Evaluation of the Minitek gram-positive set for identification of staphylococci isolated from the bovine mammary gland

Evaluation of Staph ID 32 system and Staph-Zym system for identification of coagulase-negative staphylococci

The purpose of the investigation was to evaluate two commercially available identification systems: a new modification of the Staph-Zym system (Rosco, Tåstrup, Denmark) and the Staph ID 32 API system (API System, BioMérieux, Paris, France). A local standard method to be used in routine laboratories was also evaluated. A total of 200 staphylococcal isolates, including strains from both the American Type Culture Collection and the Czechoslovak Collection of Microorganisms as well as 89 clinical isolates, were used in tests of all three identification systems. The Staph ID 32 API system identified from 50 to 100% of the reference strains and 82.1% of the clinical isolates correctly. The Staph-Zym system identified from 90 to 100% of the reference strains and 82.1% of the clinical isolates correctly. Most misidentifications were of minor importance, but in both systems major failures appeared (Staphylococcus aureus was identified as a coagulase-negative staphylococcus). Both systems needed backup from a reference laboratory to determine if two isolates were of the same strain.

Identification of veterinary pathogens by use of commercial identification systems and new trends in antimicrobial susceptibility testing of veterinary pathogens

Veterinary diagnostic microbiology is a unique specialty within microbiology. Although isolation and identification techniques are similar to those used for human pathogens, many veterinary pathogens require unique cultivation or identification procedures. Commercial identification systems provide rapid, accurate identification of human pathogens. However, the accuracy of these systems with veterinary pathogens varies widely depending on the bacterial species and the host animal from which it was isolated. Increased numbers of veterinary strains or species in the data bases of the various systems would improve their accuracy. Current procedures and interpretive criteria used for antimicrobial susceptibility testing of veterinary pathogens are based on guidelines used for human pathogens. The validity of these guidelines for use with veterinary pathogens has not been established. As with fastidious human pathogens, standardized methodologies and quality control isolates are needed for tests of organisms such as Actinobacillus pleuropneumoniae and Haemophilus somnus. Furthermore, interpretive criteria for veterinary antimicrobial agents based on the MIC for veterinary pathogens, the pharmacokinetics of the antimicrobial agent in the host animal, and in vivo efficacy of the antimicrobial agent are needed. This article reviews both the commercial identification systems evaluated with veterinary pathogens and current methods for performing and interpreting antimicrobial susceptibility tests with veterinary pathogens. Recommendations for future improvements in both areas are discussed.

Characterization of Staphylococcus hyicus with the ATB 32 Staph system and with conventional tests

The ATB 32 Staph system correctly identified 45 of 54 Staphylococcus hyicus cultures isolated from pigs and cattle. The biochemical profiles of the remaining nine cultures were not listed in the product data base. The 40 porcine and 14 bovine cultures resulted in three and seven different biochemical profiles, respectively. In parallel experiments, almost all S. hyicus cultures showed hemolytic reactions on chocolate agar, had CAMP-like reactivities in the zone of lysis of the staphylococcal beta-lysin, and had bacteriolytic properties on Micrococcus luteus cells. In addition, the S. hyicus cultures were unpigmented, were DNase positive, expressed an S. hyicus-specific teichoic acid, and were usually coagulase positive in porcine plasma. Most of the porcine strains were protein A positive, and two porcine cultures were clumping factor positive.

A convenient method for differentiation of coagulase-negative staphylococci isolated from bovine mammary glands

The utility of trehalose-mannitol broth and arabinose-cellobiose broth for identification of Staphylococcus epidermidis and novobiocin-resistant staphylococci was determined using 236 coagulase-negative staphylococci isolated from bovine mammary glands. None of the 49 S. epidermidis strains was positive in trehalose-mannitol broth; whereas, all strains of Staphylococcus hyicus, Staphylococcus chromogenes, Staphylococcus haemolyticus, Staphylococcus hominis, Staphylococcus warneri, and Staphylococcus simulans were positive. Of the novobiocin-resistant staphylococcal species, only Staphylococcus saprophyticus was negative in arabinose-cellobiose broth. Except for one strain of Staphylococcus sciuri and one strain of Staphylococcus kloosii, all remaining strains of novobiocin-resistant staphylococcal species were positive in arabinose-cellobiose broth. Results indicate that trehalose-mannitol broth is an acceptable method for identification of S. epidermidis isolated from bovine mammary glands. Furthermore, arabinose-cellobiose broth is a useful method of screening for novobiocin-resistant staphylococci.

