Showing papers in "Antimicrobial Agents and Chemotherapy in 1978"

CP-45,899, a Beta-Lactamase Inhibitor That Extends the Antibacterial Spectrum of Beta-Lactams: Initial Bacteriological Characterization

Abstract: CP-45,899 {3,3-dimethyl-7-oxo-4-thia-1-azabicyclo(3.2.0)heptane-2-carboxylic acid, 4,4-dioxide, [2S-(2α,5α)]} is an irreversible inhibitor of several bacterial penicillinases and cephalosporinases. In the presence of low concentrations of CP-45,899, ampicillin and other β-lactams readily inhibit the growth of a variety of resistant bacteria that contain β-lactamases. CP-45,899 used alone displays only weak antibacterial activity, with the notable exception of its potent effects on susceptible and resistant strains of Neisseria gonorrhoeae . CP-45,899 appears to be somewhat less potent but markedly more stable (in aqueous solution) than the recently described β-lactamase inhibitor clavulanic acid. The spectrum extensions provided by the two compounds are similar. A 1:1 mixture of CP-45,899 and ampicillin displays marked antimicrobial activity in mice experimentally infected with ampicillin-resistant Staphylococcus aureus, Haemophilus influenzae, Klebsiella pneumoniae , and Proteus vulgaris .

Amphotericin B Pharmacokinetics in Humans

Abstract: The pharmacokinetics of amphotericin B were studied in two patients at the conclusion of long-term therapy for disseminated histoplasmosis. The distribution kinetics of this drug were adequately described by a three-compartment mamillary model with a total distribution volume averaging 4 liters/kg. The elimination phase half-life of amphotericin B was approximately 15 days, reflecting slow release of amphotericin B from a peripheral compartment. In accordance with previous reports, renal excretion accounted for only 3% of total amphotericin B elimination. The pharmacokinetic model for one of the patients also was used to compare the simulated amphotericin B serum levels that would be expected if initial therapy followed two recommended regimens.

Clavulanic Acid, a Novel Inhibitor of β-Lactamases

Abstract: Clavulanic acid, Z-(2R,5R)-3-(β-hydroxyethylidene)-7-oxo-4-oxa-1-azabicyclo-[3,2,0] heptane-2-carboxylic acid, has been shown to be an effective inhibitor of the β-lactamases of the Richmond types II, III, IV, and V. Inhibition is a time-dependent reaction and is irreversible. Clavulanic acid had poor antibacterial activity against Staphylococcus aureus, Enterobacteriaceae, and Pseudomonas aeruginosa, with minimal inhibitory levels greater than 25 μg/ml. It did inhibit the majority of Neisseria gonorrhoeae at 0.1 μg/ml and Haemophilus influenzae at 6.3 μg/ml. Clavulanic acid acted synergistically with penicillins and cephalosporins to inhibit β-lactamase-producing S. aureus and Enterobacteriaceae. Clavulanic acid combined with ampicillin inhibited β-lactamase-producing N. gonorrhoeae, H. influenzae, Escherichia coli, Salmonella typhi, and Shigella sonnei.

New In Vitro Model to Study the Effect of Antibiotic Concentration and Rate of Elimination on Antibacterial Activity

Abstract: A new apparatus is described which serves to investigate the in vitro antibacterial activity of antibiotics as a function of different concentration time curves. The apparatus can be adjusted to simulate the biexponential serum level curves observed in vivo after oral or intramuscular administration. Preliminary studies were carried out with a cephalosporin derivative, cefazolin, against Escherichia coli and Klebsiella sp. strains simulating initial concentrations of 5, 10, and 20 μg/ml that decreased exponentially with half-lives of 30, 60, and 120 min. Surviving cells were counted at 1-h intervals for 10 h. In all the situations tested there was an initial phase of rapid bactericidal activity followed by a phase of bacteriostatic activity, whose length depended on the drug elimination rate but was relatively independent of the initial concentrations. Bacterial regrowth occurred when the antibiotic concentration fell below the minimum inhibitory concentration of the drug against the strains tested. The antibacterial activity of cefazolin, cephacetrile, and cephradine against E. coli and Klebsiella strains was also investigated, in a medium containing 4% human albumin, simulating the serum level curves observed in humans after an intramuscular dose of 1 g. The results obtained suggest that, for cephalosporins, a longer half-life might be more useful than higher peak levels.

