Category Archives: pathogenic

Research – Application of continuous-type pulsed ohmic heating system for inactivation of foodborne pathogens in buffered peptone water and tomato juice

Science Directl


The purpose of this study was to inactivate Escherichia coli O157:H7, SalmonellaTyphimurium, and Listeria monocytogenes by continuous-type pulsed ohmic heatingin buffered peptone water (BPW) and tomato juice. First, BPW inoculated with the three pathogens were treated at different flow rates (0.2–0.4 LPM) and treatment voltages (9.43–12.14 Vrms/cm). Both heating rate of BPW and reduction rates of pathogens increased corresponding to decreased flow rate. Accordingly, higher numbers of pathogens survived at a higher flow rate (0.4 LPM). Increasing treatment voltage was an effective way to inactivate pathogens at 0.4 LPM, but the heating rate overly accelerated with increasing voltage adversely affecting food quality. Alternatively, increasing initial temperature by preheating can help inactivate pathogens in the early treatment stage without affecting heating rate. From the BPW experiments, we identified that treatment conditions such as flow rate, voltage, and initial temperature are important factors determining pathogen inactivation performance of continuous-type ohmic heating. When applied to tomato juice, 5 log reductions of all three pathogens were achieved by applying 12.14Vrms/cm ohmic heating with 0.2 LPM flow rate after preheating sample to 50 °C with a water bath. Quality aspects of color and lycopene content were observed, and a and b values decreased after treatment. Because preheating with additional equipment is inconvenient and occupies valuable space, we developed sequential three cylinder type ohmic heating. By applying the developed sequential ohmic heating, 5 log reductions were achieved for all three pathogens without preheating under the same treatment conditions. Therefore, we concluded that sequential continuous-type ohmic heating can be used utizied effectively to control foodborne pathogensby the juice industry.

Research – Antimicrobial Activity and Action Approach of the Olive Oil Polyphenol Extract Against Listeria monocytogenes

Frontiers in Microbiology

Olive oil polyphenol extract (OOPE) has been reported to have antibacterial activity; however, its effect on Listeria monocytogenes is less studied so far. This study, thus, aimed to reveal its antimicrobial activity and action approach against L. monocytogenes via evaluating the minimum inhibitory concentration (MIC) as well as the changes of intracellular adenosine 5′-triphosphate (ATP) concentration, cell membrane potential, bacterial protein, DNA, and cell morphology. The results showed that OOPE could inhibit the growth of L. monocytogeneswith a measured MIC of 1.25 mg/ml. L. monocytogenes cells treated by OOPE showed significant reduction in intracellular ATP concentrations, bacterial protein, or DNA (p < 0.05), in comparison with those without any treatment. In addition, OOPE was observed to depolarize strain cells and alter cell morphology, resulting in damaged cell membrane and, thereby, leakage of cell fluid. These findings demonstrated that OOPE had inhibition on L. monocytogenes via its action on cells, suggesting its potential as a natural preservative.

Research – Number of foodborne illnesses associated with outbreaks in tomatoes decreased since 2001


About 48 million episodes of foodborne illness and 3,000 deaths occur per year in the United States. The most common foodborne pathogens cause an estimated annual burden of $14 billion to $36 billion. Produce has been implicated in 46 percent of foodborne illness outbreaks. Tomatoes have been the source of a number of foodborne illness outbreaks since 1998, but the annual number of foodborne illnesses associated with outbreaks in tomatoes has generally decreased since their high of nearly 900 in 2001. Ten outbreaks have caused more than 100 illnesses, while 2 were associated with deaths of individuals. In 2005 and 2006, multistate outbreaks of salmonella in tomatoes sickened 487 individuals.

Research – Antibacterial Effects of Phytic Acid against Foodborne Pathogens and Investigation of Its Mode of Action

Journal of Food Protection


This study investigated the antimicrobial mechanism of phytic acid (PA) and its antibacterial effects in combination with ethanol. The MIC of PA on Escherichia coli ATCC 11229, Staphylococcus aureus ATCC 6538P, Bacillus subtilis ATCC 6633, and Salmonella Typhimurium CICC 27483 were 0.24, 0.20, 0.26, and 0.28% (w/w), respectively. E. coli ATCC 11229 and S. aureus ATCC 6538P were selected to investigate the mechanism of PA by analyzing its effects at 1/2MIC and at MIC on the cell morphology, intracellular ATP, and cell membrane integrity. Environmental scanning electron microscope images revealed that PA was able to change the cell morphology and disrupt the intercellular adhesion. PA retarded bacterial growth and caused cell membrane dysfunction, which was accompanied by decreased intracellular ATP concentrations. Flow cytometry analysis further revealed that almost all the bacterial cells were damaged after treatment with PA at its MIC for 2 h. Moreover, PA has a synergistic antimicrobial ability when used in combination with ethanol. These results suggested that PA is effective in inhibiting growth of foodborne pathogens mainly by the mechanism of cell membrane damage and to provide a theoretical basis for the development of natural antimicrobial agents in the food industry.

