Effect of broad- and narrow-spectrum antimicrobials on Clostridium difficile and microbial diversity in a model of the distal colon

Abstract

Vancomycin, metronidazole, and the bacteriocin lacticin 3147 are active against a wide range of bacterial species, including Clostridium difficile. We demonstrate that, in a human distal colon model, the addition of each of the three antimicrobials resulted in a significant decrease in numbers of C. difficile. However, their therapeutic use in the gastrointestinal tract may be compromised by their broad spectrum of activity, which would be expected to significantly impact on other members of the human gut microbiota. We used high-throughput pyrosequencing to compare the effect of each antimicrobial on the composition of the microbiota. All three treatments resulted in a decrease in the proportion of sequences assigned to the phyla Firmicutes and Bacteroidetes, with a corresponding increase in those assigned to members of the Proteobacteria. One possible means of avoiding such "collateral damage" would involve the application of a narrow-spectrum antimicrobial with specific anti-C. difficile activity. We tested this hypothesis using thuricin CD, a narrow-spectrum bacteriocin produced by Bacillus thuringiensis, which is active against C. difficile. The results demonstrated that this bacteriocin was equally effective at killing C. difficile in the distal colon model but had no significant impact on the composition of the microbiota. This offers the possibility of developing a targeted approach to eliminating C. difficile in the colon, without collateral damage.

Fig. 1.

Effect of antimicrobials on levels of C. difficile in a model of the human distal colon. (A) Antimicrobials were administered at three time points (0, 8, and 16 h) [control, open circles; vancomycin (90 μM), black squares; metronidazole (90 μM), black circles; lacticin 3147 (270 μM), open diamonds; thuricin (90 μM), open squares]. (B) Activity (measured as zones of inhibition from a fecal cell-free supernatant in a lawn of C. difficile) recovered from colonic model at indicated time points.

Fig. 2.

Phylum level diversity of gut communities in a model of the distal colon, expressed as percentage of total population of assignable tags. Other phyla: Actinobacteria, Spirochaetes, Lentisphaerae, and Tenericutes.

Fig. 3.

Effect of thuricin CD (white squares), vancomycin (black squares), and metronidazole (black circles) on C. difficile ribotypes in RCM at 37 °C (control, open circles).

Fig. 4.

Family-level taxonomic distribution of the microbial communities present in model of the distal colon, expressed as percentage of total assignable sequences.