When cultures are negative despite clinical evidence of infection, patients are commonly treated with broad empiric antibiotic regimens. However, when cultures do return a potential pathogen, antimicrobial treatment is typically narrowed to target the organism recovered in culture. PCR combined with electrospray ionization and mass spectrometry (PCR/ESI-MS) has proven efficacy for detection of bacteria not recovered in culture when patients have a history of ongoing or prior antibiotic treatment. We sought to test the role of PCR/ESI-MS in CSF and sterile pleural fluid specimens obtained from patients receiving antimicrobial treatment for confirmed or presumed infection for detection of occult bacterial pathogens not recovered in culture.
IRB approval was obtained for testing of Culture positive CSF and pleural fluid samples by PCR/ESI-MS. Gram stain and conventional aerobic and anaerobic cultures (SHEL Lab Bactron II anaerobic chamber) were performed. PCR/ESI-MS employed a research multiplex PCR assay for detection of all known bacteria.
57 patients who had pleural fluid or CSF submitted to the diagnostic microbiology lab for culture following initiation of antimicrobial treatment were enrolled in our study. All specimens were obtained after at least one dose of antibiotic treatment. Only 7 patients had positive cultures (6 pleural fluids; 1 CSF). PCR-ESI-MS detected all organisms found in culture for all cases. In 3 cases PCR/ESI/MS detected unrecognized pathogens (Table 1).
|Pleural Fluid||MRSA||MRSA & H. influenzae|
|Pleural Fluid||E. faecalis & Bacteroides thetaiotaomicron||E. faecalis & Bacteroides thetaiotaomicron|
|Pleural Fluid||S. intermedius||S. intermedius & Fusobacterium nucleatum|
|CSF||S. intermedius||S. intermedius & Fusobacterium nucleatum & Actinomyces meyeri|
PCR/ESI-MS demonstrated unrecognized secondary pathogens in 3/7 (43%) of patients with culture confirmed infection. H. influenzae as well as strict anaerobes such as F. nucleatum and A. meyeri may not grow in culture (even with appropriate media and equipment), but may be significant pathogens. Recognition of the presence of these pathogens would likely impact clinicians decisions regarding antimicrobial treatment.
K. Lowery, Ibis Biosciences: Employee , Salary
R. Sampath, Abbott: Employee , Salary
R. Bonomo, None