Antimicrobial susceptibility and synergy studies of Stenotrophomonas maltophilia isolates from patients with cystic fibrosis

The prevalence of colistin resistance in clinical Stenotrophomonas maltophilia isolates worldwide: a systematic review and meta-analysis

While trimethoprim-sulfamethoxazole (TMP-SMX) is the first-line therapy of Stenotrophomonas maltophilia infections, colistin is one of the therapeutic options in cases of allergy or resistance to TMP-SMX. However, understanding the global status of resistance to colistin amongst S. maltophilia isolates could be helpful for appropriate antibiotic prescription. This study aimed to conduct a systematic review and meta-analysis to examine the prevalence of colistin resistance in clinical S. maltophilia isolates worldwide. According to eligibility criteria, a total of 61 studies were included in the analysis. The pooled prevalence for colistin resistance was 42% (95% CI: 35-49%), ranging from 0.1 to 97%. Subgroups analysis indicated that, the pooled prevalence of colistin resistance was 44% (95% CI: 29-60%) in 15 studies during 2000-2010, and it was estimated to be 41% (95% CI: 33-50%) in 46 articles from 2011 to 2021. It was 46% (95% CI: 35-58%) in the studies that used broth microdilution method, and 39% (95% CI: 30-49%) in the studies with other used methods. The resistance rate in Asian countries was 45% (95% CI: 31-60%), in European countries was 45% (95% CI: 34-56%) and in the countries of North and South America was 33% (95% CI: 20-46%). Our review showed notable resistance to colistin in clinical S. maltophilia isolates. Given the estimated resistance rates, alternative antibiotics could be preferred to treat serious infections due to S. maltophilia.

Global prevalence and antibiotic resistance in clinical isolates of Stenotrophomonas maltophilia: a systematic review and meta-analysis

Introduction

Stenotrophomonas maltophilia is a little-known environmental opportunistic bacterium that can cause broad-spectrum infections. Despite the importance of this bacterium as an emerging drug-resistant opportunistic pathogen, a comprehensive analysis of its prevalence and resistance to antibiotics has not yet been conducted.

Methods

A systematic search was performed using four electronic databases (MEDLINE via PubMed, Embase, Scopus, and Web of Science) up to October 2019. Out of 6,770 records, 179 were documented in the current meta-analysis according to our inclusion and exclusion criteria, and 95 studies were enrolled in the meta-analysis.

Results

Present analysis revealed that the global pooled prevalence of S. maltophilia was 5.3 % [95% CI, 4.1-6.7%], with a higher prevalence in the Western Pacific Region [10.5%; 95% CI, 5.7-18.6%] and a lower prevalence in the American regions [4.3%; 95% CI, 3.2-5.7%]. Based on our meta-analysis, the highest antibiotic resistance rate was against cefuroxime [99.1%; 95% CI, 97.3-99.7%], while the lowest resistance was correlated with minocycline [4·8%; 95% CI, 2.6-8.8%].

Discussion

The results of this study indicated that the prevalence of S. maltophilia infections has been increasing over time. A comparison of the antibiotic resistance of S. maltophilia before and after 2010 suggested there was an increasing trend in the resistance to some antibiotics, such as tigecycline and ticarcillin-clavulanic acid. However, trimethoprim-sulfamethoxazole is still considered an effective antibiotic for treating S. maltophilia infections.

The Status of Carbapenem Resistance in Cystic Fibrosis: A Systematic Review and Meta-Analysis

Background: Antibiotic resistance in cystic fibrosis (CF) is a well-known phenomenon. However, the comprehensive epidemiological impact of antibiotic resistance in CF is not clearly documented. So, this meta-analysis evaluated the proportion rates of carbapenem resistance (imipenem, meropenem, and doripenem) in CF based on publication date (1979-2000, 2001-2010, and 2011-2021), continents, pathogens, and antimicrobial susceptibility testing (AST). Methods: We searched studies in PubMed, Scopus, and Web of Science (until April 2021). Statistical analyses were conducted using STATA software (version 14.0). Results: The 110 studies included in the analysis were performed in 25 countries and investigated 13,324 pathogens associated with CF. The overall proportion of imipenem, meropenem, and doripenem resistance in CF were 43% (95% CI 36-49), 48% (95% CI 40-57), 28% (95% CI 23-33), and 45% (95% CI 32-59), respectively. Our meta-analysis showed that trends of imipenem, meropenem, and doripenem-resistance had gradual decreases over time (1979-2021). This could be due to the limited clinical effectiveness of these antibiotics to treat CF cases over time. Among the opportunistic pathogens associated with CF, the highest carbapenem resistance rates were shown in Stenotrophomonas maltophilia, Burkholderia spp., Pseudomonas aeruginosa, and Staphylococcus aureus. The highest and lowest carbapenem resistance rates among P. aeruginosa in CF patients were shown against meropenem (23%) and doripenem (39%). Conclusions: We showed that trends of carbapenem resistance had decreased over time (1979-2021). This could be due to the limited clinical effectiveness of these antibiotics to treat CF cases over time. Plans should be directed to fight biofilm-associated infections and prevent the emergence of mutational resistance. Systematic surveillance for carbapenemase-producing pathogens in CF by molecular surveillance is necessitated.

Managing Pulmonary Infection in Adults With Cystic Fibrosis: Adult Cystic Fibrosis Series

Cystic fibrosis (CF) is characterized by chronic airway infection and progressive respiratory decline. Historically, a narrow spectrum of bacterial pathogens was believed to comprise the bulk of respiratory infections in CF, with Haemophilus influenzae and Staphylococcus aureus dominating childhood infections, and Pseudomonas aeruginosa or, less commonly, a member of the Burkholderia cepacia complex becoming the dominant infecting organism in adulthood. Today, the landscape is changing for airway infection in CF. The prevalence of "less typical" gram-negative bacterial infections are rising due to a number of factors: the CF population is aging; new therapies are being introduced; antibiotic usage is increasing; diagnostic tests are evolving; and taxonomic changes are being made as new bacterial species are being discovered. Less is known about the clinical relevance and evidence for treatment strategies for many of the other lower prevalence organisms that are encountered in CF. The aim of this article was to discuss the current evidence and recommended strategies for treating airway infection in CF, focusing on bacterial infections.

Overcoming Stenotrophomonas maltophilia Resistance for a More Rational Therapeutic Approach

Stenotrophomonas maltophilia is an underappreciated source of morbidity and mortality among gram-negative pathogens. Effective treatment options with acceptable toxicity profiles are limited. Phenotypic susceptibility testing via commercial automated test systems is problematic and no Food and Drug Administration breakpoints are approved for any of the first-line treatment options for S maltophilia. The lack of modern pharmacokinetic/pharmacodynamic data for many agents impedes dose optimization, and the lack of robust efficacy and safety data limits their clinical utility. Levofloxacin has demonstrated similar efficacy to trimethoprim-sulfamethoxazole, although rapid development of resistance is a concern. Minocycline demonstrates the highest rate of in vitro susceptibility, however, evidence to support its clinical use are scant. Novel agents such as cefiderocol have exhibited promising activity in preclinical investigations, though additional outcomes data are needed to determine its place in therapy for S maltophilia. Combination therapy is often employed despite the dearth of adequate supporting data.

Antimicrobial Treatment Strategies for Stenotrophomonas maltophilia: A Focus on Novel Therapies

Stenotrophomonas maltophilia is an urgent global threat due to its increasing incidence and intrinsic antibiotic resistance. Antibiotic development has focused on carbapenem-resistant Enterobacteriaceae, Pseudomonas, and Acinetobacter, with approved antibiotics in recent years having limited activity for Stenotrophomonas. Accordingly, novel treatment strategies for Stenotrophomonas are desperately needed. We conducted a systemic literature review and offer recommendations based on current evidence for a treatment strategy of Stenotrophomonas infection.

