OXA-48-like carbapenemases in Proteus mirabilis - novel genetic environments and a challenge for detection.

OXA-48-like enzymes represent the most frequently detected carbapenemases in Enterobacterales in Western Europe, North Africa and the Middle East. In contrast to other species, the presence of OXA-48-like in Proteus mirabilis leads to an unusually susceptible phenotype with low MICs for carbapenems and piperacillin-tazobactam, which is easily missed in the diagnostic laboratory. So far, there is little data available on the genetic environments of the corresponding genes, bla_OXA-48-like, in P. mirabilis. In this study susceptibility phenotypes and genomic data of 13 OXA-48-like-producing P. mirabilis were investigated (OXA-48, n = 9; OXA-181, n = 3; OXA-162, n = 1). Ten isolates were susceptible to meropenem and ertapenem and three isolates were susceptible to piperacillin-tazobactam. The gene bla_OXA-48 was chromosomally located in 7/9 isolates. Thereof, in three isolates bla_OXA-48 was inserted into a P. mirabilis genomic island. Of the three isolates harbouring bla_OXA-181 one was located on an IncX3 plasmid and two were located on a novel MOB_F plasmid, pOXA-P12, within the new transposon Tn7713. In 5/6 isolates with plasmidic location of bla_OXA-48-like, the plasmids could conjugate to E. coli recipients in vitro. Vice versa, bla_OXA-48-carrying plasmids could conjugate from other Enterobacterales into a P. mirabilis recipient. These data show a high diversity of bla_OXA-48-like genetic environments compared to other Enterobacterales, where genetic environments are quite homogenous. Given the difficult-to-detect phenotype of OXA-48-like-producing P. mirabilis and the location of bla_OXA-48-like on mobile genetic elements, it is likely that OXA-48-like-producing P. mirabilis can disseminate, escape most surveillance systems, and contribute to a hidden spread of OXA-48-like.