[Pasteurella multocida bacteremic meningitis]. / Meningitis bacteriémica por Pasteurella multocida.

Human infections by Pasteurella multocida are usually associated with bites or scratches from dogs and cats. Many of them are accompanied by other oropharyngeal microorganisms of these animals. We herein present a case of bacteremic meningitis by P. multocida in an 86-year-old woman who was living with seven cats. Even though no skin or soft tissue infection was recorded, it is possible that a mild infection had gone undetected and a subsequent bacteremia had impacted on the meninges, or that meningitis could have occurred after nasopharyngeal colonization (not demonstrated). The isolates obtained from blood cultures and cerebrospinal fluid were identified as P. multocida by API 20NE, API 20E, and Vitek 1. In agreement with findings in the literature, this strain was susceptible to penicillin, cefotaxime, levofloxacin and tetracyclines.

[Consensus for antimicrobial susceptibility testing for Enterobacteriaceae. Subcommittee on Antimicrobials, SADEBAC (Argentinian Society of Clinical Bacteriology), Argentinian Association of Microbiology]. / Consenso sobre las pruebas de sensibilidad a los antimicrobianos en Enterobacteriaceae.

Taking into account previous recommendations from the National Committee for Clinical Laboratory Standards (NCCLS), the Antimicrobial Committee, Sociedad Argentina de Bacteriología Clínica (SADEBAC), Asociación Argentina de Microbiología (AAM), and the experience from its members and some invited microbiologists, a consensus was obtained for antimicrobial susceptibility testing and interpretation in most frequent enterobacterial species isolated from clinical samples in our region. This document describes the natural antimicrobial resistance of some Enterobacteriaceae family members, including the resistance profiles due to their own chromosomal encoded beta-lactamases. A list of the antimicrobial agents that should be tested, their position on the agar plates, in order to detect the most frequent antimicrobial resistance mechanisms, and considerations on which antimicrobial agents should be reported regarding to the infection site and patient characteristics are included. Also, a description on appropriate phenotypic screening and confirmatory test for detection of prevalent extended spectrum beta-lactamases in our region are presented. Finally, a summary on frequent antimicrobial susceptibility profiles and their probably associated resistance mechanisms, and some infrequent antimicrobial resistance profiles that deserve confirmation are outlined.

Consenso sobre las pruebas de sensibilidad a los antimicrobianos en Enterobacteriaceae / Consensus for antimicrobial susceptibility testing for Enterobacteriaceae

En este documento se elaboraron una serie de recomendaciones para el ensayo, lectura, interpretación e informe de las pruebas de sensibilidad a los antimicrobianos para las enterobacterias aisladas con mayor frecuencia de especímenes clínicos. Se adoptaron como base las recomendaciones del National Committee for Clinical Laboratory Standards (NCCLS) de los EEUU, los de la subcomisión de Antimicrobianos, de la Sociedad Argentina de Bacteriología Clínica (SADEBAC), división de la Asociación Argentina de Microbiología (AAM) y de un grupo de expertos invitados. En él se indican las resistencias naturales de los diferentes miembros que integran la familia Enterobacteriaceae y se analiza la actividad de las diferentes beta-lactamasas cromosómicas, propias de cada especie, sobre las penicilinas, cefalosporinas y carbapenemes. Se recomiendan los antimicrobianos que se deberían ensayar, ubicados estratégicamente, para detectar los mecanismos de resistencia más frecuentes y cuales se deberían informar de acuerdo a la especie aislada, el sitio de infección y el origen de la cepa (intra o extrahospitalario). Se detallan los métodos de "screening" y de confirmación fenotipíca para detectar beta-lactamasas de espectro extendido (BLEE) que son más adecuados a nuestra realidad. Por último, se mencionan patrones infrecuentes de sensibilidad/resistencia que deberían verificarse y los perfiles de sensibilidad que pueden hallarse en las distintas enterobacterias en relación con los probables mecanismos de resistencia. Se debe resaltar que el contenido de este documento debe ser considerado como recomendaciones realizadas por expertos argentinos basadas en una revisión de la literatura y datos personales.

