Different strains of Listeria monocytogenes are well known to persist in individual food processing plants and to contaminate foods for many years; however, the specific genotypic and phenotypic mechanisms responsible for persistence of these unique strains remain largely unknown. Based on sequences in comK prophage junction fragments, different strains of epidemic clones (ECs), which included ECII, ECIII, and ECV, were identified and shown to be specific to individual meat and poultry processing plants. The comK prophage-containing strains showed significantly higher cell densities after incubation at 30°C for 48 h on meat and poultry food-conditioning films than did strains lacking the comK prophage (P < 0.05). Overall, the type of strain, the type of conditioning film, and the interaction between the two were all highly significant (P < 0.001). Recombination analysis indicated that the comK prophage junction fragments in these strains had evolved due to extensive recombination. Based on the results of the present study, we propose a novel model in which the concept of defective comK prophage was replaced with the rapid adaptation island (RAI). Genes within the RAI were recharacterized as "adaptons," as these genes may allow L. monocytogenes to rapidly adapt to different food processing facilities and foods. If confirmed, the model presented would help explain Listeria's rapid niche adaptation, biofilm formation, persistence, and subsequent transmission to foods. Also, comK prophage junction fragment sequences may permit accurate tracking of persistent strains back to and within individual food processing operations and thus allow the design of more effective intervention strategies to reduce contamination and enhance food safety.Listeria monocytogenes is a unique food-borne pathogen that causes listeriosis, which ranges from febrile gastroenteritis to more severe life-threatening invasive diseases, especially for immunocompromised individuals (94). It is widely distributed in many wild and domestic animals and various natural environments and is resistant to a wide variety of environmental stresses (33). L. monocytogenes is considered a model organism for the study of host-pathogen interactions, especially as a model for intracellular pathogens of humans (47). However, L. monocytogenes may also be an excellent model for pathogenenvironment interactions, because it is well known to cycle between being a pathogen in many wild and domestic animals and a saprophyte in diverse environments, including those found in various types of food processing facilities (41). However, while much is known about the pathogenic lifestyle of L. monocytogenes, much less is known about its saprophytic lifestyle, including the genetic and phenotypic factors affecting its colonization and persistence in food processing and retail environments and subsequent transmission to ready-to-eat (RTE) foods. This has resulted in numerous costly recalls, disease cases, and outbreaks, which are often associated with high mortality (94). As a res...

Human listeriosis outbreaks in Canada have been predominantly caused by serotype 1/2a isolates with highly similar pulsedfield gel electrophoresis (PFGE) patterns. Multilocus sequence typing (MLST) and multi-virulence-locus sequence typing (MV-LST) each identified a diverse population of Listeria monocytogenes isolates, and within that, both methods had congruent subtypes that substantiated a predominant clone (clonal complex 8; virulence type 59; proposed epidemic clone 5 [ECV]) that has been causing human illness across Canada for more than 2 decades.

We identified a novel serotype 1/2a outbreak strain and 2 novel epidemic clones of Listeria monocytogenes while investigating a foodborne outbreak of listeriosis associated with consumption of cantaloupe during 2011 in the United States. Comparative analyses of strains worldwide are essential to identification of novel outbreak strains and epidemic clones.

Listeria monocytogenes is a foodborne pathogen of significant concern to the agricultural and food processing industry because of its ability to grow and persist in cool and moist environments and its association with listeriosis, a disease with a very high mortality rate. Although there have been no listeriosis outbreaks attributed to fresh mushrooms in the United States, retail surveys and recalls are evidence that L. monocytogenes contamination of mushrooms (Agaricus bisporus) can occur. The objective of this study was to determine the prevalence of Listeria spp., including L. monocytogenes, in a small-scale mushroom production facility on the campus of the Pennsylvania State University in the United States. Of 184 samples taken from five production zones within the facility, 29 (15.8%) samples were positive for Listeria spp. Among the Listeria spp. isolates, L. innocua was most prevalent (10.3%) followed by L. welshimeri (3.3%), L. monocytogenes (1.6%), and L. grayi (0.5%). L. monocytogenes was recovered only from the phase I raw material composting area. Isolates of L. monocytogenes were confirmed and serotyped by multiplex PCR. The epidemiological relatedness of the three L. monocytogenes isolates to those serotypes or lineages frequently encountered in listeriosis infections was determined by multi-virulence-locus sequence typing using six virulence genes, namely, prfA, inlB, inlC, dal, clpP, and lisR. The phylogenetic positions of the three isolates in the dendrogram prepared with data from other isolates of L. monocytogenes showed that all isolates were grouped with serotype 4a, lineage IIIA. To date, this serotype has rarely been reported in foodborne disease outbreaks.

