The effectiveness of processed grapefruit-seed extract as an antibacterial agent: II. Mechanism of action and in vitro toxicity

OBJECTIVES: Recent testimonials report grapefruit-seed extract, or GSE (Citricidal) to be effective against more than 800 bacterial and viral strains, 100 strains of fungus, and a large number of single and multicelled parasites. This study investigated GSE for antibacterial activity at varying time intervals and concentration levels and tissue toxicity at varying concentrations in an effort to determine if a concentration existed that was both microbicidal and nontoxic and in what period of time. DESIGN: Gram-negative and gram-positive isolates were introduced into graduated dilutions of GSE (twofold concentrations ranging from 1:1, through 1:512) for determination of bacterial activity. In vitro assays with human skin fibroblast cells were also performed at the same dilutions to determine toxicity. RESULTS: These tests indicated that from the 1:1 through the 1:128 concentrations, GSE remained toxic as well as bactericidal. However, test results indicated that at the 1:512 dilution, GSE remained bactericidal, but completely nontoxic. CONCLUSIONS: The initial data shows GSE to have antimicrobial properties against a wide range of gram-negative and gram-positive organisms at dilutions found to be safe. With the aid of scanning transmission electron microscopy (STEM), the mechanism of GSE's antibacterial activity was revealed. It was evident that GSE disrupts the bacterial membrane and liberates the cytoplasmic contents within 15 minutes after contact even at more dilute concentrations.     

Antibacterial activity and mechanism of action of a novel anilinouracil-fluoroquinolone hybrid compound

The anilinouracils (AUs) such as 6-(3-ethyl-4-methylanilino)uracil (EMAU) are a novel class of gram-positive, selective, bactericidal antibacterials which inhibit pol IIIC, the gram-positive-specific replicative DNA polymerase. We have linked various fluoroquinolones (FQs) to the N-3 position of EMAU to generate a variety of AU-FQ "hybrids" offering the potential for targeting two distinct steps in DNA replication. In this study, the properties of a hybrid, "251D," were compared with those of representative AUs and FQs in a variety of in vitro assays, including pol IIIC and topoisomerase/gyrase enzyme assays, antibacterial, bactericidal, and mammalian cytotoxicity assays. Compound 251D potently inhibited pol IIIC and topoisomerase/gyrase, displayed gram-positive antibacterial potency at least 15 times that of the corresponding AU compound, and as expected, acted selectively on bacterial DNA synthesis. Compound 251D was active against a broad panel of antibiotic-resistant gram-positive pathogens as well as several gram-negative organisms and was also active against both AU- and FQ-resistant gram-positive organisms, demonstrating its capacity for attacking both of its potential targets in the bacterium. 251D also was bactericidal for gram-positive organisms and lacked toxicity in vitro. Although we obtained strains of Staphylococcus aureus resistant to the individual parent compounds, spontaneous resistance to 251D was not observed. We obtained 251D resistance in multiple-passage experiments, but resistance developed at a pace comparable to those for the parent compounds. This class of AU-FQ hybrids provides a promising new pharmacophore with an unusual dual mechanism of action and potent activity against antibiotic-sensitive and -resistant gram-positive pathogens.     

The efficacy of nystatin combined with topical microbial agents in the treatment of burn wound sepsis

Pilot in vitro studies demonstrated that nystatin combined with Silvadene (silver sulfadiazine 1% [Marion Laboratories, Inc., Kansas City Mo.]) or Furacin in a 1:1 ratio was equally effective against Candida albicans and ATCC strains of Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli, but Sulfamylon (Winthrop Pharmaceuticals, Winthrop, N.Y.) combined with nystatin demonstrated an antagonistic response. Therefore we examined the susceptibility to nystatin of 165 clinical isolates, both gram-positive and gram-negative, to nystatin combined with Silvadene or Sulfamylon and 144 isolates to nystatin and Furacin. Both Silvadene and Furacin combined with nystatin were equally effective against the microorganisms as were the individual drugs. Conversely, Sulfamylon combined with nystatin lost its antimicrobial capability (93.3% resistance, p less than 0.001). On the basis of the in vitro results, 93 patients with acute burns were treated with the appropriate topical antimicrobials from April 1988 to September 1988. Of the 93 patients treated, 90 had neither a major systemic bacterial nor a Candida sepsis, and none of these patients had associated localized burn wound sepsis during their hospital stays. These 90 patients were discharged without any documented signs of infection. The average burnsize was greater than or equal to 29.44% total body surface area. These data suggest that the antimicrobial properties of nystatin, when combined with Silvadene and Furacin, remain effective. Consequently, such combinations have been effective in controlling both local and systemic Candida and bacterial burn wound sepsis.     

