Oral fluids for detection and characterization of Salmonella in commercial finisher pigs.

Salmonella remains an important pathogen in swine production due to its impact on animal health and its role in foodborne illnesses. However, routine surveillance in pigs relies largely on fecal sampling, which can be labor-intensive and difficult to scale across large production systems. This study aimed to develop and evaluate a novel approach for monitoring Salmonella in finisher pigs using oral fluids in combination with sequential enrichment, culture, and polymerase chain reaction (PCR). A cross-sectional study was conducted at three commercial finisher sites in Iowa between February and May 2025, where paired oral fluid and pooled fecal samples were collected from 51 pens. The samples were processed using sequential enrichment followed by bacteriological culture and multiplex polymerase chain reaction to detect and characterize Salmonella. Direct PCR testing of raw samples did not detect Salmonella in either sample type. However, tests performed after enrichment successfully detected the pathogen in both samples, demonstrating the importance of enrichment for molecular detection in oral fluids. The culture of enriched oral fluids yielded viable isolates suitable for serotyping, and molecular testing enabled the rapid identification of the two serotypes most relevant to swine and public health (Typhimurium and I 4,[5],12:i:-). Salmonella was detected in 86.3% of the pens using at least one method, and oral fluids demonstrated diagnostic performance comparable to pooled fecal samples. These findings establish that oral fluids, when combined with sequential enrichment, are a practical and scalable sample type for monitoring Salmonella in finisher pigs.