Chryseobacterium mulctrae sp. nov., isolated from raw cow's milk.

A Gram-stain-negative bacterial strain, designated CA10T, was isolated from bovine raw milk sampled in Anseong, Republic of Korea. Cells were yellow-pigmented, aerobic, non-motile bacilli and grew optimally at 30 °C and pH 7.0 on tryptic soy agar without supplementation of NaCl. Phylogenetic analysis based on the 16S rRNA gene sequences revealed that strain CA10T belonged to the genus Chryseobacterium, family Flavobacteriaceae, and was most closely related to Chryseobacterium indoltheticum ATCC 27950T (98.75 % similarity). The average nucleotide identity and digital DNA-DNA hybridization values of strain CA10T were 94.4 and 56.9 %, respectively, relative to Chryseobacterium scophthalmum DSM 16779T, being lower than the cut-off values of 95-96 and 70 %, respectively. The predominant respiratory quinone was menaquinone-6; major polar lipid, phosphatidylethanolamine; major fatty acids, iso-C15 : 0, summed feature 9 (iso-C17 : 1ω9c and/or C16 : 0 10-methyl), summed feature 3 (iso-C15 : 0 2-OH and/or C16 : 1ω7c) and iso-C17 : 0 3-OH. The results of physiological, chemotaxonomic and biochemical analyses suggested that strain CA10T is a novel species of genus Chryseobacterium, for which the name Chryseobacterium mulctrae sp. nov. is proposed. The type strain is CA10T (=KACC 21234T=JCM 33443T).

Inhibition of Clostridium perfringens using Bacteriophages and Bacteriocin Producing Strains.

In this study, we isolated and characterized a bacteriocin-producing strain and two bacteriophages (P4, A3), showing antimicrobial effects against Clostridium perfringens, from chicken and swine feces by the spot-on-the lawn antagonism method. The selected strain was identified as Streptococcus hyointestinalis by 16S rRNA gene sequencing. The bacteriocin from the isolated strain exhibited strong inhibitory activity against four strains of C. perfringens and all the tested strains of Listeria monocytogenes, and the bacteriocin were highly heat- and pH-stable even at pH 2, pH 10 and 121℃ for 15 min. We also evaluated the combined effects of the isolated bacteriocin and phages. Combining the phage treatments and bacteriocin resulted in a synergetic effect compared with the phage or the bacteriocin alone. In addition, during the probiotic test, the bacteriocin-producing S. hyointestinalis B19 strain reduced the population of C. perfringens significantly. Treatment with S. hyointestinalis B19 and a cocktail of lytic bacteriophages eradicated the C. perfringens KCTC 3269T, completely. Consequently, the isolated bacteriocin and bacteriophages represent candidates for effective biocontrol of C. perfringens, and bacteriocin-producing S. hyointestinalis B19 is a potential probiotic candidate for use in domestic animals.

Characterization of the Biodiversity of the Spoilage Microbiota in Chicken Meat Using Next Generation Sequencing and Culture Dependent Approach.

This study investigated the psychrotrophic bacteria isolated from chicken meat to characterize their microbial composition during refrigerated storage. The bacterial community was identified by the Illumina MiSeq method based on bacterial DNA extracted from spoiled chicken meat. Molecular identification of the isolated psychrotrophic bacteria was carried out using 16S rDNA sequencing and their putrefactive potential was investigated by the growth at low temperature as well as their proteolytic activities in chicken meat. From the Illumina sequencing, a total of 187,671 reads were obtained from 12 chicken samples. Regardless of the type of chicken meat (i.e., whole meat and chicken breast) and storage temperatures (4°C and 10°C), Pseudomonas weihenstephanensis and Pseudomonas congelans were the most prominent bacterial species. Serratia spp. and Acinetobacter spp. were prominent in chicken breast and whole chicken meat, respectively. The 118 isolated strains of psychrotrophic bacteria comprised Pseudomonas spp. (58.48%), Serratia spp. (10.17%), and Morganella spp. (6.78%). All isolates grew well at 10°C and they induced different proteolytic activities depending on the species and strains. Parallel analysis of the next generation sequencing and culture dependent approach provides in-depth information on the biodiversity of the spoilage microbiota in chicken meat. Further study is needed to develop better preservation methods against these spoilage bacteria.

Isolation and Characterization of Listeria phages for Control of Growth of Listeria monocytogenes in Milk.

In this study, two Listeria bacteriophages, LMP1 and LMP7, were isolated from chicken feces as a means of biocontrol of L. monocytogenes. Both bacteriophages had a lytic effect on L. monocytogenes ATCC 7644, 15313, 19114, and 19115. Phages LMP1 and LMP7 were able to inhibit the growth of L. monocytogenes ATCC 7644 and 19114 in tryptic soy broth at 10°C and 30°C. Nevertheless, LMP1 was more effective than LMP7 at inhibiting L. monocytogenes ATCC 19114. On the contrary, LMP7 was more effective than LMP1 at inhibiting L. monocytogenes ATCC 7644. The morphology of LMP1 and LMP7 resembled that of members of the Siphoviridae family. The growth of L. monocytogenes ATCC 7644 was inhibited by both LMP1 and LMP7 in milk; however, the growth of L. monocytogenes ATCC 19114 was only inhibited by LMP1 at 30°C. The lytic activity of bacteriophages was also evaluated at 4°C in milk in order to investigate the potential use of these phages in refrigerated products. In conclusion, these two bacteriophages exhibit different host specificities and characteristics, suggesting that they can be used as a component of a phage cocktail to control L. monocytogenes in the food industry.