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Space and time on the membrane: modelling Type VI secretion system dynamics as a state-dependent random walk

The type six secretion system (T6SS) is a transmembrane protein complex that mediates bacterial cell killing. The T6SS comprises three main components (transmembrane, baseplate and sheath/tube complexes) that are sequentially assembled in order to enable an attacking cell to transport payloads into neighbouring cells. A T6SS attack disrupts the function of essential cellular components of target cells, typically resulting in their death. While the assembled T6SS adopts a fixed position in the cell membrane of the attacking cell, the location of the firing site varies between firing events. In Serratia marcescens, a post-translational regulatory network regulates the assembly and firing kinetics of the T6SS in a manner that affects the attacking cell's ability to kill target cells. Moreover, when the ability of membrane complexes to reorient is reduced, an attacking cell's competitiveness is also reduced. In this study, we will develop a mathematical model that describes both the spatial motion and assembly/disassembly of a firing T6SS. The model represents the motion of a T6SS on the cell membrane as a state-dependent random walk. Using the model, we will explore how both spatial and temporal effects can combine to give rise to different firing phenotypes. Using parameters inferred from the available literature, we show that variation in estimated diffusion coefficients is sufficient to give rise to either spatially local or global firers.

Antimicrobial resistance in Campylobacter coli and Campylobacter jejuni from human campylobacteriosis in Taiwan, 2016-2019

Campylobacter coli and C. jejuni are highly resistant to most therapeutic antimicrobials in Taiwan, rapid diagnostics of resistance in bacterial isolates is crucial for the treatment of campylobacteriosis. We characterized 219 (40 C. coli and 179 C. jejuni) isolates recovered from humans between 2016 and 2019 using whole-genome sequencing to investigate the genetic diversity among isolates and the genetic resistance determinants associated with antimicrobial resistance. Susceptibility testing with 8 antimicrobials was conducted to assess the concordance between phenotypic resistance and genetic determinants. The conventional and core genome multilocus sequence typing analysis revealed diverse clonality among the isolates. Mutations in gyrA (T86I, D90N), rpsL (K43R, K88R), and 23S rRNA (A2075G) were found in 91.8%, 3.2%, and 6.4% of the isolates, respectively. Horizontally transferable resistance genes ant(6)-I, aad9, aph(3')-IIIa, aph(2"), blaOXA, catA/fexA, cfr(C), erm(B), lnu, sat4, and tet were identified in 24.2%, 21.5%, 33.3%, 11.9%, 96.3%, 10.0%, 0.9%, 6.8%, 3.2%, 13.2%, and 96.3%, respectively. High-level resistance to 8 antimicrobials in isolates was 100% predictable by the known resistance determinants, whereas low-level resistance to azithromycin, clindamycin, nalidixic acid, ciprofloxacin, and florfenicol in isolates was associated with sequence variations in CmeA and CmeB of the CmeABC efflux pump. Resistance-enhancing CmeB variants were identified in 62.1% (136/219) of isolates. In conclusion, an extremely high proportion of C. coli (100%) and C. jejuni (88.3%) were multidrug-resistant and a high proportion (62.5%) of C. coli isolates had been resistant to azithromycin, erythromycin, and clindamycin that would complicate the treatment of invasive campylobacteriosis in this country.

Development and Application of a Core Genome Multilocus Sequence Typing Scheme for the Health Care-Associated Pathogen Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic human pathogen that frequently causes health care-associated infections (HAIs). Due to its metabolic diversity and ability to form biofilms, this Gram-negative nonfermenting bacterium can persist in the health care environment, which can lead to prolonged HAI outbreaks. We describe the creation of a core genome multilocus sequence typing (cgMLST) scheme to provide a stable platform for the rapid comparison of P. aeruginosa isolates using whole-genome sequencing (WGS) data. We used a diverse set of 58 complete P. aeruginosa genomes to curate a set of 4,440 core genes found in each isolate, representing ∼64% of the average genome size. We then expanded the alleles for each gene using 1,991 contig-level genome sequences. The scheme was used to analyze genomes from four historical HAI outbreaks to compare the phylogenies generated using cgMLST to those of other means (traditional MLST, pulsed-field gel electrophoresis [PFGE], and single-nucleotide variant [SNV] analysis). The cgMLST scheme provides sufficient resolution for analyzing individual outbreaks, as well as the stability for comparisons across a variety of isolates encountered in surveillance studies, making it a valuable tool for the rapid analysis of P. aeruginosa genomes.

Electronic tools for infectious diseases and microbiology

Electronic tools for infectious diseases and medical microbiology have the ability to change the way the diagnosis and treatment of infectious diseases are approached. Medical information today has the ability to be dynamic, keeping up with the latest research or clinical issues, instead of being static and years behind, as many textbooks are. The ability to rapidly disseminate information around the world opens up the possibility of communicating with people thousands of miles away to quickly and efficiently learn about emerging infections. Electronic tools have expanded beyond the desktop computer and the Internet, and now include personal digital assistants and other portable devices such as cellular phones. These pocket-sized devices have the ability to provide access to clinical information at the point of care. New electronic tools include e-mail listservs, electronic drug databases and search engines that allow focused clinical questions. The goal of the present article is to provide an overview of how electronic tools can impact infectious diseases and microbiology, while providing links and resources to allow users to maximize their efficiency in accessing this information. Links to the mentioned Web sites and programs are provided along with other useful electronic tools.