Taking into account previous recommendations from the National Committee for Clinical Laboratory Standards (NCCLS), the Antimicrobial Committee, Sociedad Argentina de Bacteriología Clínica (SADEBAC), Asociación Argentina de Microbiología (AAM), and the experience from its members and some invited microbiologists, a consensus was obtained for antimicrobial susceptibility testing and interpretation in most frequent enterobacterial species isolated from clinical samples in our region. This document describes the natural antimicrobial resistance of some Enterobacteriaceae family members, including the resistance profiles due to their own chromosomal encoded beta-lactamases. A list of the antimicrobial agents that should be tested, their position on the agar plates, in order to detect the most frequent antimicrobial resistance mechanisms, and considerations on which antimicrobial agents should be reported regarding to the infection site and patient characteristics are included. Also, a description on appropriate phenotypic screening and confirmatory test for detection of prevalent extended spectrum beta-lactamases in our region are presented. Finally, a summary on frequent antimicrobial susceptibility profiles and their probably associated resistance mechanisms, and some infrequent antimicrobial resistance profiles that deserve confirmation are outlined.

Improvement of a latex agglutination test for the evaluation of oxacillin resistance in coagulase-negative staphylococci.

The "Slidex MRSA Detection" test (Denka Seiken, Japan) is a latex agglutination assay able to detect PBP2a. We evaluated its ability to differentiate mecA-positive from mecA-negative coagulase-negative staphylococci. We included 100 coagulase-negative staphylococci clinical isolates belonging to 9 species, 54 mecA positive and 46 mecA negative, as characterized by PCR. The specificity achieved using the manufacturer's instructions was 100%, but the sensitivity was only 57%. To increase sensitivity, we introduced modifications into the standard protocol. Using either large inocula or oxacillin induction before test performance, we achieved 100% sensitivity.

[Bacteremia by Brucella canis. Isolation with the Bact-Alert system]. / Bacteriemia por Brucella canis. Aislamiento con el sistema Bact-Alert.

Brucella canis and other species of the genus Brucella can cause human disease. However, this species infrequently cause human disease, including in countries where dogs population is highly infected. A 15 years old male was admitted to the hospital with 15 days history of fever without visible focus. Physical examination revealed pain at liver palpation and axillar, cervical and inguinal lymphoadenomegalies. Abdominal ultrasonography showed spleenomegally, the chest Rx and the trans thoracic echocardiogram were normal. Five blood samples were obtained and cultured in 2 standards bottles (time of positivization 72 - 64.8 hours), and 3 pediatric FAN bottles (time of positivization 74.5; 72 and 67.2 hours) (Bact-Alert system, Biomerieux, Marcy, l'Etolie, France). The microorganism was presuntive identified as B. canis, and then was confirmed in the National Reference Center Instituto ANLIS "Carlos G. Malbran". After 14 days of initiating ceftriaxone treatment the patient was afebrile. When the confirmation of Brucella was made, he was discharged and ambulatory was prescribed with doxycycline and rifampin for 21 days. Bones were not compromised and the outcome was good with complete resolution of his illness.

[Bact-Alert automatized system for blood cultures: 5 vs 7 days of incubation. First Argentine multicentre study]. / Sistema automatizado de hemocultivos Bact-Alert: 5 vs 7 dias de incubación. Primer estudio multicéntrico argentino.

Bact-Alert automatized system for blood cultures: 5 vs 7 days of incubation. First Argentine multicentre study. Between January and December 2001, we analyzed 80,141 blood cultures by the Bact-Alert system (14,960 FAN aerobics, 3,855 FAN anaerobic, 11,114 standards aerobics, 11,367 standards anaerobic, 12,054 pediatrics and 26,791 FAN pediatrics bottles) and 44.235 series from 27.615 patients at eight hospitals of Buenos Aires city, one of La Plata city and three of the Buenos Aires province. A total of 13,657 blood cultures yielded a positive result. Only 181 of them had been detected as positive between the 5th and 7th day of incubation and only 26 (0.19%) had clinical significance (Staphylococcus aureus 3; coagulase negative staphylococci 2; Enterococcus faecalis 1; Streptococcus pneumoniae 2; Campylobacter spp 1; Escherichia coli 1; Enterobacter cloacae 1; Enterobacteraerogenes 1; Citrobacter freundii 1; Klebsiella pneumoniae 1; Proteus mirabilis 1; Serratia marcescens 4; yeasts 7, including one strain of Cryptococcus neoformans). Of the total of contaminants, 38% were isolated by the anaerobic standard (65% were Propionibacterium spp and 29% coagulase negative staphylococci), 31.2% by the FAN aerobic (33.3% difphteroids and 28.9% Bacillus spp), 11.8% by the pediatric, 9% by FAN pediatric, 8.33% by aerobic standard and 1.4% by FAN anaerobic bottle. Our results show that the prolonged incubation of blood cultures for more than 5 days using the Bact-Alert system is unnecessary.

