5-epi-Sisomicin and 5-epi-Gentamicin B: substrates for aminoglycoside-modifying enzymes that retain activity against aminoglycoside-resistant bacteria.

A number of bacterial strains, each possessing a different aminoglycoside-modifying enzyme, were examined for susceptibility to sisomicin and gentamicin B and the semisynthetic derivatives 5-epi-sisomicin and 5-epi-gentamicin B. Although strains possessing AAC (6') or APH(3') enzymes were equally resistant to the 5-epi-compounds, those possessing AAC(3)-I, ANT(2"), or AAC(2') enzymes were much more sensitive to the 5-epi derivatives. Analysis of partially purified aminoglycoside-modifying enzymes from the strains showed that the 5-epi compounds were substrates even for those enzymes found in susceptible strains [AAC(3)-I, ANT(2"), and AAC(2')]. However, a more detailed study of the enzymes showed that they had much increased Km values for the 5-epi derivatives; the 5-epi compounds were much less effectively modified than the parent antibiotics. This confirms and extends the notion that enzymatic modification of aminoglycosides is not in itself sufficient to confer resistance to the drugs, but also that the modification must be efficient, as reflected in the Km values.     

Human postheparin plasma hepatic lipase activity against triacylglycerol and phospholipid substrates

Recent evidence has suggested that the major physiological substrate of the heparin-releasable (postheparin plasma) hepatic lipase is HDL₂-phospholipid. However, all the current assay methods for this enzyme are based on the use of triacylglycerol substrate. Even though both lipolytic activities of hepatic lipase are likely to be due to a single enzyme it is possible that the use of unphysiological lipid as a substrate may give misleading results. Therefore we did parallel assays of the activity of postheparin plasma hepatic lipase using triacylglycerol, monoacylglycerol and phospholipid substrates. The correlation coefficients between the three lipolytic activities were 0.95–0.98, indicating that identical results are obtained using any of these three lipids in the assay of postheparin plasma hepatic lipase.     

Serum lactate dehydrogenase activity ratios with different substrates.

1. The lactate dehydrogenase activity of 89 sera from patients suffering myocardial infarction and of 55 sera from patients with hepatocellular damage was assayed under optimal conditions using pyruvate, alpha-oxobutyrate, hydroxypyruvate and glyoxylate as substrates. Activity was also measured with lactate as substrate at different pH values. 2. The ratios of activities under these different assay conditions were calculated for both series of patients. Correct differentiations for single ratios ranged from virtually nil for hydroxypyruvate/alpha-oxobutyrate to is greater than 93 per cent for glyoxylate/hydroxypyruvate and glyoxylate/alpha-oxobutyrate. This was little improved by the use of multiple ratios involving up to seven separate assays. 3. The activity ratio of hydroxypyruvate to pyruvate which is consistently greater than unity was found to be inverted in a case of morphine poisoning.     

Cyclacillin: in vitro activity against aerobic and anaerobic bacteria.

Cyclacillin at 50 microgram/ml inhibited streptococci (100%), shigella (72%), and Bacteroides (B) fragilis ss fragilis (84%). At 100 microgram/ml it inhibited proteus (75%), B. fragilis (86%), and E. coli (50%). Cyclacillin was more effective than ampicillin against beta-lactamase-producing H. influenzae. The activity of cyclacillin was found to be more enhanced when tested in nutrient agar and Mueller-Hinton agar than in brain heart infusion agar.     

Sex differences in adenosine deaminase activity of stroke patients.

BACKGROUND: Adenosine deaminase (ADA) catalyzes the irreversible hydrolytic deamination of adenosine to inosine. The purpose of this study was to determine the plasma activities of total adenosine deaminase (ADA T), and its isoenzymes, ADA1 and ADA2, and ADA1/ADA2 ratio of male and female ischemic stroke patients. METHODS: We determined activities of plasma ADA T, ADA1, ADA2 and ADA1/ADA2 ratio in 30 patients (15 men and 15 women) with acute ischemic stroke within 12 h of the onset of the attack, as well as in 30 control subjects (15 men and 15 women) of comparable age. RESULTS: There were significant differences between the ADA1 activity and ADA1/ADA2 ratio in male and female stroke patients (p<0.05). Compared with male stroke subjects, females had higher ADA1 activity and ADA1/ADA2 ratios. There were no significant differences between activities of ADA T and ADA2 in men and women of the stroke and control groups. In addition, the Canadian Neurological Scale in men was significantly higher than that of women in the stroke group (p<0.05). CONCLUSIONS: Our results suggest that the primary mechanism in men with ischemic stroke might involve the reduction of ADA1 activity. The reduction is probably an adaptation mechanism for induced increase in adenosine availability and protection of brain to ischemic injury.     

