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Our results revealed that a 7-log reduction of Salmonella can be achieved by exposing fresh chicken litter for 80.5 to 100.8, 78.4 to 93.1, and 44.1 to 63 min at 70, 75, and 80°C, respectively, depending on initial moisture contents. However, the aged chicken litter requires more heat treatment.

Both autoclaving and dry-heat treatments were applied to dairy manure-based compost to achieve target populations of indigenous microorganisms. A 3 strain-mixture of Escherichia coli O157:H7 of ca. 2 log CFU/g was inoculated into acclimated autoclaved compost (AAC) and dry heat-treated compost (DHTC) with different moistures, and stored at 8, 22, or 30 °C. Only selected groups of microorganisms grew in AAC during acclimation, whereas the relative ratio of each group of microorganisms was maintained in DHTC after heat treatment. E. coli O157:H7 grew more in AAC than DHTC in the presence of same level of indigenous mesophiles. However, control compost (no heat treatment) did not support E. coli O157:H7 growth. Our results revealed that both the type and population of indigenous microorganisms is critical for suppressing E. coli O157:H7 growth in compost, and dry-heat treatment can result in a compost product which resembles cured compost with different levels of indigenous microorganisms., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Throughout four field trials, compost heaps covered with finished compost maintained temperatures under the physical covering that were ca. 7 to 15.5°C higher, resulting in rapid Escherichia coli O157:H7 reduction, than those of the heaps covered with fresh straw or left uncovered. Our results validated recommendations made by the U.S. Environmental Protection Agency for covering fresh compost.

A three-strain mixture of Escherichia coli O157:H7 was inoculated into fresh dairy compost (ca. 10(7) CFU/g) with 40 or 50% moisture and was placed in an environmental chamber (ca. 70% humidity) that was programmed to ramp from room temperature to selected composting temperatures in 2 and 5 days to simulate the early composting phase. The surviving E. coli O157:H7 population was analyzed by direct plating and enrichment. Optimal and suboptimal compost mixes, with carbon/nitrogen (C/N) ratios of 25:1 and 16:1, respectively, were compared in this study. In the optimal compost mix, E. coli O157:H7 survived for 72, 48, and 24 h in compost with 40% moisture and for 72, 24, and 24 h with 50% moisture at 50, 55, and 60°C, respectively, following 2 days of come-up time (rate of heating up). However, in the suboptimal compost mix, the pathogen survived for 288, 72, and 48 h in compost with 40% moisture and for 240, 72, 24 h in compost with 50% moisture at the same temperatures, respectively. Pathogen survival was longer, with 5 days of come-up time compared with 2 days of come-up. Overall, E. coli O157:H7 was inactivated faster in the compost with 50% moisture than in the compost with 40% at 55 and 60°C. Both moisture and come-up time were significant factors affecting Weibull model parameters. Our results suggest that slow come-up time at the beginning of composting can extend pathogen survival during composting. Additionally, both the C/N ratio and the initial moisture level in the compost mix affect the rate of pathogen inactivation as well.

The compost microcosm is a prime site for bacterial interaction that carries the inherent potential for disseminating antibiotic resistance through genetic exchange and subsequent land application. One hundred and thirty-six Escherichia coli isolates from compost heaps in South Carolina and California from a total of 277 compost samples were classified to phylogenetic groups, tested for resistance to 10 antibiotics, and screened for shiga toxins and integrons. Isolates that had identical antibiotic resistance patterns, grouped phylogenetically, and came from the same sample source were tested with pulsed-field gel electrophoresis. All isolates were negative for shiga toxins 1 and 2 as determined by polymerase chain reaction (PCR) assay. Resistance phenotypes comprised various combinations of seven antibiotics with a prevalence of ampicillin resistance in 63% of isolates (n = 56) from California, and tetracycline resistance in 37% of isolates (n = 62) from South Carolina. This disparity may be attributed to the differences in regional application of antibiotics as well as the origin of the waste materials in the compost itself. Phylogenetic PCR revealed that the majority of E. coli isolates (64%) belonged to groups A or B1. However, among these isolates, only 7% were resistant to two or more antibiotics as compared with 35% of isolates belonging to groups B2 and D. Integron detection by PCR revealed that nine (7.6%) E. coli isolates were positive for class I integrons, with six of the nine detected in isolates from groups B2 or D. Sequenced integrons (n = 5) were found to carry genes aadA, conferring reduced susceptibility to streptomycin, and dfrA, conferring resistance to trimethoprim. Our results suggest that E. coli isolates in compost belonging to phylogenetic groups B2 and D are more likely to contain integrons and higher levels of antibiotic resistance. The presence of multiple antibiotic resistances as well as integrons in E. coli implicates the potential for antibiotic resistance spread in the compost environment.

This study investigated the survival of heat-shocked (HS) and non-heat-shocked (NHS) Escherichia coli O157:H7 and Salmonellaenterica Typhimurium when co-composting dairy manure and vegetable wastes in a field setting. In the summer, HS E. coli O157:H7 and Salmonella survived for 7 and 2 days longer at the surface and bottom locations of the compost heaps, respectively, than NHS cultures. Both HS and NHS E. coli O157:H7 and Salmonella were detectable in all compost samples for more than 60 days in the winter. The results indicate that composting dairy manure with vegetable wastes under sub-optimal conditions may allow extended survival of pathogens in the heap at low ambient temperature. Analysis of covariance revealed that the heat-shock treatment may have induced cross-resistance to desiccation, allowing extended survival of HS E. coli O157:H7 and Salmonella at the surface of the compost heaps during the summer., (Copyright (c) 2010 Elsevier Ltd. All rights reserved.)