[Methicillin resistance detection in Staphylococcus aureus: comparison between conventional methods and MRSA-Screen latex agglutination technique]. / Detección de meticilino-resistencia en Staphylococcus aureus: comparación de métodos convencionales y aglutinación con MRSA-Screen latex.

Methicillin-resistant Staphylococcus aureus (MRSA) is a significant pathogen that has emerged over the last four decades, causing both nosocomial and community-acquired infections. Rapid and accurate detection of methicillin resistance in S. aureus is important for the use of appropriate antimicrobial therapy and for the control of nosocomial spread of MRSA strains. We evaluated the efficiency of conventional methods for detection of methicillin resistance such as the disk diffusion, agar dilution, oxacillin agar screen test, and the latex agglutination test MRSA-Screen latex, in 100 isolates of S. aureus, 79 mecA positive and 21 mecA negative. The MRSA-Screen latex (Denka Seiken, Niigata, Japón), is a latex agglutination method that detects the presence of PLP-2a, product of mecA gene in S. aureus. The PCR of the mecA gene was used as the "gold standard" for the evaluation of the different methods tested. The percentages of sensitivity and specificity were as follows: disk difusión 97 and 100%, agar dilution 97 and 95%, oxacillin agar screen test 100 and 100%, and MRSA-Screen latex, 100 and 100 %. All methods presented high sensitivity and specificity, but MRSA-Screen latex had the advantage of giving a reliable result, equivalent to PCR, in only 15 minutes.

Bacteriemia por Brucella canis. Aislamiento con el sistema Bact-Alert / [Bacteremia by Brucella canis. Isolation with the Bact-Alert system]

Brucella canis and other species of the genus Brucella can cause human disease. However, this species infrequently cause human disease, including in countries where dogs population is highly infected. A 15 years old male was admitted to the hospital with 15 days history of fever without visible focus. Physical examination revealed pain at liver palpation and axillar, cervical and inguinal lymphoadenomegalies. Abdominal ultrasonography showed spleenomegally, the chest Rx and the trans thoracic echocardiogram were normal. Five blood samples were obtained and cultured in 2 standards bottles (time of positivization 72 - 64.8 hours), and 3 pediatric FAN bottles (time of positivization 74.5; 72 and 67.2 hours) (Bact-Alert system, Biomerieux, Marcy, l’Etolie, France). The microorganism was presuntive identified as B. canis, and then was confirmed in the National Reference Center Instituto ANLIS [quot ]Carlos G. Malbran[quot ]. After 14 days of initiating ceftriaxone treatment the patient was afebrile. When the confirmation of Brucella was made, he was discharged and ambulatory was prescribed with doxycycline and rifampin for 21 days. Bones were not compromised and the outcome was good with complete resolution of his illness.

Detección de meticilino-resistencia en Staphylococcus aureus: Comparación de métodos convencionales y aglutinación con mrsa-Screen latex / Methicillin resistance detection in Staphylococcus aureus: Comparison between conventional methods and Mrsa-Screen latex agglutination technique