Antibacterial activity of the fourth-generation fluoroquinolones gatifloxacin and moxifloxacin against ocular pathogens

The ideal ophthalmic anti-infective exhibits broad-spectrum activity against gram-positive, gram-negative, and atypical bacterial species. These pathogens can cause potentially blinding infections such as keratitis and endophthalmitis, both of which are associated with ophthalmic surgery or traumatic injury. These infections often require aggressive antibacterial therapy, preferably with newer generations of antibiotics. In this study, minimal inhibitory concentration (MIC) values for gatifloxacin and moxifloxacin were determined in vitro against bacterial strains that were isolated from suspected cases of bacterial keratitis and endophthalmitis. The ocular isolates included 7 gram-positive, 4 gram-negative, and 3 atypical bacterial species. Gatifloxacin and moxifloxacin exhibited similar activity against 6 gram-positive organisms: Staphylococcus epidermidis, Staphylococcus aureus, Streptococcus pneumoniae, Streptococcus pyogenes, Bacillus cereus, and Enterococcus faecalis. MIC90 values for the drugs against these isolates ranged from 0.08 mg/mL to 0.57 mg/mL and were comparable to previously published values against isolates from patients with systemic infections. The MIC90 for gatifloxacin against Streptococcus viridans was 0.22 mg/mL compared with 0.73 mg/mL for moxifloxacin (P = .011). Among the gram-negative isolates, the mean MIC90 for gatifloxacin against Pseudomonas aeruginosa was 1.28 mg/mL compared with 2.60 mg/ mL for moxifloxacin (P = .023). MIC90 values for gatifloxacin against Klebsiella pneumoniae and Enterobacter aerogenes were one fourth to one fifth the values for moxifloxacin. For the atypicals, the MIC90 values for gatifloxacin against Nocardia asteroides and Mycobacterium chelonae were one fourth the corresponding values for moxifloxacin. Gatifloxacin demonstrated a broad spectrum of activity against several key ocular pathogens tested in this study and was at least as effective as moxifloxacin against these pathogens.     

In Vitro Susceptibility of Selected Bacteria to Three Diphosphonia Heterocyclic Compounds

The antibacterial activity of 1,1,4,4-tetraphenyl-1,4-diphosphonia-2,5-diphenylcyclohexadi-2,5-ene dichloride and two of its derivatives were screened for activity using the disk method. All derivatives exhibited antibacterial activity against gram-positive organisms tested, but little inhibition of gram-negative species was noted.     

Antimicrobial Activities of Amine- and Guanidine-Functionalized Cholic Acid Derivatives

Compounds in a series of cholic acid derivatives, designed to mimic the activities of polymyxin B and its derivatives, act as both potent antibiotics and effective permeabilizers of the outer membranes of gram-negative bacteria. Some of these compounds rival polymyxin B in antibacterial activity against gram-negative bacteria and are also very active against gram-positive organisms. Other compounds interact synergistically with hydrophobic antibiotics to inhibit bacterial growth.     

Susceptibilities of bacterial isolates from patients with cancer to levofloxacin and other quinolones.

The antibacterial activity of levofloxacin was compared with those of ofloxacin and ciprofloxacin against bacterial isolates from patients with cancer. In general, levofloxacin was as active or was twofold more active than ofloxacin and was two- to fourfold less active than ciprofloxacin against most gram-negative pathogens. Against Pseudomonas aeruginosa, ciprofloxacin was the most active agent tested (MIC for 90% of isolates tested, 1.0 microgram/ml). Overall, all three agents had similar activities against gram-positive organisms and were moderately active against methicillin-susceptible Staphylococcus aureus and coagulase-negative staphylococci, Streptococcus species, and Enterococcus species.     

