Abstract
The activities of OPT-80 against 453 intestinal bacteria were compared with those of seven other drugs. OPT-80 showed good activity against most clostridia, staphylococci, and enterococci, but streptococci, aerobic and facultative gram-negative rods, anaerobic gram-negative rods, and Clostridium ramosum were resistant. Poor activity against anaerobic gram-negative rods may maintain colonization resistance.
Drugs that are poorly absorbed orally may have a place in therapy for intestinal infections and in certain other situations in which intestinal bacteria may play a role (7). It is also important to note the activity of such drugs against members of the bowel flora that might confer colonization resistance (19). Vancomycin is used systemically for therapy of severe or multiresistant gram-positive infections and orally for Clostridium difficile infections. Although the drug is highly effective against those infections, vancomycin resistance has been observed in various organisms, including enterococci, Lactobacillus spp., Leuconostoc spp., Pediococcus spp., and staphylococci (4, 9, 15, 17). Such gram-positive organisms are often resistant to other agents as well (8).
OPT-80 is an 18-membered macrocyclic antibiotic, also known as tiacumicin B, that, like vancomycin, targets gram-positive organisms (16, 18). It is currently under development as a new, narrow-spectrum antibacterial agent to treat C. difficile-associated diarrhea (CDAD) and colitis. Toxigenic C. difficile is the causative agent in 20% of cases of antibiotic-associated diarrhea (2) and is the principal cause of antibiotic-associated colitis. Current treatments for this disease include oral vancomycin and metronidazole, but both of these drugs have a relatively broad spectrum and may exacerbate disruption of gut flora that led to CDAD originally. Indeed, a major drawback to both treatments is the incidence of recurrence of CDAD, which is approximately 20% (5). A unique feature of OPT-80 is its selectivity for Clostridium, particularly C. difficile and Clostridium perfringens; previous work has shown that the MIC for C. difficile is approximately 10- to 100-fold lower than those for other organisms, including other gram-positive organisms (1, 16, 18). OPT-80 is also primarily retained in the gut, with low levels in serum following oral administration in hamsters (16), rats, monkeys, and humans (Optimer Pharmaceuticals, personal communication).
This study was designed to evaluate the in vitro activity of OPT-80 and comparator agents against intestinal bacteria. Antimicrobial concentration ranges were selected to encompass or surpass the levels that would be achieved in the gut (to the extent that this information is available), subject to the limitations of solubility of the drugs in the testing medium. Table 1 is a summary of the range of concentrations of antimicrobial agents used during testing and the levels achieved in the bowel or feces (6, 11, 12).
TABLE 1.
Summary of drug concentrations tested and fecal drug levels reported previouslya
| Drug | Fecal drug levels (μg/g)b | Range of conc tested |
|---|---|---|
| Amoxicillin-clavulanate | 25-250 (?) | 0.03-128 |
| Ciprofloxacin | 890 | 0.03-512 |
| Clindamycin | >200 (increases up to day 5 of therapy) | 0.03-512 |
| Linezolid | 9% of dose excreted in feces as inactive metabolites | 0.25-128 |
| Metronidazole | 0-23; 2-3 | 0.25-128 |
| OPT-80 | 3,000 on 450-mg/day dosec; dosage not yet finalized | 0.03-1,024 |
| Tobramycin | 1,000-3,000 (?) | 0.25-1,024 |
| Vancomycin | 1,000-8,000 | 0.5-1,024 |
The bacteria included in this study were mostly recent isolates representative of the indigenous bowel flora. Bacteria were identified according to established procedures (10), supplemented in a number of cases by 16S rRNA sequence analysis. Drug MICs for anaerobes were determined by the NCCLS-approved Wadsworth agar dilution technique (14). Aerobic and facultative bacteria were tested according to NCCLS guidelines (13), using Mueller-Hinton (Sigma, St. Louis, Mo.) agar without blood except for Streptococcus mitis and Streptococcus sanguinis, for which 5% fresh sheep blood was added. The antimicrobial agents tested were obtained as powders from the following companies: amoxicillin, clindamycin, metronidazole, tobramycin, and vancomycin from Sigma; lithium clavulanate from GlaxoSmithKline (King of Prussia, Pa.); linezolid from Pfizer (Groton, Conn.); ciprofloxacin from ICN Biomedicals (Irvine, Calif.); and OPT-80 from Optimer Pharmaceuticals, Inc. (San Diego, Calif.).
