Acquired resistance of Listeria monocytogenes in and escaped from liver parenchymal cells to gentamicin is caused by being coated with their plasma membrane

After systemic infection, a majority of Listeria monocytogenes invade liver parenchymal cells (LPC), replicate therein and spread to neighboring cells, suggesting that 3 different types of L. monocytogenes exist in the liver: L. monocytogenes being unable to invade LPC, residing in LPC, and escaped from infected LPC. Although listeriolysin O (LLO) participates in escape of L. monocytogenes from macrophages and L. monocytogenes is susceptible to gentamicin (Gm), it remains elusive whether LLO participates in invasion/escape of L. monocytogenes into/from LPC, and whether L. monocytogenes in/escaped from LPC are susceptible to Gm. In the present study, we examined whether LLO is involved in invasion/escape of L. monocytogenes into/from LPC and whether L. monocytogenes in/escaped from LPC are susceptible to Gm. Invasion/escape of L. monocytogenes were found in LPC lines regardless of LLO expression, and L. monocytogenes in/escaped from LPC lines showed resistance to Gm. L. monocytogenes escaped from LPC lines were coated with their plasma membrane and the acquired resistance to Gm was abrogated by saponin. Our results indicate that invasion/escape of L. monocytogenes into/from LPC occur independently of LLO, and suggest that the acquired resistance of L. monocytogenes in/escaped from LPC to Gm is caused by being coated with their plasma membrane.