Literature review > Issue_5 > Review on Myziuk et al. 

There has long been and continues to exist a need for a rapid, uncomplicated diagnostic test for bacterial vaginosis (BV). Currently available detection and screening relies on the expertise in GU clinics and the Gram staining method. The interpretation of results for each individual tested is therefore slow and dependent on an expert being available to provide a reliable result. Application of the Nugent and Amsel criteria, taken as the most effective assessment for BV, is accordingly dependent on specialist interpretation and laboratory equipment.

Since the initial observation of increased sialidase activity in swab fluid taken for women with BV made by Hillier's group [1] a variety of studies have appeared showing mixed results, utilizing a variety of different substrates in order to detect the sialidase activity. The significance of the sialidase substrate is often disregarded, but as outlined below, is a fundamental issue in the design and success of a valuable test.

The appearance of the BV Blue test potentially offers a significant improvement on the current situation. The new test is compared with both Amsel and Nugent scores where the Gram stain is used for standard detection of BV. The aims of the paper are clearly outlined and presented. The BV Blue test shows excellent sensitivity, specificity, positive and negative predictive values, correlating well with the Nugent scores. The Amsel scoring system was much poorer, with only 50% sensitivity compared to 91.7% for the BV Blue test and similarly low values in comparison with the Nugent scores.

The nature of the test brings with it a number of significant advantages that underline its future potential and application. The test is rapid and can be completed while the patients are still in clinic, making general management considerably more effective and efficient. The end result depends on a color change and therefore does not rely on the interpretation of a trained expert. No laboratory equipment is needed and the test is easily carried out at any location. Simple instruction may facilitate the use of the test by patients themselves. All of these points are positive developments that will have immediate and significant impact on the application of BV detection.
Although these results are very encouraging, the size of the sample tested is small and serves only to emphasize the need for a significantly larger scale study to address the application of the BV Blue test in wider populations. Reference is made to two other studies using BV Blue and presented as posters, but these data are not included in the paper. The selected patients were attending a GU clinic, where trained personnel carried out the test (as acknowledged by the authors). The number of populations where the BV Blue test could be applied for screening is well known and will include ethnicity, different social groups, and preterm birth groups, and the application of the test in non-GU clinic setting needs to be evaluated.

The paper is frugal with regard to information concerning the basic composition and properties of the BV Blue system. The identity of the sialidase substrate is not made in the paper, although it is based on a United States patent on the preparation of chromogenic sialidase substrates [2], and the properties of the kit are not described. This precludes any judgment on the stability of the kit. As the sialidase test relies on a liquid assay, the stability of the substrate in solution will be expected to be a significant factor in the kit shelf life. There is also no information regarding the conditions for storage, which needs to be known if the kit is to be used widely employed, especially in tropical and subtropical climates. Similarly, more information concerning the stability of the chromogen formed in the test with regard to temperature and time is also needed to back up wider use of the test.

There are also several issues that arise with regard to the nature of the substrate itself. As mentioned earlier, a range of synthetic substrates for sialidase have been tested and these show varying specificity and selectivity with regard to sialidases from different organisms. This raises two important issues. Firstly, the selectivity of the substrate used for BV Blue and in other tests designed for BV detection (e.g. [4]) has been show to be very high in the populations tested, but remains untested in all of the populations relevant to BV screening (e.g ethnicity). Secondly, BV organisms have not been tested extensively for their sialidases and their synthetic substrate specificities. Variations in BV bacterial populations may arise in certain populations and lead to changes in the sialidase detection "potential" using such substrates. A full examination of these properties will also involve the inclusion of the lactobacillus species present in normal conditions in the GU tract, and which also express sialidase activities. The cut off observed with synthetic sialidase substrates used in BV Blue (given as >7.8U) and other assays requires assessment in terms of "normal" activity. Activity with physiological substrates is not a viable basis for simple and rapid sialidase tests, but will yield the physiologically relevant information regarding disease mechanisms and potential therapeutic inputs. These aspects are closely related to the properties of the sialidase produced by BV and non-BV organisms, where molecular variation is known and expected with regard to disease mechanism [3], but are not the focus of attention in this report.

In conclusion, BV Blue represents an important and valuable advance in the need to screen for BV. The paper falls short of providing a full overview of the potential for the test due to the limited size and selection of patient numbers. Longer term expectations for this and other BV testing kits using sialidase detection need to address the full range of populations to be screened, the suitability of the synthetic substrate to be used, and the stability, shelf life, and other properties of the kit provided.

In view of the increasing pressure to evaluate to role of BV with other sexually transmitted infections and preterm birth, the use of BV Blue will clearly be of great value and deserves sound examination for its application.

References:

1. Briselden, A.M., Moncla, B.J., Stevens, C.E., and Hillier, S.L. (1992). Sialidases (neuraminidases) in bacterial vaginosis and bacterial vaginosis-associated microflora. J Clin Microbiol 30, 663-666.

2. Johnson, S.C., Saeed, A., and Luo, M. (2003). Chromogenic substrates of sialidase and methods of making and using the same. In: United States patent US 6152100 B1, USA: Ibbex Inc., UAB Research Foundation, Birmingham, Alabam,a, USA.

3. Vimr, E., and Lichtensteiger, C. (2002). To sialylate, or not to sialylate: that is the question. Trends Microbiol 10, 254-257.

4. Wiggins, R., Crowley, T., Horner, P.J., Soothill, P.W., Millar, M.R., and Corfield, A.P. (2000). Use of a novel "spot test" to identify sialidase activity in vaginal swabs from women with bacterial vaginosis. J. Infect. Dis.

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