Evaluation of the Staph-Zym system with staphylococci isolated from bovine intramammary infections

A total of 148 staphylococci isolated from bovine intramammary infections were used to evaluate the Staph-Zym system (ROSCO, Taastrup, Denmark). The overall accuracy of the system was 91.9%. The system correctly identified all strains of Staphylococcus aureus, Staphylococcus simulans, and Staphylococcus xylosus and 95% of Staphylococcus intermedius strains. Of 33 Staphylococcus hyicus strains, 31 (93.9%) were classified correctly by the Staph-Zym system, as well as 8 (80%) of 10 Staphylococcus chromogenes strains. All 11 Staphylococcus epidermidis strains and the 1 Staphylococcus haemolyticus strain included in the study were identified, but the Staph-Zym system had difficulty distinguishing strains of Staphylococcus warneri and Staphylococcus hominis from other species in the S. epidermidis group. The Staph-Zym system correctly identified all six S. xylosus strains and two of three Staphyloccus sciuri strains. The Staph-Zym system was considered an acceptable alternative to conventional methods for identification of bovine mammary gland isolates.

Evaluation of the Rapid Strep system for identification of gram-positive, catalase-negative cocci isolated from bovine intramammary infections

The Rapid Strep system (Analytab Products, Plainview, NY) was used to identify 199 gram-positive, catalase-negative cocci isolated from bovine intramammary infections. The system accurately identified 88.4% of isolates. The system identified 100% of 46 Streptococcus agalactiae, 100% of 48 Streptococcus dysgalactiae, 54.5% of 11 Streptococcus equinus, and 96.2% of 53 Streptococcus uberis isolates. Enterococcus spp. were identified correctly 83.3% of the time. One of 4 Streptococcus saccharolyticus strains was identified as Streptococcus bovis, the previous classification for this organism, and 8 Streptococcus equi ssp. equi strains were misidentified as Streptococcus dysgalactiae. The Rapid Strep system was determined to be an acceptable alternative to conventional methods for identification of gram-positive, catalase-negative cocci isolated from bovine intramammary infections.

Evaluation of the Minitek Gram-Positive Set for identification of streptococci isolated from bovine mammary glands

A total of 127 isolates were used to evaluate the Minitek Gram-Positive Set for identification of streptococci cultured from bovine mammary glands. The overall accuracy of the Minitek Gram-Positive Set was 34.6%. Of 12 Streptococcus agalactiae strains, 4 (33.3%) were correctly identified. Of 43 Streptococcus dysgalactiae strains, 32 (74.4%) were identified correctly. Of 44 Streptococcus uberis strains, 42 (95.5%) were identified as Enterococcus spp. Poor performance was attributed to the limited number of veterinary strains in the data base. Incorporation of large numbers of veterinary isolates into the data base is needed for further development of this system.

Evaluation of the Staph-Zym-system for identification of Staphylococcus hyicus and Staphylococcus intermedius

The Staph-Zym system was evaluated as a means for identifying cultures of Staphylococcus hyicus isolated from pigs and bovines and cultures of Staphylococcus intermedius isolated from canines. The selected cultures had been identified by conventional methods. The Staph-Zym system correctly identified all 52 S. hyicus and all 33 S. intermedius. It is concluded that the Staph-Zym system is a practical and reliable test for identifying mostly animal pathogenic S. hyicus and S. intermedius, and might possibly be useful for veterinary microbiologists.

Identification of Enterobacteriaceae with the Minitek system

A total of 417 strains (361 Enterobacteriaceae, 56 Vibrionaceae) was examined in all the available Minitek system tests. The results were processed through four successive identification schemes devised by the manufacturer and the proportion of strains correctly identified, not identified or incorrectly identified determined for each scheme. From the results, a probability matrix was constructed incorporating all 35 Minitek tests. Test results for each strain were then processed through this matrix to determine its success in identification. From the matrix the order of separating value of the tests was determined. Forty-three of the strains were each tested three times to assess the level of test reproducibility; the corrected error rate was 0.85%.

Comparison of modified Minitek system with Staph-Ident system for species identification of coagulase-negative staphylococci

A modified Minitek system (BBL Microbiology Systems, Cockeysville, Md.) for species identification of coagulase-negative staphylococci was compared with the Staph-Ident system (Analytab Products, Plainview, N.Y.). The conventional method of Kloos and Schleifer (J. Clin. Microbiol. 1:82-88, 1975) was used as the reference method for identification. When tested with 78 coagulase-negative staphylococcal isolates from 63 children with cancer. Minitek concurred with the conventional identification in 67 (86%) isolates and Staph-Ident concurred in 61 (78%) isolates. Identification of species other than Staphylococcus epidermidis was better with Staph-Ident (19 of 23 isolates) than with Minitek (14 of 23 isolates). Concordance of results was likewise high, 88% (7 of 8) for Minitek and 100% (8 of 8) for Staph-Ident in studies with eight coagulase-negative staphylococcal strains obtained from the American Type Culture Collection (Rockville, Md.). We conclude that the modified Minitek system is a practical and reliable test for identifying coagulase-negative staphylococci in clinical microbiology laboratories. Its versatility and larger repertoire of biochemical tests may offer advantages over the Staph-Ident system.