For analysis, the bacteria tested were generally placed into genus, species, or other groups with at least 10 isolates. The ranges and the MICs at which 50 and 90% of isolates were inhibited were determined except for organisms with fewer than 10 strains tested, for which only the ranges are reported (Table 2).
TABLE 2.
In vitro activity of Optimer-80 and six comparative agents against 453 bacterial isolates
| Bacterial group (na) | Antimicrobial agent | MICc
|
Range | |
|---|---|---|---|---|
| 50% | 90% | |||
| Bacteroides fragilis group spp.b (50) | Amoxicillin-clavulanate | 1 | 16 | 0.50-32 |
| Ciprofloxacin | 16 | 128 | 8-256 | |
| Clindamycin | 4 | >128 | 0.50->128 | |
| Linezolid | 4 | 8 | 2.0-8 | |
| Metronidazole | 1 | 4 | 0.25-16 | |
| Optimer-80 | 256 | >1,024 | 256->1,024 | |
| Tobramycin | 256 | >1,024 | 256->1,024 | |
| Vancomycin | 64 | 128 | 16-256 | |
| Veillonella spp. (10) | Amoxicillin-clavulanate | 0.5 | 1 | 0.25-1 |
| Clindamycin | 0.5 | 0.5 | 0.5 | |
| Linezolid | 2 | 2 | 1.0-2 | |
| Metronidazole | 2 | 2 | 2 | |
| Optimer-80 | 32 | 128 | 16-128 | |
| Tobramycin | 16 | 64 | 8.0-64 | |
| Vancomycin | 512 | 512 | 128->1,024 | |
| Other anaerobic gram-negative rodsd (51) | Amoxicillin-clavulanate | 1 | 2 | 0.12-16 |
| Ciprofloxacin | 1 | 8 | 0.25-32 | |
| Clindamycin | 0.5 | 8 | 0.5->128 | |
| Linezolid | 1 | 2 | 0.5-4 | |
| Metronidazole | 0.25 | 4 | 0.25->128 | |
| Optimer-80 | 1,024 | >1,024 | 0.06->1,024 | |
| Tobramycin | 128 | >1,024 | 1->1,024 | |
| Vancomycin | 512 | >1,024 | 0.5->1,024 | |
| All anaerobic gram-negative species (111) | Amoxicillin-clavulanate | 1 | 8 | 0.12-32 |
| Ciprofloxacin | 1 | 32 | 0.25-256 | |
| Clindamycin | 0.5 | >128 | 0.5->128 | |
| Linezolid | 4 | 4 | 0.5-8 | |
| Metronidazole | 1 | 4 | 0.25->128 | |
| Optimer-80 | 256 | >1,024 | 0.06->1,024 | |
| Tobramycin | 256 | >1,024 | 1->1,024 | |
| Vancomycin | 128 | >1,024 | 0.5->1,024 | |
| Clostridium bifermentans (9) | Amoxicillin-clavulanate | 0.25-0.5 | ||
| Ciprofloxacin | 2.0-8 | |||
| Clindamycin | 0.5 | |||
| Linezolid | 1.0 | |||
| Metronidazole | 0.25-1 | |||
| Optimer-80 | 0.06 | |||
| Tobramycin | 4-256 | |||
| Vancomycin | 1.0 | |||
| Clostridium bolteae (7) | Amoxicillin-clavulanate | 0.5-32 | ||
| Ciprofloxacin | 8.0-64 | |||
| Clindamycin | 0.5-2 | |||
| Linezolid | 4.0 | |||
| Metronidazole | 0.25-1 | |||
| Optimer-80 | 1-64 | |||
| Tobramycin | 8-128 | |||
| Vancomycin | 1.0-16 | |||
| Clostridium clostridioforme (4) | Amoxicillin-clavulanate | 1.0-16 | ||
| Ciprofloxacin | 32 | |||
| Clindamycin | 0.5 | |||
