RESUMO
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.
Assuntos
Antibacterianos/farmacologia , Farmacorresistência Bacteriana , Escherichia coli/efeitos dos fármacos , beta-Lactamases/biossíntese , beta-Lactamas/farmacologia , Ertapenem , Escherichia coli/enzimologia , Infecções por Escherichia coli/epidemiologia , Infecções por Escherichia coli/microbiologia , Imipenem/farmacologia , Meropeném , Testes de Sensibilidade Microbiana , Mutação , Tienamicinas/farmacologia , beta-Lactamases/genéticaRESUMO
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)
Assuntos
Lactente , Pré-Escolar , Criança , Adolescente , Adulto , Humanos , Estudo Comparativo , Faringe/microbiologia , Infecções Estreptocócicas/microbiologia , Streptococcus/isolamento & purificação , Faringite/microbiologia , Streptococcus/classificação , Faringite/complicações , Streptococcus pyogenes/isolamento & purificação , Meios de Cultura , Distribuição por Idade , Argentina , Testes de Fixação do Látex , Infecções Estreptocócicas/complicaçõesRESUMO
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.
Assuntos
Lactente , Pré-Escolar , Criança , Adolescente , Adulto , Humanos , Faringite/microbiologia , Faringe/microbiologia , Infecções Estreptocócicas/microbiologia , Streptococcus/isolamento & purificação , Distribuição por Idade , Argentina , Meios de Cultura , Testes de Fixação do Látex , Faringite/complicações , Infecções Estreptocócicas/complicações , Streptococcus pyogenes/isolamento & purificação , Streptococcus/classificaçãoRESUMO
BACKGROUND: The aim of the present was to study the inhibitory and bactericide activity and risk of selection of mutants resistant or tolerant to vancomycin in strains of Staphylococcus aureus resistant to methicillin from out patient and hospitalary patients. MATERIALS AND METHODS: The minimum inhibitory concentration was obtained by the macrodilution method in liquid medium and by the Etest system. The minimum bactericide concentration was obtained by the macrodilution method in liquid medium. The selection of resistant or tolerant mutants was performed inoculating more than 5 x 10(6) UFC/ml in brain-heart agar plates and in tripteinsoya brought with different concentrations of vancomycin. RESULTS: Vancomycin showed greater inhibitory and bactericide activity in strains sensitive to methicillin of out patient and hospitalary origin with respect to strains resistant to methicillin with a minimum inhibitory concentration > 1 mg/l in 23.3, 20.0 and 70.0%, respectively and a minimum bactericide concentration of 90%, 8.16 and 64 mg/l. The incidence of tolerance was greater in the strains resistant to methicillin in comparison with the out patient and hospitalary strains sensitive to methicillin, since a minimum bactericide/inhibitory concentration greater than 4 was obtained in 63.3 in comparison with 20.0%. Only mutants with diminished sensitivity (minimum inhibitory concentration of 3 and 6 mg/l) or tolerant in strains resistant to methicillin could be selected. The increases in the minimum inhibitory concentrations were not stable, while the tolerant mutants preserved this characteristic after 20 subcultures. CONCLUSIONS: The in vitro selection of mutants with decreased sensitivity or tolerant was only obtained in strains resistant to methicillin. The changes in the minimum inhibitory concentrations were not stable in contrast to the increase in the minimum bactericide concentrations which remained unchanged. The differences in the selection of mutants with diminished sensitivity or tolerant among strains resistant and sensitive to methicillin found in this study were correlated with the differences in minimum inhibitory and bactericide concentrations and the relation between both in the clinical isolates.
Assuntos
Staphylococcus aureus/efeitos dos fármacos , Staphylococcus aureus/genética , Vancomicina/farmacologia , Resistência Microbiana a Medicamentos , Testes de Sensibilidade Microbiana , Mutação , Staphylococcus aureus/isolamento & purificaçãoRESUMO
Three carbapenem-resistant Acinetobacter baumannii isolates were collected at a hospital in Buenos Aires, Argentina. Isoelectric focusing revealed multiple beta-lactamases, with two of the isolates showing identical profiles. A pI 6.9 carbapenemase with a molecular weight of 30 kDa was purified from one of these two isolates. The enzyme was predominantly a penicillinase, with its highest Vmax for oxacillin but highest Vmax/Km for benzylpenicillin. First-generation cephalosporins and imipenem were weaker substrates than penicillins, and oxyimino-aminothiazolyl cephalosporins were essentially stable. Meropenem-hydrolysing activity was not detected, despite resistance. The carbapenemase was inhibited by clavulanic acid and tazobactam, but not by EDTA. These kinetics place the enzyme into functional group 2; as an oxacillinase it could be placed in sub-group 2d or, as a zinc-independent carbapenemase, in sub-group 2f.
