Identification of species of Abiotrophia, Enterococcus, Granulicatella and Streptococcus by sequence analysis of the ribosomal 16S-23S intergenic spacer region

Using groEL as the target for identification of Enterococcus faecium clades and 7 clinically relevant Enterococcus species

BACKGROUND/PURPOSE

Accurate identification is important for effective treatment because Enterococcus species have talents to cope with various antibiotics either by intrinsic resistance or by acquisition of mobile genetic elements. The groEL gene is a permissive target in identification of bacteria. We aimed to develop simple assays based on groEL for identification of enterococci.

RESULTS

We continued our previous work and determined groEL gene sequences of Enterococcus species isolated from clinical specimens. Phylogenetic analysis based on groEL revealed that each strain clustered well with their reference strains (bootstrap value 100%), in which Enterococcusfaecium and Enterococcusgallinarum could be split into two clades. The divergence of E. faecium was coincident with hospital-associated clade, known as clade A, and community-associated clade, known as clade B. A PCR-restriction fragment length polymorphism (PCR-RFLP) assay was therefore designed to differentiate the two E. faecium clades, based on the specific RsaI cutting sites present in the two clades. To differentiate 7 clinical relevant Enterococcus species, the multiplex PCR assay was designed to identify Enterococcusavium, Enterococcuscasseliflavus, Enterococcusfaecalis, E. faecium, E. gallinarum, Enterococcushirae and Enterococcusraffinosus. Specificity was tested with other Enterococcus species including Enterococcuscecorum, Enterococcusdurans and Enterococcusmundtii. None of these bacterial species generated products of similar size to those of the seven Enterococcus species.

CONCLUSION

The simple PCR-RFLP and multiplex PCR assays on the basis of groEL gene provided an alternative way to identify Enterococcus species.

Marteilia refringens and Marteilia pararefringens sp. nov. are distinct parasites of bivalves and have different European distributions

Marteilia refringens causes marteiliosis in oysters, mussels and other bivalve molluscs. This parasite previously comprised two species, M. refringens and Marteilia maurini, which were synonymized in 2007 and subsequently referred to as M. refringens ‘O-type’ and ‘M-type’. O-type has caused mass mortalities of the flat oyster Ostrea edulis. We used high throughput sequencing and histology to intensively screen flat oysters and mussels (Mytilus edulis) from the UK, Sweden and Norway for infection by both types and to generate multi-gene datasets to clarify their genetic distinctiveness. Mussels from the UK, Norway and Sweden were more frequently polymerase chain reaction (PCR)-positive for M-type (75/849) than oysters (11/542). We did not detect O-type in any northern European samples, and no histology-confirmed Marteilia-infected oysters were found in the UK, Norway and Sweden, even where co-habiting mussels were infected by the M-type. The two genetic lineages within ‘M. refringens’ are robustly distinguishable at species level. We therefore formally define them as separate species: M. refringens (previously O-type) and Marteilia pararefringens sp. nov. (M-type). We designed and tested new Marteilia-specific PCR primers amplifying from the 3’ end of the 18S rRNA gene through to the 5.8S gene, which specifically amplified the target region from both tissue and environmental samples.

Current Challenges of Streptococcus Infection and Effective Molecular, Cellular, and Environmental Control Methods in Aquaculture

Several bacterial etiological agents of streptococcal disease have been associated with fish mortality and serious global economic loss. Bacterial identification based on biochemical, molecular, and phenotypic methods has been routinely used, along with assessment of morphological analyses. Among these, the molecular method of 16S rRNA sequencing is reliable, but presently, advanced genomics are preferred over other traditional identification methodologies. This review highlights the geographical variation in strains, their relatedness, as well as the complexity of diagnosis, pathogenesis, and various control methods of streptococcal infections. Several limitations, from diagnosis to control, have been reported, which make prevention and containment of streptococcal disease difficult. In this review, we discuss the challenges in diagnosis, pathogenesis, and control methods and suggest appropriate molecular (comparative genomics), cellular, and environmental solutions from among the best available possibilities.

Identification of Staphylococcus spp. and detection of mecA by an oligonucleotide array

Phenotypic identification of coagulase-negative staphylococci (CoNS) is difficult and many staphylococcal species carry mecA. This study developed an array that was able to detect mecA and identify 30 staphylococcal species by targeting the internal transcribed spacer regions. A total of 129 target reference strains (30 species) and 434 clinical isolates of staphylococci were analyzed. Gene sequencing of 16S rRNA, gap or tuf genes was the reference method for species identification. All reference strains (100%) were correctly identified, while the identification rates of clinical isolates of S. aureus and CoNS were 98.9% and 98%, respectively. The sensitivity and specificity for mecA detection were 99% and 100%, respectively, in S. aureus isolates, and both values were 100% in isolates of CoNS. The assay takes 6 h from a purified culture isolate, and so far it has not been performed directly on patient samples.

