Date of Award

Spring 5-14-2016

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Advisor

Robert C. Causey

Second Committee Member

M. Susan Erich

Third Committee Member

Mark Hutchinson

Abstract

Streptococcus equi subspecies equi (S. equi), causes the potentially fatal respiratory disease in horses known as “strangles”, while the closely related Streptococcus equi subspecies zooepidemicus (S. zooepidemicus) causes potentially fatal infections in humans. A study was undertaken to determine the survival of these 2 organisms in compost. Dacron bags (5 cm x 10 cm) were filled with 4 g of a feedstock mixture of soiled equine bedding and feed waste at ratios of 3:1 (C:N ratio 40.6), 1:1 (C:N ratio 31.9), and 1:4 (C:N ratio 25.4). The Dacron bags were inoculated with approximately 10 x 1010 c.f.u. of S. zooepidemicus, stored at 21 – 23 °C for approximately 24 h, then placed in 3 compost windrows of the same 3 feedstock ratios. Streptococci were quantified immediately following inoculation in the bags, and at 48, 96, 168 and 336 h following placement in the windrow. Heavy streptococcal growth was detected immediately post inoculation, but Streptococci were not isolated 48 h after placement in the windrow, or at any subsequent time-point. Next, S. equi was inoculated into Dacron bags (soiled equine bedding to feed waste = 3:1), and the bags placed 24 h later into a compost windrow of the same feedstock ratio. Streptococci were quantified immediately post inoculation, and at 2, 4, 8, 12, 24, 48, 96, 168 and 336 h following placement in the windrow. Again, heavy numbers were detected post inoculation, but Streptococci were not detected after placement in the windrow. To rule out killing of Streptococci by microflora during the 24 h storage period, samples of soiled equine bedding, both autoclaved and non-autoclaved, were inoculated with approximately 10 x 1010 c.f.u. of S. zooepidemicus and sampled at 0, 6, 12, 24, 48, 72, 120, 168 and 264 h. In sterilized soiled equine bedding, S. zooepidemicus was isolated from 0 – 168 h, but replaced by other flora at 264 h. In non-sterilized samples, Streptococci were not present after 72 h. A repeated study with S. equi yielded similar results. There was a significant effect of sterilization on survival of Streptococci (pS. equi in equine waste, soiled equine bedding was dried at 37 °C for 48 h and sterile water then added (25 mL, 50 mL, 75 mL, 100 mL) to 100 g of dried bedding. The samples were inoculated with 10 x 1010 c.f.u of S. equi and sampled at 0, 12, 24, 36, 48, 72, 96, and 120 h. In dried bedding with no added water, S. equi was isolated from 0 – 120 h, whereas in bedding with added water, S. equi, was not isolated after 72 h. The effect of moisture content was significant at pStreptococci, indicating that normal compost microflora may provide sustainable methods for the control of human and animal pathogens.

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