Coexistence of a nonresistance-conferring IncI1 plasmid favors persistence of the
bla
CTX-M
-bearing IncFII plasmid in
Escherichia coli
Authors: He Kun , Lin Jiayu , Liang Yulei , Cui Junling , Chen Qiuru , Dong Yanbin , Ma Xiaoyuan , He Dandan , Yuan Li 
Published: April 2024

The interaction between coexisting plasmids can affect plasmid-carried resistance gene persistence and spread. However, whether the persistence of the
bla
CTX-M
gene in clinical Enterobacteriaceae is related to the interaction of coresident nonresistance-conferring plasmids has not been reported. This study was initiated to elucidate how a nonresistance-conferring IncI1 plasmid affected the
bla
CTX-M
-bearing IncFII plasmid colocated on the same cell. Herein, we constructed three isogenic derivatives of
E. coli
C600, designated as C600
FII
, C600
I1
, and C600
FII+I1
, which harbored the
bla
CTX-M
-IncFII plasmid and/or the nonresistance-IncI1 one. We discovered that strain C600
FII+I1
conferred higher fitness advantages than strain C600
FII
; also, the stability of the
bla
CTX-M
-IncFII plasmid was noticeably improved in an antibiotic-free environment when it coexisted with the IncI1 plasmid. To further explore why the IncI1 plasmid enhanced the persistence of the
bla
CTX-M
-IncFII plasmid, we assessed the
bla
CTX-M
-IncFII plasmid's copy numbers, conjugation frequencies, and
rep
gene expressions in strains C600
FII
and C600
FII+I1
. The results demonstrated that the
rep
expressions of the
bla
CTX-M
-IncFII plasmid in strain C600
FII+I1
was greatly decreased, along with the plasmid’s copy numbers and mating efficiencies, compared to those in strain C600
FII
. Moreover, further study revealed that the intracellular ATP levels of strain C600
FII+I1
were far lower than those of strain C600
FII
. Our findings confirmed that coexistence of the nonresistance-IncI1 plasmid can keep the
bla
CTX-M
-IncFII plasmid more stable by increasing the fitness advantages of the host bacteria, which will pose a threat to preventing the long-term presence of the plasmid-carried
bla
CTX-M
gene in clinical Enterobacteriaceae.

IMPORTANCE

So far, plasmid-carried
bla

CTX-M

is still the most common extended-spectrum beta-lactamase (ESBL) genotype in clinical settings worldwide. Except for the widespread use of third-generation cephalosporins, the interaction between coexisting plasmids can also affect the long-term stable existence of the
bla
CTX-M
gene; however, the study on that is still sparse. In the present study, we assess the interaction of coinhabitant plasmids
bla
CTX-M
-IncFII and nonresistance-IncI1. Our results confirmed that the increased fitness advantages of strain C600
FII+I1
were attributable to the cohabitant nonresistance-IncI1 plasmid, which largely reduced the intracellular ATP levels of host bacteria, thus decreasing the rep gene expression of the
bla
CTX-M
-IncFII plasmid, its copy numbers, and mating efficiencies, while the higher fitness advantages of strain C600
FII+I1
enhanced the persistence of the
bla
CTX-M
-IncFII plasmid. The results indicate that the nonresistance-IncI1 plasmid contributes to the long-term existence of the
bla
CTX-M
-IncFII plasmid, implying a potentially new strategy for controlling the spread of resistance plasmids in clinical settings by targeting nonresistance plasmids.