Inhibition of Pseudomonas aeruginosa exoenzyme expression by subinhibitory antibiotic concentrations

Sub-Inhibitory Antibiotic Exposure and Virulence in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a prime opportunistic pathogen, one of the most important causes of hospital-acquired infections and the major cause of morbidity and mortality in cystic fibrosis lung infections. One reason for the bacterium's pathogenic success is the large array of virulence factors that it can employ. Another is its high degree of intrinsic and acquired resistance to antibiotics. In this review, we first summarise the current knowledge about the regulation of virulence factor expression and production. We then look at the impact of sub-MIC antibiotic exposure and find that the virulence-antibiotic interaction for P. aeruginosa is antibiotic-specific, multifaceted, and complex. Most studies undertaken to date have been in vitro assays in batch culture systems, involving short-term (<24 h) antibiotic exposure. Therefore, we discuss the importance of long-term, in vivo-mimicking models for future work, particularly highlighting the need to account for bacterial physiology, which by extension governs both virulence factor expression and antibiotic tolerance/resistance.

In vitro bactericidal activity of promising nutraceuticals for targeting multidrug resistant Pseudomonas aeruginosa

OBJECTIVE

We evaluated the bactericidal activity of nutraceuticals against multidrug resistant Pseudomonas aeruginosa. The nutritionally valued herbs were screened on the basis of a matrix modeling approach and molecular docking based validation analysis.

METHODS

The database of 38 herbs developed earlier using fuzzy logic based scoring analysis was subjected to molecular docking based validation. The molecular docking (Hex 6.12) analyses of predominant phytoligands (∼10 per herb) against exoenzyme S of P. aeruginosa filtered potent herbs were selected. The preauthenticated bacterial inoculum (10(8) CFU/mL) was added to the sterile nutrient broth impregnated with standardized aqueous-alcoholic herbal extracts (1-1600 μg/mL). After overnight incubation at 37°C, antibacterial activity was evaluated in terms of minimum inhibitory and minimum bactericidal concentrations.

RESULTS

Five herbs were selected on the basis of fuzzy set scoring, an herbal informatics model, and validation analysis based on energy of docking (i.e., Evalue of 380) phytoligands with maximum scoring obtained by Glycyrrhiza glabra. Among the 5 nutraceuticals, G. glabra showed maximum bactericidal activity significantly (P < 0.05) higher than Amikacin, a standard antibiotic, which was in consonance with in silico bioprospection. Zingiber officinale, despite a low Evalue, showed considerably higher inhibition attributed to its higher flavonoid content as compared to other herbs.

CONCLUSION

G. glabra (licorice), a flavoring agent; Z. officinale (ginger), a condiment; and Mentha piperita (mint), a fragrance component, showed significant therapeutic potential against multidrug resistant strains of P. aeruginosa.

Bacterial Responses and Genome Instability Induced by Subinhibitory Concentrations of Antibiotics

Nowadays, the emergence and spread of antibiotic resistance have become an utmost medical and economical problem. It has also become evident that subinhibitory concentrations of antibiotics, which pollute all kind of terrestrial and aquatic environments, have a non-negligible effect on the evolution of antibiotic resistance in bacterial populations. Subinhibitory concentrations of antibiotics have a strong effect on mutation rates, horizontal gene transfer and biofilm formation, which may all contribute to the emergence and spread of antibiotic resistance. Therefore, the molecular mechanisms and the evolutionary pressures shaping the bacterial responses to subinhibitory concentrations of antibiotics merit to be extensively studied. Such knowledge is valuable for the development of strategies to increase the efficacy of antibiotic treatments and to extend the lifetime of antibiotics used in therapy by slowing down the emergence of antibiotic resistance.

The cystic fibrosis airway microbiome

PURPOSE OF REVIEW

Culture and molecular approaches have established that lower airway infections are polymicrobial. We consider how this new perspective in cystic fibrosis (CF) may affect treatment choices.

RECENT FINDINGS

Standard clinical microbiology of CF infection exacerbations often fails to provide indications of microbial causes that may drive the onset of exacerbation and the anticipated bacteriologic responses to the usual parenteral antibiotics prescribed as treatment. Antimicrobial responses by nonclassical members of the CF airway microbiome may explain why most patients clinically improve. These other organisms contribute to disease either directly as pathogens missed by conventional microbiology or through synergy with conventional pathogens. With these considerations, therapy may best be guided by directed antibiotic therapy to numerically significant isolates. An example is the Streptococcus milleri group, which we now believe to represent new pathogens that profile the exacerbations of infection in the CF lung and that necessitate specific antibiotic therapy to prevent loss of lung function and reduce frequency of exacerbations.

SUMMARY

A comprehensive understanding of airway infections offers the potential for improved disease management in CF patients. Accurate quantitative microbiology will be a prerequisite for routine intervention based on the polymicrobial perspective of CF infection exacerbations.

Antibiotic Treatment of Multidrug-Resistant Organisms in Cystic Fibrosis

Respiratory tract infection with eventual respiratory failure is the major cause of morbidity and mortality in cystic fibrosis (CF). Infective exacerbations need to be treated promptly and effectively to minimize potentially accelerated attrition of lung function. The choice of antibiotic depends on in vitro sensitivity patterns. However, physicians treating patients with CF are increasingly faced with infection with multidrug-resistant isolates of Pseudomonas aeruginosa. In addition, innately resistant organisms such as Burkholderia cepacia complex, Stenotrophomonas maltophilia and Achromobacter (Alcaligenes) xylosoxidans are becoming more prevalent. Infection with methicillin-resistant Staphylococcus aureus (MRSA) is also a problem. These changing patterns probably result from greater patient longevity and increased antibiotic use for acute exacerbations and maintenance care. Multidrug-resistant P. aeruginosa infection may be treated successfully by using two antibiotics with different mechanisms of action. In practice antibiotic choices have usually been made on a best-guess basis, but recent research suggests that more directed therapy can be achieved through the application of multiple-combination bactericidal testing (MCBT). Aerosol delivery of tobramycin for inhalation solution achieves high endobronchial concentrations that may overcome bacterial resistance as defined by standard laboratory protocols. Resistance to colistin is rare and this antibiotic should be seen as a valuable second-line drug to be reserved for multidrug-resistant P. aeruginosa. The efficacy of new antibiotic groups such as the macrolides needs to be evaluated.CF units should adopt strict segregation policies to interrupt person-to-person spread of B. cepacia complex. Treatment of panresistant strains is difficult and often arbitrary. Combination antibiotic therapy is recommended, usually tobramycin and high-dose meropenem and/or ceftazidime, but the choice of treatment regimen should always be guided by the clinical response.The clinical significance of S. maltophilia, A. xylosoxidans and MRSA infection in CF lung disease remains uncertain. If patients show clinical decline and are chronically colonized/infected with either of the former two pathogens, treatment is recommended but efficacy data are lacking. There are defined microbiological reasons for attempting eradication of MRSA but there are no proven deleterious effects of this infection on lung function in patients with CF. Various treatment protocols exist but none has been subject to a randomized, controlled trial. Multidrug-resistant microorganisms are an important and growing issue in the care of patients with CF. Each patient infected with such strains should be assessed individually and antibiotic treatment planned according to in vitro sensitivity, patient drug tolerance, and results of in vitro studies which may direct the physician to antibiotic combinations most likely to succeed.

