Rapid direct method for monitoring antibiotics in a mouse model of bacterial biofilm infection

We have developed a rapid, continuous method for monitoring the effectiveness of several antibacterial agents in real time, noninvasively, by using a recently described mouse model of chronic biofilm infection (J. L. Kadurugamuwa et al., Infect. Immun. 71:882-890, 2003), which relies on biophotonic imaging of bioluminescent bacteria. To facilitate real-time monitoring of infection, we used a Staphylococcus aureus isolate that was made bioluminescent by inserting a modified lux operon into the bacterial chromosome. This bioluminescent reporter bacterium was used to study the antimicrobial effects of several antibiotics belonging to different molecular families. Treatment with rifampin, tobramycin, and ciprofloxacin was started 7 days after subcutaneous implantation of catheters precolonized with 10(4) CFU of S. aureus. Three different doses of antibiotics were administered twice a day for 4 consecutive days. The number of metabolically active bacteria in untreated mice and the tobramycin- and ciprofloxacin-treated groups remained relatively unchanged over the 4-week observation period, indicating poor efficacies for tobramycin and ciprofloxacin. A rapid dose-dependent decline in metabolic activity in rifampin-treated groups was observed, with almost a 90% reduction after two doses and nearly undetectable levels after three doses. The disappearance of light emission correlated with colony counts. After the final treatment, cell numbers rebounded as a function of concentration in a time-dependent manner. The staphylococci isolated from the catheters of mice treated with rifampin were uniformly resistant to rifampin but retained their in vitro susceptibilities to tobramycin and ciprofloxacin. Since the metabolic activities of viable cells and a postantibiotic effect could be detected directly on the support matrix nondestructively and noninvasively, the methodology is specifically appealing for investigating the effects of antibiotics on biofilms in vivo. Moreover, our study points to the possible use of biophotonic imaging for the detection of the development of resistance to therapeutic agents during treatment of chronic infections in vivo.

[Conserved region analysis of aac(3)-II gene from E. coli aminoglycoside resistance strain]

According to standard K B method, bacteriostatic tests were performed to screen out aminoglycoside resistance bacteria from 47 strains of isolated E.coli. To analyze correlations between the degree of E.coli aminoglycoside resistance and aac(3)-II gene conserved region, PCR amplified aac(3)-II gene conserved regions and were analyzed by DNA sequencing. The results showed that there were two species of aac(3)-II gene type including 65G and 84T or 65A and 84C in the samples. Strains with high activity of modifying enzyme to gentamicin all were 65G and 84T aac(3)-II gene type.

Endotoxin neutralization and anti-inflammatory effects of tobramycin and ceftazidime in porcine endotoxin shock

Introduction

Antibiotics used for treatment of severe bacterial infections have been shown to exert effects on the inflammatory response in addition to their antibacterial effects. The aim of the present study was to investigate whether the biological effects of endotoxin in a porcine model could be neutralized by tobramycin, and whether tobramycin or ceftazidime was able to modulate the inflammatory response.

Method

Thirteen piglets were subjected to endotoxin infusion at an initial rate of 4 μg/kg per hour, which was reduced to 1 μg/kg per hour after 30 min. Before endotoxin infusion, the animals received saline (n = 4), ceftazidime (n = 5), or tobramycin (n = 4) at clinically relevant doses. Physiological parameters were measured and blood samples were taken hourly for 6 hours for analysis of tumour necrosis factor-α, IL-6 and endotoxin concentrations.

Results

All of the animals exhibited physiological signs of severe sepsis without major differences between the groups. Plasma endotoxin concentration was stable after 1 hour. There were no differences in endotoxin concentration or initial tumour necrosis factor-α and IL-6 concentrations between the groups. At 6 hours the IL-6 concentration was significantly lower in the ceftazidime group than in the saline group (P < 0.05), and in both the ceftazidime and the tobramycin groups there were significantly greater reductions from peak values (P < 0.05).

Conclusion

There was no neutralization of the biological effects of endotoxin in this porcine model. However, our data indicate a possible anti-inflammatory effect exerted by both ceftazidime and tobramycin, which manifested as a significantly greater reduction in IL-6 in comparison with the untreated group.

In vitro activity and synergy of bismuth thiols and tobramycin against Burkholderia cepacia complex

OBJECTIVES

To determine the susceptibility of Burkholderia multivorans and Burkholderia cenocepacia to bismuth-thiols (BTs), and to examine the synergistic effects of tobramycin and subinhibitory concentrations of BTs against these organisms.

METHODS

The susceptibilities of 25 clinical isolates each of B. multivorans and B. cenocepacia to six BTs were measured by broth dilution in accordance with NCCLS protocols. Ten strains were selected to evaluate the antimicrobial interaction between BTs and tobramycin. Fractional inhibitory concentration (FIC) and fractional bactericidal concentration (FBC) indices were calculated to assess synergy.

RESULTS

B. multivorans and B. cenocepacia showed a wide range of susceptibilities to BTs. Bismuth ethanedithiol (BisEDT) was one of the more potent BTs against these organisms (MIC50 7.8 microM), and was selected for synergy studies. Selected strains were highly resistant to tobramycin. The addition of subinhibitory concentrations of BisEDT (2 microM) reduced the MIC and MBC of tobramycin against all strains, achieving synergy in many instances. The FIC index was in the range 0.28-0.66 and the FBC in the range 0.12-0.85. Most strains became susceptible to tobramycin at clinically achievable concentrations in the presence of non-toxic BisEDT levels.

CONCLUSIONS

Treatment with subinhibitory BisEDT and tobramycin reduces the MICs and MBCs for B. multivorans and B. cenocepacia. BTs may represent an important adjunctive therapy for resistant Burkholderia cepacia complex.

Antimicrobial activity and interference of tobramycin and chloramphenicol on bacterial adhesion to intraocular lenses

The antimicrobial activities of tobramycin and chloramphenicol were evaluated by determining minimum inhibitory and bactericidal concentrations against Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis, group A, group B and group G streptococci, Klebsiella spp., Stenotrophomonas maltophilia and ciprofloxacin-resistant and -susceptible Pseudomonas aeruginosa, as well as by evaluating interference on adhesion of slime producer strains of S. aureus and P. aeruginosa to intraocular lens from tobramycin and chloramphenicol pharmaceutical products by scanning electron microscopy. Chloramphenicol was more active against Gram-positive bacteria than was tobramycin, which instead showed higher activity against ciprofloxacin-susceptible P. aeruginosa. Treatment of lenses with the antimicrobial products eradicated the bacterial biofilm, which was already notably reduced after 5 min. This activity was more pronounced for chloramphenicol against S. aureus and for tobramycin against P. aeruginosa. Bacterial adhesion was also significantly reduced when lenses colonized by P. aeruginosa were treated with chloramphenicol, even if they were resistant to this drug. In conclusion, the tested drugs showed marked antibacterial activity, particularly by interfering with bacterial biofilms. The data obtained in this study suggest a specific use of chloramphenicol in topical prophylaxis aimed at avoiding bacterial contaminations. However, further specific in vivo studies are needed to confirm these data.

What is the shelf life of physician-mixed antibiotic-impregnated calcium sulfate pellets?

This pilot study was undertaken to evaluate the short-term in vitro antimicrobial stability of both vancomycin- and tobramycin-impregnated calcium sulfate pellets mixed and stored in a clinical setting. Powdered tobramycin sulfate (500 mg) and vancomycin hydrochloride (500 mg) were blended into separate basins containing 25 g of surgical-grade calcium sulfate powder, then mixed with 8 mL of sterile saline. From this admixture, 6.0-mm pellets were produced. These were removed from the sterile container (stored at room temperature) at 1, 7, 30, 60, 90, and 120 days and tested against a variety of pathogenic bacterial isolates by using a modification of the standardized Kirby-Bauer test. Control pellets containing no antibiotic were also evaluated. There was no inhibition of bacterial growth by the non-antibiotic-impregnated (control) pellets. There was no appreciable difference in the zones of inhibition for any of the organisms with pellets stored for 1, 7, 30, 60, 90, or 120 days. Zones of inhibition for the various antibiotics to the strain of organism tested ranged from 17 mm to 30 mm, depending on the pathogenic isolate and the antibiotic evaluated. The zones of inhibition observed were similar to those designating antibiotic susceptibility in the Kirby-Bauer test. The results of this preliminary study suggest that clinician-mixed calcium sulfate pellets containing either vancomycin or tobramycin, when stored under normal room temperature and ambient humidity, appear to maintain their antimicrobial characteristics for at least 120 days.

