Antibiotics are used in animal livestock production for therapeutic treatment of disease and at subtherapeutic levels for growth promotion and improvement of feed efficiency. It is estimated that approximately 75% of antibiotics are not absorbed by animals and are excreted in waste. Antibiotic resistance selection occurs among gastrointestinal bacteria, which are also excreted in manure and stored in waste holding systems. Land application of animal waste is a common disposal method used in the United States and is a means for environmental entry of both antibiotics and genetic resistance determinants. Concerns for bacterial resistance gene selection and dissemination of resistance genes have prompted interest about the concentrations and biological activity of drug residues and break-down metabolites, and their fate and transport. Fecal bacteria can survive for weeks to months in the environment, depending on species and temperature, however, genetic elements can persist regardless of cell viability. Phylogenetic analyses indicate antibiotic resistance genes have evolved, although some genes have been maintained in bacteria before the modern antibiotic era. Quantitative measurements of drug residues and levels of resistance genes are needed, in addition to understanding the environmental mechanisms of genetic selection, gene acquisition, and the spatiotemporal dynamics of these resistance genes and their bacterial hosts. This review article discusses an accumulation of findings that address aspects of the fate, transport, and persistence of antibiotics and antibiotic resistance genes in natural environments, with emphasis on mechanisms pertaining to soil environments following land application of animal waste effluent.

https://crashrecovery.org/zika/02-14MAR2008-Antibiotic-Resistance-Genes-J.Environ.Qual.May-June2009.pdf

Fate and transport of antibiotic residues and antibiotic resistance genes following land application of manure waste.

Publisher Summary This chapter highlights how the current understanding of the mechanisms and factors influencing virus adsorption can be used to interpret and control virus behavior in the environment. An understanding of factors controlling the interaction has already led to new and improved methods for the concentration of viruses from water, and their isolation from the environment. It is evident that not all viruses behave alike toward a solid under identical conditions. Under most natural conditions viruses with a low isoelectric point appear to be more poorly adsorbed to most solid surfaces. This must be taken into consideration when evaluating concentration or treatment systems which involve adsorption. This phenomenon is also important in determining the transport of viruses in the environment. Certain enteric viruses appear to adsorb less readily to soils and aquatic sediments than others. Thus their potential transport to groundwater may be greater and they may be less likely to settle in surface waters. To take into consideration these differences in virus behavior, it is perhaps best to use viruses with widely varying isoelectric points or marked differences in hydrophobicity to evaluate the extremes in virus interaction with a given surface which could occur.

Applied and Theoretical Aspects of Virus Adsorption to Surfaces

Because of the increasing emphasis placed upon land application as a means of wastewater disposal, it is important to evaluate the influences of different factors upon virus survival in soil. The objective of this study was to measure the effects of various environmental variables on virus persistence. Test samples of soil were placed in vials, and the soil was wetted with suspensions of virus in either distilled water, unchlorinated secondary sewage effluent, or mixtures of effluent and water. The viruses used were coxsackieviruses A9 and B3, echovirus 1, poliovirus 2, rotavirus SA11, and bacteriophages T2 and MS2. The rate of virus inactivation was evaluated statistically with regard to conditions under which the vials were incubated and to the soil characteristics. The factors that were found to influence virus survival were temperature, soil moisture content, presence of aerobic microorganisms, degree of virus adsorption to the soil, soil levels of resin-extractable phosphorus, exchangeable aluminium, and soil pH. Overall, temperature and virus adsorption to soil appeared to be the most important factors affecting virus survival.

Effects of environmental variables and soil characteristics on virus survival in soil.

1. Introduction, 5



2. Direct virus detection, 6



3. Bacteriophages, 6



3.1 Somatic coliphages, 8



3.2 F+-specific bacteriophages, 9



3.3 Bacteriophages infecting Bacteroides fragilis,14



4. Summary, 15



5. Critical issues that must be addressed, 15



6. Acknowledgements, 15



7. References, 16

Bacteriophages as indicators of enteric viruses and public health risk in groundwaters.

Microorganisms migrating into and through soil from sources on the land surface may cause a serious threat to both ground and surface waters. It has been estimated that microorganisms can migrate significant distances in the field. Results from various studies suggested that preferential flow through macropores, worm holes, cracks, and fractures is the main reason for such observations. However, a quantitative representation of this phenomenon has not been provided. Microorganisms migrate through soil by advection and dispersion, while being subjected to effects of filtration, adsorption, desorption, growth, decay, sedimentation and chemotaxis. Both laboratory and field investigations have contributed important information on bacterial movement in soils. Qualitative comparisons are generally transferable from laboratory to field situations. Quantitative agreement is much more difficult to establish. Available mathematical modelling of microbial transport is limited in practical application because of the simplifying assumptions used in its development.

/pdf/transport-of-microorganisms-through-soil-55g1asdj93.pdf

Transport of microorganisms through soil

The survival of virus present in secondary effluents discharged into a cypress dome was studied. Isolations were made from concentrates of water drawn from 10-foot (304.80 cm) deep wells. Data presented show vertical and lateral virus movement as well as survival within the dome for 28 days during a period of heavy rains when no effluent was being applied. Due to the inefficiency of virus concentration procedures, it is proposed that much of the virus present was probably not demonstrated. A rapid, relatively inexpensive concentration technique for sewage influents and effluents is discussed.

https://aem.asm.org/content/aem/29/6/751.full.pdf

L. Virginia Pierce

Papers

Demonstration of virus in groundwater after effluent discharge onto soil.