Hong Kong from the blood culture and the peritoneal dialysis effluent of two patients. The strains are Gram-stain-positive, acid-fast, non-motile, non-sporulating bacilli. They grow on Columbia agar with 5 % defibrinated sheep blood and brain-heart infusion agar under aerobic conditions with 5 % CO2 at 37 °C as pink-to-orange, non-haemolytic colonies. The strains are catalase-positive and oxidase-negative, and have a unique biochemical profile distinguishable from other closely related species. DNA sequencing revealed that both isolates possessed multiple intra-genomic 16S rRNA gene copies (99.8-100 % sequence identities to Gordonia lacunae NRRL B-24551T and Gordonia terrae NRRL B-16283T). Phylogenetic analysis of the 16S rRNA gene, secA1 and gyrB showed that the two isolates formed a distinct branch within the genus Gordonia and were most closely related to G. lacunae and G. terrae. DNA-DNA hybridization demonstrated ≤53.7 % and ≤49.4 % DNA relatedness between the two isolates and G. lacunae, and between the two isolates and G. terrae, respectively. Hierarchical cluster analysis of MALDI-TOF MS main spectrum profiles showed that strains HKU50T and HKU46 were closely related to each other, but were distinct from G. lacunae, G. terrae, or any other species of the genus Gordonia in the Bruker database. The chemotaxonomic traits of the two strains were highly similar, and the major fatty acids were summed feature 4 (iso-C15 : 0 2-OH/C16 : 1trans-9), C16 : 0, C18 : 1cis-9, and tuberculostearic acid. A novel species named Gordonia hongkongensis sp. nov. is proposed to accommodate strains HKU50T and HKU46, with strain HKU50T (=CCOS 955T=CIP 111027T=NBRC 111234T=NCCP 16210T) as the type strain.

Streptobacillus hongkongensis sp. nov., isolated from patients with quinsy and septic arthritis, and emended descriptions of the genus Streptobacillus and Streptobacillus moniliformis.

Two bacterial strains, HKU33(T) and HKU34, were isolated in Hong Kong from the pus aspirated from the right peritonsillar abscess of a patient with quinsy and the left elbow joint fluid of another patient with tophaceous gout and left elbow septic arthritis, respectively. The bacteria were Gram-stain-negative, non-motile, non-spore-forming, non-haemolytic pleomorphic bacilli. They grew best on Columbia agar with 5 % defibrinated sheep blood in an anaerobic environment or aerobic environment with 5 % CO2. They also grew on chocolate agar but not on MacConkey agar. They were catalase- and cytochrome oxidase-negative. They showed a unique profile of enzyme activities distinguishable from their closely related species. Phylogenetic analysis of the complete 16S rRNA gene, and partial groEL, gyrB and recA gene sequences showed the two isolates formed a distinct branch within the family Leptotrichiaceae, being related most closely to Streptobacillus moniliformis. Hierarchical cluster analysis of mass spectra of whole-cell protein contents showed that strains HKU33(T) and HKU34 were closely related to each other, but were distinct from Streptobacillus moniliformis, Sneathia sanguinegens and 'Leptotrichia amnionii'. The DNA G+C content of strain HKU33(T) was 26.0±2.1 mol% (mean±sd; n = 3). DNA-DNA hybridization demonstrated ≤45.02 % DNA relatedness between the two isolates and Streptobacillus moniliformis CCUG 13453(T). A novel species, Streptobacillus hongkongensis sp. nov., is proposed to accommodate strains HKU33(T) and HKU34, with HKU33(T) ( = JCM 18691(T) = NCTC 13659(T) = DSM 26322(T)) designated the type strain. Emended descriptions of the genus Streptobacillus and Streptobacillus moniliformis are also given.

First report of Gordonibacter pamelaeae bacteremia.

We report the first case of Gordonibacter pamelaeae bacteremia, identified by phenotypic tests and 16S rRNA sequencing in a patient with disseminated rectosigmoid carcinoma and responsive to amoxicillin-clavulanate. The bacterium was a nonsporulating, anaerobic, gram-positive, nonmotile, coccobacillus that was catalase, arginine dihydrolase, and arginine acrylamidase positive. The gastrointestinal tract is probably its reservoir.

Susceptibility patterns of clinical and fish isolates of Laribacter hongkongensis: comparison of the Etest, disc diffusion and broth microdilution methods.

