Enhanced methods of microbial measurement and detection
Gray, Victoria Louise.
This study demonstrates the effects of different peptones, made from different biological sources and produced by numerous manufacturers, on the growth dynamics and morphology of various bacteria. The effects these differing growth medium constituents have upon the outcome of microbiological procedures, from identification of bacterial species to public health diagnostics, is of great significance. Peptones were assessed as a constituent of the pre-enrichment broth buffered peptone water. Generation times and yields at 24 h were measured using optical density techniques and were significantly affected by the type of peptone employed as nutrient source. Growth characteristics indicated that where peptones performed poorly, this was a result of poor nutrient quantities and not due to the presence of endogenous inhibitors. It is shown that Salmonella exhibit morphological differences, including cultures. which lack flagella and are consequently non-motile, dependent on the peptone constituents of the culture medium. Transfer of a flagellate Salmonella from nutritionally poor media into rich nutrient broth allowed flagella synthesis: indicating that the aflagellate form is still able to produce flagella. Amino acid sequencing of the peptones producing aflagellate organisms showed a relatively low tyrosine concentration: addition of tyrosine and glucose to these media produced flagellate salmonellae. Identification of the Salmonella serotypes is based on flagellar and somatic antigens therefore the absence of flagella may consequently affect complete identification of the serotype. Antibiotic susceptibility of the Enterobacteria was shown to be markedly affected by peptone, causing breakpoints to vary from sensitive to resistant. Thus the inclusion of different, undefined ingredients in growth media has a considerable effect upon the ability of the medium to enumerate bacteria furthermore these medium constituents affect the outcome of scientific research and should be carefully considered before work is commenced.
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