Trimethoprim-sulfamethoxazole in the treatment of Stenotrophomonas maltophilia osteomyelitis

Global prevalence and distribution of antibiotic resistance among clinical isolates of Stenotrophomonas maltophilia: A systematic review and meta-analysis

OBJECTIVES

Stenotrophomonas maltophilia (S. maltophilia), an opportunistic pathogen, causes infection in patients undergoing immunosuppressive therapy, mechanical ventilation, or catheters and in long-term hospitalized patients. Due to its extensive resistance to various antibiotics and chemotherapeutic agents, S. maltophilia is challenging to treat. Using case reports, case series, and prevalence studies, the current study provides a systematic review and meta-analysis of antibiotic resistance profiles across clinical isolates of S. maltophilia.

METHODS

A systematic literature search was performed for original research articles published in Medline, Web of Science, and Embase databases from 2000 to 2022. Statistical analysis was performed using STATA 14 software to report antibiotic resistance of S. maltophilia clinical isolates worldwide.

RESULTS

223 studies (39 case reports/case series and 184 prevalence studies) were collected for analysis. A meta-analysis of prevalence studies demonstrated that the most antibiotic resistance worldwide was to levofloxacin, trimethoprim-sulfamethoxazole (TMP/SMX), and minocycline (14.4%, 9.2%, and 1.4%, respectively). Resistance to TMP/SMX (36.84%), levofloxacin (19.29%), and minocycline (1.75%) were the most prevalent antibiotic resistance types found in evaluated case reports/case series studies. The highest resistance rate to TMP/SMX was reported in Asia (19.29%), Europe (10.52%), and America (7.01%), respectively.

CONCLUSION

Considering the high resistance to TMP/SMX, more attention should be paid to patients' drug regimens to prevent the emergence of multidrug-resistant S. maltophilia isolates.

Osteomyelitis due to Stenotrophomonas maltophilia treated with trimethoprim-sulfamethoxazole monotherapy

Stenotrophomonas maltophilia is an opportunistic infection commonly encountered in various systems of the human body and has been noted to be a rare cause of osteomyelitis. This report examines a rare case of osteomyelitis of the foot caused by S. maltophilia from a poorly managed foot wound and highlights the successful treatment of this condition with trimethoprim-sulfamethoxazole monotherapy.

Stenotrophomonas Maltophilia and Urinary Tract Infections: A Systematic Review

Stenotrophomonas maltophilia, a gram-negative bacillus well known to cause respiratory tract infections, is increasingly being reported to cause urinary tract infections (UTI). In our review of the literature comprising six articles, males were more prone to developing UTIs, with the mean age of the patients being 62.5 ±18.9 years. While several risk factors have been associated with the development of the disease, patients with underlying urological or nephrological diseases tend to develop a more severe illness. The organism was sensitive to trimethoprim-sulfamethoxazole (TMP-SMX) in the majority of cases. This systematic review also aims to shed light on the possible mechanisms of resistance adopted by the bacteria, modes of transmission, and strategies to prevent the transmission and development of the disease.

Effects of Simulated Microgravity on the Physiology of Stenotrophomonas maltophilia and Multiomic Analysis

