infectious complications , especially bloodstream infections ( bsis ) , are major causes of morbidity and mortality among patients who suffered from malignant hematological diseases and treated with intensive chemotherapeutic regimens [ 1 , 2 ] . in these clinical settings , bacterial cultures from blood are of great diagnostic value and the gold standard to detect bloodstream infections ; in addition to this , the results of blood cultures provide epidemiological data which are useful to determine empiric antibiotic therapy . however , the diagnosis of bsis is still challenging in this patient group , because about half of all bsi cases are culture negative mainly because of the frequently used prophylactic antibiotics . to overcome the inhibitory effect of antibiotics , special blood culture bottles containing resin have been developed ; thus , modest increase in the sensitivity of culture has been achieved . in the early 1970s , introducing empiric treatment protocols and antibiotic prophylaxis , increasing use of certain chemotherapeutic drugs associated with frequent oral mucositis , and frequent use of central venous catheters have changed the spectrum of pathogens in febrile neutropenic patients shifting it from gram - negative to gram - positive bacteria , especially viridans group streptococci and coagulase - negative staphylococci [ 36 ] . the aim of this study was to evaluate occurrence of bacterial species causing bloodstream infections due to febrile neutropenic episodes in the hematology ward of the university hospital in szeged , hungary , between 2005 and 2008 . between 2005 and 2008 , 469 patients with febrile neutropenia ( 230 females and 239 males , median age 60 years ) were observed in our department with various hematological diseases . collected data from patients documentations included demographics of patients , diagnosis , febrile episodes , source of fever and source of infection , neutrophil count , and clinical significance of the isolated organism . infectious complications were categorized into three groups : 1  fever of unknown origin ( fuo ) , 2  microbiologically documented infection ( mdi ) , and 3  clinically documented infection ( cdi ) . febrile neutropenia was defined if a single oral temperature was measured higher than 38.3 c , or temperature was 38.0 c or higher for 1 h. neutropenia was defined as absolute neutrophil count ( anc ) less than 0.5  10/l or less than 1.0  10/l and rapidly declined below 0.5  10/l . a single positive blood culture ( bc ) common skin contaminants ( cns , propionibacteria ) were considered significant only if they could be found in two consecutive bc samples or if there were concurrent skin , soft tissue , or catheter - related infections . bsi was defined as polymicrobial if more than 1 bacteria grew from bc on the same day . medical database of patients was used to collect information on the hematologic diseases , presence of febrile neutropenic episode , duration of neutropenia , and source of infection . bc samples were taken at the onset of fever . in patients having central venous catheters , bcs for collection of blood culture , the blood culture system ( bd bactec , beckton dickinson , usa ) including aerobic , anaerobic bottles , and bottles for fungi was used . after taking blood , bottles were immediately placed in an incubator , where these were incubated for 514 days depending on the type of the putative pathogens . in the case of positive signal produced by the instrument on the basis of bacterial or fungal growth , microscopic examinations ( phase contrast microscopy and examination of gram - stained preparations ) and columbia blood agar supplemented with 5% sheep blood ( biomrieux , marcy letoile , france ) , chocolate agar supplemented with poly - vitex ( biomrieux , marcy letoile , france ) , eosin methylene blue ( lab m , uk ) and sabouraud chloramphenicol ( bio - rad , france ) agars , and , for anaerobic culture , schaedler agar supplemented with 5% sheep blood ( bio - mrieux , marcy letoile , france ) were inoculated with one drop of blood . plates were incubated at 37 c for 24 h in a 5% co2 incubator or 37 c for 24 h under normal atmosphere or at 37 c for 48 h in an anaerobic cabinet ( concept 400 ; ruskinn technology ltd . , bridgend , uk ) under a gas composition of 85% n2 , 10% h2 , and 5% co2 . from pure culture , antibiotic susceptibility tests were performed on the basis of clinical laboratory standard institute recommendations [ 811 ] . at the onset of fever , after taking bc , broad spectrum antibiotics were started empirically ( piperacillin  tazobactam , cefepime , and imipenem or meropenem ) . changes in empiric antibiotic therapy depended on bc results and clinical response . in afebrile and culture - negative patients with stable clinical state , empiric antibiotic treatment was continued until anc reached 500/l . vancomycin was used in patients with central venous devices , persistent fever , and hypotension . on day 45 , in patients