ABSTRACT
INTRODUCTION: The occurrence of community-associated infections due to extended-spectrum ß-lactamase (ESBL)-producing Escherichia coli is increasing worldwide. These organisms are frequently resistant to many of the antimicrobial agents but remain susceptible to carbapenems. We investigated the in vitro emergence of carbapenem resistance in a collection of clinical isolates of ESBL -producing E. coli. MATERIAL AND METHODS: First and second-step resistant mutants were obtained from E. coli with ESBL. Aliquots of 50 µl containing > 109 CFU were applied to Mueller-Hinton plates containing meropenem, imipenem or ertapenem. MICs for native strains and mutants were determined using the epsilometric test (E-test). RESULTS: Resistant mutants were not selected with imipenem or meropenem. E. coli growth was observed on ertapenem (0.5 mg/L)-containing plates in 13 of 57 clinical isolates (22.8 %).The ertapenem MIC for these first-step mutants were ≥ 1 mg/L, remaining susceptible to imipenem and meropenem. The first-step mutants were used as native strains. Six second-step resistant mutants were selected with ertapenem. All were fully resistant (CMI ≥ 8 mg/L) to ertapenem, three were resistant to meropenem and one to imipenem. Four second-step resistant mutants were selected with meropenem. All were resistant to ertapenem, meropenem, and two of them were resistant to imipenem. CONCLUSIONS: Stable resistant mutants were easy to select with ertapenem among ESBL-producing E. coli. Two steps were necessary to select resistant mutants to meropenem or imipenem. The use of ertapenem in high-inoculum infections or in undrained focus of infection should be monitored to reduce the risk on selection of resistance.
Subject(s)
Anti-Bacterial Agents/pharmacology , Drug Resistance, Bacterial , Escherichia coli/drug effects , beta-Lactamases/biosynthesis , beta-Lactams/pharmacology , Ertapenem , Escherichia coli/enzymology , Escherichia coli Infections/epidemiology , Escherichia coli Infections/microbiology , Imipenem/pharmacology , Meropenem , Microbial Sensitivity Tests , Mutation , Thienamycins/pharmacology , beta-Lactamases/geneticsABSTRACT
El estreptococo beta hemolítico grupo A (EBHGA) es el agente bacteriano más frecuentemente aislado en casos de faringoamigdalitis. Otros estreptococos beta hemolíticos no A también pueden producir esta enfermedad. Ante el elevado número de aislamientos obtenidos en el año 2004 decidimosrealizar un estúdio con el objeto de evaluar la prevalÛncia de estos microorganismos durante um períodod de 5 años. Se incluyeron todos los cultivos de hisopados faríngeos que se realizaron con idéntica metodologia. Se considero nin÷s a los comprendidos entre 6 meses y 18 años de edad, y adultos a los mayores de 18 años. Los aislamientos fueron identificados según la metodologia habitual. La determinación de grupo se realizo mediante la aglutinación con partículas de látex. La recuperación de EBHGA fue significativamente mayor enniños en relación a los adultos. En el año 2004 se obtuvo una recuperación significamente mayor de EBHGA, EBHGC y EBHGG en niños y de EBHGA y EBHGG en adultos respecto respecto de los años anteriores. El aislamiento de EBHGG fue mayor en adultos. El 18.9% y el 55.8% de los estreptococos beta hemolíticos aislados en niños y adultos espectivamente no pertenecieron al grupo A. El incremento en la prevalÛncia de estreptococos betahemolíticos refuerza la buena práctica de realizar cultivos en adultos y niños así como la correcta búsqueda en el laboratório de bacteriología de los estreptococos beta hemolíticos no pertenecientes al grupo A. (AU)
Subject(s)
Infant , Child, Preschool , Child , Adolescent , Adult , Humans , Comparative Study , Pharynx/microbiology , Streptococcal Infections/microbiology , Streptococcus/isolation & purification , Pharyngitis/microbiology , Streptococcus/classification , Pharyngitis/complications , Streptococcus pyogenes/isolation & purification , Culture Media , Age Distribution , Argentina , Latex Fixation Tests , Streptococcal Infections/complicationsABSTRACT
El estreptococo beta hemolítico grupo A (EBHGA) es el agente bacteriano más frecuentemente aislado en casos de faringoamigdalitis. Otros estreptococos beta hemolíticos no A también pueden producir esta enfermedad. Ante el elevado número de aislamientos obtenidos en el año 2004 decidimosrealizar un estúdio con el objeto de evaluar la prevalência de estos microorganismos durante um períodod de 5 años. Se incluyeron todos los cultivos de hisopados faríngeos que se realizaron con idéntica metodologia. Se considero ninõs a los comprendidos entre 6 meses y 18 años de edad, y adultos a los mayores de 18 años. Los aislamientos fueron identificados según la metodologia habitual. La determinación de grupo se realizo mediante la aglutinación con partículas de látex. La recuperación de EBHGA fue significativamente mayor enniños en relación a los adultos. En el año 2004 se obtuvo una recuperación significamente mayor de EBHGA, EBHGC y EBHGG en niños y de EBHGA y EBHGG en adultos respecto respecto de los años anteriores. El aislamiento de EBHGG fue mayor en adultos. El 18.9% y el 55.8% de los estreptococos beta hemolíticos aislados en niños y adultos espectivamente no pertenecieron al grupo A. El incremento en la prevalência de estreptococos betahemolíticos refuerza la buena práctica de realizar cultivos en adultos y niños así como la correcta búsqueda en el laboratório de bacteriología de los estreptococos beta hemolíticos no pertenecientes al grupo A.