Staphylococcus aureus meticilino-resistente (MRSA) es un patógeno que ha emergido en las últimas cuatro décadas causando tanto infecciones nosocomiales como de la comunidad. La rápida y precisa detección de MRSA es relevante para guiar una apropiada terapia antibiótica y evitar la diseminación nosocomial de MRSA.En este trabajo se evaluó la eficiencia de métodos convencionales para la detección de meticilino-resistencia como difusión por discos, CIM en medio sólido, screening de oxacilina, y el nuevo test de aglutinación MRSA-Screen latex sobre 100 aislamientos de S. aureus, 79 mecA positivos y 21 mecA negativos. El test de aglutinación MRSA-Screen latex (Denka Seiken, Niigata, Japón) detecta la presencia de la PLP-2a, producto del gen mecA en cepas de S. aureus. La detección del gen mecA por PCR se utilizó como gold standard para comparar los resultados de los diferentes métodos. La sensibilidad y especificidad fueron 97 y 100 % para el método de difusión, 97 y 95 % para la CIM en medio sólido, 100 y 100 % para el screening de oxacilina y 100 y 100 % para MRSA-Screen latex. Todos los métodos presentaron alta sensibilidad y especificidad, pero el “MRSA-Screen latex” mostró la ventaja de poder brindar un resultado confiable, equivalente a la PCR, en sólo 15 minutos.

Methicillin-resistant Staphylococcus aureus (MRSA) is a significant pathogen that has emerged over the last four decades, causing both nosocomial and community-acquired infections. Rapid and accurate detection of methicillin resistance in S. aureus is important for the use of appropriate antimicrobial therapy and for the control of nosocomial spread of MRSA strains. We evaluated the efficiency of conventional methods for detection of methicillin resistance such as the disk diffusion, agar dilution, oxacillin agar screen test, and the latex agglutination test MRSA-Screen latex, in 100 isolates of S. aureus, 79 mecA positive and 21 mecA negative. The MRSA-Screen latex (Denka Seiken, Niigata, Japón), is a latex agglutination method that detects the presence of PLP-2a, product of mecA gene in S. aureus. The PCR of the mecA gene was used as the “gold standard” for the evaluation of the different methods tested. The percentages of sensitivity and specificity were as follows: disk difusión 97 and 100 %, agar dilution 97 and 95 %, oxacillin agar screen test 100 and 100 %, and MRSA-Screen latex, 100 and 100 %. All methods presented high sensitivity and specificity, but MRSA-Screen latex had the advantage of giving a reliable result, equivalent to PCR, in only 15 minutes.

Sistema automatizado de hemocultivos Bact-Alert: 5 vs 7 dias de incubación. Primer estudio multicéntrico argentino / [Bact-Alert automatized system for blood cultures: 5 vs 7 days of incubation. First Argentine multicentre study]

Bact-Alert automatized system for blood cultures: 5 vs 7 days of incubation. First Argentine multicentre study. Between January and December 2001, we analyzed 80,141 blood cultures by the Bact-Alert system (14,960 FAN aerobics, 3,855 FAN anaerobic, 11,114 standards aerobics, 11,367 standards anaerobic, 12,054 pediatrics and 26,791 FAN pediatrics bottles) and 44.235 series from 27.615 patients at eight hospitals of Buenos Aires city, one of La Plata city and three of the Buenos Aires province. A total of 13,657 blood cultures yielded a positive result. Only 181 of them had been detected as positive between the 5th and 7th day of incubation and only 26 (0.19

) had clinical significance (Staphylococcus aureus 3; coagulase negative staphylococci 2; Enterococcus faecalis 1; Streptococcus pneumoniae 2; Campylobacter spp 1; Escherichia coli 1; Enterobacter cloacae 1; Enterobacteraerogenes 1; Citrobacter freundii 1; Klebsiella pneumoniae 1; Proteus mirabilis 1; Serratia marcescens 4; yeasts 7, including one strain of Cryptococcus neoformans). Of the total of contaminants, 38

were isolated by the anaerobic standard (65

were Propionibacterium spp and 29

by the FAN aerobic (33.3

difphteroids and 28.9

by the pediatric, 9

by aerobic standard and 1.4

by FAN anaerobic bottle. Our results show that the prolonged incubation of blood cultures for more than 5 days using the Bact-Alert system is unnecessary.

[Analysis of 942 episodes of bacteremia in a cardiology institution. Experience with the Bact-Alert system]. / Análisis de 942 episodios de bacteriemia en una institución cardiológica. Experiencia con el sistema Bact-Alert.

