Identification of clinically isolated vancomycin-resistant enterococci: comparison of API and BBL Crystal systems.

Twenty-eight phenotypically separate strains of clinically isolated vancomycin-resistant enterococci have been investigated with two API identification kit systems (20 Strep and Rapid ID 32 Strep) and two BBL Crystal kits (Gram Positive and Rapid Gram Positive). All strains were identified as Enterococcus faecium by a reference laboratory. The Rapid ID 32 kit positively identified 15 of 28 strains (54%), but only two (7%) were identified correctly: 11 were identified as 'doubtful' or 'to genus level' and two gave 'unacceptable' profiles. The API 20 Strep kit identified 27 strains (96%), but only 16 (57%) were identified correctly as E. faecium. The Rapid ID 32 kit erred by either positively misidentifying vancomycin-resistant E. faecium as E. casseliflavus or E. gallinarum, or indicated that this was the most likely identification, while the API 20 Strep kit more commonly produced a misidentification as E. casseliflavus. The Crystal Gram Positive and Rapid Gram Positive kits correctly identified 26 (93%) and 27 (96%) of the strains, respectively.     

Comparison of API Rapid Strep, Baxter MicroScan Rapid Pos ID Panel, BBL Minitek Differential Identification System, IDS RapID STR System, and Vitek GPI to conventional biochemical tests for identification of viridans streptococci

Viridans group streptococci (36 stock strains and 167 single patient blood culture isolates) were assessed using API Rapid Strep, Baxter MicroScan Rapid Pos ID Panel, BBL Minitek Differential Identification System, IDS RapID STR System, and Vitek GPI methods. Identification data obtained with these systems were compared with those indicated by conventional biochemical procedures. API, Baxter MicroScan, BBL, IDS, and Vitek corresponded with conventional biochemical identification in 74%, 66%, 65%, 50%, and 61% of the isolates, respectively; using recommended supplemental tests, agreement was augmented in 9%, 11%, 20%, 11%, and 21% of the isolates, respectively. Disagreement with conventional biochemical methods occurred in 14%, 17%, 14%, 32%, and 10% of the commercial techniques, respectively; no identification was possible in 2%, 5%, fewer than 1%, 6%, and 8% of specimens, respectively. BBL, API, and Baxter MicroScan systems provided the most reliable rapid identification, although supplemental testing often was required. Until a higher percentage of correct identification data can be obtained without supplemental procedures, conventional biochemical techniques will remain the methods of choice for identification of viridans streptococci.     

Comparative Evaluation of a Commercial System for Identification of Gram-Positive Cocci

 The performance of a new commercial system for the identification of different groups of gram-positive cocci [BBL Crystal Gram-Positive (GP) Identification System; Becton Dickinson Microbiology Systems, Germany] was evaluated in comparison with two currently used commercial systems, the API Staph and the API Strep (bioMérieux Diagnostic, Germany). A total of 191 strains from seven different gram-positive genera comprising 32 different species were tested. For the BBL Crystal GP system, the correct identification rate without additional tests was 89.5% at the species level and 97.9% at the genus level. The findings suggest that the newly introduced BBL Crystal GP ID system provides an accurate method for the identification of gram-positive cocci, with an overall rate of correct species identification of about 90%, similar to that of the established API systems. Its major advantage is the extended spectrum of taxa included in a single test panel in contrast to the two different API test kits. Furthermore, the simplicity of use and the safe and rapid handling in a closed system conveniently accommodate existing laboratory workflow.     

Identification of 43 Streptococcus species by pyrosequencing analysis of the rnpB gene

Pyrosequencing technology was evaluated for identification of species within the Streptococcus genus. Two variable regions in the rnpB gene, which encodes the RNA subunit of endonuclease P, were sequenced in two reactions. Of 43 species, all could be identified to the species level except strains of the species pairs Streptococcus anginosus/S. constellatus and S. infantis/S. peroris. A total of 113 blood culture isolates were identified by pyrosequencing analysis of partial rnpB sequences. All but eight isolates could be unambiguously assigned to a specific species when the first 30 nucleotides of the two regions were compared to an rnpB database comprising 107 streptococcal strains. Principal coordinate analysis of sequence variation of strains from viridans group streptococci resulted in species-specific clusters for the mitis and the salivarius groups but not for the anginosus group. The identification capacity of pyrosequencing was compared to the biochemical test systems VITEK 2 and Rapid ID 32 Strep. The concordance between pyrosequencing and VITEK 2 was 75%, and for Rapid ID 32 Strep the corresponding figure was 77%. Isolates with discrepant identifications in the three methods were subjected to entire rnpB DNA sequence analysis that confirmed the identifications by pyrosequencing. In conclusion, pyrosequencing analysis of the rnpB gene can reliably identify Streptococcus species with high resolution.     

