Identification of Gardnerella vaginalis with the API 20 Strep system.

A total of 137 strains of Gardnerella vaginalis were examined by the API 20 Strep system. The system was shown to be reliable when the tests were compared with standard identification methods, and very little confusion occurred with streptococcal profiles; consequently, G. vaginalis has been included in the API 20 Strep data base.     

Identification of Yersinia spp. with the API 20E system.

The ability of the API 20E system to identify 105 clinical isolates of Yersinia spp. was compared with those of conventional biochemical tests at 28 and 37 degrees C. Elimination of the Voges-Proskauer test (recorded as a negative result) increased the percentage of correct identifications for Yersinia spp. from 66 to 93% when the API 20E strips were incubated at 28 degrees C.     

Identification of Enterobacteriaceae by the API 20E system.

Since the introduction of the API 20E kit a number of identification schemes have been developed by the manufacturer for use with the kit. We evaluated the success of these various schemes in identifying 206 strains belonging to 34 taxa of the family Enterobacteriaceae. Many of the strains were atypical and only 94% could be identified by our own system of 50 conventional tests and a computer program. The most advanced identification scheme so far developed for the API 20E kit (the Analytical Profile Index and complementary Computer Service) allowed 88% of the 206 strains to be correctly identified, although 2% were incorrectly identified. The tests in the API 20E kit and 52 conventional tests were separately evaluated for their ability to discriminate between the 34 taxa considered in this study. Our results suggest that replacing some of the tests in the present API 20E kit might further improve its diagnostic performance.     

Reproducibility of the analytab (API 20E) system.

The reproducibility of the Analytab (API 20E) system for identification of Enterobacteriaceae was evaluated with 110 clinical isolates. Each isolate was identified by two technologists at different times. Genus-species identification was 97.3% reproducible; however, only 55.5% of the strains gave identical reactions in all 20 of the API 20E biochemical tests on repeat testing. Of those strains which varied, 56% possessed only one variable biochemical test. The reproducibility for each biochemical test was calculated and ranged from 89 to 100%. A subset of 20 of the most variable strains was tested further under conditions of varying incubation time (15 and 22 h) and inoculum concentration (10(7), 10(5), and 10(3) colony-forming units per ml), and by having four technologists interpret the test results. The reproducibility for each biochemical test for these 20 variable strains ranged from 86 to 99%. Less variation in interpretation by technologists was seen at an incubation time of 22 h and an inoculum concentration of 10(7) colony-forming units per ml. Consideration of the reproducibility for each biochemical test can aid in determining the probability that two isolates suspected of being the same strain, but with API profiles which differ by one or more biochemical test results, are in fact the same strain. Variables such as inoculum size, incubation time, technologist interpretation, and strip variability affect the API test results and should be standardized to minimize their effects.     

Evaluation of the API 20 Strep system for species identification of streptococci isolated from bovine mastitis

A new commercial system (API 20 Strep) for the species identification of streptococci associated with bovine mastitis was compared with the conventional biochemical methods. A total of 84 strains, including Streptococcus agalactiae (13), S. dysgalactiae (16), S. uberis (24), S. faecalis (12), S. faecium (5), and S. bovis (14) were tested. Using profile index and table data issued by the manufacturer, we identified 71.4% of strains by the API 20 Strep system. Our results indicate that improvement of the identification key is needed for accurate identification of streptococci isolated from bovine mastitis.     

Identification of Bordetella avium sp. nov. by the API 20 NE system

The reactions of 47 Bordetella avium strains in the API 20 NE micro-test system were compared to those of the species Bordetella bronchi-septica, Alcaligenes faecalis and Alcaligenes denitrificans. The API 20 NE microtest system allowed separation between B. avium and the other species of Gram-negative nonfermentative rods investigated.     

Evaluation of the updated MS-2 Bacterial Identification system in comparison with the API 20E system.

