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Background Co-colonization by Pseudomonas aeruginosa and Staphylococcus aureus is frequent in cystic fibrosis patients. Polymicrobial infections involve both detrimental and beneficial interactions between different bacterial species. Such interactions potentially indirectly impact the human host through virulence, antibiosis and immunomodulation. Results Here we explored the responses triggered by the encounter of these two pathogens to identify early processes that are important for survival when facing a potential competitor. Transcriptional profiles of both bacteria were obtained after 3 h co-culture and compared to the respective mono-culture using RNAseq. Global responses in both bacteria included competition for nitrogen sources, amino acids and increased tRNA levels. Both organisms also induced lysogenic mechanisms related to prophage induction ( S. aureus ) and R- and F- pyocin synthesis ( P. aeruginosa ), possibly as a response to stress resulting from nutrient limitation or cell damage. Specific responses in S. aureus included increased expression of de novo and salvation pathways for purine and pyrimidine synthesis, a switch to glucose fermentation, and decreased expression of major virulence factors and global regulators. Conclusions Taken together, transcriptomic data indicate that early responses between P. aeruginosa and S. aureus involve competition for resources and metabolic adaptations, rather than the expression of bacteria- or host-directed virulence factors.

Bacteriophage therapy has been suggested as an alternative or complementary strategy for the treatment of multidrug resistant (MDR) bacterial infections. Here, we report the favourable clinical evolution of a 41-year-old male patient with a Kartagener syndrome complicated by a life-threatening chronic MDR Pseudomonas aeruginosa infection, who is treated successfully with iterative aerosolized phage treatments specifically directed against the patient’s isolate. We follow the longitudinal evolution of both phage and bacterial loads during and after phage administration in respiratory samples. Phage titres in consecutive sputum samples indicate in patient phage replication. Phenotypic analysis and whole genome sequencing of sequential bacterial isolates reveals a clonal, but phenotypically diverse population of hypermutator strains. The MDR phenotype in the collected isolates is multifactorial and mainly due to spontaneous chromosomal mutations. All isolates recovered after phage treatment remain phage susceptible. These results demonstrate that clinically significant improvement is achievable by personalised phage therapy even in the absence of complete eradication of P. aeruginosa lung colonization. Köhler et al. document the treatment, and clinical improvement, of a male patient with a life-threatening chronic multi-drug resistant Pseudomonas aeruginosa infection with aerosolized personalized phage therapy, in combination with intravenous antibiotic treatment.

PurposePrognosis of solid organ transplant (SOT) recipients has improved, mainly because of better prevention of rejection by immunosuppressive therapies. However, SOT recipients are highly susceptible to conventional and opportunistic infections, which represent a major cause of morbidity, graft dysfunction and mortality.MethodsNarrative review.ResultsWe cover the current epidemiology and main aspects of infections in SOT recipients including risk factors such as postoperative risks and specific risks for different transplant recipients, key points on anti-infective prophylaxis as well as diagnostic and therapeutic approaches. We provide an up-to-date guide for management of the main syndromes that can be encountered in SOT recipients including acute respiratory failure, sepsis or septic shock, and central nervous system infections as well as bacterial infections with multidrug-resistant strains, invasive fungal diseases, viral infections and less common pathogens that may impact this patient population.ConclusionWe provide state-of the art review of available knowledge of critically ill SOT patients with infections.

Bacteria communicate and cooperate to perform a wide range of social behaviors including production of extracellular products (public goods) that are crucial for growth and virulence. Their expression may be switched on by the detection of threshold densities of diffusible signals [Quorum-Sensing (QS)]. Studies using the opportunistic pathogen Pseudomonas aeruginosa suggest that QS \"cheats\"--individuals that don't respond to the QS signal, but are still able to use public goods produced by others--have a selective advantage in the presence of QS cooperators. It is, however, unclear whether this type of social exploitation is relevant in clinical contexts. Here, we report the evolutionary dynamics and virulence of P. aeruginosa populations during lung colonization of mechanically ventilated patients in the absence of antimicrobial treatments. We observed a large diversity of QS phenotypes among initial colonizing isolates. This diversity decreased over a matter of days, concomitant with a gradual increase in the proportion of QS cheating mutants (lasR mutants), which were found in 80% of the patients after 9 days of colonization. These mutants often evolved from initial wild-type genotypes. The fitness advantage of the lasR mutants is almost certainly due to social exploitation, because this advantage was only apparent in the presence of QS wild-type cells. Crucially, ventilator-associated pneumonia occurred significantly earlier in patients predominantly colonized by QS wild-type populations, highlighting the importance of QS in this clinical situation. These results demonstrate that social interactions can shape the short-term evolution and virulence of bacterial pathogens in humans, providing novel opportunities for therapy.

