Antibacterial Activity Of Gentamicin Research Articles

From Polymeric Nanoformulations to Polyphenols-Strategies for Enhancing the Efficacy and Drug Delivery of Gentamicin.

Gentamicin is an essential broad-spectrum aminoglycoside antibiotic that is used in over 40 clinical conditions and has shown activity against a wide range of nosocomial, biofilm-forming, multi-drug resistant bacteria. Nevertheless, the low cellular penetration and serious side effects of gentamicin, as well as the fear of the development of antibacterial resistance, has led to a search for ways to circumvent these obstacles. This review provides an overview of the chemical and pharmacological properties of gentamicin and offers six different strategies (the isolation of specific types of gentamicin, encapsulation in polymeric nanoparticles, hydrophobization of the gentamicin molecule, and combinations of gentamicin with other antibiotics, polyphenols, and natural products) that aim to enhance the drug delivery and antibacterial activity of gentamicin. In addition, factors influencing the synthesis of gentamicin-loaded polymeric (poly (lactic-co-glycolic acid) (PLGA) and chitosan) nanoparticles and the methods used in drug release studies are discussed. Potential research directions and future perspectives for gentamicin-loaded drug delivery systems are given.

Enhancing Antibiotics Efficacy by Combination of Kuraridin and Epicatechin Gallate with Antimicrobials against Methicillin-Resistant Staphylococcus aureus.

Staphylococcus aureus is an opportunistic pathogen and a major cause of nosocomial and community-acquired infections. The alarming rise in Methicillin-resistant S. aureus (MRSA) infection worldwide and the emergence of vancomycin-resistant MRSA strains have created an urgent need to identify new and alternative treatment options. Triple combinations of antimicrobials with different antimicrobial mechanisms may be a good choice to overcome antimicrobial resistance. In this study, we combine two natural compounds: kuraridin from Sophora flavescens and epicatechin gallate (ECG) from Camellia sinensis (Green tea), which could provide the best synergy with antibiotics against a selected panel of laboratory MRSA with known resistant mechanisms and clinical community-associated (CA) and hospital-associated (HA) MRSA as well. The combined use of ECG and kuraridin was efficacious in inhibiting the growth of a panel of tested MRSA strains. The antibacterial activities of gentamicin, fusidic acid and vancomycin could be further enhanced by the addition of ECG and kuraridin. In time-kill study, when vancomycin (0.5 μg/mL) was combined with ECG (2 μg/mL) and kuraridin (2 μg/mL), a very strong bactericidal growth inhibition against 3 tested strains ATCC25923, MRSA ST30 and ST239 was observed from 2 to 24 h. ECG and kuraridin both possess anti-inflammatory activities in bacterial toxin-stimulated peripheral blood mononuclear cells by suppressing the production of inflammatory cytokines (IL-1β, IL-6 and TNFα) and are non-cytotoxic. In a murine pneumonia model infected with ATCC25923, MRSA ST30 or ST239, the combined use of ECG and kuraridin with vancomycin could significantly reduce bacterial counts. The present findings reveal the potential of ECG and kuraridin combination as a non-toxic herbal and antibiotics combination for MRSA treatment with antibacterial and anti-inflammatory activities.

Exploring the Diverse Morphology of Porous Poly(Lactic Acid) Fibers for Developing Long-Term Controlled Antibiotic Delivery Systems.

In this study, we aimed to explore the morphologies of porous poly(lactic acid) (PLA) fibers through liquid–liquid phase separation, and investigate the relationship among pore formation, physical properties, and antibacterial activities of the fibers for identifying their potential as drug delivery carriers. Antibacterial activities of gentamicin-, kanamycin-, and amikacin-loaded PLA fibers against E. coli and S. epidermidis were evaluated. The antibacterial activity of drugs against E. coli showed the following profile: gentamicin > amikacin > kanamycin; however, S. epidermidis growth was almost completely inhibited immediately after the administration of all three drugs. The efficiency of gentamicin can be attributed to the electrostatic interactions between the positively and negatively charged antibiotic and bacterial cell membrane, respectively. Furthermore, gentamicin-loaded porous PLA fibers were evaluated as drug delivery systems. The cumulative amount of gentamicin in porous PLA nanofibers was considerably higher than that in other PLA fibers for 168 h, followed by 7:3 PLA > 6:4 PLA > 5:5 PLA > non-porous PLA. The 7:3 PLA fibers were projected to be ideal drug carrier candidates for controlled antibiotic release in delivery systems owing to their interconnected internal structure and the largest surface area (55.61 m2 g−1), pore size (42.19 nm), and pore volume (12.78 cm3 g−1).

