Biology subjects

Karlsson, P. A.

Publications and source records attributed to Karlsson, P. A..

3 recordsLinked to original sources

bioRxiv2026

Polymicrobial catheter biofilms sustain susceptible Enterococcus faecalis and Escherichia coli during β-lactam treatment

Broad-spectrum {beta}-lactam exposure can select for Enterococcus-dominated urinary communities in catheterized intensive-care patients, even when co-colonizing Escherichia coli remains susceptible. We investigated paired E. faecalis and E. coli isolates recovered before and after piperacillin-tazobactam (TZP) treatment using a catheter biofilm model and showed that their survival depends on mutualism and biofilm-dependent persistence. Without antibiotics, E. faecalis reduced E. coli biofilm formation yet promoted pre-attachment co-aggregation and reorganized mixed-biofilm architecture on the catheter. Despite TZP susceptibility and the absence of resistance determinants, catheter-associated biofilms and biofilm-dispersed cells survived concentrations 250- to 1000-fold above their MICs, whereas planktonic cells were eliminated. Survivors retained susceptibility but showed delayed regrowth, consistent with a transient persister-like state. In the post-treatment pair, each species sustained the other during recovery, coinciding with a nonsynonymous substitution in the enterococcal surface adhesin Esp. These findings show that antagonistic and cooperative interactions can coexist within catheter biofilms and enable susceptible polymicrobial communities to withstand {beta}-lactam treatment without {beta}-lactam resistance.

microbiology↗

bioRxiv2025

The pcnB gene sustains Shigella flexneri virulence

The enteropathogen Shigella flexneri employs a Type Three Secretion System (T3SS) to colonize intestinal epithelial cells. Genes encoding the T3SS are located on a large IncFII virulence plasmid, pINV. T3SS expression comes at the expense of slowed Shigella growth and is therefore strictly controlled by both transcriptional and post-transcriptional mechanisms. Following up on a recent genome-wide screen, we here show that the chromosomal gene pcnB, encoding the poly-A polymerase I (PAP-I), slows Shigella growth at 37{degrees}C, while at the same time promotes early colonization of a human epithelial enteroid model. Proteomic profiling revealed that pcnB drives global increase of the Shigella T3SS virulence program. Accordingly, pcnB sustains pINV replication to a level optimal for Shigella virulence. This is achieved through increased degradation of the antisense RNA CopA, involved in plasmid replication control. The pcnB effect on pINV replication was found to also ensure longer-term intraepithelial expansion of Shigella following human intestinal epithelium invasion. Our findings exemplify how an optimal pINV level is necessary for the execution of Shigellas infection cycle. AUTHOR SUMMARYBacterial infections represent a major global threat. Understanding the genetic determinants promoting infections is crucial to overcome this threat. Shigella is an intracellular bacterial pathogen that invades and disseminates in the intestinal epithelium, causing bacillary dysentery in humans. Shigellas ability to cause disease relies on the delivery of effector proteins into the host cells through an injection machinery, with most of the genes involved in this process located on a large virulence plasmid. Here we show that the chromosomal gene pcnB sustains an optimal virulence plasmid level. This is crucial for Shigella to maximize virulence protein expression and thereby efficiently invade, replicate and spread within the intestinal epithelium.

microbiology↗

bioRxiv2024

Heterogeneity and Metabolic Diversity among Enterococcus Species during Long-term Colonization

Urinary tract infections (UTIs), traditionally dominated by Gram-negative pathogens, are increasingly complicated by antimicrobial-resistant Enterococcus spp. in hospital settings. This study screened urine samples from 210 ICU patients at Uppsala University Hospital (June 2020 - September 2021), identifying 39 unique PhenePlate-RF types across E. faecium, E. faecalis, and E. durans. E. faecium isolates showed considerable genetic diversity, primarily within clonal complex 17 (CC17), known for its virulence and antibiotic resistance. We identified multiple lineages and sequence types (STs), such as in patient HWP143, who had isolates from both ST80 and ST22 (an ancestral CC17 lineage). Notably, metabolic adaptations, such as increased L-arabinose metabolism, and shifts in antibiotic resistance were observed. Variations and similarities in plasmid content between individual linages suggest horizontal gene transfer. E. faecalis isolates exhibited less genetic diversity but significant metabolic variability across patients and mixed infections, as seen in patient HWP051, colonized by both ST16 (CC58) and ST287. E. durans, though less common, shared important metabolic traits with E. faecium and displayed polyclonal characteristics, highlighting its potential role in UTIs and the complexity of enterococcal infections. E. durans was sometimes misidentified, underscoring the need for accurate identification methods. This research underscores the importance of understanding genetic and metabolic diversity, plasmid variations, and horizontal gene transfer in Enterococcus spp., which influence antibiotic resistance, virulence, and ultimately, treatment outcomes. IMPORTANCE STATEMENTOur study uncovers novel insights into the genetic and metabolic diversity of Enterococcus species within individual patients, focusing on E. faecium, E. faecalis, and E. durans. Unlike prior studies, which often focused on single lineages, we reveal multiple clones and lineages across individual patients, including clones from clonal complex 17 and the emerging sequence type (ST) 192, highlighting notable metabolic adaptations and shifts in antibiotic resistance. The detection of mixed colonization with varied ST-types, and E. durans misidentification by MALDI-TOF, later corrected by sequencing, further emphasizes the challenges in Enterococcus species identification. For the first time, we demonstrate likely horizontal gene transfer among E. faecium, E. faecalis, and E. durans within the same patient, underscoring the dynamic nature of these infections. Our findings have significant implications for understanding the complexity of Enterococcus infections, stressing the need to consider genetic and metabolic diversity to improve disease management and treatment outcomes.

microbiology↗