In Instituto de Cardiología y Cirugía Cardiovascular, Fundación Favaloro, between January 1996 and October 1999, 10,793 blood cultures and 942 episodes of bacteremia, corresponding to 1883 positive blood cultures, were studied by means of the Bact-Alert System (Organon Teknika), 94% being monomicrobial episodes. Gram positive bacteria were isolated in 45%, Gram negative in 52% and fungi in 3% of episodes. Associated foci of infection were: catheters 36.5%, mediastinitis 9%, pneumonia 6%, endocarditis 6%, abdominal 6%, urinary tract infections 9%, prosthesis 2.6%, empyema 0.2%, arthritis 0.1%, skin and soft tissue 2.5%, diarrhea 0.1%, aortic aneurysm 0.2%, meningitis 0.2%, pericarditis 0.3%, endarteritis 0.1%, infusion fluids 0.2% and unknown 21%. Median time (in hours) for positivization of blood cultures according to different foci were: catheters 16.4, mediastinitis 19.2, pneumonia 14.2, endocarditis 14.5, abdominal infections 11.8, urinary tract infections 13.0 and unknown origin 19.0. As for contaminating microorganisms, the value was 30.5. Seventy two percent of blood cultures became positive within 24 h, and 87% within 48 h; only 1% became positive between 5th and 7th day. There were no important differences in time to detect positive cultures according to different foci. It was not useful to incubate blood cultures more than five days, except for special circumstances, because it does not improve recovery of clinically significant microorganisms.

[Consensus on antimicrobial sensitivity tests in gram-positive cocci. Subcommittee on Antimicrobials, SADEBAC (Argentinian Society of Clinical Bacteriology), Argentinian Association of Microbiology]. / Consenso sobre las pruebas de sensibilidad a los antimicrobianos en cocos gram-positivos.

Antimicrobial susceptibility testing is mainly performed in Argentina by disk diffusion method, following National Committee for Clinical Laboratory Standards (NCCLS) recommendations. We worked out new recommendations for the reporting and interpretation of this test when dealing with gram-positive cocci, in accordance to local trends and epidemiology. General considerations for performing the diffusion assay, quality control, and an update on susceptibility testing for gram-positive cocci are reported in this first document. The present update should be considered as a group of recommendations summarized by Argentinean experts and as the result of a consensus meeting coordinated by the Subcomisión de Antimicrobianos of the Sociedad Argentina de Bacteriología Clínica (Asociación Argentina de Microbiología). Experts in antimicrobial agents were convened in order to prepare this final document. These recommendations take into account local needs, affordability and availability to be used in current practice, tending to contribute to the correct antimicrobial treatment election, according to the particular microorganism and the infection sites.

Análisis de 942 episodios de bacteriemia en una institución cardiológica: experiencia con el sistema Bact-Alert / Analysis of 942 episodes of bacteremia in a cardiology hospital

Entre enero de 1996 y octubre de 1999, se estudiaron en el Instituto Cardiovascular, Fundación Favaloro, 10.793 hemocultivos y 942 episodios de bacteriemia. Utilizando el Sistema Bact-Alert (Organon Teknika) estos cultivos fueron positivos en 1.883 casos. 94 por ciento de los episodios fueron monomicrobianos. Del total de espisodios se aislaron 45 por ciento de bacterias gram positivas, 52 por ciento de gram negativas y 3 por ciento de hongos. Los focos de infección asociados fueron: 36,5 por ciento infecciones asociadas a catéteres, 9 por ciento mediastinitis, 9 por ciento infecciones urinarias, 6 por ciento neumonías, 6 por ciento endocarditis, 6 por ciento infecciones intraabdominales, 2,6 por ciento infecciones de prótesis, 2,5 por ciento infecciones de piel y partes blandas, 0,3 por ciento pericarditis, 0,2 por ciento meningitis, 2 por ciento empiemas, 0,2 por ciento aneurismas de aorta, 0,2 por ciento infecciones por líquido de infusión contaminado, 0,1 por ciento artritis, 0,1 por ciento endarteritis, 0,1 por ciento diarreas, y foco desconocido en 21 por ciento de los casos. La mediana en horas para positivización de los hemocultivos acorde a los distinto focos fue: 16,4 para infecciones asociadas a catéteres, 19,2 mediastinitis, 14,2 neumonías, 14,5 endocarditis, 11,8 infecciones intraabdominales, 13 infecciones urinarias y 19 para bacteremias de origen desconocido. El valor fue de 30,5 h para las contaminaciones. El 72 por ciento de los hemocultivos positivos con un microorganismo considerado como clínicamente significativo se detectó a las 24 h, 87 por ciento dentro de las 48 h y sólo 1 por ciento entre el 5§ y 7§ día. No hubo diferencias importantes en el tiempo de detección de hemocultivos positivos acorde a distintos focos. Tampoco resultó de utilidad la incubación de las botellas más allá del 5§ día, excepto para circunstancias especiales, puesto que no mejoró la recuperación de microorganismos clínicamente significativos.