Antimicrobial spectrum of activity for meropenem and nine broad spectrum antimicrobials: report from the MYSTIC Program (2002) in North America

The Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Program provides susceptibility data for participating medical centers where carbapenems are utilized. The activity of meropenem and nine broad-spectrum antimicrobial agents were assessed against 3,047 bacterial isolates collected during 2002 from 16 North American sites. The overall rank order of susceptibility of the 10 antimicrobial agents tested against Gram-negative isolates was: meropenem (98%) > imipenem (97%) > cefepime (95%) > tobramycin (93%) > piperacillin/tazobactam = gentamicin (92%) > ceftazidime (91%) > ciprofloxacin (87%) > aztreonam (86%) > ceftriaxone (74%). These results and those from previous years, demonstrate the continued excellent potency and spectrum of activity for meropenem. The utility of meropenem against Pseudomonas aeruginosa isolates has increased steadily with a rise in percent susceptibility each year from 78.2% in 1999 to a present rate of 93.1% susceptible. Conversely, we showed the susceptibility for ciprofloxacin against these same P. aeruginosa isolates has decreased from 82.9 to 72.3% susceptible over four years. Many medical centers have observed a decreased activity of some aminoglycosides, cephalosporins and fluoroquinolones due to increases in rates of extended-spectrum beta-lactamases, Amp C and other resistance mechanisms. Carbapenem resistance remains rarely documented and these beta-lactamase-stable agents appear to be an alternative treatment option for serious community-acquired or nosocomial infections in high risk patient populations.

Aminoglycosides suppress tRNA processing in human epidermal keratinocytes in vitro

The ever-growing resistance of pathogens to antibiotics and the lack of potent antibacterial drugs constitute major problems in the treatment of infectious diseases. Thus, the better understanding of the mode of action of antibiotics at the molecular level is of essential importance. Accumulating evidence points towards RNA as being a crucial target of antibacterial and antiviral drugs. Interestingly, aminoglycosides, one of the most important families of antibiotics, apart from their inhibitory effect on ribosome function, reportedly interfere with various RNA molecules and in vitro suppress the proliferation of human keratinocytes. In this study we investigated the effect of the aminoglycosides neomycin B, paromomycin, tobramycin and gentamycin on ribonuclease P activity from normal human epidermal keratinocytes. All aminoglycosides tested revealed a dose-dependent inhibition of tRNA maturation, which was reduced by increasing Mg(2+) ion concentrations, indicating competition of the cationic aminoglycosides with magnesium ions required for catalysis. Our in vitro findings suggest that the inhibitory effects of aminoglycosides on tRNA processing may be implicated in the mechanisms of their antiproliferative action on human epidermal keratinocytes.

[Effect of tobramycin on characteristics of strains of Acinetobacter species]

Suppression of bacterial growth in seven strains of the Acinetobacter species after 30 min treatment with tobramycin at suprainhibitory concentrations (postantibiotic effect--PAE) and at supra-sub-inhibitory concentrations (postantibiotic effect of subinhibitory concentrations--PA SME) as well as changes in surface hydrophobicity and in the production of lipase and histamine in the exposed strains were studied. Pharmacodynamic parameters (PAE and PA SME) as well as changes in bacterial characteristics tested were dependent on antibiotic concentration and on the strain used. Suppression of bacterial growth after treatment with tobramycin at 2 x MIC was in a range of 0.6-4.5 h, a higher concentration (4 x MIC) induced a longer PAE (1.9-5.4 h). Tobramycin at supra-subinhibitory concentrations (2 x MIC + 0.2 x MIC and 4 x MIC + 0.2 x MIC) caused total suppression of bacterial growth. In the majority of the tobramycin-treated strains, an increase in hydrophobicity manifested by adherence of bacteria to xylene as well as an increase in lipolytic activity was observed. Tobramycin at the concentrations tested did not affect the production of histamine.

Molecular analysis of the plasmid-borne aacA/aphD resistance gene region of coagulase-negative staphylococci from chickens

OBJECTIVES

The aim of this study was to analyse selected coagulase-negative staphylococci from chickens for the genetic basis of plasmid-borne resistance to gentamicin, tobramycin and kanamycin, and also for the presence of Tn4001-like elements.

METHODS

Three staphylococcal strains, two Staphylococcus warneri, and one Staphylococcus sciuri, were included in this study. The gene aacA/aphD coding for a bifunctional enzyme that mediates resistance to gentamicin, tobramycin and kanamycin was detected by hybridization with a specific probe. Plasmid location of this gene was also confirmed by hybridization and conjugation. The resistance gene and its adjacent regions were cloned and sequenced.

RESULTS

Three different types of Tn4001-like elements in which the IS256 elements were largely truncated and replaced by IS257 elements were identified on large conjugative and non-conjugative plasmids of 33-43 kb in the staphylococcal strains from chickens. Seven different types of IS257-analogous insertion sequences were identified.

CONCLUSIONS

Resistance to gentamicin, tobramycin and kanamycin in three staphylococcal strains from chickens was mediated by plasmid-borne aacA/aphD genes located on structurally modified Tn4001-like elements. In one of the three plasmids studied, the arrangement of the elements in the aacA/aphD resistance gene area closely resembled that on plasmids pSH6, pSK41 and pUW3626 from Staphylococcus aureus of human origin.

Variation in the propensity to release endotoxin after cefuroxime exposure in different gram-negative bacteria: uniform and dose-dependent reduction by the addition of tobramycin

An aminoglycoside in combination with a beta-lactam antibiotic is often recommended for the treatment of severe infections. The aim of the present study was to study whether cefuroxime-induced endotoxin release could be reduced by addition of tobramycin in different Gram-negative bacteria and how endotoxin release was affected by bacterial killing rate and number of killed bacteria. Three Escherichia coli strains, 1 Klebsiella, 1 Salmonella and 1 Neisseria strain were exposed in vitro to 2, 10 and 50 x minimum inhibitory concentration of cefuroxime, tobramycin or a combination of both. The cefuroxime-induced endotoxin release in the 6 strains varied from 0.1 to 9.9 x 10(-3) EU/killed bacterium. By adding tobramycin, highly significant reductions of 96%, 93%, 97%, 86% and 85% were seen in the 3 E. coli strains and in the Klebsiella and the Salmonella strain, respectively. In the Neisseria strain, the reduction was less. Increasing doses of tobramycin or the combination led to significant endotoxin release reduction in 4/6 strains. In conclusion, addition of tobramycin reduced penicillin-binding protein-3-beta-lactam binding-induced endotoxin release in all tested Gram-negative strains, despite a large interspecies variation in the propensity to release endotoxin. Besides broadening the spectrum and increasing the killing rate, this might be of benefit in the most severe forms of sepsis.

Susceptibility testing of Pseudomonas aeruginosa isolates and clinical response to parenteral antibiotic administration: lack of association in cystic fibrosis

STUDY OBJECTIVE

To determine the relationship between the antibiotic susceptibility of Pseudomonas aeruginosa isolated from the sputum of patients with cystic fibrosis (CF) and the patient's response to parenteral antibiotic administration, we performed a retrospective analysis using data from patients in the placebo arm of a phase 3 trial of tobramycin solution for inhalation. All patients were chronically infected with P aeruginosa. Seventy-seven of the 262 patients receiving placebo experienced a pulmonary exacerbation during the trial for which they received therapy with IV tobramycin and ceftazidime. The susceptibility of the P aeruginosa isolates to ceftazidime and tobramycin was determined at trial enrollment by broth microdilution.

DESIGN

The clinical response to combination antibiotic therapy was assessed by analyzing differences in spirometry before and after antibiotic administration. The FEV(1) percent predicted at the first visit after the conclusion of antibiotic administration was compared to the FEV(1) percent predicted prior to antibiotic therapy. The results were analyzed both descriptively and by regression analyses.

RESULTS

The conditions of 54 patients improved, and those of 9 patients worsened, and in 14 patients there was no change in FEV(1) with antibiotic administration. No correlation was observed between the susceptibility of P aeruginosa to tobramycin or ceftazidime and clinical response. Only the three following variables were observed to significantly correlate with FEV(1) after antibiotic treatment on regression analysis: FEV(1) prior to treatment (p < 0.0001); number of days elapsed between the previous FEV(1) measurement and the initiation of IV antibiotic therapy (p < 0.002); and the number of days elapsed between the determination of the minimum inhibitory concentration and the initiation of IV therapy (p < 0.03). No significant trends were observed between the antibiotic susceptibility of P aeruginosa isolates and treatment outcomes.