Antimicrobial susceptibility pattern of Burkholderia cepacia complex & Stenotrophomonas maltophilia from North India: Trend over a decade (2007-2016)

Background & objectives

With increased isolation of Burkholderia cepacia complex (Bcc) and Stenotrophomonas maltophilia from clinical specimens, knowledge of their antimicrobial susceptibility trend will aid in better patient management. This study provides a comprehensive picture of this trend over a decade.

Methods

A retrospective analysis of laboratory records over 10 years for antimicrobial susceptibility pattern of Bcc and S. maltophilia was carried out. The susceptibility pattern to commonly used antimicrobials was determined using disk diffusion and compared at the beginning, mid and end of the study period.

Results

Five hundred and thirty Bcc and 665 S. maltophilia isolated over the past 10 yr were included in the study. Over the years, susceptibility of Bcc for co-trimoxazole varied as 80, 70 and 89 per cent at the beginning, middle and end of the study, respectively. Susceptibility to tetracycline was 43 per cent at the beginning of the study and that to minocycline was 100 per cent mid-study and 74 per cent at the end. Susceptibility to ceftazidime varied as 83, 60 and 65 per cent, respectively, and to meropenem, increased during the first half of the study and decreased in the second half, as 60, 70 and 43 per cent, respectively. Bcc susceptibility to levofloxacin decreased from 84 (in 2014) to 76 per cent (in 2016). S. maltophilia susceptibility to co-trimoxazole varied as 90, 82 and 87 per cent, respectively, whereas that to levofloxacin was 80, 100 and 94 per cent, respectively, during the start, mid and end of the study. Susceptibility to minocycline decreased from 100 per cent mid-study to 96 per cent at the end. Susceptibility of S. maltophilia to ceftazidime increased from 24 (in 2012) to 37 per cent (in 2016). All variations among the three phases of the study were significant for all antimicrobials tested for both the organisms.

Interpretation & conclusions

While Bcc showed increased resistance to ceftazidime, meropenem and minocycline, S. maltophilia maintained >80 per cent susceptibility to minocycline, levofloxacin and co-trimoxazole throughout the decade. By 2016, Bcc was most susceptible to co-trimoxazole, whereas S. maltophilia was most susceptible to minocycline and levofloxacin.

Stenotrophomonas maltophilia phenotypic and genotypic features through 4-year cystic fibrosis lung colonization

Introduction. Stenotrophomonas maltophilia has emerged as one of the most common multi-drug-resistant pathogens isolated from people with cystic fibrosis (CF). However, its adaptation over time to CF lungs has not been fully established.Hypothesis. Sequential isolates of S. maltophilia from a Brazilian adult patient are clonally related and show a pattern of adaptation by loss of virulence factors.Aim. To investigate antimicrobial susceptibility, clonal relatedness, mutation frequency, quorum sensing (QS) and selected virulence factors in sequential S. maltophilia isolates from a Brazilian adult patient attending a CF referral centre in Buenos Aires, Argentina, between May 2014 and May 2018.Methodology. The antibiotic resistance of 11 S. maltophilia isolates recovered from expectorations of an adult female with CF was determined. Clonal relatedness, mutation frequency, QS variants (RpfC-RpfF), QS autoinducer (DSF) and virulence factors were investigated in eight viable isolates.Results. Seven S. maltophilia isolates were resistant to trimethoprim-sulfamethoxazole and five to levofloxacin. All isolates were susceptible to minocycline. Strong, weak and normomutators were detected, with a tendency to decreased mutation rate over time. XbaI PFGE revealed that seven isolates belong to two related clones. All isolates were RpfC-RpfF1 variants and DSF producers. Only two isolates produced weak biofilms, but none displayed swimming or twitching motility. Four isolates showed proteolytic activity and amplified stmPr1 and stmPr2 genes. Only the first three isolates were siderophore producers. Four isolates showed high resistance to oxidative stress, while the last four showed moderate resistance.Conclusion. The present study shows the long-time persistence of two related S. maltophilia clones in an adult female with CF. During the adaptation of the prevalent clones to the CF lungs over time, we identified a gradual loss of virulence factors that could be associated with the high amounts of DSF produced by the evolved isolates. Further, a decreased mutation rate was observed in the late isolates. The role of all these adaptations over time remains to be elucidated from a clinical perspective, probably focusing on the damage they can cause to CF lungs.

A 10-year single-center experience on Stenotrophomonas maltophilia resistotyping in Szeged, Hungary

Stenotrophomonas maltophilia is an aerobic, oxidase-negative and catalase-positive bacillus. S. maltophilia is a recognized opportunistic pathogen. Due to the advancements in invasive medical procedures, organ transplantation and chemotherapy of malignant illnesses, the relevance of this pathogen increased significantly. The therapy of S. maltophilia infections is challenging, as these bacteria show intrinsic resistance to multiple classes of antibiotics, the first-choice drug is sulfamethoxazole/trimethoprim. Our aim was to assess the epidemiology of S. maltophilia from various clinical samples and the characterization of resistance-levels and resistotyping of these samples over a long surveillance period. The study included S. maltophilia bacterial isolates from blood culture samples, respiratory samples and urine samples and the data for the samples, received between January 2008 until December 2017, a total of 817 S. maltophilia isolates were identified (respiratory samples n = 579, 70.9%, blood culture samples n = 175, 21.4% and urine samples n = 63, 7.7%). Levofloxacin and colistin-susceptibility rates were the highest (92.2%; n = 753), followed by tigecycline (90.5%, n = 739), the first-line agent sulfamethoxazole/trimethoprim (87.4%, n = 714), while phenotypic resistance rate was highest for amikacin (72.5% of isolates were resistant, n = 592). The clinical problem of sulfamethoxazole/trimethoprim-resistance is a complex issue, because there is no guideline available for the therapy of these infections.

Investigation of Stenotrophomonas maltophilia epidemiology in a French cystic fibrosis center

BACKGROUND

Stenotrophomonas maltophilia is an emerging opportunistic pathogen. The increasing incidence is of particular concern in patients with cystic fibrosis (CF). Since 2012, the Western France has witnessed high annual prevalence of S. maltophilia colonization/infection. This retrospective cohort study investigated the epidemiology of S. maltophilia emergence in the CF center of Roscoff, Western France, a region of high prevalence of CF in Europe.

METHODS

All CF patients with S. maltophilia isolated in respiratory samples between December 2013 and February 2017 were included. For each patient the colonization status with S. maltophilia was determined. The epidemiological and microbiological characteristics collected were compared between colonization statuses.

RESULTS

S. maltophilia was isolated in 90 patients (42 males, 48 females). Mean age at first colonization was 24.4±13.5 years. Annual prevalence since 2013 was high (16-17.9%), but stable. This high prevalence is mainly due to a high rate of intermittent colonization. Only 2.8% of CF patients showed chronic colonization, with significantly more frequent co-colonization by methicillin-susceptible Staphylococcus aureus (P<0.0001) and Pseudomonas aeruginosa (P<0.05). During chronic colonization, S. maltophilia acquired resistance to cotrimoxazole and β-lactams. Interestingly, there were cases of decolonization.

CONCLUSION

This is the first epidemiological report of S. maltophilia in a French CF center. Prevalence was stable but above the national average. Most cases were intermittent; chronic colonization was rare.

Antibiotic treatment for Stenotrophomonas maltophilia in people with cystic fibrosis

BACKGROUND

Stenotrophomonas maltophilia is one of the most common emerging multi-drug resistant organisms found in the lungs of people with cystic fibrosis and its prevalence is increasing. Chronic infection with Stenotrophomonas maltophilia has recently been shown to be an independent predictor of pulmonary exacerbation requiring hospitalization and antibiotics. However, the role of antibiotic treatment of Stenotrophomonas maltophilia infection in people with cystic fibrosis is still unclear. This is an update of a previously published review.