Evaluation of the Rapid ID 32 Strep system

Objectives: To evaluate the performance of the Rapid ID 32 Strep system in the hands of clinical microbiologists without expert knowledge of streptococci or enterococci.
Methods: One hundred and twenty-two strains of streptococci and enterococci conventionally identified in a reference laboratory were sent under code numbers to a clinical microbiology laboratory and identified with the Rapid ID 32 Strep system.
Results: Regardless of whether automatic reading and identification or visual reading with identification using tables were done, 75–77% of the 122 examined strains were correctly identified, 7% were misidentified and 16–18% could not be identified with certainty to the species level. The system correctly identified the majority of the examined pyogenic streptococci and enterococci, but only two-thirds of the viridans streptococcal strains.
Conclusions: In a routine laboratory, the Rapid ID 32 Strep system can be used to give a rapid preliminary identification of streptococci and enterococci, but with viridans streptococci one would have to accept a certain risk of misidentification. The assay can, however, be used to biotype viridans streptococci in order to attempt to establish identity between separate isolates, e.g. from blood in patients suspected of having endocarditis.     

Evaluation of genotypic and phenotypic methods for differentiation of the members of the Anginosus group streptococci

The terminology and classification of the Anginosus group streptococci has been inconsistent. We tested the utility of 16S rRNA gene and tuf gene sequencing and conventional biochemical tests for the reliable differentiation of the Anginosus group streptococci. Biochemical testing included Rapid ID 32 Strep, API Strep, Fluo-Card Milleri, Wee-tabs, and Lancefield antigen typing. Altogether, 61 Anginosus group isolates from skin and soft tissue infections and four reference strains were included. Our results showed a good agreement between 16S rRNA gene and tuf gene sequencing. Using the full sequence was less discriminatory than using the first part of the 16S rRNA gene. The three species could not be separated with the API 20 Strep test. Streptococcus intermedius could be differentiated from the other two species by β-galactosidase (ONPG) and β-N-acetyl-glucosaminidase reactions. Rapid ID 32 Strep β-glucosidase reaction was useful in separating S. anginosus strains from S. constellatus. In conclusion, both 16S rRNA gene and tuf gene sequencing can be used for the reliable identification of the Anginosus group streptococci. S. intermedius can be readily differentiated from the other two species by phenotypic tests; however, 16S rRNA gene or tuf gene sequencing may be needed for separating some strains of S. constellatus from S. anginosus.     

Evaluation of the VITEK 2 system for identification and antimicrobial susceptibility testing of medically relevant gram-positive cocci

A study was conducted to evaluate the new VITEK 2 system (bioMérieux) for identification and antibiotic susceptibility testing of gram-positive cocci. Clinical isolates of Staphylococcus aureus (n = 100), coagulase-negative staphylococci (CNS) (n = 100), Enterococcus spp. (n = 89), Streptococcus agalactiae (n = 29), and Streptococcus pneumoniae (n = 66) were examined with the ID-GPC identification card and with the AST-P515 (for staphylococci), AST-P516 (for enterococci and S. agalactiae) and AST-P506 (for pneumococci) susceptibility cards. The identification comparison methods were the API Staph for staphylococci and the API 20 Strep for streptococci and enterococci; for antimicrobial susceptibility testing, the agar dilution method according to the procedure of the National Committee for Clinical Laboratory Standards (NCCLS) was used. The VITEK 2 system correctly identified to the species level (only one choice or after simple supplementary tests) 99% of S. aureus, 96.5% of S. agalactiae, 96.9% of S. pneumoniae, 92.7% of Enterococcus faecalis, 91.3% of Staphylococcus haemolyticus, and 88% of Staphylococcus epidermidis but was least able to identify Enterococcus faecium (71.4% correct). More than 90% of gram-positive cocci were identified within 3 h. According to the NCCLS breakpoints, antimicrobial susceptibility testing with the VITEK 2 system gave 96% correct category agreement, 0.82% very major errors, 0.17% major errors, and 2.7% minor errors. Antimicrobial susceptibility testing showed category agreement from 94 to 100% for S. aureus, from 90 to 100% for CNS, from 91 to 100% for enterococci, from 96 to 100% for S. agalactiae, and from 91 to 100% for S. pneumoniae. Microorganism-antibiotic combinations that gave very major errors were CNS-erythromycin, CNS-oxacillin, enterococci-teicoplanin, and enterococci-high-concentration gentamicin. Major errors were observed for CNS-oxacillin and S. agalactiae-tetracycline combinations. In conclusion the results of this study indicate that the VITEK 2 system represents an accurate and acceptable means for performing identification and antibiotic susceptibility tests with medically relevant gram-positive cocci.     