Many studies have shown that the space environment plays a pivotal role in changing the characteristics of conditional pathogens, especially their pathogenicity and virulence. However, Stenotrophomonas maltophilia, a type of conditional pathogen that has shown to a gradual increase in clinical morbidity in recent years, has rarely been reported for its impact in space. In this study, S. maltophilia was exposed to a simulated microgravity (SMG) environment in high-aspect ratio rotating-wall vessel bioreactors for 14days, while the control group was exposed to the same bioreactors in a normal gravity (NG) environment. Then, combined phenotypic, genomic, transcriptomic, and proteomic analyses were conducted to compare the influence of the SMG and NG on S. maltophilia. The results showed that S. maltophilia in simulated microgravity displayed an increased growth rate, enhanced biofilm formation ability, increased swimming motility, and metabolic alterations compared with those of S. maltophilia in normal gravity and the original strain of S. maltophilia. Clusters of Orthologous Groups (COG) annotation analysis indicated that the increased growth rate might be related to the upregulation of differentially expressed genes (DEGs) involved in energy metabolism and conversion, secondary metabolite biosynthesis, transport and catabolism, intracellular trafficking, secretion, and vesicular transport. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses showed that the increased motility might be associated the upregulation of differentially expressed proteins (DEPs) involved in locomotion, localization, biological adhesion, and binding, in accordance with the upregulated DEGs in cell motility according to COG classification, including pilP, pilM, flgE, flgG, and ronN. Additionally, the increased biofilm formation ability might be associated with the upregulation of DEPs involved in biofilm formation, the bacterial secretion system, biological adhesion, and cell adhesion, which were shown to be regulated by the differentially expressed genes (chpB, chpC, rpoN, pilA, pilG, pilH, and pilJ) through the integration of transcriptomic and proteomic analyses. These results suggested that simulated microgravity might increase the level of corresponding functional proteins by upregulating related genes to alter physiological characteristics and modulate growth rate, motility, biofilm formation, and metabolism. In conclusion, this study is the first general analysis of the phenotypic, genomic, transcriptomic, and proteomic changes in S. maltophilia under simulated microgravity and provides some suggestions for future studies of space microbiology.

Detection of Enterococcus hirae in a case of acute osteomyelitis

Enterococci are important microorganisms of the gut microbiome in many mammals and cause millions of infections annually. An increasing resistance to antibiotics has led to their emergence as superinfecting nosocomial pathogens in humans. Enterococcus hirae is rarely identified in humans. In this study, we present a case of the polymicrobial osteomyelitis involving Enterococcus hirae in a 33-year-old male patient with traumatic tibia-fibula fracture after a motor vehicle accident. He underwent a right below-the-knee amputation and antibiotics with excellent improvement. Our case study helps to confirm the unexpected presence of Enterococcus hirae in a human specimen. Further studies are needed to elucidate the clinical implications of Enterococcus hirae.

Comparative proteomic analysis to annotate the structural and functional association of the hypothetical proteins of S. maltophilia k279a and predict potential T and B cell targets for vaccination

Stenotrophomonas maltophilia is a multidrug-resistant bacterium with no precise clinical treatment. This bacterium can be a vital cause for death and different organ failures in immune-compromised, immune-competent, and long-time hospitalized patients. Extensive quorum sensing capability has become a challenge to develop new drugs against this pathogen. Moreover, the organism possesses about 789 proteins which function, structure, and pathogenesis remain obscured. In this piece of work, we tried to enlighten the aforementioned sectors using highly reliable bioinformatics tools validated by the scientific community. At first, the whole proteome sequence of the organism was retrieved and stored. Then we separated the hypothetical proteins and searched for the conserved domain with a high confidence level and multi-server validation, which resulted in 24 such proteins. Furthermore, all of their physical and chemical characterizations were performed, such as theoretical isoelectric point, molecular weight, GRAVY value, and many more. Besides, the subcellular localization, protein-protein interactions, functional motifs, 3D structures, antigenicity, and virulence factors were also evaluated. As an extension of this work, 'RTFAMSSER' and 'PAAPQPSAS' were predicted as potential T and B cell epitopes, respectively. We hope our findings will help in better understating the pathogenesis and smoothen the way to the cure.

Intra-hospital dissemination of clinical and environmental isolates of Stenotrophomonas maltophilia from Tehran

Stenotrophomonas maltophilia isolates are responsible for various hospital-acquired infections and are particularly increasing in the immunocompromised patients. The aim of this study was to determine the clonal relatedness between S. maltophilia isolates originating from the clinic and environment. A total of 150 S. maltophilia isolates from patients and 1108 environmental samples obtained in three hospitals from Tehran. Following molecular identification targeting 23S rRNA gene, the clonal relatedness of the environmental and clinical isolates was determined using pulsed field gel electrophoresis (PFGE). Of the 150 clinical and 18 environmental isolates identified using phenotypic tests, the speciation of 120 and 15 was confirmed by targeting the 23S rRNA gene. The 24 common pulsotypes (PTs) and 32 single PTs were identified by PFGE. Only a small cluster was shared among the clinic and environment within a hospital; therefore, the intra-hospital dissemination of certain isolates of S. maltophilia among the clinic and environment was demonstrated.

