Biology subjects

Echlin, H.

Publications and source records attributed to Echlin, H..

5 recordsLinked to original sources

bioRxiv2026

RNA Quality Control Enables Antibiotic Tolerance

The mechanisms underlying adaptation to antibiotic pressure within complex host environments remain incompletely understood. By experimentally evolving Streptococcus pneumoniae subjected to various antibiotics and immune states, we demonstrate populations adopting distinct adaptive strategies depending on specific selective context. General antibiotic stress drives convergent mutations in rny, encoding the RNA degradosome scaffold RNase Y, that exhibit broad-spectrum antibiotic tolerance and accelerated recovery. Single-cell transcriptomics revealed antibiotic-induced death is driven by transcriptional collapse, a catastrophic loss of RNA quantity and integrity. In contrast, rny mutants avert this via a bet-hedging strategy: a resilient minority maintains a baseline transcriptional profile, while a quiescent majority undergoes selective RNA degradation to preserve transcript fidelity. Upon stress removal, these populations execute a prioritized transcriptional ribosomal reboot, facilitating accelerated recovery. These findings identify RNA turnover as a tunable master regulator to survive combined pressures of antibiotics and immunity.

microbiology↗

bioRxiv2025

Resistance and heteroresistance as a consequence of colistin therapy during Acinetobacter baumannii murine pneumonia

Acinetobacter baumannii is an ESKAPE pathogen linked to healthcare-associated diseases. Due to evolved resistance, last-resort antibiotics such as the lipooligosaccharide (LOS)-targeting colistin are increasingly used to treat multidrug-resistant isolates. To track the evolution of colistin resistance within a host, we performed sequential oropharyngeal infections in immunocompetent or immune-depleted mice in the presence of inhaled colistin. Both resistant and heteroresistant A. baumannii strains emerged with pmrB mutations that efficiently competed with the susceptible parent in the presence of colistin. These pmrB mutants had a fitness cost in the absence of colistin treatment but retained their ability to colonize the host. In contrast, LOS-deficient A. baumannii mutants removed the target of colistin, but such mutants were unable to colonize the lung. The two pathogenic pmrB mutants showed clear evidence of LOS modification, which was linked to increased transcription of LOS modification enzymes, including the product of the cryptic eptA gene. Spontaneous insertion mutations that caused hyperexpression of eptA allowed the heteroresistant mutant to develop clinically-significant colistin resistance. Insertion mutations upstream of the eptA gene or those disrupting hns, which encodes a small histone-like protein, resulted in increased eptA transcript, linking expression of this protein to clinically significant resistance. A resistant variant derived from the heteroresistant parent was stable in the absence of drug, but continued passaging selected for colistin-resensitized pseudorevertants that were largely due to disruption of the LOS modification enzymes. Therefore, colistin heteroresistance is an early stage in the stepwise acquisition of stable colistin resistance in A. baumannii. SignificanceThe mutational pathways leading to antibiotic-resistant infections and the role of the immune system in preventing them are poorly understood. Here we employed a colistin-treated mouse pneumonia model of Acinetobacter baumannii and observed the evolution of colistin-resistant and heteroresistant mutants in immune-depleted and immunocompetent hosts, respectively. We show that mutations that result in alteration of colistins target drive evolutionary pathways to resistance, whereas removal of the target is unlikely to be clinically significant. We demonstrated that the heteroresistant mutant generates subpopulations with higher levels of resistance through insertion mutations in specific gene regions. This study furthers our understanding of how resistance emerges during infection and provides a genetic explanation for the transition from colistin heteroresistance to full resistance.

