Polymer-based microfluidic chip for rapid and efficient immunomagnetic capture and release of Listeria monocytogenes

Infections caused by foodborne pathogens such as Listeria monocytogenes pose a threat to public health while timely detection is challenging due to pathogen low numbers. The development of robust and efficient sample preparation techniques is crucial to improve detection sensitivity and workflow. Immunomagnetic separation using magnetic nanoparticles (MNPs) is attractive, as it can efficiently capture target cells. For food safety applications, a platform is needed to rapidly process large sample volumes, allowing capture and release of target bacteria conjugated to immunomagnetic nanoparticles (IMNPs). Herein, we demonstrate a method for magnetic capture and release of bacteria-IMNPs complex based on a 3D magnetic trap integrated on a polymeric microfluidic device. The 3D magnetic capture region consist of a dense array of high-aspect ratio (3 : 1) cylindrical pillars embossed in thermoplastic polymer and coated with soft ferromagnetic nickel by an electroless deposition technique. This allows the generation of strong and switchable magnetic capture regions due to the very low remanence of the nickel shell. We propose and validate an optimized configuration of capture regions for efficient localized capture and rapid release of MNPs and IMNPs conjugated to L. monocytogenes. A maximum recovery rate for MNPs corresponded to 91% while a maximum capture efficiency of 30% was obtained for live bacteria, with a minimum detectable sample concentration of ~10 cfu ml(-1) in 1 ml volume using plate-culture method. We believe that the flexible design and low-cost fabrication process of the proposed system will allow rapid sample preparation for applications beyond food and water safety, including point-of-care diagnosis.

Survival of calicivirus in foods and on surfaces: experiments with feline calicivirus as a surrogate for norovirus

Although there is a large body of evidence incriminating foods as vehicles in the transmission of norovirus, little is known about virus survival in foods and on surfaces. Feline calicivirus was used as a surrogate for norovirus to investigate its survival in representative foods of plant and animal origin and on metal surfaces. Known concentrations of feline calicivirus in a natural fecal suspension were deposited onto lettuce, strawberries, ham, or stainless steel and incubated for 7 days at refrigeration or room temperatures. Virus was recovered at 1-day intervals, and the titers of the virus were determined by plaque assay. Infectious virus was recoverable until day 7 from lettuce, ham, and stainless steel. Statistically higher titers of feline calicivirus (P < 0.05) were recovered from ham under all conditions than from lettuce, strawberries, or stainless steel. These data provide valuable information for epidemiological and monitoring purposes as well as for the development of food processing practices and appropriate strategies to inactivate norovirus and control its transmission via foods and surfaces.

Norovirus cross-contamination during food handling and interruption of virus transfer by hand antisepsis: experiments with feline calicivirus as a surrogate

While there is good epidemiological evidence for foods as vehicles for norovirus transmission, the precise means of spread and its control remain unknown. The feline calicivirus was used as a surrogate for noroviruses to study infectious virus transfer between hands and selected types of foods and environmental surfaces. Assessment of the potential of selected topicals in interrupting such virus transfer was also made. Ten microliters of inoculum of feline calicivirus deposited onto each fingerpad of adult subjects was allowed to air dry and the contaminated area on individual fingerpads was pressed (10 s at a pressure of 0.2 to 0.4 kg/cm2) onto 1-cm-diameter disks of ham, lettuce, or brushed stainless steel. The virus remaining on the donor and that transferred to the recipient surfaces was eluted and plaque assayed. Virus transfer to clean hands from experimentally contaminated disks of ham, lettuce, and stainless steel was also tested. Nearly 46 +/- 20.3, 18 +/- 5.7, and 13 +/- 3.6% of infectious virus was transferred from contaminated fingerpads to ham, lettuce, and metal disks, respectively. In contrast, approximately 6 +/- 1.8, 14 +/- 3.5, and 7 +/- 1.9% virus transfer occurred, respectively, from ham, lettuce, and metal disks to hands. One-way analysis of variance test showed that pretreatment (washing) of the fingerpads either with water or with both topical agent and water significantly (P < 0.05) reduced virus transfer to < or = 0.9%, as compared with < or = 2.3 and < or = 3.4% transfer following treatments with either 75% (vol/vol) ethanol or a commercial hand gel containing 62% ethanol, respectively. Despite wide variations in virus transfer among the targeted items used, intervention agents tested reduced virus transfer significantly (P < 0.05) when compared with that without such treatments (71 +/- 8.9%). These findings should help in a better assessment of the potential for cross-contamination of foods during handling and also assist in developing more effective approaches to foodborne spread of norovirus infections.

