Microbiological background

Abstract

Several bacteria and fungi can cause severe infections in hematology patients. During last three decades gram-positive bacteria including coagulase-negative staphylococci, viridans streptococci and enterococci have been the most frequent pathogens causing bacteremia in neutropenic patients. This picture has recently changed so that the incidence of infections with enteric gram-negatives and non-fermentative bacteria has dramatically increased and at least in some centers exceeded the rates of gram-positive bacterial infections. Particular problems included quinolone-resistantEscherichia coli, extended-spectrum beta-lactamase production in enteric bacteria and carbapenemase synthesis inE. coli, klebsiellae, Pseudomonas aeruginosaandAcinetobacter spp. Stenotrophomonas maltophiliais another important non-fermentative responsible for severe infections in this patient population. In most cases these bacteria posses various mechanisms causing multidrug resistance patterns. Prophylactic and empirical antibacterial regimens need to be adapted according to local epidemiology, particularly in those places where these resistant bacteria are prevalent both in-hospital or in the outpatient settings. Among the fungal pathogens, Aspergillus spp. AndCandida spp. are far more prevalent. Non-albicansCandida spp. are more frequently isolated thanCalbicansin patients with acute leukemia or in those undergoing stem cell transplantation.Aspergillus spp. are the leading fungal pathogens in hematological cancer patients among whichA. fumigatesis the most frequent one. Emerging triazoles resistance has been reported inA. fumigatus. Non-aspergillus mold infections have been on rise during the last two decades and this may be related with the use of antifungals with lesser or without any activity on these molds. While mortality due to A. fumigatus has been steadily decreasing in hematology patients, very high mortality rates are still being observed in those patients infected with non-aspergillus molds.