Final Report Summary - PACI (Adaptation of Pseudomonas aeruginosa to the human host during chronic infections)
Genotypic and phenotypic features of clinical melanogenic P. aeruginosa. One of the hallmarks of the opportunistic pathogen Pseudomonas aeruginosa is its ability to thrive in diverse environments that includes humans with a variety of debilitating diseases or immune deficiencies. During chronic infections, P. aeruginosa genome widely evolves. Here, we have studied the genomic sequence and phenotypic properties of melanogenic P. aeruginosa (mPA), isolated from chronically-infected patients or derivated from reference strain PAO1 and have compared them with those of their wild-type parent. Melanogenic mutants experienced a large chromosomal reduction (from 1. 06 to 3. 77 % of the whole genome). The new phenotypic properties were tentatively correlated to the deletion of genes undergone by these mutants. In comparison with their parents, melanogenic isolates were more susceptible to the antibiotics aminoglycosides (due to the deletion of the efflux pump-encoding mexXY operon), to extreme basic pH and to osmotic shock. Melanogenic strains showed an impaired fitness when cultured with compounds found in plants (terpens, aromatic amino acids) as the sole source of carbon, as the consequence of the deletion of the gny operon and hmgA gene. Despite their defect in biological fitness when cultured in rich media, half of the melanogenic strains overgrow their wild-type parent in co-culture. We speculated that the growth defect of the melanogenic mutants could be compensated by their observed resistance to the bacteriocin AP41 and/or S1, which could confer the mutant a competitive advantage over their wild-type parents in vivo. We showed that the culture supernatant of stress-induced melanogenic strain (conditions required for pyocine production) inhibits the growth of wild-type strain.
Overall, despite the fitness cost conferred by the large chromosomal deletion, mPA selected in chronically-infected patients can overgrow their wild-type parents. The lower resistance to extreme conditions (basic pH, osmotic shock) and the impaired fitness in plant compounds could reduce the adaptability of the clinical mutants to various environments and their subsequent ability to spread from the patient.
Evidence for induction of integron-based antibiotic resistance by the SOS response in a clinical setting. Hocquet D, Llanes C, Thouverez M, Kulasekara HD, Bertrand X, Patrick Pl?siat, Didier Mazel, Samuel I. Miller (2012) PLoS Pathog 8 (6): e1002778.
Bacterial resistance to ß-lactams may rely on acquired ß lactamases encoded by class 1 integron-borne genes. Rearrangement of integron cassette arrays is mediated by the integrase IntI1. It has been previously established that integrase expression can be activated by the SOS response in vitro, leading to speculation that this is an important clinical mechanism of acquiring resistance. Here we report the first in vivo evidence of the impact of SOS response activated by the antibiotic treatment given to a patient and its output in terms of resistance development. We identified a new mechanism of modulation of antibiotic resistance in integrons, based on the insertion of a genetic element, the gcuF1 cassette, upstream of the integron-borne cassette blaOXA 28 encoding an extended spectrum ß-lactamase. This insertion creates the fused protein GCUF1-OXA-28 and modulates the transcription, the translation, and the secretion of the ß lactamase in a Pseudomonas aeruginosa isolate (S-Pae) susceptible to the third generation cephalosporin ceftazidime. We found that the metronidazole, not an anti-pseudomonal antibiotic given to the first patient infected with S Pae, triggered the SOS response that subsequently activated the integrase IntI1 expression. This resulted in the rearrangement of the integron gene cassette array, through excision of the gcuF1 cassette, and the full expression the ß-lactamase in an isolate (R-Pae) highly resistant to ceftazidime, which further spread to other patients within our hospital. Our results demonstrate that in human hosts, the antibiotic-induced SOS response in pathogens could play a pivotal role in adaptation process of the bacteria.
Overall, despite the fitness cost conferred by the large chromosomal deletion, mPA selected in chronically-infected patients can overgrow their wild-type parents. The lower resistance to extreme conditions (basic pH, osmotic shock) and the impaired fitness in plant compounds could reduce the adaptability of the clinical mutants to various environments and their subsequent ability to spread from the patient.
Evidence for induction of integron-based antibiotic resistance by the SOS response in a clinical setting. Hocquet D, Llanes C, Thouverez M, Kulasekara HD, Bertrand X, Patrick Pl?siat, Didier Mazel, Samuel I. Miller (2012) PLoS Pathog 8 (6): e1002778.
Bacterial resistance to ß-lactams may rely on acquired ß lactamases encoded by class 1 integron-borne genes. Rearrangement of integron cassette arrays is mediated by the integrase IntI1. It has been previously established that integrase expression can be activated by the SOS response in vitro, leading to speculation that this is an important clinical mechanism of acquiring resistance. Here we report the first in vivo evidence of the impact of SOS response activated by the antibiotic treatment given to a patient and its output in terms of resistance development. We identified a new mechanism of modulation of antibiotic resistance in integrons, based on the insertion of a genetic element, the gcuF1 cassette, upstream of the integron-borne cassette blaOXA 28 encoding an extended spectrum ß-lactamase. This insertion creates the fused protein GCUF1-OXA-28 and modulates the transcription, the translation, and the secretion of the ß lactamase in a Pseudomonas aeruginosa isolate (S-Pae) susceptible to the third generation cephalosporin ceftazidime. We found that the metronidazole, not an anti-pseudomonal antibiotic given to the first patient infected with S Pae, triggered the SOS response that subsequently activated the integrase IntI1 expression. This resulted in the rearrangement of the integron gene cassette array, through excision of the gcuF1 cassette, and the full expression the ß-lactamase in an isolate (R-Pae) highly resistant to ceftazidime, which further spread to other patients within our hospital. Our results demonstrate that in human hosts, the antibiotic-induced SOS response in pathogens could play a pivotal role in adaptation process of the bacteria.