Stenotrophomonas maltophilia: A Rare Case of Osteomyelitis After an Open Distal Tibial Fracture

Stenotrophomonas maltophilia is a gram-negative rod rarely associated with osteomyelitis. To date, only 3 cases of osteomyelitis due to this pathogen have been previously referenced. We describe the case of a 77-year-old male who developed osteomyelitis secondary to S. maltophilia infection after an open distal tibial fracture sustained by falling off a ladder. The purpose of the present case report was to highlight this highly resistant microbe as an infectious etiology.

Stenotrophomonas maltophilia: From trivial to grievous

Stenotrophomonas maltophilia, once regarded as an organism of low virulence, has evolved as a significant opportunistic pathogen causing severe human infections in both hospital and community settings, especially amongst highly debilitated patients. Globally, S. maltophilia ranks third amongst the four most common pathogenic non-fermenting Gram-negative bacilli (NFGNBs), others being Pseudomonas aeruginosa, Acinetobacter baumannii and Burkholderia cepacia complex (Bcc). The worth of accurate identification of S. maltophilia comes to the forefront as it needs to be differentiated from other NFGNBs such as Acinetobacter, P. aeruginosa and Bcc due to its inherently contrasting antibiotic susceptibility pattern. Consequently, its correct identification is essential as no single drug is amply effective against all NFGNBs, which hinders initiation of appropriate empirical treatment resulting in increased morbidity and mortality.

Surgical management of maxillary and premaxillary osteomyelitis in a reticulated python (Python reticulatus)

CASE DESCRIPTION A 1-year-old reticulated python (Python reticulatus) was evaluated because of a 2-week history of wheezing and hissing. CLINICAL FINDINGS Rostral facial cellulitis and deep gingival pockets associated with missing rostral maxillary teeth were evident. Tissues of the nares were swollen, resulting in an audible wheeze during respiration. Multiple scars and superficial facial wounds attributed to biting by live prey were apparent. Radiographic examination revealed bilateral, focal, rostral maxillary osteomyelitis. TREATMENT AND OUTCOME Wound irrigation, antimicrobials, and anti-inflammatory drug treatment resulted in reduced cellulitis. A 3-week regimen that included empirical antimicrobial treatment and improved husbandry resulted in resolution of the respiratory sounds and partial healing of bite wounds, but radiographic evaluation revealed progressive maxillary osteomyelitis. Microbial culture of blood yielded scant gram-positive cocci and Bacillus spp, which were suspected sample contaminants. Bilateral partial maxillectomies were performed; microbial culture and histologic examination of resected bone confirmed osteomyelitis with gram-positive cocci. Treatment with trimethoprim-sulfamethoxazole was initiated on the basis of microbial susceptibility tests. Four months later, follow-up radiography revealed premaxillary osteomyelitis; surgery was declined, and treatment with trimethoprim-sulfamethoxazole was reinstituted. Eight months after surgery, the patient was reevaluated because of recurrent clinical signs; premaxillectomy was performed, and treatment with trimethoprim-sulfamethoxazole was prescribed on the basis of microbial culture of bone and microbial susceptibility testing. Resolution of osteomyelitis was confirmed by CT 11 months after the initial surgery. CONCLUSIONS AND CLINICAL RELEVANCE Focal maxillectomies and premaxillectomy were successfully performed in a large python. Surgical management and appropriate antimicrobial treatment resulted in a good outcome.