CONCLUSION

While lack of statistical significance for a trend between bacterial susceptibilities and the response to parenteral antibiotic administration does not mean that no such trend exists, the precision of the confidence intervals allows us to conclude that even if isolate antibiotic susceptibilities affect outcome, the impact would be small and not clinically relevant.

[Evaluation of a E-test method to detect bactericidy of beta lactam-aminoglycoside associations against Pseudomonas aeruginosa isolates from cystic fibrosis]

BACKGROUND

Pulmonary infectious exacerbations with Pseudomonas aeruginosa are the major problem for patients with cystic fibrosis. Emergence of multi-resistant mucoid strains leads to complicate the choice of antibiotherapy. Therefore, synergic and bactericidal treatment must be used. Then, it is interesting to estimate the bactericidal activity of antibiotics associations in order to optimise the treatment. The aim of this work is to describe a new method of bactericidal antibiotics combinations by superimposing 2 E-test strips and to compare results with those obtained with a broth bactericidal method chosen as reference method.

OBSERVATIONS

Twenty strains of P. aeruginosa (13 mucoïd and 7 non mucoïd) were selected from expectorants of cystic fibrosis children. Four antibiotics combinations were tested (ceftazidime/tobramycine, cefepime/tobramycine, ceftazidime/amikacine, cefepime/amikacine). Two antibiotics combinations by superimposing E-test strips techniques were used: maximal concentration on maximal concentration (C(max)/C(max)) and minimal inhibitory concentration on minimal inhibitory concentration (MIC/MIC). The comparison of results between killing curves and superposition of E-test strips (C(max)/C(max)) show 88% agreements, 4% major discrepancies specially with mucoid strains and 8% minor discrepancies. The Cmax/Cmax method seems to give better results than MIC/MIC method.

CONCLUSION

The superposition of E-test strips method is an attractive method: it is rapid, easy to use and well correlated to broth bactericidal method.

Significant microbiological effect of inhaled tobramycin in young children with cystic fibrosis

We conducted a double-blind, placebo-controlled, multicenter, randomized trial to test the hypothesis that 300 mg of tobramycin solution for inhalation administered twice daily for 28 days would be safe and result in a profound decrease in Pseudomonas aeruginosa (Pa) density from the lower airway of young children with cystic fibrosis. Ninety-eight subjects were to be randomized; however, the trial was stopped early because of evidence of a significant microbiological treatment effect. Twenty-one children under age 6 years were randomized (8 active; 13 placebo) and underwent bronchoalveolar lavage at baseline and on Day 28. There was a significant difference between treatment groups in the reduction in Pa density; no Pa was detected on Day 28 in 8 of 8 active group patients compared with 1 of 13 placebo group patients. We observed no differences between treatment groups for clinical indices, markers of inflammation, or incidence of adverse events. No abnormalities in serum creatinine or audiometry and no episodes of significant bronchospasm were observed in association with active treatment. We conclude that 28 days of tobramycin solution for inhalation of 300 mg twice daily is safe and effective for significant reduction of lower airway Pa density in young children with cystic fibrosis.

Contributions of antibiotic penetration, oxygen limitation, and low metabolic activity to tolerance of Pseudomonas aeruginosa biofilms to ciprofloxacin and tobramycin

The roles of slow antibiotic penetration, oxygen limitation, and low metabolic activity in the tolerance of Pseudomonas aeruginosa in biofilms to killing by antibiotics were investigated in vitro. Tobramycin and ciprofloxacin penetrated biofilms but failed to effectively kill the bacteria. Bacteria in colony biofilms survived prolonged exposure to either 10 micro g of tobramycin ml(-1)or 1.0 micro g of ciprofloxacin ml(-1). After 100 h of antibiotic treatment, during which the colony biofilms were transferred to fresh antibiotic-containing plates every 24 h, the log reduction in viable cell numbers was only 0.49 +/- 0.18 for tobramycin and 1.42 +/- 0.03 for ciprofloxacin. Antibiotic permeation through colony biofilms, indicated by a diffusion cell bioassay, demonstrated that there was no acceleration in bacterial killing once the antibiotics penetrated the biofilms. These results suggested that limited antibiotic diffusion is not the primary protective mechanism for these biofilms. Transmission electron microscopic observations of antibiotic-affected cells showed lysed, vacuolated, and elongated cells exclusively near the air interface in antibiotic-treated biofilms, suggesting a role for oxygen limitation in protecting biofilm bacteria from antibiotics. To test this hypothesis, a microelectrode analysis was performed. The results demonstrated that oxygen penetrated 50 to 90 micro m into the biofilm from the air interface. This oxic zone correlated to the region of the biofilm where an inducible green fluorescent protein was expressed, indicating that this was the active zone of bacterial metabolic activity. These results show that oxygen limitation and low metabolic activity in the interior of the biofilm, not poor antibiotic penetration, are correlated with antibiotic tolerance of this P. aeruginosa biofilm system.

Inhaled Tobramycin (TOBI??)

Specifically formulated for nebulisation using the PARI LC PLUS reusable nebuliser, tobramycin solution for inhalation (TSI) [TOBI] provides a high dose of tobramycin (an aminoglycoside antibacterial with good activity against Pseudomonas aeruginosa) to the lungs of patients with cystic fibrosis, while maintaining low serum concentrations of the drug, thus reducing the risk of systemic toxicity. Intermittent (28-day on/28-day off) treatment with TSI 300 mg twice daily significantly (p < 0.001) improved lung function and sputum P. aeruginosa density compared with placebo (randomised double-blind trials), and was significantly (p = 0.008) more effective than colistin for improvement in forced expiratory volume in 1 second (small nonblind trial) in patients aged > or =6 years with cystic fibrosis and chronic P. aeruginosa infection. Improvements in lung function were most marked in adolescent patients (aged 13-17 years) in placebo-controlled trials. Improvements were maintained for up to 96 weeks in patients in an open-label extension study. Fewer TSI than placebo recipients required parenteral antipseudomonal agents or hospitalisation. In addition, TSI 300 mg twice daily for 28 days reduced P. aeruginosa density in the lower airways of patients aged <6 years with early colonisation and cystic fibrosis, although TSI is not currently indicated in this patient group. A decrease in tobramycin susceptibility of P. aeruginosa isolates and an increase in fungal organisms (Candida albicans and Aspergillus species) during prolonged intermittent treatment with TSI 300 mg twice daily was not associated with adverse clinical outcome. There was no evidence of selection for the most resistant isolates. TSI is generally well tolerated, with no renal toxicity or hearing loss in clinical trials, although transient mild or moderate tinnitus occurred more frequently in TSI than placebo recipients. Bronchospasm after administration of TSI was transient and occurred with a similar incidence to that with placebo; TSI is preservative free and specifically formulated for the lung in terms of osmolality and pH. In conclusion, TSI provides an effective means of delivering tobramycin to the lungs of patients with cystic fibrosis with chronic P. aeruginosa infection, improving lung function and sputum P. aeruginosa density in these patients without the nephrotoxicity or ototoxicity of parenteral aminoglycosides. Further data on the potential for and clinical significance of increased tobramycin resistance and fungal colonisation during TSI treatment would be beneficial, as would longer-term data. In the meantime, TSI represents a valuable option for suppressive antipseudomonal therapy in patients with cystic fibrosis.

The integration of four major determinants of antibiotic action: bactericidal activity, postantibiotic effect, susceptibility, and pharmacokinetics

A functional pharmacokinetic/pharmacodynamic (PK/PD) index that could simultaneously describe three controlling PD variables, i.e., bactericidal activity, postantibiotic effect (PAE), and susceptibility, in relation to pharmacokinetics, was designed using an in vitro kinetic model. Tobramycin was tested against one standard and five clinical strains of Pseudomonas aeruginosa. The organisms showed minimum inhibitory concentrations (MICs) ranging between 1 and >1000 microg/ml. The model allowed antibiotic concentrations to be reduced exponentially from initial concentrations at fixed multiples of MIC. Antibiotic removal was performed when the decreasing concentrations hit the MIC of individual strain to provide a wide range of AUC(>MIC) within an identical frame of AUC(>MIC)/MIC (AUIC) values. Viable counts were measured at antibiotic addition and before/after its removal for bactericidal activity and PAE assessments. A linear relationship was observed between PAE and bactericidal rate constants, though the pattern varied among different strains. Characterization of the exposure (AUC(>MIC))-effect relationships using the Emax model revealed that the less susceptible strains displayed lower Emax and higher EC50 for both antimicrobial effects. By employing the AUIC as a common frame of reference, regression analysis showed a significant linear correlation (p < 0.05) between the mean PAE and bactericidal rate data and, thereby simultaneously defining the four contributing factors of the PK/PD system. It appears that the AUIC, by conveying the pharmacokinetic and susceptibility information, could serve as a PK/PD index in bridging the interdependency of PAE and bactericidal activity. More importantly, the collective assessment of these four factors would allow more optimal evaluation of dosage regimens.