OBJECTIVES: To determine the antibiotic susceptibility patterns of 60 strains of Laribacter hongkongensis isolated from humans and fish to eight antibiotics and compare the results obtained from broth microdilution, Etest and disc diffusion susceptibility testing. PATIENTS AND METHODS: The susceptibilities of 60 isolates of L. hongkongensis from humans with gastroenteritis and fish to eight antibiotics were tested by three methods [broth microdilution (reference method), Etest and disc diffusion] and their results were compared. RESULTS: All isolates were susceptible to imipenem and ciprofloxacin by all three methods, except for one strain which was resistant to ciprofloxacin by broth microdilution. All were susceptible to ampicillin/sulbactam by Etest and disc diffusion, but eight were resistant by broth microdilution. By broth microdilution, 90%, 100%, 46.7%, 100% and 8.3% of isolates were resistant to ampicillin, ceftriaxone, cefuroxime, erythromycin and tetracycline, respectively. Although broth microdilution generally yielded higher MICs of beta-lactams, MICs obtained with Etest were in good correlation with broth microdilution for all drugs except ampicillin/sulbactam, with >90% agreement within 2 log(2) dilutions for imipenem, ciprofloxacin, erythromycin and tetracycline. Comparison of susceptibilities between broth microdilution and the other two methods showed the highest (>95%) percentage agreement for imipenem, ciprofloxacin and tetracycline. The highest discrepancies were observed with erythromycin (58.3% agreement), with an apparent increase in susceptibility by disc diffusion. A higher proportion of human isolates than fish isolates were tetracycline-resistant by all three tests (P=0.022). CONCLUSIONS: Etest and disc diffusion appear to be reliable for evaluation of susceptibilities of L. hongkongensis to imipenem, ciprofloxacin and tetracycline. However, these methods may underestimate resistance to other beta-lactams.

Alkanindiges hongkongensis sp. nov. A novel Alkanindiges species isolated from a patient with parotid abscess.

A bacterium was isolated from the abscess pus of a 72-year-old patient with Warthin's tumor and parotid abscess. The cells were aerobic, non-motile, Gram-negative but difficult to be destained, non-sporulating, coccobacillus. The bacterium grew poorly on sheep blood agar and MacConkey agar as non-hemolytic colonies of 0.5 mm in diameter after 24h of incubation at 37 degrees C in ambient air. Growth was enhanced by Tween 80. It produces catalase but not cytochrome oxidase. Sequencing of the cloned 16S rRNA PCR products of the bacterium revealed three different 16S rRNA gene sequences, with 12 - 31 bp differences among them. Phylogenetic analysis showed that the bacterium is closely related to Alkanindiges illinoisensis, with 5.0 - 5.9% differences between the 16S rRNA gene sequence of the bacterium and that of A. illinoisensis. Tryptophan auxotrophic strain of Acinetobacter trpE27 transformed with DNA extracted from the bacterium was unable to grow on tryptophan deficient medium, indicating that the bacterium was not a strain of Acinetobacter. The G+C content of the bacterium (mean +/-SD) was 46.9+4.3%. A new species, Alkanindiges hongkongensis sp. nov., is proposed, for which HKU9T is the type strain. Isolates with "small colonies" that are apparently Acinetobacter-like species should be carefully identified. Growth enhancement with aliphatic hydrocarbons should be looked for and 16S rRNA gene sequencing performed in order to find more potential cases of Alkanindiges infections, as well as to define the epidemiology, clinical spectrum, and outcome of infections associated with this genus.

Bacteremia in a patient with colonic carcinoma caused by a novel Sedimentibacter species: Sedimentibacter hongkongensis sp. nov.

A bacterium was isolated from the blood culture of a 91-year-old patient with colonic carcinoma. The cells were strict anaerobic, motile, Gram-negative, sporulating, straight, or slightly curved rods. The bacterium grew on agar using the BACTEC anaerobic blood culture broth or buffered charcoal yeast extract agar as pinpoint colonies after 72 h of incubation at 37 degrees C in anaerobic conditions. It did not grow on blood agar, chocolate agar, MacConkey agar, nutrient agar or broth, brain heart infusion agar or broth, Brucella agar, or cooked meat medium. It produces catalase but not cytochrome oxidase. 16S rRNA gene sequencing and phylogenetic analysis showed that it is closely related to Sedimentibacter hydroxybenzoicus and Sedimentibacter saalensis, with 10.5% and 11.9% differences between the 16S rRNA gene sequence of the bacterium and those of S. hydroxybenzoicus and S. saalensis respectively. A new species, Sedimentibacter hongkongenesis sp. nov., is proposed, for which HKU2(T) is the type strain.