In vitro and in vivo antibacterial efficacies of CFC-222, a new fluoroquinolone.

CFC-222 is a novel fluoroquinolone containing a C-7 bicyclic amine moiety with potent antibacterial activities against gram-positive, gram-negative, and anaerobic organisms. We compared the in vitro and in vivo activities of CFC-222 with those of ciprofloxacin, ofloxacin, and lomefloxacin. CFC-222 was more active than the other fluoroquinolones tested against gram-positive bacteria. CFC-222 was particularly active against Streptococcus pneumoniae (MIC at which 90% of isolates are inhibited [MIC90], 0.2 microg/ml), Staphylococcus aureus (MIC90, 0.2 microg/ml for ciprofloxacin-susceptible strains), and Enterococcus faecalis (MIC90, 0.39 microg/ml). Against Escherichia coli and other members of the family Enterobacteriaceae, CFC-222 was slightly less active than ciprofloxacin (MIC90s for E. coli, 0.1 and 0.025 microg/ml, respectively). The in vitro activity of CFC-222 was not influenced by inoculum size, medium composition, or the presence of horse serum. However, its activity was decreased significantly by a change in the pH of the medium from 7.0 to 6.0, as was the case for the other quinolones tested. The in vivo protective efficacy of CFC-222 by oral administration was greater than those of the other quinolones tested in a mouse model of intraperitoneally inoculated systemic infection caused by S. aureus. CFC-222 exhibited efficacy comparable to that of ciprofloxacin in the same model of infection caused by gram-negative organisms, such as E. coli and Klebsiella pneumoniae. In this infection model, CFC-222 was slightly less active than ciprofloxacin against Pseudomonas aeruginosa. These results suggest that CFC-222 may be a promising therapeutic agent in various bacterial infections.     

The efficacy of Polysporin First Aid Antibiotic Spray (polymyxin B sulfate and bacitracin zinc) against clinical burn wound isolates

Polysporin First Aid Antibiotic Spray (Burroughs Wellcome Co., Research Triangle Park, N.C.) is a dry spray containing 200,000 units Aerosporin (polymyxin B sulfate) and 10,000 units bacitracin zinc, along with a propellant. Each 1-second spray delivers approximately 2300 units of polymyxin B sulfate and 115 units of bacitracin zinc. This study was designed to evaluate the efficacy of Polysporin Spray against various clinical isolates. Blood agar plates were inoculated with a pure culture of each isolate. Polysporin was then sprayed in an area approximately 30 mm in diameter. The area of inhibition was measured and recorded after 18 to 24 hours of incubation. A clear zone at least 20 mm in diameter with surrounding edges of growth indicated sensitivity. A zone less than 20 mm in diameter or growth over the whole plate indicated resistance. Three hundred fifty-three clinical isolates (202 gram positive and 151 gram negative) were tested. The results show that Polysporin inhibits the growth of all the gram-positive organisms, including methicillin-resistant strains of Staphylococcus. The gram-negative organisms were also sensitive to Polysporin Spray, with the exception of Serratia marcescens, Morganella morganii, and Proteus mirabilis. This study suggests that Polysporin First Aid Antibiotic Spray may be effective for wounds contaminated with gram-positive and some gram-negative organisms.     

Norfloxacin and silver-norfloxacin as topical antimicrobial agents: results of in vitro susceptibility testing against bacteria and Candida sp isolated from burn patients

Because of its broad spectrum of antibacterial action, Norfloxacin, a new quinoline carboxylic acid compound, was formulated in a topical cream base and tested for activity against a variety of bacteria and yeasts isolated from burn patients. An in vitro agar well diffusion topical susceptibility test was used. The silver salt of Norfloxacin also was tested. For comparative purposes, commonly used topical antibacterial and antifungal preparations were examined as well. No bacterial isolate tested was resistant to the action of Norfloxacin or that of silver-Norfloxacin. Furthermore, all Candida organisms assayed were susceptible to silver-Norfloxacin. All other topical agents tested had some strains of bacteria or yeast, or both, that were resistant to their action. Therefore, Norfloxacin and, particularly, silver-Norfloxacin, warrant further development as topical anti-infective agents for use in treating burn patients.     

Comparison of ofloxacin, gentamicin, and tobramycin concentrations in tears and in vitro MICs for 90% of test organisms.

