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Incidence of strains producing extended spectrum beta-lactamases in Argentina
1Department of Diseases and Clinical Microbiology, Catholic University, Buenos Aires, Argentina.
Abstract:
The incidence of strains producing transferable beta-lactamases capable of hydrolyzing third generation cephalosporins or aminothiazole-oximino substituted monobactams in five Buenos Aires hospitals during a four month period was studied. These enzymes were categorized by 1) MIC greater than or equal to 1 mg/l for third generation cephalosporins; 2) MIC less than 0.06 mg/l for third generation cephalosporins combined with clavulanic acid or sulbactam; 3) sensitivity to imipenem or cephamycins (excluding permeability mutants); and 4) transferable resistance by conjugation. Beta-lactamases hydrolyzing aminothiazole-oximino substituted monobactams were produced by 17.2% of Enterobacteriaceae from intensive care unit patients; 3.6% from inpatients of other units and 1.2% from outpatients. Producers were mainly Klebsiella spp. (45/46) resistant to aminoglycosides (most of them AAC 3'-AAC 6' producers). Three strains had a an isoelectric point of 6.0, two of 6.5 and three of 7.7. TEM-1 beta-lactamase (isoelectric point 5.4) was detected in 6/8 strains. An inocolum effect was observed in 40/46 strains. A Klebsiella pneumoniae strain preserved since 1982 also produced a transferable beta-lactamase hydrolyzing aminothiazole-oximino substituted monobactams.
Insights
Transferable beta-lactamases hydrolyzing advanced antibiotics are a growing concern, particularly in intensive care units. This study highlights their prevalence in Buenos Aires hospitals, emphasizing the need for ongoing surveillance.
Area of Science:
- Microbiology
- Infectious Diseases
- Antimicrobial Resistance
Background:
- Third-generation cephalosporins and aminothiazole-oximino substituted monobactams are critical antibiotics.
- The emergence of beta-lactamases capable of hydrolyzing these drugs poses a significant threat to public health.
- Understanding the incidence and characteristics of these enzymes is crucial for effective treatment strategies.
Purpose of the Study:
- To determine the incidence of transferable beta-lactamases targeting third-generation cephalosporins and aminothiazole-oximino substituted monobactams.
- To characterize these enzymes and their resistance mechanisms.
- To assess the prevalence of these resistant strains in different hospital units and patient populations.
Main Methods:
- Enzyme characterization based on Minimum Inhibitory Concentration (MIC) values for specific antibiotics and their combinations with beta-lactamase inhibitors.
- Assessment of sensitivity to imipenem and cephamycins, excluding permeability mutants.
- Detection of transferable resistance through conjugation experiments.
- Isoelectric focusing and identification of beta-lactamase types (e.g., TEM-1).
Main Results:
- Beta-lactamases hydrolyzing aminothiazole-oximino substituted monobactams were found in 17.2% of Enterobacteriaceae from intensive care units, 3.6% from other inpatients, and 1.2% from outpatients.
- Klebsiella spp. were the primary producers (45/46), often co-resistant to aminoglycosides.
- TEM-1 beta-lactamase was detected in a majority of tested strains, and an inoculum effect was observed in most producers.
- A historical strain of Klebsiella pneumoniae from 1982 also exhibited this resistance.
Conclusions:
- Transferable beta-lactamases hydrolyzing advanced antibiotics are prevalent in Buenos Aires hospitals, especially in intensive care settings.
- Klebsiella spp. are significant producers, frequently exhibiting co-resistance to other antibiotic classes.
- The findings underscore the need for continuous monitoring and infection control measures to combat the spread of antimicrobial resistance.