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Genetic characterization of plasmid-encoded multiple antibiotic resistance in a strain of Listeria monocytogenes
K Hadorn1, H Hächler, A Schaffner
1Institute of Medical Microbiology, University of Zurich, Switzerland.
Abstract:
One susceptible and two multiply resistant isolates of Listeria monocytogenes from a patient suffering from prosthetic valve endocarditis are described. They could not be distinguished by several typing methods. Two isolates were resistant to chloramphenicol, macrolide/lincosamide/streptogramin antibiotics and tetracycline. The resistance determinants were located on a 39 kb plasmid pWDB100 that was transferable by filter mating to several gram-positive bacteria. Evidence was obtained to support the hypothesis that the resistant variant had primarily infected the patient's blood and prosthetic valve, and later lost the resistance plasmid. The three resistance determinants showed homology to other known markers, cat221/cat223, ermB and tetM, which are frequently found in different gram-positive genera. Plasmid pWDB100 showed extensive homology to the Streptococcus agalactiae broad-host-range plasmid pIP501. It was also very similar to two listerial plasmids found in France. Thus, plasmid pWDB100 and the homologous plasmids from France, although isolated in geographically distant regions, may illustrate spread of a plasmid and its relatives.
Insights
Multiple drug-resistant Listeria monocytogenes strains were identified in a patient with prosthetic valve endocarditis. A transferable plasmid carrying resistance genes suggests potential plasmid spread among bacteria.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Listeria monocytogenes is a significant foodborne pathogen causing severe infections, particularly in vulnerable populations.
- Prosthetic valve endocarditis is a serious complication requiring effective antimicrobial treatment.
- Antibiotic resistance in L. monocytogenes poses a growing threat to public health.
Observation:
- Three L. monocytogenes isolates from a patient with prosthetic valve endocarditis were analyzed.
- Two isolates exhibited resistance to chloramphenicol, macrolides/lincosamides/streptogramins, and tetracycline.
- These resistant isolates were indistinguishable from a susceptible isolate using standard typing methods.
Findings:
- A 39 kb plasmid, designated pWDB100, carried the resistance determinants for chloramphenicol (cat221/cat223), macrolides/lincosamides/streptogramins (ermB), and tetracycline (tetM).
- Plasmid pWDB100 was transferable to other gram-positive bacteria via filter mating.
- The resistance genes showed homology to known markers, and pWDB100 shared extensive homology with Streptococcus agalactiae plasmid pIP501 and other listerial plasmids.
Implications:
- The findings suggest that the patient was initially infected with a resistant L. monocytogenes strain that may have lost the resistance plasmid during infection.
- The study highlights the potential for inter- and intra-species plasmid transfer, contributing to the spread of antibiotic resistance.
- The genetic similarity between pWDB100 and plasmids from geographically distant regions suggests a broader dissemination of resistance plasmids in gram-positive bacteria.