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Plasmid-mediated antimicrobial resistance in Haemophilus pleuropneumoniae
Abstract:
Haemophilus pleuropneumoniae, isolated from the lungs of pig, was resistant to ampicillin, streptomycin, and sulfadiazine. This isolate, SD-1, possessed 1 plasmid (pVM105) coded for resistance to ampicillin and sulfadiazine, and the other (pVM104) for resistance to streptomycin and sulfadiazine. A 2nd isolate of H pleuropneumoniae, SD-2, recovered from a pig in a different outbreak of porcine pleuropneumonia, was resistant to streptomycin and sulfadiazine. These resistance determinants were on 1 plasmid (pVM106). All 3 patients were nontransmissible and small (pVM105 = 3.6 x 10(6) daltons, pVM104 and pVM106 = 2.3 x 10(6) daltons. The basis for resistance to ampicillin, encoded on plasmid pVM105, was due to a beta-lactamase. This beta-lactamase was highly active on penicillin G and ampicillin, moderately active on cephalothin, and inactive on oxacillin, indicating a TEM type of beta-lactamase.
Insights
Two Haemophilus pleuropneumoniae isolates showed resistance to multiple antibiotics, with resistance genes located on small, non-transmissible plasmids. One isolate harbored a TEM-type beta-lactamase responsible for ampicillin resistance.
Area of Science:
- Veterinary Microbiology
- Molecular Biology
- Antimicrobial Resistance
Background:
- Haemophilus pleuropneumoniae is a significant pathogen in swine, causing economically important respiratory disease.
- Antimicrobial resistance in H. pleuropneumoniae poses a challenge to effective treatment and disease control.
- Plasmids are known vectors for antimicrobial resistance genes in bacteria.
Purpose of the Study:
- To characterize the antimicrobial resistance profiles of H. pleuropneumoniae isolates from pigs.
- To identify and analyze the plasmids carrying resistance determinants in these isolates.
- To investigate the molecular basis of ampicillin resistance.
Main Methods:
- Bacterial isolation and antimicrobial susceptibility testing.
- Plasmid DNA isolation and characterization (size determination).
- Identification of beta-lactamase activity and characterization.
Main Results:
- Two H. pleuropneumoniae isolates (SD-1 and SD-2) exhibited resistance to ampicillin, streptomycin, and sulfadiazine.
- Isolate SD-1 carried two plasmids (pVM105, pVM104), conferring resistance to ampicillin/sulfadiazine and streptomycin/sulfadiazine, respectively.
- Isolate SD-2 carried one plasmid (pVM106) for streptomycin and sulfadiazine resistance.
- All identified plasmids were small and non-transmissible.
- Ampicillin resistance in SD-1 was attributed to a TEM-type beta-lactamase.
Conclusions:
- Plasmids mediate antimicrobial resistance in H. pleuropneumoniae isolates.
- The presence of TEM-type beta-lactamase contributes to ampicillin resistance.
- Small, non-transmissible plasmids may play a role in the dissemination of resistance within specific bacterial populations.