Creeping baselines and adaptive resistance to antibiotics

The introduction of antimicrobial drugs in medicine gave hope for a future in which all infectious diseases could be controlled. Decades later it appears certain this will not be the case, because antibiotic resistance is growing relentlessly. Bacteria possess an extraordinary ability to adapt to environmental challenges like antimicrobials by both genetic and phenotypic means, which contributes to their evolutionary success. It is becoming increasingly appreciated that adaptation is a major mechanism behind the acquisition and evolution of antibiotic resistance. Adaptive resistance is a specific class of non-mutational resistance that is characterized by its transient nature. It occurs in response to certain environmental conditions or due to epigenetic phenomena like persistence. We propose that this type of resistance could be the key to understanding the failure of some antibiotic therapy programs, although adaptive resistance mechanisms are still somewhat unexplored. Similarly, hard wiring of some of the changes involved in adaptive resistance might explain the phenomenon of "baseline creep" whereby the average minimal inhibitory concentration (MIC) of a given medically important bacterial species increases steadily but inexorably over time, making the likelihood of breakthrough resistance greater. This review summarizes the available information on adaptive resistance.

Influence of adjunct azithromycin on the mortality of experimental Pseudomonas aeruginosa sepsis

The aim of this study was to determine the in vivo influence of azithromycin subinhibitory concentrations on mortality in a peritonitis-sepsis model. One hour after an intraperitoneal injection of Pseudomonas aeruginosa, mice were randomized to receive: ceftazidime, 500 mg/kg SC q4hxtwo doses alone; azithromycin, 20 mg/kg SCxone dose alone; ceftazidime plus azithromycinxone dose; ceftazidime plus azithromycinxtwo doses (1 and 24 h); ceftazidime plus prophylactic azithromycin (three doses at -48, -24, 1 h); or no treatment (control). A significant decrease in the rate of mortality was observed in animals treated with all ceftazidime plus azithromycin groups when compared with those receiving ceftazidime alone. These data indicate a potential role for adjunctive azithromycin therapy in P. aeruginosa infection.

Reduced expression of virulence factors in multidrug-resistant Pseudomonas aeruginosa strains

MDR Pseudomonas aeruginosa strains are isolated from clinical specimens with increasing frequency. It seems that acquiring genes which determine antibiotic resistance usually comes at a biological cost of impaired bacterial physiology. There is no information on investigations comparing phenotypic differences in MDR and MDS P. aeruginosa strains in literature. The study included 150 clinical P. aeruginosa isolates (75 classified as MDS and 75 as MDR). PFGE analysis revealed five pairs of identical isolates in the group of MDR strains and the results obtained for these strains were not included in the statistical analyses. MDR strains adhered to polystyrene to a lesser extent than MDS strains. The growth rate in the liquid medium was significantly lower for MDR strains. Detectable amounts of alginate were present in the culture supernatants of seven MDS and six MDR strains. The MDR P. aeruginosa strains which were investigated produced significantly lower amounts of extracellular material binding Congo Red, lower lipolytic, elastase, LasA protease, phospholipase C activity and pyocyanin quantity in culture supernatants when compared with MDS strains. No significant differences were observed between MDR and MDS strains in proteolytic activity. In conclusion, the MDR P. aeruginosa strains have impaired virulence when compared to MDS strains.

Sub-inhibitory concentrations of ceftazidime and tobramycin reduce the quorum sensing signals of Pseudomonas aeruginosa

AIM

Concentrations of antimicrobials below minimum inhibitory concentration (subMIC) may reduce the production by Pseudomonas aeruginosa of virulence factors such as elastase. We sought to determine whether the reduction in elastase production may be mediated by a reduction in acyl-homoserine lactones.

METHODS

Pseudomonas aeruginosa in broth was exposed to three conditions for ceftazidime and tobramycin: control, 6% MIC and 25% MIC. Elastase was assayed using elastin congo red. N-(3-Oxododecanoyl)-homoserine lactone (C12-HSL) and N-butyryl-homoserine lactone (C4-HSL) were assayed using biosensor Escherichia coli.

RESULTS

Elastase was unchanged with ceftazidime. Elastase was reduced by 16% at 6% MIC tobramycin and reduced by 70% at 25% MIC tobramycin (P<0.0001). As a percentage of control, C12-HSL was mean 69.4% (SEM 7.3%) at 6% MIC tobramycin, and 31.7% (3.3%) at 25% MIC tobramycin (P=0.0001). C12-HSL was 78.9% (5.3%) at 6% MIC ceftazidime and was 29.7% (1.8%) at 25% MIC ceftazidime (P=0.0001). Both ceftazidime and tobramycin were associated with reduced C4-HSL at 6% MIC and 25% MIC (P<0.03).

CONCLUSIONS

SubMIC tobramycin but not ceftazidime reduced elastase production by P. aeruginosa. In contrast, subMIC concentrations of both antimicrobials reduced C12-HSL and C4-HSL. It is unlikely that reduced HSL is the sole explanation for the reduction in elastase.

Cytokine modulating effect of ginseng treatment in a mouse model of Pseudomonas aeruginosa lung infection

The major cause of morbidity and mortality in cystic fibrosis (CF) patients is chronic Pseudomonas aeruginosa lung infection. In a mouse model of P. aeruginosa lung infection mimicking that in CF patients, the effects of ginseng treatment on cytokine responses and the correlation between the changes in cytokine production and the lung pathology were studied. Mice were challenged with alginate beads containing P. aeruginosa (10(9) CFU/ml). A saline extract of ginseng was injected subcutaneously at a dosage of 250 mg/kg of body weight/day for 7 days. Saline was used as a placebo control. One week after challenge, a significantly lower mortality was found in the ginseng treated group (P < 0.005). The lung cells from the ginseng treated group produced more interferon-gamma (IFN-gamma) (P < 0.04) and tumor necrosis factor-alpha (TNF-alpha) (P < 0.03) but less interleukin-4 (IL-4) (P < 0 .02) with a higher ratio of IFN-gamma/IL-4 (P < 0.004) after 6 and/or 24 h of incubation with specific and non-specific antigens as compared to the control group. The ginseng treated splenocytes produced more TNF-alpha (P < 0.03) and IFN-gamma (P0.05) than the control spleen cells. Furthermore, a significantly milder lung pathology (P < 0.025) and a faster bacterial clearance (P < 0.038) from the lungs were also found in the ginseng treated group compared to the control group. These results indicate a Th1-like immune response in the mice with P. aeruginosa lung infection after 7 days of ginseng treatment, which is an important mechanism accounting for ginseng's favorable action. We therefore believe that Th1 response might benefit the host with P. aeruginosa lung infection and ginseng treatment might be a promising alternative measure for the treatment of chronic P. aeruginosa lung infection in CF patients.

