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Silver metals have long been known to possess antimicrobial properties. Recently, even the nanoparticle version of silver (AgNPs) has also been established as antimicrobials. In this study AgNPs were combined with extracts of the medicinal plant Chinese honeysuckle, Lonicera japonica Thunb. The antimicrobial activity of the AgNPs-herb was tested against pathogenic Escherichia coli CMCC44113. Using different AgNPs or herb (honeysuckle water extract or HWE) ratios in the presence of a fixed concentration of E. coli CMCC44113, potencies were found to be proportional with concentrations. The antimicrobial activities of AgNPs-HWE combo were significant enhanced, when compared with solely AgNPs or HWE. Thus, atomic force microscopic and propidium monoazide-PCR were used to probe the damages caused by AgNPs-HWE combo on the cell morphology and cell membrane integrity of E. coli. The mechanism of AgNPs-HWE combo against E. coli may attribute to AgNPs leads to cell wall lysis and damages cell membrane integrity, and thus increases the penetration of HWE into the bacterium, which results in more serious damage to bacterial cells. These findings indicated that AgNPs-herb was more potent than the AgNPs alone and holds promise for the development of nanoparticle enhanced herbal pharmaceuticals.

Detecting and enumerating fecal coliforms, especially Escherichia coli, as indicators of fecal contamination, are essential for the quality control of supplied and recreational waters. We have developed a sensitive, inexpensive, and small-volume amperometric detection method for E. coli beta-galactosidase by bead-based immunoassay. The technique uses biotin-labeled capture antibodies (Ab) immobilized on paramagnetic microbeads that have been functionalized with streptavidin (bead-Ab). The bead-Ab conjugate captures E. coli from solution. The captured E. coli is incubated in Luria Bertani (LB) broth medium with the added inducer isopropyl beta-D: -thiogalactopyranoside (IPTG). The induced beta-galactosidase converts p-aminophenyl beta-D: -galactopyranoside (PAPG) into p-aminophenol (PAP), which is measured by amperometry using a gold rotating disc electrode. A good linear correlation (R2 = 0.989) was obtained between log cfu mL(-1) E. coli and the time necessary to product a specific concentration of PAP. Amperometric detection enabled determination of 2x10(6) cfu mL(-1) E. coli within a 30 min incubation period, and the total analysis time was less than 1 h. It was also possible to determine as few as 20 cfu mL(-1) E. coli under optimized conditions within 6-7 h. This process may be easily adapted as an automated portable bioanalytical device for the rapid detection of live E. coli.

Ultra-fine-ZnO showed low toxicity in complex water matrix containing multiple components such as PBS buffer and the toxic mechanism of ultra-fine-ZnO has not been clearly elucidated. In present study, enhanced antibacterial activity of 200 nm diameter ultra-fine-ZnO in PBS buffer against Bacillus cereus and Escherichia coli were observed in the presence of several organic acids in comparison with ultra-fine-ZnO in PBS buffer alone. These findings indicated that the toxic effects of the ultra-fine-ZnO was dependent on the concentration of released Zn 2+ which was affected by organic acids. The production of reactive oxygen species (ROS) did not responsible to the toxic mechanism of ultra-fine-ZnO which was tested using the antioxidant N -Acetylcysteine (NAC). Indeed, ultra-fine-ZnO induced bacteria cell membrane leakages and cell morphology damages that eventually led to cell death, which were confirmed using propidium monoazide (PMA) in combination with PCR and scanning electron microscopy (SEM). All data gathered herein suggested that released Zn 2+ played a major role in the microbial toxicity of ultra-fine-ZnO. [ABSTRACT FROM AUTHOR]

Escherichia coli O157:H7, Cronobacter spp., and Salmonella spp. are common food-borne pathogens in milk that may cause serious diseases. In the present study, we established a simple, rapid, and specific method to simultaneously detect viable E. coli O157:H7, Cronobacter spp., and Salmonella spp. in milk. Three specific genes, fliC from E. coli O157:H7, cgcA from Cronobacter spp., and invA from Salmonella spp., were selected and used to design primers and probes. False-positive results were eliminated with the use of a combined sodium deoxycholate (SD) and propidium monoazide (PMA) treatment. Using the optimized parameters, this SD-PMA treatment combined with multiplex real-time PCR (SD-PMA-mRT-PCR) detected E. coli O157:H7, Cronobacter spp. and Salmonella spp. respectively, at 10² cfu/mL in pure culture or artificially spiked skim milk samples. A reasonable recovery rate (from 100 to 107%) for detection of viable bacteria using the SD-PMA-mRT-PCR assay was obtained in the presence of dead bacteria at 107 cfu/mL. The SD-PMA-mRTPCR method developed in this study can accurately detect and monitor combined contamination with E. coli O157:H7, Cronobacter spp., and Salmonella spp. in milk and milk products. [ABSTRACT FROM AUTHOR]

Salmonella Enteritidis, Eschericha coli O157:H7 and Listeria monocytogenes are important pathogens contaminating fresh vegetables. The aim of this study was to develop a rapid and accurate approach for simultaneous detection of viable S. Enteritidis, E. coli O157:H7 and L. monocytogenes in fresh vegetables. To detect viable cells, propidium monoazide (PMA) was applied to eliminate the false-positive results. In addition, an internal amplification control (IAC) was added to the quadruplex PCR as indicator of false negative results that are mainly caused by the PCR inhibitors. The limit of detection (LOD) for the viable cells with or without PMA treatment was 10 2 CFU/mL for S. Enteritidis, 10 3 CFU/mL for E. coli O157:H7 and 10 4 CFU/mL for L. monocytogenes , showing that the PMA treatment did not influence the sensitivity. After 12 h enrichment, the PMA-mPCR-IAC combination assay could detect as low as 10 1 CFU/g for viable S. Enteritidis, E. coli O157:H7 and L. monocytogenes in spiked vegetables. The PMA-mPCR-IAC combination assay holds promise for the simultaneous detection of viable S. Enteritidis, E. coli O157:H7 and L. monocytogenes in fresh vegetables. [ABSTRACT FROM AUTHOR]

A rapid, reproducible, sensitive and specific combination assay was developed for Escherichia coli O157:H7 comprising sequential immunomagnetic separation (IMS), followed by propidium monoazide (PMA), exclusion by viable cells, internal amplification control (IAC) and polymerase chain reaction (PCR). IMS was used to improve sensitivity, reduce detection time and eliminate false positives. PMA was used to detect viable cells, and IAC was incorporated into the system to eliminate the inhibitors of PCR from the food matrix. In the presence of inhibitors, IAC produced no signal, thereby eliminating false negative results. The results indicated that the IMS cell capture efficiency was about 90% at a concentration of 1 × 106 cfu mL−1 with a detection limit of 2.1 × 102 cfu mL−1 for pure culture. In an unoptimised system, IMS–PMA–PCR with IAC showed a detection limit of 5 × 103 cfu mL−1 in spiked milk over a 240 min assay, faster than conventional methods of detection. [ABSTRACT FROM AUTHOR]