Endocarditis caused by Stenotrophomonas maltophilia: case report and review

Antimicrobial susceptibility of hospital acquired Stenotrophomonas maltophilia isolate biofilms

AIMS

We sought to characterize the antibiotic susceptibility of strains of Stenotrophomonas maltophilia isolated from clinical samples, and the role of Stenotrophomonas maltophilia biofilm in antibiotic resistance.

METHODS

Fifty-one clinical Stenotrophomonas maltophilia isolates were obtained from patients with nosocomial infection in the surgical wards and ICUs of six general hospitals in Tianjin, China. In vitro models of Stenotrophomonas maltophilia biofilms were established and confirmed by scanning electron microscopy and fluorescence microscopy with silver staining. The minimal inhibitory concentrations and biofilm inhibitory concentrations of commonly used antibiotics were determined.

RESULTS

47 of 51 strains were resistant to three or more antibiotics. 42 of 51 strains formed Stenotrophomonas maltophilia biofilms in vitro. Stenotrophomonas maltophilia biofilm formation greatly reduced sensitivity to most tested antibiotics, but not to levofloxacin. However, in the presence of erythromycin scanning electron microscopy revealed that levofloxacin inhibited Stenotrophomonas maltophilia biofilm formation. Factorial ANOVA revealed that erythromycin enhanced susceptibility to levofloxacin, cefoperazone/sulbactam, and piperacillin (p<0.05), and an ΔE model revealed that levofloxacin and erythromycin acted synergistically in biofilms, suggesting specific use of combined macrolide therapy may represent an effective treatment for Stenotrophomonas maltophilia infection.

CONCLUSIONS

Antibiotics could act synergistically to combat the protection conferred to clinical isolates of Stenotrophomonas maltophilia by biofilms. Macrolide antibiotics may be effective where used in combination.

Phenotypic Heterogeneity Affects Stenotrophomonas maltophilia K279a Colony Morphotypes and β-Lactamase Expression

Phenotypic heterogeneity at the cellular level in response to various stresses, e.g., antibiotic treatment has been reported for a number of bacteria. In a clonal population, cell-to-cell variation may result in phenotypic heterogeneity that is a mechanism to survive changing environments including antibiotic therapy. Stenotrophomonas maltophilia has been frequently isolated from cystic fibrosis patients, can cause numerous infections in other organs and tissues, and is difficult to treat due to antibiotic resistances. S. maltophilia K279a produces the L1 and L2 β-lactamases in response to β-lactam treatment. Here we report that the patient isolate S. maltophilia K279a diverges into cellular subpopulations with distinct but reversible morphotypes of small and big colonies when challenged with ampicillin. This observation is consistent with the formation of elongated chains of bacteria during exponential growth phase and the occurrence of mainly rod-shaped cells in liquid media. RNA-seq analysis of small versus big colonies revealed differential regulation of at least seven genes among the colony morphotypes. Among those, bla L1 and bla L2 were transcriptionally the most strongly upregulated genes. Promoter fusions of bla L1 and bla L2 genes indicated that expression of both genes is also subject to high levels of phenotypic heterogeneous expression on a single cell level. Additionally, the comE homolog was found to be differentially expressed in homogenously versus heterogeneously bla L2 expressing cells as identified by RNA-seq analysis. Overexpression of comE in S. maltophilia K279a reduced the level of cells that were in a bla L2-ON mode to 1% or lower. Taken together, our data provide strong evidence that S. maltophilia K279a populations develop phenotypic heterogeneity in an ampicillin challenged model. This cellular variability is triggered by regulation networks including bla L1, bla L2, and comE.

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.

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.

Lethal Pulmonary Hemorrhage Caused by a FulminantStenotrophomonas maltophiliaRespiratory Infection in an Acute Myeloid Leukemia Patient

Stenotrophomonas maltophilia (Sm) pneumonia in immunocompromized hosts is an increasingly common nosocomial infection. Even though resistant to multiple antimicrobials, this gram-negative bacteria usually does not present with a fulminant course leading to a fatal hemorrhagic respiratory infection in neutropenic patients. We report here the case of a 63-year-old woman treated by intensive chemotherapy for acute myeloid leukemia (AML) who presented while severely neutropenic and thrombocytopenic a Sm pulmonary infection with hemoptysis leading to death in 48 h. The bronchoalveolar lavage (BAL) performed shortly before death was highly hemorrhagic and contained a striking amount of extra- and intra-cellular pathogens. Blood and BAL cultures grew S. maltophilia. Post-mortem examination revealed bilateral extensive intra-alveolar hemorrhage (IAH) associated with a great amount of microorganisms and severe bone marrow aplasia was observed without evidence of leukemia residual disease. Sm pneumonia usually does not evolve into such a devastating clinical picture although infections due to the bacteria are known to be associated with high morbidity and mortality. So far, the present observation is the fourth similar case reported in the literature. Even though an early diagnosis and an adequate antibiotic prescription may improve Sm infection prognosis, S. maltophilia proves difficult to eradicate due to a high resistance rate in part intrinsic but also in part acquired.