Aims: The purpose of this study was to determine whether the methods used in compost operations of small and medium-sized poultry farms resulted in the production of an amendment free of foodborne pathogens., Methods and Results: Nine compost heaps on five South Carolina poultry farms were surveyed at different stages of the composting process. Compost samples were analysed for coliforms and enriched for Escherichia coli O157:H7, Salmonella spp. and Listeria monocytogenes. The waste materials and composting practices differed among the surveyed farms. On two farms, new materials were added to heaps that had previously completed the active composting phase. Five compost heaps did not reach an internal temperature of 55 degrees C, and c. 62% of all internal samples in the first composting phase contained moisture contents <40%. Escherichia coli was detected in 63% of the surface samples (n = 38) and 9.8% of the internal samples (n = 82) from the first composting phase, as compared with 16.7% of the surface samples (n = 12) and 0% internal samples (n = 24) from the second composting phase. Salmonella was detected in 26 and 6.1% of all surface and internal samples collected from heaps in the first composting phase, respectively, but was absent in all compost samples undergoing a second composting phase. The predominant Salmonella serotypes were Thompson, Montevideo and Anatum. Neither E. coli O157:H7 nor L. monocytogenes was detected in any of the samples., Conclusions: Our results indicate that the conditions at the compost surface are suitable for pathogen survival, and the complete composting process can result in the elimination of pathogens in poultry wastes., Significance and Impact of the Study: This research provides information regarding the effectiveness of the composting practices and microbiological quality of poultry compost produced by small- and medium-sized farms. Ensuring the safety of compost that may be applied to soils should be an integral part of preharvest food safety programme.

Pathogenic microorganisms may survive the composting process in low numbers and subsequently regrow to high levels under favorable conditions. The objective of this study was to investigate the regrowth potential of Salmonella spp., Escherichia coli O157:H7, and Listeria monocytogenes in dairy-based composts under different environmental conditions. Water extract of commercially available dairy compost was used as a model system. Cocktails of five rifampin-resistant strains of each pathogen previously grown in reduced nutrient media (1/2 or 1/10 strength of tryptic soy broth, TSB) were inoculated into water extract of compost of different ratios (1:2,1:5, and 1:10, w/v), and then stored at 35 degrees C or 22 degrees C for 7 days. The strains exhibiting greatest survival or regrowth were identified by pulsed-field gel electrophoresis (PFGE). At 22 degrees C, both E. coli O157:H7 and L. monocytogenes multiplied in all compost extracts, whereas Salmonella spp. regrew in both 1:2 and 1:5 compost extracts but not in 1:10. For all three pathogens, incubation at 22 degrees C provides better conditions for regrowth than at 35 degrees C. Both Salmonella and E. coli O157:H7 previously adapted to nutrient-limited broth (1/10 strength of TSB) regrew in compost extracts to higher populations than the control cultures grown previously in full strength of TSB. In the absence of indigenous microorganisms, all three pathogens regrew even in the most diluted sterile compost extract (1:10) with growth potentials ranging from 2.30 to 3.59 log CFU/ml. In nonsterile compost extract with ca. 5 log CFU/ml of background microorganisms, all three pathogens regrew only in the most concentrated compost extract (1:2) with much less population increases ranging from 0.70 to 1.43 log CFU/ml. Compost extract samples of all ages supported the regrowth of both Salmonella and E. coli O157:H7 with population increases ranging from 0.95 to 2.32 log CFU/ml. The PFGE patterns for E. coli O157:H7 isolates from sterile compost extracts matched with either the spinach outbreak strain or an avirulent B6914 strain. These results demonstrated that compost extract of dairy-based compost contained sufficient nutrients for pathogen regrowth. Cultures previously adapted to low nutrient media regrew to higher populations than control cultures; however, indigenous microflora suppressed the pathogen regrowth in compost extract, especially at 35 degrees C.

Studies were conducted to determine the fate of Escherichia coli O157:H7 in dairy manure-based compost in a field setting. Two trials were performed involving duplicate compost heaps constructed at an outdoor fenced site. The compost heaps were composed of dairy manure, old hay, feed waste, a mixture of sawdust and calf feces, and fresh hay. Samples of the composting mixture were inoculated with stx-negative E. coli O157:H7 B6914 at initial concentrations of 10(7) and 10(5) CFU/g for trial 1 and trial 2, respectively. Individual sample bags were placed on the surface and at three locations (top, center, and bottom) within each heap. Although the compost heaps achieved temperatures of 50 degrees C or above at all internal locations for at least 7 days, temperature stratification was observed. In trial 1, E. coli O157:H7 was detected by enrichment through 14 days within the heaps. When inoculated with 10(5) CFU/g in trial 2, E. coli O157:H7 was detected only through days 2, 2, and 5 at the top, center, and bottom locations, respectively. For both trials, the pathogen survived at the heap's surface for up to 4 months. The indicator commensal E. coli and coliforms were inactivated at a rate similar to that for E. coli O157:H7. Results indicate that composting, with periodic heap turning, can be a practical approach to inactivating E. coli O157:H7 in cattle wastes on the farm. Our data also suggest when compost heaps are not turned, E. coli O157:H7 may survive for months at the heap surface.