Assessment of macrolide and tetracycline resistance phenotypesgenotypes among streptococci isolates from bovine subclinical mastitis
Abstract number: P1001
Rato M., Bexiga R., Nunes S.F., Cavaco L., Vilela C.L., Santos-Sanches I.
Objectives: To identify macrolide/tetracycline phenotypes and genotypes among streptococcal species from bovine subclinical mastitis, valued in therapeutic policies and to evaluate the routes of gene dissemination.
Methods: A total of 32 Streptococcus agalactiae (Group B Streptococcus-GBS), 18 S. dysgalactiae subsp. dysgalactiae (Group C Streptococcus-GCS) and 30 S. uberis, from 11 farms, were included in the study. Resistance to penicillin-P, ampicillin-AMP, erythromycin-E, pirlimycin-PRL, tetracycline-T, and the constitutive macrolide-lincosamide resistance phenotype (cMLS) was evaluated by disk diffusion. Resistance genes (mefA/ermA/ermB/linB/tetM/tetO/tetT/tetS/tetQ/tetK/tetW/tetL) were PCR screened. Clonality was assessed by 80% similarity in dendrograms (BioNumerics v. 4.0 software, Applied Maths) using SmaI-pulsed field gel electrophoresis (PFGE) patterns. Cfr9I digestion was used in one SmaI-resistant GCS isolate. Presence of the composite transposon Tn1207.3/phi10394.4 encoding a methyltransferase responsible for nontypeability using SmaI, was PCR tested in all GCS isolates. This element is carried by the human pathogen S. pyogenes (Group A Streptococcus-GAS).
Results: Co-resistance to macrolides-E and lincosamides-PRL (1827%) and T-resistance (60100%) was observed in all species. Resistance to PRL and susceptibility to E (LSA phenotype) was found in GCS and S. uberis. Diverse genotypes were found: ermB/tetO/tetK in GBS; ermB/tetO or linB/tetM in GCS; ermB/tetO or linB/tetS in S. uberis. A total of three PFGE clusters comprised 72% of the GBS and four PFGE clusters comprised 53% of the S. uberis and all were found to be herd-specific. Among four PFGE clusters comprising 56% of the GCS, three included strains from different farms. Amplification of Tn1207.3/phi10394.4 left junction showed an amplicon size different from what's described for GAS and no amplification of the right junction was observed.
Conclusions: Decreased susceptibility to P and AMP was noted in all species, in contrast to other studies. Amplification of Tn1207.3/phi10394.4 left junction (despite variable size) in bovine GCS suggests that this mobile element may be inserted in the comEC locus as mapped for GAS. The linB gene, known to be carried by a large conjugative plasmid was found in S. uberis and GCS indicating a possible horizontal gene transfer event. The putative linkage of several erm/tet genes in unique strains and clones suggests vertical and horizontal gene dissemination.
|Session name:||Abstracts 20th European Congress of Clinical Microbiology and Infectious Diseases|
|Location:||Vienna, Austria, 10 - 13 April 2010|
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