Comparison of Rapid NFT system and conventional methods for identification of nonsaccharolytic gram-negative bacteria

Enzymatic substrates in microbiology

Enzymatic substrates are powerful tools in biochemistry. They are widely used in microbiology to study metabolic pathways, to monitor metabolism and to detect, enumerate and identify microorganisms. Synthetic enzymatic substrates have been customized for various microbial assays, to detect an expanding range of both new enzymatic activities and target microorganisms. Recent developments in synthetic enzymatic substrates with new spectral, chemical and biochemical properties allow improved detection, enumeration and identification of food-borne microorganisms, clinical pathogens and multi-resistant bacteria in various sample types. In the past 20 years, the range of synthetic enzymatic substrates used in microbiology has been markedly extended supporting the development of new multi-test systems (e.g., Microscan, Vitek 2, Phoenix) and chromogenic culture media. The use of such substrates enables an improvement in time to detection and specificity over conventional tests that employ natural substrates. In the era of intense developments in molecular biology, phenotypic tests involving enzymatic substrates remain useful to analyse both simple and complex samples. Such tests are applicable to diagnostic and research laboratories all over the world.

Frequency of Nonfermentative Gram-Negative Bacilli Isolated from Clinical Materials of Pacients at Universidade Federal do Ceará Hospital Complex - Brazil

Among one thousand eight hundred and thirty-four Gram-negative bacilli, isolated at Universidade Federal do Ceará hospital complex - Brazil, from January 1995 to February 1996, 456 (24.8%) were Nonfermentative Gram-Negative Bacilli (NFGNB). This study reports their identification to the species level and their frequency as well. Thirteen genera and thirty species were identified and Pseudomonas aeruginosa was the most frequent species (69.95%), followed by Acinetobacter baumannii (5.48%) and by Acinetobacter lwoffii (3.95%). Among the identified P.aeruginosa strains, 94.1% produced pigment but 7.9% of them produced pigment only after being cultivated several times. The frequency of the most species was similar to that reported in the literature.

Microbiological and clinical aspects of infection associated with Stenotrophomonas maltophilia

The gram-negative bacterium Stenotrophomonas maltophilia is increasingly recognized as an important cause of nosocomial infection. Infection occurs principally, but not exclusively, in debilitated and immunosuppressed individuals. Management of S. maltophilia-associated infection is problematic because many strains of the bacterium manifest resistance to multiple antibiotics. These difficulties are compounded by methodological problems in in vitro susceptibility testing for which there are, as yet, no formal guidelines. Despite its acknowledged importance as a nosocomial pathogen, little is known of the epidemiology of S. maltophilia, and although it is considered an environmental bacterium, its sources and reservoirs are often not readily apparent. Molecular typing systems may contribute to our knowledge of the epidemiology of S. maltophilia infection, thus allowing the development of strategies to interrupt the transmission of the bacterium in the hospital setting. Even less is known of pathogenic mechanisms and putative virulence factors involved in the natural history of S. maltophilia infection and this, coupled with difficulties in distinguishing colonization from true infection, has fostered the view that the bacterium is essentially nonpathogenic. This article aims to review the current taxonomic status of S. maltophilia, and it discusses the laboratory identification of the bacterium. The epidemiology of the organism is considered with particular reference to nosocomial outbreaks, several of which have been investigated by molecular typing techniques. Risk factors for acquisition of the bacterium are also reviewed, and the ever-expanding spectrum of clinical syndromes associated with S. maltophilia is surveyed. Antimicrobial resistance mechanisms, pitfalls in in vitro susceptibility testing, and therapy of S. maltophilia infections are also discussed.

Bacteremia in conjunction with endodontic therapy

This study characterizes oral microorganisms believed to have spread from the root canal into the blood stream during and after endodontic therapy of teeth with Asymptomatic apical periodontitis. Microbiological samples were taken under aseptic conditions from the root canal of 26 single-rooted teeth in 26 patients. In the endodontic treatment of 13 of the patients (Group 1), the first 3 reamers, sizes 15, 20 and 25, were used to a level 2 mm beyond the apical foramen. In the other 13 patients (Group 2), the instrumentation ended inside the root canal 1 mm short of the apical foramen. Blood samples were taken from the patients during the instrumentation and 10 min after the treatment was completed. Anaerobic microorganisms were isolated from all root canals. In 7 patients of Group 1, Propionibacterium acnes, Peptostreptococcus prevotii, Fusobacterium nucleatum, Prevotella intermedia and Saccharomyces cerevisiae were recovered from the blood. In 4 patients of Group 2, P. intermedia, Actinomyces israelii, Streptococcus intermedius and Streptococcus sanguis were isolated from the blood. Biochemical tests and antibiograms revealed that the isolates from the root canal and blood had identical profiles within the patients, strongly suggesting that the microorganisms isolated from the blood had the root canal as their source.