Evaluation of three rapid methods for detection of methicillin resistance in Staphylococcus aureus

The probe-based Velogene Rapid MRSA Identification Assay (ID Biomedical Corp., Vancouver, British Columbia, Canada) and the latex agglutination MRSA-Screen (Denka Seiken Co., Tokyo, Japan) were evaluated for their ability to identify methicillin-resistant Staphylococcus aureus (MRSA) and to distinguish strains of MRSA from borderline oxacillin-resistant S. aureus (BORSA; mecA-negative, oxacillin MICs of 2 to 8 microgram/ml). The Velogene is a 90-min assay using a chimeric probe to detect the mecA gene. MRSA-Screen is a 15-min latex agglutination test with penicillin-binding protein 2a antibody-sensitized latex particles. We compared these assays with the BBL Crystal MRSA ID System (Becton Dickinson, Cockeysville, Md.) and with PCR for mecA gene detection. A total of 397 clinical isolates of S. aureus were tested, consisting of 164 methicillin-susceptible strains, 197 MRSA strains, and 37 BORSA strains. All assays performed well for the identification of MRSA with sensitivities and specificities for Velogene, MRSA-Screen, and BBL Crystal MRSA ID of 98.5 and 100%, 98.5 and 100%, and 98.5 and 98%, respectively. Three MRSA strains were not correctly identified by each of the Velogene and MRSA-Screen assays, but repeat testing with a larger inoculum resolved the discrepancies. The BBL Crystal MRSA ID test misclassified four BORSA strains as MRSA. Both the Velogene and the MRSA-Screen assays are easy to perform, can accurately differentiate BORSA isolates from MRSA isolates, and provide a rapid alternative for the detection of methicillin resistance in S. aureus in clinical laboratories, especially when mecA PCR gene detection is unavailable.     

Identification of clinically relevant viridans group streptococci by phenotypic and genotypic analysis

Two phenotypic and three molecular methods were assessed for their ability to identify viridans group streptococci (VGS) to the species level. A panel of 23 clinical isolates, comprising strains isolated from infective endocarditis, blood cultures, pleural and peritoneal fluid, and 19 type/reference strains were analyzed. Identification was performed using two conventional phenotypic methods: API? rapid ID 32 Strep and the VITEK? 2 system, and genotypic analysis of the nucleotide sequence of the housekeeping gene sodA, restriction patterns generated by restriction fragment length polymorphism (RFLP) of the 16S rRNA gene and multilocus sequence analysis (MLSA) of seven housekeeping genes. The API? rapid ID 32 Strep accurately speciated 79% of the strains assessed, while the VITEK? 2 generated a successful identification for 55%, presenting limitations particularly with regard to species belonging to the mitis group. RFLP of the 16S rRNA gene correctly speciated 24% of the strains, having failed to allocate a species for 36% of the isolates examined. In contrast, sequence analysis of the sodA gene provided a correct identification for 95% of the strains assessed, while identification using the MLSA technique was unsuccessful due to practical limitations. The results generated herein indicate that no single methodology can be used to provide an accurate identification to the species level of all VGS, although nucleotide sequence analysis of the sodA gene proved to be useful in providing reliable speciation.     

Two-center collaborative evaluation of the performance of the BD Phoenix automated microbiology system for identification and antimicrobial susceptibility testing of Enterococcus spp. and Staphylococcus spp