Antimicrobial Susceptibility and Selection of Resistance Among Staphylococcus epidermidis Isolates Recovered from Patients with Infections of Indwelling Foreign Devices

Abstract: Twenty-seven isolates of Staphylococcus epidermidis from patients with prosthetic valve endocarditis or infected cerebrospinal fluid shunts were examined for susceptibility to antimicrobial agents Subpopulations resistant to 20 and 100 mug of methicillin per ml were present in 63% of the isolates (methicillin-resistant isolates) Subpopulations resistant to 20 mug of nafcillin and cephalothin per ml were found in every methicillin-resistant isolate but with frequencies (10(-50 +/- 05) and 10(-64 +/- 09), respectively) which were not always detectable by susceptibility testing Resistance to >/=16 mug of penicillin per ml was found in 80% of isolates Cephalothin, cefazolin, and cefamandole were more active than cefoxitin or cephradine, and gentamicin was more active than tobramycin or amikacin; rifampin was the single most active agent against all isolates There was no difference in susceptibility between prosthetic valve endocarditis and cerebrospinal fluid shunt infection isolates Among methicillin-resistant isolates, the phenotypic expression of resistance to methicillin or nafcillin but not to cephalothin could be enhanced by 48 h of incubation with each drug Isolates containing no methicillin-resistant subpopulations were killed by incubation with methicillin, nafcillin, or cephalothin High-level resistance to rifampin emerged in both methicillin-resistant and methicillin-sensitive isolates after 8 to 24 h of incubation with this drug The presence or absence of antibiotic-resistant subpopulations among S epidermidis isolates and their selection during treatment should be considered when therapy is devised

Piperacillin, a new penicillin active against many bacteria resistant to other penicillins.

Abstract: The in vitro activity of piperacillin, a new semisynthetic piperazine penicillin derivative, was evaluated against 626 clinical isolates and compared with the activity of other beta-lactam antibiotics. At a concentration of 0.1 microgram/ml, piperacillin inhibited all streptococci except enterococci. Non-beta-lactamase-producing staphylococci were inhibited by 1.6 microgram or less per ml. Both beta-lactamase- and non-beta-lactamase-producing Haemophilus were inhibited by 0.1 microgram/ml. Piperacillin inhibited non-beta-lactamase-producing Escherichia coli, Salmonella, and Shigella at a concentration of 6.3 micrograms/ml, but 20% of strains of these species containing type III beta-lactamase were not inhibited by 100 micrograms/ml. Piperacillin at 25 micrograms/ml, inhibited 83% of Citrobacter, 58% of Klebsiella, 88% of Enterobacter, and 50% of indole-positive Proteus, Acinetobacter, and Providencia. At 25 micrograms/ml, piperacillin inhibited 95% of Pseudomonas aeruginosa and 78% of Bacteroides fragilis. The minimal inhibitory concentration of piperacillin against Pseudomonas was affected by increasing the inoculum size and by pH. Minimum bactericidal concentrations against Pseudomonas and Serratia often were eightfold greater than the minimum inhibitory concentrations. Piperacillin was equal in activity to ampicillin against enterococci. It was more active than carbenicillin against E. coli, Klebsiella, Enterobacter, and Bacteroides. It was the most active penicillin against Pseudomonas and inhibited many strains of Pseudomonas for which the MICs of carbenicillin were above 200 micrograms/ml. Piperacillin was hydrolyzed by many different beta-lactamases. Synergistic activity of piperacillin was demonstrated when it was combined with amikacin, gentamicin, and cefazolin against P. aeruginosa and members of the Enterobacteriaceae. No antagonism was observed when piperacillin was combined with aminoglycosides; however, antagonism was observed rarely against E. coli when piperacillin was combined with cefazolin.

