TABLE 4.

Extrinsic biotic factors that influence decay rates in aquatic environments

Extrinsic factor	Modifying factor	Organism/indicator	Notes	References
Protozoan predation	Temp	Culturable E. coli, enterococci, B. fragilis, B. distasonis, and Bacteroides spp. measured by qPCR	Higher decay rate at warmer temps coinciding with increased numbers of protozoan grazers.	101, 102, 155, 157
	Prey characteristics	Culturable E. coli, E. faecalis, Staphylococcus epidermidis, E. coli O157:H7, Klebsiella pneumoniae, S. enterica	Higher decay rates for larger allochthonous organisms (e.g., E. coli) than for smaller autochthonous organisms; higher decay rates for Gram-negative bacteria than for Gram-positive bacteria; decay rates also affected by motility and virulence factors.	39, 122, 154, 158, 163, 166
	Predator/prey densities	Culturable E. coli, E. faecalis	Decay rates were positively correlated with bacterial densities.	157, 158
Indigenous microbiota (competition + predation)	Location (water/sediment)	Culturable E. coli, E. faecalis, E. coli O157:H7, S. enterica	Higher decay rate of FIB and pathogens in the water column than in sediment.	45, 122, 156
	Water type (fresh/marine)	Culturable, E. coli, enterococci	Greater decay of FIB in marine water than in freshwater, but the effect of indigenous microbiota was greater in freshwater than in marine water.	27, 28
	Nutrients	Culturable E. coli	Competition and predation increased E. coli decay rates, but higher nutrient levels mitigated these effects.	83, 90
	Source	E. coli, enterococci (by culture and qPCR), general and human-associated MST markers	FIB (from cattle manure and septage) and FIB/MST markers from septage decayed at a lower rate than FIB and MST markers from sewage and human feces.	4, 27