The performance of the BD Phoenix Automated Microbiology System (BD Diagnostic Systems, Sparks, Md.) was assessed for identification (ID) and antimicrobial susceptibility testing (AST) for the majority of clinically encountered bacterial isolates in a European collaborative two-center trial. A total of 469 bacterial isolates of the genera Staphylococcus (275 isolates), Enterococcus (179 isolates), and Streptococcus (15 isolates, for ID only) were investigated; of these, 367 were single patient isolates, and 102 were challenge strains tested at one center. Sixty-four antimicrobial drugs were tested, including the following drug classes: aminoglycosides, beta-lactam antibiotics, beta-lactam-beta-lactamase inhibitors, carbapenems, cephems, folate antagonists, quinolones, glycopeptides, macrolides-lincosamides-streptogramin B (MLS), and others. Phoenix ID results were compared to those of the laboratories' routine ID systems (API 32 Staph, API 32 Strep, and VITEK 2 [bioMérieux, Marcy l'Etoile, France]); Phoenix AST results were compared to those of frozen standard broth microdilution (SBM) panels according to NCCLS guidelines (NCCLS document M 100-S 9, approved standard M 7-A 4). Discrepant results were repeated in duplicate. Concordant IDs of 97.1, 98.9, and 100% were observed for staphylococci, enterococci, and streptococci, respectively. For AST results the overall essential agreement was 93.3%; the category agreement was 97.3%; and the very major error rate, major error rate, and minor error rate were 1.2, 1.9, and 1.3%, respectively. In conclusion, the Phoenix ID results showed high agreement with results of the systems to which they were being compared; the AST performance was highly equivalent to that of the SBM reference method.     

Rapid species identification of group C streptococci isolated from horses.

Two commercial systems, the API 20S (Analytab Products, Plainview, N.Y.) and the Rapid Strep (API System S.A., Montalieu-Vercieu, France), were evaluated for ease of use and accuracy in the rapid identification of group C streptococci isolated from horses. A total of 85 Streptococcus isolates were tested, including S. equi (67 isolates), S. zooepidemicus (13 isolates), and S. equisimilis (5 isolates). All S. equi and S. zooepidemicus isolates were correctly identified within 24 h by the Rapid Strep system. Specific grouping sera was necessary to distinguish between S. equisimilis and group G or L strains. The API 20S system did not provide species identification of any of these isolates. An identification of randomly selected isolates to species level was performed by conventional methods and confirmed the identification derived through the Rapid Strep system. Our results indicate that the Rapid Strep system is a valuable aid for species identification of equine isolates of group C streptococci.     

Accuracy of six commercially available systems for identification of members of the family vibrionaceae

Six commercially available bacterial identification products were tested with Vibrio alginolyticus (12 strains), V. cholerae (30 strains), Photobacterium (Vibrio) damselae (10 strains), V. fluvialis (10 strains), V. furnissii (4 strains), V. hollisae (10 strains), V. metschnikovii (9 strains), V. mimicus (10 strains), V. parahaemolyticus (30 strains), and V. vulnificus (10 strains) to determine the accuracy of each system for identification. The products included API 20E, Crystal E/NF, MicroScan Neg ID2 and Rapid Neg ID3, and Vitek GNI+ and ID-GNB. Each product was tested only with those species that were listed in its database. Overall, the systems correctly identified 63.9, 80.9, 63.1, 73.6, 73.5, and 77.7% of the isolates to species level, respectively. Error rates ranged from 0.8% for the API 20E to 10.4% for the Rapid Neg ID3. The API 20E gave "no identification" for 13.1% of the isolates, while the Neg ID2, GNI+, ID-GNB, and Crystal were unable to identify 1.8, 2.9, 5.0, and 6.9%, respectively. For V. cholerae, specifically, accuracy ranged from 50.0 to 96.7%, with the API 20E having the worst performance and Crystal having the best. V. fluvialis presented the biggest challenge for the API 20E and the GNI+, with probabilities averaging 10%, while V. mimicus was a major problem with the Crystal E/NF, which identified none of the strains correctly. With the Neg ID2, correct answers were often obtained only after a modified inoculation of the panel with a bacterial suspension prepared with 0.85% NaCl. Additional tests required for identification often included growth in the absence of NaCl, which is not readily available in most clinical laboratories. The only product to correctly identify at least 90% of V. cholerae strains was the Crystal E/NF, and only three of the six products, the API 20E and both of the Vitek cards, correctly identified more than 90% of the V. parahaemolyticus strains. Thus, extreme care must be taken in the interpretation of answers from these six commercially available systems for the identification of Vibrio species.     

