Coexistence of bla_NDM-1, bla_IMP-4and bla_OXA-181 in Citrobacter braakii clinical isolate in China

Citrobacter braakii (C. braakii) is a gram-negative bacterium associated with hospital-acquired infections such as respiratory tract infections and bacteremia. There has been a gradual increase in the number of C. braakii infection cases in recent years. The antimicrobial resistance level of C. braakii has been steadily increasing, and the coexistence of multiple resistance genes further complicates the selection of appropriate clinical antibiotic therapies.

we reported a multidrug-resistant C. braakii W221 co-harboring bla_NDM-1, bla_IMP-4, and bla_OXA-181 with four key resistance encoding plasmids (pW221-1, pW221-2, pW221-4 and pW221-5). The results of antimicrobial susceptibility testing indicated that W221 exhibited high-level resistance to aminoglycosides, carbapenems and ceftazidime-avibactam. Conjugation assays indicated that plasmid pW221-1, bla_NDM-1-carrying plasmid pW221-4 and bla_OXA-181-carrying plasmid pW221-5 were transferrable to Escherichia coli (E. coli). In addition, bla_NDM-1-carrying plasmid pW221-4 and bla_OXA-181-carrying plasmid pW221-5 also could transfer to Klebsiella pneumoniae. Notably, mobilizable plasmid pW221-1 not only carried multiple resistance elements (such as sul1, qnrA1, etc.) but also possessed virulence factors (vipA/tssB). We also found that bla_NDM-1, rmtC and sul1 resistance genes and virulence factor htpB co-occurred on the same mobilizable plasmid pW221-4. Detailed genetic analysis showed that multiple transposons (Tns) and insertion sequences (ISs) were found surrounding the vital resistant genes, which could stimulate mobilization of resistant determinants. bla_IMP-4 was located on the class 1 integron In823. In addition, the fosA3-bla_SHV-12-sul2-aph(3'')-Ib-aph(6)-Id -qnrS1 antibiotic resistance island (ARI) in pW221-2 was surrounded by Tn3, IS26, IS5075, ISKpn19, and Tn5403. Moreover, bla_NDM-1-carrying plasmid pW221-4 was typed as IncFII plasmid, which was known to have high-efficiency transmissibility. The bla_OXA-181 gene was characterized by the following structure: IS26-ISEc63-IS3000-bla_OXA-181-ISKpn19-ISMex22-qnrS1-ISAs17-IS26.

we isolated a C. braakii W221 co-existing bla_NDM-1, bla_IMP-4, and bla_OXA-181, and this was first reported in the world. The presence of multiple transferrable and mobilizable plasmids carrying key resistance determinants suggested that this strain may have high potential for horizontal gene transfer and rapid dissemination. These findings suggesting that clinical settings should be vigilant against the further emergence, spread and prevalence of such novel multidrug-resistant strains.