The bacteriophages in human- and animal body-associated microbial communities

Abstract

Summary Felix d’Herelle first demonstrated, about 90 years ago, the presence of bacteriophages in human and animal body microbiota. Our comprehension of the impact of naturally occurring bacteriophages on symbiotic bacteria, and of their role in general homeostasis of macro‐organism, nevertheless remains quite fragmentary. Analysis of data in various human‐ and animal body‐associated microbial systems on phage occurrence, diversity, host specificity and dynamics, as well as host occurrence, specificity and dynamics, suggests that mechanisms which stabilize phage–bacteria coexistence are not identical for either different species or different body sites. Regulation by phage infection instead probably depends on specific physical, chemical and biological conditions, e.g. pH, nutrient densities, host prevalence, relation to mucosa and other surfaces and presence of phage inhibiting substances. In some animal species intestinal bacteriophages thus appear to exert significant selective pressure over at least some resident bacterial populations, resulting in phages playing important roles in the self‐regulation of these microbial systems while at the same time contributing to maintenance of bacterial diversity (i.e. ‘killing the winner’). Emerging data additionally suggest that bacteriophage particles could play roles in regulating the immune reactions of the macro‐organism. Alternatively, for many systems links between phages and community characteristics have not been established.

Movers and shakers

“…16 Long-tailed phages presumably possess an adaptive advantage in the viscous intestinal environment, being able to "seek-out" bacterial host receptors in a more efficient manner, benefiting from rotational movement of the particle. 12 In addition, prophages induced from human fecal bacteria upon induction with DNA damaging agents have been detected by EM. Calderaro et al 17 detected phages by EM after experimental induction with mitomycin C in weakly β-hemolytic human intestinal spirochaetes isolated from patients with intestinal disturbances.…”

“…23 With respect to the RNA-containing F-specific (F-RNA) coliphages, approximately 10-20% of human feces have been found to harbor them. 12 Of the four genetic groups which have been identified, groups II and III are much more prevalent in human fecal samples than in animal fecal waste. 29,31,32 In developing a low-cost method for fecal source identification, Ebdon et al 27 reported that phages which infect the strain Bacteroides (GB-124) are specific to human feces.…”

“…Phages undoubtedly exert significant selective pressure on the members of the human intestinal microbiome, a phenomenon which has been observed in some animal species. 12 It is therefore tempting to suggest that "commensal phages" within certain individuals may play a role by infecting some of the beneficial flora, explaining the "non-responders" in some trials. The role of phages in the human intestine is an area which has received little attention and as a result, knowledge on intestinal phage diversity, numbers and functionality is limited.…”

Temperate phages both mediate and drive adaptive evolution in pathogen biofilms

“…Of particular note are the transposable class of temperate phages (also known as mutator phages), including D3112 of Pseudomonas aeruginosa (9, 10), which integrate throughout the chromosome disrupting existing genes and increasing the supply of mutations available to selection. Recent reports of high rates of phage mobilization within hosts (11) and high temperate phage abundance in humans (12), including at sites of chronic infection where phage particles have been observed to exceed bacterial host densities by 10-to 100-fold (13), suggests that temperate phages could play an important role in driving within-host evolution of bacterial pathogens. However, experimental tests of the hypothesis that temperate phages contribute to rapid evolutionary adaptation of pathogenic bacteria are lacking.…”

La phagothérapie

“…Cette diversité constitue un réservoir quasi illimité d'agents antibactériens théra-peutiques dans lequel puiser. Présents dans tous les écosystèmes, ils le sont également sur notre peau et nos muqueuses, dans notre tube digestif et notre alimentation [9]. Ils sont de puissants régulateurs naturels des populations bactériennes : dans les écosystèmes aquatiques par exemple, les phages sont responsables de la lyse quotidienne de 10 à 20 % de la biomasse bactério-planctonique [10].…”