| Linezolid | 4.0 | |||
| Metronidazole | 0.25 | |||
| Optimer-80 | 4.0-128 | |||
| Tobramycin | 16-1,024 | |||
| Vancomycin | 1.0-8 | |||
| Clostridium difficile (23) | Amoxicillin-clavulanate | 2 | 4 | 0.5-8 |
| Ciprofloxacin | 8 | 32 | 1.0-64 | |
| Clindamycin | 2 | >128 | 0.5->128 | |
| Linezolid | 4 | 32 | 1.0-32 | |
| Metronidazole | 0.25 | 0.5 | 0.25-1 | |
| Optimer-80 | 0.12 | 0.25 | 0.06-2 | |
| Tobramycin | 512 | >1,024 | 64->1,024 | |
| Vancomycin | 1 | 2 | 0.5-4 | |
| Clostridium glycolicum (9) | Amoxicillin-clavulanate | 0.25-1 | ||
| Ciprofloxacin | 1.0-16 | |||
| Clindamycin | 0.5 | |||
| Linezolid | 1.0 | |||
| Metronidazole | 0.25-0.5 | |||
| Optimer-80 | 0.06-1 | |||
| Tobramycin | 16-256 | |||
| Vancomycin | 0.5-1 | |||
| Clostridium innocuum (9) | Amoxicillin-clavulanate | 0.5-1 | ||
| Ciprofloxacin | 2.0-8 | |||
| Clindamycin | 0.5->128 | |||
| Linezolid | 2.0-4 | |||
| Metronidazole | 0.25-1 | |||
| Optimer-80 | 32-128 | |||
| Tobramycin | >1,024 | |||
| Vancomycin | 8.0-16 | |||
| Clostridium paraputrificum (8) | Amoxicillin-clavulanate | 0.25-2 | ||
| Ciprofloxacin | 1.0-4 | |||
| Clindamycin | 0.5-4 | |||
| Linezolid | 0.5 | |||
| Metronidazole | 0.25-1 | |||
| Optimer-80 | 0.06-8 | |||
| Tobramycin | 32-512 | |||
| Vancomycin | 1-2 | |||
| Clostridium perfringens (14) | Amoxicillin-clavulanate | 0.25 | 0.25 | 0.25-0.5 |
| Ciprofloxacin | 0.5 | 1 | 0.25-1 | |
| Clindamycin | 0.5 | 2 | 0.5-2 | |
| Linezolid | 2 | 4 | 1.0-4 | |
| Metronidazole | 0.5 | 2 | 0.25-2 | |
| Optimer-80 | 0.062 | 0.062 | 0.06 | |
| Tobramycin | 256 | 1,024 | 1.0-1,024 | |
| Vancomycin | 1 | 1 | 0.5-1 | |
| Clostridium ramosum (10) | Amoxicillin-clavulanate | 0.5 | 0.5 | 0.25-0.5 |
| Ciprofloxacin | 16 | 16 | 4.0-16 | |
| Clindamycin | 1 | 4 | 1.0-8 | |
| Linezolid | 8 | 16 | 8.0-16 | |
| Metronidazole | 0.5 | 1 | 0.5-2 | |
| Optimer-80 | 512 | 512 | 256-512 | |
| Tobramycin | 256 | 256 | 128-256 | |
| Vancomycin | 4 | 8 | 4.0-8 | |
| Clostridium sordellii (5) | Amoxicillin-clavulanate | 0.25 | ||
| Ciprofloxacin | 0.25 | |||
| Clindamycin | 0.5-2 | |||
| Linezolid | 1.0 | |||
| Metronidazole | 0.5 | |||
| Optimer-80 | 0.06 | |||
| Tobramycin | 2.0-256 | |||
| Vancomycin | 1.0 | |||
| Other clostridial speciese (9) | Amoxicillin-clavulanate | 0.25-2 | ||
| Ciprofloxacin | 0.25-32 | |||
| Clindamycin | 0.5-2 | |||
| Linezolid | 1.0-4 | |||
| Metronidazole | 0.25->128 | |||
| Optimer-80 | 0.06->1,024 | |||
| Tobramycin | 0.25->1,024 | |||
| Vancomycin | 1.0-64 | |||
| All Clostridium species (107) | Amoxicillin-clavulanate | 0.5 | 4 | 0.25-32 |