Carbon Catabolite Regulation of Cephalosporin Production in Streptomyces clavuligerus

Abstract: Cephalosporin production byStreptomyces clavuligerus isregulated bysome typeofcarbon catabolite control. Increasing concentrations ofpreferred carbon sources,suchasglycerol andmaltose, decreased production oftheantibiotics. Poorer carbon sources,such asa-ketoglutarate andsuccinate, ledtohighspecific production ofcephalosporins andshifted thedynamics offermentation to a greater degree ofassociation withgrowth. Theresults supporttheconceptthat thephase inwhich aproduct ismadebyamicroorganism isnotafunction ofthe particular molecule produced, butrather ofthenutritional environment presented totheorganism. Thebiosynthetic pathways leading totheproduction ofsecondary metabolites suchasantibiotics areoften connected toandinfluenced by thepathways ofprimary metabolism (4). For example, anendproduct oranintermediate of aprimary pathway frequently serves asaprecursor fortheantibiotic molecule. Suchintermediates orendproducts could bepartofa biosynthetic, amphibolic, orcatabolic pathway. Catabolic pathways involving energy metabolismoftheorganism areunder strict control in microorganisms. Whenafavored carbon/energy source isused, thecell isusually prevented from producing enzymes whichcatabolize other carboncompounds. Itispossible that suchacatabolic regulatory mechanism could also control theproduction ofsecondary metabolites. The strong influence ofcarbon sources ontheproduction ofantibiotics hasbeenreported inseveral cases (3). Ourinterest hasbeenfocused onStreptomyces ctavuligerus, whichwasfirst described byHiggensandKastner (6). Thisstrain produces four ,8-lactam antibiotics (2,7,11): twoofthese arecephalosporins [7-(5-amino-5-carboxyvaleramido)-3-carbamoyloxymethyl-3-cephem-4-carboxylic acidand7-(5-amino-5-carboxyvaleramido)- 7-methoxy-3 -carbamoyloxymethyl

Isolation and Characterization of Multiply Antibiotic-Resistant Clostridium perfringens Strains from Porcine Feces

Abstract: Multiply antibiotic-resistant strains of Clostridium perfringens were isolated from porcine feces. Strains that were resistant to tetracycline, erythromycin, clindamycin, and lincomycin were isolated, but no penicillin- or chloramphenicol-resistant strains were obtained. Typical minimal inhibitory concentrations for resistant strains were 16 to 64 μg of tetracycline per ml, 64 to >128 μg of erythromycin per ml, ≥128 μg of lincomycin per ml, and 16 to 128 μg of clindamycin per ml. Resistance to erythromycin was always associated with resistance to lincomycin and clindamycin. Minimal inhibitory concentrations were determined for 258 strains from six farms that used antibiotics in their feeds and 240 strains from five farms that did not use antibiotics. The results show that 77.9 and 22.7% of the strains from the former farms were resistant to tetracycline and erythromycin-clindamycin-lincomycin, respectively. The comparable data from the latter farms were 25.0 and 0.8%, respectively. Agarose gel electrophoresis failed to reveal a plasmid band that was common to the resistant strains but absent in the susceptible strains. Attempts to transfer tetracycline, erythromycin, and clindamycin resistance from one strain, CW459, were not successful. Antibiotic-susceptible mutants were not isolated from this strain, despite the use of a variety of curing agents. Images

Antimicrobial susceptibility of Haemophilus ducreyi

Abstract: The susceptibility of 19 isolates of Haemophilus ducreyi from a recent chancroid outbreak and four reference strains was determined in vitro to 13 antimicrobial agents. The rabbit intradermal test for virulence was positive for all of the local isolates, but not for the reference strains. The "nonvirulent" reference strains were inhibited by lower minimum inhibitory concentrations (MICs) of most agents tested. For the virulent isolates, the range of MICs (in micrograms per milliliter) of the following were: of vancomycin, 8 to 128; of polymyxin, 32 to 128; of cloxacillin, 32 to 64; of tetracycline, 0.5 to 32; of cephalothin, 4 to 8; of doxycycline, 0.25 to 8; and of kanamycin, 1 to 8. Three strains were resistant to penicillin and ampicillin (MIC >/= 128 mug/ml), and these three strains produced beta-lactamase. The remainder were susceptible to 4 mug/ml. All strains were susceptible to rifampin (MIC

beta-lactamase stability of HR 756, a novel cephalosporin, compared to that of cefuroxime and cefoxitin.

Abstract: The stability to β-lactamase hydrolysis of HR 756, a new cephalosporin antibiotic, was compared to the β-lactamase stability of cefoxitin and cefuroxime. HR 756, cefoxitin, and cefuroxime were not hydrolyzed by Richmond type I, III, IV, and V β-lactamases. Antibacterial activity of HR 756 correlated well with resistance to β-lactamase hydrolysis except against Pseudomonas aeruginosa. HR 756, cefoxitin, and cefuroxime inhibited type I β-lactamases, but not type III, IV, or V enzymes. HR 756 was the most active inhibitor.

