Sampling (IMAGE) Penn State Caption Rsearchers collected samples in apple-packing facilities in which Listeria monocytogenes has been persistent. They discovered that harmless bacteria may be sheltering the pathogens. Credit Penn State Usage Restrictions Non commercial use only License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.