Recycling of domestic food waste: Does food waste composting carry risk from total antimicrobial resistance (AMR)?

Antibiotic resistance (ABR) has now become a major global public health issue. New legislation has recently been introduced in Northern Ireland from April 2017, requiring domestic households to recycle all domestic food waste items. Resulting increases in the volume of such waste which is collected by the local council has driven technologies for the safe recycling of such material including commercial composting. Little is known about the antimicrobial resistance (AMR) profile of such composted food waste materials and hence the purpose of this paper is to characterise total AMR in bacteria isolated from such composted domestic food waste and to consider the potential public health consequences of such material.

Finished compost containing food waste material was obtained in the Spring 2017 from a local authority recycling amenity site, which freely distributes such material to the public. Total culturable populations of bacteria were isolated from the composted material and antibiotic susceptibility to six classes of antibiotics, namely florfenicol, fluoroquinolone, aminoglycoside, lincosamide, tetracycline and β-lactam was examined.

ABR was greatest for lincomycin > tobramycin > minocycline/amoxycillin > ciprofloxacin > florfenicol. In this study, there was one compost, which showed complete resistance to all antibiotics tested. No compost displayed complete antibiotic sensitivity. Two composts were considered pan-resistant, whilst four were considered multi-resistant.

This study showed that the total ABR profile of food waste compost is significant, with bacterial populations within the compost having ABR to several classes of antibiotics, which are important and sometimes critical to human health. The application of such materials to enrich and fertilise garden soils in significant volumes inadvertently allows for the artifical and man-made transfer of AMR bacteria and their genes to new environments, which have been hitherto niave to the presence of such AMR properties. The application of such compost horticulturally to enrich soils used to cultivate flowers, fruits and vegetables may have important consequences for human and animal health. Urgent work is now needed to quantify the fate of such antibiotic resistant bacteria from compost to their new environment and risk assessments made to estimate the carriage through to human health.