AmpR is a dual regulator in Stenotrophomonas maltophilia with a positive role in ß-lactam resistance and a negative role in virulence, biofilm and DSF production.

Stenotrophomonas maltophilia intrinsic resistance to ß-lactams is mediated by two chromosomal ß-lactamases, L1 and L2, whose induction depends on AmpR. Its quorum sensing (QS) signal, the diffusible signal factor (DSF), has a positive role in biofilm production, virulence and induction of ß-lactamases. We hypothesized that AmpR has a role in virulence, biofilm production and QS system. Studies were done on S. maltophilia K279a, K279a ampRFS (ampR deficient mutant) and K279aM11 (constitutively active AmpR mutant). K279a ampRFS showed the highest biofilm biomass, thickness and 3D organization. Conversely, K279aM11 was the least efficient biofilm former strain. qRT-PCR showed that spgM, related to biofilm formation and virulence, was upregulated in K279a ampRFS and downregulated in K279aM11. A constitutively active AmpR led to a reduction of DSF production, while K279a ampRFS was the highest producer. Consequently, qRT-PCR showed that AmpR negatively regulated rpfF expression. K279a ampRFS presented the highest oxidative stress resistance, overexpressed sodA gene and showed the highest virulence in the Galleria mellonella killing assay. This is the first evidence of the function of AmpR as a dual regulator in S. maltophilia with a positive role in ß-lactam resistance and a negative role in DSF production, biofilm formation, oxidative stress resistance and virulence.

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.

The rpf/DSF signalling system of Stenotrophomonas maltophilia positively regulates biofilm formation, production of virulence-associated factors and ß-lactamase induction.

Stenotrophomonas maltophilia is a multidrug-resistant opportunistic pathogen. S. maltophilia quorum-sensing system is mediated by the diffusible signal factor (DSF), which synthesis depends on rpfF. It has been reported that rpfF disruption in S. maltophilia K279a leads to a loss of DSF synthesis, reduced levels of extracellular protease, swarming motility and virulence in the Galleria mellonella model. The aim of this work was to attain a deeper knowledge of the role of the rpf/DSF signalling system in S. maltophilia biofilm formation, phenotypic traits associated with biofilm development and virulence and antimicrobial susceptibility. To this end, comparative studies were conducted on S. maltophilia K279a and K279arpfF. The results presented here put in evidence the positive role of DSF in bacterial growth, biofilm formation, swimming and twitching motilities, DNAse, lipases and siderophores production as well as resistance to oxidative stress. Interestingly, DSF seems to be essential for the development of the spatially organised structure seen in mature biofilms. Therefore, DSF from S. maltophlia K279a positively regulates biofilm formation and virulence. Furthermore, DSF is necessary for the induction of L1 and L2 ß-lactamase production in K279a. This is the first evidence of the role of the rpf/DSF signalling system in S. maltophilia ß-lactam resistance.

Stenotrophomonas maltophilia isolated from patients exposed to invasive devices in a university hospital in Argentina: molecular typing, susceptibility and detection of potential virulence factors.

Purpose. The aim of this work was to investigate the presence of selected potential virulence factors, susceptibility and clonal relatedness among 63 Stenotrophomonas maltophilia isolates recovered from patients exposed to invasive devices in a university hospital in Argentina between January 2004 and August 2012.Methodology. Genetic relatedness was assessed by enterobacterial repetitive intergenic consensus PCR (ERIC-PCR) and pulsed-field gel electrophoresis (PFGE). Isolates were characterized by antimicrobial resistance, the presence and/or expression of potential virulence determinants, and virulence in the Galleria mellonella model.Results/Key findings. ERIC-PCR generated 52 fingerprints, and PFGE added another pattern. Resistance to trimethoprim-sulfamethoxazole (6.35 %), levofloxacin (9.52 %) and ciprofloxacin (23.80 %) was detected. All isolates were susceptible to minocycline. All isolates were lipase, protease and siderophore producers, while all but Sm61 formed biofilms. However, 11/63 isolates did not amplify the major extracellular protease-coding gene (stmPr1). Sm61 is an stmPr1-negative isolate, and showed (as did Sm13 and the reference strain K279a) strong proteolysis and siderophore production, and high resistance to hydrogen peroxide. The three isolates were virulent in the G. mellonella model, while Sm10, a low-resistance hydrogen peroxide stmPr1-negative isolate, and weak proteolysis and siderophore producer, was not virulent.Conclusion. This is the first epidemiological study of the clonal relatedness of S. maltophilia clinical isolates in Argentina. Great genomic diversity was observed, and only two small clusters of related S. maltophilia types were found. Minocycline and trimethoprim-sulfamethoxazole were the most active agents. S. maltophilia virulence in the G. mellonella model is multifactorial, and further studies are needed to elucidate the role of each potential virulence factor.

