Rapid Bactericidal Effect Research Articles

Effect of a solution containing citrate/Methylene Blue/parabens on Staphylococcus aureus bacteria and biofilm, and comparison with various heparin solutions

Some antibiotic solutions increase bacterial resistance and may cause toxic side effects. Heparin, frequently used as an anticoagulant in catheter lock solutions, may cause bleeding and stimulate biofilm formation. The aim of this study was to investigate the effect of a new antibacterial/antithrombotic solution, citrate/Methylene Blue/parabens (C/MB/P), versus various heparin solutions on the viability and the structure of preformed mature biofilms of Staphylococcus aureus bacteria. The degree of eradication of both planktonic and sessile microorganisms was evaluated. The changes in the structure of biofilms after exposure to C/MB/P and several concentrations of heparin were analysed by means of confocal laser scanning microscopy. COMSTAT image analysis was utilized to compare biofilm biomass, average and maximum height, surface coverage and roughness coefficient. Viability studies were performed on both biofilms and supernatant solutions. C/MB/P, in contrast to heparin solutions, significantly reduced biofilm biomass and thickness and reduced viability by 5 log when compared with saline treatment. No viable planktonic bacteria were detected and the few remaining biofilm cells appeared to be lysed. In contrast, most heparin solutions only reduced viability up to 1.0 log and failed to eradicate planktonic bacteria. C/MB/P has a rapid bactericidal effect on the preformed, mature biofilm of S. aureus. The structural changes of biofilms treated with C/MB/P, together with the observed log reduction of viable biofilm cells, confirmed the high potential of this solution to eliminate sessile bacteria. Furthermore, the tested solution entirely eliminated planktonic bacteria detached from the biofilm.

Pharmacodynamic Studies of Vancomycin, Metronidazole and Fusidic Acid against Clostridium difficile

Background: Pharmacodynamic studies of antibiotics have attracted great interest in recent years. However, studies on the pharmacodynamics of different antibiotics against Clostridium difficile are scarce. Methods: The postantibiotic effects (PAE) and the postantibiotic sub-minimum inhibitory concentration (MIC) effects (PA SME) of vancomycin, metronidazole and fusidic acid were investigated by viable counts against three different strains of C. difficile. The killing rate and extent of the three antibiotics against the same strains were also studied by adding 2, 4, 8, 16 and 32× MIC of the three antibiotics, respectively. Results: Metronidazole exerted a very rapid bactericidal effect at concentrations of 8× MIC and above against all three strains investigated. Vancomycin gave overall less kill in comparison to metronidazole and was bacteriostatic against two of the three strains. Fusidic acid exerted a concentration-dependent killing against two of the strains. Vancomycin exerted short PAEs and PA SMEs against all three strains. Significantly longer PAEs and PA SMEs were noted for fusidic acid. Metronidazole gave similar short PAEs like vancomycin but longer PA SMEs were noted against two of the investigated strains. Conclusion: Metronidazole exerted the most prominent bactericidal effect greater than fusidic acid and greater than vancomycin. Fusidic acid gave overall the longest PAEs and PA SMEs greater than metronidazole and greater than vancomycin.

Experimental study of the efficacy of vancomycin, rifampicin and dexamethasone in the therapy of pneumococcal meningitis.

