Jong-Hyun Park

Disinfection of iceberg lettuce by titanium dioxide-UV photocatalytic reaction.

Securing the physical quality and microbial safety of fresh foods has been a major focus in the food industry. To improve quality and increase the shelf life of fresh produce, disinfection methods have been developed. Titanium dioxide (TiO2) photocatalytic reactions under UV radiation produce hydroxyl radicals that can be used for disinfection of foodborne pathogenic bacteria. We investigated the effects of TiO2-UV photocatalytic disinfection on the shelf life of iceberg lettuce. Counts of natural microflora (total aerobic bacteria, coliforms, psychrotrophic bacteria, and yeasts and molds) and inoculated pathogenic bacteria (Escherichia coli, Listeria monocytogenes, Staphylococcus aureus, and Salmonella Typhimurium) on iceberg lettuce were determined after 20-min treatments with TiO2-UV, UV radiation, a sodium hypochlorite (NaOCl) solution, and tap water. TiO2-UV treatment reduced the number of microorganisms by 1.8 to 2.8 log CFU/g compared with reductions of 0.9 to 1.4 and 0.7 to 1.1 log CFU/g obtained with UV radiation and NaOCl treatments, respectively. Treatment with tap water was used as a control and resulted in no reductions. Counts of microflora for iceberg lettuce at 4 and 25 degrees C were determined during a 9-day period. TiO2-UV treatment resulted in 1.2- and 4.3-log increases in the counts of total aerobic bacteria at 4 and 25 degrees C, respectively, compared with 1.3- to 1.6-log and 4.4- to 4.8-log increases due to UV radiation and NaOCl treatments.

Complete Genome Sequence of Enterococcal Bacteriophage SAP6

ABSTRACT Enterococcus faecalis is an important bacterium for use as a probiotic and is an opportunistic pathogen in human beings. The antibiotic resistance acquired by E. faecalis is restricted to antibiotics used in the clinical setting. While screening for alternative antibiotics for use against multidrug-resistant E. faecalis, we isolated a virulent enterococcal bacteriophage, SAP6, belonging to the family Siphoviridae. To our knowledge, this study is the first to report the complete genome sequence of bacteriophage SAP6, which might be used as a therapeutic agent in combination with alternative antibiotics for multidrug-resistant E. faecalis.

Norovirus Contamination Levels in Ground Water Treatment Systems Used for Food-Catering Facilities in South Korea

This study aimed to inspect norovirus contamination of groundwater treatment systems used in food-catering facilities located in South Korea. A nationwide study was performed in 2010. Water samples were collected and, for the analysis of water quality, the temperature, pH, turbidity, and residual chlorine content were assessed. To detect norovirus genotypes GI and GII, RT-PCR and semi-nested PCR were performed with specific NV-GI and NV-GII primer sets, respectively. The PCR products amplified from the detected strains were then subjected to sequence analyses. Of 1,090 samples collected in 2010, seven (0.64%) were found to be norovirus-positive. Specifically, one norovirus strain was identified to have the GI-6 genotype, and six GII strains had the GII, GII-3, GII-4, and GII-17 genotypes. The very low detection rate of norovirus most likely reflects the preventative measures used. However, this virus can spread rapidly from person to person in crowded, enclosed places such as the schools investigated in this study. To promote better public health and sanitary conditions, it is necessary to periodically monitor noroviruses that frequently cause epidemic food poisoning in South Korea.

Characteristics of enterotoxin distribution, hemolysis, lecithinase, and starch hydrolysis of Bacillus cereus isolated from infant formulas and ready-to-eat foods.

Bacillus cereus is a ubiquitous environmental microbe implicated as a main cause of food poisoning with various symptoms, depending on the strain type and the isolation source. In this study, the potential virulence factors and biochemical properties of B. cereus isolated from infant formulas and ready-to-eat (RTE) foods were analyzed and compared. A total of 347 B. cereus strains were isolated and identified from 687 infant food formulas and RTE food samples. All the isolates had one or more enterotoxin genes, and one-half of the strains had all 3 enterotoxin genes (hbl, nhe, and cytK) that are involved in food poisoning in humans. Here, all the 3 genes were detected in 50% of the B. cereus isolates from RTE foods and only 14% of the isolates were identified from infant formulas. The latter harbored low cytK and bceT, and very low hbl genes. Most B. cereus isolates possessed the hemolysis gene, but not the ces gene. The infant formula isolates showed stronger hemolysis activity than the other isolates. In addition, 26% of the total isolates showed low lecithinase activities and 10% showed high lecithinase activities. A greater number of isolates from the infant formula showed high lecithinase activity than those from the RTE foods. Approximately 83% of the isolates were positive and 17% were negative for starch hydrolysis. Over 90% of the RTE food isolates and only 35% of the infant formula isolates were positive for starch hydrolysis. However, all the strains possessed nhe, but their harboring patterns of hbl and cytK were significantly different. Most starch-hydrolyzing strains possessed hbl, but only 23% nonstarch-hydrolyzing isolates possessed this gene. Moreover, very low nonstarch hydrolyzing strains harbored cytK. Most nonstarch-hydrolyzing isolates showed high lecithinase and strong hemolysis activities, and very low hbl and cytK harboring. In summary, most infant formula isolates showed stronger hemolysis and higher lecithinase activities with lower frequency of harboring hbl and cytK and lower starch hydrolysis compared with RTE food isolates.