| Ciprofloxacin | 8 | 32 | 0.25-64 | |
| Clindamycin | 0.5 | 8 | 0.5->128 | |
| Linezolid | 2 | 4 | 0.5-32 | |
| Metronidazole | 0.5 | 1 | 0.25->128 | |
| Optimer-80 | 0.062 | 128 | 0.06->1,024 | |
| Tobramycin | 256 | >1,024 | 0.25->1,024 | |
| Vancomycin | 1 | 16 | 0.5-64 | |
| Anaerobic non-spore-forming gram-positive rodsf (63) | Amoxicillin-clavulanate | 0.25 | 1 | 0.25-4 |
| Ciprofloxacin | 2 | 32 | 0.25-128 | |
| Clindamycin | 0.5 | 4 | 0.25->128 | |
| Linezolid | 0.5 | 2 | 0.5-4 | |
| Metronidazole | 4 | >128 | 0.25->128 | |
| Optimer-80 | 1 | 32 | 0.06->1,024 | |
| Tobramycin | 64 | 512 | 1.0->1,024 | |
| Vancomycin | 1 | 2 | 0.5->1,024 | |
| Anaerobic gram-positive coccig (49) | Amoxicillin-clavulanate | 0.25 | 1 | 0.25-32 |
| Ciprofloxacin | 1 | 32 | 0.25-64 | |
| Clindamycin | 0.5 | 4 | 0.5->128 | |
| Linezolid | 1 | 4 | 0.5-4 | |
| Metronidazole | 0.25 | 1 | 0.25-2 | |
| Optimer-80 | 0.5 | 2 | 0.06-1,024 | |
| Tobramycin | 16 | 256 | 1.0-1,024 | |
| Vancomycin | 1 | 1 | 0.5-8 | |
| All anaerobic gram-positive species (219) | Amoxicillin-clavulanate | 0.5 | 2 | 0.25-32 |
| Ciprofloxacin | 4 | 32 | 0.25-128 | |
| Clindamycin | 0.5 | 4 | 0.25->128 | |
| Linezolid | 1 | 4 | 0.5-32 | |
| Metronidazole | 0.5 | 128 | 0.25->128 | |
| Optimer-80 | 0.12 | 64 | 0.06->1,024 | |
| Tobramycin | 128 | >1,024 | 0.25->1,024 | |
| Vancomycin | 1 | 8 | 0.5->1,024 | |
| Streptococcus, formerly S. milleri grouph (14) | Amoxicillin-clavulanate | 0.5 | 1 | 0.25-1 |
| Ciprofloxacin | 0.5 | 0.5 | 0.5 | |
| Clindamycin | 1 | 4 | 0.5-4 | |
| Metronidazole | 64 | 128 | 64-128 | |
| Optimer-80 | 32 | 32 | 16-64 | |
| Tobramycin | 128 | 256 | 32-256 | |
| Vancomycin | 1 | 1 | 1.0 | |
| Other Streptococcus speciesi (9) | Amoxicillin-clavulanate | 0.03-4 | ||
| Ciprofloxacin | 0.5-4 | |||
| Clindamycin | 0.03->128 | |||
| Metronidazole | 256->256 | |||
| Optimer-80 | 16-128 | |||
| Tobramycin | 8.0-16 | |||
| Vancomycin | 0.5-1 | |||
| Enterococcus speciesj (21) | Amoxicillin-clavulanate | 1 | 2 | 0.5-128 |
| Ciprofloxacin | 4 | 128 | 2.0->128 | |
| Clindamycin | 16 | 512 | 8.0->512 | |
| Metronidazole | >1,024 | >1,024 | >1,024 | |
| Optimer-80 | 8 | 8 | 2.0-16 | |
| Tobramycin | 32 | >1,024 | 16->1,024 | |
| Vancomycin | 1 | 4 | 0.5-4 | |
| Staphylococcus aureus and Staphylococcus epidermidisk (19) | Amoxicillin-clavulanate | 0.5 | 2 | 0.12-16 |
| Ciprofloxacin | 0.5 | 1 | 0.03-16 | |
| Clindamycin | 0.25 | 0.25 | 0.12->512 | |
| Metronidazole | 256 | >1,024 | 128->1,024 | |
| Optimer-80 | 0.5 | 2 | 0.25-2 | |