Assuntos
Acinetobacter/enzimologia , Proteínas de Bactérias , beta-Lactamases/química , beta-Lactamases/metabolismo , Acinetobacter/efeitos dos fármacos , Acinetobacter/isolamento & purificação , Argentina , Carbapenêmicos , Humanos , Imipenem/metabolismo , Imipenem/farmacologia , Focalização Isoelétrica , Meropeném , Testes de Sensibilidade Microbiana , Peso Molecular , Especificidade da Espécie , Escarro/microbiologia , Tienamicinas/metabolismo , Tienamicinas/farmacologia , Urina/microbiologia , Resistência beta-Lactâmica/genética , beta-Lactamases/efeitos dos fármacosRESUMO
BACKGROUND: To compare the bactericidal activity and frequency of mutation for meropenem and imipenem against Proteus mirabilis, Morganella morganii and Providencia rettgeri. MATERIAL AND METHODS: Minimum inhibitory concentrations (MIC) were determined by agar dilution method. Bactericidal activities were evaluated by killing curves method employing 4 and 16x MIC. One-step resistant mutant selection was performed by spreading more than 5 x 10(8) UFC/ml on cystine-lactose-electrolyte deficient agar containing 4 times the MIC of meropenem or imipenem. RESULTS: MIC were 8 to 16 times lower for meropenem. After 24 h, bactericidal activity was observed for meropenem at 4 and 16 x MIC against 76.7 and 100% of the strains in comparison to 26.7 and 83.3% with imipenem. After 24 h incubation with imipenem, re-growth occurred in 80 and 90% of P. mirabilis and M. morganii strains, respectively. Imipenem resistant mutants were selected from 3 strains of P. mirabilis. One of them was stable and MIC of meropenem and imipenem were 8 to 16-fold higher. CONCLUSIONS: From the laboratory point of view we consider that meropenem is more active against Proteeae because it was more potent in terms of inhibitory and bactericidal activity. In addition the risk to select for resistant mutants was significant with imipenem and P. mirabilis.
Assuntos
Resistência Microbiana a Medicamentos/genética , Enterobacteriaceae/efeitos dos fármacos , Imipenem/farmacologia , Proteus mirabilis/efeitos dos fármacos , Providencia/efeitos dos fármacos , Tienamicinas/farmacologia , Enterobacteriaceae/genética , Meropeném , Mutação , Proteus mirabilis/genética , Providencia/genética , Seleção GenéticaRESUMO
BACKGROUND: To evaluate the inhibitory and bactericidal activity of meropenem and imipenem against multiresistant isolates of Acinetobacter spp and to compare the frequency of mutation for both antibiotics. METHODS: Minimum inhibitory concentrations were determined by the agar dilution method. Bactericidal activities were evaluated by killing curves method employing 8 times the MIC. One-step resistant mutant selection was performed by spreading more than 5 x 10(8) ufc/ml on agar Mueller Hinton plates containing 2, 4 and 8 times the MIC of meropenem or imipenem. RESULTS: In the group of sensitive strains (MIC < 4 mg/l for imipenem and meropenem) we detected lower MIC for imipenem than meropenem (61.5% of the strains). Strains with reduced susceptibility to imipenem (MIC = 4 mg/l) were more sensitive to meropenem with MICs equivalents to the sensitive group. Bactericidal activity was detected in 6 hs for imipenem and in 24 hs for meropenem. Meropenem was bactericidal in 4 clinical isolates with MICs = 4 mg/l for imipenem and imipenem was bactericidal in laboratory mutants resistant to meropenem. It was no possible to select mutants resistant to imipenem but for meropenem the rate of mutation was 1.4 x 10(-9) to 1.0 x 10(-8). Mutants resistant to meropenem were susceptible to imipenem and 57% of them were stable. CONCLUSIONS: From the laboratory point of view we consider that imipenem is more active than meropenem because it presents lower MICs, better bactericidal activity, and no risk to select resistance. However meropenem could be useful in some strains resistant to imipenem (MIC = 4 mg/l). Cross-resistance was no detected so we consider that both antibiotics should be tested against Acinetobacter spp. because they are not equivalents.
Assuntos
Acinetobacter/efeitos dos fármacos , Imipenem/farmacologia , Tienamicinas/farmacologia , Acinetobacter/genética , Acinetobacter/isolamento & purificação , Infecções por Acinetobacter/microbiologia , Divisão Celular/efeitos dos fármacos , Resistência Microbiana a Medicamentos/genética , Resistência a Múltiplos Medicamentos/genética , Humanos , Meropeném , Testes de Sensibilidade Microbiana , Mutação , Seleção GenéticaRESUMO
BACKGROUND: To evaluate the bactericidal activity of colistin, imipenem and sulbactam against 24 Acinetobacter calcoaceticus-Acinetobacter baumannii complex isolations. METHODS: Bactericidal activity was estimated by using killing curves method. The concentrations employed were: colistin 4 mg/l, imipenem 8 mg/l and sulbactam 8 and 32 mg/l. RESULTS: Colistin was bactericidal in 24 isolations after 6 hours of incubation. When we used 8 mg/l of imipenem we detected bactericidal activity at the susceptible strains (MIC < or = 4 mg/l). We found bactericidal effect in 15 of 18 strains susceptible to sulbactam when we used 8 mg/l in killing curves after 24 hours of incubation. Using 32 mg/l we detected the same effect in 18 strains with MIC < or = 8 mg/l. CONCLUSIONS: Considering the high incidence of resistance in Acinetobacter spp. to several antibiotics including imipenem, we consider that sulbactam could be an excellent therapeutic alternative because it presents bactericidal activity in susceptible strains.
Assuntos
Acinetobacter/efeitos dos fármacos , Antibacterianos/farmacologia , Colistina/farmacologia , Imipenem/farmacologia , Sulbactam/farmacologia , Acinetobacter calcoaceticus/efeitos dos fármacos , Técnicas Bacteriológicas , Resistência Microbiana a Medicamentos , Humanos , Testes de Sensibilidade MicrobianaRESUMO
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.