with persistent fever suggesting fungal infection on the basis of clinical signs and computed tomography ( ct ) scans , amphotericin b was applied . between 2005 and 2008 , 469 patients with febrile neutropenia ( 230 females and 239 males , median age 60 years ) were observed in our department with various hematological diseases . collected data from patients documentations included demographics of patients , diagnosis , febrile episodes , source of fever and source of infection , neutrophil count , and clinical significance of the isolated organism . infectious complications were categorized into three groups : 1  fever of unknown origin ( fuo ) , 2  microbiologically documented infection ( mdi ) , and 3  clinically documented infection ( cdi ) . febrile neutropenia was defined if a single oral temperature was measured higher than 38.3 c , or temperature was 38.0 c or higher for 1 h. neutropenia was defined as absolute neutrophil count ( anc ) less than 0.5  10/l or less than 1.0  10/l and rapidly declined below 0.5  10/l . a single positive blood culture ( bc ) common skin contaminants ( cns , propionibacteria ) were considered significant only if they could be found in two consecutive bc samples or if there were concurrent skin , soft tissue , or catheter - related infections . bsi was defined as polymicrobial if more than 1 bacteria grew from bc on the same day . medical database of patients was used to collect information on the hematologic diseases , presence of febrile neutropenic episode , duration of neutropenia , and source of infection . bc samples were taken at the onset of fever . in patients having central venous catheters , bcs were taken from both central and peripheral veins . for collection of blood culture , the blood culture system ( bd bactec , beckton dickinson , usa ) including aerobic , anaerobic bottles , and bottles for fungi was used . after taking blood , bottles were immediately placed in an incubator , where these were incubated for 514 days depending on the type of the putative pathogens . in the case of positive signal produced by the instrument on the basis of bacterial or fungal growth , microscopic examinations ( phase contrast microscopy and examination of gram - stained preparations ) and columbia blood agar supplemented with 5% sheep blood ( biomrieux , marcy letoile , france ) , chocolate agar supplemented with poly - vitex ( biomrieux , marcy letoile , france ) , eosin methylene blue ( lab m , uk ) and sabouraud chloramphenicol ( bio - rad , france ) agars , and , for anaerobic culture , schaedler agar supplemented with 5% sheep blood ( bio - mrieux , marcy letoile , france ) were inoculated with one drop of blood . plates were incubated at 37 c for 24 h in a 5% co2 incubator or 37 c for 24 h under normal atmosphere or at 37 c for 48 h in an anaerobic cabinet ( concept 400 ; ruskinn technology ltd . , bridgend , uk ) under a gas composition of 85% n2 , 10% h2 , and 5% co2 . from pure culture , antibiotic susceptibility tests were performed on the basis of clinical laboratory standard institute recommendations [ 811 ] . at the onset of fever , after taking bc , broad spectrum antibiotics were started empirically ( piperacillin  tazobactam , cefepime , and imipenem or meropenem ) . changes in empiric antibiotic therapy depended on bc results and clinical response . in afebrile and culture - negative patients with stable clinical state vancomycin was used in patients with central venous devices , persistent fever , and hypotension . on day 45 , in patients with persistent fever suggesting fungal infection on the basis of clinical signs and computed tomography ( ct ) scans , amphotericin b was applied . during the four - year study period , 1,361 patients were treated in the hematology ward because of various hematological diseases . a total of 812 febrile episodes were recorded in 469 ( 34.5% ) patients , and blood was collected for microbiological culture . of the 469 patients , 128 ( 27.3% ) had acute myeloid leukemia , 85 ( 18.1% ) non - hodgkin s lymphoma , 66 ( 14.1% ) multiple myeloma , 64 ( 13.6% ) chronic lymphocytic leukemia , 41 ( 8.7% ) acute lymphoblastic leukemia , and 85 ( 18.1% ) others ( hodgkin s lymphoma , myelodysplastic syndrome , chronic myeloprolipherative disorders etc . ) ( table 1 ) . altogether , 3,714 blood culture bottles , 6.5 bottles / patient ( ranging 212 ) , were sent to the laboratory . in 126 ( 27% ) of 469 patients , only one pair of blood culture bottles was taken by febrile episodes . clinically documented infections could be observed in 430 of 812 febrile episodes ( 52.95% ) . colitis and skin and soft tissue infections were the second and third most common infections . during the microbiological culture , 759 ( 20.4% ) of 3,714 blood culture bottles gave positive signals . from the majority of positive blood culture bottles ( 509 bottles ( 67.1% ) ) , gram - positive bacteria were cultured . among gram - positive bacteria , the most frequent isolates were