Iron is a signal for Stenotrophomonas maltophilia biofilm formation, oxidative stress response, OMPs expression, and virulence.

Stenotrophomonas maltophilia is an emerging nosocomial pathogen. In many bacteria iron availability regulates, through the Fur system, not only iron homeostasis but also virulence. The aim of this work was to assess the role of iron on S. maltophilia biofilm formation, EPS production, oxidative stress response, OMPs regulation, quorum sensing (QS), and virulence. Studies were done on K279a and its isogenic fur mutant F60 cultured in the presence or absence of dipyridyl. This is the first report of spontaneous fur mutants obtained in S. maltophilia. F60 produced higher amounts of biofilms than K279a and CLSM analysis demonstrated improved adherence and biofilm organization. Under iron restricted conditions, K279a produced biofilms with more biomass and enhanced thickness. In addition, F60 produced higher amounts of EPS than K279a but with a similar composition, as revealed by ATR-FTIR spectroscopy. With respect to the oxidative stress response, MnSOD was the only SOD isoenzyme detected in K279a. F60 presented higher SOD activity than the wt strain in planktonic and biofilm cultures, and iron deprivation increased K279a SOD activity. Under iron starvation, SDS-PAGE profile from K279a presented two iron-repressed proteins. Mass spectrometry analysis revealed homology with FepA and another putative TonB-dependent siderophore receptor of K279a. In silico analysis allowed the detection of potential Fur boxes in the respective coding genes. K279a encodes the QS diffusible signal factor (DSF). Under iron restriction K279a produced higher amounts of DSF than under iron rich condition. Finally, F60 was more virulent than K279a in the Galleria mellonella killing assay. These results put in evidence that iron levels regulate, likely through the Fur system, S. maltophilia biofilm formation, oxidative stress response, OMPs expression, DSF production and virulence.

Stenotrophomonas maltophilia interferes via the DSF-mediated quorum sensing system with Candida albicans filamentation and its planktonic and biofilm modes of growth / Stenotrophomonas maltophilia interfiere a través del sistema de "quorum sensing" mediado por DSF con la filamentación y el crecimiento planctónico y en biofilm de Candida albicans

Stenotrophomonas maltophilia is a nosocomial pathogen of increasing importance. S. maltophilia K279a genome encodes a diffusible signal factor (DSF) dependent quorum sensing (QS) system that was first identified in Xanthomonas campestris pv. campestris. DSF from X. campestris is a homologue of farnesoic acid, a Candida albicans QS signal which inhibits the yeast-to-hyphal shift. Here we describe the antagonistic effects of S. maltophilia on C. albicans on filamentation as well as on its planktonic and biofilm modes of growth. To determine the role of the DSF-mediated quorum sensing system in these effects, C. albicans ATCC 10231 and C. albicans tup1 mutant, locked in the filamentous form, were grown with K279a or with its rpfF deletion mutant (DSF-). A significant reduction in viable counts of C. albicans was observed in planktonic cocultures with K279a as well as in mixed biofilms. Furthermore, no viable cells of C. albicans tup1 were recovered from K279a mixed biofilms. Fungal viability was also assessed by labeling biofilms with SYTO 9 and propidium iodide. Confocal images showed that K279a can kill hyphae and also yeast cells. Light microscopic analysis showed that K279a severely affects hyphae integrity. On the other hand, the presence of K279a rpfF did not affect fungal morphology or viability. In conclusion, we report for the first time that S. maltophilia interferes with two key virulence factors of C. albicans, the yeast-to-hyphal transition and biofilm formation. DSF could be directly responsible for these effects or may induce the gene expression involved in antifungal activity.