Susceptibility of Campylobacter fetus subsp. jejuni to Twenty-Nine Antimicrobial Agents

Abstract: The activity of 29 antimicrobial agents was tested against 95 strains of Campylobacter fetus subsp. jejuni isolated from human stools. Furazolidone and gentamycin were the most active agents. The tetracyclines, erythromycin, and chloramphenicol were very active against most of the strains, but with each antibiotic a few resistant strains were found. The penicillins were relatively inactive, and the cephalosporins tested were only active against occasional strains.

Evidence for Conversion of 5-Fluorocytosine to 5-Fluorouracil in Humans: Possible Factor in 5-Fluorocytosine Clinical Toxicity

Abstract: A gas chromatographic-mass spectrometric method for detecting 5-fluorouracil (5-FU) in serum at concentrations as low as 10 ng/ml was used to determine to what extent 5-FU was present in the serum of patients taking oral 5-fluorocytosine (5-FC). Preliminary studies in two patients and two healthy volunteers given an initial 2-g oral dose of 5-FC demonstrated sustained serum 5-FU levels (>100 ng/ml) during the 5 h after ingestion of drug. Pharmaceutical preparations of 5-FC used in these studies were shown to be insignificantly contaminated with 5-FU (<0.03%), suggesting in vivo conversion of 5-FC to 5-FU had occurred. Serum samples from seven patients with cryptococcal meningitis treated with amphotericin B and 5-FC were examined for 5-FU. Five of these patients had experienced hematological or other toxicity attributed to 5-FC at some time during the course of therapy. Of 41 serum samples, 20 were observed to have 5-FU levels greater than 1,000 ng/ml in the range observed with cancer chemotherapeutic doses of 5-FU known to be associated with hematological toxicity. It is concluded that conversion of 5-FC to 5-FU occurs in humans and furthermore that 5-FU may account for some of the toxicity observed with 5-FC.

In vitro study of clavulanic acid in combination with penicillin, amoxycillin, and carbenicillin.

Abstract: The activity of clavulanic acid alone and in combination with penicillin, amoxycillin, and carbenicillin was studied. Marked reductions in the minimum inhibitory concentrations (MICs) for a wide spectrum of beta-lactamase-producing clinical isolates were found. Of particular interest were the decreased MICs of penicillin for Bacteroides fragilis and beta-lactamase-producing strains of Neisseria gonorrhoea in the presence of the clavulanic acid. Beta-lactamase-producing strains of Escherichia coli, Klebsiella spp., and indole-negative Proteus also showed considerably increased susceptibility to amoxycillin in combination with clavulanic acid. Two beta-lactamase-producing strains of Pseudomonas aeruginosa remained resistant to carbenicillin in the presence of clavulanic acid.

Mechanism of the Antimicrobial Action of Pyrithione: Effects on Membrane Transport, ATP Levels, and Protein Synthesis

Abstract: Pyrithione is a general inhibitor of membrane transport processes in fungi. A brief preincubation of Penicillium mycelia with pyrithione resulted in a marked decrease in the activities of a variety of independently regulated transport systems, including those for inorganic sulfate, inorganic phosphate, methylamine (actually, the NH4+ permease), choline-O-sulfate, glucose, l-methionine (a specific system), and several hydrophobic l-α-amino acids (the general amino acid permease). The degree of inhibition at any fixed pyrithione concentration and exposure time increased as the pH of the incubation medium was decreased. This result strongly suggests that the active species is the un-ionized molecule and that pyrithione acts by collapsing a transmembrane ΔpH driving force. The degree of transport inhibition caused by a given concentration of pyrithione increased with increasing time of exposure to the inhibitor. However, exposure time and pyrithione concentration were not reciprocally related. At “low” pyrithione concentrations, transport inhibition plateaued at some finite value. This observation suggests that the fungi can detoxify low levels of the inhibitor. The concentration of pyrithione required for a given degree of growth inhibition increased as the experimental mycelial density increased. This phenomenon was consistent with the suggestion that the fungi are capable of inactivating pyrithione.

Azlocillin and mezlocillin: new ureido penicillins.