Consenso sobre las pruebas de sensibilidad a los antimicrobianos en cocos gram-positivos / Consensus for antimicrobial susceptibility testing for gram-positive cocci

El antibiograma por difusión en agar con discos se encuentra ampliamente difundido en nuestro medio y se basa primariamente en las recomendaciones del National Committee for Clinical Laboratory Standards (NCCLS). En este documento se elaboraron una serie de recomendaciones para el ensayo, lectura, interpretación e informe de las pruebas de sensibilidad a los antimicrobianos en cocos gram-positivos, adaptadas a la realidad argentina. En esta primera etapa se redactaron las consideraciones generales para la realización de la prueba por difusión, los controles de calidad internos para todos los microorganismos y una actualización sobre las pruebas de sensibilidad en cocos gram-positivos. Se debe resaltar que el contenido de este documento debe ser considerado como recomendaciones realizadas por expertos argentinos y que son el resultado de reuniones de consenso organizadas por la Subcomisión de Antimicrobianos de la Sociedad Argentina de Bacteriología Clínica, división de la Asociación Argentina de Microbiología. Se formó un equipo de trabajo integrado por expertos en antimicrobianos y a partir de una propuesta inicial, basada en una revisión de la literatura se fueron elaborando diversos documentos de trabajo que fueron mejorados después de ser debatidos por los miembros del grupo de trabajo hasta llegar al documento final. El criterio general fue elaborar recomendaciones acordes a las necesidades de nuestro país que puedan utilizarse en la práctica diaria con el objeto de colaborar en la adecuada elección del tratamiento antibiótico según la especie bacteriana aislada y la localización de la infección.

[Quantitative cultures from catheters, using the Brun Buisson technique]. / Cultivos cuantitativos de catéteres por la técnica de Brun Buisson.

The objective of this collaborative work carried out in the Fundación Favaloro and the Fundación para la Lucha contra las Enfermedades Neurológicas de la Infancia, was to determine optimal conditions for incubation (time and atmosphere) of quantitative cultures of catheters processed according to the technique of vortex agitation (Brun Buisson method). From 689 processed catheters, 551 yielded negative cultures. From the 138 positive cultures, 125 yielded monomicrobial cultures and 13 polimicrobial cultures (total number of microorganisms was 151). In the last situation each micoorganism was considered on an individual basis. A total of 58 episodes of catheter related bacteremias occurred, being 52 monomicrobial and 6 polimicrobial (total number of microorganisms was 64). When colony counts were compared in aerobic and in 5-10% CO2 atmospheres, a very good correlation was obtained (p = 0.27; r2 = 0.9268). No advantage was observed by incubating plates for more than 48 hours. Colony counts performed at the second versus the third day, and at the second day versus the seventh, gave very good correlation (p = 0.10 and r2 = 0.9996; p = 0.31 and r2 = 0.9995, respectively).