The novel species Streptococcus tigurinus and its association with oral infection

Streptococcus tigurinus is a novel species of viridans streptococci, shown to cause severe invasive infections such as infective endocarditis, spondylodiscitis and meningitis. S. tigurinus belongs to the Streptococcus mitis group and is most closely related to Streptococcus mitis, Streptococcus oralis, Streptococcus pneumoniae, Streptococcus pseudopneumoniae and Streptococcus infantis. The presence of S. tigurinus in the human oral cavity has been documented, including in patients with periodontal disease. This review addresses the available scientific knowledge on S. tigurinus and its association with closely related streptococci, and discusses its putative involvement in common oral infections. While there is as yet no strong evidence on the involvement of S. tigurinus with oral infections, its presence in the oral cavity and its association with endocarditis warrants special attention for a link between oral and systemic infection.

Rapid identification of bacteria and Candida pathogens in peritoneal dialysis effluent from patients with peritoneal dialysis-related peritonitis by use of multilocus PCR coupled with electrospray ionization mass spectrometry

PCR coupled with electrospray ionization mass spectrometry (PCR/ESI-MS) was compared with culture for pathogen detection in peritoneal dialysis (PD)-related peritonitis. Of 21 samples of PD effluent, PCR/ESI-MS identified microorganisms in 18 (86%) samples, including Mycobacterium tuberculosis in 1 culture-negative sample. Of 15 double-positive samples, PCR/ESI-MS and culture reached levels of agreement of 100% (15/15) and 87.5% (7/8) at the genus and species levels, respectively. PCR/ESI-MS can be used for rapid pathogen detection in PD-related peritonitis.

Streptococcus tigurinus, a novel member of the Streptococcus mitis group, causes invasive infections

We recently described the novel species Streptococcus tigurinus sp. nov. belonging to the Streptococcus mitis group. The type strain AZ_3a(T) of S. tigurinus was originally isolated from a patient with infective endocarditis. According to its phenotypic and molecular characteristics, S. tigurinus is most closely related to Streptococcus mitis, Streptococcus pneumoniae, Streptococcus pseudopneumoniae, Streptococcus oralis, and Streptococcus infantis. Accurate identification of S. tigurinus is facilitated by 16S rRNA gene analysis. We retrospectively analyzed our 16S rRNA gene molecular database, which contains sequences of all clinical samples obtained in our institute since 2003. We detected 17 16S rRNA gene sequences which were assigned to S. tigurinus, including sequences from the 3 S. tigurinus strains described previously. S. tigurinus originated from normally sterile body sites, such as blood, cerebrospinal fluid, or heart valves, of 14 patients and was initially detected by culture or broad-range 16S rRNA gene PCR, followed by sequencing. The 14 patients had serious invasive infections, i.e., infective endocarditis (n = 6), spondylodiscitis (n = 3), bacteremia (n = 2), meningitis (n = 1), prosthetic joint infection (n = 1), and thoracic empyema (n = 1). To evaluate the presence of Streptococcus tigurinus in the endogenous oral microbial flora, we screened saliva specimens of 31 volunteers. After selective growth, alpha-hemolytic growing colonies were analyzed by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) and subsequent molecular methods. S. tigurinus was not identified among 608 strains analyzed. These data indicate that S. tigurinus is not widely distributed in the oral cavity. In conclusion, S. tigurinus is a novel agent of invasive infections, particularly infective endocarditis.

The influence of iron availability on human salivary microbial community composition

It is a well-recognized fact that the composition of human salivary microbial community is greatly affected by its nutritional environment. However, most studies are currently focused on major carbon or nitrogen sources with limited attention to trace elements like essential mineral ions. In this study, we examined the effect of iron availability on the bacterial profiles of an in vitro human salivary microbial community as iron is an essential trace element for the survival and proliferation of virtually all microorganisms. Analysis via a combination of PCR with denaturing gradient gel electrophoresis demonstrated a drastic change in species composition of an in vitro human salivary microbiota when iron was scavenged from the culture medium by addition of the iron chelator 2,2'-bipyridyl. This shift in community profile was prevented by the presence of excessive ferrous iron (Fe(2+)). Most interestingly, under iron deficiency, the in vitro grown salivary microbial community became dominated by several hemolytic bacterial species, including Streptococcus spp., Gemella spp., and Granulicatella spp. all of which have been implicated in infective endocarditis. These data provide evidence that iron availability can modulate host-associated oral microbial communities, resulting in a microbiota with potential clinical impact.