With the rising development of bacterial resistance the search for new medical treatments beyond conventional antimicrobials has become a key aim of public health research. Possible innovative strategies include the inhibition of bacterial virulence. However, consideration must be given to the evolutionary and environmental consequences of such new interventions. Virulence and cooperative social behaviour of the bacterium Pseudomonas aeruginosa rely on the quorum-sensing (QS) controlled production of extracellular products (public goods). Hence QS is an attractive target for anti-virulence interventions. During colonization, non-cooperating (and hence less virulent) P. aeruginosa QS-mutants, benefiting from public goods provided by wild type isolates, naturally increase in frequency providing a relative protection from invasive infection. We hypothesized that inhibition of QS-mediated gene expression removes this growth advantage and selection of less virulent QS-mutants, and maintains the predominance of more virulent QS-wild type bacteria. We addressed this possibility in a placebo-controlled trial investigating the anti-QS properties of azithromycin, a macrolide antibiotic devoid of bactericidal activity on P. aeruginosa, but interfering with QS, in intubated patients colonized by P. aeruginosa. In the absence of azithromycin, non-cooperating (and hence less virulent) lasR (QS)-mutants increased in frequency over time. Azithromycin significantly reduced QS-gene expression measured directly in tracheal aspirates. Concomitantly the advantage of lasR-mutants was lost and virulent wild-type isolates predominated during azithromycin treatment. We confirmed these results in vitro with fitness and invasion experiments. Azithromycin reduced growth rate of the wild-type, but not of the lasR-mutant. Furthermore, the lasR-mutant efficiently invaded wild-type populations in the absence, but not in the presence of azithromycin. These in vivo and in vitro results demonstrate that anti-virulence interventions based on QS-blockade diminish natural selection towards reduced virulence and therefore may increase the prevalence of more virulent genotypes in the Hospital environment. More generally, the impact of intervention on the evolution of virulence of pathogenic bacteria should be assessed.

Background There are limited real-life data on isavuconazole prophylaxis and treatment of invasive mold infections (IMI) in hematological patients and allogeneic hematopoietic cell transplant (HCT) recipients. Objectives Primary objective was to describe the indications of real-life isavuconazole administration at a university hospital. Secondary objectives included the description of liver function tests and QTc interval between baseline and end of treatment (EOT), clinical outcomes and breakthrough IMI by the EOT. Patients/Methods This was a 5-year single-center retrospective study of all adult patients with acute myeloid leukemia and/or allogeneic HCT recipients who received isavuconazole as prophylaxis and/or treatment between June 1, 2016, and July 31, 2020. Results Among 30 identified patients, the indications for isavuconazole administration were adverse events associated with prior antifungal treatment ( N : 18, 60%: hepatotoxicity, renal insufficiency, long QTc interval, neurotoxicity, and potential drug–drug interactions in 6, 4, 3, 1 and 4 patients, respectively), clinical efficacy ( N : 5, 16.6%), and other reasons ( N : 10, 33.3%; 5/10 patients treated with isavuconazole to facilitate hospital discharge with orally administered appropriate treatment). Alanine aminotransferase significantly decreased from baseline (mean: 129 IU/L, range: 73, 202) to a mean of 48 IU/L (range: 20, 80) by day 14 ( P -value: 0.02), 23.5 IU/L (range: 20, 27) by day 28 ( P -value: 0.03) and 16.5 IU/L (range: 16, 17) by day 42 ( P -value: 0.009). The QTc interval decreased from baseline (mean: 456.8 ms, range: 390, 533) to EOT (mean: 433.8 ms, range: 400, 472; P -value: 0.03). The mean isavuconazole plasma concentration was 2.9 mg/L (range: 0.9, 6.7). There was no breakthrough IMI observed. Conclusion Isavuconazole is a safe and reliable antifungal agent in complex hematological patients, with relatively low hepatotoxicity and QTc interval shortening properties.