Comparative study using various methods for identification of Staphylococcus species in clinical specimens

Coagulase-negative staphylococci (CNS) play a predominant role in nosocomial infections. Rapid, reliable identification of these organisms is essential for accurate diagnosis and prompt effective treatment of these infections. Quite recently, the VITEK 2 g-positive (gram-positive [GP]) identification card (bioMérieux) has been redesigned for greater accuracy in the identification of gram-positive cocci. We compared the BD Phoenix (Becton Dickinson) and VITEK 2 (bioMérieux) automated microbiology systems, using their respective update version cards, and the API ID32 STAPH test. The glyceraldehyde-3-phosphate dehydrogenase (gap) gene-based T-RFLP (terminal restriction fragment length polymorphism) method was used for verifying the results. In total, 86 clinical isolates of CNS and 27 reference strains were analyzed. The results show that for identification of CNS, the automated identification methods using the newest VITEK 2 and BD Phoenix identification cards are comparable. However, API ID32 STAPH revealed more correct results compared to both automated microbiology systems. Despite the increased performance of the phenotypic automated identification systems compared to the former versions, molecular methods, e.g., the gap-based T-RFLP method, still show superior accuracy in identifying Staphylococcus species other than Staphylococcus aureus.     

Comparative evaluation of a commercial test for rapid identification of methicillin-resistant Staphylococcus aureus

The performance and ease of use of the recently introduced MRSA screen test (Denka Seiken Co. Ltd., Japan) for the identification of methicillin-resistant Staphylococcus aureus was evaluated in comparison with the BBL Crystal MRSA ID System (Becton Dickinson Europe, France). A total of 109 strains of S. aureus, consisting of 57 strains of MecA-negative S. aureus and 52 strains of MecA-positive S. aureus, were tested. With MecA PCR as the gold standard, the MRSA screen test had 98% sensitivity and 98% specificity, whereas the BBL Crystal MRSA ID System had 98% sensitivity and 95% specificity. The simplicity of use and rapid result make the MRSA screen test a valuable tool in the clinical microbiology laboratory pending demonstration of the MecA gene that should still always be done.     

Evaluation of a new system, VITEK 2, for identification and antimicrobial susceptibility testing of enterococci

We evaluated the new automated VITEK 2 system (bioMérieux) for the identification and antimicrobial susceptibility testing of enterococci. The results obtained with the VITEK 2 system were compared to those obtained by reference methods: standard identification by the scheme of Facklam and Sahm [R. R. Facklam and D. F. Sahm, p. 308-314, in P. R. Murray et al., ed., Manual of Clinical Microbiology, 6th ed., 1995] and with the API 20 STREP system and, for antimicrobial susceptibility testing, broth microdilution and agar dilution methods by the procedures of the National Committee for Clinical Laboratory Standards. The presence of vanA and vanB genes was determined by PCR. A total of 150 clinical isolates were studied, corresponding to 60 Enterococcus faecalis, 55 Enterococcus faecium, 26 Enterococcus gallinarum, 5 Enterococcus avium, 2 Enterococcus durans, and 2 Enterococcus raffinosus isolates. Among those isolates, 131 (87%) were correctly identified to the species level with the VITEK 2 system. Approximately half of the misidentifications were for E. faecium with low-level resistance to vancomycin, identified as E. gallinarum or E. casseliflavus; however, a motility test solved the discrepancies and increased the agreement to 94%. Among the strains studied, 66% were vancomycin resistant (57 VanA, 16 VanB, and 26 VanC strains), 23% were ampicillin resistant (MICs, >/=16 microgram/ml), 31% were high-level gentamicin resistant, and 45% were high-level streptomycin resistant. Percentages of agreement for susceptibility and resistance to ampicillin, vancomycin, and teicoplanin and for high-level gentamicin resistance and high-level streptomycin resistance were 93, 95, 97, 97, and 96%, respectively. The accuracy of identification and antimicrobial susceptibility testing of enterococci with the VITEK 2 system, together with the significant reduction in handling time, will have a positive impact on the work flow of the clinical microbiology laboratory.     

Evaluation of the Rapid Strep system for the identification of clinical isolates of Streptococcus species

A total of 247 strains of streptococci isolated from humans were tested for identification in the Rapid Strep system. The identification rates and identification levels were different for each Streptococcus species. Our data indicate that the Rapid Strep system will identify nearly all the beta-hemolytic Streptococcus species if serological procedures are used in conjunction with the rapid physiological procedures. Of the group D streptococci, 98% of the enterococci and 95% of the non-enterococci were correctly identified. Of the commonly occurring viridans species, 85% were correctly identified, but only 10% of the less frequently occurring viridans species were identified. A total of 90% of the Streptococcus pneumoniae and 60% of the Aerococcus strains were correctly identified.     

Comparison of identifications of human and animal source gram-negative bacteria by API 20E and crystal E/NF systems.