High-throughput prediction of tablet weight and trimethoprim content of compound sulfamethoxazole tablets for controlling the uniformity of dosage units by NIR

This paper establishes a novel method to simultaneously predict the tablet weight (TW) and trimethoprim (TMP) content of compound sulfamethoxazole tablets (SMZCO) by near infrared (NIR) spectroscopy with partial least squares (PLS) regression for controlling the uniformity of dosage units (UODU). The NIR spectra for 257 samples were measured using the optimized parameter values and pretreated using the optimized chemometric techniques. After the outliers were ignored, two PLS models for predicting TW and TMP content were respectively established by using the selected spectral sub-ranges and the reference values. The TW model reaches the correlation coefficient of calibration (R(c)) 0.9543 and the TMP content model has the R(c) 0.9205. The experimental results indicate that this strategy expands the NIR application in controlling UODU, especially in the high-throughput and rapid analysis of TWs and contents of the compound pharmaceutical tablets, and may be an important complement to the common NIR on-line analytical method for pharmaceutical tablets.

Diagnosis, Treatment, and Outcome of Stenotrophomonas maltophilia Discitis and Cervical Osteomyelitis: A Case Report and Review of the Literature

CASE

A fifty-six-year-old man presented with a three-month history of worsening neck pain and weakness of the right arm. Magnetic resonance imaging revealed C5-C6 osteomyelitis and discitis and a prevertebral abscess from C3 to C7. He underwent staged instrumented anterior and posterior spinal fusion from C5 to C7, with an anterior C5-C6 cervical discectomy and a C6 corpectomy. Intraoperative cultures exhibited growth of Stenotrophomonas maltophilia. The patient subsequently received five months of oral trimethoprim/sulfamethoxazole therapy. At twelve months postoperatively, he had full recovery of motor strength bilaterally.

CONCLUSION

Osteomyelitis with S. maltophilia is associated with agricultural-machinery-related injuries. Surgical intervention for cervical osteomyelitis should be considered if the patient presents with a neurologic deficit or a paravertebral abscess.

An overview of various typing methods for clinical epidemiology of the emerging pathogen Stenotrophomonas maltophilia

Typing of bacterial isolates has been used for decades to study local outbreaks as well as in national and international surveillances for monitoring newly emerging resistant clones. Despite being recognized as a nosocomial pathogen, the precise modes of transmission of Stenotrophomonas maltophilia in health care settings are unknown. Due to the high genetic diversity observed among S. maltophilia clinical isolates, the typing results might be better interpreted if also environmental strains were included. This could help to identify preventative measures to be designed and implemented for decreasing the possibility of outbreaks and nosocomial infections. In this review, we attempt to provide an overview on the most common typing methods used for clinical epidemiology of S. maltophilia strains, such as PCR-based fingerprinting analyses, pulsed-field gel electrophoresis, multilocus variable number tandem repeat analysis, and multilocus sequence type. Application of the proteomic-based mass spectrometry by matrix-assisted laser desorption ionization-time of flight is also described. Improvements of typing methods already in use have to be achieved to facilitate S. maltophilia infection control at any level. In the near future, when novel Web-based platforms for rapid data processing and analysis will be available, whole genome sequencing technologies will likely become a highly powerful tool for outbreak investigations and surveillance studies in routine clinical practices.

Combined use of Ilizarov external fixation and Papineau technique for septic pseudoarthrosis of the distal tibia in a patient with diabetes mellitus

The surgical treatment of open pilon fractures has a high complication rate especially in diabetic patients. In this article, we present a case of an infected tibial non-union after an open reduction and internal fixation in a diabetic patient, treated with Ilizarov external fixation combined with Papineau technique. Combined use of external fixation and Papineau technique can provide an alternative option for the treatment of septic pseudoarthrosis of the distal tibia.

Recurrent Stenotrophomonas maltophilia bacteremia after iliac crest bone graft harvest

We describe a rare case of recurrent Stenotrophomonas maltophilia bacteremia in a previously healthy 45-year-old man. The infection was caused by osteomyelitis at the site of an iliac crest bone graft harvest. A genetic analysis using enterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC-PCR) revealed that the blood isolates and pathogens obtained from the surgical wound were identical. Initial treatment with levofloxacin and cefozopran was ineffective, but the patient's infection was successfully treated by long-term administration of latamoxef and trimethoprim-sulfamethoxazole. The present case suggests that attention should be given to the possibility of S. maltophilia infection in any situations.