Abstract: The activity of azlocillin and mezlocillin, new semisynthetic ureido penicillins, was investigated and compared with that of other known beta-lactam antibiotics. At a concentration of 25 mug/ml, azlocillin inhibited 74% of Enterobacter, 97% of Proteus mirabilis, 64% of Citrobacter, 91% of Pseudomonas aeruginosa, and 82% of Bacteroides strains tested. Mezlocillin inhibited 86% of Shigella, 96% of Enterobacter, 80% of indole-positive Proteus, 88% of Bacteroides, and 63% of Pseudomonas strains tested. Azlocillin was more active against Pseudomonas than was ticarcillin, carbenicillin, or mezlocillin. Mezlocillin was more active than carbenicillin and ampicillin against Escherichia coli, Klebsiella, Enterobacter, Citrobacter, Acinetobacter, Serratia, and Bacteroides. Azlocillin and mezlocillin were less active than cefazolin against beta-lactamase-producing E. coli and Klebsiella strains but more active than cefazolin against Enterobacter, indole-positive Proteus, Acinetobacter, Citrobacter, and Serratia strains. Both compounds showed activity equivalent to that of cefoxitin against Bacteroides isolates. Both agents were destroyed by many of the beta-lactamases from gram-negative organisms.

Inactivation of herpes simplex viruses by nonionic surfactants.

Abstract: Inactivation of herpes simplex viruses (HSV) by nonionic surfactants is reported. Nonionic surface-active agents which possessed ether or amide linkages between the hydrophillic and hydrophobic portions of the molecule rapidly inactivated the infectivity of HSV. The activity came from the ability of nonionic surfactants to dissolve lipid-containing membranes. This was verified by observing surfactant destruction of mammalian cell plasma membranes and HSV envelopes. Proprietary vaginal contraceptive formations containing nonionic surfactants also inactivated HSV infectivity. These data suggest that nonionic surfactants in appropriate formulation could effectively prevent HSV transmission.

Treatment of Experimental Herpesvirus Infections with Phosphonoformate and Some Comparisons with Phosphonoacetate

Abstract: Phosphonoformate (PF) at a concentration of 5 to 10 μg/ml inhibited the growth of type 1 strains of herpes simplex virus (HSV) in tissue culture, whereas 20 to 30 μg/ml was required for inhibition of type 2 strains and about 50 μg/ml was required for murine cytomegalovirus. In mice inoculated intraperitoneally or intracerebrally with HSV or intraperitoneally with murine cytomegalovirus, treatment with 250 to 400 mg of PF per kg twice daily for 5 days had only minimal effectiveness. When mice were inoculated intravaginally (i.vg.) with HSV type 2 and treated i.vg. with 10% PF beginning 3 h after viral inoculation, treatment was effective in completely inhibiting viral replication in the genital tract. If i.vg. therapy was initiated 24 h after infection, when the mice had a mean virus titer of 105 plaque-forming units in vaginal secretions, a significant reduction in the mean virus titer was observed on days 3, 5, and 7 after infection as compared with control animals. In guinea pigs treated i.vg. with 10% PF beginning 6 h after i.vg. inoculation with HSV type 2 there was also complete inhibition of viral replication in the genital tract, and no extenal lesions developed. When therapy was initiated 24 h after infection there was a 4 to 5-log decrease in viral titers on days 3, 5, and 7 of the infection and a slight delay in the development of external lesions.

Mode of Action of Quindoxin and Substituted Quinoxaline-di-N-Oxides on Escherichia coli

Abstract: The effect of quindoxin on the synthesis of deoxyribonucleic acid (DNA), ribonucleic acid, and protein in Escherichia coli KL 399 was examined under aerobic and anaerobic conditions. In the absence of oxygen the synthesis of DNA was completely inhibited by 10 ppm of quindoxin, whereas the syntheses of ribonucleic acid and protein were not affected. Quinoxalin-di-N-oxides (QdNO) induce degradation of DNA in both proliferating and non-proliferating cells. polA, recA, recB, recC, exrA, and uvrA mutants were more susceptible than the corresponding repair-proficient strains. All strains were more resistant in the presence of oxygen. Quindoxin was reduced to quinoxalin-N-oxide by intact E. coli cells or by a cell-free E. coli extract. Electron spin resonance measurements demonstrated the generation of free radicals during the reduction of quindoxin. Oxygen or deficiency of energy sources impaired the antibiotic activity and the reduction of QdNO. The QdNO reductase activity was demonstrated to be lower in QdNO-resistant mutants than in the susceptible parent strain. Based on these results it is concluded that an intermediate of reduction, probably a free radical, is responsible for the lethal effect of quindoxin. With three independent techniques no evidence has been found for binding of quindoxin to DNA.