microbiology↗

bioRxiv2022

Pneumococcal Evasion of Antibiotics via Metabolic Adaptation During Infection

Streptococcus pneumoniae is a major human pathogen of global health concern, causing a range of mild to severe infections, including acute otitis media, pneumonia, sepsis, and meningitis. The rapid emergence of antibiotic resistance among S. pneumoniae isolates poses a serious public health problem worldwide. Resistant pneumococcal strains have rendered the mainstay treatment with beta-lactams, fluoroquinolones, and macrolides, ineffective. Antibiotic resistance in S. pneumoniae has spread globally via the emergence of de novo mutations and horizontal transfer of resistance. Fluoroquinolone resistance in S. pneumoniae is an intriguing case because the prevalence of fluoroquinolone resistance does not correlate with increasing usage, as is often the case with other classes of antibiotics. In this study, we demonstrated that deleterious fitness costs constrain the emergence of individual fluoroquinolone resistance mutations in either topoisomerase IV or gyrase A in S. pneumoniae. Generation of double point mutations in the target enzymes in topoisomerase IV and gyrase A conferred high-level fluoroquinolone resistance while restoring fitness comparable to the sensitive wild-type. During an in vivo model of antibiotic resistance evolution, S. pneumoniae was able to circumvent deleterious fitness costs imposed by resistance determinants through development of antibiotic tolerance through metabolic adaptation that reduced the production of reactive oxygen species, an effect that could be recapitulated pharmacologically. The metabolic mutants conferring tolerance resulted in a fitness benefit during infection following antibiotic treatment with fluroquinolones. These data suggest that emergence of fluoroquinolone resistance is tightly constrained in S. pneumoniae by host fitness tradeoffs and that mutational pathways involving metabolic networks to enable tolerance phenotypes may be an important contributor to the evasion of antibiotic mediated killing.

microbiology↗

bioRxiv2020

Identification of colonisation and virulence determinants of Streptococcus pneumoniae via experimental evolution in mouse infection models

Streptococcus pneumoniae is a commensal of the human nasopharynx and a major cause of respiratory and invasive disease. Pneumococcus stimulates upper respiratory tract inflammation that promotes shedding from mucosal surfaces and transmission to new hosts. Colonisation and transmission are partially antagonistic processes. Adhesion to surfaces and evasion of host responses favours the former, whilst detachment, promoted by inflammation, is necessary for the latter. We sought to determine how adaptation and evolution of pneumococcus within its nasopharyngeal niche might progress when selective pressures associated with transmission were removed. This was achieved by serial passage of pneumococci in mouse models of nasopharyngeal carriage, manually transferring bacteria between mice. To assess the role of host environmental factors on pneumococcal evolution, we also performed analogous experimental evolution in a mouse pneumonia model, passaging pneumococci through lungs. Nasopharynx-passaged pneumococci became more effective colonisers, whilst those evolved within lungs showed reduced virulence. We observed selection of mutations in genes associated with cell wall biogenesis and metabolism in both nasopharynx and lung lineages, but identified prominent examples of parallel evolution that were niche specific. We focussed on gpsA, a gene in which the same single nucleotide polymorphism arose in two independently evolved nasopharynx-passaged lineages. We identified a single nucleotide change conferring resistance to oxidative stress and enhanced nasopharyngeal colonisation potential. We show that gpsA is also a frequent target of mutation during human colonisation. These findings highlight the role played by the host environment in determining trajectories of bacterial evolution and the potential of experimental evolution in animal infection models for identification of novel pathogen virulence and colonisation factors.

microbiology↗

bioRxiv2020

Respiratory bacteria stabilize and promote airborne transmission of influenza A virus

Influenza A virus (IAV) is a major pathogen of the human respiratory tract where the virus co-exists and interacts with bacterial populations comprising the respiratory microbiome. Synergies between IAV and respiratory bacterial pathogens promote enhanced inflammation and disease burden that exacerbate morbidity and mortality. We demonstrate that direct interactions between IAV and encapsulated bacteria commonly found in the respiratory tract promote environmental stability and infectivity of IAV. Antibiotic-mediated depletion of the respiratory bacterial flora abrogated IAV transmission in ferret models, indicating that these viral-bacterial interactions are operative for airborne transmission of IAV. Restoring IAV airborne transmission in antibiotic treated ferrets by co-infection with Streptococcus pneumoniae confirmed a role for specific members of the bacterial respiratory community in promoting IAV transmission. These results implicate a role for the bacterial respiratory flora in promoting airborne transmission of IAV.

microbiology↗