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

Abstract

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.Since Escherichia coli O157:H7 was first identified as a human pathogen (27,33), investigations have demonstrated that human disease outbreaks are often linked to a bovine food source or bovine waste-contaminated water (2,7,30,39). Although most of the known outbreaks of E. coli O157:H7-associated disease in humans are food borne or waterborne, several recent studies indicate that a significant number of human infections are acquired from direct contact with cattle, the environment, or unknown sources (1,12,30,34). An accepted premise is that the reduction of the number of cattle infected with E. coli O157:H7 or the elimination of E. coli O157:H7 from cattle will effect a reduction in the rate of disease in humans. To this end, a great deal of research has focused on describing the ecology and epidemiology of E. coli O157:H7 in cattle, with the hope of identifying interventions to reduce its prevalence in cattle (11,16,17,19,20,23,24,28,29). Within this body of research, numerous methods for detecting E. coli O157:H7 in bovine fecal samples have been developed and used (8,9,22,36,37,40). The reported sensitivities of detection by these various methods vary greatly, and problems occur when data from studies that have used methods with disparate sensitiv...

Escherichia coli O157:H7 in Environments of Culture-Positive Cattle

“…The number of E. coli O157: H7/g feces ranged from 3.5 ϫ 10 5 CFU/g to levels detectable only by enrichment culture (defined as Ͻ10 1 CFU/g). The pattern of carriage of E. coli O157:H7 by the experimentally inoculated steers was similar to that of cattle carrying the bacteria naturally, showing wide variation in duration of fecal positive status and in fecal counts of E. coli O157:H7 (1,11,14,18,24,26).…”

Role of Escherichia coli O157:H7 Virulence Factors in Colonization at the Bovine Terminal Rectal Mucosa

“…Recently, the recto-anal junction (RAJ) mucosa was identified as the primary site of E. coli O157:H7 colonization in cattle (47). Based on this finding, we demonstrated that culture of recto-anal mucosal swabs (RAMS) is easier and more sensitive than fecal culture to detect the bacteria (51) and that administration of E. coli O157:H7 to the terminal rectal mucosa is a reliable method to establish colonized cattle experimentally (58). Development of effective interventions to reduce bovine carriage of E. coli O157:H7 will rely on understanding the bacterial factors involved in E. coli O157:H7 colonization and persistence at the RAJ mucosa.…”

Involvement of theEscherichia coliO157:H7(pO157)ecfOperon and Lipid A Myristoyl Transferase Activity in Bacterial Survival in the Bovine Gastrointestinal Tract and Bacterial Persistence in Farm Water Troughs

“…To isolate and identify E. coli O157 strains from bovine samples, D-sorbitol MacConkey agar plates supplemented with 4-methylumbelliferyl-␤-D-glucuronide (MUG), cefixime, and potassium tellurite (SMAC-CTM) (40) or D-sorbitol agar plates supplemented with neutral red and MUG (SNM) (17 g of Bacto Peptone, 3 g of yeast extract, 5 g of NaCl, 10 g of D-sorbitol, 0.3% neutral red, 15 g of Bacto Agar, 0.1 g of MUG [pH 7.3] per liter of distilled water) were used. Trypticase soy broth (TSB; BBL/Becton Dickinson) was used for enrichment culture as previously described (40). For the motility assay, 0.3% soft agar (10 g of tryptone, 3 g of NaCl, 3 g of agar per liter of distilled water) was used.…”