Enhanced detection of bacteremia with a new BACTEC resin blood culture medium.

In this multicenter study, 621 sets of blood culture specimens were drawn from 280 patients who were suspected of being septic and who were receiving antimicrobial therapy. Equal volumes of each specimen were inoculated into BACTEC 6B and 16B media. The 16B medium contained adsorbent and cationic resins for neutralizing the effects of the drugs. Of the 621 sets drawn, there were 72 positive cultures in 16B and 52 positive cultures in 6B. In 23 cases the organism was detected only in the 16B medium, and in 3 cases the organism was detected in 6B only. The remaining 49 positives were detected in both culture bottles. In 13 of these 49 cultures, detection in 16B was made between 1 and 5 days earlier than in 6B, whereas 3 of 49 specimens were detected 1 day earlier in 6B; the remaining 33 cultures became positive at approximately the same time in both media. There were a total of 43 patients with positive cultures in this study. Of these patients, 28 had sepsis detected in both the 16B and 6B media. The 6B medium alone detected an additional three cases of sepsis, and the 16B resin medium alone identified 12 additional cases. Supplementary culturing of samples from patients receiving antimicrobial therapy significantly increased the number of positive cultures and positive patients, as well as significantly shortening the time to positivity in these cultures.

Isolation of Legionella pneumophila from clinical specimens: salutary effects of lung tissue dilution.

Diagnosis of legionnaires' disease is seldom confirmed by isolation of Legionella pneumophila. In 2 cases, isolates were obtained using inoculums of diluted lung tissue suspension, even though no growth ocurred when undiluted suspensions were used. It is speculated that tissue dilution decreases the concentration of antimicrobial agents and antibacterial properties associated with lung host defense mechanisms, which allows improved recovery rates. This technique is recommended when attempting isolation of L. pneumophila from clinical specimens.

Effect of blood dilution on recovery of organisms from clinical blood cultures in medium containing sodium polyanethol sulfonate.

This clinical study was designed to evaluate the standard laboratory protocol that requires blood specimens be diluted with greater than or equal to 10 volumes of media. Blood was collected from hospitalized patients, and 1 ml was inoculated into each of three vials containing 2.3, 7.3, and 24 ml of BACTEC 6B aerobic medium resulting in dilutions of 1:4, 1:10, and 1:30, respectively. The three test vials were treated identically, and the study was carried out at four hospitals. Of the 2,550 sets of vials inoculated, 174 were positive with clinically significant isolates from 105 patients. There was no difference in the number of positive cultures recovered by 24 h (67%) or 48 h (90%) from any dilution. These percentages agreed with other reports from BACTEC users. The number of positive vials (139, 144, 147, respectively) at each dilution was not significantly different, indicating that all three dilutions showed equal recovery of pathogenic microorganisms. Despite this overall equality, two patients, one on antibiotic therapy, were found to have correlated cultures which failed to grow at the 1:4 dilution. This finding implies that a 1:4 dilution of blood cannot be recommended unequivocably despite the higher overall recovery rate of positive cultures.