The recently updated MS-2 Bacterial Identification system software (Abbott Laboratories, Diagnostic Division, Irving, Tex.) was compared with the original MS-2 Bacterial Identification software and the API 20E, using 968 strains of Enterobacteriaceae. The updated MS-2 software correctly identified 94.4% of the isolates tested. API 20E and the original MS-2 software correctly identified 91 and 85.3% of the strains, respectively. MS-2 responses were considered to be equivocal (needing additional tests for verification) if the percent likelihood values were less than 80%. The percentage of equivocal responses was reduced from 6.5% with the original software to 2.2% with the updated software, and the percentage of incorrect identifications was reduced from 8.2 to 3.4% with the original and updated software, respectively. Organisms belonging to 25 taxonomic groups were tested. Direct comparison of the two MS-2 programs showed that the updated MS-2 software increased the identification accuracy of Salmonella spp., Enterobacter cloacae, Providencia stuartii, Escherichia coli, Shigella spp., Klebsiella pneumoniae, Serratia marcescens, Proteus mirabilis, and Acinetobacter calcoaceticus. A decrease in accuracy was seen with Citrobacter freundii, Hafnia alvei, Enterobacter agglomerans, and Yersinia pseudotuberculosis when the updated software was used. The remaining 12 taxonomic groups were not affected by the software changes. The updated MS-2 software appears to significantly improve the identification accuracy of the MS-2 Bacterial Identification system.     

Identification of Pseudomonas, Flavobacterium, and Alcaligenes with the API 20 NE system

The API 20 NE system is designed for the rapid identification of Gram negative rods other than Enterobacteriaceae. It has been compared to conventional methods in the characterization of 404 strains representative of 23 species belonging to 3 genera: Pseudomonas (236 strains), Flavobacterium (133 strains) and Alcaligenes (35 strains). The system consists of 9 enzymatic tests and 12 carbohydrate assimilation tests. A 7-digit numerical profile is obtained by an octal coding of the test results. The strains are identified by comparing the numerical profile to those of species listed in a profile index. The API 20 NE tests showed 99-100% correlation with corresponding conventional methods except in indole production (96.5%) for which we observed 14 false negative reactions in testing F. meningosepticum and CDC groups IIb and IIf. The API 20 NE system presented 94.1% identification to the species level and 96.3% to the genus level in agreement with conventional biochemical methods. Among the correctly identified strains, 7.4% (30) gave an erroneous or unlisted numerical profile in the first version of the Profile Index and required the use of the computer. Among the misidentified strains 2%, (8) were assigned to the right genus but wrong species, 0.7% (3) were placed in the wrong genus and 1% (4) gave a doubtful profile with one or more tests compared to the profiles listed.     

Identification of coagulase-negative staphylococci with the API staph system.

A kit for the identification of staphylococci based on the biochemical criteria proposed by Kloos and Schleifer (W.E. Kloos and K.H. Schleifer, J. Clin. Microbiol., 1:82-88, 1975) is now available commercially. The system was used to identify 100 strains of coagulase-negative staphylococci isolated from various body sites as the primary etiological agent of clinical infection. The increasing importance of staphylococci and their resistance to antibiotics provided the rationale for such an investigation. Over 90% of the Staphylococcus isolates were easily identified as to their species on the basis of their reaction profile to 19 biochemical tests included in the kit. The remainder, which showed minor variations, could also be assigned to the various species. Identification of the isolates was as follows: S. epidermidis, 54; S. haemolyticus, 5; S. simulans, 2; S. hominis, 1; S. capitis, 4; S. cohnii, 2; S. warneri, 2; S. xylosus, 8; and S. saprophyticus, 22. Antibiotic sensitivity patterns were determined for each of the isolates. Novobiocin resistance was detected in strains of S. saprophyticus and S. xylosus, a property hitherto recognized in Micrococcus sp. type 3 causing bacteriuria in young women. Resistance to penicillin was widespread among strains of several species, whereas resistance to tetracycline was mainly confined to strains of S. epidermidis. General resistance to sulfamethoxazole and nalidixic acid was found among all strains, with almost uniform sensitivity to the other drugs tested.     

Identification of Yersinia species by the API 20E.

A prospective study was performed to assess the effectiveness of the API 20E in the identification of 183 Yersinia isolates incubated at 28 degrees C for 18 to 24 h. The results showed an overall correct-identification rate of 90%, with positive predictive values for Yersinia enterocolitica and Yersinia frederiksenii of 94 and 92%, respectively. Yersinia intermedia results were unacceptable.     