Cultivos cuantitativos de catéteres por la técnica de Brun Buisson / Quantitative cultures from catheters, using the Brun Buisson technique

The objective of this collaborative work carried out in the Fundación Favaloro and the Fundación para la Lucha contra las Enfermedades Neurológicas de la Infancia, was to determine optimal conditions for incubation (time and atmosphere) of quantitative cultures of catheters processed according to the technique of vortex agitation (Brun Buisson method). From 689 processed catheters, 551 yielded negative cultures. From the 138 positive cultures, 125 yielded monomicrobial cultures and 13 polimicrobial cultures (total number of microorganisms was 151). In the last situation each micoorganism was considered on an individual basis. A total of 58 episodes of catheter related bacteremias occurred, being 52 monomicrobial and 6 polimicrobial (total number of microorganisms was 64). When colony counts were compared in aerobic and in 5-10 CO2 atmospheres, a very good correlation was obtained (p = 0.27; r2 = 0.9268). No advantage was observed by incubating plates for more than 48 hours. Colony counts performed at the second versus the third day, and at the second day versus the seventh, gave very good correlation (p = 0.10 and r2 = 0.9996; p = 0.31 and r2 = 0.9995, respectively).

[Comparison of different detection methods for methicillin resistance in Staphylococcus aureus]. / Comparación de diferentes métodos para la detección de resistencia a meticilina en Staphylococcus aureus.

The investigation of methicillin resistance in Staphylococcus aureus (MRSA) is a serious problem for the physician and microbiologist. Accurate and rapid detection is essential for the use of appropriate antimicrobial therapy and for the control of nosocomial spread of the resistant strain. The performance characteristics of the MicroScan Overnight Conventional Pos Combo 12 panels (MOCP), BBL Crystal MRSA ID (CR), E-test and agar screen plate (Muller Hinton agar with oxacillin 6 micrograms/ml and 4% NaCl) (AS) were evaluated for the detection of oxacillin resistance. Thirty S. aureus clinically significant strains with different PFGE (Pulse Field Gel Electrophoresis) banding pattern were tested, and 22 of them were mecA positive by PCR. These strains were also analyzed by mecA and Tn554 polymorphism. All mecA positive strains were classified as methicillin resistant by MOCP and E-test. CR and AS failed to detect oxacillin resistance in 2 strains. One false positive was only detected by E-test. Accurate testing for the presence of MRSA may reduce the need for empiric therapy with vancomycin for patients with staphylococcal infections. According to our results the best performance was obtained with MOCP. However, as a rapid method, CR gave acceptable sensitivity for clinical purposes.

Comparación de diferentes métodos para la detección de resistencia a meticilina en Staphylococcus aureus / [Comparison of different detection methods for methicillin resistance in Staphylococcus aureus]

The investigation of methicillin resistance in Staphylococcus aureus (MRSA) is a serious problem for the physician and microbiologist. Accurate and rapid detection is essential for the use of appropriate antimicrobial therapy and for the control of nosocomial spread of the resistant strain. The performance characteristics of the MicroScan Overnight Conventional Pos Combo 12 panels (MOCP), BBL Crystal MRSA ID (CR), E-test and agar screen plate (Muller Hinton agar with oxacillin 6 micrograms/ml and 4

NaCl) (AS) were evaluated for the detection of oxacillin resistance. Thirty S. aureus clinically significant strains with different PFGE (Pulse Field Gel Electrophoresis) banding pattern were tested, and 22 of them were mecA positive by PCR. These strains were also analyzed by mecA and Tn554 polymorphism. All mecA positive strains were classified as methicillin resistant by MOCP and E-test. CR and AS failed to detect oxacillin resistance in 2 strains. One false positive was only detected by E-test. Accurate testing for the presence of MRSA may reduce the need for empiric therapy with vancomycin for patients with staphylococcal infections. According to our results the best performance was obtained with MOCP. However, as a rapid method, CR gave acceptable sensitivity for clinical purposes.

[Utility of prolonged incubation and terminal subcultures of blood cultures from immunocompromised patients]. / Utilidad de la incubación prolongada y de los subcultivos terminales de hemocultivos de pacientes inmunocomprometidos.