Synergistic ROS-Associated Antimicrobial Activity of Silver Nanoparticles and Gentamicin Against Staphylococcus epidermidis.

IntroductionIncreasing bacteria resistance to antibiotics is a major problem of healthcare system. There is a need for solutions that broaden the spectrum of bactericidal agents improving the efficacy of commonly used antibiotics. One of the promising directions of search are silver nanoparticles (obtained by different methods and displaying diversified physical and chemical properties), and their combination with antibiotics.PurposeIn this study, we tested the role of reactive oxygen species in the mechanism of synergistic antibacterial activity of gentamicin and Tween-stabilized silver nanoparticles against gentamicin-resistant clinical strains of Staphylococcus epidermidis.MethodsSynergistic bactericidal activity of gentamicin and silver nanoparticles stabilized with non-ionic detergent (Tween 80) was tested by the checkerboard titration method on microtiter plates. Detection of reactive oxygen species was based on the chemiluminescence of luminol.ResultsHydrophilic non-ionic surface functionalization of silver nanoparticles enabled the existence of non-aggregated active nanoparticles in a complex bacterial culture medium. Tween-stabilized silver nanoparticles in combination with gentamicin exhibited bactericidal activity against multidrug-resistant biofilm forming clinical strains of Staphylococcus epidermidis. A synergistic effect significantly decreased the minimal inhibitory concentration of gentamicin (the antibiotic with numerous undesirable effects). Gentamicin significantly enhanced the generation of reactive oxygen species by silver nanoparticles.ConclusionGeneration of reactive oxygen species by Tween-coated metallic silver nanoparticles was significantly enhanced by gentamicin, confirming the hypothesis of oxidative-associated mechanism of the synergistic antibacterial effect of the gentamicin-silver nanoparticles complex.

Plasma-Deposited Nanocapsules Containing Coatings for Drug Delivery Applications.

Coatings consisting in gentamicin-containing nanocapsules have been synthetized by means of an aerosol-assisted atmospheric pressure plasma deposition process. The influence of different parameters affecting the process has been extensively investigated by means of a morphological and chemical characterization of the coatings. Scanning electron microscopy highlighted the presence of nanocapsules whose size and abundance depend on power input and deposition time. A detailed analysis carried out with matrix-assisted laser desorption ionization coupled to high-resolution mass spectrometry allowed to detect and identify the presence of gentamicin embedded in the coatings and its rearrangement, as a result of the interaction with the plasma. The release of gentamicin in water has been monitored by means of UV-vis fluorescence spectroscopy, and its biological activity has been evaluated as well by the disk diffusion assay against Staphylococcus aureus and Pseudomonas aeruginosa. It is confirmed that the antibacterial activity of gentamicin is preserved in the plasma-deposited coatings. Preliminary cytocompatibility investigations indicated that eukaryotic cells well tolerate the release of gentamicin from the coatings.

Synergistic or Antagonistic Effects of Probiotics and Antibiotics- Alone or in Combination- on Antimicrobial-Resistant Pseudomonas aeruginosa Isolated from Burn Wounds

