Daniel P. Bonner

Azthreonam (SQ 26,776), a synthetic monobactam specifically active against aerobic gram-negative bacteria.

Azthreonam (SQ 26,776) is a synthetic monocyclic beta-lactam antimicrobial agent belonging to the monobactam family (Sykes et al., Nature [London] 291:489-491, 1981), members of which are characterized by having the 2-oxoazetidine-1-sulfonic acid moiety. Azthreonam exhibits a high degree of stability to beta-lactamases and is specifically active against aerobic gram-negative bacteria, including Pseudomonas aeruginosa. Its activity against these organisms was in general equal or superior to that observed with the third-generation cephalosporins, cefotaxime and ceftazidime. Like penicillins and cephalosporins, azthreonam interacts with essential penicillin-binding proteins of gram-negative bacteria. Azthreonam protected mice against experimental infections produced by a range of gram-negative bacteria, exhibiting efficacy comparable to that of cefotaxime and ceftazidime.

Resistance caused by decreased penetration of beta-lactam antibiotics into Enterobacter cloacae.

Strains of Enterobacter cloacae were selected on the basis of resistance to aztreonam, ceftazidime, moxalactam, or imipenem. All strains produced the same E2 beta-lactamase, with an isoelectric point greater than 9.5 and with high hydrolytic activity in the presence of cephaloridine. Resistance to beta-lactams could not be correlated with the amount of beta-lactamase present in the various strains. beta-Lactamase activity was induced strongly by moxalactam and imipenem in the wild-type and moxalactam-resistant strains, with beta-lactamase representing as much as 4% of the total cellular protein after induction (2 X 10(5) molecules per cell). Ceftazidime and aztreonam were poor inducers. None of the antibiotics studied was readily hydrolyzed by the E2 beta-lactamase; aztreonam and moxalactam inhibited the enzyme with apparent Ki values of 1.2 and 100 nM, respectively. Aztreonam, which bound covalently to the E2 beta-lactamase with a half-life of 2.3 h at 25 degrees C, was used to measure penetrability of beta-lactam into the periplasmic space of the resistant E. cloacae strains. In all of the E2-producing organisms studied, a significant permeability barrier existed. A maximum concentration of 0.02 microgram of aztreonam per ml should have saturated the periplasmic beta-lactamase in the highest enzyme producers studied. However, fully active beta-lactamase was observed in the periplasm of cells exposed to aztreonam at concentrations at least 1,000-fold higher than that theoretically necessary to inhibit the total enzyme within the cell. Thus, the major cause for resistance to beta-lactam antibiotics in these E. cloacae strains was lack of penetration across the outer membrane.

Correlation between Genotype and Phenotypic Categorization of Staphylococci Based on Methicillin Susceptibility and Resistance

ABSTRACT Positive correlation between methicillin and oxacillin susceptibility test results and the detection of themecA gene was observed forStaphylococcusaureus, S. epidermidis, and S. haemolyticus as well as among mecA+ strains of other species of coagulase-negative staphylococci (CNS). However, at least 50% of themecA-negative strains of these other species of CNS were falsely classified as methicillin and oxacillin resistant.

In Vitro and In Vivo Activities of a Novel Cephalosporin, BMS-247243, against Methicillin-Resistant and -Susceptible Staphylococci

ABSTRACT The recent emergence of methicillin-resistant Staphylococcus aureus (MRSA) with decreased susceptibility to vancomycin has intensified the search for alternative therapies for the treatment of infections caused by this organism. One approach has been to identify a β-lactam with improved affinity for PBP 2a, the target enzyme responsible for methicillin resistance in staphylococci. BMS-247243 is such a candidate, with MICs that inhibit 90% of isolates tested (MIC90s) of 4, 2, and 8 μg/ml for methicillin-resistant strains of S. aureus, S. epidermidis, and S. haemolyticus, respectively, as determined on plates with Mueller-Hinton agar and 2% NaCl. The BMS-247243 MICs for MRSA were minimally affected by the susceptibility testing conditions (inoculum size, prolonged incubation, addition of salt to the test medium) or by staphylococcal β-lactamases. BMS-247243 MIC90s for methicillin-susceptible staphylococcal species ranged from ≤0.25 to 1 μg/ml. The BMS-247243 MIC90 for β-lactamase-producing S. aureus strains was fourfold higher than that for β-lactamase-nonproducing strains. BMS-247243 is hydrolyzed by staphylococccal β-lactamases at 4.5 to 26.2% of the rates measured for cephaloridine. The affinity of BMS-247243 for PBP 2a was >100-fold better than that of methicillin or cefotaxime. BMS-247243 is bactericidal for MRSA, killing the bacteria twice as fast as vancomycin. These in vitro activities of BMS-247243 correlated with its in vivo efficacy against infections in animals, including the neutropenic murine thigh and rabbit endocarditis models involving MRSA strains. In conclusion, BMS-247243 has in vitro and in vivo activities against methicillin-resistant staphylococci and thus may prove to be useful in the treatment of infections caused by these multidrug-resistant organisms.

