A downstream process control tool based on the redox dye resazurin for rapid and accurate measurement of microbial metabolic activity

Many sophisticated water treatment plants need a reliable, fast, and economical microbial load detection method. We refined a colorimetric assay using the redox dye resazurin to assess viable microorganisms. Here, we have used a mixed bacterial suspension of significant multi-drug-resistant coliform bacteria isolated from hospital wastewater and constructed a resazurin reduction calibration curve which could accurately predict the level of microbial contamination. The number of viable microorganisms was calculated from calibration curve in terms of log colony forming units (CFU) per milliliter. Ultrasonication disinfection of bacterial suspension for a duration of 50 min measured by resazurin assay depicted a reduction of 16.94%, 26.48%, and 37.69% at 410 W, 580 W, and 700 W, respectively. A synergistic effect of the combined methods of ultrasonication and heat disinfection treatments on raw wastewater and secondary wastewater effluent was observed and was also evaluated using both resazurin assay and standard plate count method. For raw wastewater, about 1.8 log reduction was observed for ultrasonication alone and 4 log CFU/mL reduction for thermosonication. In the secondary wastewater effluent, a reduction of 2.9 and 3.2 log CFU/mL was recorded for ultrasonication and thermosonication respectively. Resazurin microbial viability test results were highly comparable with conventional colony plate count for all treatment procedures, suggesting its appropriateness for quick and reliable wastewater sample microbial viability monitoring.

Pseudocatalytic Hydrogels with Intrinsic Antibacterial and Photothermal Activities for Local Treatment of Subcutaneous Abscesses and Breast Tumors

The intimate relationship between bacteria and tumors has triggered a lot of activities in the development and design of bioactive materials to concurrently respond to antitumor and antibacterial demands. Herein, a pseudocatalytic hydrogel (AM-I@Agar) with intrinsic antibacterial and photothermal activities, synthesized by incorporating prefabricated amylose-iodine nanoparticles into low-melting-point agarose hydrogel, is explored as a bioactive agent for local treatment of subcutaneous abscesses and breast tumors. The AM-I@Agar hydrogel depicts the ability of pseudocatalytic O₂ generation from H₂ O₂ to alleviate hypoxia. Meanwhile, the AM-I@Agar hydrogel exhibits temperature self-regulation features, beneficial for avoiding thermal injury during photothermal therapy owing to thermochromic properties. Upon local injection into a subcutaneous abscess, methicillin-resistant Staphylococcus aureus is effectively eliminated by the AM-I@Agar hydrogel, and complete skin recovery is achieved in 8 d, demonstrating much better antibacterial effects compared with penicillin, a small-molecule antibiotic. AM-I/5-FU@Agar hydrogel, obtained after loading 5-fluorouracil (5-FU), significantly inhibits tumors in both normal 4T1 tumor-bearing mice and MRSA-infected 4T1 tumor-bearing mice models via a synergistic photothermal-chemo effect, and shows treatment efficiency superior to that achieved with photothermal therapy or 5-FU alone. This work provides a concept for the design and development of bioactive agents for potential management of bacteria-associated cancer.

Antimicrobial photodynamic inactivation of wastewater microorganisms by halogenated indole derivative capped zinc oxide

Novel 5-bromoindole (5B)-capped zinc oxide (ZnO) nanoparticles (5BZN) were synthesized to improve the antibacterial, antibiofilm, and disinfection processes for the control of microorganisms in wastewater treatment. When exposed to 5BZN, the biofilm density and cell attachment were reduced dramatically, as measured by scanning electron microscopy (SEM). The 5BZN were also investigated for photodynamic treatment of multidrug-resistant (MDR) bacteria and toxicity. The combination of 5B and ZnO exhibited strong antibacterial and antibiofilm activities against MDR bacteria even at low doses (20 μg/mL). After 12.5 mW/cm² blue LED irradiation, the composite 5BZN showed superior photodynamic inactivation of two wastewater MDR, Enterobacter tabaci E2 and Klebsiella quasipneumoniae SC3, with cell densities reduced by 3.9 log CFU/mL and 4.7 log CFU/mL, respectively, after 120 min. The mechanism of bacterial inactivation was studied using a scavenging investigation, and H₂O₂ was identified mainly as the reactive species for bacterial inactivation. The 5BZN exhibited higher photodynamic inactivation towards the total coliform bacteria in wastewater effluents under a blue LED light intensity of 12.5 mW/cm² with almost complete inactivation of the coliform bacteria cells within 40 min. Furthermore, when 5BZN (100 mg/L) was added to the reactor, the level of tetracycline antibiotic degradation was increased by 63.6% after 120 min. The toxicity test, animal model nematode studies and seed germination assays, showed that 5BZN is harmless, highlighting its tremendous potential as a self-healing agent in large-scale photodynamic disinfection processes.

Terpinolene as an enhancer for ultrasonic disinfection of multi-drug-resistant bacteria in hospital wastewater

The present study reports for the first time, a novel disinfection method that combines ultrasonication with a natural biocide terpinolene to inhibit tough and opportunistic antimicrobial-resistant (AMR) microorganisms isolated from hospital wastewater treatment plant (HWWTP). The enhancement of the disinfection process was evaluated for the effect of ultrasonication power, operating temperature, and inoculum size. A hybrid methodology combining terpinolene with traditional physico-chemical method of acoustic cavitation delivered efficient disinfection of the secondary effluent of field scale HWWTP, amended with a higher inoculum size of multi-drug-resistant coliform bacteria Enterobactor sp., Citrobacter freundii, and Klebsiella pneumonia. A bacterial load of 6.4 log CFU/mL was completely eliminated in 25 min. The present study also reports that due to the hybrid process, a very small concentration of 0.312 mM (0.25 × Minimum Inhibitory Concentration or MBC) of terpinolene was enough to completely disinfect the multi-drug-resistant coliforms. The leakage of intracellular nucleic acids during the disinfection process suggested disruption of cell membrane as the primary mechanism of disinfection followed by disruption of cellular metabolic function measured by respiratory chain dehydrogenase activity. Moreover, this study is the first to prove that terpinolene remained stable even after the cavitation process, thus revealing possibilities of recycling of the natural compound for wastewater disinfection. The results of the present research suggest that using terpinolene as a bio-additive can efficiently eliminate hazardous multi-drug-resistant bacteria and drastically reduce operational time and cost thus rendering it suitable to replace conventional wastewater disinfection.

Biocides as Biomedicines against Foodborne Pathogenic Bacteria

Biocides are currently considered the first line of defense against foodborne pathogens in hospitals or food processing facilities due to the versatility and efficiency of their chemical active ingredients. Understanding the biological mechanisms responsible for their increased efficiency, especially when used against foodborne pathogens on contaminated surfaces and materials, represents an essential first step in the implementation of efficient strategies for disinfection as choosing an unsuitable product can lead to antibiocide resistance or antibiotic–biocide cross-resistance. This review describes these biological mechanisms for the most common foodborne pathogens and focuses mainly on the antipathogen effect, highlighting the latest developments based on in vitro and in vivo studies. We focus on biocides with inhibitory effects against foodborne bacteria (e.g., Escherichia spp., Klebsiella spp., Staphylococcus spp., Listeria spp., Campylobacter spp.), aiming to understand their biological mechanisms of action by looking at the most recent scientific evidence in the field.