Evolution of bla genes from SHV family

Abstract number: 1733_73

Mendonça N., Caniça M.

Objectives: SHV (sulfhydryl variable) is the most prevalent family of b-lactamases produced by Klebsiella pneumoniae strains, an important mechanism of resistance to b-lactam antibiotics. The aim of the study was to evaluate the diversity and molecular evolution of blaSHV genes family.

Methods: PCR specific for blaSHV gene and nucleotide sequencing were performed in 212 clinical K. pneumoniae strains isolated in Portugal (years 1998–2005). In addition 59 blaSHV sequences were downloaded from NCBI GenBank database. All sequences were analysed by Bionumerics software and a specific blaSHV gene fragment of 825bp was used to align all sequences. Phylogenetic and molecular evolutionary analysis was conducted using MEGA software.

Results: Among the 271 sequences analysed we detected 64 different blaSHV gene sequence frameworks (SFWs), from which 40 were here firstly identified. The 64 SFWs emerged from the combination of silent mutations at 38 different nucleotide positions. Silent mutations A402®G, G705®A and C786®G may be considered hot spots, as they appeared in a higher frequency (92%, 62% and 49%, respectively) than others. Phylogenetic analysis showed that the SFW (named ad) presenting those 3 mutations is a possible common ancestral.

Among the 212 blaSHV genes sequenced by us, 58 (27%) were identified as blaSHV-11. This gene showed the highest diversity as it presented 17 different SFWs, followed by 54 (26%) blaSHV-1 genes detected with 13 SFWs, and by 30 (14%) blaSHV-28 genes with only 2 SFWs associated (``a'' and ``r''). The 111 different sequences of blaSHV genes studied in the phylogenetic approach, presented a total of 53 non-synonymous mutations and 38 synonymous mutations, which allowed to the construction of an unrooted tree.

Overall, the majority of blaSHV-1 and blaSHV-11 sequence genes had the higher number of different SFWs (18 and 20, respectively) and were on opposite sides of the evolutionary tree, which may imply a divergent evolution. Furthermore, the majority of extended-spectrum b-lactamase (ESBL) coding genes (63%) could be detected within the same branch of the unrooted tree, which may indicate a common ancestral or origin.

Conclusions: This study demonstrated that blaSHV genes descend from a yet unidentified common ancestor. The high diversity of blaSHV genes suggests their contribution to the rapid evolution toward blaESBL-SHV genes coding to ESBL enzymes and thus to the emergence of resistance to third generation cephalosporins.

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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