Background: Bacterial burn infections are one of the serious infections and since their treatment with antibiotics is very difficult, infection control in such wounds is very important. Therefore, methods should be sought to enhance the effects of antibiotics and also reduce the resistance to them. It seems that probiotics have antimicrobial features and are effective in wound healing. Objectives: The current study aimed at evaluating and comparing the antimicrobial effects of antibiotics and probiotics, as well as their combination on bacterial burn infections. Methods: Thirty clinically resistant Pseudomonas aeruginosa species isolated from hospitalized patients with burn wounds were collected. Antibacterial activity of five antibiotics and 11 probiotic strains, and also their combination were evaluated by disk diffusion method. One-way ANOVA and Tukey post hoc test were used for data analysis. Results: It was found that the effect of inhibitory zone in combination use of tetracycline + a probiotic strain was more than using the antibiotic and probiotic alone. Also, the current study found that among the probiotics, Lactobacillus plantarum 299v had the highest effect, although not significant, on resistant P. aeruginosa. The current study explained that the inhibitory effect of L. plantarum 299v was significantly higher than that of ciprofloxacin (P = 0.009). In addition, antibacterial activity of gentamicin + L. salivarius (ES1) was significantly higher compared with that of gentamicin + L. routeri (P = 0.01). Conclusions: The current study explained that probiotics had a useful potential inhibitory effect on the growth of the pathogens. The study showed that in most cases, inhibitory zones of probiotics were greater than those of antibiotics as well as combination of antibiotic + probiotic. But, there was an exception in tetracycline, which had synergistic effect with probiotics. Conversely, in the cases of imipenem and chloramphenicol, addition of probiotics had antagonistic effects. Further studies are needed to describe different results. Therefore, it seems that the type of antibiotics and probiotics are important to create the synergistic or antagonistic effects. © 2018, Archives of Clinical Infectious Diseases.

Peripheral Blood Plasma Clot as a Local Antimicrobial Drug Delivery Matrix.

Platelet-free blood plasma clots were loaded either with antibiotics (vancomycin, gentamicin, or linezolid) at concentrations of 5-300 μg/mL or with silver ions (silver acetate) at concentrations of 3.3-129 μg/mL. The release of antibiotics or silver from the clot matrix was analyzed after repeated immersion of the plasma clots using reversed-phase high-performance liquid chromatography (RP-HPLC) or atomic absorption spectroscopy (AAS). The antimicrobial activity was tested against Staphylococcus aureus; tissue cell compatibility was analyzed using human mesenchymal stem cells (hMSC). Fibrin fiber thickness of the clots was analyzed by scanning electron microscopy. While addition of linezolid and vancomycin did not significantly change the fibrin fiber thickness, gentamicin and silver ions led to an increase in fiber thickness. All antibiotics showed a concentration-dependent burst-like release from the plasma clots within 1 h followed by a general decay in elution. The release of vancomycin and gentamicin, or silver lasted up to 7 days (depending on initial concentrations), but lasted only up to 4 h for linezolid. A correlation (p < 0.0001) was noted between the concentration of released antibiotics analyzed by HPLC and antimicrobial activity (agar diffusion test). A decrease in antibacterial activity of gentamicin- and vancomycin-containing clots occurred within 4 or 5 days. In contrast, the corresponding antibacterial activity of plasma clots containing linezolid was limited to 3 h. Antibacterial activity of plasma clots containing silver at the highest concentrations decreased after day 3, but clots with lower concentrations induced incomplete bacterial lysis or displayed no antibacterial activity. The antibiotic-containing clots did not induce cytotoxic effects on the embedded hMSC in contrast to all clots containing silver. Our results indicate that an autologous plasma clot can be used to deliver antibiotics such as vancomycin and gentamicin in combination with hMSC and the antibacterial effects persist for days without inducing cytotoxic effects on the embedded stem cells.

A comparative study on antibacterial activities of chitosan based products and their combinations with gentamicin against S. epidermidis and E. coli

Antibacterial activity of chitosan, and a graft copolymer based on chitosan namely chitosan-graft-poly(N-vinyl imidazole), (Chi-graft-PNVI), was studied against Staphylococcus epidermidis (S. epidermidis) and Escherichia coli (E. coli). The graft copolymer was prepared by two different methods; via an N-protection route and without N-protection to observe the effect of free amine groups on the antibacterial activity. It was further investigated whether a combination of each of these products would produce a synergetic effect with the antibiotic gentamicin against S. epidermidis and E. coli compared to gentamicin alone. Antibacterial activity was determined by the inhibition zone measurement method. Results reveal an improvement in the antibacterial activity of gentamicin, when combined with chitosan or chitosan-based biomaterials against S. epidermidis and E. coli compared to that of gentamicin itself. When gentamicin is used in combination with Chi-graft-PNVI prepared via N-protection, antibacterial activity against S. epidermidis is three times higher in comparison with the activity of gentamicin alone according to the inhibition zone measurements. Gentamicin produces an inhibition zone of 8.2 ± 0.2 mm against S. epidermidis when undiluted, while the inhibition zone increases to 25.8 ± 0.7 mm in combination with Chi-graft-PNVI prepared via N-protection. These combinations have a potential to form a basis for new formulations of gentamicin with improved antibacterial activity and might allow usage of decreased doses of the antibiotic.

