Relates to bacterial contamination or the possibility of bacterial contamination.
This might be foods becoming contaminated by cleaning fluids (during processing or storage).
It could also be the ingredients being affected by pesticides during growth, or other chemical contamination such as oil or paint off machinery.
This could be bits of glass, metal, wood, jewellery, cigarette ends or insects in food.
It could also be badly sealed packaging that could allow the product to be contaminated