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.

Trimethoprim-sulfamethoxazole therapy for children with acute osteomyelitis

BACKGROUND

The emergence of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) has complicated the conventional management of osteomyelitis. While oral clindamycin is commonly used to treat acute CA-MRSA osteomyelitis, the emergence of inducible clindamycin resistance among CA-MRSA isolates has made alternative therapy necessary. The excellent oral bioavailability, susceptibility profile, favorable palatability, and low cost of trimethoprim-sulfamethoxazole (TMP-SMX) make this drug an attractive option for treating osteomyelitis, yet its clinical efficacy for osteomyelitis has not been established.

METHODS

Between October 1998 and September 2009, 20 children who received a TMP-SMX-containing regimen for acute osteomyelitis at All Children's Hospital were identified from hospital records, and their cases reviewed for clinical outcome and drug safety.

RESULTS

Patients ranged in age from 9 months to 17 years. Twelve (60%) of the patients were male. Causative pathogens were found in 8 (40%) cases of which 5 were CA-MRSA and 3 were methicillin-susceptible Staphylococcus aureus. Eleven patients (55%) received TMP-SMX as their primary therapy. The median dose of TMP-SMX was 16.4 mg/kg/d. During TMP-SMX therapy, 8 patients (40%) experienced adverse events; all were considered mild. Duration of total therapy was 26 to 59 days, with a median of 40 days. All 20 patients were considered cured of their infection at the end of therapy.

CONCLUSION

Orally administered TMP-SMX appears to be a useful and well-tolerated therapy for treatment of acute osteomyelitis in children. Further prospective comparative studies will be needed to confirm this observation.

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.

Role of excessive inflammatory response to Stenotrophomonas maltophilia lung infection in DBA/2 mice and implications for cystic fibrosis

Stenotrophomonas maltophilia is a pathogen that causes infections mainly in immunocompromised patients. Despite increased S. maltophilia isolation from respiratory specimens of patients with cystic fibrosis (CF), the real contribution of the microorganism to CF pathogenesis still needs to be clarified. The aim of the present study was to evaluate the pathogenic role of S. maltophilia in CF patients by using a model of acute respiratory infection in DBA/2 mice following a single exposure to aerosolized bacteria. The pulmonary bacterial load was stable until day 3 and then decreased significantly from day 3 through day 14, when the bacterial load became undetectable in all infected mice. Infection disseminated in most mice, although at a very low level. Severe effects (swollen lungs, large atelectasis, pleural adhesion, and hemorrhages) of lung pathology were observed on days 3, 7, and 14. The clearance of S. maltophilia observed in DBA/2 mouse lungs was clearly associated with an early and intense bronchial and alveolar inflammatory response, which is mediated primarily by neutrophils. Significantly higher levels of interleukin-1beta (IL-1beta), IL-6, IL-12, gamma interferon (IFN-gamma), tumor necrosis factor alpha (TNF-alpha), GROalpha/KC, MCP-1/JE, MCP-5, macrophage inflammatory protein 1alpha (MIP-1alpha), MIP-2, and TARC were observed in infected mice on day 1 with respect to controls. Excessive pulmonary infection and inflammation caused systemic effects, manifested by weight loss, and finally caused a high mortality rate. Taken together, our results show that S. maltophilia is not just a bystander in CF patients but has the potential to contribute to the inflammatory process that compromises respiratory function.

Stenotrophomonas maltophilia: an emerging opportunist human pathogen

Stenotrophomonas maltophilia has emerged as an important opportunistic pathogen in the debilitated host. S maltophilia is not an inherently virulent pathogen, but its ability to colonise respiratory-tract epithelial cells and surfaces of medical devices makes it a ready coloniser of hospitalised patients. S maltophilia can cause blood-stream infections and pneumonia with considerable morbidity in immunosuppressed patients. Management of infection is hampered by high-level intrinsic resistance to many antibiotic classes and the increasing occurrence of acquired resistance to the first-line drug co-trimoxazole. Prevention of acquisition and infection depends upon the application of modern infection-control practices, with emphasis on the control of antibiotic use and environmental reservoirs.

