Hygiene of Products

Researchers at Woods End examine potato pathogen subsamples in windrow composting of potato culls

Testing Composts for Bacterial Content and Hygiene Quality

There is increasing public awareness about bacteria in the food chain due to constantly recurring instances of contamination largely based on soil treatments. Potential pathogens of a plant, animal and human nature may be transferred from incompletely processed manures and recycled organic matter (compost and plant debris), when added to soil. There is a need to properly assess the potential risks in view of anticipated end-use before assigning significance to a bacterial or fungal hygiene test. The best defense in a quality control program is to be well informed by appropriate tests.

“High-end-use” applications of recycled organic matter such as consumer growing media, gardens, playgrounds and parks and sports turf, comprise uses where certainty of absence of bacterial pathogens is extremely important. Such products must be adequately tested following processing and before sales. While composting has the great potential to reduce pathogenic content, it is now generally recognized by microbiologists to be an unreliable means to do so, due to natural variability in biological systems.

Woods End Laboratories has had three decades of intensive laboratory and field experience for examining the presence and fate of fungal and bacterial organisms in recycled wastes. The firm has also recently published extensive bacterial hygiene test data on recycled organic matter composts in the Journal of Food Protection (Vol 2:2009 – see reprint section).

Decision Tree for Testing Organisms

IN EVENT OF NO TESTS: Many products are not tested or no indication of cleanliness is provided. If hygiene information does not exists it is prudent to assume that the product is not hygienic and to act accordingly – anything less that this has increased risk potential.

IF CHOICE FOR TESTING EXISTS: It is best to plan to test by selecting an organism that gives maximum information under the circumstances and from this, to draw conclusions as to whether or not pathogens could be there that are significant for the end-use. With compost and soil amendments fecal coliforms continue to be a very appropriate indicator for pathogen cleanliness. A more conservative tests would use  Clostridium perfringens since it is pathogenic, it  survives extreme temperatures and will grow under varied conditions and is virtually always present in feces. If it is absent, then most likely other pathogens will also be absent.

INDICATOR TESTS: It is common to choose a microbe that gives information from which extrapolation of pathogen status is performed. This is called INDICATOR testing. For example, fecal coliform and E.coli are always found in bird and mammal feces but only some E. coli are pathogenic. The presence of E. coli therefore indicates generally the presence of feces and the potential for toxigenic factors. If E .coli is not present, then the assumption is that pathogenic strains of E. coli such as E. coli-O157:H7 are also not present. Woods End data shows that many composted achieve true pathogenic-free status; the data also reveal that green-waste may contain as much pathogen potential as manure-based materials.

Is the Presence of One Type of Non-pathogenic Bacterium a Valid Indication of Likely Pathogen Presence?

1. Presently, the field of pathogen testing is changing rapidly. All things are and should always be open for challenge and discovery of error, of course.
2. A National Research Council report (2002) recommends using C. perfringens as indicator bacterium for compost pathogen evaluation.
3. Agencies in Europe presently require that compost be Salmonella-free (non-detect on 50g) and have established limits for E.coli, E.coli 0157:H7, Listeria and Campylobacter.

Citations

• TM. Scott, J B. Rose, T M. Jenkins, S R. Farrah, and J Lukasik. “Microbial Source Tracking: Current Methodology and Future Directions”. Applied and Env Microbiol. Dec 2002. p.5796-5803.
• EPA Health Effects Criteria for Fresh Recreational Waters. EPA-600/1-84-004. Section 2.
• V J. Harwood, A D. Levine, T M. Scott, V Chivukula, J Lukasik, Sl Farrah, J B. Rose (2005) “Validity of the Indicator Organism Paradigm fort Pathogen Reduction in Reclaimed Water and Public Health Protection.” Appl Env Microbiology, p. 3163-3170.
• Brinton et al. (2009) Occurrence and Levels of Fecal Indicators and Pathogenic Bacteria in Market-Ready Recycled Organic Matter Composts. Journal of Food Protection, Vol. 72, No. 2, 2009, Pages 332–339

(c) 2005-2010 Woods End Lab. Permission to reprint granted with attribution.