Survival of Stenotrophomonas maltophilia following exposure to concentrations of tobramycin used in aerosolized therapy for cystic fibrosis patients

Prevalence, trends and outcomes of long-term inhaled antibiotic treatment in people with cystic fibrosis without chronic Pseudomonas aeruginosa infection - A European cystic fibrosis patient registry data analysis

BACKGROUND

Long-term treatment with inhaled antibiotics is recommended for people with cystic fibrosis (pwCF) chronically infected with Pseudomonas aeruginosa (PA). However, pwCF without chronic PA infection are also commonly treated with inhaled antibiotics. Using data from the European Cystic Fibrosis Patient Registry (ECFSPR) we aimed to determine the prevalence and factors associated with inhaled antibiotic treatment in pwCF without chronic PA infection, and long-term outcomes with inhaled antibiotics use.

METHODS

The ECFSPR was searched for pwCF 6 years of age and older who were not chronically infected with PA at baseline. Factors associated with inhaled antibiotic use were first assessed through a logistic regression. From this model a propensity score was computed for each individual, providing the likelihood of being treated with inhaled antibiotics. Long-term outcomes with and without inhaled antibiotics were assessed separately for propensity scores tertiles.

RESULTS

7210 pwCF without chronic PA infection at baseline were included, with 2722 (37.75%) receiving long-term treatment with inhaled antibiotics. Treatment with inhaled antibiotics was more prevalent with severe genotype, diabetes, pancreatic insufficiency, and past infection with chronic PA (OR 3.8, 95% CI, 2.88-5.04). Treatment with inhaled antibiotics was not associated with a reduced risk for acquisition of PA or other resistant pathogens, or with improved lung function decline, mortality, or transplantation.

CONCLUSIONS

Many pwCF without chronic PA infection are receiving long-term treatment with inhaled antibiotics despite lack of support from clinical trials or practice guidelines. We did not observe improve outcomes with inhaled antibiotics. Our findings suggest controlled studies evaluating specific inhaled antibiotic regimens targeting specific pathogens or indications be performed to determine their effect.

Stenotrophomonas maltophilia and Its Ability to Form Biofilms

In the last ten years, Stenotrophomonas maltophilia has gained increasing interest as an important agent of infection, which is why it has come to be recognized as a serious cause of nosocomial infections related to bloodstream infections, pneumonia, and cancer, mainly in patients with intensive care, and is associated with high mortality rates in immunocompromised patients, with prolonged hospital stays and extensive use of antimicrobials. The importance of this microorganism lies in its low pathogenicity, high multiresistance to various antibiotics, and frequent and persistent isolation in predisposed patients. In addition, few studies have evaluated its epidemiology and clinical relevance. The pathogenesis of biofilms lies mainly in the fact that they can generate persistent chronic infections that are difficult to eradicate. To this extent, it is important to make the characteristics of the biofilm formation behavior of Stenotrophomonas maltophilia known and generate more knowledge about its colonization or infection in humans through this review, which discusses more recent information.

The Effects of Antibiotic Combination Treatments on Pseudomonas aeruginosa Tolerance Evolution and Coexistence with Stenotrophomonas maltophilia

The Pseudomonas aeruginosa bacterium is a common pathogen of cystic fibrosis (CF) patients due to its ability to evolve resistance to antibiotics during treatments. While P. aeruginosa resistance evolution is well-characterized in monocultures, it is less well-understood in polymicrobial CF infections. Here, we investigated how exposure to ciprofloxacin, colistin, or tobramycin antibiotics, administered at sub-minimum inhibitory concentration (MIC) doses, both alone and in combination, shaped the tolerance evolution of P. aeruginosa (PAO1 lab and clinical CF LESB58 strains) in the absence and presence of a commonly co-occurring species, Stenotrophomonas maltophilia. The increases in antibiotic tolerances were primarily driven by the presence of that antibiotic in the treatment. We observed a reciprocal cross-tolerance between ciprofloxacin and tobramycin, and, when combined, the selected antibiotics increased the MICs for all of the antibiotics. Though the presence of S. maltophilia did not affect the tolerance or the MIC evolution, it drove P. aeruginosa into extinction more frequently in the presence of tobramycin due to its relatively greater innate tobramycin tolerance. In contrast, P. aeruginosa dominated and drove S. maltophilia extinct in most other treatments. Together, our findings suggest that besides driving high-level antibiotic tolerance evolution, sub-MIC antibiotic exposure can alter competitive bacterial interactions, leading to target pathogen extinctions in multispecies communities. IMPORTANCE Cystic fibrosis (CF) is a genetic condition that results in thick mucus secretions in the lungs that are susceptible to chronic bacterial infections. The bacterial pathogen Pseudomonas aeruginosa is often associated with morbidity in CF and is difficult to treat due to its high resistance to antibiotics. The resistance evolution of Pseudomonas aeruginosa is poorly understood in polymicrobial infections that are typical of CF. To study this, we exposed P. aeruginosa to sublethal concentrations of ciprofloxacin, colistin, or tobramycin antibiotics in the absence and presence of a commonly co-occurring CF species, Stenotrophomonas maltophilia. We found that low-level antibiotic concentrations selected for high-level antibiotic resistance. While P. aeruginosa dominated in most antibiotic treatments, S. maltophilia drove it into extinction in the presence of tobramycin due to an innately higher tobramycin resistance. Our findings suggest that, besides driving high-level antibiotic tolerance evolution, sublethal antibiotic exposure can magnify competition in bacterial communities, which can lead to target pathogen extinctions in multispecies communities.

