Deletion of pT181-like sequence in an smr-encoding mosaic plasmid harboured by a persistent bovine Staphylococcus warneri strain.
OBJECTIVE
The aim was to study the persistence and characteristics of Staphylococcus warneri strains resistant to quaternary ammonium compounds (QACs), including sequencing and analysis of two plasmids proved to carry the smr gene.


METHODS
During a 3.5 year period quarter milk samples were collected on three occasions from all lactating cows in a dairy herd. The samples were screened with regard to QAC-resistant bacteria using a selective medium. Thirty randomly selected QAC-resistant S. warneri were typed by PFGE and subjected to plasmid isolation and analysis followed by gene detection using PCR. Two smr-containing plasmids in S. warneri isolates were sequenced.


RESULTS
All isolates from the initial collection of quarter milk contained smr residing on a 5.8 kb plasmid (pSW174), which contained regions with high similarities to various plasmids, including pT181, pSK108 and pPI-2. The pT181-like sequence was flanked by 148 bp direct repeats, denoted ISLE49, with high similarity to previously reported sequences of approximately 148 bp, including ISLE39 flanking the insertion sequence IS257 in methicillin-resistant Staphylococcus aureus. All isolates from subsequent collections of quarter milk harboured a smaller smr-containing plasmid (pSW49). Sequence analyses revealed pSW49 (3552 bp) to be an in-part deleted version of pSW174 (5767 bp).


CONCLUSIONS
The IS-associated elements found in this study may have a wider role in the integration and excision of DNA sequences in staphylococci than previously reported. The mosaic plasmid structure based on genetic elements of various origins contributes to further knowledge on the flexibility of smr-encoding plasmids.
Bjorland
Jostein
J
Norwegian School of Veterinary Science, PO Box 8146 Dep, N-0033 Oslo, Norway. jostein.bjorland@veths.no
Steinum
Terje
T
Sunde
Marianne
M
Waage
Steinar
S
Sviland
Ståle
S
Oppegaard
Hanne
H
Heir
Even
E
D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D002417:Cattle; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D016521:Electrophoresis, Gel, Pulsed-Field; D008826:Microbial Sensitivity Tests; D008892:Milk / Q000382:microbiology; D008969:Molecular Sequence Data; D010957:Plasmids / Q000235:genetics*; D016133:Polymerase Chain Reaction; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D017384:Sequence Deletion; D013210:Staphylococcus / Q000187:drug effects / Q000235:genetics* / Q000302:isolation & purification
D001426:Bacterial Proteins; D000644:Quaternary Ammonium Compounds