The object of the study was to assess the efficacy of rifampicin and the combination of rifampicin plus vancomycin in a rabbit model of experimental penicillin-resistant pneumococcal meningitis. We also studied the effect of concomitant dexamethasone on the CSF antibiotic levels and inflammatory parameters. The rabbit model of pneumococcal meningitis was used. Groups of eight rabbits were inoculated with 106 cfu/mL of a cephalosporin-resistant pneumococcal strain (MIC of cefotaxime/ceftriaxone 2 mg/L). Eighteen hours later they were treated with rifampicin 15 mg/kg/day, vancomycin 30 mg/kg/day or both plus minus dexamethasone (0.25 mg/kg/day) for 48 h. Serial CSF samples were withdrawn to carry out bacterial counts, antibiotic concentration and inflammatory parameters. Rifampicin and vancomycin promoted a reduction of >3 log cfu/mL at 6 and 24 h, and cfu were below the level of detection at 48 h. Combination therapy with vancomycin plus rifampicin was not synergic but it had similar efficacy to either antibiotic alone and it was able to reduce bacterial concentration below the level of detection at 48 h. Concomitant use of dexamethasone decreased vancomycin levels when it was used alone (P< 0.05), but not when it was used in combination with rifampicin. Rifampicin alone at 15 mg/kg/day produced a rapid bactericidal effect in this model of penicillin-resistant pneumococcal meningitis. The combination of vancomycin and rifampicin, although not synergic, proved to be equally effective. Using this combination in the clinical setting may allow rifampicin administration without emergence of resistance, and possibly concomitant dexamethasone administration without significant interference with CSF vancomycin levels.

Bactericidal properties of moxifloxacin and post-antibiotic effect.

The time-kill kinetics and post-antibiotic effect (PAE) of moxifloxacin were studied for strains of Streptococcus pneumoniae, Streptococcus pyogenes, Haemophilus influenzae, Staphylococcus aureus and Escherichia coli. Moxifloxacin had a bactericidal effect against all strains tested, with the least rapid bactericidal effect being against S. pyogenes and the most rapid effect against S. aureus and E. coli. The PAE of moxifloxacin was similar to that of other fluoroquinolones and increased with increasing concentration. No association was found between the bactericidal effect of moxifloxacin and the duration of PAE. Gram-positive and gram-negative organisms were also exposed to concentrations of moxifloxacin, sparfloxacin and amoxycillin that simulated the drug concentrations obtained in human serum after standard oral dosing schedules. Simulation of moxifloxacin concentrations in human serum reduced viable counts more effectively and more rapidly than shown in time-kill experiments; in contrast, sparfloxacin and amoxycillin were less effective than when constant concentrations of these antibacterials were used.

In vitro reduction of endotoxin concentrations with the 5S fragment of immunoglobulin G.

Endotoxin has long been implicated as an inducer for the development and progression of gram-negative sepsis. Accordingly, antiendotoxin therapy has been considered one of the major targets for the treatment of sepsis. To investigate the influence of a human immunoglobulin G (IgG) derivative, the 5S fragment of IgG (5S-IgG; Gamma-Venin, Centeon Pharma GmbH, Frankfurt-Niederrad, Germany), on endotoxin release during bacterial proliferation and under antibiotic bactericidal action, time-kill studies were performed by using Escherichia coli ATCC 25922 starting inocula of 10(3), 10(5), and 10(7) CFU/ml with cefotaxime (120 microg/ml) alone and in combination with 5S-IgG (2,100 microg/ml). Samples were collected for bacterial colony count and endotoxin concentration determinations; the area under the free endotoxin concentration curve (AUFEC) was calculated by using the trapezoidal rule. Colony counts showed that cefotaxime had a rapid bactericidal effect because it achieved greater than a 4-log decrease in the numbers of E. coli CFU per milliliter over the first 2 h; the addition of 5S-IgG did not appear to alter the kinetics of killing. Comparison of the AUFEC revealed that the addition of 5S-IgG resulted in a mean reduction of 50, 66, and 27% in the free endotoxin concentration at starting inocula of 10(3), 10(5), and 10(7) CFU/ml, respectively. Moreover, experiments were conducted with a starting inoculum of 10(5) CFU/ml and various amounts of 5S-IgG (2 to 20 mg/ml) to further investigate the dose-effect relation of 5S-IgG on endotoxin release. Decreased AUFECs were observed with increasing concentrations of 5S-IgG, suggesting the dose-dependent antiendotoxin activity of 5S-IgG. Further study is required to investigate the mechanism(s) responsible for this observation, the biological significance of this antiendotoxin activity, and the potential utility of 5S-IgG as an adjuvant therapy in the treatment of gram-negative sepsis.