Antibacterial activity of niridazole against Salmonellae.

Fifty-six strains, representing eight species of salmonellae of diverse geographic origin and possessing a variety of antimicrobial resistance profiles, were tested for susceptibility to niridazole by the agar dilution method. Calculated MICs for 50 and 90% of strains were 4.8 and 16.0 mg/liter, respectively, with a susceptibility range of 0.25 to 32 mg/liter. No obvious species differences were noted. Niridazole was found to be rapidly and powerfully bactericidal. No significant difference was detected between MICs and MBCs. Except for a strain-dependent effect with a subset of multiply resistant salmonella isolates, no inoculum effect was demonstrated.     

N-formimidoyl thienamycin (MK0787): in vitro activity against anaerobic bacteria.

The in vitro activity of N-formimidoyl thienamycin (MK0787) was tested against 239 anaerobic bacteria clinical isolates: 70 of Bacteroides fragilis, 18 of B. distasonis, 16 of B. thetaiotaomicron, 10 of B. vulgatus, 24 of Bacteroides spp., 22 of B. melaninogenicus (all three subspecies), 26 of Fusobacterium spp., 10 of Peptococcus spp., 15 of Peptostreptococcus spp., 15 of Clostridium perfringens, and 13 of Clostridium spp. Ninety-five percent of the isolates were inhibited by less than or equal to 0.125 microgram/ml, and all were inhibited by less than or equal to 4 micrograms/ml.     

Comparative in vitro activity of ceftriaxone against anaerobic bacteria.

The in vitro activity of ceftriaxone was compared with those of other recently introduced beta-lactam antimicrobial agents (cefoperazone, cefotaxime, and moxalactam) and with those of cefoxitin, clindamycin, and metronidazole against 227 strains of anaerobic bacteria. The data obtained in this investigation suggest that ceftriaxone, like a majority of the new beta-lactam antimicrobial agents, may be of limited value in the treatment of serious infections involving anaerobic bacteria.     

Bactericidal activity of ramoplanin against antibiotic-resistant enterococci.

Ramoplanin, a new lipoglycodepsipeptide antibiotic, was uniformly active against 65 strains of enterococci, including strains highly resistant to vancomycin, penicillin G, and gentamicin. MBCs were usually within a fourfold dilution of the MICs. In time-kill studies, ramoplanin alone demonstrated dose-dependent bactericidal activity against enterococcal strains that resisted killing by vancomycin or penicillin in combination with gentamicin.     

The activity of hydroxynaphthoquinones against Leishmania donovani.

The hydroxynaphthoquinones, buparvaquone, 250C80 and 56W82, showed high activity in vitro against Leishmania donovani amastigotes in mouse peritoneal macrophages, with ED50 values of 0.05, 2.95 and 13.82 microM, respectively. Fourteen other hydroxynaphthoquinones were tested, of which only 566C80 and 608C86 showed significant activity against amastigotes. Buparvaquone, 250C80 and 56W82 were also highly-active against cultured promastigotes. In a BALB/c mouse model, treatment with 100 mg/kg/day for five days with buparvaquone, 250C80 and 566C80 (atovaquone) reduced liver amastigote numbers by 60%, 22% and 30.5%, respectively.     

Comparative activity of ciprofloxacin against anaerobic bacteria.

The in vitro activity of ciprofloxacin was assessed against 362 strains of anaerobic bacteria and compared with that of cefoxitin, clindamycin, metronidazole, and mezlocillin. Only 31% of the strains tested were susceptible to ciprofloxacin. The other agents were active against most of the strains tested.     

