Experimental Evaluation of Fecal-Mediated Transfer of Salmonella Typhi From Blattella germanica to Mice.

Blattella germanica (German cockroaches) are recognized as potential carriers of intestinal pathogens, yet their role in delivering human pathogens to mammals via fecal contamination has not been experimentally evaluated. In this study, we established an experimental model using 100 B. germanica infected with a fluorescently labeled Salmonella enterica serovar Typhi Ty21a strain and assessed their ability to contaminate food and water. Fluorescent signals were detected in both midgut tissues and fecal matter of cockroaches within 6 h postinfection, peaking at 1 day (midgut: 4.52 × 1010 relative fluorescence unit [RFU] and feces: 6.12 × 108 RFU) and persisting up to 7 days. Importantly, cockroach-derived fecal suspensions administered to BALB/c mice resulted in rapid and transient intestinal exposure, with detectable bacterial signals in mouse feces within 30 min (1.13 × 103 to 1.08 × 104 RFU) and in intestinal tissues for up to 12 h; no fluorescent signal was detected thereafter (up to 7 days). Fluorescence quantification showed a positive correlation with viable bacterial counts (CFUs) (R 2 = 0.78, p < 0.05), supporting use of RFU as a proxy for Ty21a sfgfp abundance. Collectively, these findings support the potential role of B. germanica as a mechanical vector that can contaminate food and water and facilitate fecal-oral exposure of mammals to Salmonella under enclosed conditions.