Antibacterial Effects of Lactoferrin and a Pepsin-Generated Lactoferrin Peptide Against Helicobacter pylori in vitro

<i>Helicobacter pylori</i> is an etiologic agent of gastritis and peptic ulcer disease in humans. We investigated the antibacterial activities of lactoferrin and Lactoferricin^® (an antimicrobial peptide derived from lactoferrin) against this bacterium. The minimum bactericidal concentrations of bovine and human lactoferrins were 1.25 to 2.50mg/mL, while it was greater than 5.0mg/L for bovine Lactoferricin^®. Time-kill studies with <i>H. pylori</i> grown in brucella broth demonstrated that the antibacterial effects of the lactoferrins were dose-dependent within the range of 0.8 to 2.0mg/mL and began when the cells were in the exponential phase of growth. Iron-saturated lactoferrin did not inhibit the growth of <i>H. pylori</i>. Bovine Lactoferricin^® showed only weak activity against <i>H. pylori</i> in brucella broth, however, a rapid bactericidal effect was observed in 1% Bacto-peptone medium within 1 hour of exposure at concentrations in the range of 0.1 to 1.0mg/mL. Under these conditions, bovine lactoferrin showed little effect. Moreover, bovine Lactoferricin^® inhibited the urease activity of <i>H. pylori</i>, which is one of the virulence factors of this bacterium. These results indicate that <i>H. pylori</i> is susceptible to inhibition and inactivation by both lactoferrin and Lactoferricin^® in laboratory media. The antibacterial effect of lactoferrin appeared to be dependent on its iron status, the cellular phase of growth, and has a mechanism of action different from that of Lactoferricin^®.

Comparison of the bactericidal action of amikacin, netilmicin and tobramycin in free and liposomal formulation against Pseudomonas aeruginosa.

The rates at which free, cationic and anionic liposomal forms of amikacin, netilmicin and tobramycin kill Pseudomonas aeruginosa were studied in vitro. Control inocula with no antibiotic yielded 6.76, 9.53 and 9.74 log CFU/ml at 0, 6 and 24 h, respectively. Empty anionic or cationic liposomes had no effect on bacterial growth. The killing rates of free antibiotics against the bacterial strain were not enhanced by the addition of either empty anionic or cationic liposomes. After 6 and 24 h of exposure at 1, 2 and 4 times the minimum inhibitory concentrations, free amikacin, netilmicin and tobramycin demonstrated a more rapid bactericidal effect than encapsulated anionic or cationic liposomes. The killing rates of liposomal aminoglycosides were lower than those of free aminoglycosides at identical concentrations, suggesting that only fractions of the encapsulated drugs were released from liposomes.

A suggested approach to once‐daily aminoglycoside dosing.

1. The aminoglycoside antibiotics are 50 years old. Their success and continuing use can be attributed to various factors including rapid concentration-dependent bactericidal effect, synergism with beta-lactam antibiotics, clinical effectiveness, a low rate of true resistance and low cost. 2. The aminoglycosides remain drugs of choice in many circumstances including septicaemia, other serious infections due to Gram negative bacilli, and bacterial endocarditis. 3. Nephrotoxicity and ototoxicity have been the main drawbacks clinically for the aminoglycosides. 4. There has been an evolution in dosing strategies largely aimed at reducing toxicity. Therapeutic drug monitoring has been used extensively to assist dosing, and target concentrations have been advocated, such as peak concentrations of between 6 and 10 mg l-1 and through concentrations of < 2 mg l-1 for gentamicin, tobramycin and netilmicin. 5. Recently there has been a minor revolution in the approach to aminoglycoside dosing, with a change to larger doses, given less frequently. In its most convenient form this is 'Once-daily aminoglycoside dosing'. It offers the hope of better efficacy, less toxicity, and easier administration and monitoring. 6. This article summarises the background of aminoglycoside usage, leading up to the recent changes in dosing strategy.

Bactericidal effect of beta-lactams and amikacin alone or in association against Klebsiella pneumoniae producing extended spectrum beta-lactamase.

