JAC Advance Access originally published online on January 31, 2006
Journal of Antimicrobial Chemotherapy 2006 57(3):450-460; doi:10.1093/jac/dki492
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Diversity and evolution of blaZ from Staphylococcus aureus and coagulase-negative staphylococci
1 Department of Veterinary Pathobiology, The Royal Veterinary and Agricultural University, 4 Stigbøjlen, DK-1870 Frederiksberg C., Denmark; 2 Danish Institute for Food and Veterinary Research, 27 Bülowsvej, DK-1790 Copenhagen, Denmark
Received 6 July 2005; returned 1 November 2005; revised 13 December 2005; accepted 15 December 2005
* Corresponding author. Tel: +45-35282784; Fax: +45-35282757; E-mail: jeo{at}kvl.dk
Objectives: To elucidate the diversity and evolutionary history of plasmid- and chromosomally-located blaZ, to detect indications of frequent exchange of blaZ between human and bovine staphylococci and to estimate the frequency of transfer of blaZ between coagulase-negative staphylococci (CoNS) and Staphylococcus aureus of bovine origin.
Methods: blaZ was detected in 143 strains of penicillin-resistant S. aureus and CoNS from five Danish cattle herds (n = 25/23), random CoNS isolates from Denmark (n = 37), a collection of S. aureus from six different countries (n = 52), humans in Denmark (n = 3) and ß-lactamase control strains (n = 3). The sequence was determined in 105 strains and compared to published sequences by pairwise and multiple alignments. Maximum likelihood analysis was performed including bootstrap analysis. Parsimony, neighbour joining and consensus comparisons were performed for recombination. The localization of blaZ was determined by Southern blotting in 108 isolates.
Results: All penicillin-resistant strains carried blaZ and showed a similar organization of blaR1 and blaZ. The blaZ gene was localized to a plasmid in only 16 of the resistant strains. Sixty-nine sequences representing 105 isolates and sequences retrieved from public databases were compared. A phylogenetic tree showed that blaZ exists in three evolutionary lines: one group was of plasmid origin, one group was of chromosomal origin and one intermediate group. Sixty-nine sequence types were demonstrated. They translated into 11 BlaZ protein types. The major types all contained strains of both human and bovine origin, and more than one Staphylococcus species, demonstrating a shared gene pool. In a comparison of S. aureus and CoNS obtained from five Danish cattle herds, the same type of blaZ was only detected in one case.
Conclusions: Results indicated a separate evolution for plasmid- and chromosomally-encoded blaZ. Although a common gene pool seems to exist among staphylococci, exchange of blaZ between strains and species is judged to be an extremely rare event.
Keywords: mastitis , penicillin , ß-lactamases
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