Subject(s)
Infant , Child, Preschool , Child , Adolescent , Adult , Humans , Pharyngitis/microbiology , Pharynx/microbiology , Streptococcal Infections/microbiology , Streptococcus/isolation & purification , Age Distribution , Argentina , Culture Media , Latex Fixation Tests , Pharyngitis/complications , Streptococcal Infections/complications , Streptococcus pyogenes/isolation & purification , Streptococcus/classificationABSTRACT
BACKGROUND: To evaluate the in vitro activity of the ampicillin-sulbactam and amoxicillin-clavulanic acid against Escherichia coli isolations resistant to ampicillin and amoxicillin and the efficacy of the disks of ampicillin sulbactam 10/10 microgram and amoxicillin-clavulanic acid 20/10 micrograms to differentiate the susceptible (S) and resistant (R) isolates. METHODS: We evaluated the in vitro susceptibility of 100 consecutive clinical isolates of ampicillin and amoxicillin resistant E. coli by the broth macrodilution method and disk diffusion test against ampicillin-sulbactam and amoxicillin-clavulanic acid. RESULTS: For amoxicillin-clavulanic acid the 64% of the isolates were susceptible, 34% were moderately susceptible and 2% were resistant. In contrast, the in vitro activity of ampicillin-sulbactam was inferior since 13% of the isolates were susceptible, 24% moderately susceptible and 63% were resistant. By using the disk of ampicillin-sulbactam 10/10 microgram we found a 13% of very major errors and a 44% of minor errors when we consider the actual rules of NCCLS (R < or = 11 mm and S > or = 15 mm). The best results were achieved when we took into account zone size < or = 15 mm as R and > or = 20 mm as S; however, the level of errors was high too (25% minor errors). For the disk of amoxicillin-clavulanic acid 20/10 micrograms we found a 31% of minor errors when using the advised break points (R < or = 13 mm and S > or = 18 mm). CONCLUSIONS: We consider that the disk diffusion tests are not applicable to these combinations when E. coli isolates resistant to aminopenicillin are evaluated. We advise not to extrapolate the results of sensibility or resistance from one combination to the other because it presents a different in vitro activity.
Subject(s)
Amoxicillin/pharmacology , Ampicillin/pharmacology , Anti-Bacterial Agents/pharmacology , Clavulanic Acids/pharmacology , Escherichia coli/drug effects , Sulbactam/pharmacology , Clavulanic Acid , Microbial Sensitivity Tests , Predictive Value of Tests , Reproducibility of ResultsABSTRACT
BACKGROUND: Evaluation of the incidence, tolerance and the bactericidal activity against penicillin, ampicillin, cefotaxime, gentamicin and the combination of penicillin plus gentamicin, ampicillin plus gentamicin, cefotaxime plus gentamicin and cefotaxime plus ampicillin in 22 clinical isolates of Streptococcus agalactiae. METHODS: Killing curves were performed. The concentrations of antibiotics was selected taking into account its level in cerebrospinal fluid. RESULTS: We detected 5 (22.7%) tolerant strains to penicillin and ampicillin and 2 of them (9.0%) were also tolerant to cefotaxime. Bactericidal activity was seen in a 100% of the strains against the association penicillin plus gentamicin, ampicillin plus gentamicin and cefotaxime plus gentamicin, being greater than the bactericidal activity against cefotaxime (77.3%), penicillin, ampicillin and cefotaxime plus ampicillin (54.5% respectively). CONCLUSIONS: Considering the high incidence of tolerance and the deficient bactericidal activity of the beta-lactam antibiotics against tolerant and no tolerant strains, it seems necessary to include gentamicin in the treatment of Streptococcus agalactiae severe infections. Several studies of experimental models must be performed to verify in vivo, the in vitro results.