| Tobramycin | 0.5 | 1 | 0.25-2 | |
| Vancomycin | 2 | 4 | 1.0-4 | |
| Total for all strains (453)l | Amoxicillin-clavulanate | 1 | 16 | 0.03->128 |
| Ciprofloxacin | 2 | 32 | 0.03-512 | |
| Clindamycin | 0.5 | 512 | 0.03->512 | |
| Linezolid | 2 | 4 | 0.5-32 | |
| Metronidazole | 1 | >1,024 | 0.25->1,024 | |
| Optimer-80 | 8 | 1,024 | 0.06->1,024 | |
| Tobramycin | 64 | >1,024 | 0.25->1,024 | |
| Vancomycin | 2 | >1,024 | 0.5->1,024 | |
n, number of strains tested.
Bacteroides distasonis (7), Bacteroides fragilis (13), Bacteroides ovatus (10), Bacteroides thetaiotaomicron (10), Bacteroides vulgatus (10).
Minimum inhibitory concentrations (MICs) are listed in micrograms/milliliter. 50%, MIC at which 50% of isolates tested were inhibited; 90%, MIC at which 90% of isolates tested were inhibited.
Bilophila wadsworthia (10), Fusobacterium mortiferum (3), Fusobacterium necrophorum (3), Fusobacterium nucleatum (4), Fusobacterium varium (2), Porphyromonas spp. (11), Prevotella spp. (8), Sutterella wadsworthensis (10).
Clostridium bartlettii (1), Clostridium butyricum (2), Clostridium disporicum (1), Clostridium hypermegas (1), Clostridium orbiscindens (1), Clostridium subterminale (1), Clostridium species (1), Clostridium tertium (1).
Actinomyces meyeri (1), Actinomyces odontolyticus (5), Actinomyces viscosus (2), Atopobium minutum (3), Bifidobacterium adolescentis (3), Bifidobacterium breve (1), Bifidobacterium dentium (2), Bifidobacterium species (3), Collinsella aerofaciens (7), Eggerthella lenta (5), Eubacterium biforme (1), Eubacterium cylindroides (1), Eubacterium limosum (5), Eubacterium saburreum (3), Lactobacillus catenaforme (1), Lactobacillus jensenii (4), Lactobactillus fermentum (1), Lactobacillus species (4), Propionibacterium avidum (1), Propionibacterium acnes (7), Propionibacterium propionicus (1), Propionibacterium species (2).
Anaerococcus prevotii (7), Anaerococcus tetradius (6), Finegoldia magna (7), Peptoniphilus asaccharolyticus (6), Peptostreptococcus anaerobius (7), Peptostreptococcus micros (6), Ruminococcus gnavus (4), Ruminococcus species (5), Ruminococcus torques (1).
Streptococcus anginosus (7), Streptococcus constellatus (4), Streptococcus intermedius (3).
Streptococcus mitis (3), Streptococcus salivarius (3), Streptococcus sanguinis (3).
Enterococcus avium (1), Enterococcus faecalis (14), Enterococcus faecium (6).
Staphylococcus aureus (9), Staphylococcus epidermidis (10).
Not all data are shown (data for 60 strains of aerobic or facultatively gram-negative bacilli are not shown).
