Comparison of Rectoanal Mucosal Swab Cultures and Fecal Cultures for Determining Prevalence of Escherichia coli O157:H7 in Feedlot Cattle

Abstract

We compared fecal samples with samples collected with rectoanal mucosa swabs (RAMS) to determine the prevalence of Escherichia coli O157 in feedlot cattle (n ‫؍‬ 747). Escherichia coli O157 was detected in 9.5% of samples collected with RAMS and 4.7% of samples tested by fecal culture. Pulsed-field gel electrophoresis analysis of isolates suggested that the strains colonizing the rectoanal junction were the same as those from the feces. Mucosal swab sampling was more sensitive than fecal sampling for determining the prevalence of E. coli O157 in feedlot cattle.Escherichia coli O157 is an important food-borne pathogen (15), and cattle are considered the major reservoir (2, 5). Early studies indicated the prevalence of E. coli O157 in cattle feces to be less than 2% of the cattle population (8, 10). However, molecular and immunomagnetic separation techniques have estimated that number to be closer to 20 to 30% in the summer months (4,7,9,17,22). Two major patterns of E. coli O157 shedding in the feces of cattle have been suggested: transient, in which animals shed the organism only briefly after picking it up from the environment, and colonized, in which the organism is shed for an extended period of time after presumptive colonization in the gastrointestinal tract (18). Recent findings suggest that E. coli O157 specifically colonizes the lymphoid follicle-dense mucosal epithelium at the terminal rectum, located approximately 2 to 5 cm proximal to the rectoanal junction (16). Based on this observation, Rice et al. (18) developed a rectoanal mucosal swab (RAMS) technique to sample the mucosal surface of the rectoanal junction. The objectives of this study were to compare the two collection methods, feces sampling and the RAMS technique, for detecting the prevalence of E. coli O157 in feedlot cattle and to use genetic subtyping by pulsed-field gel electrophoresis (PFGE) to compare isolates obtained by the two collection methods.Crossbred beef steers (n ϭ 747) from two different feedlots were used in this study. Diets consisted of approximately 94% concentrate (dry-rolled or steam-flaked corn) and 6% forage (alfalfa hay). The collection of RAMS samples was performed according to Rice et al. (18). The swabs were placed into culture tubes containing 3 ml of gram-negative broth (BD, Franklin Lakes, N.J.) with 0.05 mg/liter of cefixime, 10 mg/liter of cefsulodin, and 8 mg/liter of vancomycin (GNccv) and held on ice until transported to the laboratory. Fecal samples (at least 10 g) were taken immediately following the RAMS procedure by rectal palpation and stored on ice in individually sealed bags until transported to the laboratory. The RAMS sample was vortexed for 1 min, and 1 ml of the broth was transferred to 9 ml of GNccv. Approximately 1 g of subsample was placed in 9 ml of GNccv by using a sterile transfer stick. The procedures for enrichment, immunomagnetic separation, selective isolation, and identification of E. coli O157 from RAMS and fecal samples were according to Sargeant et al. (22). PFGE analysis was perf...

‘Super' or just ‘above average'? Supershedders and the transmission of Escherichia coli O157:H7 among feedlot cattle

“…Note that these sensitivities encompass the whole sampling procedure (sample capture, transportation and laboratory work); and not just the laboratory benchmark sensitivity, which could reasonably be assumed to be the same for both tests. The faecal test sensitivity is likely to be lower because of the dilution of the bacteria with faeces, which coincides with most of the existing literature [24,45,46], but not all [47][48][49]. It is unsurprising that there is some variation between studies as the sensitivity is likely to depend strongly on the exact sampling protocol and study design.…”

Comparison of Cultures from Rectoanal-Junction Mucosal Swabs and Feces for Detection of Escherichia coli O157 in Dairy Heifers

“…Therefore, an animal that was E. coli O157 positive as determined from a fecal sample was almost always identified as culture positive by RAMS culture. This is consistent with previous findings (9,21) and confirms these findings for the first time for a large cohort of naturally infected dairy heifers sampled longitudinally over time. The use of IMS is often considered to be the most sensitive culture method for screening cattle for E. coli O157, but RAMS culture has the advantage of being less costly and more rapid than IMS, and only the direct method yields quantitative results.…”

“…Recent findings (15,19) that the rectoanal-junction mucosa is a major colonization site for E. coli O157:H7 in the bovine intestine also suggest that host colonization factors may play an important role. Rectoanal mucosal swab (RAMS) culture has been shown to be more sensitive than fecal culture for dairy (21) and feedlot (9) cattle. Immunomagnetic separation (IMS) (23) of E. coli O157 from fecal samples after enrichment culture is often used to increase the sensitivity of fecal culture, but this technique is expensive and does not provide quantitative information in the form of bacterial counts/sample.…”

Rectoanal Junction Colonization of Feedlot Cattle by Escherichia coli O157:H7 and Its Association with Supershedders and Excretion Dynamics

“…In concurrence with other studies (8,12,25), RAJ swabbing is a more sensitive means of detecting E. coli O157:H7 in cattle than fecal sampling. Sampling individual cattle requires direct livestock handling and is more technically and practically challenging than fecal pat sampling.…”