Effect of Taurine on the antimicrobial efficiency of Gentamicin.

Gentamicin is mainly used in severe infections caused by gram-negatives. However toxicity including nephrotoxicity and ototoxicity is one of the most important complications of its treatment. The production of free radicals seems to be involved in gentamicin toxicity mechanism. Taurine, a major intracellular free β-amino acid, is known to be an endogenous antioxidant. So potentially the co-therapy of taurine and gentamicin would reduce the adverse effects of the antibiotic. In this study, we wished to know the effect of taurine on the antibiotic capacity of gentamicin. strainsof P. aeruginosa, E. coli, S. aureus and S. epidermidis were used as test organisms. Minimum inhibitory concentrations of gentamicin in the presence and absence of taurine at quantities from 40 to 2 mg/L were determined using macro-dilution method. MICs were determined in the various concentrations of taurine for bacterial indicators. The MIC values of gentamicin for P. aeruginosa, S. aureus and E. coli remained unchanged in the values of 2.5, 5 and 20 μg/ml respectively in the absence and presences of different concentrations of taurine. The bactericidal activity of gentamicin against S. epidermidis was increased by addition of taurine in the concentrations higher than 6 mg/L. According to our study the antibacterial activity of gentamicin against the indicator microorganisms were not interfere with taurine at selected concentrations. Further in vivo studies are needed to establish if a combination of gentamicin and taurine would have the same effect.

Novel bioactive hydrophobic gentamicin carriers for the treatment of intracellular bacterial infections

Gentamicin (GEN) is an aminoglycoside antibiotic with a potent antibacterial activity against a wide variety of bacteria. However, its poor cellular penetration limits its use in the treatment of infections caused by intracellular pathogens. One potential strategy to overcome this problem is the use of particulate carriers that can target the intracellular sites of infection. In this study GEN was ion-paired with the anionic AOT surfactant to obtain a hydrophobic complex (GEN–AOT) that was formulated as a particulated material either by the precipitation with a compressed antisolvent (PCA) method or by encapsulation into poly(d,l-lactide-co-glycolide) (PLGA) nanoparticles (NPs). The micronization of GEN–AOT by PCA yielded a particulated material with a higher surface area than the non-precipitated complex, while PLGA NPs within a size range of 250–330nm and a sustained release of the drug over 70days were obtained by preparing the NPs using the emulsion solvent evaporation method. For the first time, GEN encapsulation efficiency values of ∼100% were achieved for the different NP formulations with no signs of interaction between the drug and the polymer. Finally, in vitro studies against the intracellular bacteria Brucella melitensis, used as a model of intracellular pathogen, demonstrated that the bactericidal activity of GEN was unmodified after ion-pairing, precipitation or encapsulation into NPs. These results encourage their use for treatment for infections caused by GEN-sensitive intracellular bacteria.

Effect of Bacterial Media on the Evaluation of the Antibacterial Activity of a Biomaterial Containing Inorganic Antibacterial Reagents or Antibiotics

Several studies have been performed to assess the effectivesness of the antibacterial coating of a biomaterial to reduce surgical site infection. However, evaluations of these materials are inconsistent, and therefore it is difficult to compare their antibacterial performance. In this study, we evaluated the influence of different media such as nutrient broth (NB), Mueller-Hinton broth (MHB) and fetal bovine serum (FBS) on the antibacterial activity of AgNO3- or gentamicin-added bone cement using a modified ISO 22196 standard to devise a method to evaluate the antibacterial activity of biomaterials in vitro. The antibacterial activity results against Staphylococcus aureus and Escherichia coil were different in each medium. The antibacterial activity of AgNO3 in FBS was lower than the other media, whereas the antibacterial activity of gentamicin in FBS was higher than in the other media. It was assumed that the fluctuating antibacterial activity was influenced by serum components. The results showed that the ISO 22196 antibacterial evaluation method is suitable to evaluate antibacterial biomaterials after modifying the medium to FBS.

Culture and antibiotic susceptibility of Bartonella quintana in human erythrocytes.

