Cystic Fibrosis-Associated Stenotrophomonas maltophilia Strain-Specific Adaptations and Responses to pH

A guide to Stenotrophomonas maltophilia virulence capabilities, as we currently understand them

The Gram-negative pathogen Stenotrophomonas maltophilia causes a wide range of human infections. It causes particularly serious lung infections in individuals with cystic fibrosis, leading to high mortality rates. This pathogen is resistant to most known antibiotics and harbors a plethora of virulence factors, including lytic enzymes and serine proteases, that cause acute infection in host organisms. S. maltophilia also establishes chronic infections through biofilm formation. The biofilm environment protects the bacteria from external threats and harsh conditions and is therefore vital for the long-term pathogenesis of the microbe. While studies have identified several genes that mediate S. maltophilia's initial colonization and biofilm formation, the cascade of events initiated by these factors is poorly understood. Consequently, understanding these and other virulence factors can yield exciting new targets for novel therapeutics.

Myxinidin-Derived Peptide against Biofilms Caused by Cystic Fibrosis Emerging Pathogens

Chronic lung infections in cystic fibrosis (CF) patients are triggered by multidrug-resistant bacteria such as Pseudomonas aeruginosa, Achromobacter xylosoxidans, and Stenotrophomonas maltophilia. The CF airways are considered ideal sites for the colonization and growth of bacteria and fungi that favor the formation of mixed biofilms that are difficult to treat. The inefficacy of traditional antibiotics reinforces the need to find novel molecules able to fight these chronic infections. Antimicrobial peptides (AMPs) represent a promising alternative for their antimicrobial, anti-inflammatory, and immunomodulatory activities. We developed a more serum-stable version of the peptide WMR (WMR-4) and investigated its ability to inhibit and eradicate C. albicans, S. maltophilia, and A. xylosoxidans biofilms in both in vitro and in vivo studies. Our results suggest that the peptide is able better to inhibit than to eradicate both mono and dual-species biofilms, which is further confirmed by the downregulation of some genes involved in biofilm formation or in quorum-sensing signaling. Biophysical data help to elucidate its mode of action, showing a strong interaction of WMR-4 with lipopolysaccharide (LPS) and its insertion in liposomes mimicking Gram-negative and Candida membranes. Our results support the promising therapeutic application of AMPs in the treatment of mono- and dual-species biofilms during chronic infections in CF patients.

Activity of Delafloxacin and Levofloxacin against Stenotrophomonas maltophilia at Simulated Plasma and Intrapulmonary pH Values

Fluoroquinolones have become a popular treatment option for Stenotrophomonas maltophilia infections. Although levofloxacin is most commonly used, delafloxacin demonstrates comparable in vitro activity when evaluated under standard susceptibility testing conditions at neutral pH. At acidic pH, the activity of the anionic delafloxacin is improved, while the activity of the zwitterionic levofloxacin is reduced. Because the human respiratory tract has a pH of ~6.6 and is the most common site of S. maltophilia infection, it is vital to understand the activity of these agents in this environment. Therefore, levofloxacin and delafloxacin were tested against clinical S. maltophilia isolates via broth microdilution testing (n = 37) and time-kill analysis (n = 5) in neutral cation-adjusted Mueller-Hinton broth (CAMHB) (pH 7.3) and acidic CAMHB (aCAMHB) (pH 6.5). In CAMHB, MIC50 values were similar between levofloxacin and delafloxacin (8 mg/L versus 8 mg/L). In aCAMHB, levofloxacin MICs did not change, while delafloxacin MICs decreased by a median of 4 log2 dilutions (MIC50 values of 8 mg/L versus 0.25 mg/L). In time-kill analyses, levofloxacin and delafloxacin at the maximum drug concentration for the free drug (fCmax) were bactericidal against 3 and 2 isolates in CAMHB, respectively. In aCAMHB, levofloxacin was not bactericidal against any isolate, while delafloxacin was bactericidal against the same 2 isolates. Relative to CAMHB, levofloxacin activity was reduced by 2.5 log10 CFU/mL in aCAMHB, whereas delafloxacin activity was increased 2.7 log10 CFU/mL. Although the bactericidal activity of levofloxacin against S. maltophilia was attenuated in an acidic environment in this study, the increased potency of delafloxacin at pH 6.5 did not translate into improved bactericidal activity in time-kill analyses, compared to pH 7.3. IMPORTANCE Stenotrophomonas maltophilia most often infects the lungs, where the physiologic environment is naturally slightly acidic (pH ~6.6), compared to most parts of the body (such as the bloodstream), which have neutral pH values (~7.4). Pneumonia due to S. maltophilia is often treated with the antibiotic levofloxacin, despite the activity of levofloxacin being known to be impaired at acidic pH. Unfortunately, currently available methods for susceptibility testing of levofloxacin against S. maltophilia are performed at a neutral pH and therefore may not accurately represent the activity of levofloxacin at the site of infection in the lungs. A similar but newer antibiotic in the same class as levofloxacin, namely, delafloxacin, is not affected by being in an acidic environment and may actually work better at lower pH values. Therefore, the purpose of this study was to investigate whether one drug might be better than the other in this setting by testing each agent's ability to kill S. maltophilia at pH 7.3 and pH 6.5. These findings could then be used to design confirmatory studies that may ultimately impact which drug is given to patients with lung infections due to S. maltophilia.