Concentrations of three anti-infective agents in tear film were monitored after one topical application in rabbits. Ofloxacin concentrations exceeded the MIC for 90% of the organisms tested (MIC90) (gram-negative and gram-positive organisms) for 240 min. Tobramycin concentrations exceeded the MIC90 for 10 min. Gentamicin concentrations exceeded the MIC90 for 20 min for gram-positive organisms and 120 min for gram-negative organisms.     

Therapeutic efficacy of timentin and augmentin versus silvadene in burn wound infections

Successful closure of thermal injuries, by either skin graft or delayed wound closure, largely depends on the ability to control the number of bacteria in the wound. The purpose of this study was to investigate the efficacy of two new antimicrobial agents, ticarcillin and clavulanate (Timentin) and amoxicillin and clavulanate (Augmentin), in the infected thermal injury. The therapeutic results were compared with the model treated with the standard topical silver sulfadiazine (Silvadene). Seventy-six Sprague-Dawley rats received a 20% full-thickness thermal injury and were then divided into six treatment groups. Three of the groups were inoculated topically with 10(8) Pseudomonas aeruginosa/ml, and three of the groups received topical inoculation of 10(8) Staphylococcus aureus/ml. The groups inoculated with P. aeruginosa received either intraperitoneal Timentin, topical Silvadene, or placebo treatment. The groups inoculated with S. aureus were treated with either enteral Augmentin, topical Silvadene, or placebo. The animals received 10 days of therapy and underwent tissue biopsies on alternate days. Statistical analysis showed that the level of bacteria in the wounds compared with the control group was significantly (p less than 0.05) decreased for both antibiotics tested as measured by quantitative wound biopsies. These studies demonstrate the efficacy of systemic Timentin and Augmentin in the infected thermal injury.     

Laboratory evaluation of the Anderson Technical semiautomated susceptibility testing system.

Anderson Technical, Inc. has developed rapid, semiautomated equipment for antimicrobial susceptibility testing. A total of 310 fresh clinical bacterial isolates (226 gram-negative and 75 gram-positive) were tested with the Anderson Technical system and compared with those of Micro-Media Systems, Inc. For the gram-positive organisms, 74.3% of the test pairs had identical minimum inhibitory concentration values, whereas 99.1 and 0.9% of the test pairs had minimal inhibitory concentration values differing by less than or equal to 1 and greater than 1 dilution level, respectively. Identical minimum inhibitory concentration values were obtained for 67.2% of the gram-negative test pairs, whereas 97.6 and 2.4% differed by less than or equal to 1 and greater than 1 dilution level, respectively. For all organisms tested, 98.0% differed by less than or equal to 1 dilution level. The Anderson Technical equipment proved to be a rapid and flexible system for microdilution testing.     

In Vitro Bactericidal Effectiveness of Four Aminoglycoside Antibiotics

The antibacterial activity of four aminoglycoside antibiotics (gentamicin, Sch 13706, tobramycin, and sisomicin) was tested against eight gram-negative and three gram-positive species. A total of 323 strains were studied by the broth dilution technique. Tobramycin and sisomicin had greater bacteriostatic and bactericidal activity against Pseudomonas strains than did gentamicin and Sch 13706. Of the four antibiotics, sisomicin was most active against Klebsiella, Enterobacter, Escherichia coli, indole-negative and -positive Proteus, and Streptococcus pyogenes. Gentamicin was most effective against Serratia. A fourfold or greater difference existed frequently between the minimal inhibitory and bactericidal concentrations of all antibiotics against Enterobacter and Serratia. This difference was greatest with tobramycin. Staphylococcus aureus was highly susceptible, Providencia relatively resistant, and enterococcus uniformly resistant to the antibiotics studied. Agar diffusion susceptibility testing with gentamicin and tobramycin showed that organisms susceptible to less than 6.2 mug/ml usually yielded zones 17 to 26 mm in diameters. Zones of 15 to 16 mm represented intermediate susceptibility which varied with the organism and antibiotic. Several Serratia strains required 6.2 to 12.5 mug of gentamicin/ml or 25 to 50 mug of tobramycin/ml for bactericidal activity despite minimal inhibitory concentrations of 0.09 to 3.1 mug/ml and zone sizes greater than 13 and 17 mm, respectively. Studies with Enterobacter and tobramycin yielded similar results.     