Identification ofCorynebacterium jeikeium andCorynebacterium CDC group D 2 with the API 20 strep system

A total of 170 strains ofCorynebacterium jeikeium and 23 strains ofCorynebacterium group D2 were examined in three British laboratories using the API 20 Strep identification system and three supplementary tests (catalase production, urease production and nitrate reduction). The isolates were collected from clinical specimens in various laboratories over a three-year period. The two species produced consistent reactions in these tests after 24 h. Two tests were highly discriminatory, with positive reactions for ribose fermentation seen forCorynebacterium jeikeium while urease production was observed withCorynebacterium group D2. This method allows routine clinical laboratories to rapidly identify these emerging pathogens.     

Nutritional requirements of Corynebacterium pyogenes.

The nutritional requirements of Corynebacterium pyogenes (strains C100, 5, and 1909), a commonly encountered animal pathogen, were determined in this study. A semidefined medium (SDM) containing glucose, HCO3-, hemin, charcoal-treated Trypticase, and a defined mixture of purines and pyrimidines, amino acids, and minerals which supported optimal growth of C. pyogenes was employed in all nutritional studies. Adenine and uracil were required for optimal growth of strains 5 and C100 but were not required for strain 1909. Riboflavin and nicotinic acid were required for good growth of all three strains; biotin and thiamin were stimulatory but did not appear to be required for growth. Hemin and NaHCO3 were stimulatory for growth, whereas lipoic acid and Tween 80 were neither stimulatory nor required for growth. The replacement of Trypticase with a specific peptide fraction (obtained by fractionation of Trypticase on Sephadex G-25) rich in dipeptides gave growth comparable to that in SDM, indicating a peptide requirement for the growth of C. pyogenes. It was of considerable interest that growth comparable to that in SDM was obtained when Trypticase was replaced by inositol (1 microgram/ml of SDM).     

Identification of Staphylococcus species with the API STAPH-IDENT system

The API STAPH-IDENT system was compared with conventional methods for the identification of 14 Staphylococcus species. Conventional methods included the Kloos and Schleifer simplified scheme and DNA-DNA hybridization. The API STAPH-IDENT strip utilizes a battery of 10 miniaturized biochemical tests, including alkaline phosphatase, urease, beta-glucosidase, beta-glucuronidase, and beta-galactosidase activity, aerobic acid formation from D-(+)-mannose, D-mannitol, D-(+)-trehalose, and salicin, and utilization of arginine. Reactions of cultures were determined after 5 h of incubation at 35 degrees C. Results indicated a high degree of congruence (greater than 90%) between the expedient API system and conventional methods for most species. The addition of a test for novobiocin susceptibility to the API system increased the accuracy of identification of S. saprophyticus, S. cohnii, and S. hominis, significantly. Several strains of S. hominis, S. haemolyticus, and S. warneri which were difficult to separate with the Kloos and Schleifer simplified scheme were accurately resolved by the API system.     

Identification of coagulase-negative staphylococci with the API STAPH-IDENT system

A group of 300 clinically derived isolates of coagulase-negative staphylococci were tested in parallel with the API STAPH-IDENT system (Analytab Products) and 14 conventional biochemical tests contained in Kloos and Schleifer's simplified scheme for identification of human Staphylococcus species. STAPH-IDENT is a miniaturized biochemical test strip that incorporates four synthetic chromogenic substrates, urea, arginine, and four carbohydrates and that requires only a 5-h test period. Use of the STAPH-IDENT system alone allowed correct or partly correct classification of 67% (201 of 300) of the study isolates. However, if a supplemental test was performed (most often novobiocin susceptibility), correct classification of an additional 25.7% (77) was possible, for a total of 92.7% of isolates identified to the species level. Species correctly identified included 94% (116 of 123) of Staphylococcus epidermidis isolates, 98% (63 of 64) of S. saprophyticus, 71% (34 of 48) of S. hominis, 100% (22) of S. simulans, 100% (18) of S. haemolyticus, 100% (17) of S. warneri, and 100% (8) of S. capitis. Fourteen percent (42 of 300) of profile codes encountered in this study were not included in the STAPH-IDENT profile register, but were included in Analytab Products' expanded computer data base.     

