[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.

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.

[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.

[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.

[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.

[Blood cultures: use of presumptive antiobiograms]. / Hemocultivos: utilidad de los antibiogramas presuntivos.

Mortality associated to bacteremia varies between 20 and 40% depending upon several factors, such as focus of infection, microorganism, host conditions, etc. It has also been documented that mortality may double when the patient does not receive antibiotic treatment to which the microorganism is susceptible. The objective of our work has been to determine the correlation between disk diffusion antibiogram according to NCCLS guidelines, from isolated colonies, and the one performed directly from the blood culture flask. During 1996, in the Institute of Cardiology and Cardiovascular Surgery (ICYCC) in Buenos Aires City, 81 episodes of bacteremia were studied. In every case, an antibiogram was carried out: 1) from the bottle: a- Directly (D), harvesting 20 microliters in Mueller Hinton agar, b- Diluted (d), previous centrifugation and Gram staining to adjust turbidity equivalent to 0.5 Mc Farland; 2) from isolated colonies, according to NCCLS guidelines. There were almost no major errors, except with two strains of Enterobacter cloacae versus cephalotin. The diluted method was not so convenient to read inhibition zones, especially with staphylococci. With gram-positive bacteria, the main problems appeared in the direct method with erythromycin, oxacillin and ciprofloxacin because of minor errors. With gram-negative bacteria, major errors were observed in the direct method, mainly with piperacillin (7%) and to a lesser extent with piperacillin tazobactam (2%). Except for imipenem, trimethoprim sulfamethoxazoie and cefotaxime, all antimicrobial agents presented minor errors with both methodologies. Based upon the high rate of minor errors, we consider it is important to confirm results obtained with the standard technique (NCCLS), considering as presumptive those results from the blood culture bottles (D and d).

[Bact-Alert system for hemocultures: evaluation of terminal subcultures]. / Sistema bact-alert de hemocultivos: evaluación de los subcultivos terminales.

Few laboratory microbiological procedures are as important as the isolation of microorganisms from blood. To evaluate the usefulness of the terminal subcultures, 5669 blood cultures giving negative results after 7 days of incubation in the Bact/Alert System (Organon Teknika) were studied. Bottles were distributed as follows: 1562 adult aerobic bottles, 119 adult anaerobic bottles, 3960 pediatric bottles and 28 FAN bottles. From 5669 blood cultures, 10 subcultures that yielded growth had not been detected by the system. These included 5 adult aerobic bottles and 5 pediatric bottles, 7 of these microorganisms were considered contaminants according to clinical data (2 Micrococcus spp, 1 staphylococci coagulase negative, 1 Burkholderia cepacia, 1 Peptoestreptococcus spp, 1 Corynebacterium spp, 1 Scedosporium spp) while the other 3 were considered true bacteremia (1 Pseudomonas aeruginosa, 1 Proteus mirabilis, 1 Streptococcus sanguis), although no one made any change in treatment on the basis of the previous isolation. Based on these results the routinary utilization of terminal subcultures is not advisable and should be used only for special cases or a second system of blood culture should be added according to clinical or epidemiological data.

[Evaluation of the reincubation of positive blood cultures for detection in the BACT-ALERT system for the detection of polymicrobial bacteremia]. / Evaluación de la reincubación de hemocultivos positivos por el sistema BACT-ALERT para la detección de bacteriemias polimicrobianas.

Between February and September 1997, 6588 blood cultures at the Instituto de Cardiología y Cirugía Cardiovascular and Hospital de Niños Ricardo Gutiérrez were studied by using the Bact-Alert system (Organon Teknika) 341 contaminants and 294 episodes of bacteremia (600 samples) were analyzed. From these samples, 280 (95.3%) were monomicrobial episodes and 14 (4.7%) polymicrobial episodes. Positive blood cultures detected by the Bact-Alert system were processed and then reincubated during 7 days, when they were Gram stained and subcultured in blood agar, chocolate agar (both in 5-10% CO2), laked blood agar supplemented with hemin and vitamin K in anaerobic atmosphere (only anaerobic bottles) and CLDE (aerobic conditions). Following reincubation, 3 out of 14 polymicrobial bacteremias were detected, rising the level of detection from 3.7% to 4.7%. Taking into account the total number of bacteremias, only in 3 out of 294 (1%), a second microorganism was detected. Otherwise, in blood cultures where a contaminating microorganism was initially isolated, no further isolates representing a true bacteremia were recovered. Reincubation and terminal subculture of initially positive blood cultures did not provide relevant data in order to change therapeutic measures in the studied population. Due to the increase in costs and labor we consider that this methodology is not routinely advised.

