To facilitate monitoring of culture media, a simple quantitative streaking technique, implying ever-decreasing numbers of colony-forming units per surface area, as in spiral plating, was developed. The procedure evaluates, in quantitative terms, the ability of media (1) to support the formation of colonies by organisms that it was designed to grow and (2) to resist colonization by organisms that it is expected to suppress. The procedure was therefore termed ecometric evaluation. The ecometric results appeared to agree well with observations made on productivity and selectivity of the media studied during routine examination of specimens. These encouraging results prompted further, rigorous standardization of ecometry. A template was developed to standardize inoculation and the depth of the agar was controlled to within +/- 10%. Finally the attributes of the inocula used were accurately defined. The standardized ecometric technique has been found useful for the following purposes: (1) to assess the practical significance of the inhibitory effect of gentamicin observed in some moulds and yeasts (this was solved by replacing poorer basal media by one particular richer modification, viz, yeast morphology agar); (2) the development of a blood-free selective enumeration medium for Campylobacter jejuni, i.e. sulphide iron motility agar plus the combination of antibiotics suggested by Skirrow (1977); and (3) verification of the absence of antimicrobial activity of enzyme preparations, e.g. catalase, used in culture media to remedy sublethal damage in certain groups of bacteria. Ecometric evaluation can now be recommended for (1) routine monitoring of consignments of dehydrated or ready-to-use, purchased media; and (2) in-house checking of the functioning of medium preparation departments. Only occasionally is it necessary to use conventional counting techniques to confirm the results.

A PCR for the detection of Taylorella equigenitalis, the causative agent of contagious equine metritis, was developed and evaluated. A genus-specific primer-probe set was derived from the 16S ribosomal DNA sequences. The PCR was specific and amplified a 585-bp product from all 64 available T. equigenitalis isolates. This PCR product hybridized with a specific probe in a dot spot assay. A variety of microorganisms from the genital tracts of horses or with a close phylogenetic relationship to T. equigenitalis did not yield a visible PCR product and were all negative in the dot spot hybridization assay. The results of the PCR assay were compared with those of culture by using 191 genital swabs from horses of several breeds. We demonstrate that the sensitivity of the PCR assay is superior to that of culture. The assay is most sensitive when DNA from culture plates incubated for at least 2 days is used. Of the tested samples, 1.5% were positive in the culture assay, whereas 35% were positive in the culture PCR assay. PCR-positive samples were obtained from all breeds tested. This means that many T. equigenitalis-carrying horses go unidentified by the current culturing technique. This affects current views about the spread and control of T. equigenitalis.

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