Stenotrophomonas maltophilia: a serious and rare complication in patients suffering from burns

Stenotrophomonas maltophilia is rarely implicated in clinical infections but it constitutes a significant nosocomial pathogen, especially in immunocompromised patients. This report describes the first case of a generalised infection caused by S. maltophilia that included bacteremia, wound and respiratory tract infection in a patient suffering from burns. Given the emergence of S. maltophilia nosocomial infections, especially in patients with burns, isolation of the bacterium from blood cultures should prompt the commencement of adequate antibiotic treatment.

Mutations in gyrA and parC QRDRs are not relevant for quinolone resistance in epidemiological unrelated Stenotrophomonas maltophilia clinical isolates

Clinical strains of Stenotrophomonas maltophilia are often highly resistant to multiple antibiotics and this resistance is steadily rising. Quinolones are included in the group of antimicrobial agents to which this microorganism is developing resistance. Therefore, the aim of this study was to analyze the epidemiological relationship among 22 clinical isolates of S. maltophilia as well as the molecular mechanisms responsible for the acquisition of quinolone-resistance in these strains. The results of the pulsed-field gel electrophoresis (PFGE) showed an heterogenicity of 82% among the strains used in the study. On the other hand, no amino acid changes were found in the quinolone resistance-determining region (QRDR) of either gyrA and parC genes among quinolone-susceptible and -resistant S. maltophilia strains. Besides, the amino acid of the GyrA found in the position equivalent to Ser-83 of E. coli was Gln instead of a Ser or Thr, the amino acids usually encountered in this position among Gram-negative bacteria. The results suggest that there is not a relationship between the presence of this Gln and the resistance to quinolones in S. maltophilia. We can conclude that, contrary to what has been described in other microorganisms, in these S. maltophilia isolates, the development of resistance to quinolones was not related to mutations in the QRDR of gyrA and parC genes. Thus, to our knowledge, this is the first report describing this phenomenon.

Infective endocarditis in the injection drug user

Although infective endocarditis is certainly not the most common infection seen in injecting drug users, it is the infection that clinicians most commonly think of when they consider infectious complications of injected drug use. The microbiology of infective endocarditis in injection drug users has remained relatively stable over the last several decades. Tricuspid valve endocarditis has been associated most frequently with injection drug use, but recent reports have suggested that involvement of left-sided valves is seen more often now than in the past. The use of transesophageal echocardiography has greatly advanced the ability to diagnose infective endocarditis and the cardiac complications of valvular infection.

Fulminant Stenotrophomonas maltophilia soft tissue infection in immunocompromised patients: an outbreak transmitted via tap water

Soft tissue infection caused by Stenotrophomonas maltophilia is uncommon, but nosocomial infections had been reported. We describe herein 2 young female patients, with severe neutropenia, on broad spectrum antimicrobial agents for neutropenic fever, with Hickman-type central venous catheter, who developed mucocutaneous and soft tissue infections with rapidly progressive and devastating course. Cultures from the skin of both patients and from blood of one of them grew S. maltophilia. Both patients died and post mortem examination of the patient with S. maltophilia bacteremia revealed extensive soft tissue necrosis and a vegetation on the mitral valve that grew S. maltophilia. The infection occurred in both patients at the same time and in the same ward. Epidemiological study was done, and surveillance cultures grew the organism from the faucets from the room of 1 patient and also from some of the neighboring rooms in our ward but not from any other ward nor in the water reservoir of the building.

Stenotrophomonas maltophilia endocarditis: a systematic review

The disease characteristics, management, and outcome of Stenotrophomonas maltophilia endocarditis were evaluated by examining the reports on the subject identified through a comprehensive literature search. Twenty-three (17 male) cases of S.. maltophilia endocarditis were identified. Mean age was 41 +/- 15 years. All patients presented with fever. Prosthetic valves were involved in 12 (52%) cases. Among native valves, the aortic valve was most frequently involved (50%), followed by the tricuspid valve (36%). Twenty (87%) patients had underlying risk factors for the development of endocarditis, including prior valvular or congenital heart disease surgery (60%), intravenous drug abuse (32%), and infected intravascular lines (18%). The endocarditis was postoperative in 14 patients. Seventeen (74%) patients experienced complications including septic embolism (23%), cardiac abscesses (23%), and congestive heart failure (18%). A combination of two or more antibiotics was used in all cases except one. The frequently used antibiotics were aminoglycosides (59%), trimethoprim-sulfamethoxazole (48%), and penicillins (48%). One half of the patients required cardiac surgery, but the proportion of surgically treated cases was higher among prosthetic valve endocarditis (62%). Mortality was 39% and was equally distributed between patients with prosthetic and native valve endocarditis. The S. maltophilia endocarditis carries high complication and mortality rates. The antibiotic regimen should consist of a combination of multiple antibiotics guided by the sensitivity panel. Early surgery may be considered in patients not responding to antibiotic treatment and in those with prosthetic valve endocarditis.