OBJECTIVES

The objective of our review is to assess the effectiveness of antibiotic treatment for Stenotrophomonas maltophilia in people with cystic fibrosis. The primary objective is to assess this in relation to lung function and pulmonary exacerbations in the setting of acute pulmonary exacerbations. The secondary objective is to assess this in relation to the eradication of Stenotrophomonas maltophilia.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis Trials Register, compiled from electronic database searches and handsearching of journals and conference abstract books. We also searched a registry of ongoing trials and the reference lists of relevant articles and reviews. Date of latest search: 03 March 2020.

SELECTION CRITERIA

Randomized controlled trials of Stenotrophomonas maltophilia mono-infection or Stenotrophomonas maltophilia co-infection with Pseudomonas aeruginosa in either the setting of an acute pulmonary exacerbation or a chronic infection treated with suppressive antibiotic therapy.

DATA COLLECTION AND ANALYSIS

Both authors independently assessed the trials identified by the search for potential inclusion in the review.

MAIN RESULTS

We identified only one trial of antibiotic treatment of pulmonary exacerbations that included people with cystic fibrosis with Stenotrophomonas maltophilia. However, this trial had to be excluded because data was not available per pathogen.

AUTHORS' CONCLUSIONS

This review did not identify any evidence regarding the effectiveness of antibiotic treatment for Stenotrophomonas maltophilia in people with cystic fibrosis. Until such evidence becomes available, clinicians need to use their clinical judgement as to whether or not to treat Stenotrophomonas maltophilia infection in people with cystic fibrosis. Randomized clinical trials are needed to address these unanswered clinical questions.

Evaluation of the Treatment of Stenotrophomonas maltophilia in Tracheostomy-Dependent Pediatric Patients

OBJECTIVE

Tracheostomy-dependent pediatric patients will often have respiratory cultures positive for Stenotrophomonas maltophilia (multidrug-resistant Gram-negative rod). There are limited data available to guide treatment in this population. The objective of this single-center, retrospective study was to evaluate if antibiotic treatment of S maltophilia improved clinical outcomes in tracheostomy-dependent pediatric patients.

METHODS

We included tracheostomy-dependent pediatric patients who had a respiratory culture positive for S maltophilia. Patients were divided into 2 groups: 1) treatment and 2) no treatment.

RESULTS

Forty patients with 55 encounters were included in this study. S maltophilia was treated with sulfamethoxazole-trimethoprim in 20 encounters (19 patients) and no antimicrobial treatment was given in 35 encounters (30 patients). The time to return to stable respiratory status was 5 days (0-10) (median [range]) in the treated group and 4 days (0-19) in the untreated group (p = 0.52). There was no statistically significant difference in time to baseline respiratory status between patients treated and those not treated for S maltophilia. There was no difference in hospital length of stay between patients who were or not treated.

CONCLUSIONS

Based on these results, these data would suggest that there might not be a benefit to treating cultures positive for S maltophilia in tracheostomy-dependent pediatric patients.

Epidemiological Trends and Resistance Associated with Stenotrophomonas maltophilia Bacteremia: A 10-Year Retrospective Cohort Study in a Tertiary-Care Hospital in Hungary

Stenotrophomonas maltophilia has been recognized as an emerging nosocomial pathogen in invasive infections of immunocompromised, severely debilitated patients with significant underlying illnesses. The first-choice drug in these infections is sulfamethoxazole-trimethoprim (SMX/TMP), and resistance to this antimicrobial is a daunting challenge for clinicians. The aim of this study was to assess the prevalence of S. maltophilia bacteremia and SMX/TMP-resistance levels at a tertiary-care university hospital. A total of 175 episodes of S. maltophilia bacteremia were identified (2008-2012: n = 82, 2013-2017: n = 93; p = 0.061), 52% of affected patients were 60 years of age, and had recent surgery, severe injuries or underlying conditions (malignant hematologic diseases and solid tumors) in their history. Sixteen percent of isolates were resistant to SMX/TMP (2008-2012: n = 13.8%, 2013-2017: n = 17.2%; p = 0.076), and out of the resistant strains, 32.7% were also resistant to levofloxacin and colistin. Our findings on the SMX/TMP-resistance were similar to global literature data.

Antimicrobial susceptibility of non-fermenting Gram-negative pathogens isolated from cystic fibrosis patients

Non-fermenting Gram-negative bacteria (NFGNB) are increasingly cultured in respiratory samples from cystic fibrosis (CF) patients. This study determined the antimicrobial susceptibility of clinical CF respiratory isolates from distinct geographical regions. A total of 286 isolates (106 Stenotrophomonas maltophilia, 100 Burkholderia spp., 59 Achromobacter spp., 12 Pandoraea spp., 9 Ralstonia spp.) from the Netherlands, Northern Ireland, Spain, USA and Australia were tested. MIC_50/90 values and susceptibility categorisation were determined. Trimethoprim/sulfamethoxazole (SXT) was the most active compound for all micro-organisms (MIC₅₀, 0.12-4 mg/L; MIC₉₀, 1-16 mg/L). For S. maltophilia, 47% and 62% of isolates were susceptible to SXT according to CLSI and EUCAST breakpoints, respectively. Ceftazidime presented lower susceptibility (35%; MIC₅₀, 32 mg/L; MIC₉₀, 256 mg/L). MIC₉₀ values for tobramycin and colistin were >128 mg/L and >16 mg/L, respectively. Regarding Burkholderia, 72%, 56% and 44% were susceptible to SXT, ceftazidime and meropenem, respectively. For both ceftazidime and meropenem, MIC₅₀ and MIC₉₀ values were within the intermediate or resistant category. The most active antibiotics for Achromobacter spp. were SXT (MIC₅₀, 0.5 mg/L; MIC₉₀, 8 mg/L) and imipenem (MIC₅₀, 2 mg/L; MIC₉₀, 8 mg/L). SXT, imipenem and ciprofloxacin were active against 12 Pandoraea spp. (MIC₅₀, 0.12-4 mg/L; MIC₉₀, 1-8 mg/L). Ciprofloxacin (MIC₅₀, 4 mg/L) and SXT (MIC₅₀, 1 mg/L) were the only active antibiotics for Ralstonia spp. There were no statistically significant differences in susceptibility rates between countries. NFGNB other than Pseudomonas aeruginosa are potential pathogens in CF. SXT was demonstrated to be the most active compound against these isolates.

Severe hepatic abscess: Conservative treatment of multi-organ infection by Stenotrophomonas maltophilia. A case report

Introduction

Stenotrophomonas Malthophilia (SM) is generally considered a nosocomial pathogen but it has also been reported as a cause of community-acquired systemic infection. We reported a rare case of SM multi-organ infection involving the liver and the left ocular region.

Presentation of the case

A 64 years old man presented with fever for 4 days and acute blindness of the left eye. We performed an abdomen and head CT scan that identified respectively a liver lesion in central region, likely a hepatic abscess, and inflammation process involving the left eye. After 5 days of antibiotic therapy, no improvement of the clinical condition was noted. A CT guided drainage of the hepatic abscess was performed. SM was identified in the content of the drain and selected antibiotic therapy with combination of tygecycline and TMP-SMX was immediately initiated.After 15 days of the selected therapy, the hepatic abscess and the left eye infection were completely resolved but unfortunately the patient reported permanent blindness.

Discussion

Several studies identified most of the SM infections as nosocomial, however that can be excluded in this case because the patient presented signs of severe systemic infection 72 h before the hospitalization. The conservative treatment, with a combination of CT guided drainage and selected antibiotic therapy, gave good results.

Conclusion

Although SM is thought to be a nosocomial pathogen, it can be involved in severe systemic sepsis affecting different organs outside the hospital setting. Fortunately, the combination of tigecycline with TMP-SMX seems to be the best therapeutic option.

Contact Allergy to Polymyxin B Among Patients Referred for Patch Testing

BACKGOUND

Polymyxin B is not included in most standard contact allergen series. The aim of this study was to determine the prevalence of contact sensitization to polymyxin B in a population of patients referred for patch testing.