Effect of aminoglycosides (sub-MICs) on adherence of coagulase-negative Staphylococci to intraocular lens surface

The authors evaluated the in vitro effects of subinhibitory concentrations (sub-MICs) of aminoglycosides (gentamicin, netilmicin and tobramycin) on the adherence of coagulase-negative staphylococcus to intraocular lens (PMMA, acrylic and heparin) surface. The five strains of coagulase-negative Staphylococcus epidermidis used (S. epidermidis IMe7, IMe11, IMe27, IMe29 and IMe31) were tested for their ability to produce slime. The minimum inhibitory concentrations (MIC) indicated high susceptibility in vitro to the antibiotics and homogeneous values. The adhesion tests without antibiotics (K1, K2 and K3) for every time considered (30 min, 60 min and 180 min) and for all examined strains showed more constant adhesive activity on the surface of acrylic intraocular lens (IOLs) than on the surface of heparin IOLs. The aminoglycosides tested were able to reduce adhesivity by coagulase-negative S. epidermidis slime to the IOL surfaces, even at sub-MICs. The documentation obtained by scanning electron microscope shows the growth of a strain of S. epidermidis IMe11 after 180 minutes of contact which remains adherent to the surface of the acrylic IOLs.

Class 1 integron-associated tobramycin-gentamicin resistance in Campylobacter jejuni isolated from the broiler chicken house environment

Using PCR, we screened 105 isolates of poultry-associated Campylobacter jejuni for the presence of class 1 integrons. Of those isolates, 21% (22 of 105) possessed the integrase gene, but only 5 isolates produced an amplicon in a 5'-3' conserved sequence PCR directed toward amplification of the resistance cassettes. DNA sequencing demonstrated that all five isolates possessed the aminoglycoside resistance gene, aacA4.

Analogy between temperature-dependent and concentration-dependent bacterial killing

In this article an analogy between temperature-dependent and concentration-dependent bacterial killing is described. The validation process of autoclaves uses parameters such as reduction rate constant k, decimal reduction time D and resistance coefficient z from an imaginary microorganism to describe the sterilization process. Total lethality of the process is calculated as the integral of the lethality (a function of the temperature) over time. In the case of concentration-dependent killing-i.e. using antibiotic drugs-the k-value is not necessarily a constant; it is the difference between growth and killing of the microorganism. Equations are derived for the decimal reduction time D and resistance coefficient z. Pharmacodynamic models of tobramycin, ciprofloxacin and ceftazidime are used to demonstrate that there is an optimal concentration for all three drugs: C(opt-tobra)=3.20 MICmg/l, C(opt-cipro)=3.45 MICmg/l and C(opt-cefta)=1.35 MICmg/l.

[Antibacterial activities and PK/PD parameters of aminoglycosides against recent clinical isolates of gram-negative rods]

We examined antibacterial activities and PK/PD parameters of six kinds of aminoglycosides against seven bacterial species of clinical isolates in 2001. Aminoglycoseides examined were gentamicin (GM), dibekacin (DKB), tobramycin (TOB), amikacin (AMK), netilmicin (NTL), and isepamicin (ISP), and bacterial isolates used were each 50 strains of Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Citrobacter freundii, Proteus spp., Serratia marcescens and Pseudomonas aeruginosa. All aminoglycosides showed good activities with low MICs against 6 species of Enterobacteriacea except S. marcescens. Eight strains (3.2%) among them were resistant to one or more aminoglycosides. Resistance to multiple aminoglycosides were detected in 16 strains (32%) of S. marcescens, among which 13 strains were resistant to AMK but susceptible to ISP. Three (6%) strains of P. aeruginosa were resistant to multiple drugs, one of which was resistant to all six aminoglycosides, and others were moderately susceptible to AMK and ISP, and susceptible to GM, AMK and ISP. Using a ratio of peak serum concentration to MIC90 (Cmax/MIC90) or a ratio of area under the curve to MIC90 (AUC/MIC90) as a pharmacokinetic and pharmacodynamic (PK/PD) parameter, we estimated the efficacy of the drug. An excellent effect of ISP, which was injected intramuscularly or intravenously at a dose of 400 mg, was expected for strains of Enterobacteriacea except S. marcescens. The Cmax/MIC90 ratios for S. marcescens were comparably higher in GM and ISP and that for P. aeruginosa were rather high in TOB when compared to other aminoglycosides. Another PK/PD parameter, AUC/MIC90 ratio, was high enough in NTL and ISP for Enterobacteriacea, suggesting good efficacy of these drugs. The (AUC/MIC90) ratios for S. marcescens were comparably high in GM and ISP, and that for P. aeruginosa were high in TOB, DKB, and ISP.

Screening of Salmonella isolates from a turkey production facility for antibiotic resistance

An ecological survey was conducted from April 1997 to June 1999 on four turkey flocks (F1 to F4). Turkey cecal contents, litter, waterers, feed, feeders, and environmental swabs were analyzed. Presence of Salmonella was determined using conventional microbiological screening techniques and confirmed by serology. Positive isolates were serotyped and screened for antibiotic resistance. From a total of 69 Salmonella isolates 25% were resistant to one or more antibiotics including gentamicin (G), spectinomycin (SP), streptomycin (S), tetracycline (T), tobramycin (TO), and trimethoprim/sulfamethoxazole. Isolates included 45 S. heidelberg, 13 S. senftenberg, 7 S. muenster, 2 S. anatum, and 2 S. worthington. Resistance to antibiotic(s) was highest among waterer isolates (55%) followed by environmental swabs (43%), feeder content samples (33%), turkey cecal contents (26%), and litter samples (5%). Frequencies of antibiotic-resistant Salmonella in F1, F2, and F4 were 27, 13, and 40%, respectively. Salmonella was undetected in F3. In F1, S. heidelberg from cecal content and waterer samples was resistant to G, SP, S, and T, whereas S. anatum from waterer samples was resistant to T and S. In F2, S. worthington from litter and feeder content samples was resistant to T, and in F4, S. muenster from environmental swabs was resistant to TO, S, SP, and G. Identifying preharvest sources and characterizing serotype and antibiotic-resistance profile can assist poultry producers and integrators in tracking movement of Salmonella on turkey farms.

Invitro comparative evaluation of aminoglycosides at a cancer centre

A comparative study of in vitro activity of amikacin, gentamicin, netilmicin, tobramycin and isepamicin was done. A total of 200 clinical isolates of Gram negative organisms from various clinical sources were tested. E.Coli was the most frequently isolated organism followed by Pseudomonas spp., Klebsiella spp., Proteus spp., Acinetobacter spp. and Enterobacter spp. Of the 5 aminoglycosides tested, isepamicin showed the highest numbers of susceptible isolates followed by amikacin, netilmicin, gentamicin and tobramycin. MIC 90 value of isepamicin was lower as compared to amikacin.

Incorporation of tobramycin into biomimetic hydroxyapatite coating on titanium

Calcium phosphate coatings containing an antibiotic were produced on titanium alloy (Ti6Al4V) implants using a biomimetic approach. Thin, amorphous calcium phosphate (ACP) coatings were first deposited onto Ti6Al4V plates by immersion in 5 times concentrated simulated body fluid (SBF), for 24h at 37 degrees C. The ACP-coated implants were then immersed in a supersaturated calcium phosphate (SCP) solution containing 0, 100, 200, 400, 600 or 800 mg/l of tobramycin for 48 h at 37 degrees C. A carbonated hydroxyapatite (CHA) layer, approximately 40 microm thick, was formed. Approximately 3 microg/mg of tobramycin was co-precipitated with the CHA crystals onto titanium alloy plates, using 800mg/l tobramycin in the coating solution. For comparison, plasma-sprayed calcium phosphate coatings were also immersed in solutions containing 100, 200, 400 or 1,000 mg/l of tobramycin for 10, 40 min, or 48 h. A maximum of about 0.3 microg/mg could be adsorbed onto the plasma-sprayed calcium phosphate coating with the comparable concentration of 800 mg/l in solution. The dissolution of coating and release of tobramycin were also measured in vitro using saline solution buffered at pH 5.0 or 7.3 at 37 degrees C. The release rate of tobramycin was faster at pH 7.3 than at pH 5, with 50 and 4 microg/ml/min, respectively. Tobramycin released from the biomimetic-coated plates could inhibit growth of Staphylococcus aureus bacteria. The result of this study, therefore, indicates that the biomimetic CHA coatings containing antibiotics could be used to prevent post-surgical infections in orthopaedic or trauma.

