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Multiple-antibiotic resistance mediated by structurally related IncL/M plasmids carrying an extended-spectrum
L Villa1, C Pezzella, F Tosini
1Laboratory of Bacteriology and Medical Mycology, Istituto Superiore di Sanità, Rome, Italy.
Abstract:
A conjugative IncL/M plasmid (pSEM) conferring resistance to gentamicin, amikacin, kanamycin, sulfonamides, and expanded-spectrum cephalosporins was found in pathogenic strains of Salmonella enterica serotype Typhimurium. Resistance to aminoglycosides was encoded by a sul1-type class 1 integron (In-t3). An extended-spectrum beta-lactamase gene, bla(SHV-5), was identified 3. 5 kb downstream of the integrase (intI1) gene of In-t3. Nucleotide sequence analysis of the 5.3-kb bla(SHV-5)-In-t3 region of pSEM highlighted striking similarities with IncL/M plasmids isolated from nosocomial gram-negative pathogens, conferring resistance to expanded-spectrum cephalosporins and aminoglycosides.
Insights
A novel IncL/M plasmid, pSEM, in Salmonella Typhimurium confers resistance to multiple antibiotics, including aminoglycosides and cephalosporins. This plasmid carries a class 1 integron and an extended-spectrum beta-lactamase gene, highlighting potential for antimicrobial resistance spread.
Area of Science:
- Microbiology
- Genetics
- Infectious Diseases
Background:
- Pathogenic Salmonella enterica serotype Typhimurium strains can harbor antimicrobial resistance genes.
- Conjugative plasmids play a significant role in the dissemination of antibiotic resistance among bacteria.
- Nosocomial infections are often associated with multidrug-resistant gram-negative pathogens.
Purpose of the Study:
- To characterize the genetic elements responsible for antibiotic resistance in a specific strain of Salmonella Typhimurium.
- To investigate the structure and potential dissemination mechanisms of the identified resistance plasmid.
- To compare the identified plasmid with other known resistance plasmids found in pathogens.
Main Methods:
- Plasmid isolation and characterization.
- Nucleotide sequencing of the resistance-conferring region.
- Comparative sequence analysis with existing plasmid databases.
Main Results:
- A conjugative IncL/M plasmid (pSEM) was identified in Salmonella Typhimurium.
- The plasmid harbors a sul1-type class 1 integron (In-t3) conferring resistance to aminoglycosides and sulfonamides.
- An extended-spectrum beta-lactamase gene (blaSHV-5) was located downstream of the integron, conferring resistance to expanded-spectrum cephalosporins.
Conclusions:
- The pSEM plasmid carries a significant multidrug resistance gene cassette.
- The genetic organization of the blaSHV-5-In-t3 region shows similarity to IncL/M plasmids from other gram-negative pathogens.
- This finding underscores the potential for horizontal gene transfer and the spread of multidrug resistance in clinical settings.