METHODS

A retrospective cohort study design was used to collect data on 795 patients referred to the contact dermatitis clinic of the McGill University Health Centre, as well as to the office of one of the authors (L.M.), between March 2014 and November 2015. Patients were patch tested to the North American Contact Dermatitis Group baseline series and polymyxin B sulfate 3% in petrolatum.

RESULTS

Out of 795 tested individuals, 18 were allergic to polymyxin B, for a prevalence of 2.3%. The eruptions affected almost all body parts, but mostly the face. The degree of reaction ranged from 1+ to 2+. Isolated reactions to polymyxin B occurred in 9 (50%) patients, whereas reactions to bacitracin and polymyxin B were seen in the other 9. Only 1 patient reacted to bacitracin, polymyxin B, and neomycin (11.1%). Most reactions (12/18) were from past exposure to polymyxin B.

CONCLUSIONS

Allergic reactions to polymyxin B are not rare, and this antibiotic warrants inclusion in the standard patch testing series.

Evaluation of trimethoprim-sulfamethoxazole based combination therapy against Stenotrophomonas maltophilia: in vitro effects and clinical efficacy in cancer patients

OBJECTIVES

The aim of this study was to evaluate the in vitro effects and clinical efficacies of trimethoprim-sulfamethoxazole (SXT) combined with other antimicrobial agents against Stenotrophomonas maltophilia.

METHODS

In vitro analysis was conducted on 89 S. maltophilia strains isolated from blood and the respiratory tract between June 2012 and October 2014. Levofloxacin (LVX), ticarcillin-clavulanic acid (TIM), and minocycline (MIN) were selected for an examination of their effects when individually combined with SXT by the checkerboard method. In addition, 29 S. maltophilia bacteremia cases were reviewed and the clinical efficacies of SXT-based combination therapies were analyzed.

RESULTS

SXT+LVX showed synergy in 21, no interactions in 61, and antagonism in 7. SXT+TIM showed synergy in 71, and no interactions in 18. SXT+MIN showed synergy in 10, and no interactions in 79. The review of clinical data indicated that a combination of SXT+fluoroquinolone was not associated with improved prognosis compared with monotherapy.

CONCLUSIONS

The in vitro data indicated that SXT+TIM had beneficial microbiological effects and was not antagonistic. Our in vitro and clinical data analyses do not support the routine use of SXT+fluoroquinolone combination therapy for S. maltophilia infection.

Antibiotic treatment for Stenotrophomonas maltophilia in people with cystic fibrosis

BACKGROUND

Stenotrophomonas maltophilia is one of the most common emerging multi-drug resistant organisms found in the lungs of people with cystic fibrosis and its prevalence is increasing. Chronic infection with Stenotrophomonas maltophilia has recently been shown to be an independent predictor of pulmonary exacerbation requiring hospitalization and antibiotics. However, the role of antibiotic treatment of Stenotrophomonas maltophilia infection in people with cystic fibrosis is still unclear. This is an update of a previously published review.

OBJECTIVES

The objective of our review is to assess the effectiveness of antibiotic treatment for Stenotrophomonas maltophilia in people with cystic fibrosis. The primary objective is to assess this in relation to lung function and pulmonary exacerbations in the setting of acute pulmonary exacerbations. The secondary objective is to assess this in relation to the eradication of Stenotrophomonas maltophilia.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis Trials Register, compiled from electronic database searches and handsearching of journals and conference abstract books. We also searched a registry of ongoing trials and the reference lists of relevant articles and reviews.Date of latest search: 27 May 2016.

SELECTION CRITERIA

Any randomized controlled trial of Stenotrophomonas maltophilia mono-infection or Stenotrophomonas maltophilia co-infection with Pseudomonas aeruginosa in either the setting of an acute pulmonary exacerbation or a chronic infection treated with suppressive antibiotic therapy.

DATA COLLECTION AND ANALYSIS

Both authors independently assessed the trials identified by the search for potential inclusion in the review.

MAIN RESULTS

The initial search strategy identified only one trial of antibiotic treatment of pulmonary exacerbations that included people with cystic fibrosis with Stenotrophomonas maltophilia. However, this trial had to be excluded because data was not available per pathogen.

AUTHORS' CONCLUSIONS

This review did not identify any evidence regarding the effectiveness of antibiotic treatment for Stenotrophomonas maltophilia in people with cystic fibrosis. Until such evidence becomes available, clinicians need to use their clinical judgement as to whether or not to treat Stenotrophomonas maltophilia infection in people with cystic fibrosis. Randomized clinical trials are needed to address these unanswered clinical questions.

Update on infections caused by Stenotrophomonas maltophilia with particular attention to resistance mechanisms and therapeutic options

Stenotrophomonas maltophilia is a Gram-negative, biofilm-forming bacterium. Although generally regarded as an organism of low virulence, S. maltophilia is an emerging multi-drug resistant opportunistic pathogen in hospital and community settings, especially among immunocompromised hosts. Risk factors associated with S. maltophilia infection include underlying malignancy, cystic fibrosis, corticosteroid or immunosuppressant therapy, the presence of an indwelling central venous catheter and exposure to broad spectrum antibiotics. In this review, we provide a synthesis of information on current global trends in S. maltophilia pathogenicity as well as updated information on the molecular mechanisms contributing to its resistance to an array of antimicrobial agents. The prevalence of S. maltophilia infection in the general population increased from 0.8-1.4% during 1997-2003 to 1.3-1.68% during 2007-2012. The most important molecular mechanisms contributing to its resistance to antibiotics include β-lactamase production, the expression of Qnr genes, and the presence of class 1 integrons and efflux pumps. Trimethoprim/sulfamethoxazole (TMP/SMX) is the antimicrobial drug of choice. Although a few studies have reported increased resistance to TMP/SMX, the majority of studies worldwide show that S. maltophilia continues to be highly susceptible. Drugs with historically good susceptibility results include ceftazidime, ticarcillin-clavulanate, and fluoroquinolones; however, a number of studies show an alarming trend in resistance to those agents. Tetracyclines such as tigecycline, minocycline, and doxycycline are also effective agents and consistently display good activity against S. maltophilia in various geographic regions and across different time periods. Combination therapies, novel agents, and aerosolized forms of antimicrobial drugs are currently being tested for their ability to treat infections caused by this multi-drug resistant organism.

Mechanisms of antimicrobial resistance in Gram-negative bacilli

The burden of multidrug resistance in Gram-negative bacilli (GNB) now represents a daily issue for the management of antimicrobial therapy in intensive care unit (ICU) patients. In Enterobacteriaceae, the dramatic increase in the rates of resistance to third-generation cephalosporins mainly results from the spread of plasmid-borne extended-spectrum beta-lactamase (ESBL), especially those belonging to the CTX-M family. The efficacy of beta-lactam/beta-lactamase inhibitor associations for severe infections due to ESBL-producing Enterobacteriaceae has not been adequately evaluated in critically ill patients, and carbapenems still stands as the first-line choice in this situation. However, carbapenemase-producing strains have emerged worldwide over the past decade. VIM- and NDM-type metallo-beta-lactamases, OXA-48 and KPC appear as the most successful enzymes and may threaten the efficacy of carbapenems in the near future. ESBL- and carbapenemase-encoding plasmids frequently bear resistance determinants for other antimicrobial classes, including aminoglycosides (aminoglycoside-modifying enzymes or 16S rRNA methylases) and fluoroquinolones (Qnr, AAC(6′)-Ib-cr or efflux pumps), a key feature that fosters the spread of multidrug resistance in Enterobacteriaceae. In non-fermenting GNB such as Pseudomonas aeruginosa, Acinetobacter baumannii and Stenotrophomonas maltophilia, multidrug resistance may emerge following the sole occurrence of sequential chromosomal mutations, which may lead to the overproduction of intrinsic beta-lactamases, hyper-expression of efflux pumps, target modifications and permeability alterations. P. aeruginosa and A. baumannii also have the ability to acquire mobile genetic elements encoding resistance determinants, including carbapenemases. Available options for the treatment of ICU-acquired infections due to carbapenem-resistant GNB are currently scarce, and recent reports emphasizing the spread of colistin resistance in environments with high volume of polymyxins use elicit major concern.