Bartonella quintana, the agent of trench fever, has recently been implicated in various diseases, in particular, bacteremia and endocarditis in homeless people. The host cell of Bartonella spp. is believed to be the erythrocyte, and in the present study we demonstrate that B. quintana can be cultured in vitro in human erythrocytes. The bacteria were found to be intraerythrocytic by laser confocal microscopy with Bartonella species-specific monoclonal antibodies. Infections with B. quintana decreased the life span of erythrocytes in culture from 8.6 to 4.8 days. In the culture system we found that most of the antibiotics that we tested (doxycycline, fluoroquinolone compounds, and beta-lactams) were not bactericidal. Gentamicin was bactericidal at 4 micro g/ml, as was rifampin, but to a lesser extent. At this concentration, gentamicin has been shown to enter erythrocytes slowly and to reach a peak level of 0.26 micro g/ml after 24 h. At 0.26 micro g/ml, however, we found that gentamicin was not able to kill extracellular B. quintana, even after 96 h of incubation. We hypothesize that erythrocytes may be a reservoir for B. quintana and that the bactericidal activity of gentamicin that we observed occurs mainly when the bacteria emerge from the erythrocytes and are found extracellularly. It would appear that gentamicin should be administered for at least 5 days to cure patients infected with B. quintana.

Bactericidal activity of gentamicin against Enterococcus faecalis in vitro and in vivo.

The activity of gentamicin at various concentrations against two strains of Enterococcus faecalis was investigated in vitro and in a rabbit model of aortic endocarditis. In vitro, gentamicin at 0.5 to 4 times the MIC failed to reduce the number of bacteria at 24 h. Rabbit or human serum dramatically increased gentamicin activity, leading to a >/=3-log(10) CFU/ml decrease in bacterial counts when the drug concentration exceeded the MIC. Susceptibility testing in the presence of serum was predictive of in vivo activity, since gentamicin alone significantly reduced the number of surviving bacteria in the vegetations if the peak-to-MIC ratio was greater than 1. However, gentamicin selected resistant mutants in rabbits. The intrinsic activity of gentamicin should be taken into account in evaluation of combinations of gentamicin and cell wall-active agents against enterococci.

Comparative efficacy of successive exposure of Pseudomonas aeruginosa to gentamicin and ceftazidime

Aminoglycoside and β-lactam antibiotics, when used in combination, are usually given simultaneously, however, successive administration may be more efficient. The killing capacity was used to assess the effect of time intervals between low and high concentrations (2–8×MICs) of gentamicin and/or ceftazidime on Pseudomonas aeruginosa and to determine which drug is better to be administered first. The killing capacity after exposure to the antibiotic for 1 h were compared: (i) cells treated with gentamicin alone; (ii) cells treated with ceftazidime alone; and (iii) ceftazidime was added to (i) or (iv) gentamicin was added to (ii) at 0, 1 and 3 h of antibiotic removal. The bactericidal activity of gentamicin was potentiated and the viable cells decreased up to 6 h after antibiotic removal when the ceftazidime was added at O and at 1 h but the extent of bactericidal activity was reduced, when it was added at 3 h after gentamicin removal. Alternatively, treating the cells first with ceftazidime and then gentamicin was added after drug removal at O and at 1 h resulted in a marked decline in the viable cells, while addition of gentamicin after 3 h from ceftazidime removal, the extent of bactericidal activity was reduced. The non-treated cells with gentamicin started to grow heavily within 6 h of ceftazidime removal. No viable cells were detected after overnight incubation in cultures treated first with 6 or 8×MIC of gentamicin for 0.5 or 1 h. This in vitro study suggests that the optimum interval between gentamicin and ceftazidime doses, which gave the maximum bactericidal effect and the time before re-growth, appeared to be 1–2 h.

Antibiotic-impregnated heart valve sewing rings for treatment and prophylaxis of bacterial endocarditis.

