More sensitive methods for diagnosing infection with Schistosoma japonicum are needed as control becomes more effective. We compared a real-time polymerase chain reaction (PCR) for stool samples with conventional diagnostic methods in a study of 1,727 persons from Anhui Province, China. Seroprevalence determined by using an indirect hemagglutination assay (IHA) was much higher (26.1%) than the prevalence in stool-based tests, which were 5.3%, 3.2%, and 3.0% for PCR, hatching test, and Kato-Katz thick smear, respectively. A large proportion of the positive stool samples were only positive in one or two tests. The PCR showed better agreement with IHA than the other two stool-based tests. A commonly used diagnostic algorithm with initial screening for antibodies and subsequent testing with the Kato-Katz thick smear of the seropositive results would have resulted in treatment of 22 people compared with 50 people if the PCR replaced the Kato-Katz thick smear. As prevalence and intensity decrease, the benefit of increased sensitivity using the PCR must be weighed against additional costs.

Natural transformation in bacteria facilitates the uptake and genomic integration of exogenous DNA. This allows horizontal exchange of adaptive traits not easily achieved by point mutations, and has a major role in the acquisition of adaptive traits exemplified by antibiotic resistance determinants and vaccination escape. Mechanisms of DNA uptake and genomic integration are well described for several naturally transformable bacterial species; however, the selective forces responsible for its evolution and maintenance are still controversial. In this study we evolved transformation-proficient and -deficient Acinetobacter baylyi for 175 days in serial transfer cultures where stress was included. We found that natural transformation-proficient populations adapted better to active growth and early stationary phase. This advantage was offset by the reduced performance in the late stationary/death phase. We demonstrate fitness trade-offs between adaptation to active growth and survival in stationary/death phase caused by antagonistic pleiotropy. The presented data suggest that the widely held assumption that recombination speeds up adaptation by rapid accumulation of multiple adaptive mutations in the same genetic background is not sufficient to fully account for the maintenance of natural transformation in bacteria.

The persistence of plasmids in bacterial populations represents a puzzling evolutionary problem with serious clinical implications due to their role in the ongoing antibiotic resistance crisis. Recently, major advancements have been made towards resolving this “plasmid paradox” but mainly in a non-clinical context. Here we propose an additional explanation for the maintenance of multidrug resistance (MDR) plasmids in clinical Escherichia coli strains. After co-evolving two MDR plasmids encoding last resort carbapenem resistance with an extraintestinal pathogenic E. coli strain, we observed that chromosomal media adaptive mutations in the global regulatory systems CCR (Carbon Catabolite Repression) and ArcAB (Aerobic Respiration Control) pleiotropically improved the maintenance of both plasmids. Mechanistically, a net downregulation of plasmid gene expression reduced the fitness cost. Our results suggest that global chromosomal transcriptional re-wiring during bacterial niche-adaptation may facilitate plasmid maintenance.