Mutations in may confer resistance to gentamicin in .

Listeriosis, a foodborne infection caused by , could lead to febrile listerial gastroenteritis and a more invasive form which is often associated with a high mortality and hospitalisation rate. Gentamicin, used as an adjunct therapy with ampicillin, remains the treatment of choice for this life-threatening and invasive infection. Nevertheless, there is little data on gentamicin resistance determinants in . In this study, we selected and characterised B2b, a gentamicin-resistant mutant derived from ATCC 19115 to determine the target(s) of resistance in after exposure to gentamicin. Whole-genome sequencing was carried out to identify the mutation site(s) and possible mechanism(s) of resistance. The mutant was characterised using antimicrobial susceptibility testing and PCR. For biological verifications, complementation and allelic exchange mutagenesis were carried out. We found that the gentamicin resistance in B2b was caused by a 10 bp deletion in which encodes a gamma subunit of the ATP synthase in . Using PCR, various other mutations were identified in other gentamicin resistant mutants derived from ATCC 19115. In addition, the mutation from B2b, when introduced into , also caused gentamicin resistance in this species. Hence, mutations appear to be important determinants of gentamicin resistance not only in but possibly also in other species.