coagulase - negative staphylococci ( 65% ) , staphylococcus aureus ( 10% ) , enterococcus spp . ( 6.7% ) , popionibacterium acnes ( 5.7% ) , -hemolytic streptococci ( 3.1% ) , streptococcus pneumoniae ( 2.8% ) , -hemolytic streptococci ( 2.4% ) , clostridium spp . ( 1.4% ) , and others ( 3% ) ( including listeria monocytogenes , nocardia farcinica , gemella spp . , micrococcus spp . , brevibacterium spp . , and gram - positive nonidentified bacteria ) high prevalence of escherichia coli ( 52% ) could be detected in these specimens , while 14% of samples contained pseudomonas aeruginosa , 9.6% klebsiella spp . , 8% enterobacter spp . , 3.6% citrobacter spp . , 2% stenotrophomonas maltophilia , 1.6% acinetobacter spp . , and 1.6% fusobacterium spp . only six bottles proved to be positive for fungi during the examined period ; in two cases , candida albicans and also , in two bottles , candida tropicalis could be detected , while two other bottles were positive for cryptococcus spp . among gram - positive isolates , coagulase - negative staphylococci ( cns ) were identified in 331 cases . these blood culture samples were collected from 161 febrile episodes of 149 patients . in 50 febrile neutropenic episodes , cns were relevant as a causative agent of fever because of the coexistence of skin , soft tissue , and central venous catheter - related infections . in the case of the remaining 111 cases , contamination could be the source of cns . among rarely isolated pathogens , listeria sp . was identified from one patient with acute myeloid leukemia ( aml ) due to second relapse in 2006 . the patient had clinically documented pneumonia and was treated with ampicillin . in 2006 and 2008 , blood culture sample was taken from peripheral vein . in this case , the patient was treated empirically with levofloxacin . the other patient suffered from relapsed hodgkin lymphoma and was treated according to eshap chemotherapeutic regimen ( combination of high - dose cytosine - arabinosid , methylprednisolone , cisplatin , and etoposide ) through the central venous line . two pairs of blood culture samples were taken due to febrile episode from catheter , and b. cepacea was grown from each samples . n. farcinica was isolated from a patient with large granular lymphocytic ( lgl ) leukemia . he underwent six cycles of combined chemotherapeutic treatment ( cyclophosphamide , vincristine , and prednisolone ) and later had long term steroid therapy due to coombs positive hemolytic anemia and active hemolytic events . on hospital admission , ct scan showed multiple lesions with perifocal oedema , but stereotactic core biopsy from lesions could not be performed because of the patient s severe clinical status . from one pair of blood culture , n. farcinica was isolated , but the patient died before adequate therapy could start . during the examined period , four cases of bacteremia caused by fusobacterium nucleatum two patients had acute myeloid leukemia , one patient had acute myelomonocytic leukemia , and one patient suffered from pre - b - cell lymphoblastic leukemia . two patients received chemotherapy before positive blood culture ; one of them had oral mucositis associated with the applied chemotherapy . this may have influence on the applied chemotherapy ; dose reduction or treatment delays can be observed frequently when febrile neutropenia is present , and this also has unfavorable long - term outcome in otherwise curable malignancy . bloodstream infections are among the most important bacterial infections , despite the development in the field of microbiological diagnosis and antimicrobial therapy ; these infections are responsible for the large proportion of nosocomial infections worldwide . in the early 1960s , the importance of bloodstream infection in neutropenic patients had been recognized ; thus , empirical treatment protocols were established for mainly gram - negative bacteria . later , the spectrum of pathogens associated with bsi shifted from gram - negative bacteria to gram - positive bacteria due to the increased use of antibiotic prophylaxis and indwelling catheters allowing colonizations and infections with the skin flora . nowadays , the most common pathogens isolated from blood are coagulase - negative staphylococci and various antibiotic - resistant bacteria . in the majority of cases , the source of these infections is unknown in spite of various efforts to find them . recognition of changes in the epidemiology of bsis is very important to modify the antibiotic policy because , on the basis of these findings , we can reduce the infection - related morbidity and mortality [ 15 , 16 ] . during the four - year study period , the incidence of bacteremia was 20.4% . showed that the incidence of bacteremia was 23% when they examined over two thousand patients with febrile neutropenia in cancer patients , while viscoli et al . found that bacteremia occurred in 29% of patients with febrile neutropenia [ 17 , 18 ] . our findings correlated with