Ten extended spectrum beta-lactamases producing strains of Klebsiella pneumoniae characterized by analytical isoelectric focusing and studied for their susceptibility to beta-lactam antibiotics, either alone or in combination with a beta-lactamase inhibitor (clavulanic acid and sulbactam) and in association with amikacin. The extended spectrum beta-lactamases were derived from either TEM (CTX-1 = TEM-3) or SHV (CAZ-4 = SHV-5). Killing curves were studied with antibiotics at clinical by achievable concentrations, at MIC and MIC x 4. At MIC, cefotetan, cefotaxime and ceftazidime lacked bactericidal activity. Imipenem was more rapidly bactericidal than meropenem or co-amoxiclav. At MIC x 4, cefotetan and cefotaxime exhibited bactericidal effect but this was less than for imipenem which gave a reduction of 4 log10 of the inoculum. Cefotaxime plus sulbactam gave no bactericidal effect compared with cefotaxime plus co-amoxiclav. A bactericidal effect with cefotaxime plus sulbactam was seen with the addition of amikacin. At clinical concentrations cefotaxime plus co-amoxiclav +/- amikacin was as efficient as imipenem +/- amikacin with a rapid bactericidal effect (5-6 log10 in 30-60 min). We proposed that cefotaxime+co-amoxiclav might be considered as an alternative to imipenem for the treatment of extended spectrum beta-lactamase associated K. pneumoniae injections.

Aminoglycosides

Despite their nephrotoxic and ototoxic side effects, AG remain useful antibiotics because of their major, rapid, and dose-dependent bactericidal effects. Combination therapy with an AG appears particularly important in neutropenic and other high-risk patients to provide broad-spectrum bactericidal activity, synergism, and reduction of emergence of resistant pathogens. OD AG therapy is associated with high peak levels in serum that maintain efficacy and low-to-undetectable trough levels in serum that attenuate the risk of toxicity. Administration of short-term OD AG therapy to patients not at risk without renal impairment may not absolutely require dosing monitoring. This therapeutic strategy has been proved useful in clinical trials, now including febrile episodes in neutropenic patients, but it should be avoided during infections in which antimicrobial synergism is required, such as enterococcal endocarditis.

Inhibition of Listeria in Buffer, Broth, and Milk by Enterocin 1146, a Bacteriocin Produced by Enterococcus faecium

Enterocin 1146, a bacteriocin produced by Enterococcus faecium. DPC1146, has a rapid bactericidal effect on Listeria in buffer systems, broth, and milk. In trypticase soy broth, increasing the bacteriocin dose and/or decreasing the pH extended the lag phase of Listeria innocua. A logarithmic relationship was found between response (as proportion of survivors or growth compared to a control) and dose. Increasing the inoculum level of the indicator reduced the effectiveness of enterocin 1146. Log-phase cells of L. innocua were more resistant than stationary-phase cells in both broth and buffer systems. In milk treated with 250 arbitrary units of enterocin 1146/ml and inoculated with 103 or 105 CFU/ml of Listeria monocytogenes Scott A, populations reached only 5–14% of the control after 24 h at 30°C, with numbers exceeding 107, while at 6°C a slow decrease in population was found.

Antimicrobial and Anti-Plaque Activity of AT-Alkyl-M- (2-aminoethyl)piperidine against Dental Plaque Bacteria

□ Five N'-alkyl-N-(2-aminoethyl)piperidines were synthesized and their in vitro antimicrobial activities were tested against four microorganisms related to dental caries (Streptococcus mutans, S. sobrinus, Actinomyces viscosus, and A. naeslundii) which are known to be implicated in dental caries. The tetradecyl and hexadecyl derivatives possessed good bacteriostatic activity. Some derivatives exhibited a rapid bactericidal effect against S. mutans and S. sobrinus in aqueous solution. These compounds also possessed surfactant properties and anti-plaque activity.