Complete Genome of Temperate Phage ENT39118 from Cronobacter sakazakii

ABSTRACT Cronobacter sakazakii infection is particularly harmful to infants, and putative virulence factors of prophage origin have been identified in C. sakazakii. In this study, the phage ENT39118 was isolated from wild-type C. sakazakii; it belongs to the family Siphoviridae. The genomic sequence of phage ENT39118 was composed of circular double-stranded DNA with a length of 39,012 bp. The sequence of ENT39118 showed weak sequence similarity to some reported regions of the prophage sequences in the C. sakazakii BAA-894 genome. To our knowledge, this is the first study of the genomic sequencing and annotation of this temperate phage, which was obtained from a C. sakazakii isolate from powdered infant formula.

Distribution of six exotoxin genes and production of L2-HBL and nheA proteins in six Bacillus cereus isolates from infant formula and produce

Six Bacillus cereus exotoxin genes were isolated from infant formula and produce. The lytic components of hemolysin BL and non-hemolytic enterotoxin were produced in culture media. Three strains isolated from produce harbored nheA, hblC, bceT, and cytK. Infant formula strains harbored nheA. Produce strains expressed hblC when grown in a synthetic medium and rehydrated infant formula. Infant formula strains expressed nheA when cultured in both a synthetic medium and infant formula. Produce strains expressed nheA in the synthetic medium, but not in infant formula. Expression of nheA is influenced by nutrients in the culture medium and to the strain.

Safety of using Escherichia coli bacteriophages as a sanitizing agent based on inflammatory responses in rats

Use of bacteriophages as sanitizing agents has received much attention. However, safety in humans is debatable. To determine inflammatory immune responses against bacteriophages, rats were treated with a 8 log plaque-forming cocktail of 5 bacteriophages for pathogenic Escherichia coli per day for 4 weeks. Food consumption, feeding efficiency, and body weight of rats treated with the cocktail were not different from controls. Phages were not detected in the sera of phage-fed rats with no changes in organ weights. Notable changes were not observed upon histopathological examination of the liver, kidney, and spleen. Pro-inflammatory cytokine mRNA expression, except COX-2 (2.4x increase), remained unaffected after treatment with the phage cocktail. No remarkable changes were observed for levels of 12 pro-inflammatory cytokines in sera. Inflammatory responses in rats orally treated with a phage cocktail were not observed. Bacteriophages for E. coli are indicated as immunologically safe in rats.

Comparative genomic analysis of novel bacteriophages infecting Vibrio parahaemolyticus isolated from western and southern coastal areas of Korea

Vibrio parahaemolyticus, a foodborne pathogen, has become resistant to antibiotics. Therefore, alternative bio-control agents such bacteriophage are urgently needed for its control. Six novel bacteriophages specific to V. parahaemolyticus (vB_VpaP_KF1~2, vB_VpaS_KF3~6) were characterized at the molecular level in this study. Genomic similarity analysis revealed that these six bacteriophages could be divided into two groups with different genomic features, phylogenetic grouping, and morphologies. Two groups of bacteriophages had their own genes with different mechanisms for infection, assembly, and metabolism. Our results could be used as a future reference to study phage genomics or apply phages in future bio-control studies.

Characteristics and growth inhibition of isolated bacteriophages for Enterococcus faecalis

Enterococcus faecalis has been used as a starter for fermented food and probiotics, but it can produce biogenic amine in foods and also cause infectious diseases in humans. The antibiotic resistance acquired by E. faecalis restricts antibiotic prescriptions in clinical settings. Bacteriophages EFP4 and EFP7 for E. faecalis, isolated from soil samples, impeded E. faecalis growth. Morphological analysis showed that bacteriophages EFP4 and EFP7 belonged to the Siphoviridae. Bacteriophages EFP4 and EFP7 were susceptible to temperatures above 70°C; however, stability was slightly reduced to 2–3 log PFU/mL after 30 min in 70% ethanol. Two bacteriophages did not suffer phage resistant in E. faecalis for 24 h. Therefore, bacteriophages EFP4 and EFP7, after more study, are candidates for use in biocontrol and controlled fermentation of E. faecalis through food applications.

Isolation of Enterococcus from powdered infant and follow-on formulas, and their antibiotic susceptibilites

Enterococcus spp. from powdered infant formula and follow-on formulas were identified and characterized for antibiotic susceptibility to confirm the enterococcal safety. Seventy-three Enterococcus from 96 powdered infant formulas and 26 strains from 33 follow-on formulas were isolated. More than 90% of Enterococcus in the foods were E. faecium. E. casseliflavus, and E. faecalis were also isolated. All Enterococcus were sensitive to ampicillin, penicillin, tetracycline, and vancomycin. However, 2 E. casseliflavus showed low resistance to vacomycin by minimum inhibitory concentration 4.0 μg/mL. Multiplex PCR indicated no existence of highly hazardous vancomycinresistant vanA and vanB genes. The isolates also showed the broad susceptibilities to erythromycin, ripampin, and streptomycin. Major strains of about 60% were intermediately and highly resistant to erythromycin and streptomycin, respectively. However, Enterococcus resistances to those antibiotics were not high and similar to those of Enterococcus from the other evaluated foods. Therefore, it appeared that powdered infant formula and follow-on formula might be safe to Enterococcus with regard to vancomycin and the antibiotics.