p.g/ml (8). The 22 MSSA isolates were all recent blood isolates from the Clinical Microbiology Laboratory of the Harbor-UCLA Medical Center; the 26 MRSA isolates (kindly provided by Francisco Sapico, Downey, Calif.) were also recent clinical isolates from a variety of body sites. There were no duplicate isolates from individual patients. The isolates were maintained on Mueller-Hinton (MH) agar slants until the susceptibility studies were performed.Antibiotics. Vancomycin was supplied by Eli Lilly & Co. (Indianapolis, Ind.), and rifampin was provided by MerrillDow Research (Indianapolis, Ind.). Stock solutions of each agent at a concentration of 10,000 ,ug/ml were prepared and kept at -70°C until thawed on the day of the in vitro studies.Antibiotic susceptibility testing. The MICs and MBCs of vancomycin and rifampin against these 48 isolates were determined by the microtiter broth dilution technique (14). Pilot MIC and MBC determinations in our laboratory, utilizing several study staphylococcal isolates, disclosed close agreement between results in the microtiter and macrobroth dilution methods (15). Fifty-microliter volumes of each antibiotic in twofold serial dilutions were added to a separate microtiter row of wells. A 50-,ul sample of each MRSA or MSSA isolate grown in MH broth (MHB) to mid-logarithmic phase (-2 h) was added to each antibiotic-containing well and mixed without splashing by a microdiluter to achieve a final concentration of -2 x 105 CFU/ml. The final drug concentrations in the wells were 0.007 to 16 ,ug/ml for both drugs. These concentrations were chosen to encompass readily attainable levels in serum for each agent at standard clinical dosages (1, 13). For each isolate tested, one microtiter well contained only the organism in antibiotic-free MHB as a growth control. After inoculation and gentle mixing, all plates were incubated for 24 h at either 30°C for

The bactericidal activities of penicillin G and ampicillin alone were compared with those of their combinations with streptomycin or gentamicin against 17 strains of lactobacilli classified as tolerant to various fl-lactam antibiotics. The penicillin G combinations with streptomycin and gentamicin were synergistic against 17 and 16 of these strains, respectively, whereas the corresponding ampicillin-aminoglycoside combinations were synergistic against 12 and 15 strains, respectively. Importantly, synergy was manifested at concentrations of these antibiotics that are attained in serum after their administration in conventional dose regimens. In no instances were combinations antagonistic. These in vitro observations provide a partial explanation for the favorable results obtained in preliminary clinical evaluations of the benefits of combination regimens in the treatment of lactobacillus infections refractory to single-drug therapy.Serious lactobacillus infections, particularly endocarditis, often result in therapeutic failure when treated with seemingly appropriate singledrug antibiotic regimens, despite readily achievable minimal inhibitory concentrations (MICs) (1,3,20). Our previous studies indicated that this disparity between in vitro susceptibility data and in vivo efficacy may be partially explicable on the basis of "antibiotic tolerance" exhibited by a number of Lactobacillus strains (3-5). The marked discrepancy between MICs and minimal bactericidal concentrations (MBCs) for individual Lactobacillus isolates (1, 3-5) and preliminary clinical evaluations suggesting efficacy of penicillin-aminoglycoside regimens in cases of refractory lactobacillus endocarditis (1,3,20) prompted the present study to Organisms were maintained in chopped meat-glucose broth (Scott Laboratories, Fiskeville, R.I.) and were transferred monthly into fresh media until the susceptibility testing was performed. In the week before testing, one additional transfer was done. All susceptibility studies were performed anaerobically.Antibiotic tolerance. These 17 isolates were confirmed as penicillin and ampicillin tolerant by the following criteria: (i) MBC/MIC ratios of 232:1 (18); and (ii) slow bactericidal effect on timed-kill analysis (<99.9% killing at 24 to 48 h).MBC/MIC ratios. MICs and MBCs were determined for penicillin G and ampicillin by a modified broth dilution technique as previously described (4), using prereduced Mueller-Hinton (MH) broth (BBL Microbiology Systems, Cockeysville, Md.) with 0.2% yeast extract and 0.05% L-cysteine. This medium has a maximal concentration of 0.5 mg per 100 ml of magnesium and 3.1 mg per 100 ml of calcium.Penicillin G and ampicillin were supplied by USP Standards, Rockville, Md. Stock solutions (8,000 ,ug/ ml) of each agent were prepared and stored at -20°C until the day of the study. Serial twofold dilutions were made of both antibiotics and added to broth under anaerobic conditions. A final inoculum of approximately 2 x 105 colony-forming units (CFU) per antibiotic-containing tube was use...

