Evaluation of two BBL Crystal systems for identification of some clinically important gram-negative bacteria.

The BBL Crystal system (Becton Dickinson Microbiology Systems, Cockeysville, Md.) is a miniaturized bacterial identification method employing modified conventional and chromogenic substrates. Two products are currently available, the Rapid Stool/Enteric ID Kit and the Enteric/Nonfermenter ID Kit, each comprising thirty tests. We report an evaluation of both systems (using database version 1.1 for both) in the identification of 51 gram-negative taxa likely to be encountered commonly in the clinical laboratory. In all, 266 strains were tested in the Enteric/Nonfermenter ID Kit, and these represented 36 taxa of the family Enterobacteriaceae (188 strains), 5 oxidase-positive fermentative taxa (26 strains), and 10 nonfermentative taxa (52 strains). The majority of these same strains (203 of 266) were also tested in the Rapid Stool/Enteric ID Kit. The Enteric/Nonfermenter ID Kit performed as follows: Enterobacteriaceae, 93% correct, 6% not identified, and 1% incorrect; oxidase-positive fermenters, 88, 12, and 0%, respectively; and nonfermenters, 100% correct, although several only to the genus or group level. The Rapid Stool/Enteric ID Kit gave the following results: Enterobacteriaceae, 91% correct, 7% not identified, and 2% incorrect; oxidase-positive fermenters, 80, 13, and 7%, respectively (but results were based on only 15 strains); and nonfermenters, 100% correct (but results were based on only 11 strains). We found the systems extremely easy and rapid to use, and for the Enteric/Nonfermenter ID Kit an identification rate of 100% in 40 of 51 taxa was achieved, with corresponding figures of 29 of 39 taxa for the Rapid Stool/Enteric ID Kit.     

Test reproducibility of the API (20E), Enterotube, and Pathotec systems.

Thirty-three strains of bacteria (30 Enterobacteriaceae and one strain each of Aeromonas formicans, A. hydrophila, and Plesiomonas shigelloides) were tested three times in each of 27 conventional tests and in the API, Enterotube, and Pathotec systems. The results obtained were analysed for test reproducibility within each kit, correlation of the kit tests with the equivalent conventional media, and the identification of the strains by the kits. Difficulties in evaluation and comparison of identifications are discussed. A practical evaluation of the kits was also made.     

Immunological clearance of 75Se-labelled Trypanosoma brucei in mice. III. Studies in animals with acute infections.

Using trypanosomes labelled with [75Se]-methionine a series of experiments was conducted to investigate antibody production in mice with acute fulminating T. brucei infections. As measured by the hepatic uptake of radiolabelled parasites, we were unable to demonstrate any evidence of antibody-mediated uptake by the liver in such mice. It was concluded that this was not due to impaired macrophage function but was caused by the inability of antibody production to cope with the massive parasitaemias produced by rapidly-replicating infections so that effective opsonization of the parasites did not occur. In contrast, a train of trypanosome which causes a more chronic infection, although initially having a similar replication, although initially having a similar replication rate, subsequently switched t a slower one and thereby allowed antibody to reach levels which permitted effective opsonization. There was no evidence that the parasite caused any significant suppression of antibody responses in these acute infections since inoculation with trypanosomes of one stock at the same time as vaccination with irradiated organisms of a second stock did not prevent the development of antibody to the latter, as measured by the hepatic uptake of radiolabelled parasites.     

The VP7 gene of a new G serotype of human rotavirus (B37) is similar to G3 proteins in the antigenic c region

The human rotavirus isolate B37 has a characteristic "super-short" RNA electropherotype and has been shown to represent a new VP7 serotype (M. J. Albert, L. E. Unicomb, and R. F. Bishop, 1987, J. Clin. Microbiol. 25, 183-185). The VP7 gene was cloned, and its nucleotide and predicted amino acid sequences were compared to other published VP7 gene sequences. Consistent with the serological evidence, two major antigenic regions of the B37 VP7 (i.e., regions A and B) differ in sequence from those of other G serotypes. Unexpectedly, the C antigenic region shows close similarity to G3 rotaviruses, but we were unable to detect a serological relationship using serotype 3 monoclonal antibodies.     

A comparison of two anti-neuraminidase monoclonal antibodies by complement activation

The specificities of two anti-neuraminidase monoclonal antibodies have been compared by their ability to fix complement. They were found to differ to some extent in their reactivity with a range of N2 influenza viruses. Thus, as in the case of anti-hemagglutinin antibodies, anti-neuraminidase monoclonal antibodies are able to detect subtle structural changes in the viral antigen. Although both monoclonal antibodies fixed complement with intact virus, neither one fixed complement when complexed with isolated neuraminidase “heads”.     

Comparison of Southern transfer hybridization and dot filter hybridization for detection of cervical human papillomavirus infection with types 6, 11, 16, 18, 31, 33, and 35

A commercial dot filter hybridization kit (Virapap Kit) was compared with Southern transfer hybridization for the detection of seven types of human papillomavirus (HPV) in cervical specimens from 450 consecutive females attending a sexually transmitted diseases clinic. In comparison with Southern transfer hybridization, performed with the same probes used in the dot filter kit, the sensitivity, specificity, and positive and negative predictive values of dot filter hybridization were 90%, 94%, 74%, and 98%, respectively. Among patients with cervical cytologic dysplasia, HPV DNA was detected in 44% by dot filter hybridization and in 35% by Southern transfer hybridization. Although 26% of specimens positive by dot filter hybridization were not confirmed by Southern transfer hybridization, cervical dysplasia was detected in 5 (25%) of 20 with HPV DNA detected by dot filter hybridization alone, compared with 25 (8%) of those with no definitive evidence of HPV by either method (P = 0.009) and with 16 (30%) of 53 with HPV DNA detected by both methods (P = 0.7). The kappa statistic for interobserver and intraobserver reproducibility for interpretation of blots was similar for the two methods. The dot filter hybridization method evaluated appears to be a satisfactory alternative to Southern transfer hybridization for detection of HPV DNA.     

Effect of finite phosphor thickness on detective quantum efficiency

In this paper we describe theoretically the relationship between the finite thickness of a phosphor screen and its spatial-frequency-dependent detective quantum efficiency DQE(f-). The finite thickness of the screen causes a variation in both the total number of light quanta emitted from the screen in a burst from a given x-ray interaction and in the spatial distribution of the quanta within the light burst [i.e., shape or point spread function (PSF) of the light burst]. The variation in magnitude of the burst gives rise to a spatial-frequency-independent reduction in DQE, characterized by the scintillation efficiency As. The variation in PSF causes a roll off in DQE with increasing spatial frequency which we have characterized by the function Rc(f). Both As and Rc(f) can be determined from the moments of the distribution of the spatial Fourier spectrum of light bursts emitted from the phosphor and thus they are related: As is a scaling factor for Rc(f). Our theory predicts that it is necessary for all light bursts which appear at the output to have the same magnitude to maximize As and the same shape to maximize Rc(f). These requirements can lead to the result that the fluorescent screen with the highest modulation transfer function will not necessarily have the highest DQE(f) even at high spatial frequencies.