Antimicrobial susceptibility and synergistic activity of meropenem against Gram-negative non-fermentative bacteria isolated from cystic fibrosis patients

The objective of the present study was to evaluate the activity of meropenem (a beta-lactam carbapenem with good bactericidal potency and a very wide spectrum of activity) and of ticarcillin, ceftazidime ciprofloxacin, tobramycin, cefepime, which are the most commonly used antimicrobial agents for treatment of pulmonary infections associated with CF. The effect of these antibiotics was tested on 27 multiresistant strains isolated from 24 CF patients during 2000 and 2001. Furthermore, the in vitro synergistic effect of meropenem in association with the other antibiotics was evaluated. Ciprofloxacin, ticarcillin, meropenem and ceftazidime had the most activity and inhibited 66%, 37%, 36% and 33% of strains respectively. The addition of a second antibiotic to meropenem resulted in a synergistic effect on 5 (18.5%) isolates; on average 2.8 synergistic combinations where determined per strain. Of these 27 isolates, antagonism was observed in 3 (11%) strains (1 antagonistic combination per strain). Our study suggests that selecting effective double antibiotic therapy cannot be made empirically for CF patients infected with Gram-negative multiresistant bacilli. Therefore in vitro methods for testing double antibiotic combinations are mandatory.

Some properties of Plesiomonas shigelloides treated with aminoglycosides

The effect of aminoglycoside antibiotics (amikacin, gentamicin, netilmicin and tobramycin) at sublethal concentrations (sub-MICs) on some properties of Plesiomonas shigelloides strains was evaluated. All agents decreased the bacterial surface hydrophobicity. Amikacin (1/4 of the MIC) and netilmicin (1/4 and 1/8 of the MIC) changed the hydrophobic character of P. shigelloides surface to a hydrophilic one. Treatment of the strains with aminoglycosides decreased also motility, netilmicin being the most effective. No significant changes were found in lipolytic activity of antibiotic-treated strains. In the majority of cases aminoglycosides increased sensitivity of bacteria to hydrogen peroxide. The tested antibiotics did not induce production of short-chained N-acylhomoserine lactones signal molecules. Aminoglycosides at sub-MICs affected important activities of P. shigelloides potentially associated with their virulence in dependence on strain, antibiotic and concentration.

Potential virulence-associated properties of Plesiomonas shigelloides strains

Serotyping and some potential virulence-associated markers were investigated in Plesiomonas shigelloides strains isolated from humans, animals and aquatic environments. Surface properties of these strains were evaluated using Congo red binding, salt-aggregation test, bacterial adherence to xylene and motility. Production of pancreatic elastase, proteinase (consistent with subtilisin Carlsberg), triacylglycerol lipase, histidine decarboxylase and beta-hemolysin was also determined. In addition, detection of signal molecules such as C4-C8 unsubstituted N-acylhomoserine lactones (AHLs) was performed. The serological typing of the P. shigelloides strains showed that the isolates belonged to 13 different serovars. The majority of the strains were hydrophobic and motile. The strains produced low levels of elastase, proteinase and histidine decarboxylase whereas triacylglycerol lipase activity was relatively high. Only 23.3 % of the strains produced hemolysin. The AHLs signal molecules were not detected. P. shigelloides strains were able to produce a variety of potential virulence markers which may be involved in the pathogenesis of Plesiomonas-associated infections.

New medical management techniques for acute exacerbations of chronic rhinosinusitis

In the past 2 years, intranasal nebulized medications have emerged as a widely prescribed treatment for medical management of chronic rhinosinusitis. This represents an innovative and advanced approach to treating acute exacerbations of chronic rhinosinusitis topically. The use of specially formulated medication compounds delivered by unique nebulization equipment is reviewed in the treatment of patients with chronic sinus disease. Scientific data including related upper and lower respiratory literature is included, as well as the important aspects of factors affecting nebulized medication delivery to the sinuses. The benefits, effectiveness, risks, and adverse effects of intranasal nebulized medications are also addressed. A treatment algorithm identifying appropriate use of nebulized medications in the treatment plan for chronic sinusitis patients is then presented in diagrammatic format.

Bactéries pathogènes dans la mucoviscidose

Since the CF gene identification in 1989 and despite the improvement of our knowledge in the physiopathology of the disease, bronchopulmonary infection determines the vital prognosis. Following Staphylococcus aureus infection, patients are colonized or colonized by Pseudomonas aeruginosa, greatly involved in the pulmonary deterioration. Other bacteria may be involved Burkholderia cepacia, Stenotrophomonas maltophilia, Alcaligenes sp. Intensive antibiotic treatment of primocolonisation helps to prevent or delay chronic colonisation. Chronic colonization needs a rational long term antibiotic strategy to prevent the occurrence of multiresistant germs; antibiotic cures are performed every 3 or 4 months before pulmonary exacerbation symptoms.

Regulation of antibiotic production in root-colonizing Peudomonas spp. and relevance for biological control of plant disease

Certain strains of fluorescent pseudomonads are important biological components of agricultural soils that are suppressive to diseases caused by pathogenic fungi on crop plants. The biocontrol abilities of such strains depend essentially on aggressive root colonization, induction of systemic resistance in the plant, and the production of diffusible or volatile antifungal antibiotics. Evidence that these compounds are produced in situ is based on their chemical extraction from the rhizosphere and on the expression of antibiotic biosynthetic genes in the producer strains colonizing plant roots. Well-characterized antibiotics with biocontrol properties include phenazines, 2,4-diacetylphloroglucinol, pyoluteorin, pyrrolnitrin, lipopeptides, and hydrogen cyanide. In vitro, optimal production of these compounds occurs at high cell densities and during conditions of restricted growth, involving (i) a number of transcriptional regulators, which are mostly pathway-specific, and (ii) the GacS/GacA two-component system, which globally exerts a positive effect on the production of extracellular metabolites at a posttranscriptional level. Small untranslated RNAs have important roles in the GacS/GacA signal transduction pathway. One challenge in future biocontrol research involves development of new strategies to overcome the broad toxicity and lack of antifungal specificity displayed by most biocontrol antibiotics studied so far.

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.

Toxinogenicity and markers of pathogenicity of Pseudomonas aeruginosa strains isolated from patients with tumor diseases

Potential virulence factors (elastase, proteinase, lipase, phospholipase C, alginate) as well as surface properties (hydrophobicity, motility) were determined in 103 Pseudomonas aeruginosa strains isolated from patients with cancer. Nontypable strains were the dominant group (60%), followed by serotypes O11 (17%), O12 (7%) and O4 (5%). Seventy-one strains (69%) produced high level of elastase (10-60 mg/L), 87% of the strains possessed high activity of proteinase (bacterial) (10-250 mg/L) and 69% of the strains demonstrated higher level of lipase (20-150 U/mL); these elevated levels of enzymes were associated mainly with nontypable strains. On the other hand, 79% of the strains did not produce or produced only a low level of phospholipase C and 60% of isolates did not manifest any or very low production of alginate. Hydrophobicity demonstrated by adherence of the bacteria to xylene was shown by 69% of strains; 94% of strains aggregated with ammonium sulfate. Motility in the range of 31-80 mm was found in 76 strains (74%). The considerable virulence of tested P. aeruginosa strains was confirmed. The nontypable strains manifested the most frequent group with high level of elastase, proteinase, lipase, hydrophobicity and motility.