Prosthetic heart valve sewing rings were impregnated with gentamicin crobefat (EMD 46217), a poorly soluble gentamicin salt, gentamicin sulfate, and clindamycin palmitate to prevent early prosthetic endocarditis. MICs and MBCs of gentamicin and/or clindamycin were tested against several pathogens of early prosthetic endocarditis. The combination of gentamicin and clindamycin was found to be effective against most relevant bacterial pathogens. With an in vitro pharmacokinetic model, the antibacterial activity of gentamicin and clindamycin was tested against Staphylococcus aureus and Escherichia coli. High gentamicin levels over the first 24 h were required for a strong reduction of bacterial counts of both strains. Equal amounts of gentamicin and clindamycin sustained the antibacterial effect and prevented regrowth. The most effective release curves of gentamicin and clindamycin found with an in vitro model were used for monitoring release profiles of these antibiotics from impregnated sewing rings by investigating combinations of gentamicin sulfate, gentamicin crobefat, and clindamycin palmitate. Sewing rings impregnated with 4 mg of gentamicin sulfate, 14 mg of gentamicin crobefat, and 20 mg of clindamycin palmitate gave an initial gentamicin burst and afterwards yielded a lower sustained release of gentamicin and clindamycin palmitate. These in vitro release kinetics were confirmed in vivo by pharmacokinetic analysis after intramuscular implantation of impregnated sewing ring segments. Gentamicin and active clindamycin palmitate metabolites were obtained at the implantation site for at least 2 weeks in concentrations of 3 and 5 micrograms per g of muscle, respectively. The investigated method of impregnation holds promise for revision implants after prosthetic valve endocarditis. It may also serve as a prophylactic tool for routine use against this disease.

Ultrasonic enhancement of antibiotic action on gram-negative bacteria.

The effect of gentamicin upon planktonic cultures of Pseudomonas aeruginosa, Escherichia coli, Staphylococcus epidermidis, and Staphylococcus aureus was measured with and without application of 67-kHz ultrasonic stimulation. The ultrasound was applied at levels that had no inhibitory or bactericidal activity against the bacteria. Measurements of the MIC and bactericidal activity of gentamicin against planktonic cultures of P. aeruginosa and E. coli demonstrated that simultaneous application of 67-kHz ultrasound enhanced the effectiveness of the antibiotic. A synergistic effect was observed and bacterial viability was reduced several orders of magnitude when gentamicin concentrations and ultrasonic levels which by themselves did not reduce viability were combined. As the age of the culture increased, the bacteria became more resistant to the effect of the antibiotic alone. Application of ultrasound appeared to reverse this resistance. The ultrasonic treatment-enhanced activity was evident with cultures of P. aeruginosa and E. coli but was not observed with cultures of gram-positive S. epidermidis and S. aureus. These results may have application in the treatment of bacterial biofilm infections on implant devices, which infections are usually more resistant to antibiotic therapy.

Bactericidal activity of gentamicin against S. aureus. In vitro study questions value of prolonged high concentrations.

Bactericidal activity of gentamicin against 4 strains of Staphylococcus aureus was investigated in vitro using Mueller-Hinton broth (MH) and surgical wound fluid (WF) as test media. 6 concentrations of gentamicin were tested ranging from 1-1024 micrograms/mL. During the first hour of incubation, there was a marked concentration-dependent kill rate, approximately 3 x 10(3) times in WF and 10(2) times in MH. After the first hour of incubation, the kill rate was independent of the concentration in both media. Our study questions the benefit of the prolonged and high wound concentrations of gentamicin obtained after application of gentamicin-containing PMMA.

Synovial fluid pH, cytologic characteristics, and gentamicin concentration after intra-articular administration of the drug in an experimental model of infectious arthritis in horses