Isolate W14(T) recovered from a household tooth brush holder was found to be gram-negative, a facultative anaerobic, non-motile, capsulated, and a non-endospore-forming straight rod. Based on phylogenetic analysis with 16S rRNA gene sequence, isolate W14(T) was affiliated to the genus Klebsiella. The closest phylogenetic relative was K. oxytoca with 99 % similarity in the 16S rRNA gene sequence. The major whole-cell fatty acids were C(16:0) (31.23 %), C(18:1ω6c)/C(18:1ω7c) (21.10 %), and C(16:1ω7c)/C(16:1ω6c) (19.05 %). The sequence similarities of isolate W14(T) based on rpoB, gyrA, and gyrB were 97, 98, and 98 % with K. oxytoca, and 97, 93, and 90 % with K. mobilis (=Enterobacter aerogenes), respectively. The ribotyping pattern showed a 0.46 similarity with K. oxytoca ATCC 13182(T) and 0.24 with K. mobilis ATCC 13048(T). The DNA G+C content of isolate W14(T) was 54.6 mol%. The DNA-DNA relatedness was 55.7 % with K. oxytoca ATCC 13182(T). Using the identification technology of MALDI-TOF mass spectrometry, the top matches for this isolate were K. oxytoca ATCC 13182(T) (Match Factor Score 1.998) and K. mobilis (Score 1.797). On the basis of phenotypic, biochemical, chemotaxonomic, and molecular studies, isolate W14(T) could be differentiated from other members of the genus Klebsiella including K. mobilis. Therefore, it is proposed that isolate W14(T) (=ATCC BAA-2403(T)=DSM 25444(T)) should be classified as the type strain of a novel species of the genus Klebsiella, K. michiganensis sp. nov.

We provide molecular phylogenetic evidence that the obscure genera Palmophyllum Kütz. and Verdigellas D. L. Ballant. et J. N. Norris form a distinct and early diverging lineage of green algae. These palmelloid seaweeds generally persist in deep waters, where grazing pressure and competition for space are reduced. Their distinctness warrants recognition as a new order, the Palmophyllales. Although phylogenetic analyses of both the 18S rRNA gene and two chloroplast genes (atpB and rbcL) are in agreement with a deep-branching Palmophyllales, the genes are in conflict about its exact phylogenetic placement. Analysis of the nuclear ribosomal DNA allies the Palmophyllales with the prasinophyte genera Prasinococcus and Prasinoderma (Prasinococcales), while the plastid gene phylogeny placed Palmophyllum and Verdigellas as sister clade to all other Chlorophyta.

No abstract

Numerous isolates of the green halophile Dunaliella were studied as part of a survey of microbial diversity at the Great Salt Plains (GSP) in Oklahoma, USA. The GSP is a large (∼65 km2) salt flat with extreme temporal and spatial fluctuations in salinity and temperature. Although the flagellate halophile Dunaliella is common worldwide, nearly all cultured isolates are from saline habitats that are primarily aquatic rather than primarily terrestrial. The diverse GSP Dunaliella strains exhibit three morphotypes: a predominantly motile form, a motile form with a prominent palmelloid phase (nonmotile, mucilage rich), and a palmelloid form with a weakly motile phase. All had broad salinity optima well below typical in situ salinities at the GSP, and two of the palmelloid isolates grew as well in freshwater as in highly saline media. Molecular phylogenetic and evolutionary analyses revealed that Dunaliella from the GSP (and two similar habitats in the Great Basin, USA) are allied with D. viridis Teodor. but possess phylogenetic diversity in excess of existing global isolates from aquatic habitats. In addition, isolates from primarily terrestrial habitats exhibit statistically higher rates of nucleotide substitution than the phylogenetically homogeneous set of primarily aquatic Dunaliella taxa. We hypothesize that dynamically extreme saline soil habitats may select for different and more diverse Dunaliella lineages than more stable saline aquatic habitats. We also propose Dunaliella as a tractable microbial model for in situ testing of evolutionary and phylogeographic hypotheses.