Septicemia associated with Stenotrophomonas maltophilia in a West African dwarf crocodile (Osteolaemus tetraspis subsp. tetraspis)

A 17-year-old male captive West African dwarf crocodile (Osteolaemus tetraspis subsp. tetraspis) died 1 month after fighting with a penmate. Abrasions were present on the head and mandible. Necropsy revealed a vegetative valvular lesion of the left atrioventricular valve, miliary foci of necrosis in the endocardium and myocardium, multiple duodenal and rectal ulcers, and serous atrophy of body fat. Stenotrophomonas maltophilia was isolated in pure culture from lung, liver, and kidney. Gram-negative bacilli were seen histologically in the valvular lesion and in foci of necrosis in the myocardium, liver, spleen, pancreas, kidney, and intestine. Septic thrombi in multiple tissues, arteritis, and pneumonia were additional histologic lesions. Findings indicated that the crocodile died from acute S. maltophilia septicemia, although the primary site of infection was not determined. Stenotrophomonas maltophilia is ubiquitous in the environment and is recognized as an important nosocomial pathogen in humans.

Nonrespiratory Stenotrophomonas maltophilia infection at a children's hospital

To describe Stenotrophomonas maltophilia infection in children, we reviewed the medical records of patients with isolates from nonrespiratory sites and identified 85 episodes, 51 (60%) of which represented true infection. Forty-two episodes (82.4%) were hospital acquired. Commonly associated with S. maltophilia infection were underlying illness (in 90.2% of cases), previous hospitalizations (in 78.7%), previous antibiotic exposure (in 78.4%), and the presence of a central venous catheter (in 76.5%). Polymicrobial isolates were obtained in 70.6% of episodes; Pseudomonas aeruginosa and Acinetobacter species were the most common coisolates. Bloodstream infection was the most frequent clinical syndrome (32 [63%] of 51 episodes). Fever or sepsis occurred in 22 (69%) and shock in 10 (31%) of 32 episodes. Infection at other sites was less severe. The most active antibiotics in vitro were trimethoprim-sulfamethoxazole and ticarcillin-clavulanate. The overall and attributable mortality rates were 12.5% and 6.3%, respectively. S. maltophilia appears to be an important cause of nosocomially acquired bacteremia in children. The significance in children of isolation from other sites is less clear.

Stenotrophomonas maltophilia endocarditis of prosthetic aortic valve: report of a case and review of literature

Stenotrophomonas Maltophilia (previously known as Xanthomonas maltophilia and Pseudomonas maltophilia ) is an aerobic, nonfermenting, gram-negative bacillus, which has emerged as a serious nosocomial pathogen in patients with compromised immunity. It is a rare cause of endocarditis with only 20 cases previously reported in medical literature. The risk factors associated with S maltophilia endocarditis include intravenous drug abuse, dental treatment, previous cardiac surgery, and infected intravascular devices. S maltophilia is resistant to multiple antibiotics, which leads to frequent therapeutic failures. Although the optimal antibiotic treatment for S maltophilia endocarditis remains unknown, most of the patients received 2 or more antibiotics. We report a case of S maltophilia endocarditis of prosthetic aortic valve, associated with a painless aortic dissection, that responded well to a combination of ciprofloxacin and chloramphenicol. The literature is reviewed to elaborate the disease characteristics, the treatments used, and the prognosis of the S maltophilia endocarditis.

Molecular investigation of Stenotrophomonas maltophilia isolates exhibiting rapid emergence of ticarcillin-clavulanate resistance

The prevalence of Stenotrophomonas maltophilia resistance to ticarcillin-clavulanate has dramatically increased in our hospital over the past few years. Sixty-six clinical isolates, collected from 61 patients, were tested for antibiotic susceptibility and genotyped by two different enterobacterial repetitive intergenic consensus-PCR (ERIC-PCR) systems. Although two small outbreaks were identified in the medical intensive care unit, the remaining 58 strains generated 48 different PCR patterns. The rapid emergence of resistance in S. maltophilia occured in absence of an epidemic and was probably influenced by increasing-b-lactam use in our hospital.