Colistimethate sodium for the treatment of chronic pulmonary infection in cystic fibrosis: an evidence-based review of its place in therapy

Chronic bacterial respiratory-tract infections are a major driving force in the pathogenesis of cystic fibrosis (CF) lung disease and promote chronic lung-function decline, destruction, and progression to respiratory failure at a premature age. Gram-negative bacteria colonizing the airways in CF are a major problem in CF therapy due to their tendency to develop a high degree of resistance to antibiotic agents over time. Pseudomonas aeruginosa is the dominating bacterial strain infecting the CF lung from early childhood on, and multiresistant strains frequently develop after years of therapy. Colistin has been used for treating pulmonary bacterial infections in CF for decades due to its very good Gram-negative activity. However, drawbacks include concerns regarding toxicity when being applied systemically, and the lack of approval for application by inhalation in the USA for many years. Other antibiotic substances for systemic use are available with good to excellent Gram-negative and anti-Pseudomonas activity, while there are only three substances approved for inhalation use in the treatment of chronic pulmonary infection with proven benefit in CF. The emergence of multiresistant strains leaving nearly no antibiotic substance as a treatment option, the limited number of antibiotics with high activity against P. aeruginosa, the concerns about increasing the risk of antibiotic resistance by continuous antibiotic therapy, the development of new drug formulations and drug-delivery devices, and, finally, the differing treatment strategies used in CF centers call for defining the place of this "old" drug, colistimethate, in today's CF therapy. This article reviews the available evidence to reflect on the place of colistimethate sodium in the therapy of chronic pulmonary infection in CF.

Stenotrophomonas maltophilia in Mexico: antimicrobial resistance, biofilm formation and clonal diversity

Stenotrophomonas maltophilia is an important multidrug-resistant nosocomial pathogen associated with high mortality. Our aim was to examine antimicrobial susceptibility, biofilm production and clonal relatedness of clinical isolates of S. maltophilia. S. maltophilia isolates were collected between 2006 and 2013 from two tertiary care hospitals in Mexico. Antimicrobial susceptibility was evaluated by the broth microdilution method. PCR was used to determine the presence of β-lactamase genes L1 and L2. Biofilm formation was assessed with crystal violet staining. Clonal relatedness was determined by PFGE. Among the 119 collected S. maltophilia isolates, 73 (61.3%) were from the respiratory tract. Resistance levels exceeded 75% for imipenem, meropenem, ampicillin, aztreonam, gentamicin and tobramycin. Resistance to trimethoprim-sulfamethoxazole was 32.8%. L1 and L2 genes were detected in 77.1% (91/118) and 66.9% (79/118) of isolates, respectively. All S. maltophilia strains were able to produce biofilms. Strains were classified as weak (47.9%, 57/119), moderate (38.7%, 46/119), or strong (13.4%, 16/119) biofilm producers. A total of 89 distinct PFGE types were identified and 21.6% (22/102) of the isolates were distributed in nine clusters. This is the first study in Mexico to reveal characteristics of clinical isolates of S. maltophilia. Clonal diversity data indicate low cross-transmission of S. maltophilia in a hospital setting. The high antibiotic resistance underscores the need for continuous surveillance of S. maltophilia in hospital settings in Mexico.

When does 2 plus 2 equal 5? A review of antimicrobial synergy testing

In this age of emerging antibiotic resistance, limited therapeutic options exist for treating multidrug-resistant organisms. Combination therapy is commonly employed to manage these infections despite little laboratory guidance as to the efficacy of this approach. Synergy testing methods have been used to assess the interaction of antibiotic combinations in vitro. This review will discuss the four primary methods used to assess synergy, as well as the data that exist for testing of cystic fibrosis. In the final analysis, this review concludes that there is not enough evidence to endorse synergy testing for routine clinical use.

Antibiotic treatment for Stenotrophomonas maltophilia in people with cystic fibrosis

BACKGROUND

Stenotrophomonas maltophilia is one of the most common emerging multi-drug resistant organisms found in the lungs of people with cystic fibrosis and its prevalence is increasing. Chronic infection with Stenotrophomonas maltophilia has recently been shown to be an independent predictor of pulmonary exacerbation requiring hospitalization and antibiotics. However, the role of antibiotic treatment of Stenotrophomonas maltophilia infection in people with cystic fibrosis is still unclear.

OBJECTIVES

The objective of our review is to assess the effectiveness of antibiotic treatment for Stenotrophomonas maltophilia in people with cystic fibrosis. The primary objective is to assess this in relation to lung function and pulmonary exacerbations in the setting of acute pulmonary exacerbations. The secondary objective is to assess this in relation to the eradication of Stenotrophomonas maltophilia.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis Trials Register, compiled from electronic database searches and handsearching of journals and conference abstract books. We also searched a registry of ongoing trials and the reference lists of relevant articles and reviews.Date of latest search: 20 February 2014.

SELECTION CRITERIA

Any randomized controlled trial of Stenotrophomonas maltophilia mono-infection or Stenotrophomonas maltophilia co-infection with Pseudomonas aeruginosa in either the setting of an acute pulmonary exacerbation or a chronic infection treated with suppressive antibiotic therapy.

DATA COLLECTION AND ANALYSIS

Both authors independently assessed the trials identified by the search for potential inclusion in the review.

MAIN RESULTS

The initial search strategy identified only one study of antibiotic treatment of pulmonary exacerbations that included cystic fibrosis patients with Stenotrophomonas maltophilia. However, this study had to be excluded because data was not available per pathogen.

AUTHORS' CONCLUSIONS

This review did not identify any evidence regarding the effectiveness of antibiotic treatment for Stenotrophomonas maltophilia in people with cystic fibrosis. Until such evidence becomes available, clinicians need to use their clinical judgement as to whether or not to treat Stenotrophomonas maltophilia infection in patients with cystic fibrosis. Randomized clinical trials are needed to address these unanswered clinical questions.

Susceptibility of Stenotrophomonas maltophilia clinical strains in China to antimicrobial combinations

We aimed to investigate the activity levels of several combinations of antimicrobials against Stenotrophomonas maltophilia. In this study, the antimicrobial susceptibility of S. maltophilia clinical isolates was determined, and the synergistic activity of three pairs of antimicrobial combinations was evaluated by the fractional inhibitory concentration index (FICI). The antimicrobial susceptibility in vitro against 83 S. maltophilia strains was greater for minocycline (80·7%) than for trimethoprim-sulfamethoxazole (51·8%), and levofloxacin (50·6%). The rate of resistance was highest for ticarcillin-clavulanate and ceftazidime (63·8%) and resistance to trimethoprim-sulfamethoxazole (TMP-SMX) was 48·2%. All three combinations were tested against susceptible isolates. Two of the combinations, TMP-SMX+ceftazidime and levofloxacin+ceftazidime were more effective than the combination of TMP-SMX+levofloxacin. We recommend acquiring more clinical data in order to explore combination therapy, which is a promising treatment of S. maltophilia infections.

Life-threatening hemorrhagic pneumonia caused by Stenotrophomonas maltophilia in the treatment of hematologic diseases

Since the late 1990s, Stenotrophomonas maltophilia (S. maltophilia) has become one of the most common nonfermenting Gram-negative bacilli that cause opportunistic infection. Patients with hematologic diseases are the most risky candidate for S. maltophilia pneumonia or sepsis because of chemotherapy-induced neutropenia or immunodeficiency. Frequent exposure to broad-spectrum antibiotics and prolonged insertion of central venous catheter further enhance the risk of S. maltophilia infection. One of the most severe S. maltophilia infections is hemorrhagic pneumonia. This type of infection is mostly fatal because of pulmonary alveolar hemorrhage that leads to acute respiratory failure. Furthermore, S. maltophilia exhibits a high-level intrinsic resistance to conventional antibiotics such as β-lactams and aminoglycosides and, more recently, the increasing acquired resistance to co-trimoxazole and quinolones. According to our experienced and previously reported cases, all of the patients with hemorrhagic pneumonia caused by S. maltophilia had a fatal course within a few days after the onset of the pneumonia. In this article, we perform a systematic review on a total 30 cases of hemorrhagic pneumonia induced by S. maltophilia from our institutions and the literature, and we describe its early diagnosis, prophylaxis, and recommended therapeutic strategy for the infection in the treatment of hematologic disease.

