Comparative study for conjugative plasmids carrying CTX-M genes in Escherichia coli nosocomial isolates

Abstract number: 1733_85

Fursova N., Abaev I., Korobova O., Pecherskikh E., Shishkova N., Pryamchuk S., Kruglov A., Ivanov D., Weigel L., Rasheed J.

Objectives: In previous studies we have shown that CTX-M is the most prevalent type of extended-spectrum b-lactamase (ESBL) among recent clinical isolates of Enterobacteriaceae (2003 to 2005 isolates, 14 hospitals across Russian Federation). The blaCTX-M enzymes accounted for 75% of ESBLs. Major groups included CTX-M-1-related enzymes (91%) (in most cases CTX-M-15), CTX-M-9-like (7%), CTX-M-2-like (1%), and a combination of CTX-M-1 and -9-related genes (1%). To determine the potential for spread of CTX-M genes from isolates of Escherichia coli, CTX-M-positive strains were analysed for plasmids, location of CTX-M genes, and the ability to transfer plasmids with CTX-M by conjugation.

Methods: The presence of blaCTX-M-1, blaCTX-M-2, and blaCTX-M-9 genes, as well as blaTEM and blaSHV genes, in ESBL-producing E. coli (n = 161) isolates was analysed by PCR. Conjugations were performed in broth using E. coli C600 (RifRAzR) recipient strain. Antimicrobial resistance phenotypes of donors and transconjugants were determined by disc diffusion and broth microdilution methods. Plasmids were extracted by the alkaline hydrolysis method. blaCTX-M genes were localised to plasmids by DNA-DNA hybridisation using high-sensitive kit Alk-Phos (Amersham). Probes have been generated by amplification of CTX-M genes using universal primers.

Results: Transconjugants were identified for 35 (approx. 22%) of the E. coli isolates including: blaCTX-M-1 gene (27), blaCTX-M-9 gene (7), and blaCTX-M-2 gene (1). Transfer of blaCTX-M-1 was usually observed on the same plasmid with blaTEM. In contrast, the blaCTX-M-9 gene was frequently on a separate replicon from blaTEM (Table 1). In addition to the ESBL genes, transconjugants acquired resistance to doxycycline, gentamicin, amikacin, ciprofloxacin, and sulfonamides (in different combinations). Clinical isolates had 1–12 plasmids of different molecular weights. blaCTX-M genes were consistently transferred on large plasmids (more than 100 Kb).

Conclusion: Clinical isolates of E. coli isolated in the Russian Federation harbour CTX-M-type ESBLs that are located on high molecular weight conjugative plasmids. In many cases genes encoding resistance mechanisms to several groups of antimicrobial agents were located on the same plasmid capable of horizontal transfer between bacterial strains. These data suggest that the CTX-M-type enzymes, along with multidrug resistance, have the potential to become a widespread problem in this region.

Total strainsSuccessful donorsTransconjugants
CTX-M1 (n = 128)CTX-M1 (n = 3)CTX-M1 (n = 3)
CTX-M1 + TEM (n = 23)CTX-M1 + TEM (n = 19); CTX-M1 (n = 4)  
CTX-M1 + TEM + SHV (n = 1)TEM + SHV (n = 1)  
CTX-M9 (n = 29)CTX-M9 (n = 1)CTX-M9 (n = 1)
CTX-M9 + TEM (n = 6)CTX-M9 + TEM (n = 2); CTX-M9 (n = 4)  
CTX-M2 (n = 4)CTX-M2 (n = 1)CTX-M2 (n = 1)

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Location: ICC, Munich, Germany
Presentation type:
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