Antibodies against beta-lactamase can improve ceftazidime treatment of lung infection with beta-lactam-resistant Pseudomonas aeruginosa in a rat model of chronic lung infection

To test the hypothesis that antibodies against the chromosomal beta-lactamase of Pseudomonas aeruginosa (a beta ab) might act as beta-lactamase inhibitors in patients with cystic fibrosis and chronic lung infection with P. aeruginosa, we compared in a rat model of chronic lung infection the efficacy of treatment with ceftazidime in beta-lactamase-immunized (group I) and non-immunized (group II) rats. Chronic lung infection was established with alginate-embedded P. aeruginosa producing high amounts of beta-lactamase in 133 Lewis rats. Prior to infection, group I (66 rats) was immunized three times at 2-week intervals with purified beta-lactamase in incomplete Freund's adjuvant (IFA) and group II (67 rats) received IFA. Ceftazidime treatment was initiated after challenge and continued for 10 days, after which the rats were sacrificed and the lung bacteriology and pathology were analysed. Rat serum was analysed for the beta-lactamase inhibitory activity and a beta ab-specific IgG and IgG subclasses titres. Beta-lactamase inhibitory activity was found only in sera of rats belonging to group I and it was used to divide these rats into two subgroups: rats whose sera inhibited > or = 75% of beta-lactamase activity (responders) and rats whose sera inhibited < or = 25% of beta-lactamase activity (non-responders). The responder subgroup had significantly smaller pathological areas in the lungs and lower cfu/ml lung homogenate compared to the non-immunized group (p=0.02 and p=0.01, respectively) and compared to the non-responder subgroup (p=0.008 and p=0.0001, respectively). On the day of challenge, significantly higher titres of a beta ab-specific IgG and IgG subclasses antibodies were found in the responders compared to the non-responders (p<0.0001). In the responder subgroup the avidity of IgG a beta ab was significantly higher than in the non-responder subgroup (p=0.0003). Our study showed that a beta ab with beta-lactamase inhibitory activity raised by immunization with beta-lactamase can improve the outcome of treatment with ceftazidime of resistant P. aeruginosa in a rat model of chronic lung infection.

Gerimax ginseng regulates both humoral and cellular immunity during chronic Pseudomonas aeruginosa lung infection

BACKGROUND

Chronic lung infection among patients with cystic fibrosis (CF), diffused panbronchiolitis, and chronic obstructive bronchiecteisis is often because of Pseudomonas aeruginosa. High morbidity and mortality in patients with CF are because of P. aeuruginosa that undergoes genotypic and phenotypic changes during prolonged stay in the lung resulting in increased antibiotic resistance, necessitating a search for alternative or supplement drugs.

OBJECTIVE

In this study we compared the therapeutical effect of Gerimax (Dansk Droge A/S, Ishøj, Denmark) ginseng with placebo control by using a rat model of chronic P. aeruginosa lung infection mimicking that in patients with CF.

METHODS AND INTERVENTIONS

The animals were challenged intratracheally with the prototypic P. aeruginosa PAO1 in alginate beads (1 x 10(9) colony-forming units per milliliter [CFU/mL]) followed by subcutaneous injection of ginseng extract (150 mg/kg body weight once per day) and examined on days 7 and 21.

RESULTS

The day 7 analyses show that ginseng treatment resulted in lowering serum immunoglobulin M (IgM) and lung interleukin-4 (IL-4) levels compared to the control group. On day 21, higher lung IgA, upregulated serum IgG2a, stronger lung responses of interferon-gamma, IL-4, and tumor necrosis factor-alpha with milder lung pathology and enhanced lung bacteriology were detected in the ginseng-treated group when compared to those of the control group.

CONCLUSION

These results suggest that the Gerimax ginseng treatment can modulate the immune system in favor of clearing the infection with P. aeruginosa in the lungs of rats. Thus, ginseng might be a promising alternative supplement for the treatment of chronic P. aeruginosa lung infection in patients with CF.

Lower concentrations of clarithromycin suppress urease activity, motility, and binding to gastric epithelial cells in Helicobacter pylori isolates

BACKGROUND

Our previous study showed that histological scores of gastric mucosal inflammation and Helicobacter pylori density decreased even in patients who failed to eradicate Helicobacter pylori after antimicrobial therapy including clarithromycin. This may reflect indirect suppressive effects of lower concentrations of clarithromycin on Helicobacter pylori, as suggested in other Gram-negative rod infections.

AIMS

To investigate whether clarithromycin suppresses virulence factors of Helicobacter pylori at sub-minimal inhibitory concentration.

METHODS

Six clarithromycin-susceptible Helicobacter pylori isolates and 7 clarithromycin-resistant isolates were obtained from patients with peptic ulcer disease. These isolates were analysed for urease activity, motility, and ability to bind to gastric epithelial cells after they were incubated with or without clarithromycin at sub-minimal inhibitory concentrations.

RESULTS

Incubation of Helicobacter pylori isolates with clarithromycin at sub-minimal inhibitory concentrations reduced urease activity motility, and binding to gastric epithelial cells in a dose-dependent manner. These findings were observed both in clarithromycin-susceptible and resistant strains.

CONCLUSIONS

Suppressive effects of clerithromycin on virulence factors of Helicobacter pylori at sub-minimal inhibitory concentrations may be associated with observed attenuation of gastric inflammation and Helicobacter pylori density in patients who failed in bacterial eradication after triple therapy including clarithromycin.

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.

Pseudomonas aeruginosa and the in vitro and in vivo biofilm mode of growth

The biofilm mode of growth is the survival strategy of environmental bacteria like Pseudomonas aeruginosa. Such P. aeruginosa biofilms also occur in the lungs of chronically infected cystic fibrosis patients, where they protect the bacteria against antibiotics and the immune response. The lung tissue damage is due to immune complex mediated chronic inflammation dominated by polymorphonuclear leukocytes releasing proteases and oxygen radicals.

Effect of subinhibitory concentrations of macrolides on expression of flagellin in Pseudomonas aeruginosa and Proteus mirabilis

In the present study we showed by molecular analysis that the inhibition of motility by macrolides in Proteus mirabilis and Pseudomonas aeruginosa was well correlated with the loss of the expression of flagellin. Erythromycin, clarithromycin, and azithromycin at subinhibitory concentrations (sub-MICs) suppressed the expression of flagellin dose dependently. Azithromycin had the strongest inhibitory effect on the expression of P. aeruginosa flagellin, whereas 16-membered rokitamycin had only a weak inhibitory effect. These results indicate the potential effectiveness of sub-MICs of erythromycin, clarithromycin, and azithromycin for the treatment of patients with P. mirabilis and P. aeruginosa infections.

