Characterization of a novel Tn6485h transposon carrying both blaIMP-45 and blaAFM-1 integrated into the IncP-2 plasmid in a carbapenem-resistant Pseudomonas aeruginosa

OBJECTIVES

To characterize a carbapenem-resistant Pseudomonas aeruginosa (CRPA) with an IncP-2 plasmid containing a novel transposon, Tn6485h, which carries both blaIMP-45 and blaAFM-1.

METHODS

Antimicrobial susceptibility testing and filter mating experiment were performed on PA942. The stability of the plasmid carrying both blaIMP-45 and blaAFM-1 was carried out. We determined the growth rate of the transconjugant to investigate fitness cost. Additionally, whole-genome sequencing and genomic analysis were performed on PA942.

RESULTS

PA942 strain was resistant to most antibiotics except for ciprofloxacin and colistin. Bioinformatics analysis confirmed that PA942 contains an IncP-2 plasmid with a novel transposon Tn6485h carrying both blaIMP-45 and blaAFM-1. The plasmid pPA942-IMP45 can be transferred into recipient bacteria PAO1Rif with an efficiency of 2.2 × 10-7 and the transconjugant PAO1Rif/ pPA942-IMP45 can be stably inherited for 10 generations in the absence of antibiotics.

CONCLUSION

We report a carbapenem-resistant P. aeruginosa strain with an IncP-2 plasmid containing a novel transposon, Tn6485h, which carries both blaIMP-45 and blaAFM-1. The IncP-2 plasmid and transposon Tn6485h may contribute to the spread of MBL genes. Therefore, effective measures to prevent the spread of these plasmids should be taken.

In Vivo Development of Aztreonam Resistance in Meropenem-Resistant Pseudomonas aeruginosa Owing to Overexpression of the blaPDC-16

The rapid acquisition of antibiotic resistance of Pseudomonas aeruginosa has been a complex problem in clinics. Two meropenem-resistant P. aeruginosa isolates were collected from the same patient on May 24, 2021, and June 4, 2021, respectively. The first was susceptible to aztreonam, while the second displayed resistance. This study aimed to identify the genetic differences between two P. aeruginosa isolates and uncover alterations formed by the within-host bacterial evolution leading to aztreonam resistance during therapy. Strains were subjected to antimicrobial susceptibility testing using the broth microdilution method. Genomic DNAs were obtained to identify their genetic differences. The relative mRNA levels of β-lactam-resistance genes were determined by real-time PCR. Both isolates belonged to ST 773 high-risk clones with the same antibiotic resistance genes, eliminating the possibility of horizontally obtaining resistance genes. Reverse transcription (RT)-PCR results showed that the blaPDC-16 mRNA level in the second one was about 1,500 times higher than that in the first one. When 3-aminophenyl boronic acid was added, the second strain recovered its susceptibility to aztreonam, which confirmed that the overexpression of blaPDC-16 was the main reason for the isolate's resistance to aztreonam. Compared to the first strain, the second showed a single amino acid substitution in AmpR located upstream of blaPDC-16, which may contribute to the upregulation of blaPDC-16 and lead to aztreonam resistance. AmpR plays an essential role in regulating antibiotic resistance in P. aeruginosa, and there is a need to be alert to clinical treatment failures associated with mutations in ampR. IMPORTANCE Pseudomonas aeruginosa is notorious for being highly resistant to antimicrobial agents. In this study, two P. aeruginosa strains isolated from the same patient with different susceptibility to aztreonam were used to illustrate the within-host resistance evolution process of P. aeruginosa. Both isolates, which belonged to a ST773 high-risk clone, had the same β-lactam resistance genes (blaPDC-16, blaIMP-45, blaOXA-1, and blaOXA-395), which means the second isolate might have been derived from the first isolate by gaining aztreonam resistance via mutations associated with aztreonam resistance relative genes. Subsequently, we found that mutation in ampR may be the cause of aztreonam resistance in the second isolate. Mutation in ampR leads to its loss of control over blaPDC-16, allowing overexpression of blaPDC-16 and further resistance to aztreonam. This study revealed that ampR plays an essential role in regulating antibiotic resistance in P. aeruginosa. There is a need to be alert to clinical treatment failures associated with mutations in ampR.