Monotherapy with fluoroquinolone or trimethoprim-sulfamethoxazole for treatment of Stenotrophomonas maltophilia infections

The treatment of choice for Stenotrophomonas maltophilia is trimethoprim-sulfamethoxazole (SXT). Fluoroquinolones (FQs) have in vitro activity against S. maltophilia; however, there is limited published information on their effectiveness. The purpose of this study is to compare the effectiveness of FQs and SXT for the treatment of S. maltophilia. A retrospective review of 98 patients with S. maltophilia infections who received SXT or FQ monotherapy was conducted. Patients ≥18 years old with a positive culture for S. maltophilia and clinical signs of infection who received treatment for ≥48 h were included. Microbiological cure and clinical response were evaluated at the end of therapy (EOT). In-hospital mortality and isolation of nonsusceptible isolates were also evaluated. Thirty-five patients received SXT, and 63 patients received FQ; 48 patients received levofloxacin, and 15 patients received ciprofloxacin. The most common infection was pulmonary. The overall microbiological cure rate at EOT was 63%. Thirteen of 20 patients (65%) who received SXT and 23 of 37 patients (62%) who received FQ had microbiological cure at EOT (P = 0.832). The overall clinical success rate was 55%, 52% for those who received FQ and 61% for those who received SXT (P = 0.451). In-hospital mortality was 24%, with similar rates in the two groups (25% for FQ versus 22% for SXT; P = 0.546). Development of resistance on repeat culture was 30% for FQ and 20% for SXT (P = 0.426). Fluoroquinolone and SXT monotherapies may be equally effective for the treatment of S. maltophilia infections. Resistance was documented in subsequent isolates of S. maltophilia in both groups.

Current dilemmas in antimicrobial therapy in cystic fibrosis

The majority of cystic fibrosis (CF)-related morbidity and mortality is caused by pulmonary damage due to recurrent and chronic infections. Considerable improvements in the survival of individuals with CF have been achieved in recent decades, some of which may be due to better management of common pathogens such as Staphylococcus aureus and Pseudomonas aeruginosa. While the search continues for the optimal approach for prophylaxis, eradication and maintenance treatment of infections, there are several unanswered questions, posing dilemmas related to various therapeutic choices. Microbes pose additional challenges by adapting to CF lungs and developing treatment resistance. Several new, highly antimicrobial-resistant pathogens have emerged. Their pathogenic role in the progression of CF lung disease is not yet clear and effective treatment approaches have not been defined. There is an urgent need for well-designed comparative clinical trials of new antibiotic strategies.

Biofilm compared to conventional antimicrobial susceptibility of Stenotrophomonas maltophilia Isolates from cystic fibrosis patients

Stenotrophomonas maltophilia is a multidrug-resistant organism increasingly isolated from the lungs of cystic fibrosis (CF) patients. One hundred twenty-five S. maltophilia isolates from 85 CF patients underwent planktonic and biofilm susceptibility testing against 9 different antibiotics, alone and in double antibiotic combinations. When S. maltophilia isolates were grown as a biofilm, 4 of the 10 most effective antibiotic combinations included high-dose levofloxacin and 7 of the 10 combinations included colistin at doses achievable by aerosolization.

Antimicrobial susceptibility of stenotrophomonas maltophilia isolates from Korea, and the activity of antimicrobial combinations against the isolates

The aim of this study was to determine antimicrobial susceptibility of recent clinical Stenotrophomonas maltophilia isolates from Korea, and to compare the activity levels of several combinations of antimicrobials. A total of 206 non-duplicate clinical isolates of S. maltophilia was collected in 2010 from 11 university hospitals. Antimicrobial susceptibility testing was performed using the Clinical Laboratory Standards Institute agar dilution method. In vitro activity of antimicrobial combinations was tested using the checkerboard method. The susceptibility rates to trimethoprim-sulfamethoxazole and minocycline were 96% and 99%, respectively. The susceptibility rate to levofloxacin was 64%. All of four antimicrobial combinations showed synergy against many S. maltophilia isolates. A combination of trimethoprim-sulfamethoxazole plus ticarcillin-clavulanate was most synergistic among the combinations. None of the combinations showed antagonistic activity. Therefore, some of the combinations may be more useful than individual drugs in the treatment of S. maltophilia infection. Further clinical studies are warranted to validate our in vitro test results.

Combination therapy for treatment of infections with gram-negative bacteria

Combination antibiotic therapy for invasive infections with Gram-negative bacteria is employed in many health care facilities, especially for certain subgroups of patients, including those with neutropenia, those with infections caused by Pseudomonas aeruginosa, those with ventilator-associated pneumonia, and the severely ill. An argument can be made for empiric combination therapy, as we are witnessing a rise in infections caused by multidrug-resistant Gram-negative organisms. The wisdom of continued combination therapy after an organism is isolated and antimicrobial susceptibility data are known, however, is more controversial. The available evidence suggests that the greatest benefit of combination antibiotic therapy stems from the increased likelihood of choosing an effective agent during empiric therapy, rather than exploitation of in vitro synergy or the prevention of resistance during definitive treatment. In this review, we summarize the available data comparing monotherapy versus combination antimicrobial therapy for the treatment of infections with Gram-negative bacteria.

Stenotrophomonas maltophilia in Malaysia: molecular epidemiology and trimethoprim-sulfamethoxazole resistance

OBJECTIVES

Stenotrophomonas maltophilia is a recently identified nosocomial pathogen in Malaysia. Despite limited pathogenicity, its rate of isolation has increased in recent years. The aim of this study was to investigate the antibiotic susceptibility patterns, antibiotic resistance determinants, and the epidemiology of S. maltophilia at the largest tertiary care hospital in Malaysia.

METHODS

This study was carried out from January to December 2008. Sixty-four S. maltophilia isolates were investigated for their antibiotic susceptibility patterns by disk diffusion test and E-test. The antibiotic resistance mechanism for trimethoprim-sulfamethoxazole (TMP-SMX) was assessed by PCR for sul1, sul2, qac/smr, and class 1 integrons in general. Epidemiological relatedness among isolates was determined by pulsed-field gel electrophoresis (PFGE).

RESULTS

The highest number of S. maltophilia infections was observed in the intensive care unit (ICU) (n=13; 20.3%), while the lowest number of infections was seen in the neurology, psychiatric, and dermatology wards (each n=1; 1.6%). All isolates were susceptible to minocycline. One isolate was resistant to TMP-SMX with a minimum inhibitory concentration (E-test) >32 mg/l. The strain carried the sul1 gene and class 1 integron. None of the isolates were positive for the qac/smr genes. Although the data suggest the potential for patient to patient transmission, most of the S. maltophilia strains showed unrelated PFGE patterns and were considered to be genetically diverse.

CONCLUSION

The increasing number of S. maltophilia isolates seen in the ICU, their resistance to mainstay antibiotics, their genetically diverse nature, and possible cross-transmission within the hospital, strongly underscores the need for continuous surveillance for S. maltophilia in the hospital setting.

Stenotrophomonas maltophilia infections in a general hospital: patient characteristics, antimicrobial susceptibility, and treatment outcome

Introduction

Stenotrophomonas maltophilia is acquiring increasing importance as a nosocomial pathogen.

Methods

We retrospectively studied the characteristics and outcome of patients with any type of S. maltophilia infection at the University Hospital of Heraklion, Crete, Greece, between 1/2005–12/2010. S. maltophilia antimicrobial susceptibility was tested with the agar dilution method. Prognostic factors for all-cause in-hospital mortality were assessed with multivariate logistic regression.