Early diagnosis of Exophiala CAPD peritonitis by 18S ribosomal RNA gene sequencing and its clinical significance.

Phenotypic identification of fungi in clinical microbiology laboratories is often difficult and late, especially for slow growing and rarely encountered fungi. We describe the application of 18S ribosomal RNA (rRNA) gene sequencing in the early diagnosis of a case of Exophiala peritonitis. A yeast-like fungus was isolated from the dialysate fluid of a 66-year-old man undergoing continuous ambulatory peritoneal dialysis. It grew slowly after 12 days of incubation to yield mature cultures to permit recognition of microscopic features resembling those of Exophiala, a dematiacerous mold. 18S rRNA gene sequencing provided results 12 days earlier than phenotypic identification and revealed 15 base difference (0.9%) between the isolate and Exophiala sp. strain GHP 1205 (GenBank Accession no. AJ232954), indicating that the isolate most closely resembles a strain of Exophiala species. The patient responded to 4 weeks of intravenous amphotericin B therapy. Early identification of the fungus was important for the choice of anti-fungal regimen. As opportunistic fungal infections in immunocompromised patients are globally emerging problems, the development of molecular techniques for fungal identification is crucial for early diagnosis and appropriate treatment.

Streptococcus sinensis may react with Lancefield group F antiserum.

Lancefield group F streptococci have been found almost exclusively as members of the 'Streptococcus milleri' group, although they have been reported very occasionally in some other streptococcal species. Among 302 patients with bacteraemia caused by viridans streptococci over a 6-year period, three cases were caused by Streptococcus sinensis (type strain HKU4T, HKU5 and HKU6). All three patients had infective endocarditis complicating their underlying chronic rheumatic heart diseases. Gene sequencing showed no base differences between the 16S rRNA gene sequences of HKU5 and HKU6 and that of HKU4T. All three strains were Gram-positive, non-spore-forming cocci arranged in chains. All grew on sheep blood agar as alpha-haemolytic, grey colonies of 0.5-1 mm in diameter after 24 h incubation at 37 degrees C in ambient air. Lancefield grouping revealed that HKU5 and HKU6 were Lancefield group F, but HKU4T was non-groupable with Lancefield groups A, B, C, D, F or G antisera. HKU4T was identified by the Vitek system (GPI), API system (20 STREP) and ATB system (ID32 STREP) as 99 % Streptococcus intermedius, 51.3 % S. intermedius and 99.9 % Streptococcus anginosus, respectively. Using the same tests, HKU5 was identified as 87 % Streptococcus sanguinis/Streptococcus gordonii, 59 % Streptococcus salivarius and 99.6 % S. anginosus, respectively, and HKU6 as 87 % S. sanguinis/S. gordonii, 77 % Streptococcus pneumoniae and 98.3 % S. anginosus, respectively. The present data revealed that a proportion of Lancefield group F streptococci could be S. sinensis. Lancefield group F streptococci should not be automatically reported as 'S. milleri'.

Thermo-tolerant Campylobacter fetus bacteraemia identified by 16S ribosomal RNA gene sequencing: an emerging pathogen in immunocompromised patients.

Eight Campylobacter isolates that were able to grow at 25 degrees C and 42 degrees C and had the same biochemical profile were isolated from the blood of eight immunocompromised patients. Conventional biochemical tests were unable to determine whether they were isolates of thermo-tolerant C. fetus, H2S-negative C hyointestinalis, or a new Campylobacter species. Sequencing of the 16S ribosomal RNA genes showed that all eight isolates had the same nucleotide sequence and this was identical to that of C. fetus (GenBank accession no. AF219233). All eight patients had underlying disease and two died despite antibiotic treatment. Because of the ability of C fetus to grow over a wide range of temperatures and a higher incidence of bacteraemia by this organism than C. jejuni in the past 5 years in Hong Kong, thermo-tolerant C fetus may be an emerging pathogen in immunocompromised patients in the years to come.

A novel MLST sequence type discovered in the first fatal case of Laribacter hongkongensis bacteremia clusters with the sequence types of other human isolates.