Susceptibility of Oral Bacteria to Phenoxyethanol and Phenoxyethanol/ Chlorhexidine Combinations

A total of 57 bacterial strains (26 different species) which may be isolated from subgingival plaque were tested for their in vitro susceptibility to phenoxycthanol, a commonly-used antiseptic and preservative. Ninety-five percent of the strains, including those associated with chronic inflammatory periodontal disease, were susceptible to concentrations of phenoxyethanol used topically (2% w/v). Phenoxyethanol at a concentration of 1% (w/v) was also found that to have a rapid bactericidal effect achieving a 99.9% kill in 5 minutes or less for species such as Bacterodides gingivalis, Fusobacterium nucleatum, Eikenella corrodens, and Wolinella recta. Addition of chlorhexidine to phenoxyethanol resulted in a mixture with increased antibacterial activity. For most bacterial strains, the presence of chlorhexidine resulted in at least a four-fold decrease in the concentration of pheoxyethanol required for inhibition of growth. These results imply that phenoxyethanol may be useful in the treatment of chronic inflammatory periodontal disease either by itself or in combination with chlorhexidine.

Bacteriostatic and bactericidal activity of azithromycin against Haemophilus influenzae

Macrolide antibiotics, commonly used in upper and lower respiratory tract infections, are inconsistently active against Haemophilus influenzae. The new azalide, azithromycin, was compared with erythromycin and roxithromycin against this pathogen. Azithromycin (MIC range 0.06-1 mg/l) was four to eight times more potent than erythromycin (MIC range 0.5-8 mg/l) and roxithromycin (MIC range 0.5-16 mg/l). At 1 mg/l, 100% of the strains of H. influenzae were inhibited by azithromycin compared with 16% with erythromycin and 5% with roxithromycin. Azithromycin exhibited a rapid bactericidal effect, with a 99.9% kill at 4 h. The MBC was equal to or up to four-times greater than the MIC.

Evaluation of the antimicrobial activity of citral

Citral showed appreciable antimicrobial activity against Gram‐positive and Gram‐negative bacteria as well as fungi. Media composition and inoculum size had no observable effect on activity but alkaline pH increased citral activity. The growth rates of Escherichia coli cultures were reduced at concentrations of citral ≥0·01% v/v while concentrations ≥0·03% v/v produced rapid reduction in viable cells followed by limited regrowth. In a non‐growth medium, 0·08% and 0·1% v/v showed rapid bactericidal effects. Citral may therefore be of preservative use in addition to its other uses in the food, soap and cosmetic industries.

Absence of a postantibiotic effect in experimental Pseudomonas endocarditis treated with imipenem, with or without gentamicin.

We found an in vitro postantibiotic effect (PAE) of 3-4 h for imipenem and of approximately 5 h for imipenem plus gentamicin against Pseudomonas aeruginosa. We therefore evaluated these antibiotics in a rat model of pseudomonas endocarditis. A rapid bactericidal effect was initially observed in vegetations from rats treated with imipenem alone or in combination with gentamicin. Bacterial counts rose rapidly, however, as soon as levels of imipenem in vegetations fell below the minimal inhibitory concentration (i.e., no PAE was demonstrated). Levels of gentamicin in vegetations were similar to those that had enhanced the bactericidal effect of imipenem and had resulted in a 5-h PAE in vitro. The presence in vitro of a PAE for imipenem, with or without gentamicin, does not necessarily predict its presence in vivo in pseudomonas endocarditis in the rat.

Ciprofloxacin: in vitro activity, mechanism of action, and resistance.

Ciprofloxacin is a new fluoroquinolone that is highly active against many diverse microorganisms. At concentrations of less than 1 microgram/mL it is active against most gram-negative bacteria, including Enterobacteriaceae, Haemophilus, Neisseria, and other Pasteurellaceae, Vibrionaceae, and various species of Pseudomonas and Acinetobacter. Most staphylococci, including strains resistant to methicillin, are also susceptible to ciprofloxacin. Streptococci are not highly susceptible to ciprofloxacin, and obligate anaerobes are generally resistant to this and other quinolones. Ciprofloxacin, like other quinolones, inhibits DNA gyrase, but its bactericidal effects are not completely reversible by inhibitors of protein or RNA synthesis. Thus, unlike many other quinolones, ciprofloxacin may have multiple lethal effects. Resistance is less readily selected in vitro by ciprofloxacin than by nalidixic acid, and single-step mutants usually remain susceptible to clinically achievable concentrations. Resistance mediated by mutations in genes altering DNA gyrase and expression of outer membrane proteins has been described for ciprofloxacin and other quinolones. The antimicrobial spectrum and potency of ciprofloxacin, coupled with its rapid bactericidal effects, make this fluoroquinolone a promising new antimicrobial agent.