Results

Sixty-eight patients (median age: 70.5 years; 64.7% males) with S. maltophilia infection, not related to cystic fibrosis, were included. The 68 patients were hospitalized in medical (29.4%), surgical (26.5%), hematology/oncology departments (23.5%), or the intensive care units (ICU; 20.6%). The most frequent infection types were respiratory tract (54.4%), bloodstream (16.2%), skin/soft tissue (10.3%), and intra-abdominal (8.8%) infection. The S. maltophilia-associated infection was polymicrobial in 33.8% of the cases. In vitro susceptibility was higher to colistin (91.2%), trimethoprim/sulfamethoxazole and netilmicin (85.3% each), and ciprofloxacin (82.4%). The empirical and the targeted treatment regimens were microbiologically appropriate for 47.3% and 63.6% of the 55 patients with data available, respectively. Most patients received targeted therapy with a combination of agents other than trimethoprim/sulfamethoxazole. The crude mortality and the mortality and the S. maltophilia infection-related mortality were 14.7% and 4.4%, respectively. ICU hospitalization was the only independent prognostic factor for mortality.

Conclusion

S. maltophilia infection in a general hospital can be associated with a good prognosis, except for the patients hospitalized in the ICU. Combination reigmens with fluoroquinolones, colistin, or tigecycline could be alternative treatment options to trimethoprim/sulfamethoxazole.

Antibiotic treatment for Stenotrophomonas maltophilia in people with cystic fibrosis

BACKGROUND

Stenotrophomonas maltophilia is one of the most common emerging multi-drug resistant organisms found in the lungs of people with cystic fibrosis and its prevalence is increasing. Chronic infection with Stenotrophomonas maltophilia has recently been shown to be an independent predictor of pulmonary exacerbation requiring hospitalization and antibiotics. However, the role of antibiotic treatment of Stenotrophomonas maltophilia infection in people with cystic fibrosis is still unclear.

OBJECTIVES

The objective of our review is to assess the effectiveness of antibiotic treatment for Stenotrophomonas maltophilia in people with cystic fibrosis. The primary objective is to assess this in relation to lung function and pulmonary exacerbations in the setting of acute pulmonary exacerbations. The secondary objective is to assess this in relation to the eradication of Stenotrophomonas maltophilia.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis Trials Register, compiled from electronic database searches and handsearching of journals and conference abstract books. We also searched a registry of ongoing trials and the reference lists of relevant articles and reviews.Date of latest search: 06 July 2011.

SELECTION CRITERIA

Any randomized controlled trial of Stenotrophomonas maltophilia mono-infection or Stenotrophomonas maltophilia co-infection with Pseudomonas aeruginosa in either the setting of an acute pulmonary exacerbation or a chronic infection treated with suppressive antibiotic therapy.

DATA COLLECTION AND ANALYSIS

Both authors independently assessed the trials identified by the search for potential inclusion in the review.

MAIN RESULTS

The initial search strategy identified only one study of antibiotic treatment of pulmonary exacerbations that included cystic fibrosis patients with Stenotrophomonas maltophilia. However, this study had to be excluded because data was not available per pathogen.

AUTHORS' CONCLUSIONS

This review did not identify any evidence regarding the effectiveness of antibiotic treatment for Stenotrophomonas maltophilia in people with cystic fibrosis. Until such evidence becomes available, clinicians need to use their clinical judgement as to whether or not to treat Stenotrophomonas maltophilia infection in patients with cystic fibrosis. Randomized clinical trials are needed to address these unanswered clinical questions.

Combination antimicrobial susceptibility testing of multidrug-resistant Stenotrophomonas maltophilia from cystic fibrosis patients

Stenotrophomonas maltophilia is increasingly being isolated from the respiratory tract of individuals with cystic fibrosis, and, because of its multidrug-resistant nature, the selection of suitable treatment regimens can be problematical. Etest methodology was used to facilitate MIC and antimicrobial combination testing on 80 isolates of S. maltophilia cultured from the respiratory tract of Scottish individuals with cystic fibrosis between 2001 and 2010. The overall rate of susceptibility for the 1,410 MIC tests was 23.1%, and resistance was 68.9%. The most active antimicrobials were minocycline, co-trimoxazole, and doxycycline, with 92.4%, 87.3%, and 58.8% of isolates being susceptible, respectively. Of the 517 combinations, 13.2% were synergistic, with the most synergistic being ticarcillin/clavulanate plus aztreonam (91.7% synergistic), ticarcillin/clavulanate plus colistin (40%), and ticarcillin/clavulanate plus levofloxacin (19.4%). Colistin plus tobramycin was the only antagonistic combination (0.2%). By the median susceptible breakpoint index, the most active combinations were minocycline plus co-trimoxazole (median index, 20), minocycline plus piperacillin-tazobactam (median, 20), and co-trimoxazole plus ceftazidime (median, 16.5). The increasing problem of multidrug resistance in organisms recovered from the respiratory tracts of individuals with cystic fibrosis is not going to go away. Current susceptibility testing methods do not address the slow-growing organisms associated with chronic infection, and interpretive standards are based on achievable blood levels of antimicrobials. Addressing these issues specifically for organisms recovered from the respiratory tracts of individuals with cystic fibrosis should lead to better therapeutic outcomes and improved wellbeing of individuals with cystic fibrosis.

Rapidly progressive fatal hemorrhagic pneumonia caused by Stenotrophomonas maltophilia in hematologic malignancy

BACKGROUND

Pneumonia caused by Stenotrophomonas maltophilia is rare, but can be lethal in severely immunocompromised patients. However, its clinical course remains unclear.

PATIENTS AND METHODS

Patients with pneumonia caused by S. maltophilia in Toranomon Hospital (890 beds, Tokyo, Japan) were reviewed retrospectively between April 2006 and March 2010.

RESULTS

During the study period, 10 cases of S. maltophilia pneumonia were identified. Seven patients had acute myeloid leukemia, 2 had myelodysplastic syndrome, and 1 had malignant lymphoma. All patients developed symptoms after allogeneic hematopoietic stem cell transplantation (HSCT). Five patients received first cord blood transplantation (CBT), 4 patients received second CBT, and 1 patient received first peripheral blood stem cell transplantation (PBSCT). The overall incidence of S. maltophilia pneumonia among 508 patients who received HSCT during the period was 2.0%. The incidence was 0% (0/95) in patients after bone marrow transplantation, 0.8% (1/133) after PBSCT, and 3.2% (9/279) after CBT. Pneumonia developed a median of 13.5 days (range, 6-40) after transplantation. At onset, the median white blood cell count was 10/μL (range, 10-1900), and the median neutrophil count was 0/μL (range, 0-1720). In all patients, S. maltophilia bacteremia developed with bloody sputum or hemoptysis. The 28-day mortality rate was 100%; the median survival after onset of pneumonia was 2 days (range, 1-10).

CONCLUSIONS

Hemorrhagic S. maltophilia pneumonia rapidly progresses and is fatal in patients with hematologic malignancy. Attention should be particularly paid to the neutropenic phase early after HSCT or prolonged neutropenia due to engraftment failure. A prompt trimethoprim-sulfamethoxazole-based multidrug combination regimen should be considered to rescue suspected cases of S. maltophilia pneumonia in these severely immunosuppressed patients.

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.

Expression of Sme efflux pumps and multilocus sequence typing in clinical isolates of Stenotrophomonas maltophilia

BACKGROUND

Stenotrophomonas maltophilia has emerged as an important opportunistic pathogen, which causes infections that are often difficult to manage because of the inherent resistance of the pathogen to a variety of antimicrobial agents. In this study, we analyzed the expressions of smeABC and smeDEF and their correlation with antimicrobial susceptibility. We also evaluated the genetic relatedness and epidemiological links among 33 isolates of S. maltophilia.

