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.

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

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).