[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.

[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).

[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.

[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.

[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.

[The microbiology laboratory in the diagnosis of bacteremia associated with catheters]. / El laboratorio de microbiología en el diagnóstico de la bacteriemia relacionada con los catéteres.

Catheter related sepsis is an outstanding problem in patients in every age group. The microbiological diagnosis should consider the main pathways of infection (catheter-skin interface, endoluminal). With this aim we analysed 1496 central and peripheral short term catheters and 119 episodes of catheter related bacteremia. Catheters were cultured according to the quantitative technique of Brun Buisson (QT), the semiquantitative technique of Maki (SQ) and qualitative broth culture (QL). The following results of sensitivity, specificity, positive predictive value, negative predictive value and Youden index were obtained: SQ = 87%, 88%, 40%, 99%, 0.75; QT (> or = 10(2) CFU/ml) = 88%, 89%, 43%, 99%, 0.77; QT (> or = 10(3) CFU/ml) = 77%, 92%, 48%, 97%, 0.69; QL = 94%, 68%, 20%, 99%, 0.62. Results of SQ and QT > or = 10(2) were comparable, nevertheless, the addition of QT to SQ increased the detection of bacteremia by 12.8%, while in the opposite situation the increase was 10%. According to this, it is advisable to combine routinely SQ and QT. Finally, in 42 episodes of bacteremia related to implanted catheters processed by quantitative differential culture of blood drawn through the catheter and blood drawn through the peripheral vein the relationships were: > 1000 in 79% of cases, between 100 and 1000 in 9% of cases and between 5 and 10 in just 5% of cases.

[Monitoring antibiotic resistance in Argentina. The WHONET program, 1995-1996]. / Vigilancia de la resistencia a los antibacterianos en Argentina. Programa WHONET, 1995-1996. Red Nacional de Laboratorios que participan en el Programa WHONET.

The World Health Organization has implemented a surveillance program for antimicrobial resistance that is known as WHONET. In Argentina the program was developed through a network of 23 public and private hospitals that participate in national and international quality-control programs. Between January 1995 and December 1996, the antimicrobial susceptibility of 16,073 consecutive clinical isolates was determined, using the recommended standards of the National Committee for Clinical Laboratory Standards of the United States of America. More than half of the Escherichia coli urinary isolates were resistant to ampicillin and more than 30% to trimethoprim/sulfamethoxazole (SXT). When the percentage of resistant isolates from outpatients (OPs) was compared to that observed in hospitalized patients (HPs), a marked difference in antimicrobial activity was noted in the case of gentamicin (2% from OPs resistant vs. 8% from HPs resistant), norfloxacin (2% vs. 6%), and third-generation cephalosporins (7% vs. 15%). Of the Klebsiella pneumoniae isolates recovered from blood cultures, 71% and 60% showed resistance to third-generation cephalosporins and to gentamicin, respectively. The overall rate of oxacillin resistance in Staphylococcus aureus was 39%. Around half of the Enterococcus spp. isolates showed high resistance to aminoglycosides, but resistance to glycopeptides was not found. In Argentina, ampicillin and SXT were not suitable for treating diarrhea. Shigella flexneri had a higher number of isolates resistant to both of those drugs (87% and 74%, respectively) than Sh. sonnei did (47% and 71%, respectively). About 40% of the Salmonella spp. isolated in pediatric hospitals were resistant to third-generation cephalosporins. When microorganisms causing bacterial meningitis were examined, Streptococcus pneumoniae showed a resistance rate of 18% to penicillin and Haemophilus influenzae a resistance rate of 19% to ampicillin. These rates are within the intermediate range reported for other countries of the Americas and for Europe.

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.

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.

Procesamiento bacteriológico y micológico de muestras de infecciones de vías respiratorias superiores: otitis media (OMA) y sinusitis / Processing specimens of upper respiratory tract infections for bacteria and fungi: otitis media and sinusitis

Las infecciones del tracto respiratorio superior son la causa infecciosa más frecuente de consulta al médico. En el caso de la otitis media y sinusitis aguda, los agentes etiológicos más frecuentes son S. pneumoniae, H. influenzae no "b" y M. catarrhalis; en tanto que en las formas crónicas aumenta la incidencia de anaerobios, bacilos gram negativos y S. aureus. La punción de oído medio y de senos paranasales se recomienda para casos puntuales como inmunocomprometidos, fracaso terapéutico, complicaciones supurativas, neonatos con otitis media, pacientes intubados con sinusitis y tal vez pacientes provenientes de áreas con alto porcentaje de cepas resistentes