Summary auto-generated
This article describes a systematic approach for identifying Pseudomonas species and related non-fermenting, Gram-negative bacteria in a clinical laboratory setting. Researchers at St Thomas's Hospital developed practical identification schemes for 428 bacterial isolates from 1970 onwards. The methodology employed standard biochemical tests including oxidation-fermentation, oxidase activity, motility, and carbohydrate metabolism assays using ammonium salt sugars. Organisms were initially subdivided into groups based on three key tests, then differentiated using targeted additional tests to create simplified identification tables. The most complex table required only 16 tests compared to 29-30 tests in other published schemes. The system successfully identified 96% of isolates to species level, including common pathogens like Pseudomonas aeruginosa and related species. The authors emphasized that accurate species identification was essential for epidemiological investigations of hospital-associated infections. Their simplified dichotomous approach proved practical for routine clinical laboratory use while maintaining diagnostic accuracy for organisms frequently encountered in clinical specimens from intensive care settings.
Key findings
- A simplified identification scheme using only 16 tests maximum successfully identified 96% of 428 Gram-negative non-fermenting bacterial isolates to species level
- Three initial tests—oxidation-fermentation, oxidase activity, and motility—effectively subdivided organisms into manageable groups for differential testing
- Pseudomonas aeruginosa was consistently identified by characteristic pigment production on King's media and positive gluconate, urea, casein, and gelatin tests
- Alkali production in oxidation-fermentation medium proved a useful characteristic for differentiating certain pseudomonads and related bacteria from typical non-reactive organisms
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Abstract
Non-fermenting, catalase-positive Gram-negative bacilli that grow on nutrient agar are often isolated in clinical laboratories. We have applied biochemical techniques appropriate to a typical clinical microbiology laboratory, and for the most part described in Cowan and Steel's Manual for the identification of medical bacteria (Cowan, 1974), to 428 clinical isolates and have evolved a scheme for their identification. Organisms were subdivided into groups on the basis of three tests, namely the glucose oxidation-fermentation test and tests for oxidase activity and motility. A choice was then made among other tests to produce indentification tables, containing only the most useful tests, for the various groups. The most complicated table has only 16 tests. This simple system identified 96.5% of the 428 organisms, as well as many subsequent isolates of the more common organisms.