Research – Growth of Salmonella and Other Foodborne Pathogens on Inoculated Inshell Pistachios during Simulated Delays between Hulling and Drying

Journal of Food Protection


During harvest, pistachios are hulled, separated in water into floater and sinker streams (in large part on the basis of nut density), and then dried before storage. Higher prevalence and levels of Salmonella were previously observed in floater pistachios, but contributing factors are unclear. To examine the behavior of pathogens on hulled pistachios during simulated drying delays, floater and sinker pistachios collected from commercial processors were inoculated at 1 or 3 log CFU/g with cocktails of Salmonella and in some cases Escherichia coli O157:H7 or Listeria monocytogenes and incubated for up to 30 h at 37°C and 90% relative humidity. Populations were measured by plating onto tryptic soy agar and appropriate selective agars. In most cases, no significant growth (P > 0.05) of Salmonella was observed in the first 3 h after inoculation in hulled floaters and sinkers. Growth of Salmonella was greater on floater pistachios than on corresponding sinkers and on floater pistachios with ≥25% hull adhering to the shell surface than on corresponding floaters with <25% adhering hull. Maximum Salmonella populations (2 to 7 log CFU/g) were ∼2-log higher on floaters than on corresponding sinkers. The growth of E. coliO157:H7 and Salmonella on hulled pistachios was similar, but a longer lag time (approximately 11 h) and significantly lower maximum populations (4 versus 5 to 6 log CFU/g; P < 0.05) were predicted for L. monocytogenes. Significant growth of pathogens on hulled pistachios is possible when delays between hulling and drying are longer than 3 h, and pathogen growth is enhanced in the presence of adhering hull material.

  • Foodborne pathogens multiplied on undried inshell pistachios.

  • Pathogen growth was greater when hull material was present.

  • Drying delays of >3 h led to significant increases in pathogen populations.

  • Managing drying delays will reduce the risk for growth of foodborne pathogens.

Research – Differences Among Incidence Rates of Invasive Listeriosis in the U.S. FoodNet Population by Age, Sex, Race/Ethnicity, and Pregnancy Status, 2008–2016

Mary Ann Leibert listeria

Listeria monocytogenes is a foodborne pathogen that disproportionally affects pregnant females, older adults, and immunocompromised individuals. Using U.S. Foodborne Diseases Active Surveillance Network (FoodNet) surveillance data, we examined listeriosis incidence rates and rate ratios (RRs) by age, sex, race/ethnicity, and pregnancy status across three periods from 2008 to 2016, as recent incidence trends in U.S. subgroups had not been evaluated. The invasive listeriosis annual incidence rate per 100,000 for 2008–2016 was 0.28 cases among the general population (excluding pregnant females), and 3.73 cases among pregnant females. For adults ≥70 years, the annual incidence rate per 100,000 was 1.33 cases. No significant change in estimated listeriosis incidence was found over the 2008–2016 period, except for a small, but significantly lower pregnancy-associated rate in 2011–2013 when compared with 2008–2010. Among the nonpregnancy-associated cases, RRs increased with age from 0.43 (95% confidence interval: 0.25–0.73) for 0- to 14-year olds to 44.9 (33.5–60.0) for ≥85-year olds, compared with 15- to 44-year olds. Males had an incidence of 1.28 (1.12–1.45) times that of females. Compared with non-Hispanic whites, the incidence was 1.57 (1.18–1.20) times higher among non-Hispanic Asians, 1.49 (1.22–1.83) among non-Hispanic blacks, and 1.73 (1.15–2.62) among Hispanics. Among females of childbearing age, non-Hispanic Asian females had 2.72 (1.51–4.89) and Hispanic females 3.13 (2.12–4.89) times higher incidence than non-Hispanic whites. We observed a higher percentage of deaths among older patient groups compared with 15- to 44-year olds. This study is the first characterizing higher RRs for listeriosis in the United States among non-Hispanic blacks and Asians compared with non-Hispanic whites. This information for public health risk managers may spur further research to understand if differences in listeriosis rates relate to differences in consumption patterns of foods with higher contamination levels, food handling practices, comorbidities, immunodeficiencies, health care access, or other factors.

Research – PopPUNK advances speed of bacterial pathogen surveillance

Science Daily

In a study published today in Genome Research, researchers developed PopPUNK (Population Partitioning Using Nucleotide K-mers), a computational tool for analyzing tens of thousands of bacterial genomes in a single run, up to 200-fold faster than previous methods. Researchers envision PopPUNK will expedite the identification of bacterial strains as the scale of bacterial genomes being sequenced increases and, importantly, allow public health agencies to quickly identify outbreak strains that pose a public health risk.