Valganciclovir (VGC) is administered as prophylaxis to kidney transplant recipients (KTR) CMV donor (D)+/recipient (R)− and CMV R+ after thymoglobulin-induction (R+/TG). Although VGC dose adjustments based on renal function are recommended, there is paucity of real-life data on VGC dosing and associations with clinical outcomes. This is a retrospective Swiss Transplant Cohort Study-embedded observational study, including all adult D+/R− and R+/TG KTR between 2010 and 2020, who received prophylaxis with VGC. The primary objective was to describe the proportion of inappropriately (under- or over-) dosed VGC week-entries. Secondary objectives included breakthrough clinically significant CMV infection (csCMVi) and potential associations between breakthrough-csCMVi and cytopenias with VGC dosing. Among 178 KTR, 131 (73.6%) patients had ≥2 week-entries for the longitudinal data of interest and were included in the outcome analysis, with 1,032 VGC dose week-entries. Overall, 460/1,032 (44.6%) were appropriately dosed, while 234/1,032 (22.7%) and 338/1,032 (32.8%) were under- and over-dosed, respectively. Nineteen (14.5%) patients had a breakthrough-csCMVi, without any associations identified with VCG dosing ( p = 0.44). Unlike other cytopenias, a significant association between VGC overdosing and lymphopenia (OR 5.27, 95% CI 1.71–16.22, p = 0.004) was shown. VGC prophylaxis in KTR is frequently inappropriately dosed, albeit without meaningful clinical associations, neither in terms of efficacy nor safety.

The metabolically versatile Gram-negative bacterium Pseudomonas aeruginosa inhabits terrestrial, aquatic, animal-, human-, and plant-host-associated environments and is an important causative agent of nosocomial infections, particularly in intensive-care units. The population genetics of P. aeruginosa was investigated by an approach that is generally applicable to the rapid, robust, and informative genotyping of bacteria. DNA, amplified from the bacterial colony by circles of multiplex primer extension, is hybridized onto a microarray to yield an electronically portable binary multimarker genotype that represents the core genome by single nucleotide polymorphisms and the accessory genome by markers of genomic islets and islands. The 240 typed P. aeruginosa strains of diverse habitats and geographic origin segregated into two large nonoverlapping clusters and 45 isolated clonal complexes with few or no partners. The majority of strains belonged to few dominant clones widespread in disease and environmental habitats. The most frequent genotype was represented by the sequenced strain PA14. Core and accessory genome were found to be nonrandomly assembled in P. aeruginosa. Individual clones preferred a specific repertoire of accessory segments. Even the most promiscuous genomic island, pKLC102, had integrated preferentially into a subset of clones. Moreover, some physically distant loci of the core genome, including oriC, showed nonrandom associations of genotypes, whereas other segments in between were freely recombining. Thus, the P. aeruginosa genome is made up of clone-typical segments in core and accessory genome and of blocks in the core with unrestricted gene flow in the population.

Abstract In Pseudomonas aeruginosa many of the clinically relevant resistance mechanisms result from changes in gene expression as exemplified by the Mex drug efflux pumps, the AmpC β-lactamase and the carbapenem-specific porin OprD. We used quantitative real-time-PCR to analyze the expression of these genes in susceptible and antibiotic-resistant laboratory and clinical strains. In nalB mutants, which overexpress OprM, we observed a four- to eightfold increase in the expression of mexA, mexB, and oprM genes. MexX and mexY genes were induced eight to 12 times in the presence of 2 mg L−1 tetracycline. The mexC/oprJ and mexE/oprN gene expression levels were increased 30- to 250-fold and 100- to 760-fold in nfxB and nfxC mutants, respectively. We further found that in defined laboratory strains expression levels of ampC and oprD genes paralleled β-lactamase activity and OprD protein levels, respectively. Our data support the use of quantitative real-time-PCR chain reaction for the analysis of the antimicrobial resistance gene expression in P. aeruginosa.