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item Cray, Paula

Submitted to: American Veterinary Medical Association Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/15/2005
Publication Date: 7/15/2005
Citation: Cray, P.J. 2005. Culturing bacteria: a lifetime of challenges. American Veterinary Medical Association Abstract. July 16 - 20, 2005. Minneapolis, MN.

Interpretive Summary:

Technical Abstract: Although many countries have interests in conducting a monitoring program, planning in the early stages will increase the likelihood of obtaining relevant, comparable data to assess trends over time. Considerations must include selection of sentinel and other relevant organisms, sampling and culture of the isolates, and test methodologies. Failure to standardize surveillance systems will lead to misinterpretation of the data and development of research programs needed to fill in information gaps. Bacteriologic culture is often the only means available to isolate and identify bacterial strains of interest. However, there are many methods available and results often differ between methods making comparisons difficult. Samples may include feces, tissue, insects, dust, feed and feed components and others. Each sample type may require special culture needs/considerations, such as pre-enrichment to resuscitate injured cells, temperature, and use of antimicrobials to decrease competing organisms. Sensitivity of the method must also be considered as bacterial numbers are often low and unevenly dispersed throughout the sample. It is becoming more evident that use of selective media may result in the selection of a subpopulation of bacteria with specific phenotypic and genotypic characteristics which may not be representative of the entire culture population. Reporting of any data would be accurate for a particular method as described, but it would be inaccurate to report that it is representative of the general population of bacteria within that sample if antimicrobials were used as a selection factor. Additionally, there appears to be a high likelihood that multiple serotypes or aggregation between serotypes can occur. Care must be taken when designing sampling strategies which could influence population analysis. Further, additional studies are required to better understand the 'subpopulations' of bacteria within a sample. It may be that the isolate attributed to a 'subpopulation' may in fact be more virulent, better able to establish itself within the host, causing either disease, carriage, or both, and may also be more likely to have a resistance attribute associated with its genome and may readily acquire additional resistance genes over time. Conversely, other populations may be exquisitely sensitive to antimicrobials and easily eliminated within the host. Thus, it is possible that the isolation and characterization of dominant populations may mask characterization of the more important subpopulation when considering animal and human health issues.