Although vancomycin showed relatively poor activity against gram-negative anaerobes, including the Bacteroides fragilis group, these organisms are usually suppressed in the intestinal tract by the very high levels achieved in the bowel by oral administration (Finegold et al., unpublished data).
OPT-80 was distinctly less active against the B. fragilis group than vancomycin. Vancomycin had good activity against all clostridia, whereas OPT-80 had fairly good activity against Clostridium bolteae and Clostridium clostridioforme, fair activity against Clostridium innocuum, and relatively poor activity against C. ramosum. It is interesting that among the clostridia studied, susceptibility or resistance to OPT-80 correlated with the taxonomic clusters of clostridia (3) to which they belong. Clostridia that were very sensitive to OPT-80 were all in clostridial clusters I and XI; those that were less susceptible belong to clusters XIVa, XVI, and XVIII. Both OPT-80 and vancomycin had good activity against most anaerobic gram-positive non-spore-forming rods and anaerobic gram-positive cocci. Vancomycin had better activity against streptococci, both showed good activity against enterococci and staphylococci, and both had poor activity against nonanaerobic gram-negative bacilli (data for the latter group not shown).
C. difficile-associated colitis has generally responded well to therapy with vancomycin, metronidazole, or bacitracin, all administered orally; the current data indicate that it should respond well to oral OPT-80 as well, but studies on this are not available yet. Additional indications for therapy with some or all of the drugs in this study include neutropenic enterocolitis, intestinal colonization with vancomycin-resistant enterococci and staphylococci or antibiotic-resistant viridans group streptococci in an immunocompromised host, preoperative bowel preparation, d-lactic acidosis, bowel bacterial overgrowth syndrome, and investigational use in late-onset autism (7).
Factors that would help determine the relative utility of these various agents would include such things as usefulness of the compounds for therapy of serious systemic infections, levels of drug achieved in the gastrointestinal tract, maintenance of colonization resistance in the bowel, bactericidal activity, drug allergy, absorbability of the drugs with oral administration, gastrointestinal and systemic toxicity, frequency with which resistance develops, cross-resistance with other compounds (particularly those that are used systemically), frequency of dosage required, patient tolerance of the medication (over prolonged periods in the case of autism), palatability, ease of administration to young children (liquid preparation preferred), and cost. Clinical studies are needed to assess the clinical utility of the various drugs with good activity against intestinal bacteria in these situations.
Acknowledgments
This study was funded by Optimer Pharmaceuticals, Inc., San Diego, Calif., and Veterans Administration Merit Review research funds.
REFERENCES
- 1.Ackermann G., B. Loffler, D. Adler, and A. C. Rodloff. 2004. In vitro activity of OPT-80 against Clostridium difficile. Antimicrob. Agents Chemother. 48:2280-2282. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Bartlett, J. G. 1992. Antibiotic-associated diarrhea. Clin. Infect. Dis. 15:573-581. [DOI] [PubMed] [Google Scholar]
- 3.Collins, M. D., P. A. Lawson, A. Willems, J. J. Cordoba, J. Fernandez-Garayzabal, P. Garcia, J. Cai, H. Hippe, and J. A. E. Farrow. 1994. The phylogeny of the genus Clostridium: proposal of five new genera and eleven new species combinations. Int. J. Syst. Bacteriol. 44:812-826. [DOI] [PubMed] [Google Scholar]
- 4.Derlot, E., and P. Courvalin. 1991. Mechanisms and implications of glycopeptide resistance in enterococci. Am. J. Med. 91:82S-85S. [DOI] [PubMed] [Google Scholar]
- 5.Fekety, R. 1997. Guidelines for the diagnosis and management of Clostridium difficile-associated diarrhea and colitis. Am. J. Gastroenterol. 92:739-750. [PubMed] [Google Scholar]
- 6.Finegold, S. M., G. E. Mathisen, and W. L. George. 1983. Changes in human intestinal flora related to the administration of antimicrobial agents, p. 355-446. In D. J. Hentges (ed.), Human intestinal microflora in health and disease. Academic Press, Inc., New York, N.Y.