Laribacter hongkongensis is a gram-negative, facultative anaerobic, motile, S-shaped, asaccharolytic, urease-positive bacillus in the Neisseriaceae family of ß-proteobacteria. To date, all patients with L. hongkongensis infection have survived, including the two patients with L. hongkongensis bacteremia and patients with L. hongkongensis gastroenteritis. In this study, we describe the clinical, microbiological and molecular characterization of the first fatal case associated with L. hongkongensis bacteremia in a patient with colonic carcinoma that metastasized to the liver. The identity of the isolate was confirmed via phenotypic tests and 16S rRNA gene sequencing. Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), using the Bruker database extended with L. hongkongensis reference strains, also identified the isolate as L. hongkongensis, with a top match score of 2.473. Multilocus sequence typing revealed a new sequence type (ST), and phylogenetic analysis and eBURST demonstrated unambiguously that the ST of the isolate was clustered with two other STs found exclusively in human patients, consistent with the theory that some clones of L. hongkongensis could be more virulent than others. Underlying liver diseases and ascites potentially represent distinct risk factors for invasive L. hongkongensis infection. More widespread use of MALDI-TOF MS for identification and improvements of selective media should facilitate the identification of more cases of L. hongkongensis infection.

Leptotrichia hongkongensis sp. nov., a novel Leptotrichia species with the oral cavity as its natural reservoir.

A straight, non-sporulating, Gram-variable bacillus (HKU24(T)) was recovered from the blood culture of a patient with metastatic breast carcinoma. After repeated subculturing in BACTEC Plus Anaerobic/F blood culture broth, HKU24(T) grew on brucella agar as non-hemolytic, pinpoint colonies after 96 h of incubation at 37 degrees C in an anaerobic environment and aerobic environment with 5% CO2. Growth was enhanced with a streak of Staphylococcus aureus. HKU24(T) was non-motile and catalase-negative, but positive for alkaline phosphatase, beta-glucosidase, and alpha-glucosidase. It hydrolyzed phenylphosphonate and reduced resazurin. 16S rRNA, groEL, gyrB, recA, and rpoB sequencing showed that HKU24(T) occupies a distinct phylogenetic position among the Leptotrichia species, being most closely related to Leptotrichia trevisanii. Using HKU24(T) groEL, gyrB, recA, and rpoB gene-specific primers, fragments of these genes were amplified from one of 20 oral specimens. Based on phenotypic and genotypic characteristics, we propose a new species, Leptotrichia hongkongensis sp. nov., to describe this bacterium.

Bacteremia caused by Solobacterium moorei in a patient with acute proctitis and carcinoma of the cervix.

We describe a case of Solobacterium moorei bacteremia in a 43-year-old woman presenting with acute proctitis complicating radiotherapy for cervical carcinoma. Phenotypic tests failed to identify the bacterium, which was subsequently identified by 16S rRNA gene sequencing. 16S rRNA gene sequencing could help better define the pathogenicity of S. moorei.

Anaerospora hongkongensis gen. nov. sp. nov., a novel genus and species with ribosomal DNA operon heterogeneity isolated from an intravenous drug abuser with pseudobacteremia.

A bacterium was isolated from the blood culture of an intravenous drug abuser with pseudobacteremia. The cells were strictly anaerobic, straight or slightly curved, sporulating, Gram-negative rods. It grew on sheep blood agar as non-hemolytic, pinpoint colonies after 48 hr of incubation at 37 C in an anaerobic environment. It was motile but did not produce catalase or cytochrome oxidase. 16S ribosomal DNA (rDNA) sequencing revealed three different copies of 16S rDNA sequences. More than 90% of the differences among them were due to differences in the lengths of the sequences. Phylogenetically, the bacterium is clustered with Dendrosporobacter, Sporomusa, and Propionispora, the other three genera of anaerobic, sporulating, Gram-negative rods. There were 8.6-11.1% differences between the 16S rDNA sequences of the bacterium and that of D. quercicolus, 4.7-15.1% differences between the 16S rDNA sequences of it and those of S. acidovorans, S. aerivorans, S. malonica, S. ovata, S. paucivorans, S. silvacetica, S. spaeroides, and S. termitida, and 7.6-13.1% differences between the 16S rDNA sequences of it and those of P. hippei and P. vibrioides. The G+C content of the bacterium (mean +/- SD) was 46.8 +/- 3.2%. For these reasons, a new genus and species, Anaerospora hongkongensis gen. nov. sp. nov., is proposed, for which HKU15T is the type strain.