Multiple combination bactericidal antibiotic testing for patients with cystic fibrosis infected with Burkholderia cepacia

Most Burkholderia cepacia strains are resistant to many, or all, of the antibacterial agents commonly used in cystic fibrosis (CF), and selection of appropriate antibiotics for treatment of pulmonary exacerbations is therefore difficult. We developed a technique for rapid in vitro testing of multiple antibiotic combinations for B. cepacia isolates. For each of 119 multi-drug-resistant isolates of B. cepacia, our multiple combination bactericidal test (MCBT) studied the bactericidal activity of 10 to 15 antimicrobial agents using 225 +/- 97 single, double, and triple antibiotic combinations. Of the 119 isolates, 50% were resistant to all single antibiotics tested, 8% were resistant to all two-drug antibiotic combinations, but all were inhibited by at least one bactericidal triple-drug combination. When used alone, meropenem, ceftazidime and high-dose tobramycin (200 microg/ml) were bactericidal against only 47, 15, and 14% of in vitro isolates, respectively. Using a double antibiotic combination improved bactericidal activity; meropenem-minocycline, meropenem-amikacin, and meropenem-ceftazidime combinations were bactericidal against 76, 73, and 73% of isolates, respectively. However, 47% of isolates demonstrated antagonism (growth of an organism when a second antibiotic was added to a bactericidal single antibiotic). Triple antibiotic combinations that contained tobramycin, meropenem, and an additional antibiotic were most effective, and were bactericidal against 81 to 93% of isolates. We conclude that triple-antibiotic combinations are more likely than double and single antibiotic combinations to be bactericidal against B. cepacia in vitro. MCBT testing is a useful technique to help clinicians decide on appropriate nonantagonistic combination antibiotic therapy for patients with CF infected with B. cepacia.

Alterations in surface hydrophobicity of Acinetobacter baumannii induced by meropenem

Six strains of Acinetobacter baumannii out of eleven strains tested revealed a strong hydrophobic character. This was demonstrated by adherence of bacteria to xylene in the range of 90-94%. Changes in surface hydrophobicity of these strains were studied after treatment with meropenem at subinhibitory concentrations (sub-MICs) (1/4, 1/8, 1/16 or 1/32 of the MICs). All strains showed a reduced adherence to xylene after the action of meropenem at 1/4 or 1/16 of the MICs. Hydrophobicity of the treated bacteria was decreased to 1.3-70% (1/16 of the MICs) or to 12-86% (1/4 of the MICs), depending on the strain. A decrease in surface hydrophobicity of three strains was also observed after their exposure to meropenem at 1/8 of the MICs (to 18-71% of the control values). Meropenem at 1/32 of the MICs practically did not affect bacterial hydrophobic properties, with the exception of one strain.

The in vitro effect of imipenem and ofloxacin on enzymic activity of Klebsiella strains

Fifty seven Klebsiella strains, viz. K. pneumoniae (28), K. planticola (19), K. oxytoca (6), K. ornithinolytica (3) and K. terrigena (1) possessed lipolytic and urealytic activity. The effect of imipenem and ofloxacin at subinhibitory concentrations (sub-MICs) on these enzymic activities of 4 strains was studied. At all the concentrations tested (mainly at 1/4 of the MICs) imipenem enhanced lipase activity manifested by cleavage of the substrate Tween 20. The effect of ofloxacin was strain- and concentration-dependent but in most cases lipolytic activity was also increased. The antibiotics practically did not affect the urease activity of the strains.

Beneficial effect of adjunctive azithromycin in treatment of mucoid Pseudomonas aeruginosa pneumonia in the murine model

While a time-kill methodology noted no appreciable improvement in bactericidal activity with the addition of azithromycin (AZM) to a ceftazidime (CAZ) regimen, data from the murine pneumonia model showed that the addition of AZM significantly improved survival compared to treatment with CAZ alone. These data suggest that AZM might be a useful adjunctive therapy in the management of pneumonia resulting from mucoid isolates of Pseudomonas aeruginosa.

Quinolone signaling in the cell-to-cell communication system of Pseudomonas aeruginosa

Numerous species of bacteria use an elegant regulatory mechanism known as quorum sensing to control the expression of specific genes in a cell-density dependent manner. In Gram-negative bacteria, quorum sensing systems function through a cell-to-cell signal molecule (autoinducer) that consists of a homoserine lactone with a fatty acid side chain. Such is the case in the opportunistic human pathogen Pseudomonas aeruginosa, which contains two quorum sensing systems (las and rhl) that operate via the autoinducers, N-(3-oxododecanoyl)-L-homoserine lactone and N-butyryl-L-homoserine lactone. The study of these signal molecules has shown that they bind to and activate transcriptional activator proteins that specifically induce numerous P. aeruginosa virulence genes. We report here that P. aeruginosa produces another signal molecule, 2-heptyl-3-hydroxy-4-quinolone, which has been designated as the Pseudomonas quinolone signal. It was found that this unique cell-to-cell signal controlled the expression of lasB, which encodes for the major virulence factor, LasB elastase. We also show that the synthesis and bioactivity of Pseudomonas quinolone signal were mediated by the P. aeruginosa las and rhl quorum sensing systems, respectively. The demonstration that 2-heptyl-3-hydroxy-4-quinolone can function as an intercellular signal sheds light on the role of secondary metabolites and shows that P. aeruginosa cell-to-cell signaling is not restricted to acyl-homoserine lactones.

Quinolone signaling in the cell-to-cell communication system of Pseudomonas aeruginosa

Numerous species of bacteria use an elegant regulatory mechanism known as quorum sensing to control the expression of specific genes in a cell-density dependent manner. In Gram-negative bacteria, quorum sensing systems function through a cell-to-cell signal molecule (autoinducer) that consists of a homoserine lactone with a fatty acid side chain. Such is the case in the opportunistic human pathogen Pseudomonas aeruginosa, which contains two quorum sensing systems (las and rhl) that operate via the autoinducers, N-(3-oxododecanoyl)-L-homoserine lactone and N-butyryl-L-homoserine lactone. The study of these signal molecules has shown that they bind to and activate transcriptional activator proteins that specifically induce numerous P. aeruginosa virulence genes. We report here that P. aeruginosa produces another signal molecule, 2-heptyl-3-hydroxy-4-quinolone, which has been designated as the Pseudomonas quinolone signal. It was found that this unique cell-to-cell signal controlled the expression of lasB, which encodes for the major virulence factor, LasB elastase. We also show that the synthesis and bioactivity of Pseudomonas quinolone signal were mediated by the P. aeruginosa las and rhl quorum sensing systems, respectively. The demonstration that 2-heptyl-3-hydroxy-4-quinolone can function as an intercellular signal sheds light on the role of secondary metabolites and shows that P. aeruginosa cell-to-cell signaling is not restricted to acyl-homoserine lactones.

