An overview of calf diarrhea - infectious etiology, diagnosis, and intervention

Cho, Yong-il; Yoon, Kyoung-Jin

to an ELISA [113] . The surface of latex particles is coated with antigen or antibody. The particles can then capture antibody or the target antigen, respectively. This test has been applied to detect a wide range of targets such as bacteria, virus, hormones, drugs, and serum protein [105] . Latex particles are made of synthetic rubber and emulsified as billions of micelles of the same size with a desired diameter. Particle size typically ranges between 0.05 to 2 μm in diameter, and the presence of sulfate ions provides an inherent negative surface charge to the particles [109] . The prepared latex particles can be further functionalized by special processes such as amidation, amination, carboxyation, hydroxylation, or magnetization to increase their binding stability and analyte attachment depending upon the purpose of the test [109] . For cases of calf diarrhea, the LAT has been frequently performed to identify E. coli K99 + [18] . Fecal samples are collected from diarrheic calves and sent to a diagnostic lab for evaluation. Once the E. coli is isolated, the bacterial suspension is mixed with latex beads coated with anti-E coli K99 + antibody and incubated under specific conditions. Agglutination of the latex beads can be clearly visualized when K99 antigen is present in the isolated E. coli. The latex agglutination test is frequently employed in diagnostic labs because this method can serve as a semi-quantified test and is relatively cheap with rapid turnaround [47] . Caution should be taken when interpreting marginal results since false positive/negative results frequently occur due to non-specific binding or interference [113] .