Bacterial growth in chicken breast fillet submitted to temperature abuse conditions

Low temperatures do not impair the bacterial plasmid conjugation on poultry meat

Conjugation plays an important role in the dissemination of antimicrobial resistance genes. Besides, this process is influenced by many biotic and abiotic factors, especially temperature. This study aimed to investigate the effect of different conditions of temperature and storage (time and recipient) of poultry meat, intended for the final consumer, affect the plasmid transfer between pathogenic (harboring the IncB/O-plasmid) and non-pathogenic Escherichia coli organisms. The determination of minimal inhibitory concentrations (MIC) of ampicillin, cephalexin, cefotaxime, and ceftazidime was performed before and after the conjugation assay. It was possible to recover transconjugants in the poultry meat at all the treatments, also these bacteria showed a significant increase of the MIC for all antimicrobials tested. Our results show that a non-pathogenic E. coli can acquire an IncB/O-plasmid through a conjugation process in poultry meat, even stored at low temperatures. Once acquired, the resistance genes endanger public health especially when it is about critically and highly important antimicrobials to human medicine.

Highly efficient low-temperature biodegradation of polyethylene microplastics by using cold-active laccase cell-surface display system

To eliminate efficiency restriction of polyethylene microplastics low-temperature biodegradation, a novel InaKN-mediated Escherichia coli surface display platform for cold-active degrading laccase PsLAC production was developed. Display efficiency of 88.0% for engineering bacteria BL21/pET-InaKN-PsLAC was verified via subcellular extraction and protease accessibility, exhibiting an activity load of 29.6 U/mg. Cell growth and membrane integrity revealed BL21/pET-InaKN-PsLAC maintained stable growth and intact membrane structure during the display process. The favorable applicability was confirmed, with 50.0% activity remaining in 4 days at 15 °C, and 39.0% activity recovery retention after 15 batches of activity substrate oxidation reactions. Moreover, BL21/pET-InaKN-PsLAC possessed high polyethylene low-temperature depolymerizing capacity. Bioremediation experiments proved that the degradation rate was 48.0% within 48 h at 15 °C, and reached 66.0% after 144 h. Collectively, cold-active PsLAC functional surface display technology and its significant contributions to polyethylene microplastics low-temperature degradation constitute an effective improvement strategy for biomanufacturing and microplastics cold remediation.

Building “First Expire, First Out” models to predict food losses at retail due to cold chain disruption in the last mile

Current less-than-truckload (LTL) shipping practices allow for temperature abuse (TA) in the last segment (last mile) of the food supply chain. When this TA is combined with “First In, First Out” product rotation methods, it could lead to food spoilage and food waste; therefore, data-based decision models are needed to aid retail managers. An experiment was designed using pallets (4 layers/pallet × 5 boxes/layer) of commercially produced boneless chicken breast filet trays. The pallets were exposed to 24 h of simulated LTL TA (cyclic 2 h at 4°C, then 2 h at 23 ± 2°C). Filet temperatures were recorded for all 20 boxes using dataloggers with thermocouple wires. Additionally, microbiological sampling of filets [aerobic plate counts (APC) and psychrotrophic plate counts (PSY)] was conducted before (0 h of LTL TA) and after (24 h of LTL TA) the TA experiment for select boxes of the pallet and compared to control filets (maintained at 4°C). After TA, a shelf-life experiment was conducted by storing filets from predetermined boxes at 4°C until spoilage (7 log CFU/ml). Temperature and microbiological data were augmented using Monte Carlo simulations (MC) to build decision making models using two methods; (1) the risk of each box on the pallet reaching the bacterial “danger zone” (>4°C) was determined; and (2) the risk-of-loss (shelf-life < 4 days; minimum shelf-life required to prevent food waste) was determined. Temperature results indicated that boxes on the top and bottom layers reached 4°C faster than boxes comprising the middle layers while the perimeter boxes of each layer reached 4°C faster than centrally located boxes. Shelf-life results indicate simulated LTL TA reduced shelf-life by 2.25 and 1.5 days for APC and PSY, respectively. The first MC method showed the average risk of boxes reaching 4°C after 24 h of simulated LTL TA were 94.96%, 43.20%, 27.20%, and 75.12% for layers 1–4, respectively. The second MC method indicated that exposure at >4°C for 8 h results in a risk-of-loss of 43.8%. The findings indicate that LTL TA decreases shelf-life of chicken breast filets in a heterogenous manner according to location of boxes on the pallet. Therefore, predictive models are needed to make objective decisions so that a “First Expire, First Out” method can be implemented to reduce food wastes due to TA during the last mile.

Bioaerosol Seasonal Variation and Contribution to Airborne Particulate Matter in Huangshi City of Central China

Ambient bioaerosols affect ecosystems and public health, but their seasonal variations and their contributions to aerosol particles are limitedly understood. Ambient bioaerosols in PM2.5 and PM10 samples were measured in Huangshi City, Hubei Province of China from April 2018 to December 2018. Bioaerosols were measured using a fluorescence microscope after staining with 4′, 6-diamino-2-phenylindole dihydrochloride (DAPI) following a direct staining technique. The bioaerosol number concentrations ranged from 0.12 to 15.69 # cm−3 for PM2.5 and 0.22 to 18.20 # cm−3 for PM10, with averages of 2.79 # cm−3 and 4.66 # cm−3, respectively. The bioaerosol concentrations of PM2.5 and PM10 varied significantly by seasons and were arranged in the following descending order: spring > fall > winter > summer. Bioaerosol numbers were dominated by fine particles of 0.37–2.5 μm diameter, while the spring bioaerosol particles were detected at the peak concentration of 0.56–1 μm diameter. Bioaerosol fractions accounted for 18.3 ± 10.6% PM10 mass and 13.7 ± 12.5% PM2.5 mass. Bioaerosol concentrations were increased during the haze event, but the increased amounts were not as large as those of the dust event, and higher bioaerosol contributions to PM were observed in the dust event than in the haze event. As enhanced emission controls have reduced PM concentrations in China, bioaerosols can be important contributors to PM mass.