A review of the abundance, behaviour and detection of clostridial pathogens in agricultural soils

Abstract

The soil is a reservoir for various clostridial pathogens, with agricultural soils representing a major source of contamination for overlying crops and grazing livestock. Understanding the prevalence and behaviour of pathogens in these soils is fundamental to ascertaining and mitigating the risk of disease from agroecosystems. This article reviews research pertaining to the overall distribution and abundance of clostridial pathogens in the soil while identifying possible environmental and soil factors influencing their behaviour. Large‐scale soil screens have identified pathogens across the globe, although some Clostridium botulinum toxinotypes are more prevalent in certain geographic regions. Faecal inputs and organic waste amendments to the soil can elevate the levels of enteric clostridial pathogens in the soil and the subsequent disease risk, as highlighted by case–control studies. The ability of Clostridia to sporulate results in their long‐term persistence post‐introduction, increasing the time period for disease transmission. Regularly or permanently saturated soils may also enhance survival, or potentially facilitate the regrowth of some indigenous or introduced Clostridia. This is supported by the high prevalence of Clostridia in paddy soils, greater detection of pathogens in flooded soils, and the higher onset of some clostridial diseases in regions with poorly drained soils. Future research should elucidate soil types and environmental conditions which can enhance pathogen survival/regrowth. The adoption of molecular and sequencing technologies for future diagnostics can facilitate more sensitive detection and a higher resolution of pathogen typing, allowing a better understanding of pathogen population dynamics in farm soils and disease epidemiology. Highlights Understanding the behaviour of soil‐borne clostridial pathogens is key for disease management. Soil, environmental and management factors affecting pathogen survival/introduction are discussed. Soil waterlogging and application of organic soil amendments may increase the number of soil pathogens. More pathogen surveillance and standardisation of diagnostics to better understand behaviour is needed.

Manure contamination with Clostridium botulinum after avian botulism outbreaks: management and potential risk of dissemination

“…Regarding conditions associated with C botulinum detection in poultry manure, this study shows that C botulinum was detected significantly more frequently at lower temperatures (28.1°C vs 38.7°C) and more frequently on the surface, with a mean temperature of 21.1°C vs 44.2°C deeper in the pile. The optimal growth temperature for C botulinum is between 30°C and 42°C, although it can survive between 10°C and 48°C 30 depending on the BoNT types and C botulinum group. The mean temperature measured at a depth of around 50 cm is most frequently within this interval and could allow the initiation of spore germination.…”

Clostridium botulinum type C, D, C/D, and D/C: An update

“…The contamination of susceptible birds and the initiation of a “carcass-maggot” amplifying cycle can lead to the development of outbreaks of botulism in the avifauna ( Wobeser, 1997 ; Soos and Wobeser, 2006 ). Type E, mainly identified in the northernmost regions of the northern hemisphere, is closely associated with aquatic, marine or freshwater ecosystems ( Dolman, 1957 ; Haagsma, 1991 ; Horowitz, 2010 ; Espelund and Klaveness, 2014 ; Palmer et al, 2019 ). Carriage by fish is most often intestinal ( Bott et al, 1966 , 1968 ; Yule et al, 2006 ); the contamination can lead to mortality in certain species more sensitive to toxin E. The disease can also spread to aquatic or coastal birds (fish-eating birds in particular), sometimes causing the death of thousands of individuals ( EPA, 2013 ).…”

Special section on soil and human health – An editorial

“…Clostridium is a genus of bacteria that causes a number of human diseases including botulism, gas gangrene and tetanus. Palmer et al () investigated the distribution and abundance of clostridial pathogens in soil as well as environmental and soil factors that might influence the bacteria's behaviour. Clostridial pathogens have been documented in soils worldwide, and the amendment of soil with manure and organic wastes was identified as a major route of bacteria introduction to the soil.…”

“…The incorporation of modern molecular and sequencing techniques into future studies was also recommended. Palmer et al () concluded that understanding clostridial pathogen amount, distribution and behaviour in soil was important because agricultural soil is the first control point in the food contamination pathway.…”