Multiple antibiotic resistance in Stenotrophomonas maltophilia: involvement of a multidrug efflux system

Clinical strains of Stenotrophomonas maltophilia are often highly resistant to multiple antibiotics, although the mechanisms of resistance are generally poorly understood. Multidrug resistant (MDR) strains were readily selected by plating a sensitive reference strain of the organism individually onto a variety of antibiotics, including tetracycline, chloramphenicol, ciprofloxacin, and norfloxacin. Tetracycline-selected MDR strains typically showed cross-resistance to erythromycin and fluoroquinolones and, in some instances, aminoglycosides. MDR mutants selected with the other agents generally displayed resistance to chloramphenicol and fluoroquinolones only, although two MDR strains (e.g., K1385) were also resistant to erythromycin and hypersusceptible to aminoglycosides. Many of the MDR strains expressed either moderate or high levels of a novel outer membrane protein (OMP) of ca. 50 kDa molecular mass, a phenotype typical of MDR strains of Pseudomonas aeruginosa hyperexpressing drug efflux systems. Indeed, the 50-kDa OMP of these S. maltophilia MDR strains reacted with antibody to OprM, the outer membrane component of the MexAB-OprM MDR efflux system of P. aeruginosa. Similarly, a ca. 110-kDa cytoplasmic membrane protein of these MDR strains also reacted with antibody to the MexB component of the P. aeruginosa pump. The outer and cytoplasmic membranes of several clinical S. maltophilia strains also reacted with the anti-OprM and anti-MexB antibodies. N-terminal amino acid sequencing of a cyanogen bromide-generated peptide of the 50-kDa OMP of MDR strain K1385, dubbed SmeM (Stenotrophomonas multidrug efflux), revealed it to be very similar to a number of outer membrane multidrug efflux components of P. aeruginosa and Pseudomonas putida. Deletion of the L1 and L2 beta-lactamase genes confirmed that these enzymes were responsible for the bulk of the beta-lactam resistance of K1385 and its parent. Still, overexpression of the MDR efflux mechanism in an L1- and L2-deficient derivative of K1385 did yield a modest increase in resistance to a few beta-lactams. These data are consistent with the MDR efflux mechanism(s) playing a role in the multidrug resistance of S. maltophilia.

Infective endocarditis due to Stenotrophomonas (Xanthomonas) maltophilia

Stenotrophomonas maltophilia (formerly Xanthomonas maltophilia) is a gram-negative bacillus increasingly associated with serious nosocomial infections. Here, the case of a 69-year-old female patient who developed prosthetic valve endocarditis associated with this organism is described. A review of the literature revealed only 18 previous reports; eight involved native valves, the remainder prosthetic valves. Most cases were associated with risk factors, including intravenous drug abuse (6 patients), infected intravenous lines (4 patients) or a recent invasive procedure (3 patients). The course of the disease appears to be indolent, but is otherwise similar to infective endocarditis associated with other gram-negative organisms. Antimicrobial therapy is complicated by multiple drug resistance of the organism; cotrimoxazole may be beneficial, if the isolate is susceptible, in combination with another agent. Five of nine (55%) patients who underwent valve replacement survived, as compared to three of seven (43%) who received antibiotic therapy only. Hence, surgery is not essential for survival in every case and depends as much on the individual patient's course as on established criteria for valve replacement in prosthetic valve endocarditis.

Microbiological and clinical aspects of infection associated with Stenotrophomonas maltophilia

The gram-negative bacterium Stenotrophomonas maltophilia is increasingly recognized as an important cause of nosocomial infection. Infection occurs principally, but not exclusively, in debilitated and immunosuppressed individuals. Management of S. maltophilia-associated infection is problematic because many strains of the bacterium manifest resistance to multiple antibiotics. These difficulties are compounded by methodological problems in in vitro susceptibility testing for which there are, as yet, no formal guidelines. Despite its acknowledged importance as a nosocomial pathogen, little is known of the epidemiology of S. maltophilia, and although it is considered an environmental bacterium, its sources and reservoirs are often not readily apparent. Molecular typing systems may contribute to our knowledge of the epidemiology of S. maltophilia infection, thus allowing the development of strategies to interrupt the transmission of the bacterium in the hospital setting. Even less is known of pathogenic mechanisms and putative virulence factors involved in the natural history of S. maltophilia infection and this, coupled with difficulties in distinguishing colonization from true infection, has fostered the view that the bacterium is essentially nonpathogenic. This article aims to review the current taxonomic status of S. maltophilia, and it discusses the laboratory identification of the bacterium. The epidemiology of the organism is considered with particular reference to nosocomial outbreaks, several of which have been investigated by molecular typing techniques. Risk factors for acquisition of the bacterium are also reviewed, and the ever-expanding spectrum of clinical syndromes associated with S. maltophilia is surveyed. Antimicrobial resistance mechanisms, pitfalls in in vitro susceptibility testing, and therapy of S. maltophilia infections are also discussed.