Use of the API rapid NFT system for identifying nonfermentative and fermentative marine bacteria

Thirty-five American Type Culture Collection type strains of marine bacteria were used to evaluate the Rapid NFT system (API Analab Products, Plainview, N.Y.) for use in identifying heterotrophic marine bacteria. The 21 biochemical and assimilation tests on the Rapid NFT test strips were treated according to the manufacturer's protocol, which included use of AUX medium (provided with the Rapid NFT system) for preparing assimilation tests, and by substituting phenol red broth base (BBL Microbiology Systems, Cockeysville, Md.) with and without an oil overlay for the AUX medium. A seven-digit numerical profile was obtained for each NFT test strip from each of the three procedures and matched to its corresponding number in the Rapid NFT identification codebook. Also, all biochemical and assimilation test results were analyzed with SASTAXAN and SAS/GRAPH programs (SAS Institute, Inc., Cary, N.C.); similarity matrices were computed for all 35 strains. For comparison purposes, bacterial strains were grouped at a similarity level of 70%. The results indicated a low efficacy of identification for all three procedures. In addition, similarity matrix analysis showed more cohesive grouping based on results of phenol red broth base-treated strains than for the AUX medium provided by the manufacturer. However, none of the three treatments provided exclusive grouping of type strains at the genus level. Thus, the reliability of the data obtained from the NFT system and modifications thereof should be evaluated carefully when environmental isolates are characterized.

Identification of clinical isolates of gram-negative nonfermentative bacteria by an automated cellular fatty acid identification system

An automated cellular fatty acid (CFA) bacterial identification system, Microbial Identification System (MIS; Microbial ID, Newark, Del.), was compared with a conventional system for the identification of 573 strains of gram-negative nonfermentative bacteria. MIS identifications were based exclusively on the CFA composition following 22 to 26 h of growth at 28 degrees C on Trypticase soy agar. MIS identifications were listed with a confidence measurement (similarity index [SI]) on a scale of 0 to 1.0. A value of greater than or equal to 0.5 was considered a good match. The MIS correctly listed as the first choice 478 of 532 (90%) strains contained in the data base. However, only 314 (59%) had SI values of greater than or equal to 0.5. Of the 54 strains in which there was not agreement, 37 belonged to the genera Acinetobacter, Moraxella, or Alcaligenes or were Pseudomonas pickettii. Reproducibility studies suggest that SI variation is most likely a function of a difference in culture age at the time of analysis, which is due to the relatively low temperature and time of incubation. Other discrepancies were attributable to insufficiently characterized library entries or an inability to differentiate chemotaxonomically closely related species. The MIS, as the first automated CFA identification system, is an accurate, efficient, and relatively rapid method for the identification of gram-negative nonfermentative bacteria. The development of a CFA library with the media and incubation conditions routinely used for the isolation of clinical pathogens could further decrease the identification time and provide an increase in accuracy.

Evaluation of the Titertek-NF system for identification of gram-negative nonfermentative and oxidase-positive fermentative bacteria

The Titertek-NF (TT-NF) system (Flow Laboratories GmbH, Meckenheim, Federal Republic of Germany) was evaluated for the identification of 1,289 strains of gram-negative, nonfermentative bacteria and some gram-negative, oxidase-positive bacteria. The oxidase test was also performed. Identifications were classified as correct, not identified (two or more taxa possible and identification score of less than 80%; supplementary tests for furthering the identification were not performed), and incorrect. Correct identification results were further subdivided by the correct level of species or biotype identification as greater than or equal to 98% (category a), 90 to 97% (category b), and 80 to 89% (category c). When compared with conventional identification results, the TT-NF system correctly identified 90.3% of strains (1,164 of 1,289 strains), with 72.5% (935 strains) belonging to category a, 14.7% of strains (189 strains) belonging to category b, and 3.1% of strains (40 strains) belonging to category c. Among the remaining strains, 104 (8.1%) were not identified and 14 (1.1%) were misidentified, and the system failed to generate identification results for 7 strains (0.5%). Reactions within the TT-NF system were reproducible, with an estimated probability of erroneous test results of 0.2%.

Comparison of rapid NFT and API 20E with conventional methods for identification of gram-negative nonfermentative bacilli from pharmaceuticals and cosmetics

The accuracy of the Rapid NFT and the API 20E identification systems was evaluated by comparing them with conventional biochemical methods for the identification of gram-negative, nonfermentative bacilli. The organisms were recovered from preserved, nonsterile pharmaceutical and cosmetic products. A total of 123 test isolates that are commonly encountered in these products were used. By using the criteria of accurate and reliable identification without employing additional tests, Rapid NFT was found to be more accurate after 48 h of incubation than API 20E for characterizing isolates to the species level. Therefore, close agreement between NFT and conventional methods for identification of industrial gram-negative isolates provides evidence that the Rapid NFT system is an improved and rapid method for identifying these organisms to the species level with minimal use of supplementary tests.