SUMMARY Chemical and cytologic effects and bactericidal activity of gentamicin in septic synovial fluid were evaluated in an experimental model of infectious arthritis in horses. Septic arthritis was induced by inoculation of approximately 7.5 × 106 colony-forming units of Escherichia coli into 1 antebrachiocarpal joint in each of 16 clinically normal adult horses. Clinical signs of septic arthritis were evident 24 hours after inoculation. Horses were allotted to 3 groups: group-1 horses (n = 5) each were given 150 mg of gentamicin (50 mg/ml; 3 ml) intra-articularly (ia); group-2 horses (n = 5) each were given 2.2 mg of gentamicin/kg of body weight, iv, every 6 hours; and group-3 horses (n = 6) each were given buffered gentamicin, consisting of 3 mEq of sodium bicarbonate (1 mEq/ml; 3 ml) and 150 mg of gentamicin (50 mg/ml; 3 ml), ia. Synovial fluid specimens were obtained at posttreatment hour (pth) 0, 0.25, 1, 4, 8, 12, and 24 via an indwelling intra-articular catheter. Synovial fluid pH was evaluated at pth 0, 0.25, and 24. Microbiologic culture and cytologic examination were performed on synovial fluid specimens obtained at pth 0 and 24, and gentamicin concentration was measured in all synovial fluid specimens. At pth 0, E coli was isolated from synovial fluid specimens obtained from all horses. Synovial fluid pH was lower (range, 7.08 to 7.16) and wbc count was higher (range, 88,000 to 227,200 cells/μl) and predominantly neutrophilic (95 to 99%) at pth 0 than before inoculation. Synovial fluid pH was lowered further (mean, pH 6.63) after ia administration of gentamicin in group-1 horses; mean pH remained unchanged (7.07) after buffered-gentamicin administration in group-3 horses. At pth 0.25, mean peak synovial fluid gentamicin concentration in horses of groups 1 and 3 (4,745 and 6,190 μg/ml, respectively) was 1,000 times greater than that in group-2 horses (5.1 μg/ml) at the same time. Synovial fluid gentamicin concentration in group-1 and group-3 horses was always greater than that in group-2 horses and remained greater than a minimal inhibitory concentration of gentamicin (2 μg/ml) against many common equine bacterial pathogens for at least 24 hours after injection. Further, the calculated apparent half-life and clearance of gentamicin in synovial fluid calculated after ia administration were similar in horses of groups 1 and 3. By pth 24, E coli could not be isolated from synovial fluid specimens obtained from group-1 horses. However, moderate to heavy growth of E coli was isolated from synovial fluid specimens obtained at pth 24 from horses in groups 2 and 3 (80 and 66%, respectively). In selected cases, ia administration of unbuffered gentamicin may be a useful supplement to drainage, lavage, and systemic antibacterial and anti-inflammatory treatment in horses with naturally acquired infectious arthritis.

Antibacterial activities of various aminoglycosides against clinically isolated methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) were isolated from samples collected from various patients during 1986, and antibacterial activities of 6 aminoglycosides (AGs) (netilmicin (NTL), gentamicin (GM), sisomicin (SISO), dibekacin (DKB), tobramycin (TOB) and amikacin (AMK] and 4 beta-lactam antibiotics (cefazolin (CEZ), cefmetazole (CMZ), cloxacillin (MCIPC) and methicillin (DMPPC) against these MRSA were evaluated. Among these 6 AGs, NTL was the most potent, and its MIC50 and MIC80 were 1.56 and 3.13 micrograms/ml, respectively. Antibacterial activities of GM, SISO, DKB and TOB were weak, and MIC50's of GM and DKB were both 100 micrograms/ml, while those of SISO and TOB were 50 and greater than 100 micrograms/ml, respectively. Frequency of highly resistant specimens to AMK was rather low and its MIC50 and MIC80 were 12.5 and 25 micrograms/ml, respectively. As for antibacterial activities of the above 4 beta-lactam antibiotics, the MIC50 and MIC80 of CMZ were 6.25 and 12.5 micrograms/ml, respectively, and therefore, its antibacterial activity to MRSA is relatively good. However, MIC50's of CEZ, MCIPC and DMPPC were all greater than 100 micrograms/ml, showing poor antibacterial activities. Recently, MRSA became a problem in various fields of clinical practice, and a number of literatures reporting refractory infections caused by MRSA have been published. Since MRSA is featured as multiply resistant bacteria, it is known that MRSA is resistant to the majority of existing antibiotics (penicillins, cephems, macrolides, AGs, etc.). In 1985, we reported results of our study concerning the antibacterial activities of a number of CEPs and some of AGs against multiply resistant S. aureus including MRSA.(ABSTRACT TRUNCATED AT 250 WORDS)

Inability of gentamicin and fosfomycin to eliminate intracellular Enterobacteriaceae

The ability of gentamicin and fosfomycin to kill Salmonella typhimurium and Escherichia coli in a HeLa cell culture system was investigated. Antibiotic activity against extracellular, cell membrane-attached and intracellular bacteria were determined. Both gentamicin and fosfomycin had the same low ability to kill intracellular bacteria. The efficacy of fosfomycin against extracellular bacteria was also low, whereas gentamicin rapidly killed such bacteria. These observations show that intracellular enterobacteria are protected from the bactericidal activity of gentamicin and fosfomycin.