Inhibition of Herpesvirus Replication and Herpesvirus-Induced Deoxyribonucleic Acid Polymerase by Phosphonoformate

Abstract: Phosphonoformate was found to be an inhibitor of the deoxyribonucleic acid polymerase induced by the herpesvirus of turkeys. The apparent inhibition constants were 1 to 3 μM. Phosphonoformate was also able to block the replication in cell culture of Marek's disease herpesvirus, the herpesvirus of turkeys, and herpes simplex virus. It was as effective as phosphonoacetate. Phosphonoformate was not an effective inhibitor of a phosphonoacetate-resistant mutant of the herpesvirus of turkeys nor of its induced deoxyribonucleic acid polymerase.

Piperacillin: Human Pharmacokinetics After Intravenous and Intramuscular Administration

Abstract: The pharmacokinetics of piperacillin were studied in a total of 26 Caucasian normal male volunteers. Single intramuscular doses of 0.5, 1.0, and 2.0 g were given to three groups, each containing eight volunteers. Mean peak serum concentrations of 4.9, 13.3, and 30.2 mug/ml were assayed at 30 to 50 min, and measurable levels were present up to 4, 6, and 8 h, respectively, after dosing. Single intravenous bolus doses of 1.0, 2.0, 4.0, and 6.0 g were given to four groups of five subjects, and mean serum concentrations of 70.7, 199.5, 330.7, and 451.8 mug/ml were measured at the end of the injections. The antibiotic had a mean terminal serum half-life of 60 to 80 min after the intramuscular doses and 36 to 63 min after intravenous administrations, depending on the dose. The apparent distribution volume was 20 to 24 liters/1.73 m(2), and distribution volume at steady state was 16 to 19 liters/1.73 m(2). Mean urinary recovery in 24 h was 74 to 89% for the intravenous doses and 57 to 59% for the intramuscular doses. The piperacillin-creatinine clearance ratios indicated that the proportion of renal excretion of piperacillin through tubular secretion was 56 to 73%, and this was confirmed by the renal clearance data from eight volunteers receiving probenecid treatment before the piperacillin dose. Probenecid (1 g given orally before administration of piperacillin) increased peak serum concentration by 30%, terminal serum half-life by 30%, and the area under the plasma concentration curve by 60%, and it decreased the apparent distribution volume by 20% and the renal clearance of the intramuscularly administered (1 g) antibiotic by 40%. Injections of piperacillin by both parenteral routes were well tolerated.

Single and combination antibiotic therapy of Staphylococcus aureus experimental endocarditis: emergence of gentamicin-resistant mutants

Abstract: The efficacy of nafcillin and gentamicin used alone and in combination at doses giving serum concentrations comparable to those achieved in patients was studied in rabbits with experimental Staphylococcus aureus endocarditis. The organism used was a penicillinase-producing, methicillin-susceptible, clinical isolate. The addition of gentamicin to nafcillin significantly increased the rate of killing of organisms in valvular vegetations, compared to the effect of nafcillin alone. Gentamicin alone delayed mortality but was not effective in reducing the bacterial populations of the vegetations. Bacteremia persisted in the animals treated with gentamicin alone, in contrast to the groups treated with nafcillin or the combination. Selection of a subpopulation of aminoglycoside-resistant small-colony variants occurred in animals treated with gentamicin alone. This variant was subsequently employed in the rabbit model and produced endocarditis, metastatic infection, and bacteremia comparable to those caused by the parent strain. Animals with infection produced by the variant died later than animals infected by the parent strain. Nafcillin was equally effective in reducing the population of both parent and variant strains in vitro and in therapy of the infected animals. Population studies showed the variant to be a mutant emerging at a rate of 1.9 x 10(-7). It was shown to differ from the parent strain in coagulase and hemolysin production, colonial morphology, and aminoglycoside susceptibility, but was similar by light and electron microscopy and in phage type, pigmentation of colonies, deoxyribonuclease production, mannitol fermentation, and growth rate.

Iodometric assay method for beta-lactamase with various beta-lactam antibiotics as substrates.

