Biofilm formation in Gardnerella vaginalis
Gardnerella vaginalis is the causative agent of bacterial vaginosis, the most common vaginal infection. Biofilm formation by G. vaginalis is necessary for the pathogenesis of the infection. MADELINE and colleagues conducted an evolve and re-sequence experiment in the laboratory, selecting for biofilm formation by G. vaginalis by serial passaging on plastic plates. They observed increased biofilm formation and increased cell aggregation. Short-read sequencing of populations at intervals throughout the experiment was conducted in order to measure changes in allele frequency.
Antibiotic resistance in Clostridioides difficile
Hospital-acquired C. difficile infection has become an epidemic, and treatments are decreasing in efficacy. Highly transmissible strains of C. difficile are resistant to the first-line antibiotic metronidazole, however the genetic basis of resistance is not known. We hypothesize that metronidazole resistance contributed to epidemic spread of C. difficile, and therefore resistance-associated loci are be under positive selection. We surveyed C. difficile clinical isolates using a genome-wide association study (GWAS). We identified a SNP in the promotor region of nimB which confers metronidazole resistance and is associated with rapid clonal transmission. Notably, the nimB SNP co-occurs with a SNP in gyrA associated with fluoroquinolone resistance, and both SNPs are under positive selection. Taken together, we conclude that metronidazole resistance conferred by the nimB SNP plays a role in the high transmissibility of epidemic, antibiotic-resistant C. difficile.