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High frequency of association between CTX-M-beta-lactamase-coding genes and the ISEcp1 insertion element

Abstract number: 902_p1471

Pimkin M.

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Objectives:

CTX-M beta-lactamases are becoming an increasingly alarming problem throughout the world due to their fast spread. This is often addressed to the possible transfer of CTX-M-coding genes with mobile genetic elements. Indeed, several studies have shown an association of blaCTX-M genes with the ISEcp1 insertion sequence or the putative recombinase gene orf513. However, such studies have been confined to relatively small numbers of strains. We have studied the association of blaCTX-M genes with ISEcp1 using a large collection of CTX-M-producing enterobacterial strains obtained from 21 Russian hospitals.

Methods:

The strains studied were 28 Escherichia coli (EC), 87 Klebsiella pneumoniae (KP) and 36 Proteus mirabilis (PM). They comprised 17, 48 and 22 distinct genetic types, respectively, as determined by ERIC-PCR and RAPD typing and produced CTX-M-1-cluster enzymes (94.7%), i.e. CTX-M-3 and CTX-M-15, and a CTX-M-2-cluster enzyme (5.3%) – CTX-M-5. Two PCRs with ISEcp1-specific primers were used to identify the linkage of blaCTX-M genes with ISEcp1. One forward primer (F1) matched the 3’-end sequence of tnpA and another (F2) matched the right terminal repeat (RTR) sequence of ISEcp1. A common reverse primer (R) was located internally to blaCTX-M. Previously characterised EC and Citrobacter freundii strains harbouring blaCTX-M genes associated with either ISEcp1 or orf513 were included as positive and negative controls, respectively.

Results:

Positive PCR results with primers F2-R were observed for 28 (100%) EC, 86 (98.9%) KP and 35 (97.2%) PM isolates. Amplification with primers F1-R additionally confirmed the association of blaCTX-M genes with ISEcp1 in 25 (89.3%) EC, 85 (97.7%) KP and 34 (94.4%) PM isolates. According to the length of PCR products, ISEcp1 was located approximately 50 bp upstream of the CTX-M ORFs in all EC, KP and PM isolates expressing CTX-M-1-cluster enzymes and approximately 20 bp upstream of blaCTX-M-5 in eight EC isolates. An insertion of ~700 bp sequence between tnpA and RTR was detected in a single KP isolate of a unique genetic type. Two isolates (PM and KP) which failed to produce PCR products with either of the primer pairs also represented unique genetic types.

Conclusions:

We conclude that CTX-M-coding genes of different genetic subtypes have a strong association with the ISEcp1 insertion element in nosocomial Enterobacteriaceae from Russia. This in part may explain their notoriously rapid spread.

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Session Details

Date: 01/08/2007
Time: 00:00-00:00
Session name: XXIst ISTH Congress
Subject:
Location: Oxford, UK
Presentation type:
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