Conceptual Exchanges for Understanding Free-Living and Host-Associated Microbiomes

Whether a microbe is free-living or associated with a host from across the tree of life, its existence depends on a limited number of elements and electron donors and acceptors. Yet divergent approaches have been used by investigators from different fields. The "environment first" research tradition emphasizes thermodynamics and biogeochemical principles, including the quantification of redox environments and elemental stoichiometry to identify transformations and thus an underlying microbe. The increasingly common "microbe first" research approach benefits from culturing and/or DNA sequencing methods to first identify a microbe and encoded metabolic functions. Here, the microbe itself serves as an indicator for environmental conditions and transformations. We illustrate the application of both approaches to the study of microbiomes and emphasize how both can reveal the selection of microbial metabolisms across diverse environments, anticipate alterations to microbiomes in host health, and understand the implications of a changing climate for microbial function.

Advances in the Microbiology of Stenotrophomonas maltophilia

Stenotrophomonas maltophilia is an opportunistic pathogen of significant concern to susceptible patient populations. This pathogen can cause nosocomial and community-acquired respiratory and bloodstream infections and various other infections in humans. Sources include water, plant rhizospheres, animals, and foods. Studies of the genetic heterogeneity of S. maltophilia strains have identified several new genogroups and suggested adaptation of this pathogen to its habitats. The mechanisms used by S. maltophilia during pathogenesis continue to be uncovered and explored. S. maltophilia virulence factors include use of motility, biofilm formation, iron acquisition mechanisms, outer membrane components, protein secretion systems, extracellular enzymes, and antimicrobial resistance mechanisms. S. maltophilia is intrinsically drug resistant to an array of different antibiotics and uses a broad arsenal to protect itself against antimicrobials. Surveillance studies have recorded increases in drug resistance for S. maltophilia, prompting new strategies to be developed against this opportunist. The interactions of this environmental bacterium with other microorganisms are being elucidated. S. maltophilia and its products have applications in biotechnology, including agriculture, biocontrol, and bioremediation.

Friends or enemies? The complicated relationship between Pseudomonas aeruginosa and Staphylococcus aureus

Pseudomonas aeruginosa (Pa) and Staphylococcus aureus (Sa) are opportunistic pathogens that are most commonly co-isolated from chronic wounds and the sputum of cystic fibrosis patients. Over the last few years, there have been plenty of contrasting results from studies involving P. aeruginosa and S. aureus co-cultures. The general concept that P. aeruginosa outcompetes S. aureus has been challenged and there is more evidence now that they can co-exist. Nevertheless, it still remains difficult to mimic polymicrobial infections in vitro and in vivo. In this review, we discuss recent advances in regard to Pa-Sa molecular interactions, their physical responses, and in vitro and in vivo models. We believe it is important to optimize growth conditions in the laboratory, determine appropriate bacterial starting ratios, and consider environmental factors to study the co-existence of these two pathogens. Ideally, optimized growth media should reflect host-mimicking conditions with or without host cells that allow both bacteria to co-exist. To further identify mechanisms that could help to treat these complex infections, we propose to use relevant polymicrobial animal models. Ultimately, we briefly discuss how polymicrobial infections can increase antibiotic tolerance.

