* Firm says independent test found no traces of ST6 strain
* Health ministry says traces of listeria were found there
* RCL was part of polony recall that affected Tiger Brands
* Government had traced ST6 strain to Tiger Brands plant (Adds health ministry comment, Shoprite's further recall)
JOHANNESBURG, March 16 (Reuters) - Independent tests at RCL Foods' processed meat factory have found no traces of a listeria strain that has killed 180 people in South Africa since January last year, the food producer said on Friday.
Health authorities ordered a recall of processed meat known as polony made by Tiger Brands and RCL Foods nearly two weeks ago, in response to the listeria outbreak, the worst ever documented with nearly 950 reported cases.
The government traced the ST6 strain that caused it to a factory owned by Tiger Brands, sending its shares tumbling, while RCL Foods' Wolwehoek plant was also put under investigation.
RCL said on Friday independent tests showed no traces of that strain of bacteria. "Tests have shown that the plant is clear of ...ST6," the firm said in a statement.
Shares in RCL closed up 5.65 percent to 19.25 rand.
However, the health ministry said traces of listeria were recovered from Wolwehoek and "this state of affairs has not changed."
"We are awaiting whole genome sequencing results which will be available early next week," it said in a statement issued after the market close.
While ST6 has been responsible for the vast majority of cases in the outbreak, a small number have involved other strains of listeria.
Authorities are also examining a second Tiger Brands factory.
Both companies, which say they are cooperating with the authorities, have suspended output of processed meat at their plants.
Separately, retail group Shoprite Holdings said it had recalled a batch of Farmer's Deli red and smoked viennas - also a type of processed meat - from its shelves after testing revealed traces of listeria in one batch.
Further tests would be carried to determine if levels of the bacteria were harmful, it said.
Shoprite recalled some cold meat products after the outbreak was confirmed at Tiger's Enterprise Foods.
Farmer's Deli is a platform for producers of traceable, certified-organic products from Malta, Sicily, North Italy and Spain, according to its website. (Additional reporting by Nqobile Dludla Editing by James Macharia and John Stonestreet)