Granulicatella infection: diagnosis and management

Granulicatella species, along with the genus Abiotrophia, were originally known as 'nutritionally variant streptococci'. They are a normal component of the oral flora, but have been associated with a variety of invasive infections in man and are most noted as a cause of bacterial endocarditis. It is often advised that Granulicatella endocarditis should be treated in the same way as enterococcal endocarditis. We review here the published data concerning diagnosis and treatment of Granulicatella infection, and include some observations from local cases, including four cases of endocarditis.

Streptococcus tigurinus sp. nov., isolated from blood of patients with endocarditis, meningitis and spondylodiscitis

Four Gram-stain-positive, catalase-negative, coccus-shaped bacterial strains were isolated from multiple blood cultures of patients with endocarditis, meningitis and spondylodiscitis. The isolates were tentatively identified as viridans streptococci on the basis of phenotypic characteristics. Comparative 16S rRNA gene sequencing studies showed that the organisms were members of the Streptococcus mitis group but did not correspond to any recognized species. The nearest phylogenetic relative was S. mitis ATCC 49456(T), with 98.6% sequence similarity. The representative strain AZ_3a(T) showed less than 96.8, 97.6, 94.5 and 95.5% similarity to the phylogenetically most closely related species by recA, rpoB, sodA and groEL gene sequence analysis, respectively. DNA-DNA hybridization analyses showed a low reassociation value of 32.2% between strain AZ_3a(T) and S. mitis DSM 12643(T). Reassociation values with members of other S. mitis group species ranged from 27.3 to 49.7%. The G+C content of the DNA was 40.0 mol%. Based on our biochemical and molecular analyses, the isolates represent a novel species, for which the name Streptococcus tigurinus sp. nov. is proposed. The type strain is AZ_3a(T) ( = CCOS 600(T)  = DSM 24864(T)).

Identification of clinically important anaerobic bacteria by an oligonucleotide array

Anaerobic bacteria can cause a wide variety of infections, and some of these infections can be serious. Conventional identification methods based on biochemical tests are often lengthy and can produce inconclusive results. An oligonucleotide array based on the 16S-23S rRNA intergenic spacer (ITS) sequences was developed to identify 28 species of anaerobic bacteria and Veillonella. The method consisted of PCR amplification of the ITS regions with universal primers, followed by hybridization of the digoxigenin-labeled PCR products to a panel of 35 oligonucleotide probes (17- to 30-mers) immobilized on a nylon membrane. The performance of the array was determined by testing 310 target strains (strains which we aimed to identify), including 122 reference strains and 188 clinical isolates. In addition, 98 nontarget strains were used for specificity testing. The sensitivity and the specificity of the array for the identification of pure cultures were 99.7 and 97.1%, respectively. The array was further assessed for its ability to detect anaerobic bacteria in 49 clinical specimens. Two species (Finegoldia magna and Bacteroides vulgatus) were detected in two specimens by the array, and the results were in accordance with those obtained by culture. The whole procedure of array hybridization took about 8 h, starting with the isolated colonies. The array can be used as an accurate alternative to conventional methods for the identification of clinically important anaerobes.

Identification of non-fermenting Gram-negative bacteria of clinical importance by an oligonucleotide array

Many species of non-fermenting Gram-negative bacilli (non-fermenters) are important opportunistic and nosocomial pathogens. Identification of most species of non-fermenters by phenotypic characteristics can be difficult. In this study, an oligonucleotide array was developed to identify 38 species of clinically relevant non-fermenters. The method consisted of PCR-based amplification of 16S-23S rRNA gene intergenic spacer (ITS) regions using bacterial universal primers, followed by hybridization of the digoxigenin-labelled PCR products with oligonucleotide probes immobilized on a nylon membrane. A total of 398 strains, comprising 276 target strains (i.e. strains belonging to the 38 species to be identified) and 122 non-target strains (i.e. strains not included in the array), were analysed by the array. Four target strains (three reference strains and one clinical isolate) produced discrepant identification by array hybridization. Three of the four discordant strains were found to be correctly identified by the array, as confirmed by sequencing of the ITS and 16S rRNA genes, with the remaining one being an unidentified species. The sensitivity and specificity of the array for identification of non-fermenters were 100 and 96.7%, respectively. In summary, the oligonucleotide array described here offers a very reliable method for identification of clinically relevant non-fermenters, with results being available within one working day.

Rapid identification of beta-hemolytic streptococci by fluorescence in situ hybridization (FISH)

Rapid identification of pathogenic, beta-hemolytic streptococci is important for treatment decisions. We evaluated fluorescence in situ hybridization (FISH) for this purpose using 23 reference strains, 157 clinical isolates, and 80 blood cultures showing streptococci in the Gram stain. With a sensitivity and specificity in excess of 99%, FISH proved to be suitable for rapid identification of beta-hemolytic streptococci in a diagnostic laboratory.