Prevalence and Survival of Stenotrophomonas Species in Milk and Dairy Products in Egypt

Stenotrophomonas maltophilia is a nosocomial, multidrug-resistant pathogen that causes significant economic losses in milk production and deterioration of dairy product quality. This study investigates the prevalence and the survival of S. maltophilia under different food preservation conditions. A total of 240 samples, including farm-sourced milk, dairy shop purchased milk, Kareish cheese, Domiati cheese, ice cream, yoghurt, cooking butter, and unpasteurized cream were collected from various locations in Beni-Suef Governorate, Egypt. Thirty samples of each product were analyzed by standard biochemical tests for the presence of Stenotrophomonas spp., which was isolated from 36% (87/240) of the examined samples. The highest prevalence was observed in ice cream (80%), followed by unpasteurized cream (67%), whereas the lowest incidence was in Domiati cheese (3.3%). S. maltophilia, identified by PCR, was found only in unpasteurized cream (13%), cooking butter (10%), ice cream (6.7%), and dairy shop milk (3.3%). We also studied the viability of S. maltophilia in laboratory manufactured cream, butter, and cheese under different preservation conditions. S. maltophilia was able to survive for 30, 30, 28, 30, and 8 d in the inoculated cream, butter 0% salt, butter 3% salt, cheese 0% salt, and cheese 6% salt, respectively. Thus, S. maltophilia was able to survive more than predicted in all products in this study. This suggests that strains of S. maltophilia may develop adaptive strategies that enable survival under different food preservation conditions, which contradicts previous knowledge about the sensitivity of this microbe to environmental stress conditions. Our overall aim was to draw attention to the prevalence and future potential for increased public health significance of Stenotrophomonas spp.

Genomic information on Stenotrophomonas maltophilia ST264 isolated from a cystic fibrosis pediatric patient in Brazil

Stenotrophomonas maltophilia is one of the Gram-negative bacilli most frequently found in the airways of cystic fibrosis patients. This opportunistic pathogen is intrinsically multidrug-resistant, and therefore, its treatment presents a challenge. The genetic characterization of S. maltophilia is largely unknown, especially from those strains that colonize/infect the airways of cystic fibrosis patients. This work reports the draft genome sequences of three S. maltophilia isolates recovered from the sputum of a cystic fibrosis pediatric patient in Southeast Brazil. Several resistance- and virulence-related genes were detected. Furthermore, one intact phage and one incomplete prophage region were also identified in all strains. Multilocus sequence typing showed that all strains belonged to a new sequence type (ST264). Interestingly, all S. maltophilia strains were genetically identical, showing persistence for at least 16 months. To our knowledge, this is the first report of S. maltophilia draft genome sequences obtained from a cystic fibrosis pediatric patient in Brazil.

Two forms of phosphomannomutase in gammaproteobacteria: The overlooked membrane-bound form of AlgC is required for twitching motility of Lysobacter enzymogenes

Lysobacter enzymogenes, a member of Xanthomonadaceae, is a promising tool to control crop-destroying fungal pathogens. One of its key antifungal virulence factors is the type IV pili that are required for twitching motility. Transposon mutagenesis of L. enzymogenes revealed that the production of type IV pili required the presence of the Le2152 gene, which encodes an AlgC-type phosphomannomutase/phosphoglucomutase (PMM). However, in addition to the cytoplasmic PMM domain, the Le2152 gene product contains a ~200-aa N-terminal periplasmic domain that is anchored in the membrane by two transmembrane segments and belongs to the dCache superfamily of periplasmic sensor domains. Sequence analysis identified similar membrane-anchored PMMs, encoded in conserved coaBC-dut-algC gene clusters, in a variety of gammaproteobacteria, either as the sole PMM gene in the entire genome or in addition to the gene encoding the stand-alone enzymatic domain. Previously overlooked N-terminal periplasmic sensor domains were detected in the well-characterized PMMs of Pseudomonas aeruginosa and Xanthomonas campestris, albeit not in the enzymes from Pseudomonas fluorescens, Pseudomonas putida or Azotobacter vinelandii. It appears that after the initial cloning of the enzymatically active soluble part of P. aeruginosa AlgC in 1991, all subsequent studies utilized N-terminally truncated open reading frames. The N-terminal dCache sensor domain of AlgC is predicted to modulate the PMM activity of the cytoplasmic domain in response to as yet unidentified environmental signal(s). AlgC-like membrane-bound PMMs appear to comprise yet another environmental signalling system that regulates the production of type IV pili and potentially other systems in certain gammaproteobacteria.