Olga Mihaela Dorobăţ, Al. Rafila
Institutul Naţional de Boli Infecţioase “Prof. Dr. Matei Balş”, Bucureşti
Abstract
The detection of bloodstream infections (BSI) is one of the most important tasks performed in clinical microbiology laboratory. Rapid and reliable detection of BSI includes identification of pathogens at species level and determination of antibiotic susceptibility patterns which are crucial because: patients can be treated with appropriate antimicrobial agents; the prognosis of the patient can be improved and the acquisition of resistance of the pathogen may be reduced; overall hospital costs for medical care will be reduced. Considerable efforts have been made to develop rapid, sensitive and specific assays for the detection of causative organism. Current automated continuous monitoring blood-culture systems permit a more rapid detection of bacteremia and fungemia comparative with manual methods. An overnight agar medium subculture from positive blood-culture bottle is the initial step for identification and antimicrobial susceptibility testing (AST) of pathogens causing bacteremia. This conventional culture method is time-consuming and several days are usually needed for microbial recovery, identification and AST. Automated systems for the identification and AST are able to generate accurate results in 2 to 12 h. Direct identification from positive blood-culture bottles in automated systems showed a variable correlation rate compared with standard method (31 to 96%). Direct AST performed from positive blood-culture bottles, using automated systems, like Phoenix, VITEK and VITEK 2, Sensititre, MicroScan and MICRONAUT, with a pre-determined dilution protocol, provides accurate results for most organism-antibiotic combination. New techniques have been introduced in last years for early diagnostic of bacterial infections by identifying bacterial genome. Rapid identification (4-5h) by new Genotyping technology (DNA strip) is now possible for many species of Gram negative rods and Gram positive bacteria together with the determination of methicillin, penicillin, vancomycin, erythromycin and aminoglycoside resistance. rRNA assay in blood cultures is highly sensitive (100%) and specific (96%). Real time PCR for nuc gene encoding nuclease and mec A gene encoding for methicillin resistance from blood-culture bottles yields a rapid identification (2-3h) of S. aureus and coagulase-negative staphylococci, including those methicillin-resistant.