Survival of Salmonella spp. in Composting using Vial and Direct Inoculums Technique

TL;DR

This study compares the survival of Salmonella spp. in composting using direct and vial inoculation techniques, showing that direct contact leads to faster pathogen die-off at high temperatures, ensuring compost safety.

Contribution

It introduces a comparative analysis of Salmonella survival using direct versus vial inoculation methods during composting, highlighting the impact of contact on pathogen reduction.

Findings

Salmonella spp. was eliminated in 8 days with direct inoculation.

Vial inoculation resulted in longer survival of Salmonella spp.

High temperatures (66°C) effectively reduced Salmonella in direct contact samples.

Abstract

The survival of Salmonella spp. as pathogen indicator in composting was studied. The inoculums technique was used to gives the known amounts of Salmonella spp. involved in composting. The inoculums of Salmonella spp. solution was added directly into the compost material. The direct inoculum was compared with inoculums in vial technique. The Salmonella spp. solution placed into a vial and inserted into the middle of compost material before starting the composting process. The conventional method that is used for the enumeration of Salmonella spp. is serial dilution followed by standard membrane filtration as recommended in the compost quality standard method PAS 100 and the British Standard (BS EN ISO 6579:2002). This study was designed to investigate the relationship of temperature and contact material that may also involve in pathogen activation specifically to Salmonella spp. The exposure to an average temperature during composting of about 55-60{\deg}C was kept for at least 3 days as it was reported sufficiently kills the vast majority of enteric pathogen (Deportes et al., 1995). The amount of Salmonella spp. and temperature for both samples was set as indicator to determine the survival of Salmonella spp. in direct and non-direct inoculums. This study gives the figures of die-off rate for Salmonella spp. during composting. The differentiation between direct contact (Sample A) and non-contact of Salmonella spp. with compost material (Sample B) during composting was also revealed. The results from laboratory scale of composting study has been showed that after 8 days (which included at least at 66{\deg}C) the numbers of Salmonella spp. in Sample A were below the limits in UK compost standard (known as PAS 100)(BSI, 2005) which required the compost to be free of Salmonella spp. Meanwhile, Sample B still gives high amount of Salmonella spp. in even after composting for 20 days.