Enhanced liposome-mediated activity of piperacillin against staphylococci.

This study showed that encapsulation of the beta-lactam antibiotic piperacillin (PIP) by liposomes prepared with phosphatidylcholine and cholesterol (1:1) protected the drug from hydrolysis by staphylococcal beta-lactamase. This was demonstrated by growth inhibition of Staphylococcus aureus in the presence of the liposomal preparation containing PIP at a 50% MIC. Growth inhibition was also seen when exogenous beta-lactamase was added. Furthermore, adsorption of PIP onto the surface of liposomes containing buffer conferred a significant degree of protection against enzymatic hydrolysis of the drug, thus enhancing its antistaphylococcal activity.     

Decreased activity of erythromycin against Streptococcus pyogenes in Taiwan.

A total of 78 clinical isolates of Streptococcus pyogenes were collected from January 1992 through December 1993 from patients in southern Taiwan. The in vitro activities of 10 antimicrobial agents were determined by the agar dilution method. Penicillin, cephalothin, cefotaxime, vancomycin, and ofloxacin were shown to be active against S. pyogenes isolates, with MICs at which 90% of isolates are inhibited (MIC90s) being < or = 0.03, < or = 0.13, < or = 0.13, < or = 0.13, and < or = 0.25 microgram/ml, respectively. Erythromycin and azithromycin both had poor activities (MIC50s, 16 and >128 micrograms/ml, respectively; MIC90s, >128 and >128 micrograms/ml, respectively). The activities of tetracycline, clindamycin, and chloramphenicol against a significant number of these isolates were also limited. As the MICs of clindamycin and chloramphenicol for the isolates increased, the MICs of the two macrolides also increased. Clindamycin, chloramphenicol, and the two macrolides were less potent against isolates recovered form throat swab samples than against those from blood or other sources. Isolates of the T12 and T1 serotypes accounted for 53.8% of all isolates. The majority (87.5%) of the isolates recovered from throat swab samples were of the T12 serotype, whereas 19.2% of the isolates recovered from blood were of the T12 serotype. In contrast, 66.7% of the isolates of the T1 serotype were derived from blood but none were derived from throat swab samples. Of the 33 T12 serotype isolates, erythromycin MICs for 78.8% of the isolates were >128 micrograms/ml. Because of the poor activities of erythromycin and azithromycin against S. pyogenes isolates from patients in southern Taiwan, these drugs should no longer be considered the drugs of choice for the management of group A streptococcal infections among patients who live in this area.     

Macromolecular chromogenic substrates for measuring proteinase activity

BACKGROUND: Proteinase activities are often measured using chromogenic substrates that are much smaller than physiological substrates. METHODS: The hydrodynamic size of macromolecular substrates (macrosubstrates) prepared by linking small chromogenic substrates to polyethylene glycol was determined by gel filtration. Efficiency of macrosubstrate cleavage by proteinases and alpha(2)-macroglobulin-proteinase complexes was monitored spectrophotometrically. RESULTS: Macrosubstrates had hydrodynamic radii of approximately 20 A, similar to proteins with a molecular weight of 18,000. Different macrosubstrates served as efficient substrates for chymotrypsin, trypsin, and thrombin. Linking small substrates to a polymer variably affected substrate efficiency, with the impact on activity ranging from a 60-fold decrease to a 30-fold increase. Proteinases complexed with alpha(2)-macroglobulin had approximately 10-fold lower activity vs macrosubstrates than small substrates. CONCLUSIONS: Macrosubstrates are efficient substrates that allow decreased measurement of sterically hindered proteinase molecules such as alpha(2)-macroglobulin-proteinase complexes. Thus, macrosubstrates may provide more accurate functional assays of proteinases such as coagulation factors.     

Antiviral activity of oxetanocins against varicella-zoster virus.