- 7.Finegold, S. M., D. Molitoris, Y. Song, C. Liu, M.-L. Vaisanen, E. Bolte, M. McTeague, R. Sandler, H. Wexler, E. M. Marlowe, M. D. Collins, P. A. Lawson, P. Summanen, M. Baysaller, T. J. Tomzynski, E. Read, E. Johnson, R. Rolfe, P. Nasir, H. Shah, D. A. Haake, P. Manning, and A. Kaul. 2002. Gastrointestinal microflora studies in late-onset autism. Clin. Infect. Dis. 35(Suppl. 1):S6-S16. [DOI] [PubMed] [Google Scholar]
- 8.Hershberger, E., S. Donabedian, K. Konstantinou, and M. J. Zervos. 2004. Quinupristin-dalfopristin resistance in gram-positive bacteria: mechanism of resistance and epidemiology. Clin. Infect. Dis. 38:92-98. [DOI] [PubMed] [Google Scholar]
- 9.Hiramatsu, K. 2001. Vancomycin-resistant Staphylococcus aureus: a new model of antibiotic resistance. Lancet Infect. Dis. 1:147-155. [DOI] [PubMed] [Google Scholar]
- 10.Jousimies-Somer, H. R., P. Summanen, D. M. Citron, E. J. Baron, H. M. Wexler, and S. M. Finegold. 2002. Wadsworth-KTL anaerobic bacteriology manual, 6th ed. Star Publishing Co., Belmont, Calif.
- 11.Kucers, A., and N. M. Bennett. 1987. The use of antibiotics, 4th ed. J.B. Lippincott Co., Philadelphia, Pa.
- 12.Medical Economics Staff (ed.). 2003. Physicians' desk reference, 57th ed. Thomson Healthcare, Montvale, N.J.
- 13.National Committee for Clinical Laboratory Standards. 1997. Methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically. Approved standard, 4th ed. NCCLS document M7-A4. National Committee for Clinical Laboratory Standards, Wayne, Pa.
- 14.National Committee for Clinical Laboratory Standards. 2001. Methods for antimicrobial susceptibility testing of anaerobic bacteria. Approved standard, 5th ed. NCCLS document M11-A5. National Committee for Clinical Laboratory Standards, Wayne, Pa.
- 15.Smith, T. L., M. L. Pearson, K. R. Wilcox, C. Cruz, M. V. Lancaster, B. Robinson-Dunn, F. C. Tenover, M. J. Zeros, J. D. Band, E. White, and W. R. Jarvis. 1999. Emergence of vancomycin resistance in Staphylococcus aureus. N. Engl. J. Med. 340:49-53. [DOI] [PubMed] [Google Scholar]
- 16.Swanson, R. N., D. J. Hardy, N. L. Shipkowitz, C. W. Hanson, N. C. Ramer, P. B. Fernandes, and J. J. Clement. 1991. In vitro and in vivo evaluation of tiacumicins B and C against Clostridium difficile. Antimicrob. Agents Chemother. 35:1108-1111. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 17.Tacconelli, E., M. Tumbarello, K. Donati, M. Bettio, T. Spanu, F. Leone, L. A. Sechi, S. Zanetti, G. Fadda, and R. Cauda. 2001. Glycopeptide resistance among coagulase-negative staphylococci that cause bacteremia: epidemiological and clinical findings from a case-control study. Clin. Infect. Dis. 33:1628-1635. [DOI] [PubMed] [Google Scholar]
- 18.Theriault, R. J., J. P. Karkowski, M. Jackson, R. L. Girolami, B. N. Sunga, C. M. Vojtko, and L. J. Coen. 1987. Tiacumicins, a novel complex of 18-membered macrolide antibiotics. I. Taxonomy, fermentation, and antibacterial activity. J. Antibiot. 40:567-574. [DOI] [PubMed] [Google Scholar]
- 19.Volaard, E. J., and H. A. L. Clasener. 1994. Colonization resistance. Antimicrob. Agents Chemother. 38:409-414. [DOI] [PMC free article] [PubMed] [Google Scholar]