Stenotrophomonas maltophilia es un patógeno nosocomial de importancia creciente. El genoma de S. maltophilia K279a codifica un factor de señalización difusible (DSF), autoinductor de "quorum sensing" (QS), identificado previamente en Xanthomonas campestris pv. campestris. El DSF de X. campestris es homólogo del ácido farnesoico, señal de QS de Candida albicans, que inhibe la transición levadura-hifa. En este trabajo se describe el efecto antagónico de S. maltophilia sobre la filamentación y el crecimiento planctónico y en biofilms de C. albicans. Para determinar la participación del sistema de QS mediado por el DSF en dichos efectos, C. albicans ATCC 10231 y la mutante C. albicans tup1, que solo crece en forma filamentosa, fueron cultivadas en presencia de K279a o de su mutante K279a rpfF (DSF-). Se observó una reducción significativa del número de viables de C. albicans en cultivos planctónicos y biofilms desarrollados en presencia de K279a. Es de señalar que no se recuperaron células viables de C. albicans tup1 a partir de biofilms mixtos en presencia de K279a. Las imágenes de microscopía confocal revelaron que K279a produce la muerte de hifas y levaduras en biofilms mixtos teñidos con ioduro de propidio y SYTO 9. El análisis por microscopía óptica mostró que K279a afecta la integridad de las hifas. En cambio, la presencia de K279a rpfF no afectó la morfología ni la viabilidad fúngica. En conclusión, informamos por primera vez que S. maltophilia interfiere con dos factores de virulencia de C. albicans, la transición levadura-hifa y la formación de biofilms. Estos efectos pueden ser mediados por el DSF en forma directa o a través de la inducción de genes involucrados en la actividad antifúngica.

Stenotrophomonas maltophilia interferes via the DSF-mediated quorum sensing system with Candida albicans filamentation and its planktonic and biofilm modes of growth.

Stenotrophomonas maltophilia is a nosocomial pathogen of increasing importance. S. maltophilia K279a genome encodes a diffusible signal factor (DSF) dependent quorum sensing (QS) system that was first identified in Xanthomonas campestris pv. campestris. DSF from X. campestris is a homologue of farnesoic acid, a Candida albicans QS signal which inhibits the yeast-to-hyphal shift. Here we describe the antagonistic effects of S. maltophilia on C. albicans on filamentation as well as on its planktonic and biofilm modes of growth. To determine the role of the DSF-mediated quorum sensing system in these effects, C. albicans ATCC 10231 and C. albicans tup1 mutant, locked in the filamentous form, were grown with K279a or with its rpfF deletion mutant (DSF-). A significant reduction in viable counts of C. albicans was observed in planktonic cocultures with K279a as well as in mixed biofilms. Furthermore, no viable cells of C. albicans tup1 were recovered from K279a mixed biofilms. Fungal viability was also assessed by labeling biofilms with SYTO 9 and propidium iodide. Confocal images showed that K279a can kill hyphae and also yeast cells. Light microscopic analysis showed that K279a severely affects hyphae integrity. On the other hand, the presence of K279a rpfF did not affect fungal morphology or viability. In conclusion, we report for the first time that S. maltophilia interferes with two key virulence factors of C. albicans, the yeast-to-hyphal transition and biofilm formation. DSF could be directly responsible for these effects or may induce the gene expression involved in antifungal activity.

Siderophores of Stenotrophomonas maltophilia: detection and determination of their chemical nature.

Stenotrophomonas maltophilia is an emerging nosocomial pathogen. Despite the broad spectrum of syndromes associated with S. maltophilia infections, little is known about its virulence factors, including siderophore production. The aims of this work were to detect S. maltophilia siderophores and to determine their chemical nature. We studied 31 S. maltophilia isolates from device-associated infections, recovered over the period 2006-2011 at Hospital de Clínicas José de San Martín, Buenos Aires, Argentina, and the strain K279a, whose genome has been fully sequenced. The production of siderophores was screened by the chrome azurol S (CAS) agar assay, previously modified to detect siderophores in this species. When grown on modified CAS agar plates, all the clinical isolates and K279a were CAS-positive for siderophore production. In order to determine the chemical nature of siderophores, the Csáky (hydroxamate-type) and Arnow (catechol-type) assays were used. All S. maltophilia isolates produced catechol-type siderophores, but hydroxamate-type siderophores were not detected.