Abstract: The rapid fixed-time assay for penicillinase was modified for measuring β-lactamase activity with twelve substrates, i.e., benzylpenicillin, ampicillin, cloxacillin, methicillin, carbenicillin, cefazolin, cephalothin, cephaloglycin, cephalexin, cephalosporin C, 7-aminocephalosporanic acid, and cefoxitin. The method depends upon the reduction of iodine by the hydrolyzed substrate. Determined experimentally, 1 mol of hydrolyzed penicillins consumed 3.4 to 4.0 mol of iodine (I2). Iodine consumption of hydrolyzed cephalosporins varied widely from 1.7 for cephalothin to 3.7 for cefazolin. The method is useful for routine assay of β-lactamase activity with various substrates.

In vitro activity of antimicrobial agents on Legionnaires disease bacterium.

Abstract: Six isolates of Legionnaires disease bacteria were tested for their susceptibility to 22 antimicrobial agents. The most active agent was rifampin (minimal inhibitory concentration,

HR 756, a highly active cephalosporin: comparison with cefazolin and carbenicillin.

Abstract: HR 756, a new parenteral cephalosporin, was compared with cefazolin and carbenicillin for activity against a total of 264 strains of Pseudomonas aeruginosa, Escherichia coli, Klebsiella spp., Proteus mirabilis, Proteus spp. (indole positive), Enterobacter spp., Salmonella typhi, Serratia marcescens, Providencia stuartii, and Staphylococcus aureus. In every comparison, except that with the last organism, HR 756 was clearly more active than cefazolin and carbenicillin. All three compounds had similar activity against penicillin-susceptible staphylococci; against penicillin-resistant strains, HR 756 and cefazolin were equally active and superior to carbenicillin. HR 756 was compared with penicillin for activity against strains of Streptococcus pyogenes, Lancefield group D streptococci, and Neisseria gonorrhoeae; with ampicillin against Haemophilus influenzae; and with cefoxitin against Bacteriodes fragilis. HR 756 was clearly more active than the respective reference compounds in all of these comparisons, except those involving the streptococci. HR 756 and penicillin were essentially equally active against S. pyogenes; against Lancefield group D, penicillin was 32 times as active as HR 756. HR 756 not only compared favorably with the reference compounds with respect to relative activity, but also effected growth inhibition of essentially all test organisms (P. aeruginosa and group D streptococci excepted) at remarkably low concentrations ranging from 0.015 to 2.0 μg/ml. A series of seven transfers of selected strains of E. coli, Klebsiella spp., S. aureus, and P. aeruginosa through medium containing HR 756 led to emergence of strains with significant levels of resistance to the agent. Resistance to HR 756 was retained for at least seven transfers through plain medium.

Combined Activity of Clavulanic Acid and Ticarcillin Against Ticarcillin-Resistant, Gram-Negative Bacilli

Abstract: Fifty-one clinical isolates of ticarcillin-resistant, gram-negative bacilli were tested for susceptibility to combinations of ticarcillin and clavulanic acid (BRL 14151), a potent beta-lactamase inhibitor. Minimal inhibitory concentrations (MICs) were measured by a microdilution method, and minimal bactericidal concentrations for selected strains were measured by the broth dilution method. Ticarcillin MICs were ≥128 μg/ml for all and ≥512 μg/ml for 38 (75%) of the strains. Thirty-nine strains of Enterobacteriaceae tested included Escherichia coli (14), Klebsiella pneumoniae (16), Citrobacter sp. (3), Enterobacter sp. (3), Salmonella enteritidis (1), Serratia marcescens (1), and Proteus mirabilis (1). Ticarcillin MICs for 34 strains (88%) were lowered at least threefold by the addition of 1.0 μg of clavulanic acid per ml. Against 33 strains (85%), the MICs were 64 μg or less per ml in the presence of 5 μg of clavulanic acid per ml. In contrast, the MICs for seven of eight strains of Pseudomonas aeruginosa were unaffected by the addition of up to 10 μg of clavulanic acid per ml. Ticarcillin with 5 μg of clavulanic acid per ml was bactericidal against ticarcillin-resistant (MIC ≥ 2,048 μg/ml) E. coli, K. pneumoniae, Enterobacter, and P. mirabilis.

