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Molecular analysis of naturally occuring ermC-encoding plasmids in staphylococci isolated from animals with and
G Lodder1, C Werckenthin, S Schwarz
1Institut für Kleintierforschung der Bundesforschunganstalt für Landwirtschaft (FAL), Celle, Germany.
Abstract:
A total of 16 epidemiologically unrelated macrolide-resistant staphylococcal isolates of various animal origins were investigated for the molecular basis of macrolide resistance with respect to previous contact of their host animals with macrolides and lincosamides. All isolates carried ermC-encoding plasmids of 2.3-4.0 kbp. The eight plasmids of staphylococci from animals which had not received macrolides or lincosamides showed inducible ermC gene expression and did not exhibit alterations in the ermC regulatory region. The remaining eight plasmids expressed the ermC gene constitutively. Six of these plasmids were from staphylococci from animals which had received tylosin or spiramycin as feed additives or lincomycin for therapeutic purposes. All constitutively expressed ermC genes revealed either sequence deletions or sequence duplications in their ermC regulatory region, as detected by a PCR assay and by sequence analysis. These sequence deletions and duplications found in naturally occurring plasmids corresponded closely to the mutations seen in the ermC-encoding plasmids after growth of an inducibly resistant strain in the presence of non-inducing macrolides or lincosamides under in vitro conditions.
Insights
Macrolide resistance in staphylococci from animals is linked to ermC-encoding plasmids. Constitutive ermC gene expression, often due to regulatory region mutations, arises after animal exposure to macrolides or lincosamides.
Area of Science:
- Veterinary Microbiology
- Molecular Biology
- Antimicrobial Resistance
Background:
- Macrolide and lincosamide resistance in staphylococci is a growing concern in animal health.
- The ermC gene is a common determinant of this resistance, often located on plasmids.
- Understanding the molecular basis of resistance is crucial for effective antimicrobial stewardship.
Purpose of the Study:
- To investigate the molecular mechanisms of macrolide resistance in staphylococcal isolates from animals.
- To correlate resistance mechanisms with the history of macrolide and lincosamide exposure in host animals.
- To identify specific genetic alterations in the ermC gene and its regulatory region.
Main Methods:
- Analysis of 16 epidemiologically unrelated macrolide-resistant staphylococcal isolates from various animal origins.
- Plasmid isolation and characterization, including size determination (2.3-4.0 kbp).
- Polymerase Chain Reaction (PCR) assay and sequence analysis to detect alterations in the ermC regulatory region.
- Investigation of ermC gene expression (inducible vs. constitutive).
Main Results:
- All 16 isolates harbored ermC-encoding plasmids.
- Staphylococci from animals with no prior macrolide/lincosamide exposure showed inducible ermC expression without regulatory region alterations.
- Eight isolates exhibited constitutive ermC expression, with six linked to prior tylosin, spiramycin, or lincomycin exposure.
- Constitutive expression correlated with sequence deletions or duplications in the ermC regulatory region.
- Observed mutations mimicked those induced in vitro by macrolides/lincosamides.
Conclusions:
- Macrolide and lincosamide exposure in animals selects for staphylococci with constitutively expressed ermC genes.
- Sequence alterations in the ermC regulatory region are key mechanisms driving constitutive resistance.
- These findings highlight the impact of antimicrobial use on the molecular evolution of resistance in animal-associated staphylococci.