Impact of indigenous microorganisms on Escherichia coli O157:H7 growth in cured compost

Factors Influencing the Persistence of Salmonella Infantis in Broiler Litter During Composting and Stabilization Processes and Following Soil Incorporation

Broiler litter (BL), a by-product of broiler meat production, is frequently contaminated with Salmonella and other zoonotic pathogens. To ensure the safety of crop production chains and limit pathogen spread in the environment, a pre-treatment is desired before further agricultural utilization. The objective of this study was to characterize the effect of physico-chemical properties on Salmonella persistence in BL during composting and stabilization and following soil incorporation, toward optimization of the inactivation process. Thirty-six combinations of temperature (30, 40, 50, and 60°C), water content (40, 55, and 70%; w/w), and initial pH (6, 7, and 8.5) were employed in static lab vessels to study the persistence of Salmonella enterica serovar Infantis (S. Infantis; a multidrug-resistant strain) during incubation of artificially-inoculated BL. The effect of aeration was investigated in a composting simulator, with controlled heating and flow conditions. Temperature was found to be the main factor significantly influencing Salmonella decay rates, while water content and initial pH had a secondary level of influence with significant effects mainly at 30 and 40°C. Controlled simulations showed faster decay of Salmonella under anaerobic conditions at mesophilic temperatures (<45°C) and no effect of NH3 emissions. Re-wetting the BL at mesophilic temperatures resulted in Salmonella burst, and led to a higher tolerance of the pathogen at increased temperatures. Based on the decay rates measured under all temperature, water content, and pH conditions, it was estimated that the time required to achieve a 7 log10 reduction in Salmonella concentration, ranges between 13.7–27.2, 6.5–15.6, 1.2–4.7, and 1.3–1.5 days for 30, 40, 50, and 60°C, respectively. Inactivation of BL indigenous microbial population by autoclaving or addition of antibiotics to which the S. Infantis is resistant, resulted in augmentation of Salmonella multiplication. This suggests the presence of microbial antagonists in the BL, which inhibit the growth of the pathogen. Finally, Salmonella persisted over 90 days at 30°C in a Vertisol soil amended with inoculated BL, presumably due to reduced antagonistic activity compared to the BL alone. These findings are valuable for risk assessments and the formulation of guidelines for safe utilization of BL in agriculture.

Survival of Escherichia coli O157 in autoclaved and natural sandy soil mesocosms

While the soil microbiome may influence pathogen survival, determining the major contributors that reduce pathogen survival is inconclusive. This research was performed to determine the survival of E. coli O157 in autoclaved and natural (unautoclaved) sandy soils. Soils were inoculated with three different E. coli O157 strains (stx1+/stx2+, stx1-/stx2-, and stx1-/stx2+), and enumerated until extinction at 30°C. There was a significant difference in the survival of E. coli O157 based on soil treatment (autoclaved versus natural) at 30°C on days 1 (P = 0.00022), 3, (P = 2.53e-14), 7 (P = 5.59e-16), 14 (P = 1.072e-12), 30 (P = 7.18e-9), and 56 (P = 0.00029), with greater survival in autoclaved soils. The time to extinction (two consecutive negative enrichments) for all three strains was 169 and 84 days for autoclaved and natural soils, respectively. A separate E. coli O157 trial supplemented with 16S rRNA gene sequencing of the soil microbiome was performed at 15°C and 30°C on days 0, 7, 14, and 28 for each soil treatment. Greater species richness (Chao1, P = 2.2e-16) and diversity (Shannon, P = 2.2e-16) was observed in natural soils in comparison with autoclaved soils. Weighted UniFrac (beta-diversity) showed a clear distinction between soil treatments (P = 0.001). The greatest reduction of E. coli O157 was observed in natural soils at 30°C, and several bacterial taxa positively correlated (relative abundance) with time (day 0 to 28) in these soils (P < 0.05), suggesting that the presence of those bacteria might cause the reduction of E. coli O157. Taken together, a clear distinction in E. coli O157 survival, was observed between autoclaved and natural soils along with corresponding differences in microbial diversity in soil treatments. This research provides further insights into the bacterial taxa that may influence E. coli O157 in soils.

Bioremediation of gaseous methyl tert-butyl ether by combination of sulfuric acid modified bagasse activated carbon-bone biochar beads and Acinetobacter indicus screened from petroleum contaminated soil

Combination of sulfuric acid modified bagasse activated carbon-bone biochar beads and Acinetobacter indicus screened from petroleum contaminated soil was the best condition for gaseous methyl tert-butyl ether (MTBE) removal. It was found that H₂SO₄ modified bagasse AC in powder form had higher adsorption capacity (989.33 mg g^-1) than that in bead form (1.94 mg g^-1). In addition, bone biochar in powder form (3.51 mg g^-1) also had higher adsorption capacity than that in bead form (1.63 mg g^-1). This was the fact that material beads contained high moisture content that inhibited the penetration of gaseous MTBE into the material. And a mixed material of H₂SO₄ modified bagasse AC-bone biochar beads had the highest adsorption capacity (2.22 mg g^-1) compared to individual H₂SO₄ modified bagasse AC beads (1.94 mg g^-1) and bone biochar beads (1.63 mg g^-1) due to a mixed material had more rough surface and high surface area on its material. So, gaseous MTBE can penetrate through this material more easily. Although the maximum adsorption capacity of H₂SO₄ modified bagasse AC in powder form was the highest but microorganism cannot sustain and survive in this form for a long time. Therefore, the material beads were more suitable for microorganism to grow and degrade gaseous MTBE. Microorganism can degrade MTBE and caused no secondary wastes. Moreover, A. indicus was a novel strain for MTBE removal that has not been previously reported. Therefore, a combination of A. indicus-mixed material beads was a good choice for MTBE removal in a biofilter system.