Identification of the Enterobacteriaceae: a comparison of the Enterotube II with the API 20E.

Two commercial methods for the identification of the Enterobacteriaceae, API 20E and Enterotube II, were compared using the results obtained with 235 cultures of fresh clinical isolates. Enterotube II was an improvement on the original Enterotube, but the availability of two differing indices, one using the Voges-Proskauer (VP) test result and one without, is criticised.     

Rapid identification of antibiotic-resistant corynebacteria with the API 20S system

The API 20S system (Analytab Products, Plainview, N.Y.) was evaluated for the rapid identification of multiply antibiotic-resistant aerobic diphtheroids. Sixty-eight clinical isolates of multiply resistant Centers for Disease Control group JK and group D2 corynebacteria had API 20S profiles which were clearly different from those of a number of strains of other Corynebacterium species which were tested. The API 20S system allowed more rapid identification of antibiotic-resistant diphtheroids than conventional biochemical tests. Its use for corynebacteria other than group JK and group D2 is not recommended at this time.     

Rapid identification of Prototheca species by the API 20C system.

The conventional auxanographic method of testing for the assimilation of carbohydrates and alcohols by the various species of Prototheca requires at least 2 weeks of incubation at 25 to 30 degrees C before definitive results are obtained. Even though Prototheca spp., in culture as well as in fixed tissues, can be identified more rapidly by fluorescent-antibody techniques in which species-specific reagents are used, such diagnostic facilities and reagents are not available in most diagnostic laboratories. The API 20C clinical yeast identification system, a commercially available ready-to-use micromethod, was found to permit the definitive identification of P. stagnora, P. wickerhamii, and P. zopfii within 4 days.     

Use of the API 20E system to identify veterinary Enterobacteriaceae.

A total of 503 veterinary enteric bacterial pathogens obtained from state veterinary diagnostic laboratories were tested on API 20E strips to determine whether this rapid microidentification system could be utilized for veterinary clinical microbiology. The API 20E strip accurately identified 96% of the veterinary isolates and misidentified 3%. Identifications by the API system and the diagnostic laboratories were in agreement in 85% of the isolates, disagreement on 16% of the isolates, and 1% were not identified by the API strip. Differences in identification occurred primarily in distinguishing between Klebsiella and Enterobacter and between Enterobacter and Escherichia coli. These disagreements were most often due to incorrect identifications by the diagnostic laboratory rather than by the API system. Biotype differences between human and veterinary isolates were compared. Significant differences were noted in several biochemical reactions. The main differences observed for E. coli isolates were in ornithine decarboxylase production and melibiose fermentation. The largest differences for Salmonella occurred in arginine dihydrolase production, citrate utilization, and inositol fermentation, whereas for Klebsiella pneumoniae the main differences were noted in urease production and nitrate reduction. These biotype differences, however, did not affect the accurate identification of organisms on the API strip.     

Use of the API 20E system for rapid identification of Enterobacteriaceae (six hours) (author's transl)

The authors propose a modification of the method of use of the API 20E system permitting more rapid identification of Enterobacteriaceae within six hours (3 hours preculture and 3 hours incubation on an API 20E plate) it was possible to identify correctly 67% of 192 strains studied at species level and 75.5% studied at generic level. One may note four mistakes (2.1%) of which 3 were minor, (species within the same genus). The construction of a base of numerical data adapted to the technic within six hours would no doubt permit us to reduce the percentage undetermined.     

Rapid identification of group D streptococci with the API 20S system

The API 20S system (Analytab Products) was evaluated as a means of identifying 209 isolates of Lancefield group D streptococci to the species level. Results were compared with those from a conventional tube biochemical identification system and from serological grouping. Use of the latest 20S computerized data base allowed species identification of 97% (203 of 209) of test isolates after a 4-h incubation period and 99% (208 of 209) of test isolates if supplemental overnight biochemical tests were used to clarify the identity of five Streptococcus bovis-variant isolates. The API 20S system appears to be a convenient and accurate method for rapid, same-day species identification of group D streptococci.