A feline kidney cell line-based plaque assay for feline calicivirus, a surrogate for Norwalk virus

Feline calicivirus (FCV) has been used by researchers as a surrogate for Norwalk virus (NV), since they share a similar genomic organization, physicochemical characteristics, and are grouped in the same family, Caliciviridae. Unlike NV, however, FCV can grow in established cell lines and produce a syncytial form of cytopathic effect. In this report, we describe the development and standardization of a plaque assay for FCV using monolayers of an established line of feline kidney (CrFK) cells in 12-well cell culture plates. The assay method has demonstrated reproducibility, ease of performance and resulted in clear plaque zones, readable in 24 h after virus inoculation. The infectivity titre of the virus by this plaque assay agreed well with tissue culture infectious dose(50) (TCID(50)) determinations. The described plaque assay would be a valuable tool in conducting various quantitative investigations using FCV as a model for NV and Norwalk-like viruses (NLV).

Rapid concentration and detection of hepatitis A virus from lettuce and strawberries

Immunomagnetic beads-PCR (IM-PCR), positively-charged virosorb filters (F), or a combination of both methods (F-IM-PCR) were used to capture, concentrate and rapidly detect hepatitis A virus (HAV) in samples of lettuce and strawberries experimentally contaminated. Direct reverse transcriptase-polymerase chain reaction (RT-PCR) amplification of the collected HAV-beads complex showed a detection limit of 0.5 plaque forming units (PFU) of the virus present in 1-ml of wash solution from the produce, which was several hundred-fold more sensitive than that demonstrated by RT-PCR. In separate trials, virus-containing wash solutions from the produce were passed through the filters and the captured virus was eluted with 10 ml volumes of 1% beef extract. Of the 62% filter-captured HAV, an average of 34.8% was eluted by the 1% beef extract. PCR amplification of 2 microl from this eluate failed to produce a clear positive band signal. As little as 10 PFU, present on each piece of the lettuce or strawberry, was detectable by the F-IM-PCR, which was almost 20 times less sensitive than the detection limit of 0.5 PFU by the IM-PCR. However, considering the large volumes (< or =50 ml) used in the F-IM-PCR, the sensitivity of detection could be much greater than that of the IM-PCR, which was restricted to < or =20 ml volumes. These data indicate that the F-IM-PCR method provides the potential for a greater sensitivity of detection than the IM-PCR, since low levels of virus could be detected from large volumes of sample than possible by the IM-PCR method. Although positively-charged filters captured a greater amount of virus than both the IM-PCR and F-IM-PCR methods, direct PCR amplification from beef extract eluates was not successful in detecting HAV from produce.

Contamination of foods by food handlers: experiments on hepatitis A virus transfer to food and its interruption

Hepatitis A virus (HAV) is an important pathogen which has been responsible for many food-borne outbreaks. HAV-excreting food handlers, especially those with poor hygienic practices, can contaminate the foods which they handle. Consumption of such foods without further processing has been known to result in cases of infectious hepatitis. Since quantitative data on virus transfer during contact of hands with foods is not available, we investigated the transfer of HAV from artificially contaminated fingerpads of adult volunteers to pieces of fresh lettuce. Touching the lettuce with artificially contaminated fingerpads for 10 s at a pressure of 0.2 to 0.4 kg/cm(2) resulted in transfer of 9.2% +/- 0.9% of the infectious virus. The pretreatments tested to interrupt virus transfer from contaminated fingerpads included (i) hard-water rinsing and towel drying, (ii) application of a domestic or commercial topical agent followed by water rinsing and towel drying, and (iii) exposure to a hand gel containing 62% ethanol or 75% liquid ethanol without water rinsing or towel drying. When the fingerpads were treated with the topical agents or alcohol before the lettuce was touched, the amount of infectious virus transferred to lettuce was reduced from 9.2% to between 0.3 and 0.6% (depending on the topical agent used), which was a reduction in virus transfer of up to 30-fold. Surprisingly, no virus transfer to lettuce was detected when the fingerpads were rinsed with water alone before the lettuce was touched. However, additional experiments with water rinsing in which smaller volumes of water were used (1 ml instead of 15 ml) showed that the rate of virus transfer to lettuce was 0.3% +/- 0.1%. The variability in virus transfer rates following water rinsing may indicate that the volume of water at least in part influences virus removal from the fingerpads differently, a possibility which should be investigated further. This study provided novel information concerning the rate of virus transfer to foods and a model for investigating the transfer of viral and other food-borne pathogens from contaminated hands to foods, as well as techniques for interrupting such transfer to improve food safety.

