8 research outputs found
Novel Methods for Analysing Bacterial Tracks Reveal Persistence in Rhodobacter sphaeroides
Tracking bacteria using video microscopy is a powerful experimental approach to probe their motile behaviour. The
trajectories obtained contain much information relating to the complex patterns of bacterial motility. However, methods for
the quantitative analysis of such data are limited. Most swimming bacteria move in approximately straight lines,
interspersed with random reorientation phases. It is therefore necessary to segment observed tracks into swimming and
reorientation phases to extract useful statistics. We present novel robust analysis tools to discern these two phases in tracks.
Our methods comprise a simple and effective protocol for removing spurious tracks from tracking datasets, followed by
analysis based on a two-state hidden Markov model, taking advantage of the availability of mutant strains that exhibit
swimming-only or reorientating-only motion to generate an empirical prior distribution. Using simulated tracks with varying
levels of added noise, we validate our methods and compare them with an existing heuristic method. To our knowledge this
is the first example of a systematic assessment of analysis methods in this field. The new methods are substantially more
robust to noise and introduce less systematic bias than the heuristic method. We apply our methods to tracks obtained
from the bacterial species Rhodobacter sphaeroides and Escherichia coli. Our results demonstrate that R. sphaeroides exhibits
persistence over the course of a tumbling event, which is a novel result with important implications in the study of this and
similar species
Near surface swimming of Salmonella Typhimurium explains target-site selection and cooperative invasion
Targeting of permissive entry sites is crucial for bacterial infection. The targeting mechanisms are incompletely understood. We have analyzed target-site selection by S. Typhimurium. This enteropathogenic bacterium employs adhesins (e.g. fim) and the type III secretion system 1 (TTSS-1) for host cell binding, the triggering of ruffles and invasion. Typically, S. Typhimurium invasion is focused on a subset of cells and multiple bacteria invade via the same ruffle. It has remained unclear how this is achieved. We have studied target-site selection in tissue culture by time lapse microscopy, movement pattern analysis and modeling. Flagellar motility (but not chemotaxis) was required for reaching the host cell surface in vitro. Subsequently, physical forces trapped the pathogen for âŒ1.5-3 s in "near surface swimming". This increased the local pathogen density and facilitated "scanning" of the host surface topology. We observed transient TTSS-1 and fim-independent "stopping" and irreversible TTSS-1-mediated docking, in particular at sites of prominent topology, i.e. the base of rounded-up cells and membrane ruffles. Our data indicate that target site selection and the cooperative infection of membrane ruffles are attributable to near surface swimming. This mechanism might be of general importance for understanding infection by flagellated bacteria
Molecular epidemiology of mastitis pathogens of dairy cattle and comparative relevance to humans
Mastitis, inflammation of the mammary gland, can be caused by a wide range of organisms, including gram-negative and gram-positive bacteria, mycoplasmas and algae. Many microbial species that are common causes of bovine mastitis, such as Escherichia coli, Klebsiella pneumoniae, Streptococcus agalactiae and Staphylococcus aureus also occur as commensals or pathogens of humans whereas other causative species, such as Streptococcus uberis, Streptococcus dysgalactiae subsp. dysgalactiae or Staphylococcus chromogenes, are almost exclusively found in animals. A wide range of molecular typing methods have been used in the past two decades to investigate the epidemiology of bovine mastitis at the subspecies level. These include comparative typing methods that are based on electrophoretic banding patterns, library typing methods that are based on the sequence of selected genes, virulence gene arrays and whole genome sequencing projects. The strain distribution of mastitis pathogens has been investigated within individual animals and across animals, herds, countries and host species, with consideration of the mammary gland, other animal or human body sites, and environmental sources. Molecular epidemiological studies have contributed considerably to our understanding of sources, transmission routes, and prognosis for many bovine mastitis pathogens and to our understanding of mechanisms of host-adaptation and disease causation. In this review, we summarize knowledge gleaned from two decades of molecular epidemiological studies of mastitis pathogens in dairy cattle and discuss aspects of comparative relevance to human medicine