METHODS

In total, 33 S. maltophilia strains were isolated from patients in a tertiary hospital in Daejeon. Minimum inhibitory concentrations (MICs) of 11 antimicrobial agents were determined by using agar dilution method and E-test (BioMérieux, France). Real-time PCR analysis was performed to evaluate the expression of the Sme efflux systems in the S. maltophilia isolates. Additionally, an epidemiological investigation was performed using multilocus sequence typing (MLST) assays.

RESULTS

The findings of susceptibility testing showed that the majority of the S. maltophilia isolates were resistant to β-lactams and aminoglycosides. Twenty-one clinical isolates overexpressed smeABC and showed high resistance to ciprofloxacin. Moreover, a high degree of genetic diversity was observed among the S. maltophilia isolates; 3 sequence types (STs) and 23 allelic profiles were observed.

CONCLUSIONS

The smeABC efflux pump was associated with multidrug resistance in clinical isolates of S. maltophilia. In particular, smeABC efflux pumps appear to perform an important role in ciprofloxacin resistance of S. maltophilia. The MLST scheme for S. maltophilia represents a discriminatory typing method with stable markers and is appropriate for studying population structures.

Stenotrophomonas maltophilia: emerging disease patterns and challenges for treatment

Stenotrophomonas maltophilia is a ubiquitous organism associated with opportunistic infections. In the immunocompromised host, increasing prevalence and severity of illness is observed, particularly opportunistic bloodstream infections and pneumonia syndromes. In this article, the classification and microbiology are outlined, together with clinical presentation, outcomes and management of infections due to S. maltophilia. Although virulence mechanisms and the genetic basis of antibiotic resistance have been identified, a role for standardized and uniform reporting of antibiotic sensitivity is not defined. Infections due to S. maltophilia have traditionally been treated with trimethoprim-sulfamethoxazole, ticarcillin-clavulanic acid, or fluoroquinolone agents. The use of combination therapies, newer fluoroquinolone agents and tetracycline derivatives is discussed. Finally, measures to prevent transmission of S. maltophilia within healthcare facilities are reported, especially in at-risk patient populations.

Chronic Stenotrophomonas maltophilia infection and exacerbation outcomes in cystic fibrosis

BACKGROUND

Chronic Stenotrophomonas maltophilia infection is a risk factor for pulmonary exacerbation in cystic fibrosis (CF) but its impact on subsequent clinical outcomes is unknown. The aim of this study was to determine the effect of chronic S. maltophilia infection and associated antimicrobial therapy on the recovery of forced expiratory lung volume in 1s (FEV(1)) following pulmonary exacerbation.

METHODS

This was a retrospective cohort study of patients with CF followed at The Hospital for Sick Children and St. Michael's Hospital from 1997 to 2008. The primary outcome was the difference in FEV(1) percent predicted from baseline to follow up after a pulmonary exacerbation. Secondary outcomes for the effect of antimicrobial therapy included time to subsequent exacerbation.

RESULTS

There were 1667 pulmonary exacerbations in 440 CF patients. Patients with chronic S. maltophilia infection did not recover their baseline FEV(1) following 31% of exacerbations and had an overall mean FEV(1) decline of 1.84% predicted after exacerbation. Older (p=0.02), female (p=0.02) patients with lower BMI z score (p=0.002) and Burkholderia cepacia complex infection (p=0.005), but not chronic S. maltophilia infection (p=0.86), had a greater decrease in follow up FEV(1)% pred compared to baseline. The number of days of antibiotic therapy against S. maltophilia during a pulmonary exacerbation was not associated with a significant difference in the FEV(1) recovery (p=0.69) or with a longer time to subsequent pulmonary exacerbation (p=0.56).

CONCLUSIONS

Although CF patients experience a significant decline in lung function following exacerbation, chronic S. maltophilia infection and associated antimicrobial therapy do not affect subsequent lung function recovery.

Clinical and microbiologic outcomes in trauma patients treated for Stenotrophomonas maltophilia ventilator-associated pneumonia

STUDY OBJECTIVES

To determine clinical and microbiologic plus clinical success rates in critically ill trauma patients who received treatment for Stenotrophomonas maltophilia ventilator-associated pneumonia (VAP).

DESIGN

Retrospective medical record review.

SETTING

Level I trauma intensive care unit of a large academic medical center.

PATIENTS

A total of 101 patients who developed S. maltophilia VAP between January 1997 and December 2007.

MEASUREMENTS AND MAIN RESULTS

Patients' baseline demographic and clinical characteristics, as well as characteristics of their VAP, were documented. The primary study outcome was the rate of clinical success in patients with S. maltophilia VAP; a secondary outcome was microbiologic plus clinical success rate in these patients. Standard definitions were employed to determine these outcomes related to VAP treatment. The study population had higher injury severity scores and a higher rate of traumatic brain injury than is typically observed in the study's intensive care unit. The median time to diagnosis of S. maltophilia VAP was 15 days (interquartile range 11-24 days). Stenotrophomonas maltophilia was the sole organism isolated in 34% of patients; the other patients had polymicrobial VAP. Despite inadequate empiric antibiotic therapy being administered to 97% of the patients, the overall clinical success rate was 87%. The microbiologic plus clinical success rate was 82%. The most common treatments for S. maltophilia VAP were trimethoprim-sulfamethoxazole (77 patients received monotherapy, 9 received combination therapy) and ciprofloxacin (6 patients received monotherapy, 8 received combination therapy); all-cause and VAP-related mortality rates were 13% and 7%, respectively.

CONCLUSION

Critically ill trauma patients with S. maltophilia VAP responded well to therapy despite high rates of inadequate empiric antibiotic administration. Trimethoprim-sulfamethoxazole was the most common therapy, but clinical success rates did not differ significantly based on antibiotic selection. This study adds significantly to the available S. maltophilia VAP outcomes data.

Challenging and emerging pathogens in cystic fibrosis

Cystic fibrosis (CF) lung disease is characterised by chronic inflammation and infection. Patients are predominantly infected by specific pathogens, of which Staphylococcus aureus and Pseudomonas aeruginosa are the most important. In recent years however there has been an increasing number of reports on potentially emerging and challenging pathogens like Stenotrophomonas maltophilia, Non-tuberculous mycobacteria, highly prevalent P. aeruginosa clones, methicillin resistant Staphylococcus aureus and Burkholderia cepacia. Also, a role for viral infections in the pathogenesis of CF lung disease has increasingly been recognised. It is not always clear whether or how these pathogens influence the progression of CF lung disease and how they should be treated. In this review, the epidemiology and clinical impact of these pathogens is discussed. Furthermore, treatment strategies of these pathogens in a CF setting are reviewed.

Discrepancies between various methods in susceptibility testing and epidemiological analysis of Stenotrophomonas maltophilia clinical isolates

The susceptibility of 25 Stenotrophomonas maltophilia (S. maltophilia) clinical isolates to four different antimicrobials (trimethoprim/sulfomethoxazole, piperacillin/tazobactam, ceftazidime, ciprofloxacin) were investigated by disk diffusion, E-test and commercial Sensititre and PASCO broth microdilution techniques. Discrepancies between the results of broth microdilution and the other methods studied were characterized as very major, major and minor errors. Using the broth microdilution as the reference method, 24% of the isolates were found susceptible to trimethoprim/ sulfamethoxazole, 24% to ceftazidime, 0% to piperacillin/tazobactam and 12% to ciprofloxacin. Good correlation was observed between the two broth microdilution Sensititre and PASCO for all antibiotics tested. Disc diffusion and E-test generated inconsistent results for all agents except trimethoprim/sulfamethoxazole. A great genomic diversity was demonstrated within the S. maltophilia strains tested. Although our results confirm that trimethoprim-sulfamethoxazole had some in vitro activity against S. maltophilia, further clinical studies are necessary to evaluate the clinical efficacy of these compounds for the treatment of S. maltophilia infections, since no randomized controlled trials have been carried out and no correlation between the clinical response and susceptibility testing results has been reported. Furthermore, the high genomic diversity observed in the S. maltophilia strains indicates the need for careful epidemiological evaluation especially in nosocomial outbreaks.