Effects of ginseng treatment on neutrophil chemiluminescence and immunoglobulin G subclasses in a rat model of chronic Pseudomonas aeruginosa pneumonia

Chronic Pseudomonas aeruginosa lung infection in cystic fibrosis (CF) patients is almost impossible to eradicate with antibiotic treatment. In the present study, the effects of treatment with the Chinese herbal medicine ginseng on blood polymorphonuclear leukocyte (PMN) chemiluminescence and serum specific antibody responses were studied in a rat model of chronic P. aeruginosa pneumonia mimicking CF. An aqueous extract of ginseng was administered by subcutaneous injection at a dosage of 25 mg/kg of body weight/day for 2 weeks. Saline was used as a control. Two weeks after the start of ginseng treatment, significantly increased PMN chemiluminescence (P Collapse

Key Words Collapse

MESH Headings

• Animals
• Antibodies, Bacterial/blood
• Bronchoalveolar Lavage Fluid/cytology
• Cystic Fibrosis/complications
• Disease Models, Animal
• Female
• Immunoglobulin G/blood
• Luminescent Measurements
• Lung/pathology
• Macrophages, Alveolar/immunology
• Macrophages, Alveolar/metabolism
• Neutrophil Activation
• Neutrophils/immunology
• Panax/therapeutic use
• Phytotherapy
• Plant Extracts/therapeutic use
• Plants, Medicinal
• Pneumonia, Bacterial/drug therapy
• Pneumonia, Bacterial/immunology
• Pneumonia, Bacterial/pathology
• Pseudomonas Infections/drug therapy
• Pseudomonas Infections/immunology
• Pseudomonas Infections/pathology
• Pseudomonas aeruginosa/immunology
• Rats
• Rats, Inbred Lew
• Respiratory Burst

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Affiliation(s)

Z Song Department of Clinical Microbiology, Rigshospitalet, Copenhagen, Denmark
A Kharazmi
H Wu
V Faber
C Moser
H K Krogh
J Rygaard
N Hoiby

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Pseudomonas aeruginosa exoenzyme S is a mitogen but not a superantigen for human T lymphocytes

Virtually all cystic fibrosis (CF) patients become infected with Pseudomonas aeruginosa, and once the infection is established, the organism is rarely cleared. One of the P. aeruginosa virulence factors, exoenzyme S, has been shown to correlate with increased morbidity and mortality both in rat models of chronic pulmonary inflammation and in human CF patients. It has previously been shown that exoenzyme S is a potent stimulus for the proliferation of T cells in greater than 95% of adults, which could contribute to the pathogenesis of CF. The goal of this study was to determine the mechanism of T-cell stimulation by exoenzyme S in an effort to shed light on the immune response and contribute to understanding its role in P. aeruginosa pathogenesis. The current studies demonstrate that exoenzyme S stimulates naive T cells, since fetal blood lymphocytes proliferated and adult lymphocytes that expressed CD45RA proliferated. The percentage of T cells activated by exoenzyme S after a 4-h culture (as measured by CD69 surface expression) was intermediate in magnitude compared to levels induced by a panel of superantigens and mitogens. To determine the mechanism of activation, the requirement for accessory cells was investigated. The proliferative response to exoenzyme S was dependent on the presence of accessory cells but was not blocked by an anti-DR antibody. Exoenzyme S activated both CD4(+) and CD8(+) T cells, but CD4(+) T cells were preferentially activated. The Vbeta repertoire of donor T cells showed no preferential activation or preferential expansion after stimulation by exoenzyme S, suggesting that it is not a superantigen. Taken together, our data suggest that exoenzyme S is a T-cell mitogen but not a superantigen. Activation of a large percentage of T lymphocytes by exoenzyme S may produce a lymphocyte-mediated inflammatory response that should be considered in the pathogenesis of CF.

Postantibiotic effects and postantibiotic sub-MIC effects of ciprofloxacin, pefloxacin and amikacin on the biological properties of Salmonella strains

The postantibiotic effect (PAE) and the postantibiotic sub-MIC effect (PASME) of ciprofloxacin, pefloxacin and amikacin were studied for Salmonella typhimurium and S. enteritidis strains. PAE was induced by 2 x and 4 x MIC of antibiotics studied for 0.5 h. After PAE and PASME their effect on prophage induction of a lysogenic S. typhimurium strain and on Congo red binding for both strains as a marker of their surface hydrophobicity was examined. The longest PAE was found after treatment with ciprofloxacin, higher values being observed with S. typhimurium. PAEs of pefloxacin and amikacin were much lower, except for the suprainhibitory concentration 4 x MIC of amikacin with S. enteritidis (6.9h). PASMEs of ciprofloxacin did not allow any regrowth of either strain. For other antibiotics the PASMEs were different while concentrations of 2 x MIC + 0.2 x MIC and 0.3 x MIC, and of 4 x MIC + 0.1 x MIC, 0.2 x MIC and 0.3 x MIC of amikacin did not allow any regrowth of S. enteritidis. PAEs of the antibiotics tested did not affect the Congo red binding by both Salmonella strains, but the PAEs of ciprofloxacin and pefloxacin expressively induced a prophage of lysogenic S. typhimurium strain. We noted the influence of Congo red binding after applying 4 x MIC + 0.1 x MIC, 0.2 x MIC and 0.3 x MIC of amikacin for S. typhimurium and 2 x MIC + 0.1 x MIC for S. enteritidis.

Hydrophobicity and outer membrane proteins of Shigella dysenteriae type 1 after treatment with subinhibitory concentrations of aminoglycosides

Hydrophobicity and profiles of outer membrane proteins of Shigella dysenteriae type 1 after treatment with subinhibitory concentrations (1/2 or 1/4 of the MIC) of aminoglycosides were studied. The antimicrobial activity of the antibiotics tested was 3.12 mg/L (amikacin, tobramycin) and 6.25 mg/L (gentamicin). The hydrophobicity of the cell surface of S. dysenteriae type 1 was decreased after exposure to all aminoglycosides at a concentration of 1/2 of the MICs; 1/4 of the MICs of the antibiotics did not affect bacterial aggregation in the presence of ammonium sulfate. SDS-polyacrylamide gel electrophoresis showed that the profiles of outer membrane proteins of the strain treated with aminoglycosides at both subinhibitory concentrations were not changed as compared to the control.

Precipitating Pseudomonas aeruginosa antibodies and antimicrobial therapy in cystic fibrosis patients

Forty patients with cystic fibrosis were studied bacteriologically and serologically. Precipitating Pseudomonas aeruginosa antibodies were monitored by crossed-immunoelectrophoresis (CIE) in order to evaluate the possibility of preventing chronic colonization by Pseudomonas aeruginosa by cycles of antimicrobial therapy. Sputum or pharyngeal aspirate and serum samples from all patients were analyzed by means of spread on selective media and CIE, respectively. Significant differences in the number of precipitins were obtained: noncolonized and intermittently colonized patients had no precipitins, whereas the number of precipitins in the chronically colonized patients varied from 11 to 44. An increase in the number of precipitins could be a good marker for initiation of therapy with antimicrobial agents that are either active against Pseudomonas aeruginosa or able to inhibit the release of virulence factors.

Postantibiotic effects of subinhibitory concentrations of some antibiotics and their influence on Pseudomonas aeruginosa enzymic activity

The postantibiotic effects of subinhibitory concentrations (PA SMEs) and virulence factor alterations induced by ciprofloxacin, tobramycin and netilmicin in Pseudomonas aeruginosa were studied. After induction of the postantibiotic phase (PA) (2x or 4x MIC) the cultures were exposed to subinhibitory concentrations (0.1, 0.2 and 0.3x MIC) of the same antibiotic (PA SME). The regrowth of treated as well as control cultures was followed for 24 or 45 h. In the sterile culture filtrates obtained from these bacterial cultures, elastase and proteinase were determined. Ciprofloxacin and aminoglycosides exhibited PA SMEs of 35-35 h for certain combinations of supra-subinhibitory antibiotic concentrations. Longer PA SMEs were observed after treatment with higher sub-MICs. Tobramycin at 0.2 and 0.3x MIC (postantibiotic phase induced by 2x MIC) and at alt sub-MICs added to the bacteria previously exposed to 4x MIC do not allow any regrowth of bacterial culture. PA SMEs of tested antibiotics affected virulence factors of P. aeruginosa. Elastase compared to proteinase was suppressed more effectively. Ciprofloxacin at 0.3x MIC reduced elastase and proteinase activity most significantly (to 14.2 and 60% of the control values).