We investigated the efficacy of a potent new antipseudomonal /3-lactam agent, ceftazidime, in a model of right-sided Pseudomonas endocarditis in 72 rabbits. Animals received either: no therapy (controls), amikacin (15 mg/kg/day), ceftazidime (100 mg/kg/day) or amikacin + ceftazidime. Amikacin + ceftazidime was significantly more effective than single-drug regimens in terms of reduction of mortality (p < 0.01), prevention of pulmonary infarction (p < 0.05), reduction of mean vegetation titers of Pseudomonas aeruginosa (p < 0.05-p < 0.0005), sterilization of vegetations (p < 0.0005) and reduction in prevalence of bacteriologic relapses after therapy (p < 0.005). There was no development of resistance in vivo to either amikacin or ceftazidime.

killing: 25% of the strains were killed by 0.4 ,ug or less of amphotericin B alone per ml, and 75% of the strains were killed with the addition of 6.25 ,ug of rifampin per ml. In vivo studies are needed for confinnation of the usefulness of combined amphotericin B and rifampin therapy.Despite an interval of 21 years since its introduction, amphotericin B remains the most efficacious agent in the treatment of systemic mycoses (4). Numerous attempts to reduce the toxicity of amphotericin B have met with limited success. Currently, the most satisfactory ways to limit the undesirable side effects of the drug are to reduce the total quantity administered or to give amphotericin B over a prolonged time period (every-other-day dosage). One method to reduce the amount without compromising efficacy is to combine the drug with a compound which increases killing of organisms by combined action without adding toxicity. Tetracycline, 5-fluorocytosine, rifampin, actinomycin D, and mycophenolic acid glucuronide have all shown a propensity to increase the potency of amphotericin against various fungi and yeasts (8,9).Although Candida species are generally susceptible to relatively small quantities of amphotericin B, Candida endophthalmitis, endocarditis, meningitis, osteomyelitis, peritonitis, pancreatitis, arthritis, and systemic candidiasis are difficult to treat. Reports of all these Candida infections have increased impressively. This study was designed to determine the potential for rifampin to increase the potency of amphotericin B against multiple clinical isolates of Candida in vitro at clinically achievable levels of both drugs and to evaluate the microtiter system for testing synergism with these antifungal components. MATERIALS AND METHODSForty strains of Candida were tested. Twenty-eight strains were isolated from the laboratory of Harbor General Hospital; the remaining strains were from the American Type Culture Collection (Rockville, Md.).These were the same strains used in a previous study of the combined activity of 5-fluorocytosine and amphotericin B and were identified and maintained as previously described (11

Diagenetic alteration of original high-Mg calcite crinoid skeletal material was achieved by reaction of the calcium carbonate with isotopically light meteoric water. The light 61s0 values (-10.57 + 0.74%,, PDB) are a reflection of the water source, whereas the 613C values (-3.49 + 2.63%,, PDB) are a consequence of the high reactive-organic-matter content in the sediments of the Brush Creek at Sewickley, Pennsylvania. High Fe (22 970 + 30 440 ppm) and Mn (3760 + 1450 ppm) contents suggest further that the diagenetic fluids were reducing waters that reacted with the crinoid ossicles in the shallow-burial marine and meteoric environments.Four different types of pyrite are found within crinoid ossicles. Framboidal pyrite, aggregate pyrite, and nanopyrite are generally found in the pores of the stereom. Micropyrite, which is present in the form of octahedral, dodecahedral, and pyritohedral crystals, and nanopyrite and aggregate pyrite replace the calcitic stereom. The degree of pyritization and the pore filling increase toward the outer periphery of the crinoid ossicles. Pyrite formation of the crinoid ossicles took place in two stages. In stage I, upon death, the crinoids disarticulated and were quickly buried. In this shallow sediment layer (1 -10 cm) the pore water was both undersaturated with respect to calcite and oxidizing. This brought about oxidation of the organic tissue in the stroma of the crinoids and selective dissolution of the high-Mg calcite skeletons. With further burial in stage 11, in the presence of reactive organic matter local iron was solubilized, marine sulphate was reduced to sulphide, and isotopically light carbon was produced by bacterial action. Reactive iron combined with sulphur to form framboidal and nanopyrite in the pores of the stereoms. With further burial the micropyrite formed in the crinoid ossicles. Termination of the pyritization process came about with depletion of the iron and (or) sulphur, and this process proceeded very rapidly under shallow-burial conditions while the crinoids resided in the microbial sulphate-reduction zone of the marine-phreatic environment.Fossils are preserved in different stages, with brachiopod valves preserved in their original low-Mg calcite mineralogy, whereas molluscs and crinoids show the complete trend from preserved aragonite and high-Mg calcite, respectively, to diagenetic low-Mg calcite. The preservation potential of fossils is closely linked to the thermodynamic stability of the skeletal carbonate in the presence of diagenetic fluids. Carbon/sulphur ratios support the assertion that Brush Creek sediments were deposited in normal marine waters and favour generally oxic redox conditions for Pennsylvanian seawater.L'altkration diagknktique du matCriel squelettique des Crinoides, form6 initialement de calcite riche en Mg, a kt6 accomplie par la kaction du carbonate de calcium avec une eau mtttorique isotopiquement pauvre. Les valeurs faibles de 6180 (-10,57 + 0.74%,, PDB) reflbtent la nature m&me de la masse d'eau, tandis que les valeurs de 613C...