Invasive Streptococcus iniae infections outside North America.

Streptococcus iniae, a fish pathogen causing infections in aquaculture farms worldwide, has only been reported to cause human infections in North America. In this article, we report the first two cases of invasive S. iniae infections in two Chinese patients outside North America. While the first patient presented with bacteremic cellulitis, which is the most common presentation in previous cases, the second patient represents the first recognized case of S. iniae osteomyelitis. Both S. iniae strains isolated from the two patients were either misidentified or unidentified by three commercial systems and were only identified by 16S rRNA gene sequencing. Since no currently available commercial system for bacterial identification includes S. iniae in its database, 16S rRNA gene sequencing is the most practical and reliable method to identify the bacterium at the moment. In contrast to the distinct genetic profile described previously in clinical isolates from Canada, the present two isolates and a clinical isolate from a Canadian patient were found to be genetically unrelated, as demonstrated by pulsed-field gel electrophoresis. Morphologically, colonies of both isolates were also larger, more beta-hemolytic and mucoid, which differ from the usual morphotype described for S. iniae. Owing to their habit of cooking and eating fresh fish, the Asian population is strongly associated with S. iniae infections. As a result of the difficulty in making microbiological diagnosis in patients with cellulitis and the problem of identification in most clinical microbiology laboratories, the prevalence of S. iniae infections, especially in the Asian population, may have been under-estimated.

Relatively alcohol-resistant mycobacteria are emerging pathogens in patients receiving acupuncture treatment.

Acupuncture has been gaining popularity as a form of alternative medicine. In the past, only blood-borne viruses and anecdotal reports of bacterial infections have been associated with acupuncture. We report on four patients with mycobacterial infections complicating acupuncture who were encountered in a 2-year period. All had clinical and/or radiological lesions at acupuncture point- and meridian-specific locations. There was no other history of trauma or other clinical foci of infections, and the chest radiographs were normal. Histological studies of biopsy specimens of all four patients showed changes compatible with chronic inflammation, with granulomatous inflammation present in three patients and acid-fast bacilli present in two. Conventional biochemical tests and whole-cell fatty acid analysis for identification were inconclusive for all four nonpigmented mycobacteria recovered from tissue biopsies. 16S rRNA gene sequencing showed that the strains from two patients were Mycobacterium chelonae and that those from the other two were Mycobacterium nonchromogenicum. Alcohol resistance assay using the quantitative suspension test revealed that all four strains showed prolonged survival in 75% alcohol compared to other skin flora. Mycobacterial infections transmitted by acupuncture are an emerging problem. A high index of suspicion is essential to recognize this clinical syndrome, and strict implementation of proper infection control guidelines for acupuncture is mandatory.

Streptococcus sinensis sp. nov., a novel species isolated from a patient with infective endocarditis.

A bacterium was isolated from the blood culture of a patient with infective endocarditis. The cells were facultative anaerobic, nonsporulating, gram-positive cocci arranged in chains. The bacterium grows on sheep blood agar as alpha-hemolytic, gray colonies of 0.5 to 1 mm in diameter after 24 h of incubation at 37 degrees C in ambient air. Growth also occurs in 10 or 40% bile and on bile esculin agar but not in 6% NaCl. No enhancement of growth is observed in 5% CO(2). It is nongroupable with Lancefield groups A, B, C, D, F, or G antisera and is resistant to optochin and bacitracin. The organism is aflagellated and is nonmotile at both 25 and 37 degrees C. It is Voges-Proskauer test positive. It produces leucine arylamidase and beta-glucosidase but not catalase, urease, lysine decarboxylase, or ornithine decarboxylase. It hydrolyzes esculin and arginine. It utilizes glucose, lactose, salicin, sucrose, pullulan, trehalose, cellobiose, hemicellulase, mannose, maltose, and starch. 16S rRNA gene sequencing showed that there were 3.6, 3.7, 4.3, 4.7, and 5.9% differences between the 16S rRNA gene sequence of the bacterium and those of Streptococcus gordonii, Streptococcus intermedius, Streptococcus constellatus, Streptococcus sanguis, and Streptococcus anginosus, respectively. The G+C content of it (mean plus minus standard deviation) was 53.0% plus minus 2.9%. Based on phylogenetic affiliation, it belongs to the mitis or anginosus group of Streptococcus. For these reasons a new species, Streptococcus sinensis sp. nov., is proposed, for which HKU4 is the type strain. Further studies should be performed to ascertain the potential of this bacterium to become an emerging cause of infective endocarditis.