An evaluation of six-year Stenotrophomonas maltophilia infections in a university hospital

Background

Stenotrophomonas maltophilia is a Gram-negative bacillus and opportunistic emergent pathogen causing hospital-acquired infections (HAIs). Due to risk factors such as prolonged intensive care unit stay and invasive procedures, it has become one of the leading causes of HAIs.

Objective

The aim of this study was to evaluate the epidemiology of S.maltophilia infections over a six-year period at Düzce University Hospital, Turkey.

Methods

The incidence, clinical characteristics, antimicrobial susceptibility and outcomes of nosocomial S. maltophilia infections during this period were retrospectively analyzed.

Results

During the study period, 67 samples obtained from 61 patients were identified. Pneumonias (82%) were the most common HAIs, followed by bloodstream infections (10.5%), urinary tract infections (3%), skin and soft tissue infections (3%) and surgical site infection (1.5%). Admission to intensive care, hospitalization exceeding 30 days, and previous use of broad-spectrum antibiotics constituted risk factors. Resistance to cotrimoxazole (6%) was lower than that to levofloxacin (18%).

Conclusion

The most important risk factors for S.maltophilia infection in patients are previous exposure to antibiotics, prolonged hospitalization and invasive procedures such as mechanic ventilation. Discharging patients as early as possible with the rational use of antibiotics may be effective in reducing S. maltophilia infections and resistance rates.

Niche partitioning of a pathogenic microbiome driven by chemical gradients

Environmental microbial communities are stratified by chemical gradients that shape the structure and function of these systems. Similar chemical gradients exist in the human body, but how they influence these microbial systems is more poorly understood. Understanding these effects can be particularly important for dysbiotic shifts in microbiome structure that are often associated with disease. We show that pH and oxygen strongly partition the microbial community from a diseased human lung into two mutually exclusive communities of pathogens and anaerobes. Antimicrobial treatment disrupted this chemical partitioning, causing complex death, survival, and resistance outcomes that were highly dependent on the individual microorganism and on community stratification. These effects were mathematically modeled, enabling a predictive understanding of this complex polymicrobial system. Harnessing the power of these chemical gradients could be a drug-free method of shaping microbial communities in the human body from undesirable dysbiotic states.

Stenotrophomonas maltophilia: an emerging global opportunistic pathogen

Stenotrophomonas maltophilia is an emerging multidrug-resistant global opportunistic pathogen. The increasing incidence of nosocomial and community-acquired S. maltophilia infections is of particular concern for immunocompromised individuals, as this bacterial pathogen is associated with a significant fatality/case ratio. S. maltophilia is an environmental bacterium found in aqueous habitats, including plant rhizospheres, animals, foods, and water sources. Infections of S. maltophilia can occur in a range of organs and tissues; the organism is commonly found in respiratory tract infections. This review summarizes the current literature and presents S. maltophilia as an organism with various molecular mechanisms used for colonization and infection. S. maltophilia can be recovered from polymicrobial infections, most notably from the respiratory tract of cystic fibrosis patients, as a cocolonizer with Pseudomonas aeruginosa. Recent evidence of cell-cell communication between these pathogens has implications for the development of novel pharmacological therapies. Animal models of S. maltophilia infection have provided useful information about the type of host immune response induced by this opportunistic pathogen. Current and emerging treatments for patients infected with S. maltophilia are discussed.

Stenotrophomonas maltophilia contamination of nebulizers used to deliver aerosolized therapy to inpatients with cystic fibrosis

There is circumstantial evidence that nebulizer equipment may be a source of Stenotrophomonas maltophilia for patients with cystic fibrosis. Eighty-nine inpatient nebulizers were examined for evidence of S. maltophilia contamination of which nine (10%) yielded 14 strains of the bacterium. Environmental samples were obtained from 73 different sites on the ward, of which 17 (23%) yielded a further 21 strains. Positive sites included taps, sink drains, and potable water. Genotyping using ERIC-PCR and pulsed-field gel electrophoresis revealed that two pairs of patients' nebulizers were contaminated with closely related strains. None of the S. maltophilia isolates obtained from the ward environment shared genotypes with those obtained from the nebulizers. The frequency of isolation of S. maltophilia from potable water sources on the ward suggests that contamination may result from using it to clean reusable nebulizer equipment, particularly if this is followed by inadequate drying. Although the actual source of S. maltophilia contamination of hospital-use nebulizer equipment in this study remained elusive, these results have important infection control implications.