Phylogenetic analysis of viridans group streptococci causing endocarditis

Identification of viridans group streptococci (VGS) to the species level is difficult because VGS exchange genetic material. We performed multilocus DNA target sequencing to assess phylogenetic concordance of VGS for a well-defined clinical syndrome. The hierarchy of sequence data was often discordant, underscoring the importance of establishing biological relevance for finer phylogenetic distinctions.

Oligonucleotide array-based identification of species in the Acinetobacter calcoaceticus-A. baumannii complex in isolates from blood cultures and antimicrobial susceptibility testing of the isolates

Acinetobacter calcoaceticus, A. baumannii, Acinetobacter genomic species (gen. sp.) 3, and Acinetobacter gen. sp. 13TU, which are included in the A. calcoaceticus-A. baumannii complex, are difficult to distinguish by phenotypic methods. An array with six oligonucleotide probes based on the 16S-23S rRNA gene intergenic spacer (ITS) region was developed to differentiate species in the A. calcoaceticus-A. baumannii complex. Validation of the array with a reference collection of 52 strains of the A. calcoaceticus-A. baumannii complex and 137 strains of other species resulted in an identification sensitivity and specificity of 100%. By using the array, the species distribution of 291 isolates of the A. calcoaceticus-A. baumannii complex from patients with bacteremia were determined to be A. baumannii (221 strains [75.9%]), Acinetobacter gen. sp. 3 (67 strains [23.0%]), Acinetobacter gen. sp. 13TU (2 strains [0.7%]), and unidentified Acinetobacter sp. (1 strain [0.3%]). The identification accuracy of the array for 12 randomly selected isolates from patients with bacteremia was further confirmed by sequence analyses of the ITS region and the 16S rRNA gene. Antimicrobial susceptibility testing of the 291 isolates from patients with bacteremia revealed that A. baumannii strains were less susceptible to antimicrobial agents than Acinetobacter gen. sp. 3. All Acinetobacter gen. sp. 3 strains were susceptible to ampicillin-sulbactam, imipenem, and meropenem; but only 67.4%, 90%, and 86% of the A. baumannii strains were susceptible to ampicillin-sulbactam, imipenem, and meropenem, respectively. The observed significant variations in antimicrobial susceptibility among different species in the A. calcoaceticus-A. baumannii complex emphasize that the differentiation of species within the complex is relevant from a clinical-epidemiological point of view.

PCR-RFLP assay for species and subspecies differentiation of the Streptococcus bovis group based on groESL sequences

The sequence diversity of groESL genes among Streptococcus bovis group isolates was analysed, including five reference strains and 36 clinical isolates. Phylogenetic analysis of the groES and groEL sequences showed that the isolates that belonged to the same species or subspecies usually clustered together. The intergenic spacer region between groES and groEL was variable in size (67–342 bp) and sequence and appeared to be a unique marker for species or subspecies determination. Sequence similarities of the groESL genes among species and subspecies ranged from 84.2 to 99.0 % in groES, and from 88.0 to 99.0 % in groEL. Based on the sequences determined, a Streptococcus bovis group-specific PCR assay was developed, which may provide an alternative means of distinguishing the bovis group from other viridans streptococci. Restriction digestion of the amplicon with AclI further differentiated the species and subspecies.

Specific detection of reverse transcription-loop-mediated isothermal amplification amplicons for Taura syndrome virus by colorimetric dot–blot hybridization

The goal of this study was to develop a field diagnosis system based on isothermal reverse transcription-loop-mediated amplification (RT-LAMP) for shrimp Taura syndrome virus (TSV), placing emphasis on specific and simple detection of the LAMP amplicons. After a single-tube RT-LAMP reaction for TSV was established, colorimetric dot-blot hybridization (DBH) was adopted to detect signals only from the target-derived amplicons. The results showed that the modified DBH offered unambiguous and sensitive detection of the TSV RT-LAMP amplicons without the UV cross-linking and denaturation steps. Together, TSV RT-LAMP-DBH assay reached the same dilution point as reverse transcription-nested polymerase chain reaction-agarose gel electrophoresis (RT-nPCR-AGE) for TSV detection. Specificity of the assay was demonstrated by the absence of DBH signal from yeast tRNA and various shrimp viruses. TSV RT-LAMP-DBH was applied to 125 Penaeus vannamei and demonstrated a very good concordance (kappa value, 0.823) with RT-nPCR-AGE assay in detection efficiency. Furthermore, a one-step guanidinium thiocyanate (GuSCN) homogenization method was established to provide RNA extraction efficiency comparable to that of the TRIzol Reagent for RT-LAMP. Requiring simply a heating apparatus, the GuSCN RNA extraction-isothermal RT-LAMP-DBH protocol has the potential for further development for diagnosis of diseases in the field.