Therapeutic options for Stenotrophomonas maltophilia infections beyond co-trimoxazole: a systematic review

BACKGROUND

Stenotrophomonas maltophilia has emerged as an important opportunistic pathogen, causing infections whose management is often problematic due to its inherent resistance to many antibiotics, making co-trimoxazole the main therapeutic option. However, there are cases in which either due to antimicrobial resistance or allergic reactions and intolerance to co-trimoxazole this antibiotic cannot be administered. We sought to evaluate the available clinical evidence regarding potentially effective alternative antibiotics for the treatment of S. maltophilia infections.

METHODS

The literature search was performed in the PubMed and Scopus databases. The search string used was 'Stenotrophomonas maltophilia OR Xanthomonas maltophilia'.

RESULTS

Thirty-one case reports and 5 case series were retrieved including a total of 49 patients with a variety of infections. Twenty of 49 cases (40.8%) were treated with ciprofloxacin as monotherapy or in combination with other antibiotics; 12 of 49 cases (24.5%) were treated with ceftriaxone- or ceftazidime-based regimens; and 6 of 49 cases (12.2%) were treated with ticarcillin- or ticarcillin/clavulanate-based regimens. The cure or improvement rates were 18 cases (90%), 8 (75%) and 4 (66.7%), respectively. The remaining 11 patients received various antimicrobials including aminoglycoside-based regimens, carbapenems, levofloxacin, chloramphenicol, aztreonam, minocycline and other beta-lactams.

CONCLUSIONS

The limited available data suggest that ciprofloxacin, ceftazidime or ceftriaxone, and ticarcillin/clavulanate, alone or in combination with other antibiotics, may be considered as alternative options beyond co-trimoxazole.

Spondylodiscitis due to Stenotrophomonas maltophilia

Stenotrophomonas maltophilia is an increasingly recognized cause of severe nosocomial infections, especially in immunocompromised patients. Community-acquired infections have also been reported. Spondylodiscitis due to S. maltophilia has only once before been described in the literature. We present a case of spondylodiscitis due to community-acquired S. maltophilia infection in a renal transplant recipient with liver cirrhosis.

Immunostimulatory properties of the emerging pathogen Stenotrophomonas maltophilia

Stenotrophomonas maltophilia is a multiple-antibiotic-resistant opportunistic pathogen that is being isolated with increasing frequency from patients with health-care-associated infections and especially from patients with cystic fibrosis (CF). While clinicians feel compelled to treat infections involving this organism, its potential for virulence is not well established. We evaluated the immunostimulatory properties and overall virulence of clinical isolates of S. maltophilia using the well-characterized opportunistic pathogen Pseudomonas aeruginosa PAO1 as a control. The properties of CF isolates were examined specifically to see if they have a common phenotype. The immunostimulatory properties of S. maltophilia were studied in vitro by stimulating airway epithelial and macrophage cell lines. A neonatal mouse model of pneumonia was used to determine the rates of pneumonia, bacteremia, and mortality, as well as the inflammatory response elicited by S. maltophilia infection. Respiratory and nonrespiratory S. maltophilia isolates were highly immunostimulatory and elicited significant interleukin-8 expression by airway epithelial cells, as well as tumor necrosis factor alpha (TNF-alpha) expression by macrophages. TNF-alpha signaling appears to be important in the pathogenesis of S. maltophilia infection as less than 20% of TNFR1 null mice (compared with 100% of wild-type mice) developed pneumonia and bacteremia following intranasal inoculation. The S. maltophilia isolates were weakly invasive, and low-level bacteremia with no mortality was observed. Despite the lack of invasiveness of S. maltophilia, the immunostimulatory properties of this organism and its induction of TNF-alpha expression specifically indicate that it is likely to contribute significantly to airway inflammation.