Composting To Inactivate Foodborne Pathogens for Crop Soil Application: A Review

Compost is organic material that has been degraded into a nutrient-stabilized humus-like substance through intense microbial activity, which can provide essential plant nutrients (nitrogen, phosphorus) to aid in the growth of fruits and vegetables. Compost can be generated from animal waste feedstocks; these can contain human pathogens, which can be inactivated through the heat and microbial competition promoted during the composting process. Outbreaks of infections caused by bacterial pathogens such as Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes on fruit and vegetable commodities consumed raw emphasize the importance of minimizing the risk of pathogenic contamination on produce commodities. This review article investigates factors that affect the reduction and survival of bacterial foodborne pathogens during the composting process. Interactions with indigenous microorganisms, carbon:nitrogen ratios, and temperature changes influence pathogen survival, growth, and persistence in finished compost. Understanding the mechanisms of pathogen survival during the composting process and mechanisms that reduce pathogen populations can minimize the risk of pathogen contamination in the cultivation of fruits and vegetables.

Metaproteomics reveals major microbial players and their biodegradation functions in a large-scale aerobic composting plant

Composting is an appropriate management alternative for municipal solid waste; however, our knowledge about the microbial regulation of this process is still scare. We employed metaproteomics to elucidate the main biodegradation pathways in municipal solid waste composting system across the main phases in a large-scale composting plant. The investigation of microbial succession revealed that Bacillales, Actinobacteria and Saccharomyces increased significantly with respect to abundance in composting process. The key microbiologic population for cellulose degradation in different composting stages was different. Fungi were found to be the main producers of cellulase in earlier phase. However, the cellulolytic fungal communities were gradually replaced by a purely bacterial one in active phase, which did not support the concept that the thermophilic fungi are active through the thermophilic phase. The effective decomposition of cellulose required the synergy between bacteria and fungi in the curing phase.

Rapid identification of Campylobacter jejuni from poultry carcasses and slaughtering environment samples by real-time PCR

The objective of this study was to develop a real-time PCR assay for rapid identification of Campylobacter jejuni and to apply the method in analyzing samples from poultry processing. A C. jejuni-specific primer set targeting a portion of the C. jejuni hippuricase gene was developed. The specificity of the newly designed primer pair was verified using 5 C. jejuni strains and 20 other bacterial strains. Sensitivity was determined to be as low as 1 genome copy per reaction. A total of 73 samples were collected at different sites along the processing line during 2 visits to a poultry slaughterhouse and were examined by direct plating onto modified charcoal cefoperazone deoxycholate agar or after enrichment in Bolton broth followed by plating on modified charcoal cefoperazone deoxycholate agar. The newly developed real-time PCR assay was used to identify the presumptive colonies as belonging to C. jejuni. A real-time PCR assay targeting 16S ribosomal RNA was also applied to determine Campylobacter spp. prevalence. Results from the real-time PCR analysis indicated considerable variability in Campylobacter contamination, with incidence rates of 72.7 and 27.6% for sampling days A and B, respectively. Campylobacter was isolated from 100% of prescalded and preeviscerated carcasses on sampling day A. In contrast, on sampling day B, the highest number of Campylobacter-positive carcasses was recovered after evisceration (60%). The chilling process significantly reduced (P < 0.05) Campylobacter population, but the percentage of positive samples on sampling day A increased to 80%. All samples collected from the processing environment, except scalding tank 3 and the prechiller and chiller tanks, were 100% positive on day A, whereas no campylobacters were isolated from machinery on sampling day B. Our results revealed the widespread of C. jejuni in poultry processing and proved that the newly developed real-time PCR assay is a simple, specific, and inexpensive method for rapid C. jejuni identification. The newly developed PCR method can be easily used in laboratories for reliable and unambiguous identification of C. jejuni in poultry samples.

A glimpse of Escherichia coli O157:H7 survival in soils from eastern China

Escherichia coli O157:H7 (E. coli O157:H7) is an important food-borne pathogen, which continues to be a major public health concern worldwide. It is known that E. coli O157:H7 survive in soil environment might result in the contamination of fresh produce or water source. To investigate how the soils and their properties affect E. coli O157:H7 survival, we studied E. coli O157:H7 survival dynamics in 14 soils collected in eastern China from the warm-temperate zone to subtropical zone. Results showed that E. coli O157:H7 survival as a function of time can be well described by the Weibull model. The calculated td values (survival time to reach the detection limit, 100 colony forming units per gram oven-dried weight of soil) for the test soils were between 1.4 and 25.8 days. A significantly longer survival time (td) was observed in neutral or alkaline soils from north-eastern China (the warm-temperate zone) than that in acidic soils from south-eastern China (the subtropical zone). Distinct E. coli O157:H7 survival dynamics was related to soil properties. Stepwise multiple regression analysis revealed that the td values were significantly enhanced by soil microbial biomass carbon and total nitrogen, but were significantly reduced by amorphous Al2O3 and relative abundance of Chloroflexi. It should pay more attention to E. coli O157:H7 long survival in soils and its potential environmental contamination risk.