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The soil saprophyte Bacillus cereus forms biofilms at solid-liquid interfaces. The composition of the extracellular polymeric matrix is not known, but biofilms of other bacteria are encased in polysaccharides, protein, and also extracellular DNA (eDNA). A Tn917 screen for strains impaired in biofilm formation at a solid-liquid interface yielded several mutants. Three mutants deficient in the purine biosynthesis genes purA, purC, and purL were biofilm impaired, but they grew planktonically like the wild type in Luria-Bertani broth. Biofilm populations had higher purA, purC, and purL transcript ratios than planktonic cultures, as measured by real-time PCR. Laser scanning confocal microscopy (LSCM) of BacLight-stained samples indicated that there were nucleic acids in the cell-associated matrix. This eDNA could be mobilized off the biofilm into an agarose gel matrix through electrophoresis, and it was a substrate for DNase. Glass surfaces exposed to exponentially growing populations acquired a DNA-containing conditioning film, as indicated by LSCM. Planktonic exponential-phase cells released DNA into an agarose gel matrix through electrophoresis, while stationary-phase populations did not do this. DNase treatment of planktonic exponential-phase populations rendered cells more susceptible than control populations to the DNA-interacting antibiotic actinomycin D. Exponential-phase purA cells did not contain detectable eDNA, nor did they convey a DNA-containing conditioning film to the glass surface. These results indicate that exponential-phase cells of B. cereus ATCC 14579 are decorated with eDNA and that biofilm formation requires DNA as part of the extracellular polymeric matrix.

We conducted a single-center, randomized, placebo-controlled trial to determine whether streptokinase instillations adjunctive to chest tube drainage reduce the need for surgery and improve outcome in patients with pleural empyema. Fifty-three patients (frank pus aspirated, 81%; microbiological agent cultured, 62%; mean effusion pH, 6.6 +/- 0.4) received antibiotic treatment, chest tube drainage, and once-daily pleural rinses with either normal saline or normal saline with streptokinase (250,000 IU). Nine patients were excluded for various reasons before pleural rinses were started. Streptokinase (n = 22) was instilled over 4.5 +/- 2 days and saline (n = 22) was instilled over 3 +/- 1.3 days. One patient in each group died during treatment. Clinical treatment success and need for referral to surgery were the main outcome measures. No difference was observed after 3 days. After 7 days, streptokinase-treated patients had a higher clinical success rate (82 vs. 48%, p = 0.01) and fewer referrals for surgery (45 vs. 9%, p = 0.02). No significant radiologic or functional differences were observed between groups during follow-up over 6 months. We conclude that intrapleural streptokinase adjunctive to chest tube drainage reduces the need for surgery and improves the clinical treatment success in patients with pleural empyema.

The ability to quantify the number and kinds of microorganisms within a community is fundamental to the understanding of the structure and function of an ecosystem. The simple morphology of most microbes provides few clues for their identification and physiological traits are often ambiguous. In addition, many organisms resist cultivation, which is essential to their characterization. Recombinant DNA techniques have provided a means whereby many of the obstacles associated with cultivation and description can be overcome and subsequently has allowed many new insights into the complexity of natural microbial communities. Molecular approaches based on 16S ribosomal RNA (rRNA) sequence analysis allow direct investigation of the community structure, diversity, and phylogeny of microorganisms in almost any environment, while quantification of the individual types of microorganisms or entire microbial communities may be addressed by nucleic acid hybridization techniques. Furthermore, the use of fluorescently labeled population-specific rRNA probes allows microscopic examination of individual cells in complex microbial assemblages as well as their interactions in situ. In this review, we discuss strategies for characterizing microbial communities without the need for cultivation.