Traitement anti-infectieux vis-a-vis du Pseudomonas aeruginosa et autres bacilles a gram negatif dans la mucoviscidose

In cystic fibrosis patients, bronchial infection with Pseudomonas aeruginosa (PA) is frequent, occurring often early in life. It becomes chronic because of a particular relationship between bacteria and host. Intensive antibiotic treatment often permits a transient eradication. When infection becomes chronic, antibiotics must be prescribed in a way to afford resistance. Efficacy of nebulized antibiotics is now recognized. Problems persist. Because of the difficulty to eradicate PA, new strategies may consist in diminishing the pathogenicity of PA, by inhibiting adhesion and virulence factors' production.

Antimicrobial susceptibility profile of molecular typed cystic fibrosis Stenotrophomonas maltophilia isolates and differences with noncystic fibrosis isolates

Multiresistance in Stenotrophomonas maltophilia limits the effectiveness of antimicrobial therapy for infections due to this organism. It can be of special concern in cystic fibrosis (CF) patients due to frequent antimicrobial administration. The in vitro activity of 41 antimicrobial agents against 76 epidemiologically defined CF S. maltophilia isolates by pulsed-field-gel electrophoresis (PFGE) technique under XbaI and SpeI restriction was compared with that obtained with 51 non-CF strains recovered from respiratory sources. Minimal inhibitory concentrations (MICs) were determined with the standard National Committee for Clinical Laboratory Standards agar dilution technique, but with 24-hr incubation. Forty-seven different PFGE profiles were observed within 76 S. maltophilia CF isolates. Minocycline (resistance rate, 0%; MIC(90), 1 microg/ml), doxycycline (6.4%; 8 microg/ml), trovafloxacin (4.2%; 2 microg/ml), moxifloxacin (6.3%; 2 microg/ml), clinafloxacin (6.3%; 2 g/ml), and moxalactam (17.0%; 64 g/ml) displayed low resistance rates. On the contrary, resistance rates were higher with ceftazidime (70.0%; 256 microg/ml), cefepime (83.0%; 128 microg/ml), piperacillin (87.2%; >1,024 microg/ml), ticarcillin (87.2%; >512 microg/ml), and aztreonam (95.7%; >1,024 microg/ml). Clavulanate reverted resistance to ticarcillin and aztreonam in 40.4% and 31.7% of strains, respectively. Aminoglycosides displayed reduced activities with susceptibility rates lower than 20% and MIC(90) higher than 128 microg/ml. With the exception of trimethoprim-sulfamethoxazole (25.4 vs. 31.3%), CF isolates were more resistant than non-CF isolates. Remarkably, resistance was enhanced in S. maltophilia isolates persistently recovered in chronically colonized patients. Susceptibility analysis demonstrated higher resistance rates among CF S. maltophilia isolates when compared with respiratory isolates from non-CF patients. Moreover, persistently recovered CF S. maltophilia isolates were more resistant than sporadic non-CF isolates.

Nebulized antibiotics in cystic fibrosis

Nebulization is a useful administration route in cystic fibrosis (CF) as it delivers antibiotics directly to the endobronchial site of infection and is associated with decreased toxicity because of limited systemic absorption. It is assumed that the concentration of antibiotics in bronchial secretions should be as high as 10 times the minimum inhibiting concentration to allow penetration of antibiotics into biofilms, suppress inhibitory factors and promote bactericidal effectiveness. However, effective aerosol delivery is compromised by nebulizers with limited capacity to produce particles of a size in the respirable range. Three antibiotics are commonly used for inhalation: tobramycin, amikacin and colistin (colomycin). Placebo-controlled studies evaluating antibiotic aerosol maintenance in stable patients chronically infected with Pseudomonas aeruginosa indicate a significant improvement of lung function and a reduction of the number of hospital admissions for an acute exacerbation of CF. TOBI is a recently marketed preservative- and sulfate-free formula of tobramycin, specially designed for diffusion in the bronchioles and optimal tolerance. A wide-scope study involving 520 patients compared TOBI (300 mg twice daily; n = 258) with placebo (n = 262) for three 28-day cycles with each cycle separated by a 28-day period of no treatment. Respiratory function was significantly improved as early as in the second week and remained so for the rest of the trial even during periods without aerosol treatment. There was also a parallel decrease in the relative risk of hospitalization, the number of days of hospitalization and the number of days on intravenous antipyocyanic treatment. Toxicity studies carried out so far have shown no renal or ototoxicity with nebulized tobramycin. Introduction or selection of resistant bacteria is relatively rare but remains a matter of concern. Aerosol maintenance treatment with an appropriate antibiotic in a high enough dosage can be recommended for patients with CF who are chronically infected with P. aeruginosa.