NASHVILLE, Tenn. -- Not all Escherichia coli is created the same. E. coli O157:H7 is only one of the shigatoxin-producing E. coli (STECs) of interest. At the National Cattlemen’s Beef Association’s Cattlemen’s College Feb. 1, Terry Arthur, PhD, Meat Animal Research Center, spoke about STECs and their prevalence on hides and in lairage.

“Cattle hide is the major source for E. coli O157:H7carcass contamination at processing,” Arthur said.

He described a 2003 study in a commercial processing plant that used a chemical hide sanitizer for dehairing on cattle post-slaughter. Incoming animals were 77% positive for the pathogen. Of those cattle that did not get chemically dehaired, 50% were positive for E. coli. Only 1.3% of the cattle that were chemically dehaired were positive for E. coli.

“We wanted to determine in a given pen what was the rate of shedding that would cause 50% to have contamination on hide?” Arthur said. “What would an effective pre-harvest program look like?”

A study followed 300 animals over nine months and looked at fecal shedding and how it affected hide contamination. Animals were categorized into four E. coli-shedding groups:

  • Cattle that were not shedding E. coli O157:H7;
  • Low shedders at less than 200 CFU/g;
  • High shedders over 200 CFU/g to 10,000 CFU/g; and
  • Super shedders over 10,000 CFU/g

“Once you cross 20% fecal prevalence, hide prevalence goes to about 100%,” Arthur said. “If you can develop pre-harvest intervention to keep fecal prevalence below 20% and keeping shedding below 200 CFU/g, you have something that will reduce hide contamination.”

But contamination can continue after the animal leaves the feedlot.

Cattle were sampled at the feedlot before being loaded onto trucks, trucks were sampled, and cattle were sampled again at processing. What was discovered was that hide prevalence increased when cattle were sampled on the slaughter chain. What this means, Arthur said, is that “effective feedlot intervention may be negated by transport and lairage issues.”

Fingerprinting of the bacterial isolates that were found showed that on 29% of the isolates on the hide and carcass at the processing plant matched the feedlot isolates. Arthur said 2% matched isolates from the truck, and 69% were of unknown origin.

“This told us there is a large amount of contamination occurring after animals leave the feedlot. Over 80% of the isolates on the carcasses did not come from the feedlot,” he said.

According to Arthur, a typical commercial plant has many areas where as many as 4,000 cattle can go through a day, including the loading dock, scale, holding pens, alleys, snakes and tubs.

“As animals come through they pick up contamination from super shedders,” he said.

The good news, Arthur said, is sampling showed that in plants with a hide wash cabinet, only 4% of the cattle were positive for E. coli O157:H7.

“Contamination from lairage is easily washed off if the plant has the ability to do so,” he said,  adding that the majority of plants have gone to using hide wash cabinets, but he’d like to see it more widely used across the industry.

Super shedders are the major contributors to E. coli O157:H7 in the feedlot and likely in lairage.

“The lairage environment can be a larger contributor to E. coli contamination than the production environment,” Arthur said. “Some form of hide intervention should be used to remove lairage-derived contamination, and we need to identify components of super-shedding.”