Emergence of an Extensive Drug Resistant Pseudomonas aeruginosa Strain of Chicken Origin Carrying blaIMP-45, tet(X6), and tmexCD3-toprJ3 on an IncpRBL16 Plasmid

This study reports an extensively drug resistant Pseudomonas aeruginosa strain PA166-2 which was of chicken origin and carrying blaIMP-45, tet(X6) and tmexCD3-toprJ3 on a single plasmid. The strain was characterized by antimicrobial susceptibility testing, resistance gene screening, conjugation assay, whole-genome sequencing, and bioinformatics analysis. Strain PA166-2 was resistant to tigecycline and carbapenems. It belonged to ST313 and carried a plasmid pPA166-2-MDR, which belongs to the incompatibility group IncpRBL16. pPA166-2-MDR harbored a 78 Kb multidrug resistance (MDR) region carrying an array of antimicrobial resistance genes, including blaIMP-45, tet(X6), and tmexCD3-toprJ3. The gene blaIMP-45 was inserted into the backbone of plasmid pPA166-2-MDR within a class 1 integron, In786. tmexCD3-toprJ3 in plasmid pPA166-2-MDR was inserted in umuC, constituting the genetic context of ISCfr1-tnfxB3-tmexC3-tmexD3-toprJ3-△umuC. The genetic context of tet(X6) in this plasmid was identical to that of other reported plasmid-borne tet(X) variants, namely, tet(X6)-abh-guaA-ISVsa3. To the best of our knowledge, this is the first report of the cooccurrence of blaIMP-45, tet(X6), and tmexCD3-toprJ3 in one plasmid in Pseudomonas sp. The emergence of plasmid-mediated tigecycline resistance genes tmexCD3-toprJ3 and tet(X6), as well as carbapenemase genes from chickens expanded the global transmission of vital resistance genes. Findings from us and from others indicate that plasmids of the incompatibility group IncpRBL16 may serve as a reservoir for carbapenem and tigecycline resistance determinants. IMPORTANCE Pseudomonas aeruginosa is an opportunistic pathogen that causes infections that are difficult to treat. This study reported, for the first time, the occurrence of last-resort antibiotic resistance determinants blaIMP-45, tet(X6), and tmexCD3-toprJ3 on a single plasmid in P. aeruginosa from chickens. The P. aeruginosa strain belonged to ST313 and was resistant to last-line antibiotics, namely, carbapenems and tigecycline. The plasmid carrying the last-line resistance genes belonged to the incompatibility group IncpRBL16, which was reported to contain different profiles of accessory modules and thus carried diverse collections of resistance genes. The emergence of plasmid-mediated tigecycline resistance genes tmexCD3-toprJ3 and tet(X6), as well as carbapenemase genes, from chickens expanded the global transmission of vital resistance genes. The results in this study highlighted that IncpRBL16 plasmids may serve as a reservoir for the dissemination of resistance genes. Control measures should be implemented to prevent the further dissemination of such strains.

An IncP-2 plasmid sublineage associated with dissemination of blaIMP-45 among carbapenem-resistant Pseudomonas aeruginosa

IMP-45, a variant of IMP-9, is one of the dominant metallo-β-lactamases (MBLs) in clinical carbapenem-resistant Pseudomonas aeruginosa (CRPA) isolates in China. The aim of this study was to investigate the distribution and mechanism of dissemination of bla_IMP-45. MBL genes were detected by PCR in 173 non-duplicate CRPA isolates collected from Hospital HS in Shanghai and 605 P. aeruginosa isolates from a multicenter surveillance of bla_IMP-45 in China. In total, 17 IMP-45-producers (14 from Hospital HS and 3 from other hospitals) were identified. Molecular typing identified an outbreak of 11 IMP-45-producing ST508 CRPA in the ICU of Hospital HS. Conjugation assays and whole genome sequencing were conducted among IMP-45-producers. Genomic comparison revealed that 16 bla_IMP-45-carrying plasmids (9 from this study and 7 from GenBank) shared a similar backbone with IncP-2 bla_IMP-9-carrying plasmid pOZ176 but lacked repA-oriV-parAB region. repA2 gene was presented in pOZ176, bla_IMP-45-carrying plasmids (17 from this study and 7 from GenBank) and 15 megaplasmids from GenBank. Phylogenetic analysis of repA2 showed that most bla_IMP-45-carrying plasmids were clustered into a sublineage separate from the one containing pOZ176. This IncP-2 plasmid sublineage contributed to the dissemination of bla_IMP-45 among genetically diverse P. aeruginosa and recruited multiple resistance genes during its evolution.