RESUMEN
Neonatal calf diarrhea (NCD) is frequently associated with single or mixed viral, bacterial and/or protozoal infections. Consequently, laboratory diagnostic of NCD usually requires specific tests for each potential agent; a time-consuming, laborious and expensive process. Herein, we describe an end-point multiplex PCR/reverse transcription-PCR (RT-PCR) for detection of five major NCD agents: bovine rotavirus (BRV), bovine coronavirus (BCoV), Escherichia coli K99 (E. coli K99), Salmonella enterica (S. enterica) and Cryptosporidium parvum (C. parvum). Initially, we selected and/or designed high-coverage primers. Subsequently, we optimized multiplex PCR/RT-PCR conditions. Next, we evaluated the analytical sensitivity of the assay and assessed the performance of the reaction by testing 95 samples of diarrheic calf feces. The analytical specificity was evaluated against bovine viral diarrhea virus (BVDV), E. coli heat-stable enterotoxin (STa) and Eimeria spp. The detection limit of our assay was about 10 infectious units of BRV, 10-2 dilution of a BCoV positive sample pool, about 5 × 10-4 CFU for S. enterica, 5 × 10-6 CFU for E. coli K99 and 50 oocysts for C. parvum. No non-specific amplification of other bovine diarrhea agents was detected. Out of 95 samples analyzed, 50 were positive for at least one target, being 35 single and 15 mixed infections. BRV was the most frequent agent detected in single infections (16/35), followed by Cryptosporidium spp. (11/35), which was the most frequent in mixed infections (11/15). Positive and negative multiplex results were confirmed in individual reactions. In conclusion, we described an end-point multiplex PCR/RT-PCR for faster and easier NCD diagnosis, which may be useful for routine diagnosis and surveillance studies.