the abovementioned literature data because , from the majority of blood culture bottles ( 13.7% ) , gram - positive bacteria were isolated . sixty - five percent of gram - positive bacteria belonged to coagulase - negative staphylococci . however , in a study by winston et al . in north america , gram - negative bacteria ( 55.6% )   were responsible for the majority of bacteremia in febrile neutropenic patients . at the same time , other authors from italy or france showed that the most important isolates in neutropenic patients are gram - positive bacteria , including coagulase - negative staphylococci or streptococci , while gram - negative organisms including e. coli or klebsiella spp . and p. aeruginosa constitute smaller portion of the isolates [ 20 , 21 ] . in our case , the most frequently used empirical treatment in this patient group is piperacillin  tazobactam or , if the patient has colitis or the possibility of abdominal infection is arisen , imipenem or meropenem is the frequently used antibiotic . thus , the increased incidence of gram - positive bacteria can be explained by the applied empirical antibiotic treatment , while the presence of coagulase - negative staphylococci could be attributed to the frequently used central venous catheters . the incidence of bacterial species in blood cultures can be influenced by the applied chemotherapy . in our case , 30% of patients with acute leukemia received high - dose ara - c chemotherapy , and 15% and 12% of patients were treated with fludarabin and ara - c plus idarubicin , respectively . on the basis of literature data , increasing prevalence of gram - positive cocci in febrile neutropenic patients could be observed after highdose cytarabine chemotherapy ; this was confirmed by our results . showed that the prevalence of staphylococci is higher than the prevalence of streptococci and enterococci in febrile neutropenic patients . similarly , our results confirmed this because , among gram - positive bacteria , the majority of the isolated strains were coagulase - negative staphylococci ; 6.7% and only 2.4% of gram - positive bacteria belonged to enterococcus spp . and -hemolytic streptococci , respectively . a total of 331 blood culture samples proved to be positive for coagulase - negative staphylococci and were collected from 161 febrile episodes of 149 patients . in 50 febrile neutropenic episodes , coagulase - negative staphylococci were relevant pathogen of fever because of the coexistence of skin , soft tissue , and central venous catheter - related infection . the remaining 111 cases were supposed to be contamination . from 32.9% of positive blood cultures bottles , gram - negative bacteria were cultured ; the majority of these proved to be positive for e. coli ( 52% ) . the second most common isolate was p. aeruginosa ( 14% ) , while the third one was klebsiella spp . in this review , the results of four articles were analyzed , and , among gram - negative organisms , the most important pathogens were also e. coli , klebsiella spp . , and p. aeruginosa . among rarely isolated bacteria , achromobacter xylosoxidans and burkholderia cepacia are usually associated with catheter - related sepsis , while s. maltophilia can cause mainly nosocomial bacteremia   and the possible source of haemophilus influenzae , neisseria spp . , and gemella spp . because of the possible presence of unusual pathogens , such as anaerobic bacteria or fastidious microorganisms , the use of various blood culture bottles including anaerobic bottles should be considered . because of its rapid progression of infection in febrile neutropenic patients and difficulties in distinguishing infection from noninfected patients on the basis of clinical presentation in this patient group , the use of empirical antibiotic treatment is essential and may provide the possibility to reach better outcome .
from year to year , it is important to get an overview of the occurrence of causative agents in febrile neutropenic patients to determine the empiric treatment . 
 thus our aims were to evaluate a four - year period regarding the prevalence of bloodstream infections and the most important causative agents . during this period , 
 1,361 patients were treated in our hematology ward because of various hematological disorders . 
 812 febrile episodes were recorded in 469 patients . at that time , 3,714 blood culture ( bc ) bottles were sent for microbiological investigations , 759 of them gave positive signal . from the majority of positive blood culture bottles ( 67.1% ) , 
 gram - positive bacteria , mainly coagulase - negative staphylococci ( cns ) , were grown . 
 gram - negative bacteria were isolated from 32.9% of the positive blood culture bottles , in these cases the leading pathogen was escherichia coli . 
 the high prevalence of cns was attributed to mainly contamination , while lower positivity rate for gram - negative bacteria was associated with the use of broad - spectrum empiric antibiotic treatment .