Aminoglycoside antibiotics induce pH-sensitive activation of the calcium-sensing receptor

The aminoglycoside antibiotic (AGA) neomycin is a known agonist of the extracellular calcium-sensing receptor (CaR). To test whether other AGA drugs stimulate the CaR, we studied the relative effects of four AGAs on intracellular Ca(2+) concentration ([Ca(2+)](i)) using CaR-transfected human embryonic kidney (HEK)-293 cells. Gentamicin, tobramycin, and neomycin evoked dose-dependent increases in [Ca(2+)](i) with EC(50) values of 258, 177, and 43 microM, respectively, in CaR-transfected, but not in non-transfected cells. Kanamycin was ineffective at doses <1mM. Thus, AGAs stimulate the CaR with a rank order of potency that correlates positively with the number of their attached amino groups. The CaR is expressed on the apical surface of renal proximal tubule cells, which is also the site of AGA endocytosis and nephrotoxicity. In the current study, reducing extracellular pH from 7.4 to 6.9, to mimic the luminal pH of the proximal tubule, enhanced the sensitivity of the CaR to tobramycin, suggesting that the AGAs may be more potent CaR agonists in the proximal tubule than elsewhere. This pH effect was not observed when stimulating CaR with the non-ionizable agonist, Gd(3+), suggesting that the enhanced AGA effect is due to increased ionization of the drug. Thus, we show that a number of AGA drugs are capable of CaR activation and that their potency most likely relates to the number of their amino side chains and to their pH-dependent charge characteristics. The contribution of CaR activation to the pharmacological/toxicological effects of these AGAs remains to be determined.

Aminoglycoside suppression of a premature stop mutation in a Cftr-/- mouse carrying a human CFTR-G542X transgene

Cystic fibrosis (CF) is caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) protein. Since approximately 5% of all mutant CF alleles are stop mutations, it can be calculated that approximately 10% of CF patients carry a premature stop mutation in at least one copy of the CFTR gene. Certain ethnic groups, such as the Ashkenazi Jewish population, carry a much higher percentage of CF stop mutations. Consequently, a therapeutic strategy aimed at suppressing this class of mutation would be highly desirable for the treatment of this common genetic disease. We have shown previously that aminoglycoside antibiotics can suppress premature stop mutations in the CFTR gene in a bronchial epithelial cell line [Nat Med (1997) 3:1280]. To address whether aminoglycosides can suppress a CFTR premature stop mutation in an animal model, we constructed a transgenic mouse with a null mutation in the endogenous CFTR locus (Cftr-/-) that also expressed a human CFTR-G542X cDNA under control of the intestinal fatty acid binding protein promoter. We then investigated whether the daily administration of the aminoglycoside antibiotics gentamicin or tobramycin could restore the expression of a detectable level of CFTR protein. Immunofluorescence staining of intestinal tissues from Cftr-/- hCFTR-G542X mice revealed that gentamicin treatment resulted in the appearance of hCFTR protein at the apical surface of the glands of treated mice. Weaker staining was also observed in the intestinal glands following tobramycin treatment. Short-circuit current measurements made on intestinal tissues from these mice demonstrated that a significant number of positive cAMP-stimulated transepithelial chloride current measurements could be observed following gentamicin treatment (P=0.008) and a near significant number following tobramycin treatment (P=0.052). When taken together, these results indicate that gentamicin, and to a lesser extent tobramycin, can restore the synthesis of functional hCFTR protein by suppressing the hCFTR-G542X premature stop mutation in vivo.

[Species composition and antibiotic sensitivity of staphylococci isolated from patients with furunculosis]

Biological properties and sensitivity to modern antibacterial drugs 54 strains of staphylococci isolated under furunculosis have been studied with the aim to optimize this disease treatment. Staphylococcus aureus was revealed with frequency 35.2 +/- 6.50%, S. epidermidis (31.5 +/- 6.32%), S. warneri (16.7 +/- 5.08%), S. hominis (7.4 +/- 3.56%), S. haemolyticus and S. saprophyticus (3.7 +/- 2.57%) as well as S. lentus (1.9 +/- 1.86%) were identified among coagulase-negative staphylococci. Methycillin-resistant staphylococci were isolated from 25.92% of patients with furunculosis. High level of resistance of furunculosis agents to erythromycin, clarythromycine, cephtriaxon, pephloxacyne, tetracycline, doxycycline, levomycetine and phosphomycine has been registered. Basing on the study of isolates antibioticograms, cephasoline is recommended as the selected drug under furunculosis, and tobramycin as the reserve antibiotic. Autovaccine was also made for the patients treatment.

Characterization of methicillin-resistant Staphylococcus aureus strains susceptible to tobramycin

Gentamicin-susceptible, methicillin-resistant, Stapylococcus aureus strains (GS-MRSA) emerged in 1992 in various Parisian hospitals and have subsequently been isolated from all French hospitals. This new GS-MRSA epidemic clone accounted for 50% of MRSA strains in 1996 and for 85% in 2000 in our hospital. We have observed a parallel increase in the prevalence of tobramycin and amikacin-susceptible GS-MRSA (TKS-MRSA). The number of TKS-MRSA strains per 100 MRSA strains has steadily increased from 3.1 in 1996 to 24.0 in 2000. Genotypic characterization of TKS-MRSA strains showed that these strains are a phenotypic variant of the dominant clone of GS-MRSA. To improve our understanding of the changes in methicillin-resistant Staphylococcus aureus (MRSA) susceptibility to non-beta-lactam antibiotics, gentamicin- and amikacin-susceptible MRSA (TKS-MRSA) from our acute-care hospital were compared with TKS-MRSA isolated from a long-term care hospital located in another region of France. The nature of the care facility did not seem to play a major role in the hospital dissemination of TKS-MRSA. We also found that changes in antibiotic use alone do not account for the emergence of these strains.

Adaptive resistance to benzalkonium chloride, amikacin and tobramycin: the effect on susceptibility to other antimicrobials

AIMS

To produce strains of antimicrobial-resistant Pseudomonas aeruginosa via adaptation to benzalkonium chloride, amikacin and tobramycin and to then examine the incidence, or otherwise, of cross-resistance between antibiotics and between antibiotics and benzalkonium chloride.

METHODS AND RESULTS

Adaptation was obtained by progressive subculturing in subinhibitory concentrations of the antimicrobials. Pseudomonas aeruginosa NCIMB 10421 adapted to grow in high concentrations of benzalkonium chloride (BC) had lower MIC to antibiotics than the wild type, whereas Ps. aeruginosa adapted to grow in antibiotics had greater MIC to benzalkonium by a small degree.

CONCLUSIONS

Adaptive resistance to BC of Ps. aeruginosa generally produced cultures with a decrease in resistance to several antibiotics. Adaptive resistance to the aminoglycosides Ak and Tm produced a low-level increase in tolerance to BC. The adaptive mechanisms of resistance appear to be different for the different types of antimicrobials used.

SIGNIFICANCE AND IMPACT OF THE STUDY

The relationships between biocide and antibiotic resistance are complex. It appears, from this study, that an organism resistant to a common biocide can become sensitive to antibiotics, but the converse was not true. Could this observation be used in a strategy to alleviate antibiotic resistance?