The value of blind terminal subcultures (7 and 30 days) and prolonged incubation (30 days) of blood cultures from immunosuppressed patients was analyzed in the Fundación Favaloro, the Fundación para la Lucha contra las Enfermedades Neurológicas de la Infancia and the Hospital de Niños Ricardo Gutiérrez. A total of 2707 blood cultures and 369 patients were included (transplantation of solid organs 154, oncohematologic disorders 106 and solid tumors 109). Bact-Alert bottles were incubated at 35 degrees C for 30 days in the Bact-Alert System. Bottles with positive signals were routinely removed, and aliquots of the broth were Gram stained and subcultured aerobically in chocolate agar and Sabouraud agar. A total of 136 bacteremic episodes were obtained. The positivization time of blood cultures was 81.6% at 24 h, 93.3% at 48 h, 94.5% at 72 h and 97.7% within 7 days. Only 3 (2.2%) episodes were positive by blind terminal subcultures and 1 (0.75%) by prolonged incubation (14 days). The median time and range of positivization in hours were 13.8 and 2.2-168, respectively. The microorganisms isolated were coagulase negative staphylococci (n = 24), Klebsiella pneumoniae (n = 22), Staphylococcus aureus (n = 21), Escherichia coli (n = 18), Acinetobacter spp (n = 9), Candida spp (n = 8), Pseudomonas aeruginosa (n = 6), Enterobacter cloacae (n = 5), Stenotrophomonas maltophilia (n = 5), Enterococcus faecalis, Salmonella spp and Capnocytophaga sputigena (n = 2), Enterobacter aerogenes, Enterococcus faecium, Citrobacter diversus, Candida albicans, Klebsiella oxytoca, Chryseomonas luteola, Serratia marcescens, Abiotrophia spp, Campylobacter jejuni, Moraxella catarrhalis, Moraxella urethralis, Neisseria sicca, beta hemolytic group G streptococci, Rhodococcus equi, Micrococcus spp, Cryptococcus neoformans and Streptococcus mitis (n = 1). In our experience, blind terminal subcultures and prolonged incubation of blood cultures from immunosuppressed patients are unnecessary and cost expensive.

Utilidad de la incubación prolongada y de los subcultivos terminales de hemocultivos de pacientes inmunocomprometidos / Utility of prolonged incubation and terminal subcultures of blood cultures from immunocompromised patients

The value of blind terminal subcultures (7 and 30 days) and prolonged incubation (30 days) of blood cultures from immunosuppressed patients was analyzed in the Fundación Favaloro, the Fundación para la Lucha contra las Enfermedades Neurológicas de la Infancia and the Hospital de Niños Ricardo GutiÚrrez. A total of 2707 blood cultures and 369 patients were included (transplantation of solid organs 154, oncohematologic disorders 106 and solid tumors 109). Bact-Alert bottles were incubated at 35 degrees C for 30 days in the Bact-Alert System. Bottles with positive signals were routinely removed, and aliquots of the broth were Gram stained and subcultured aerobically in chocolate agar and Sabouraud agar. A total of 136 bacteremic episodes were obtained. The positivization time of blood cultures was 81.6 at 24 h, 93.3 at 48 h, 94.5 at 72 h and 97.7 within 7 days. Only 3 (2.2) episodes were positive by blind terminal subcultures and 1 (0.75) by prolonged incubation (14 days). The median time and range of positivization in hours were 13.8 and 2.2-168, respectively. The microorganisms isolated were coagulase negative staphylococci (n = 24), Klebsiella pneumoniae (n = 22), Staphylococcus aureus (n = 21), Escherichia coli (n = 18), Acinetobacter spp (n = 9), Candida spp (n = 8), Pseudomonas aeruginosa (n = 6), Enterobacter cloacae (n = 5), Stenotrophomonas maltophilia (n = 5), Enterococcus faecalis, Salmonella spp and Capnocytophaga sputigena (n = 2), Enterobacter aerogenes, Enterococcus faecium, Citrobacter diversus, Candida albicans, Klebsiella oxytoca, Chryseomonas luteola, Serratia marcescens, Abiotrophia spp, Campylobacter jejuni, Moraxella catarrhalis, Moraxella urethralis, Neisseria sicca, beta hemolytic group G streptococci, Rhodococcus equi, Micrococcus spp, Cryptococcus neoformans and Streptococcus mitis (n = 1). In our experience, blind terminal subcultures and prolonged incubation of blood cultures from immunosuppressed patients are unnecessary and cost expensive.