Pharmacodynamic parameters of aminoglycosides and their effect on exoenzymes of Pseudomonas aeruginosa

Aminoglycosides at 2x or 4x minimum inhibitory concentration induced postantibiotic effects against Pseudomonas aeruginosa lasting 3.5-4.9 h (gentamicin) and 0.5-3.7 h (selemycin). Postantibiotic effects of subinhibitory concentrations of the aminoglycosides tested were substantially longer. Some combinations of supra- and subinhibitory concentrations of antibiotics did not even allow any regrowth of the bacterial strain. The postantibiotic effects and postantibiotic effects of subinhibitory concentrations of gentamicin and selemycin were associated with changes of P. aeruginosa elastase and proteinase. Combinations of supra- and subinhibitory concentrations more pronouncedly suppressed enzymic activities than did suprainhibitory concentrations alone.

Pseudomonas aeruginosa exoenzyme S induces proliferation of human T lymphocytes

Pseudomonas aeruginosa is a gram-negative bacterium that is responsible for devastating acute and chronic infections, which include bronchiectasis in cystic fibrosis, nosocomial pneumonia, and infection of burn wounds. Previous studies have demonstrated that these patients have impaired host responses, including cell-mediated immune responses, which are important in anti-Pseudomonas host defense. The P. aeruginosa exoproduct, exoenzyme S, has a number of characteristics which suggest that it might be important in cell-mediated immunity. To determine whether exoenzyme S activates lymphocytes to proliferate, peripheral blood mononuclear cells (PBMC) from normal volunteers were stimulated with purified exoenzyme S, and the lymphocyte response was assessed by measuring [3H]thymidine uptake and by counting the number of cells after various times in culture. Ninety-five percent of healthy adult donors had a lymphocyte response to exoenzyme S. The optimal lymphocyte response occurred on day 7, with 4 x 10(5) PBMC per microtiter well when cells were stimulated with 10 micrograms exoenzyme S per ml. [3H]thymidine uptake correlated with an increase in the number of mononuclear cells, indicating that proliferation occurred. In unseparated PBMC, T cells, and to a lesser extent B cells, proliferated. Purified T cells proliferated, while purified B cells proliferated only after the addition of irradiated T cells. Thus, T lymphocytes are necessary and sufficient for the proliferative response to exoenzyme S. We speculate that exoenzyme S from P. aeruginosa is important in T-lymphocyte-mediated host defense to P. aeruginosa. In strategies to enhance impaired cell-mediated immunity, exoenzyme S should be considered as a potential stimulant.

Antimicrobial efficacy of quaternary bisammonium salts and the effect of their sub-MICs on Pseudomonas aeruginosa virulence factors

Antipseudomonadal activity of homologous series of six quaternary bisammonium salts (QBAS) (4,7-dioxo-3,8-dioxadekan-1,1-[bis(alkyldimethyldiammonium dibromide)] as well as the effect of their subinhibitory concentrations (sub-MICs) on Pseudomonas aeruginosa virulence factors was studied. Antibacterial activity of QBAS increased up to a certain length of the chain and then decreased with further elongation. All the tested sub-MICs of QBAS caused a significant suppression of phospholipase C activity (to 0-41%). Elastase and proteinase activity were less efficiently reduced. A more effective decrease of these activities was only found after treatment with one-fourth of the MICs of the tested substances. QBAS caused only an erratic decrease of alginate production.

Expression of recombinant exoenzyme S of Pseudomonas aeruginosa

The structural gene for the 49-kDa form of exoenzyme S (exoS) isolated from Pseudomonas aeruginosa 388 was expressed in both Escherichia coli and P. aeruginosa PA103. Expression of exoS in E. coli under the transcriptional regulation of the T7 promoter yielded a soluble cytosolic protein with an apparent molecular mass of 49 kDa, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Expression of exoS in P. aeruginosa PA103 under the transcriptional regulation of the 0.9 kbp of Pseudomonas chromosomal DNA flanking the 5' end of exoS yielded a nitrilotriacetic acid-inducible extracellular protein with an apparent molecular mass of 49 kDa. Recombinant ExoS (rExoS) reacted with the anti-49-kDa form of exoenzyme S immunoglobulin G, existed as an aggregate as determined by gel filtration chromatography, and ADP-ribosylated soybean trypsin inhibitor at a specific activity that was similar (within twofold) to that of native exoenzyme S. Allelic exchange of exoS with a tetracycline gene cartridge yielded a strain of P. aeruginosa 388 that did not express detectable amounts of either ExoS in an immunoblot analysis using the anti-49-kDa form of exoenzyme S immunoglobulin G or ADP-ribosyltransferase activity under standard enzyme assay conditions. Expression of catalytically active rExoS in E. coli demonstrated that exoS was necessary and sufficient for the factor-activating exoenzyme S-dependent ADP-ribosyltransferase activity of exoenzyme S. Expression of nitrilotriacetic acid-inducible rExoS in P. aeruginosa PA103 demonstrated that the 0.9 kbp of Pseudomonas chromosomal DNA flanking the 5' end of exoS encoded a functional exoenzyme S promoter. Expression analysis and allelic exchange experiments suggest that the 49- and 53-kDa forms of exoenzyme S are encoded by separate genes.

Enzymic and permeability activity of Pseudomonas aeruginosa after treatment with sub-MICs of organic ammonium salts

The effects of subinhibitory concentrations (1/4, 1/8, 1/16 of the MIC) of 12 organic ammonium salts of A (hard-alkyltrimethylammonium bromides) and B (soft--2-(dodecanoylamino)ethylalkyldimethylammonium bromides) homologous series on phospholipase C, proteinase, elastase and permeability activity were studied. The substances with longer substituents were more effective in reducing phospholipase C activity (hard and soft series) as well as proteinase (hard series). Phospholipase C was the most frequently and the most markedly inhibited enzyme. The organic ammonium salts were less effective in inhibiting elastase and permeability activity. Only one of the substances under study reduced all the tested activities.

Pharmacodynamic effects of subinhibitory concentrations of imipenem on Pseudomonas aeruginosa in an in vitro dynamic model

The postantibiotic effect (PAE), sub-MIC effect (SME), and postantibiotic sub-MIC effect (PASME) of imipenem on Pseudomonas aeruginosa were investigated with an in vitro dynamic model reproducing in vivo elimination kinetics of the antibiotic. The PASMEs were constantly longer than the corresponding SMEs, but differences between them were not statistically significant. Both PASMEs and SMEs were initially bactericidal and were significantly longer than PAEs. The mean values of both PASMEs and SMEs were over 12 h. SMEs appear to be more relevant for the bacterial growth kinetics than PAEs.