Bronchial reactions to the inhalation of high-dose tobramycin in cystic fibrosis

It has been established that inhaled tobramycin has a positive effect on respiratory function in Pseudomonas-aeruginosa positive patients with cystic fibrosis (CF). In a previous study the authors reported that low-dose tobramycin preparations containing the preservative phenol caused significant bronchial obstruction. Recently, high-dose tobramycin preparations with and without preservatives/phenol have become available. To assess the airway response to these preparations flow/volume curves in 12 patients with CF (four males, eight females, mean age+/-SD=19.0+/-7.4 yrs) were measured. The tobramycin preparations: Nebicina 2.0 mL (150 mg, containing the preservative phenol), Distobram 3.0 mL (150 mg, containing preservatives), Tobi 5.0 mL (300 mg), Tobi 2.5 mL (150 mg), and Tobi 5.0 mL, were used after bronchodilator application. Immediately and/or 5 min after the tobramycin inhalations there was a significant fall in lung function with the different preparations. There was no significant difference between preparations with and without preservatives/phenol. The bronchial obstruction was comparable to that observed after the inhalation of low-dose tobramycin and after saline. After 10 min of inhalation, the lung function returned to baseline values. Most patients preferred the Tobi 2.5 mL and disliked the Nebicina preparation due to the unpleasant taste. Preceding treatment with bronchodilators prevented the decline in lung function. Assessment of bronchial response at the first nebulisation of high-dose tobramycin and, in case of significant obstruction, beta-agonists in combination with the antibiotic inhalation are recommended.

Colistin stimulates the activity of neutrophil elastase and Pseudomonas aeruginosa elastase

Nonantimicrobial effects of antibiotics may contribute to their activity in the treatment of infective airway disease. The aim of this study was to identify antibiotics used for the treatment of infection in cystic fibrosis that may alter the activity of human neutrophil elastase (HNE) and Pseudomonas aeruginosa elastase (PE). The effect of antibiotics on the activity of purified HNE and PE, and HNE in sputum was assessed using colourimetric and fluorescent substrate assays by kinetic measurements, and by examining the interaction of HNE with inhibitors. Ceftazidime, tobramycin, and gentamycin slightly inhibited purified HNE activity whereas erythromycin and colistin significantly stimulated purified HNE and PE (395 and 557%, respectively). However, only colistin increased HNE activity in sputum (+102%) and was therefore studied in more detail. This increase in activity was not due an interference with the specific inhibition of HNE by alpha1-antitrypsin but colistin was found to reverse the inhibitory effects of small molecular weight molecules like heparin. Colistin increases the activity of human neutrophil elastase and Pseudomonas aeruginosa elastase, two proteases that contribute to the pathogenesis of cystic fibrosis airway disease.

Clinically relevant aminoglycosides can suppress disease-associated premature stop mutations in the IDUA and P53 cDNAs in a mammalian translation system

Recent studies have suggested that the use of aminoglycosides to suppress disease-causing nonsense mutations may be a promising new therapy for a large number of genetic diseases. However, gentamicin is currently the only clinically relevant aminoglycoside shown to suppress premature stop mutations in a mammalian system. We compared the ability of the clinically approved aminoglycosides gentamicin, tobramycin, and amikacin to suppress premature stop mutations. Using readthrough reporter constructs as well as mammalian cDNAs containing naturally occurring premature stop mutations, we found that each of these aminoglycosides can suppress many premature stop mutations in a context-dependent manner in a mammalian translation system. Our results indicate that the tetranucleotide termination signal (the stop codon and the nucleotide 3' of the stop codon) is the primary determinant for aminoglycoside-mediated suppression. The levels of termination suppression achieved by tobramycin were substantially lower than those observed with gentamicin. In contrast, amikacin stimulated suppression in a manner that was generally similar to gentamicin. Amikacin produced higher levels of readthrough than gentamicin at some contexts, demonstrating a unique pattern of context dependence. Experiments with mammalian cDNAs confirmed these results and demonstrated that these aminoglycosides can also suppress disease-associated premature stop mutations previously identified in the IDUA gene (responsible for the lysosomal storage disease mucopolysaccharidosis I) and the P53 gene (associated with many forms of cancer). Taken together, these results suggest that amikacin represents an alternative to gentamicin for suppression therapy in certain contexts, thus providing a means of optimizing the efficacy of aminoglycoside-mediated suppression of premature stop mutations.

A component of innate immunity prevents bacterial biofilm development

Antimicrobial factors form one arm of the innate immune system, which protects mucosal surfaces from bacterial infection. These factors can rapidly kill bacteria deposited on mucosal surfaces and prevent acute invasive infections. In many chronic infections, however, bacteria live in biofilms, which are distinct, matrix-encased communities specialized for surface persistence. The transition from a free-living, independent existence to a biofilm lifestyle can be devastating, because biofilms notoriously resist killing by host defence mechanisms and antibiotics. We hypothesized that the innate immune system possesses specific activity to protect against biofilm infections. Here we show that lactoferrin, a ubiquitous and abundant constituent of human external secretions, blocks biofilm development by the opportunistic pathogen Pseudomonas aeruginosa. This occurs at lactoferrin concentrations below those that kill or prevent growth. By chelating iron, lactoferrin stimulates twitching, a specialized form of surface motility, causing the bacteria to wander across the surface instead of forming cell clusters and biofilms. These findings reveal a specific anti-biofilm defence mechanism acting at a critical juncture in biofilm development, the time bacteria stop roaming as individuals and aggregate into durable communities.

Corneal Pharmacodynamics After Photorefractive Keratectomy and Laser in situ Keratomileusis in Rabbits

PURPOSE

To evaluate changes in corneal pharmacodynamics after PRK and LASIK in rabbits.

METHODS

Two groups of five rabbits (10 eyes) each received PRK and LASIK, and an unoperated third group was used as a control. Dexamethasone, efflumidex, diclofenac, and tobramycin were applied. Anterior chamber aqueous was collected every 20 minutes and analyzed by spectrophotometry. Histological studies were performed to find drug deposits in the cornea.

RESULTS

The coefficient of diffusion after PRK was determined for dexamethasone (3.2 x 10(-4) cm/min), efflumidex (1.4 x 10(-4)), diclofenac (7.4 x 10(-5)), and tobramycin (5.4 x 10(-6)). After LASIK, the coefficient of diffusion for dexamethasone was 3.4 x 10(-5); efflumidex, 1.7 x 10(-5); diclofenac, 8.8 x 10(-6); and tobramycin, 2.4 x 10(-6) cm/min. Total time of passing through the cornea after PRK and LASIK was also measured: dexamethasone 45 and 70 min, efflumidex 50 and 115 min, diclofenac 60 and 200 min, and tobramycin 335 and 690 min. Histologically a drug deposit area was found in corneas after LASIK under the flap. In the control group, coefficient of diffusion for dexamethasone was 1.2 x 10(-5) cm/min, efflumidex 1.5 x 10(-5), diclofenac 6.4 x 10(-6), and tobramycin 2.1 x 10(-6). Total time of passing through the cornea for the control group for dexamethasone was 60 min, efflumidex 105 min, diclofenac 160 min, and tobramycin 540 min.

CONCLUSIONS

Coefficient of diffusion increased after photorefractive surgery.

[Characteristics of pharmacodynamics of drugs after excimer laser surgery (an experimental study)]

Pharmacodynamics of dexamethasone, fluoromethanol, sodium diclofenak, and tobramicin after photorefraction keratectomy (PRK) and intrastromal laser keratectomy (ILK) was studied in rabbits. Eximer laser operations modulated the barrier functions of the cornea. The highest concentrations of drugs in anterior chamber humor during the first 20 min after instillations was observed after ILK in comparison with the control (intact cornea). The highest coefficient of effective drug diffusion through the cornea was observed after PRK in comparison with ILK. The drug efficiency was higher after ILK than after PRK, which is seen from the maximum concentrations of drugs entering the cornea immediately after instillation and prolongation of the drug effect due to its decelerated diffusion through the cornea.

Rapidly growing members of the genus Mycobacterium affecting dogs and cats

Rapidly growing members of the genus Mycobacterium were most often associated with chronic (2 to 72 months), nonhealing skin lesions of dogs and cats. Mycobacterium fortuitum (M. fortuitum) was the most commonly isolated mycobacterium obtained from these lesions, although M. chelonae-abscessus and M. flavescens were occasionally encountered. Isolates were tested in vitro to various antimicrobial agents and found to be susceptible to amikacin (100% of the isolates), cefoxitin (93.8%), ciprofloxacin (75%), clarithromycin (71.4%), doxycycline (28.6%), erythromycin (6.2%), gentamicin (68.8%), kanamycin (75%), minocycline (81.3%), streptomycin (14.3%), tobramycin (43.8%), trimethoprim/sulfonamides (57.1%), and vancomycin (15.4%).

Bactericidal effect of combinations of antibiotic and antineoplastic agents against Staphylococcus aureus and Escherichia coli

BACKGROUND

The bactericidal effect of some antibiotic and antineoplastic agents commonly used in clinical practice was investigated to analyse whether the combinations act synergistically, have indifferent or antagonistic antibacterial effects compared to the effect of the antibiotics alone.