Heat inactivation of hepatitis A virus in dairy foods

Experiments were performed to determine the thermal resistance of hepatitis A virus (HAV) in three types of dairy products containing increased amounts of fat content (skim milk, homogenized milk; 3.5% MFG, and table cream; 18% MFG). HAV-inoculated dairy products were introduced into custom-made U-shaped microcapillary tubes that in turn were simultaneously immersed in a waterbath, using custom-made floating boats and a carrying platform. Following exposure to the desired time and temperature combinations, the contents of each of the tubes was retrieved and was tested by plaque assay to determine the reduction in virus titer. Our data indicated that < 0.5 min at 85 degrees C was sufficient to cause a 5-log reduction in HAV titer in all three dairy products, whereas at 80 degrees C, < or = 0.68 min (for skim and homogenized milk), and 1.24 min (for cream) were needed to cause a similar log reduction. Using a nonlinear two-phase negative exponential model (two-compartment model) to analyze the data, it was found that at temperatures of 65, 67, 69, 71, and 75 degrees C, significantly (P < 0.05) higher exposure times were needed to achieve a 1-log reduction in virus titer in cream, as compared to skim and homogenized milk. For example, at 71 degrees C, a significantly (P < 0.05) higher exposure time of 0.52 min (for cream) was needed as compared to < or = 0.18 min (for skim and homogenized milk) to achieve a 1-log reduction in virus titer. A similar trend of inactivation was observed at 73 and 75 degrees C where significantly (P < 0.05) higher exposure times of 0.29 to 0.36 min for cream were needed to cause a 1-log reduction in HAV in cream, as compared to < or = 0.17 min for skim and homogenized milk. This study has provided information on the heat resistance of HAV in skim milk, homogenized milk, and table cream and demonstrated that an increase in fat content appears to play a protective role and contributes to the heat stability of HAV.

Fatty acid profiles of Chlamydia using capillary gas chromatography

Fatty acid profiles of purified elementary bodies of Chlamydia trachomatis (CT) serotypes D, G and L3 were investigated by gas liquid chromatography (GLC) utilizing three fused silica capillary columns of different polarities. CT serotype C and C. psittaci (CP) strain DD34 were investigated using one column only due to the lack of adequate quantities of purified material. Significantly similar fatty acid profiles were observed in the serotypes examined. However, based on the percentage ratio of 13-methyl tetradecanoate (i-15:0) to 12-methyl tetradecanoate (a-15:0), serotypes D and L3, with ratios of 0.18 and 0.19, respectively, could be differentiated from serotypes C and G with ratios of 1.3 and 1.5, respectively. CP demonstrated a ratio of 0.4, thus differentiating it from the CT serotypes examined. Fatty acids i-15:0 and a-15:0 were absent in uninfected McCoy cells. Results were significantly comparable in all three capillary columns. This study suggests that GLC could be used for identification and differentiation of Chlamydia serotypes.

In vivo modulation of thymus-derived lymphocytes with monoclonal antibodies in mice. III. Spontaneous and natural cytotoxic effector cells

Cytotoxic effector cell populations in murine spleen can be characterized by the phenotype of the cytotoxic cells or the nature of target cells. Lytic events can be antigen-specific, MHC-restricted and clonal, or target cell-specific but apparently non-MHC-restricted. Two cytotoxic effectors of this latter category are spontaneous and natural killers. Normal spleen cells from (BALB/c X DBA/2J)F1 mice (CDF1) cultured without added antigen develop a population of Thy-1+ spontaneous cytotoxic lymphocytes (SCTL) that lyse the DBA/2J mastocytoma P815, as well as the BALB/c-derived plasmacytomas MOPC-11 and SP2/0. Cold target competition experiments reveal the BALB/c-derived plasmacytomas MOPC-11, SP2/0, J558 and the A strain-derived T cell lymphoma YAC-1, but not normal lymphoblasts, block the lysis of P815 target cells. Thus, while these tumour cells appear to express common antigens which are recognized by SCTL cells, plasmacytomas such as J558 are not susceptible to lysis by SCTL. The relationship of SCTL to natural killer (NK) cells was examined. In-vivo treatment of mice with monoclonal anti-Thy-1 antibody leads to a rapid loss of SCTL and precursors from the spleen, but there is a concomitant increase in NK cell activity.