Several new nucleosides with an oxetanosyl-N-glycoside group, named oxetanocins, were evaluated for their antiviral activities against varicella-zoster virus (VZV) in human embryo lung cells. 9-(2-deoxy-2-hydroxy-methyl-beta-D-erythro-oxetanosyl)guanine (OXT-G) and 9-(2-deoxy-2-hydroxymethyl-beta-D-erythro-oxetanosyl)-2- aminoadenine were effective against not only thymidine kinase-positive (TK+) VZV (YS strain) but also thymidine kinase-negative (TK-) VZV (YSR strain), whereas carbocyclic OXT-G was effective against TK+ VZV but not against TK- VZV. [3H]OXT-G was incorporated into TK+ VZV-infected cells and TK- VZV-infected cells more than into mock-infected cells and was converted into the triphosphate form.     

Comparative in vitro activity of coumermycin against methicillin-resistant Staphylococcus aureus.

Coumermycin was the most active agent in vitro against methicillin-resistant Staphylococcus aureus when compared with fusidic acid, imipenem, rifampin, trimethoprim-sulfamethoxazole, and vancomycin. The MICs of coumermycin ranged from 0.002 to greater than 4 micrograms/ml and from 0.5 to greater than 4 micrograms/ml for inocula of 10(4) and 10(6) CFU/ml, respectively. The combination of coumermycin with either cephalothin or ciprofloxacin showed some synergy; antagonism was found with gentamicin.     

The in-vitro activity of drugs against Blastocystis hominis.

The development of an assay to measure the sensitivity of drugs against Blastocystis hominis using the incorporation of 3H-hypoxanthine is described. The activity of 42 compounds have been measured. Four of the 5-nitroimidazoles tested (satranidazole, S75 0400 A, flunidazole and ronidazole) were found to be more active than metronidazole, the drug commonly used to treat infections caused by B. hominis in humans. Other potentially useful compounds include emetine, furazolidone and quinacrine. Ketoconazole and iodoquinol reported to have therapeutic activity in infections caused by this parasite were found to be significantly less active than metronidazole.     

Intracellular activity of azithromycin against bacterial enteric pathogens.

Azithromycin, a new azalide antibiotic, is active in vitro against a variety of enteric bacterial pathogens. Since it is concentrated inside human neutrophils and other cells, it might be particularly useful in the treatment of infections caused by enteropathogens that invade host tissues. The intracellular activity of azithromycin against several enteric pathogens that had been phagocytosed by neutrophils was determined. Azithromycin was effective in reducing the intracellular viabilities of almost all strains tested, including representative strains of Salmonella, Shigella, and enteroinvasive, enteropathogenic, enterotoxigenic, and enterohemorrhagic Escherichia coli. Erythromycin was also effective in this model system, although azithromycin was generally more effective than erythromycin against strains of invasive enteric pathogens. Cefotaxime reduced intracellular bacterial viability to a lesser extent than either azithromycin or erythromycin. The presence of neutrophils did not significantly affect the activity of azithromycin in this system. Azithromycin may be a useful agent for the treatment of bacterial diarrhea, and clinical trials should be considered.     

Bactericidal activity of oxacillin against beta-lactamase-hyperproducing Staphylococcus aureus.

The bactericidal activity of oxacillin against beta-lactamase-hyperproducing strains of Staphylococcus aureus for which the MIC by MicroScan was 1 or 2 micrograms/ml after incubation for 24 h was evaluated by MBC studies and kill kinetics methods. MBC and kill kinetics tests were both performed using Mueller-Hinton broth (MHB), with and without 2% NaCl supplementation, and incubation at 30 and 35 degrees C. When MBC testing was performed with salt-supplemented MHB, the oxacillin MBC/MIC ratio was greater than 8 for 17 and 16 of 17 S. aureus isolates at 30 and 35 degrees C, respectively. With unsupplemented MHB, the MBC/MIC ratio was greater than 8 for nine and six strains at 30 and 35 degrees C, respectively. Five representative strains were selected for kill kinetics studies under the four different test conditions. Oxacillin appeared more bactericidal by the kill kinetics method than by MBC testing. Moreover, salt supplementation did not affect the results of kill kinetics studies as dramatically as it did the MBC results. Thus, bactericidal testing results are markedly influenced by the technique employed, and further in vivo studies are necessary to fully evaluate the efficiency of oxacillin against beta-lactamase-hyperproducing strains of S. aureus.