METHODS

The rate of killing of meropenem, ceftazidime and tobramycin was studied against six different strains of Staphylococcus aureus and Escherichia coli, and the results were compared to the rate of killing of the antibiotics in combination with the cytostatic drugs doxorubicin, etoposide and 5-fluorouracil (5-FU).

RESULTS

Tobramycin showed synergy against two strains of S. aureus after 3 h in the presence of 5-FU and against one strain of S. aureus in the presence of doxorubicin. Meropenem induced an antagonistic bactericidal effect against one isolate of S. aureus after 24 h. Ceftazidime expressed an indifferent bactericidal effect together with the cytostatic agents. The antineoplastic agents had no impact on the bacterial killing of any of the antibiotics against E. coli.

CONCLUSIONS

Tobramycin expressed a significantly better bactericidal effect against S. aureus after 3 h in the presence of doxorubicin and 5-FU than tobramycin alone. Meropenem expressed antagonism against one clinical strain of S. aureus, but the cytostatic drugs did not affect the killing of other strains tested. Ceftazidime expressed indifferent bactericidal activity together with the antineoplastic agents.

In vitro activity of the aerosolized agents colistin and tobramycin and five intravenous agents against Pseudomonas aeruginosa isolated from cystic fibrosis patients in southwestern Germany

Three hundred and eighty-five mucoid and non-mucoid strains of Pseudomonas aeruginosa isolated from 192 sputa from 57 adult cystic fibrosis patients were studied. Susceptibility testing using an agar dilution technique was performed for ceftazidime, ciprofloxacin, fosfomycin, meropenem and piperacillin, and the aerosolized agents colistin and tobramycin. Meropenem, ceftazidime and piperacillin were the most potent agents (susceptibility 86.2%, 84.2% and 84%, respectively). Tobramycin and colistin susceptibility rates were lower, but in light of higher intrabronchial concentrations of these drugs a greater percentage of strains might still be clinically susceptible. Only 46.2% and 41.8% of isolates were susceptible to ciprofloxacin and fosfomycin, respectively.

Outbreak caused by tobramycin-resistant Pseudomonas aeruginosa in a bone marrow transplantation unit

Between May and August 1995, 5 patients in a bone marrow transplantation (BMT) ward developed bacteremia caused by Pseudomonas aeruginosa resistant to tobramycin (TRPA). Previously, isolates of TRPA had been limited to patients who were treated in 1 intensive care unit (ICU) of this tertiary care teaching hospital in Helsinki, Finland. To study whether the outbreak was caused by a single or multiple strains of P. aeruginosa, 102 isolates of TRPA from clinical samples obtained from different hospital units and 22 isolates obtained from the hospital environment were characterized by pulsed-field gel electrophoresis. All isolates from hematological patients produced 1 unique fragment pattern, which was also isolated from 3 ICU patients before the BMT ward outbreak began as well as from 5 shower heads in the BMT ward. The outbreak in the BMT ward was successfully controlled by eradicating the probable environmental source--contaminated hand showers--but the endemic infections continued in the ICU.

Comparison of two culture methods for detection of tobramycin-resistant gram-negative organisms in the sputum of patients with cystic fibrosis

A culture method utilizing quantitative plating on antibiotic-containing media has been proposed as a technique for the detection of tobramycin-resistant organisms that is more sensitive than standard methods. Typical sputum culture methods quantitate the relative amounts of each distinct morphotype, followed by antibiotic susceptibility testing of a single colony of each morphotype. Sputum specimens from 240 cystic fibrosis patients were homogenized, serially diluted, and processed in parallel by the standard method (MacConkey agar and OF basal medium with agar, polymyxin, bacitracin, and lactose) and by plating on antibiotic-containing media (MacConkey agar with tobramycin added at 25 microg/ml [MAC-25] and 100 microg/ml [MAC-100]). MICs of tobramycin were determined for all Pseudomonas aeruginosa isolates by broth microdilution. Growth of P. aeruginosa on MAC-25 was considered to be equivalent to a tobramycin MIC of > or = 16 microg/ml, and growth on MAC-100 was considered to be equivalent to a tobramycin MIC of > or = 128 microg/ml. Analysis of method-specific detection rates showed that tobramycin-containing medium was more sensitive than the standard method for the detection of tobramycin-resistant P. aeruginosa, Stenotrophomonas maltophilia, and Achromobacter xylosoxidans but was less sensitive for the detection of Burkholderia cepacia than the standard method. When MICs for P. aeruginosa that grew on tobramycin-containing medium were tested by broth microdilution, the MICs for 28 of 121 strains (23%) growing on MAC-25 and 22 of 56 strains (39%) growing on MAC-100 were MICs < 16 and < 128 microg/ml, respectively. Addition of a tobramycin-containing MacConkey plate to the routine media for sputum culture may provide additional, clinically relevant microbiologic data.

Biofilms and planktonic cells of Pseudomonas aeruginosa have similar resistance to killing by antimicrobials

Biofilms are considered to be highly resistant to antimicrobial agents. Strictly speaking, this is not the case-biofilms do not grow in the presence of antimicrobials any better than do planktonic cells. Biofilms are indeed highly resistant to killing by bactericidal antimicrobials, compared to logarithmic-phase planktonic cells, and therefore exhibit tolerance. It is assumed that biofilms are also significantly more tolerant than stationary-phase planktonic cells. A detailed comparative examination of tolerance of biofilms versus stationary- and logarithmic-phase planktonic cells with four different antimicrobial agents was performed in this study. Carbenicillin appeared to be completely ineffective against both stationary-phase cells and biofilms. Killing by this beta-lactam antibiotic depends on rapid growth, and this result confirms the notion of slow-growing biofilms resembling the stationary state. Ofloxacin is a fluoroquinolone antibiotic that kills nongrowing cells, and biofilms and stationary-phase cells were comparably tolerant to this antibiotic. The majority of cells in both populations were eradicated at low levels of ofloxacin, leaving a fraction of essentially invulnerable persisters. The bulk of the population in both biofilm and stationary-phase cultures was tolerant to tobramycin. At very high tobramycin concentrations, a fraction of persister cells became apparent in stationary-phase culture. Stationary-phase cells were more tolerant to the biocide peracetic acid than were biofilms. In general, stationary-phase cells were somewhat more tolerant than biofilms in all of the cases examined. We concluded that, at least for Pseudomonas aeruginosa, one of the model organisms for biofilm studies, the notion that biofilms have greater resistance than do planktonic cells is unwarranted. We further suggest that tolerance to antibiotics in stationary-phase or biofilm cultures is largely dependent on the presence of persister cells.

Effect of sulfur hexafluoride gas on antibacterial activity of antibiotics in vitro against agents causing endophthalmitis

BACKGROUND

We conducted a study to evaluate the effect of sulfur hexafluoride gas (SF(6)) on the antibacterial activity of antibiotics in vitro against Staphylococcus aureus, Staphylococcus epidermidis and Pseudomonas aeruginosa, which are common endophthalmitis-causing agents.

METHODS

In this experimental study, antibiotic susceptibility tests were prepared according to the National Committee for Clinical Laboratory Standards macrobroth dilution method. Müller-Hinton broth was the test medium. Standard P. aeruginosa (ATCC 27853), S. epidermidis (ATCC 12228) and S. aureus (ATCC 29213) strains were studied. For P. aeruginosa ceftazidime, ofloxacin and tobramycin dilutions, and for S. epidermidis and S. aureus, cefazolin, ofloxacin and tobramycin dilutions were prepared identically in two sets of tubes. One set of tubes, into which pure SF(6) was injected, was defined as the SF(6) group. The other set of tubes, into which no SF(6) was injected, was taken as the control group. To determine the minimal bactericidal concentrations of the antibiotics, subcultures were made onto Müller-Hinton agar, and the colonies were counted after 18 h of incubation at 37 degrees C.

RESULTS

The minimal inhibitory concentrations of the antibiotics in the SF(6) group were found to be identical with those of the control group. However, the minimal bactericidal concentrations of the antibiotics were found to be at least two dilutions lower in the SF(6) group than in the control group, except for the minimal bactericidal concentration of cefazolin for S. aureus, which was found to be one dilution lower in the SF(6) group.

