A farm attraction in Devon is expected to be tested later to establish whether there is a link to a possible E. coli outbreak involving three children.
World of Country Life in Exmouth has voluntarily closed its deer run and animal petting areas on the advice of the Health Protection Agency.
The results of the tests are expected to take a few days.
South West Tourism has warned that changes to petting guidelines could put some farm attractions out of business.
The government is said to be considering whether to revise its advice on children's contact with farm animals.
Professor Hugh Pennington, an expert in microbiology, has urged parents to "think hard" about allowing under-fives to touch animals at petting farms.
But Malcolm Bell, chief executive of South West Tourism, said: "Families are a big part of our market and a big part of that is going to wildlife and animal attractions and farms.
"If you suddenly start saying that children under fives should not go near petting farms then you're actually going to seriously start to affect their viability, if not turn many farm attractions unviable."
Symptoms of E. coli include diarrhoea and vomiting. This can lead to dehydration which can be dangerous in young children and, in acute cases, can result in kidney failure.
Nine children are in hospital following an outbreak at Godstone Farm in Surrey, in which 67 cases have been confirmed. They are said to be stable and improving.
The three children at the centre of the Devon outbreak are also said to be recovering well.
Two other UK farms have also closed amid E. coli fears.
They include White Post Farm in Nottinghamshire which has had two confirmed cases of the E. coli O157 strain and a further two potential cases, and Horton Park Children's Farm in Epsom -which closed over hygiene concerns.