This study compared the abilities of API 20E and BBL Crystal E/NF identification systems to correctly identify human and animal source gram-negative bacilli of known identifications, as provided by the American Type Culture Collection, Rockville, Md., and the Research Diagnostic and Investigative Laboratory, Columbia, Mo. Also addressed in the comparison are the cost, the relative ease of performing and interpreting the tests, and the potential problems surrounding each system. The two systems were comparable in terms of their respective costs and abilities to identify the bacteria tested. The cost per test was calculated as $4.69 for API 20E and $4.62 for Crystal E/NF. Of the animal source bacteria tested, Crystal E/NF identified 68% to the correct genus and species and 90% to the correct genus or group. The remaining 10% of the animal source bacteria were unidentified by Crystal. Human source bacteria tested by BBL Crystal E/NF gave very similar results: 47% correctly identified to genus and species, 90% correctly identified to genus or group, 7% unidentified, and 3% incorrectly identified. API 20E results were as follows for animal source bacteria: 53% correctly identified to genus and species, 76% correctly identified to genus or group, and 24% unidentified; the results for human source bacteria were as follows: 40% correctly identified to genus and species, 83% correctly identified to genus or group, and 17% unidentified. API 20E has a slightly more labor-intensive protocol for setting up the test than BBL Crystal E/NF but produced fewer questionable results.     

Difficulties in detection and identification of Enterococcus faecium with low-level inducible resistance to vancomycin, during a hospital outbreak

Between June and November 2004, a vancomycin-resistant Enterococcus faecium (VRE) strain was isolated from 13 patients in the haematology/bone marrow transplant unit. There were difficulties in identifying the organism, which had low-level, inducible vancomycin resistance, and standard screening methods did not reveal carriage in patients or their contacts. These technical failures led to spread of VRE and delays in providing appropriate management, which might otherwise have been avoided. Therefore, we reviewed our laboratory methods and compared three identification systems to determine which would best identify this VRE strain. The VITEK  2 (BioMerieux) correctly identified, as E. faecium , only two of 16 isolates, whereas API Rapid ID 32 Strep (BioMerieux) and Phoenix 100 (Becton Dickinson and Co.) correctly identified 13 of 15 and 12 of 13 isolates tested, respectively. Isolates from urine, tested by the CLSI disk diffusion method, were apparently susceptible or of intermediate susceptibility to vancomycin, upon primary testing. VITEK  2 and Phoenix 100 identified all isolates as vancomycin-resistant, although the MICs, measured by Etest, were in the susceptible range for three of 16 isolates. Reducing the vancomycin concentration in screening media substantially increased the sensitivity for detection of VRE. Isolates were characterized as genotype van B2/3 by PCR and were indistinguishable from each other by pulsed-field gel electrophoresis. VRE with low-level inducible resistance can be missed by routine screening methods. Better identification and screening methods for detection of low-level vancomycin resistance are needed to improve surveillance and prevent transmission of VRE.     

Use of sodA sequencing for the identification of clinical isolates of coagulase-negative staphylococci

This study evaluated the possible advantages provided by a genotypic method over commercially available biochemical systems for the identification of clinical isolates of coagulase-negative staphylococci (CNS). Partial sequencing of the sodA gene was performed for 168 coagulase-negative clinical isolates of staphylococci identified previously with the ID32 STAPH system. Of these, 101 (60.1%) were identified to the species level with ID32 STAPH, while 67 (39.9%) were misidentified or not identified with certainty. Sequencing of sodA proved useful for resolving all ambiguities or inconclusive identifications generated by the commercially available biochemical identification system.     

Evaluation of the rapid strep system for species identification of streptococci

The Rapid Strep system (API System S.A., Montalieu-Vercieu, France) was evaluated, without additional tests, in the identification of 209 streptococci. Organisms included 59 beta-hemolytic, 36 group D, 24 Streptococcus pneumoniae, and 90 viridans group streptococci. The Rapid Strep system correctly identified to species level 69.5% of the beta-hemolytic strains, 100% of the group D strains, none of the S. pneumoniae strains, and 84.5% of the viridans group streptococci. The method provided excellent identification rates of groups A, B, and D but failed to differentiate between groups C and G. The method for preparation of suspensions for the Rapid Strep system, as initially recommended by the manufacturer, was responsible for the failure to identify S. pneumoniae. This method was subsequently modified to yield a heavier inoculum; all 10 pneumococcal strains tested with the revised inoculum method were correctly identified. Good identification rates of commonly encountered viridans strains were found. The Rapid Strep system represents a worthwhile advance in streptococcal species identification, especially for group D and viridans strains.