CONCLUSION

SF(6) was found to potentiate the in vitro antibacterial activity of ofloxacin and tobramycin against S. aureus, S. epidermidis and P. aeruginosa, ceftazidime against P. aeruginosa, and cefazolin against S. epidermidis. Experimental animal studies are required to determine the role of SF(6) in the management of endophthalmitis.

Gene expression in Pseudomonas aeruginosa biofilms

Bacteria often adopt a sessile biofilm lifestyle that is resistant to antimicrobial treatment. Opportunistic pathogenic bacteria like Pseudomonas aeruginosa can develop persistent infections. To gain insights into the differences between free-living P. aeruginosa cells and those in biofilms, and into the mechanisms underlying the resistance of biofilms to antibiotics, we used DNA microarrays. Here we show that, despite the striking differences in lifestyles, only about 1% of genes showed differential expression in the two growth modes; about 0.5% of genes were activated and about 0.5% were repressed in biofilms. Some of the regulated genes are known to affect antibiotic sensitivity of free-living P. aeruginosa. Exposure of biofilms to high levels of the antibiotic tobramycin caused differential expression of 20 genes. We propose that this response is critical for the development of biofilm resistance to tobramycin. Our results show that gene expression in biofilm cells is similar to that in free-living cells but there are a small number of significant differences. Our identification of biofilm-regulated genes points to mechanisms of biofilm resistance to antibiotics.

Effects of antibiotics on morphologic characteristics and migration of canine corneal epithelial cells in tissue culture

OBJECTIVE

To determine effects of commonly used ophthalmic antibiotics on cellular morphologic characteristics and migration of canine corneal epithelium in cell culture.

SAMPLE POPULATION

Corneal epithelial cells harvested from corneas of 12 euthanatized dogs and propagated in cell culture.

PROCEDURE

Cells were treated with various antibiotics after a defect was created in the monolayer. Cellular morphologic characteristics and closure of the defect were compared between antibiotic-treated and control cells.

RESULTS

Cells treated with ciprofloxacin and cefazolin had the greatest degree of rounding, shrinkage, and detachment from plates. Cells treated with neomycin-polymyxin B-gramicidin and gentamicin sulfate had rounding and shrinkage but with less detachment. Cells treated with tobramycin and chloramphenicol grew similarly to control cells. On the basis of comparisons of defect circumference between control cells and cells exposed to antibiotics, tobramycin affected cellular migration the least.

CONCLUSIONS AND CLINICAL RELEVANCE

Effects of ciprofloxacin and cefazolin on morphologic characteristics of canine corneal epithelial cells in vitro should be taken into consideration before using these antibiotics for first-line of treatment for noninfected ulcers. Of the antibiotics tested that have a primarily gram-negative spectrum of coverage, gentamicin inhibited corneal epithelial cell migration and had greater cytopathologic effects than tobramycin did. For antibiotics with a gram-positive coverage, chloramphenicol had no cytopathologic effects on cells in comparison to cefazolin, which caused most of the cells to shrink and detach from the plate. Polymyxin B-neomycin-gramicidin was midrange in its effects on cellular morphologic characteristics and migration.

Aminoglycoside binding to human and bacterial A-Site rRNA decoding region constructs

The 16S bacterial ribosomal A-site decoding rRNA region is thought to be the pharmacological target for the aminoglycoside antibiotics. The clinical utility of aminoglycosides could possibly depend on the preferential binding of these drugs to the prokaryotic A-site versus the corresponding A-site from eukaryotes. However, quantitative aminoglycoside binding experiments reported here on prokaryotic and eukaryotic A-site RNA constructs show that there is little in the way of differential binding affinities of aminoglycosides for the two targets. The largest difference in affinity is 4-fold in the case of neomycin, with the prokaryotic A-site construct exhibiting the higher binding affinity. Mutational studies revealed that decoding region constructs retaining elements of non-Watson-Crick (WC) base pairing, specifically bound aminoglycosides with affinities in the muM range. These studies are consistent with the idea that aminoglycoside antibiotics can specifically bind to RNA molecules as long as the latter have non-A form structural elements allowing access of aminoglycosides to the narrow major groove.

Alginate overproduction affects Pseudomonas aeruginosa biofilm structure and function

During the course of chronic cystic fibrosis (CF) infections, Pseudomonas aeruginosa undergoes a conversion to a mucoid phenotype, which is characterized by overproduction of the exopolysaccharide alginate. Chronic P. aeruginosa infections involve surface-attached, highly antibiotic-resistant communities of microorganisms organized in biofilms. Although biofilm formation and the conversion to mucoidy are both important aspects of CF pathogenesis, the relationship between them is at the present unclear. In this study, we report that the overproduction of alginate affects biofilm development on an abiotic surface. Biofilms formed by an alginate-overproducing strain exhibit a highly structured architecture and are significantly more resistant to the antibiotic tobramycin than a biofilm formed by an isogenic nonmucoid strain. These results suggest that an important consequence of the conversion to mucoidy is an altered biofilm architecture that shows increasing resistance to antimicrobial treatments.

A simple infection model using pre-colonized implants to reproduce rat chronic Staphylococcus aureus osteomyelitis and study antibiotic treatment

Staphylococcus aureus biofilms formed on medical implants represent a serious problem, being difficult to eradicate with antibiotic therapy and leading to chronic infections. Simplified in vivo and in vitro antibiotic susceptibility assays using biofilm bacteria are needed. In this work, a novel chronic osteomyelitis infection model was developed in rats in the absence of bacterial suspension, requiring the use of only 10(6) bacteria in biofilms at the site of surgery, with a full success in reproducing infection. Stainless-steel implants pre-colonized for 12 h with a highly adherent S. aureaus isolate were introduced into the rat tibiae. In animals not submitted to antibiotic treatment, infection was found in the implants and spread to bone in all cases, indicating the high efficacy of the model to reproduce osteomyelitis. The effect of a 21-day treatment with cefuroxime, vancomycin, tobramycin or ciprofloxacin on infection was studied in this model 42 days after surgery. Bone colonization was inhibited by vancomycin and cefuroxime. Cefuroxime (the most efficient antibiotic, able to sterilize 1 out of 8 implants) reduced the number of bacteria in biofilms adhered to implants at a higher extent than vancomycin, trobramycin and ciprofloxacin. Analogous observations were made in this work in vivo and in vitro on the relative antibiotic efficacy against S. aureus biofilm bacteria. suggesting the usefulness of both tests as a potential tool to study antibiotic suceptibility, and the need for new antimicrobials against these bacteria.

Pharmacokinetics and pharmacodynamics of aztreonam and tobramycin in hospitalized patients

BACKGROUND

Pharmacokinetic/pharmacodynamic (PK/PD) optimization of antibiotic therapy has been shown to improve outcomes in several antibiotic classes. Despite the frequent use of beta-lactams, clinical data in humans remain limited.

OBJECTIVE

This study evaluated the relationship between serum pharmacokinetics, pharmacodynamics, pathogen susceptibility, and clinical outcomes in patients receiving aztreonam or tobramycin monotherapy.

METHODS

The case-report forms of hospitalized patients who received either aztreonam or tobramycin for a bacterial infection in 3 clinical trials conducted between 1982 and 1984 were reviewed for the present study. A pathogen was identified for all included patients, and susceptibility testing was performed to determine the minimum inhibitory concentration (MIC) for each agent. Pharmacokinetic parameters for each antibiotic were determined using population modeling, and variables potentially related to outcomes were evaluated using tree-based modeling, logistic regression, and nonlinear regression methods.

RESULTS

Data from 91 patients were analyzed, 68 treated with aztreonam monotherapy and 23 treated with tobramycin monotherapy. Of the types of infections treated, 39 were intra-abdominal, 42 involved the lower respiratory tract, and 10 involved the skin and skin structures. The pharmacodynamic ratio of the 24-hour area under the curve (AUC24) to the MIC was associated with clinical outcome for both antibiotics: aztreonam and to-bramycin patients with ratios meeting or exceeding the respective 24-hour inverse serum inhibitory titer breakpoints of 184 and 110 were significantly more likely to achieve a successful outcome than were those with ratios not meeting these values (P < 0.01). The probabilities of clinical success in patients at or above and below the AUC24/MIC breakpoints were a respective 85% and 53% for aztreonam and 80% and 47% for tobramycin (both, P < 0.01). When all patients were considered, the likelihood of achieving cure was 5.1 times greater in patients exceeding the target ratios (P < 0.01).

CONCLUSION

PK/PD optimization of both aztreonam and tobramycin is associated with improved patient outcomes.