A note on positive BACTEC readings produced by Mycoplasma

Evaluation of BacT/ALERT system for detection of Mycoplasma hominis in simulated blood cultures

We used simulated blood cultures inoculated with clinical isolates of Mycoplasma hominis to determine whether liquid media of the BacT/ALERT (Organon Teknika, Durham, N.C.) will support growth of this fastidious organism and whether its presence can generate a positive signal with the instrument. Viability of clinical isolates of M. hominis was maintained for 7 days in BacT/ALERT media, and organisms were able to multiply when 1% gelatin was added to neutralize the mycoplasmastatic effects of the sodium polyanetholsulfonate anticoagulant. Without the addition of gelatin to BacT/ALERT bottles, the mycoplasmas declined in numbers or became completely nonviable. Mycoplasmal growth was further enhanced in BacT/ALERT PF both supplemented with gelatin, arginine, and DNA in comparison to broth with only gelatin added. No BacT/ALERT bottles containing M. hominis in simulated blood cultures were flagged positive by the instrument, despite growth of microorganisms of up to 10(7) CFU/ml after incubation for up to 7 days, suggesting that inadequate CO(2) production or some other mechanism prevents the instrument from recognizing the presence of the organism and its metabolic products. The fastidious cultivation requirements and relatively slow growth of M. hominis warrant that dependence on automated systems and techniques designed to detect conventional bacteria will not be reliable for recovery of M. hominis and that specialized media and incubation conditions designed for optimum cultivation of mycoplasmas should be employed when this organism is suspected on clinical grounds.

Update on detection of bacteremia and fungemia

The presence of microorganisms in a patient's blood is a critical determinant of the severity of the patient's illness. Equally important, the laboratory isolation and identification of a microorganism present in blood determine the etiologic agent of infection, especially when the site of infection is localized and difficult to access. This review addresses the pathophysiology and clinical characteristics of bacteremia, fungemia, and sepsis; diagnostic strategies and critical factors in the detection of positive blood cultures; characteristics of manual and instrument approaches to bacteremia detection; approaches for isolating specific microorganisms associated with positive blood cultures; and rapid methods for the identification of microorganisms in blood cultures.

Detection of Mycoplasma hominis septicemia by radiometric blood culture

The ease with which Mycoplasma hominis can be recovered and the frequency of its occurrence in septicemia may not be fully appreciated. We detected the growth of M. hominis radiometrically with an automated blood culture instrument. The organism grew in both aerobic and anaerobic culture media, but the cultures were not visibly positive. It was necessary to stain the cultures with acridine orange to visualize M. hominis and to subculture them on Columbia base sheep blood agar to confirm the positive growth index indicated by the instrument. Sodium polyanetholesulfonate inhibited the growth of M. hominis and is not recommended for use as the anticoagulant when blood is cultured for Mycoplasma spp.