Haemophilus parasuis genotyping is currently used for characterization and selection of strains to be included in autogenous vaccines. Haemophilus parasuis has one of the highest genetic variabilities among swine bacterial pathogens. Genotyping has been extremely useful to characterize the population structure of this bacterium, identify prevalent groups of strains affecting North American swine herds, and to monitor the emergence of new virulent clones. More info.
Genotyping of A. suis isolates obtained from U.S. swine herds revealed that this bacterium is highly clonal. Contrary to H. parasuis, for which more than 90 different strains have been reported, only 12 strains have been identified for A. suis so far. One of these strains was highly prevalent (55.71%) among the isolates characterized. This strain was identified in 20 out of 30 herds evaluated, and was detected in animals from all production stages (neonatal, nursery, finishing, and adult pigs). This isolate is now being further evaluated as a potential universal vaccine candidate. More info.
The Streptococcus suis database is used by field veterinarians for selection of autogenous vaccine strains. This database has also been used as a surveillance tool to address the public health risk S. suis represents in the U.S. for those working with swine. We have identified at least 3 S. suis isolates originated from 3 different swine herds that were identical to a human isolate based on ERIC-PCR, BOX-PCR, Multilocus Sequence Typing, and serotyping. The first human case of S. suis meningitis in the U.S was described in 2006, and the human isolate could not be linked to any swine source due to the lack of a surveillance system. That surveillance system is now in place and ready to be used. More info.
The value of A. pleuropneumoniae genotyping relies on tracking the introduction of new strains into swine herds. There is no value in using this technique for selection of vaccine candidates, as the Apx toxins are the main virulence factors produced by this pathogen and these toxins are not characterized by genotyping. The App genomic database has been very useful to troubleshoot the identification of Actinobacillus sp. biochemically similar to A. pleuropneumoniae that were isolated from clinical samples. More info.
Salmonella sp. genotyping is a useful tool to troubleshoot unexpected serotyping results. We have encountered a few field isolates that cannot be typed by traditional methods. Genotyping demonstrated that these were atypical Salmonella choleraesuis isolates that lacked the necessary surface antigens used for serotyping.We have also used genotyping to differentiate live vaccine strains from virulent field isolates. Genotyping can accurately identify the SC-54 vaccine strain (BI Enterisol Ileitis), for example. We are currently developing additional tests to be able to differentiate the Argus (Intervet) vaccine strain from field isolates.
Escherichia coli genotyping is mainly used to compare non-virulent vaccine strains to virulent field strains isolated from clinical cases. Many herds use this tool to monitor vaccine strains, as a QAQC measure.
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