Structure-guided discovery of novel aminoglycoside mimetics as antibacterial translation inhibitors

We report the structure-guided discovery, synthesis, and initial characterization of 3,5-diamino-piperidinyl triazines (DAPT), a novel translation inhibitor class that targets bacterial rRNA and exhibits broad-spectrum antibacterial activity. DAPT compounds were designed as structural mimetics of aminoglycoside antibiotics which bind to the bacterial ribosomal decoding site and thereby interfere with translational fidelity. We found that DAPT compounds bind to oligonucleotide models of decoding-site RNA, inhibit translation in vitro, and induce translation misincorporation in vivo, in agreement with a mechanism of action at the ribosomal decoding site. The novel DAPT antibacterials inhibit growth of gram-positive and gram-negative bacteria, including the respiratory pathogen Pseudomonas aeruginosa, and display low toxicity to human cell lines. In a mouse protection model, an advanced DAPT compound demonstrated efficacy against an Escherichia coli infection at a 50% protective dose of 2.4 mg/kg of body weight by single-dose intravenous administration.     

In Vitro Activity of Furazlocillin (Bay k 4999) Compared with Those of Mezlocillin, Piperacillin, and Standard Beta-Lactam Antibiotics

The activity of furazlocillin (Bay k 4999) was compared with those of mezlocillin, piperacillin, and standard beta-lactam antibiotics against a number of gram-positive and gram-negative organisms. These new expanded-spectrum penicillins were less active than penicillin G against most gram-positive organisms. Furazlocillin, mezlocillin, and piperacillin showed activity comparable to ampicillin and penicillin G against Haemophilus influenzae and penicillin-susceptible neisseriae, respectively. None of the drugs tested was effective against penicillin-resistant gonococci. The activity of furazlocillin was greater than that of mezlocillin, piperacillin, ampicillin, or carbenicillin against many Enterobacteriaceae. However, certain beta-lactam-resistant strains among these organisms were not highly susceptible to any of the three new penicillins. Furazlocillin was less active than piperacillin against Pseudomonas aeruginosa but was more active than carbenicillin or mezlocillin. Inoculum effects and discrepancies between minimal inhibitory concentrations and minimal bactericidal concentrations were observed with furazlocillin, mezlocillin, and piperacillin against several genera. The kinetics of bacterial killing by the new penicillins were often slow and incomplete over 24 h, especially in tests with Enterobacter and P. aeruginosa. Synergy was demonstrated between furazlocillin and aminoglycosides against a variety of gram-negative bacilli and Streptococcus faecalis.     

Incidence of beta-lactamase production among out patient clinical isolates in Middle Eastern countries and their antibiotic susceptibilities. Middle Eastern Study Group.

In a multicenter survey in seven Middle Eastern countries, 1,827 clinical isolates from patients with community-acquired infections (outpatients) were examined for both production of beta-lactamase and their susceptibility to commonly prescribed antibiotics. Of these isolates, 63% were gram-negative and 37% were gram-positive organisms. beta-lactamase was produced by 65% of all isolates, representing 61 and 75% of gram-negative and gram-positive organisms, respectively. Using standardized disk susceptibility testing, high rates of resistance were observed among gram-negative and gram-positive organisms, respectively, for penicillin (86 and 75%), ampicillin (67 and 66%) and amoxicillin (58 and 52%). Resistance to tetracycline and co-trimoxazole were also seen, but to a lesser degree. Susceptibility of these organisms towards the cephalosporins cepharadine, cephalexin and cefadroxil ranged from 30 to 70%, which appears to correlate fairly closely with the prevalence of beta-lactamase production. Cefuroxime inhibited about 94 and 79% of gram-positive and gram-negative organisms, respectively, regardless of the production of beta-lactamase. These data are valuable since antibiotic therapy is usually instituted on a best-guess principle against the most likely potential pathogens.     

