Rectoanal mucosal swab culture is more sensitive than fecal culture and distinguishes Escherichia coli O157:H7-colonized cattle and those transiently shedding the same organism

Enrichment and direct (nonenrichment) rectoanal mucosal swab (RAMS) culture techniques were developed and compared to traditional fecal culture for the detection of Escherichia coli O157:H7 in experimentally infected and naturally infected cattle. Holstein steers (n = 16) orally dosed with E. coli O157:H7 were sampled after bacterial colonization starting 15 days postinoculation. Enrichment RAMS cultures (70.31% positive) were more sensitive than enrichment fecal cultures with 10 g of feces (46.88% positive) at detecting E. coli O157:H7 (P < 0.01). Holstein bull calves (n = 15) were experimentally exposed to E. coli O157:H7 by penning them with E. coli O157:H7-positive calves. Prior to bacterial colonization (1 to 14 days postexposure), enriched fecal cultures were more sensitive at detecting E. coli O157:H7 than enriched RAMS cultures (P < 0.01). However, after colonization (40 or more days postexposure), the opposite was true and RAMS culture was more sensitive than fecal culture (P < 0.05). Among naturally infected heifers, enriched RAMS or fecal cultures were equally sensitive (P = 0.5), but direct RAMS cultures were more sensitive than either direct or enriched fecal cultures at detecting E. coli O157:H7 (P < 0.01), with 25 of 144, 4 of 144, and 10 of 108 samples, respectively, being culture positive. For both experimentally and naturally infected cattle, RAMS culture predicted the duration of infection. Cattle transiently shedding E. coli O157:H7 for <1 week were positive by fecal culture only and not by RAMS culture, whereas colonized animals (which were culture positive for an average of 26 days) were positive early on by RAMS culture. RAMS culture more directly measured the relationship between cattle and E. coli O157:H7 infection than fecal culture.