Effects of subinhibitory concentrations of antibiotics on biological properties of Salmonella typhimurium

We followed the effects of subinhibitory concentrations (sub-MICs) of 7 antibiotics (ticarcilin, cefotaxim, streptomycin, gentamicin, ciprofloxacin, pefloxacin, mitomycin C) on the sensitivity of a Salmonella typhimurium strain to standard bacteriophages, on the phage DNA as well as on the factors of virulence (permeability and cytotoxic activity). The phage type was not changed by the sub-MICs of the tested antibiotics. However, differences were found in culture filtrates prepared from the bacterial suspensions of the strain cultivated with the sub-MICs. Marked inducing effects on phage DNA were exhibited by mitomycin C (1/2, 1/4, 1/8 of the MIC), pefloxacin (1/2, 1/4, 1/8 of the MIC) and ciprofloxacin (1/2, 1/4, weakly also 1/8 of the MIC). Ticarcilin (1/2 of the MIC), like the aminoglycosides streptomycin and gentamicin (1/2, 1/4, 1/8 of the MIC), had a weak effect. Sub-MICs of the studied antibiotics (with the exception of 1/8 of the MIC of ciprofloxacin and 1/4 of the MIC of ticarcilin) decreased the permeability reaction in rabbit skin. Most effective was streptomycin (1/2 of the MIC). Sub-MICs of the tested antibiotics (with the exception of 1/4 and 1/8 of the MIC of ciprofloxacin and 1/4 of the MIC of pefloxacin) caused also an inhibition of the factor responsible for morphological changes on Vero cells. Gentamicin and streptomycin were effective at all the sub-MICs tested.

Comparative in vitro exoenzyme-suppressing activities of azithromycin and other macrolide antibiotics against Pseudomonas aeruginosa

The inhibitory effects of azithromycin (AZM), a new 15-membered macrolide antibiotic, on the production of exotoxin A, total protease, elastase, and phospholipase C by Pseudomonas aeruginosa were determined, and the virulence-suppressing effects of AZM were compared with those of erythromycin (EM), roxithromycin (RXM), and rokitamycin (RKM). The effect of exposure of P. aeruginosa PA103 or B16 in cultures to sub-MICs of these macrolide antibiotics on the production of exoenzymes was determined. AZM suppressed the in vitro production of extracellular and intracellular exotoxin A by P. aeruginosa PA103 more than did EM, even at a concentration of only 2 micrograms/ml. At concentrations of between 4 and 32 micrograms/ml, AZM also inhibited total protease, elastase, and phospholipase C production by P. aeruginosa B16 more than did EM, RXM, and RKM. AZM was effective in suppressing exotoxin A and total protease production through 24 h of incubation in the presence of drug at sub-MICs, but it had no significant effect on either the growth of P. aeruginosa or its total protein production. Moreover, at a concentration of 4 micrograms/ml, AZM suppressed exoenzyme production by other strains of P. aeruginosa more than did EM. These findings indicate that AZM, EM, RXM, and RKM each has an inhibitory effect on exoenzyme production separate from the antimicrobial effect and that, of these macrolides, AZM has the strongest virulence-suppressing effect.

Construction and characterization of chromosomal insertional mutations of the Pseudomonas aeruginosa exoenzyme S trans-regulatory locus

Exoenzyme S is an ADP-ribosyltransferase produced by Pseudomonas aeruginosa. Synthesis of exoenzyme S depends on an intact trans-regulatory locus encoding three protein products, ExsC, ExsB, and ExsA. To identify the phenotype of ExsC, -B, and -A mutants in exoenzyme S production, specific insertional mutations with the streptomycin resistance-encoding omega interposon were introduced into cloned DNA and returned to the chromosomes of P. aeruginosa PA103, PAO1, and PAK. Southern blot analysis was used to confirm insertion of omega and resolution of vector sequences. Exoenzyme S expression was measured in parental and mutant derivatives by Western blot (immunoblot) analysis and ADP-ribosyltransferase activity measurement. A complete set of mutations were obtained in strains PAK and PAO1, but in strain PA103, only an insertion in the exsA coding region was identified. Southern blot analysis demonstrated that extensive duplication and rearrangement of the PA103 chromosomal trans-regulatory locus occurred when exsC::omega or exsB::omega recombination events were attempted. Exoenzyme S antigen was not detectable in the supernatant or lysate fractions of mutant strains by Western blot analysis. ADP-ribosyltransferase activity was detected in the lysate but not in the supernatant fractions of mutant derivatives. The general secretion pathway appeared to function normally in mutant strains, as elastase, exotoxin A, and phospholipase C were measured in the supernatants of parental and mutant strains. Several differences were noted when the extracellular protein profiles of parental strains were compared with similar samples from the insertional mutant strains. Some of these differences appeared to be unrelated to exoenzyme S. These data suggest that insertional inactivation of the exoenzyme S trans-regulatory locus may affect a subset of other extracellular proteins.

Regular three monthly oral ciprofloxacin in adult cystic fibrosis patients infected with Pseudomonas aeruginosa

In 31 adult patients with cystic fibrosis (CF) who were chronically infected with Pseudomonas aeruginosa we examined the effect of giving regular three monthly oral ciprofloxacin. Patients received ciprofloxacin or placebo for 10 days every 3 months for 1 yr in a randomized, double-blind, placebo-controlled study. During each course of treatment patients receiving ciprofloxacin reported an improvement in cough, sputum production and peak expiratory flow (PEF) P = < 0.005. During the year of study patients receiving ciprofloxacin showed an improvement in PEF when compared with those receiving placebo (P = < 0.05) but the changes in FEV1 and FVC were not statistically different in either group. Regular oral ciprofloxacin was well tolerated but did not prevent hospital admissions or reduce the number of courses of intravenous antibiotics throughout the year. The median MIC to ciprofloxacin in the active treatment group rose from 0.5 mg l-1 to 0.75 mg l-1 during treatment. We conclude that CF patients are likely to benefit from oral ciprofloxacin for exacerbations of respiratory symptoms. However, regular treatment with ciprofloxacin over 1 yr improves PEF but does not reduce the rate of hospital admissions with acute exacerbations of respiratory symptoms.

Alterations in Pseudomonas aeruginosa exoproducts by sub-MICs of some antibiotics

Aminoglycoside antibiotics, most effective at the level of 1/4 of the MIC, suppressed all the tested activities of P. aeruginosa, except cytotoxicity. Proteinase activity was decreased to 60% (gentamicin) and 63% (streptomycin), permeability was reduced to 61% (gentamicin) and 73% (streptomycin), phospholipase C to 13% (gentamicin) and 51% (streptomycin) of the control values. Subinhibitory concentrations of beta-lactams inhibited only phospholipase C activity to 89% (ticarcillin) and 64% (cefotaxim) of the control values. These antibiotics did not suppress the cytotoxic activity and increased protease activity up to 155% (ticarcillin) and 192% (cefotaxim) as well as permeability up to 121% (ticarcillin) and 154% (cefotaxim) of the control values.