In vitro activity and mode of action of fluoroquinolones.

The in vitro activity of nine fluoroquinolones has been determined by agar dilution method against 1100 clinical isolates of different microorganisms: 412 Enterobacteriaceae, 93 non-fermenters, 398 enteropathogens, 140 Gram-positive cocci, 31 Haemophilus and 26 gonococci. The bactericidal activity tested in broth against different representative isolates was generally similar to the inhibitory concentration. Killing kinetics studied in different isolates of Enterobacteriaceae, in Pseudomonas aeruginosa, Vibrio cholerae, Staphylococcus aureus and Streptococcus faecalis showed a very rapid bactericidal effect, after 2 to 8 h of contact, in all species except in Streptococcus faecalis.

Activity in vitro of CGP 31608, a new penem antibacterial agent.

The in-vitro activity of CGP 31608 (hereinafter termed CGP), a new penem, was tested by an agar dilution technique in comparison with imipenem, Sch 34343, cefotaxime, ceftazidime, aztreonam, ampicillin, gentamicin and ciprofloxacin. 480 clinical isolated were tested, some of which were selected because of their multiple resistance. CGP showed consistent activity against a wide range of species, having MIC90 values of 2-8 mg/l for almost all Enterobacteriaceae, Pseudomonas spp., Haemophilus spp., Corynebacterium spp. and Bacteroides spp. It was the most active agent tested against staphylococci having an MIC90 of 0.25 mg/l, showing no reduction in activity against methicillin-resistant strains. Lesser activity was observed against some streptococci, Proteus spp. and clostridia. Tests carried out in broth demonstrated that CGP activity was constant over a pH range of 6-8 and was unaffected by the presence of 50% serum or 50% urine. The rate of killing of CGP, gentamicin, cefotaxime and ciprofloxacin was investigated in broth against log and stationary-phase cultures of Staphylococcus aureus and Escherichia coli. The most rapid rate of kill was seen with ciprofloxacin, while CGP exhibited a more rapid bactericidal effect than cefotaxime against Staph. aureus. The stability of CGP was studied at two concentrations in serum, broth and phosphate buffer at 4 degrees C, room temperature and 37 degrees C. In serum the half-life was 112 h at 4 degrees C, 35 h at room temperature and 11.4 h at 37 degrees C. Protein binding tested at concentrations of 5-100 mg/l was 2-6.3%.

Involvement of penicillin-binding protein 2 with other penicillin-binding proteins in lysis of Escherichia coli by some beta-lactam antibiotics alone and in synergistic lytic effect of amdinocillin (mecillinam).

Compared with cefotaxime, ceftazidime, moxalactam, and aztreonam, ceftriaxone produced the best lytic and bactericidal effects when each was added at about 10 times the MIC to Escherichia coli W7. When each of these antibiotics was added at its MIC, only bacteriostasis occurred, but the simultaneous addition of amdinocillin (mecillinam) was synergistic in causing rapid lysis and bactericidal effects. Induction of lysis of two E. coli mutants containing either a thermosensitive penicillin-binding protein (PBP) 2 or 3 by relatively PBP 3-specific (aztreonam) and PBP 2-specific (amdinocillin) antibiotics indicated that inhibition of only PBPs 2 and 3 can cause lysis. Examination of the interactions of cefotaxime, aztreonam, and cefsulodin, with or without amdinocillin, with their targets suggested that other combinations of PBPs could be involved in the onset of lysis. However, inhibition of both PBPs 2 and 3 may explain the better lysis-inducing activity of ceftriaxone (which binds well to both of these PBPs), as well as the synergistic effect of amdinocillin when added together with low concentrations of other beta-lactam antibiotics that interact with PBP 3.