Advantages of BACTEC hypertonic culture medium for detection of Haemophilus influenzae bacteremia in children

Enhanced detection of Candida in blood cultures with the BACTEC 460 system by use of the aerobic-hypertonic (8B) medium

The blood culture records during the 6-year period 1984-9 were reviewed to compare the performance of the BACTEC aerobic (6B) and aerobic-hypertonic (8B) media for the recovery of Candida spp. and Torulopsis glabrata from blood. There were 137 positive blood culture sets that contained both a 6B and an 8B bottle. Sixty-eight different yeasts were recovered from 65 patients including 35 Candida albicans, 19 C. tropicalis, 6 C. parapsilosis, 4 C. krusei, 1 C. pseudotropicalis and 3 Torulopsis glabrata. The 8B medium detected 120 of the positive cultures (87.6%) and was the only positive medium in 35 (25.6%) sets, while the 6B medium detected 102 positive cultures (74.4%) and was the only positive medium in 17 (12.4%) sets (P less than 0.04). For those sets in which both bottles were positive, radiometric detection occurred first in the 8B bottle in 39 sets and first in the 6B bottle in 11 sets (P less than 0.001). The superior performance of the 8B bottle was not related to the administration of amphotericin B. Cultures of stock strains of C. albicans, C. tropicalis, and C. parapsilosis in 6B and 8B media with and without added blood confirmed the finding that 8B was substantially superior to 6B for the detection of candidaemia. It is concluded that an 8B bottle should be included in the blood culture set whenever candidaemia is suspected.

Comparative evaluation of radiometric tryptic soy broth versus radiometric tryptic soy broth with 10% sucrose for detection of bacteremia and fungemia in pediatric patients

We compared BACTEC radiometric blood culture media with (8B) and without (6B) 10% sucrose for the detection of bacteremia and fungemia in pediatric patients at four university teaching hospitals that used identical methods for obtaining and processing specimens. Overall, the yields of microorganisms from 5,714 blood culture sets were no different in the two media, although a trend was noted favoring 6B for the detection of pneumococci. Speed of detection of positive results was faster in the 6B than in the 8B medium (P less than 0.05), largely due to the faster detection of Staphylococcus aureus in the 6B medium. We conclude that, overall, with pediatric patients the hypertonic 8B radiometric medium has no advantage and that it possibly has a modest disadvantage, compared with isotonic 6B radiometric medium.

Detection of bloodstream infections in children

A critical responsibility of the clinical microbiology laboratory serving clinicians who care for infected children is accurate and timely detection of bacteremia. Blood culture protocols which are suitable for processing adult specimens are not necessarily the first choice for processing pediatric specimens. In this review, the following aspects of detection of bacteremia in children are covered: obtaining blood culture specimens from children, including skin disinfection, specimen volume and timing of specimen collection; the array of blood culture methods available, focusing upon conventional, radiometric, infrared spectroscopic and manometric broth cultures, as well as biphasic agar/broth and lysis direct plating techniques: the strengths and weaknesses of the various methods; and recommendations to laboratories for selection of a blood culture method based upon the laboratory's staffing level.

Endocarditis from a dental focus. Importance of oral hygiene in valvar heart disease

Fastidiously growing bacteria more and more are recognised as a source of infectious endocarditis. Over recent years, three new cases of endocarditis caused by Actinobacillus actinomycetemcomitans were diagnosed in our institution. The rise in frequency is possibly secondary to better laboratory skills. Two patients with Actinobacillus (Haemophilus) actinomycetemcomitans endocarditis presented the classical history of preexisting valvar disease together with poor dental hygiene. The third patient had no congenital or rheumatic preexisting lesion to the valves. The distal part of a ventriculo-atrial drainage device had caused microtrauma to the tricuspid valve. The right-sided endocarditis in this patient was complicated by pulmonary septic emboli. Dental origin of the infection was very likely in this patient too. No dental procedure had been performed in the months preceding the endocarditis of our three patients. They presented endocarditis with an oral microorganism in the absence of any dental manipulation. All three had very poor dental hygiene. Better dental care could possibly have prevented this serious complication.

Comparison of radiometric and conventional culture systems in detecting Haemophilus influenzae type b bacteremia in rats

To compare the efficiency of detecting Haemophilus influenzae type b bacteremia by the BACTEC radiometric system (RS; Johnston Laboratories, Inc., Towson, Md.) and a conventional Trypticase soy broth (BBL Microbiology Systems, Cockeysville, Md.) blood culture system (TSB), we developed an in vivo model of bacteremia in rats. After intravenous injection of 50 to 200 CFU into adult rats, there was a linear logarithmic increase in CFU per milliliter of rat blood during the first 10 h (r = 0.98), allowing accurate prediction of the level of bacteremia with time. Culture bottles were inoculated with 0.5 ml of blood obtained by cardiac puncture and processed as clinical samples in the microbiology laboratory with our RS and conventional protocols. We found the following. (i) The first detection of bacteremia by RS was similar to that by TSB if a Gram stain of the TSB was done on day 1 and was superior if that smear was omitted (P less than 0.01). (ii) The detection times in both systems were comparable at different magnitudes of bacteremia (10(1) to 10(4) CFU/ml). (iii) Supplementation of inoculated bottles with 2 ml of sterile rat blood interfered with Gram stain detection in TSB but resulted in increased 14CO2 production in RS. (iv) No difference in detection time was found between RS and TSB for four different clinical isolates. These studies show that, in a biologically relevant model, the detection of positive blood cultures for H. influenzae type b by RS was comparable to or better than detection by TSB when blood was processed analogously to clinical specimens.

Laboratory experience with radiometric detection of bacteremia with three culture media

In two long-term studies, the BACTEC radiometric system for detection of bacteremia was evaluated with three culture media each: (i) BACTEC media 6A (for aerobes) and 7B (for anaerobes) plus a thioglycolate medium and (ii) BACTEC media 6A, 7B, and 8A (hypertonic). In study 1, clinically significant isolates were identified in 1,873 (13.9%) of 13,432 blood cultures with all three media. The thioglycolate medium revealed 143 (1.1%) organisms not recovered from the 6A and 7B media. In study 2, isolates were identified in 1,135 (12.9%) of 8,759 cultures with all three media; 104 (1.2%) organisms were isolated only from the hypertonic medium. The increased yield of positive cultures in the three-medium system is likely due to the larger volume of blood cultured.