Susceptibility of clinical isolates of bacteria to cefoxitin and cephalothin

The susceptibility of 4,929 unselected clinical isolates of bacteria to cefoxitin and cephalothin was determined by the single-disk method, using a computer-associated electronic zone analyzer to obtain, record, and process measurements of sizes of zones of inhibition. Both cefoxitin and cephalothin were effective against most gram-positive strains, including Staphylococcus aureus, S. epidermidis, micrococci, and all streptococci except enterococci. The three strains of Listeria monocytogenes tested were susceptible to cephalothin but resistant to cefoxitin. There was little difference between the cefoxitin and cephalothin susceptibility of Salmonellae, Citrobacter sp., Enterobacter sp., Proteus mirabilis, and Pseudomonas sp. Cefoxitin was more effective then cephalothin against Escherichia coli, Klebsiella sp., Serratia sp., indole-positive Proteus sp., Providence sp., Flavobacter sp., Herellea vaginicola, and Mima polymorpha. Cefoxitin also appeared to exhibit enhanced activity, as compared with cephalothin, against Bacteroides sp. Thus cefoxitin appears to have a very broad antibacterial spectrum which is greater than that of cephalothin, especially against gram-negative strains.     

Comparative in vitro activity of levofloxacin and ciprofloxacin against bacterial isolates from neutropenic patients

BACKGROUND: Novel fluoroquinolones have been recently introduced in the management of neutropenic patients because of their increased activity against gram-positive and gram-negative micro-organisms. METHODS: The activities of levofloxacin and ciprofloxacin were determined by the E test against 223 bacterial isolates from patients with haematological malignancies. RESULTS: In general, the activity of levofloxacin was comparable to that of ciprofloxacin. Levofloxacin was somewhat more active against methicillin-resistant Staphylococcus aureus isolates. All methicillin-susceptible S. aureus isolates were inhibited by ciprofloxacin and levofloxacin at a concentration of < or =0.5 and < or =0.25 microg/ml, respectively. Among gram-negative isolates tested, levofloxacin was significantly (p < 0.001) more active than ciprofloxacin against Stenotrophomonas maltophilia, inhibiting 68 and 53% of these isolates, respectively. CONCLUSIONS: Levofloxacin was not superior to ciprofloxacin in its overall antibacterial activity, although small differences between these agents were seen depending on the species tested. In particular, our data suggested that levofloxacin may potentially be used for the management of S. maltophilia infections in neutropenic patients.     

Comparative in vitro antimicrobial activity of a novel quinolone, garenoxacin, against aerobic and anaerobic microbial isolates recovered from general, vascular, cardiothoracic and otolaryngologic surgical patients

OBJECTIVES: The aim of the study was to analyse the susceptibility of unique and non-duplicate aerobic and anaerobic isolates from surgical patients to a novel des-F(6)-quinolone (garenoxacin) and other selected antimicrobial agents. METHODS: Eleven hundred and eighty-five aerobic and anaerobic isolates from general, vascular, cardiothoracic and otolaryngologic surgical patients were tested for susceptibility to garenoxacin and seven other antibiotics (ciprofloxacin, moxifloxacin, levofloxacin, piperacillin/tazobactam, imipenem, clindamycin and metronidazole) using the referenced microbroth and agar-dilution method. RESULTS: Garenoxacin exhibited greater antimicrobial activity than comparator quinolones such as ciprofloxacin, levofloxacin and other antimicrobials when tested against selected gram-positive organisms. The in vitro aerobic and anaerobic activity of garenoxacin was similar to that of moxifloxacin. All fluoroquinolones tested were effective against most gram-negative facultative anaerobes including Escherichia coli. Garenoxacin and moxifloxacin demonstrated similar in vitro antimicrobial activity against selected anaerobic gram-positive and gram-negative anaerobic bacteria such as members of the Bacteroides fragilis group. Overall, the in vitro activity of the advanced spectrum quinolones against anaerobic surgical isolates compared favourably with selected comparator agents, metronidazole, imipenem and piperacillin/tazobactam. CONCLUSIONS: These findings suggest that 82.4% of aerobic surgical isolates were susceptible to a concentration of garenoxacin < or = 1.0 mg/L, whereas 84.5% of the anaerobic isolates were susceptible to a garenoxacin concentration < or = 1.0 mg/L. Garenoxacin may be a valuable surgical anti-infective for treatment of serious head and neck, soft tissue, intra-abdominal and diabetic foot infections.