The airline stopped using Gate Gourmet after trace amounts of the dangerous bacteria were found at its LAX facility, but it was found on surfaces that do not come into contact with food, officials said.
No illnesses were reported.
A spokesperson said the catering kitchen was treated and noted the airline uses the company at other locations.
The airline said it was making alternate arrangements for catering services from other providers, but some flights may be affected over the next few days. Until a new catering service is found, travelers who are affected will be provided with electronic travel vouchers to use on future flights.