Molecular characterization of addiction systems of plasmids encoding extended-spectrum beta-lactamases in Escherichia coli.
OBJECTIVE
Escherichia coli producing CTX-M-type extended-spectrum beta-lactamases (ESBLs) are spreading worldwide. The aim of this work was to investigate the addiction systems carried by the replicons involved in the emergence and spread of ESBLs in relation to ESBL and replicon types.


METHODS
A collection of 125 TEM, SHV and CTX-M ESBL-producing E. coli isolates and their 125 transconjugants or transformants was analysed. Five plasmid protein antitoxin-regulated systems and three plasmid antisense RNA-regulated systems were sought by PCR.


RESULTS
Two hundred and ninety-eight plasmid addiction systems were detected in the parental strains (mean 2.38, range 0-6 per strain) and 86 were detected in the recipient strains (mean 0.69, range 0-5 per strain). PemKI, CcdAB, Hok-Sok and VagCD were the most frequently represented systems in both recipient and parental strains. The parental SHV and CTX-M ESBL-producing strains had more addiction systems than the TEM ESBL producers. In the recipient strains, the frequency of addiction systems was significantly higher in IncF plasmids. Among the IncF replicons carrying CTX-M-type enzymes, the frequency of addiction systems was significantly higher in IncF plasmids carrying CTX-M-15 (mean 3.5) or CTX-M-9 (mean 4) than in those carrying CTX-M-14 (mean 0.6).


CONCLUSIONS
In E. coli producing CTX-M-15 or CTX-M-9 ESBLs, plasmids bearing the bla(CTX-M) gene have multiple addiction systems that could contribute to their maintenance in host strains.
Université Pierre et Marie Curie-Paris-6, Faculté de Médecine, Site Saint-Antoine, Laboratoire de Bactériologie, ER8 Paris, France.
Basma
B
Mnif
Sophie
S
Vimont
Anders
A
Boyd
Emilie
E
Bourit
Bertrand
B
Picard
Catherine
C
Branger
Erick
E
Denamur
Guillaume
G
Arlet
D003227:Conjugation, Genetic; D004269:DNA, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics* / Q000302:isolation & purification; D029968:Escherichia coli Proteins / Q000235:genetics*; D005798:Genes, Bacterial; D010957:Plasmids; D016133:Polymerase Chain Reaction; D014170:Transformation, Genetic; D001618:beta-Lactamases / Q000235:genetics*
D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D001618:beta-Lactamases