Analysis of a viridans group strain reveals a case of bacteremia due to lancefield group G alpha-hemolytic Streptococcus dysgalactiae subsp equisimilis in a patient with pyomyositis and reactive arthritis.

Streptococcus dysgalactiae is classified by a combination of phenotypic and genotypic characteristics into Lancefield group C alpha-hemolytic Streptococcus dysgalactiae subsp. dysgalactiae and Lancefield group C, group G, and group L beta-hemolytic Streptococcus dysgalactiae subsp. equisimilis. In this study, we report the isolation of a catalase-negative, alpha-hemolytic, optochin- and bacitracin-resistant viridans group strain, which does not grow in 10 or 40% bile, on MacConkey agar or bile esculin agar, or in 6% NaCl, from the blood culture of a 73-year-old woman with pyomyositis and poststreptococcal reactive arthritis. Lancefield grouping revealed that the strain was a group G streptococcus. The Vitek system (GPI) showed that it was unidentified, and the API system (20 STREP) showed that it was 95.7% S. dysgalactiae subsp. dysgalactiae. 16S rRNA gene sequencing showed that it was a strain of S. dysgalactiae. Based on phylogenetic affiliation with 16S rRNA gene or GroEL amino acid (another bacterial gene, in addition to 16S rRNA gene, that is highly conserved) sequences, the strain is most closely related to Lancefield group C beta-hemolytic S. dysgalactiae subsp. equisimilis. PCR amplification and sequencing of the streptolysin S structural gene (sagA) and M protein gene (emm) hypervariable region showed the presence of these suspected primary virulence factors. Further studies would delineate whether the isolate is just a hemolysin-deficient variant of group G beta-hemolytic S. dysgalactiae subsp. equisimilis or a novel type of S. dysgalactiae. The present case showed that group G alpha-hemolytic S. dysgalactiae subsp. equisimilis can be associated with serious invasive infection and poststreptococcal sequelae.

Usefulness of the MicroSeq 500 16S ribosomal DNA-based bacterial identification system for identification of clinically significant bacterial isolates with ambiguous biochemical profiles.

Due to the inadequate automation in the amplification and sequencing procedures, the use of 16S rRNA gene sequence-based methods in clinical microbiology laboratories is largely limited to identification of strains that are difficult to identify by phenotypic methods. In this study, using conventional full-sequence 16S rRNA gene sequencing as the "gold standard," we evaluated the usefulness of the MicroSeq 500 16S ribosomal DNA (rDNA)-based bacterial identification system, which involves amplification and sequencing of the first 527-bp fragment of the 16S rRNA genes of bacterial strains and analysis of the sequences using the database of the system, for identification of clinically significant bacterial isolates with ambiguous biochemical profiles. Among 37 clinically significant bacterial strains that showed ambiguous biochemical profiles, representing 37 nonduplicating aerobic gram-positive and gram-negative, anaerobic, and Mycobacterium species, the MicroSeq 500 16S rDNA-based bacterial identification system was successful in identifying 30 (81.1%) of them. Five (13.5%) isolates were misidentified at the genus level (Granulicatella adiacens was misidentified as Abiotrophia defectiva, Helcococcus kunzii was misidentified as Clostridium hastiforme, Olsenella uli was misidentified as Atopobium rimae, Leptotrichia buccalis was misidentified as Fusobacterium mortiferum, and Bergeyella zoohelcum was misidentified as Rimerella anatipestifer), and two (5.4%) were misidentified at the species level (Actinomyces odontolyticus was misidentified as Actinomyces meyeri and Arcobacter cryaerophilus was misidentified as Arcobacter butzleri). When the same 527-bp DNA sequences of these seven isolates were compared to the known 16S rRNA gene sequences in the GenBank, five yielded the correct identity, with good discrimination between the best and second best match sequences, meaning that the reason for misidentification in these five isolates was due to a lack of the 16S rRNA gene sequences of these bacteria in the database of the MicroSeq 500 16S rDNA-based bacterial identification system. In conclusion, the MicroSeq 500 16S rDNA-based bacterial identification system is useful for identification of most clinically important bacterial strains with ambiguous biochemical profiles, but the database of the MicroSeq 500 16S rDNA-based bacterial identification system has to be expanded in order to encompass the rarely encountered bacterial species and achieve better accuracy in bacterial identification.