Different genetic elements carrying the tet(W) gene in two human clinical isolates of Streptococcus suis.
The genetic support for tet(W), an emerging tetracycline resistance determinant, was studied in two strains of Streptococcus suis, SsCA and SsUD, both isolated in Italy from patients with meningitis. Two completely different tet(W)-carrying genetic elements, sharing only a tet(W)-containing segment barely larger than the gene, were found in the two strains. The one from strain SsCA was nontransferable, and aside from an erm(B)-containing insertion, it closely resembled a genomic island recently described in an S. suis Chinese human isolate in sequence, organization, and chromosomal location. The tet(W)-carrying genetic element from strain SsUD was transferable (at a low frequency) and, though apparently noninducible following mitomycin C treatment, displayed a typical phage organization and was named ΦSsUD.1. Its full sequence was determined (60,711 bp), the highest BLASTN score being Streptococcus pyogenes Φm46.1. ΦSsUD.1 exhibited a unique combination of antibiotic and heavy metal resistance genes. Besides tet(W), it contained a MAS (macrolide-aminoglycoside-streptothricin) fragment with an erm(B) gene having a deleted leader peptide and a cadC/cadA cadmium efflux cassette. The MAS fragment closely resembled the one recently described in pneumococcal transposons Tn6003 and Tn1545. These resistance genes found in the ΦSsUD.1 phage scaffold differed from, but were in the same position as, cargo genes carried by other streptococcal phages. The chromosome integration site of ΦSsUD.1 was at the 3' end of a conserved tRNA uracil methyltransferase (rum) gene. This site, known to be an insertional hot spot for mobile elements in S. pyogenes, might play a similar role in S. suis.
Department of Biomedical Sciences, Polytechnic University of Marche, Ancona, Italy.
Claudio
C
Palmieri
Maria Stella
MS
Princivalli
Andrea
A
Brenciani
Pietro E
PE
Varaldo
Bruna
B
Facinelli
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics; D003227:Conjugation, Genetic; D004251:DNA Transposable Elements / Q000235:genetics*; D004269:DNA, Bacterial / Q000235:genetics; D005798:Genes, Bacterial; D006801:Humans; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D017422:Sequence Analysis, DNA; D013290:Streptococcal Infections / Q000382:microbiology*; D017011:Streptococcus suis / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D013752:Tetracycline / Q000494:pharmacology; D013753:Tetracycline Resistance / Q000235:genetics*
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D013752:Tetracycline