Susceptibility of Anaerobic Bacteria to Ten Antimicrobial Agents

Abstract: The susceptibility pattern of 265 anaerobic bacteria from clinical isolates to 10 antimicrobial agents was investigated by the agar dilution technique. Penicillin G, in a concentration of 16 μg/ml, was active against most organisms, important exceptions being 12% of Bacteroides melaninogenicus and 24% of B. fragilis strains. The susceptibility of strains to ampicillin was similar to their susceptibility to penicillin G. Carbenicillin, at ≤128 μg/ml, inhibited all but a few strains. Cefamandole was less active than the penicillins; 82% of B. melaninogenicus , 32% of B. fragilis , and 75% of Fusobacterium strains were inhibited by ≤16 μg/ml. A trend towards tetracycline resistance was seen in many bacterial groups, especially Bacteroides, Fusobacterium , and Clostridium . All organisms were susceptible to chloramphenicol and clindamycin in concentrations of ≤16 μg/ml and ≤4 μg/ml, respectively. Erythromycin was less active than clindamycin against all strains tested. Metronidazole and tinidazole were active against most anaerobes, but resistance of a few strains in each group was encountered. The increased resistance of B. melaninogenicus strains to penicillin, and emergence of anaerobes resistant to >16 μg of imidazole per ml may have therapeutic implications.

Killing of Intraphagocytic Staphylococcus aureus by Dihydrostreptomycin Entrapped Within Liposomes

Abstract: Liposomes (phospholipid vesicles) may serve as vehicles of antibiotic transport to intracellular sites. Liposomes containing entrapped dihydrostreptomycin enhanced killing of Staphylococcus aureus contained within phagocytic vacuoles.

Enzymatic Modification of Aminoglycoside Antibiotics: 3-N-Acetyltransferase with Broad Specificity that Determines Resistance to the Novel Aminoglycoside Apramycin

Abstract: Examination of a number of R-plasmid-containing bacterial isolates of animal origin has revealed the presence of a new aminoglycoside acetyltransferase (3- N ) with a broad substrate range that includes all the disubstituted 2-deoxystreptamine antibiotics and also the novel monosubstituted antibiotic apramycin. Antibiotic derivatives acylated with hydroxyaminobutyric acid at the 1-amino position were not modified by the enzyme.

In Vitro Activity of Rifampin Alone and in Combination with Nafcillin and Vancomycin Against Pathogenic Strains of Staphylococcus aureus

Abstract: Twenty strains of Staphylococcus aureus isolated from patients with endocarditis were examined in vitro for susceptibility to rifampin, nafcillin, and vancomycin and to combinations of rifampin with nafcillin or vancomycin. Minimum bactericidal concentrations of rifampin ranged from 0.0031 to 0.0125 mug/ml, of nafcillin ranged from 0.078 to 0.312 mug/ml, and of vancomycin ranged from 0.312 to 1.25 mug/ml. The combination of rifampin with nafcillin was synergistic for 12 strains; the combination of rifampin plus vancomycin was synergistic for 5 of the isolates.

Cefuroxime, a Beta-Lactamase-Resistant Cephalosporin with a Broad Spectrum of Gram-Positive and -Negative Activity

Abstract: The in vitro activity of cefuroxime, a cephalosporin antibiotic, was investigated against 604 isolates and compared with the activity of other β-lactam compounds. Cefuroxime had activity comparable to that of other cephalosporins, including cefamandole and cefoxitin, against streptococcal and staphylococcal species; most streptococci were inhibited by 0.1 μg or less per ml, and staphylococci were inhibited by 1.6 μg or less per ml. Enterococci were relatively resistant. Cefuroxime inhibited β-lactamase-producing Neisseria gonorrhoeae and Haemophilus influenzae. Cefuroxime had excellent activity against members of the Enterobacteriaceae; 83% of β-lactamase-producing Escherichea coli, 100% of Salmonella, 100% of Klebsiella, 90% of Proteus mirabilis, 95% of Citrobacter, 56% of Enterobacter, and 58% of Shigella were inhibited by 12.5 μg/ml. Cefuroxime had activity comparable to that of cefamandole and cefoxitin; it inhibited isolates of E. coli and Klebsiella resistant to cefamandole and inhibited Enterobacter and Citrobacter resistant to cefoxitin. Many isolates of Serratia, some indole-positive strains of Proteus, and Bacteroides fragilis were resistant to cefuroxime. Resistance of cefuroxime to hydrolysis by β-lactamases played a major role in its activity against both gram-positive and gram-negative organisms.