Comparative Killing Rates of Fluoroquinolones and Cell Wall-Active Agents

ABSTRACT Killing rates of fluoroquinolones, β-lactams, and vancomycin were compared against Enterobacteriaceae, Staphylococcus aureus, pneumococci, streptococci, and Enterococcus faecalis. The times required for fluoroquinolones to decrease viability by 3 log10 were 1.5 h forEnterobacteriaceae, 4 to 6 h for staphylococci, and ≥6 h for streptococci and enterococci. Thus, the rate of killing by fluoroquinolones is organism group dependent; overall, they killed more rapidly than β-lactams and vancomycin.

Comparative Chemotherapeutic Activity of Amphotericin B and Amphotericin B Methyl Ester

The comparative efficacy of amphotericin B and amphotericin B methyl ester (AME) against experimental histoplasmosis, blastomycosis, cryptococcosis, and candidosis in mice was assessed by determining the effect of daily intraperitoneal therapy on 21-day survival and persistence of organisms in internal organs. AME, like amphotericin B, was effective against each of the experimental infections, but the efficacy was lower than the parent compound. For Histoplasma and Blastomyces infections the mean effective dose (ED50) of amphotericin B was 0.3 mg/kg, whereas the corresponding values for AME, respectively, were 2.4 and 2.8 mg/kg. For Cryptococcus infection the ED50 for amphotericin B was 0.2 mg/kg compared with 2.0 mg/kg for AME. The ED50 of amphotericin B for Candida infection was lower than 0.05 mg/kg and the value of AME was between 0.5 to 0.05 mg/kg. The colony counts from internal organs of the surviving animals after the therapeutic regimens were compatible with the data on survival.

Improved sensitivity in assays for binding of novel beta-lactam antibiotics to penicillin-binding proteins of Escherichia coli.

Tigemonam and temocillin, but not aztreonam, bound to penicillin-binding proteins (PBPs) 1a and 3 of Escherichia coli with apparent improved affinity when challenged with benzylpenicillin at lowered temperatures. Half times for deacylation of the tigemonam-PBP complexes were shorter than were those of the corresponding aztreonam-PBP complexes. The implications of the routine testing of PBP affinities are discussed. Images

Kinetics of Testosterone Induced-Cholesterol Synthesis in Rat Ventral Prostate

Summary The absolute cholesterol content and rate of cholesterol synthesis was compared in rat ventral prostates obtained from adult normal and castrated rats. Cholesterol content and synthesis reduces to about 8–12% in the ventral prostate of castrated animals as compared to normal rats. Daily testosterone injections to castrated rats elicits a sharp increase in cholesterol content which correlates with an increase in prostate weight. The rate of cholesterol synthesis per microgram of prostatic DNA increases steeply 2 days after testosterone administration and then goes down and reaches a steady state after 5 days.

The effect of fetal bovine serum on polyene macrolide antibiotic cytotoxicity and antifungal activity.

SummaryThe relationships between fetal bovine serum (FBS) concentration and polyene macrolide antibiotic cytotoxicity to animal cells and to fungi were evaluated. The toxicity of amphotericin B (AB) and its derivative, amphotericin B methyl ester (AME), toward KB cells was found to be directly related to fetal bovine serum concentration. At higher FBS levels, increased concentrations of AB and AME were required to reduce 72-hr KB viable cell numbers to 50% of control values. Similarly, polyene macrolide antibiotic levels required to inhibit the growth ofSaccharomyces cerevisiae to 50% of controls, and for obtaining minimum fungicidal concentrations (MFC), were greater when higher levels of FBS were used. In addition, AME was less toxic than AB toward KB cells grown in media containing 2, 5, 10, 15 or 20% FBS, whereas the antifungal activities of AB and AME were similar. AME was also capable of eliminatingCandida albicans, Saccharomyces cerevisiae, Aspergillus niger orFusarium moniliforme from KB cultures at antibiotic levels which exhibited less cell toxicity than did the concentrations of AB required for a similar response. These findings indicate that AME may be a potentially useful antifungal antibiotic for tissue culture systems.

Absence of cholesterogenesis regulation in the liver and prostate of the BIO 87.20 hamster

Normal, adult golden Syrian hamsters and the inbred stain BIO 87.20 Syrian hamsters were maintained on either control, cholesterol, candicidin or clofibrate diets for time periods of up to 4 months. The ventral prostate gland in both species was found to synthesize cholesterol at a greater rate than the liver. Also, our results show that, while hepatic cholesterol synthesis in the normal Syrian hamster is under feedback control with dietary cholesterol, hepatic cholesterol synthesis in the BIO 87.20 hamster, and prostatic cholesterol synthesis in either species, is under no such control. This apparent regulatory defect in the BIO 87.20 hamster, which results in a dramatic accumulation of cholesterol in the liver and serum, renders this animal a potentially valuable in vivo model for the study of cholesterol-related disorders.