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Extended-spectrum beta-lactamase in Proteus mirabilis
S Mariotte1, P Nordmann, M H Nicolas
1Laboratoire de Microbiologie, Hôpital Ambroise Paré, Faculté de Médicine, Paris-Ouest, Boulogne, France.
Abstract:
Over a period of one month, five isolates of Proteus mirabilis resistant to extended-spectrum cephalosporins colonized or infected five patients of the same intensive care unit. The antibiotic resistance phenotype and the metabolic profiles of the five strains were identical. All five produced a plasmid-mediated extended-spectrum beta-lactamase closely related to TEM-3/CTX-1 according to its pI (6.3), to its substrate profile and to the hybridization of the corresponding gene with blaTEM-3 specific oligonucleotide probes. Ability to produce this enzyme transferred by conjugation to Escherichia coli along with aminoglycoside and sulphonamide resistance. These resistance markers were encoded by a plasmid, (pAP1) which was identical in all five isolates but which was different from the TEM-3 beta-lactamase plasmids found in other Enterobacteriaceae. Plasmid pAP1 differed by its smaller size (47 kb), its EcoRI restriction pattern, its resistance co-markers (AAC(6') and sulphonamide only) and its much lower transfer frequency (2 x 10(-8)). Furthermore this plasmid did not belong to any known Enterobacteriaceae incompatibility group.
Insights
Five intensive care unit patients were infected by Proteus mirabilis resistant to extended-spectrum cephalosporins. A novel plasmid, pAP1, mediated this resistance, differing from previously identified TEM-3 beta-lactamase plasmids.
Area of Science:
- Microbiology
- Infectious Diseases
- Molecular Biology
Background:
- Extended-spectrum cephalosporins are crucial antibiotics.
- Antibiotic resistance in intensive care units (ICUs) poses a significant threat.
- Proteus mirabilis is an opportunistic pathogen often associated with healthcare-associated infections.
Purpose of the Study:
- To investigate the emergence of extended-spectrum cephalosporin resistance in Proteus mirabilis within an ICU.
- To characterize the genetic basis of this antibiotic resistance.
- To determine the epidemiological relatedness of the resistant isolates.
Main Methods:
- Phenotypic characterization of Proteus mirabilis isolates, including antibiotic susceptibility testing and metabolic profiling.
- Molecular analysis to identify beta-lactamase production, including isoelectric focusing (pI) and gene hybridization.
- Plasmid analysis, including conjugation experiments, size determination, restriction enzyme digestion (EcoRI), and incompatibility grouping.
- Antimicrobial resistance gene identification (e.g., AAC(6')).
Main Results:
- Five identical isolates of Proteus mirabilis resistant to extended-spectrum cephalosporins were identified in an ICU over one month.
- All isolates produced a novel plasmid-mediated extended-spectrum beta-lactamase (ESBL) similar to TEM-3/CTX-1.
- The resistance determinants were located on a unique 47 kb plasmid (pAP1), which also conferred aminoglycoside (AAC(6')) and sulphonamide resistance.
- Plasmid pAP1 exhibited a low transfer frequency and did not belong to known Enterobacteriaceae incompatibility groups, distinguishing it from other TEM-3 plasmids.
Conclusions:
- A distinct plasmid, pAP1, is responsible for the spread of extended-spectrum cephalosporin resistance in Proteus mirabilis within this ICU.
- The unique characteristics of pAP1 suggest a potentially novel mechanism of resistance dissemination.
- This finding highlights the need for vigilant surveillance of emerging antibiotic resistance mechanisms in critical care settings.