Michael Pendleton

Understanding E. coli internalization in lettuce leaves for optimization of irradiation treatment

Irradiation penetrates food tissues and effectively reduces the number of food microorganisms in fresh produce, but the efficacy of the process against internalized bacteria is unknown. The objective of this study was to understand the mechanisms of pathogen colonization of plants relative to lettuce leaf structures so that radiation treatment of fresh leafy vegetables can be optimized. Leaves of iceberg, Boston, green leaf, and red leaf lettuces were cut into pieces, submerged in a cocktail mixture of two isolates of Escherichia coli (Rifampicin resistant), and subjected to a vacuum perfusion process to force the bacterial cells into the intercellular spaces in the leaves. Sixty bags containing 20g of lettuce each were tested. The inoculated leaves were gamma irradiated (Lanthanum-140, 0.16kGy/h) at 0.25-1.0-kGy (surface dose values), with increments of 0.25kGy at 15 degrees C. Microbial analysis was performed right after irradiation, including non-irradiated leaf pieces (controls). A dose uniformity ratio (max/min dose) of 2.8 was set to confirm the effect of non-uniform dose distribution. Calculated D(10)-values varied between 48 and 62% based on the dose distribution from the entrance dose. However, despite the subtle differences in composition and structure among the four lettuce varieties, the D(10)-values were not significantly different. Irradiation up to 1.0-kGy resulted in 3-4-log reduction of internalized E. coli on the lettuce leaves. The SEM images suggest that the contamination sites of pathogens in leafy vegetables are mainly localized on crevices and into the stomata. This study shows that irradiation effectively reduces viable E. coli cells internalized in lettuce, and decontamination is not influenced by lettuce variety. Ionizing irradiation effectively reduced the population of internalized pathogen in a dose-dependent manner and could be used as an effective killing step to mitigate the risk of foodborne disease outbreaks.

Pollen as atmospheric cloud condensation nuclei

Anemophilous (wind-dispersed) pollen grains are emitted in large quantities by vegetation in the midlatitudes for reproduction. Pollen grains are coarse particles (5–150 µm) that can rupture when wet to form submicron subpollen particles (SPP) that may have a climatic role. Laboratory CCN experiments of six fresh pollen samples show that SPP activate as CCN at a range of sizes, requiring supersaturations from 0.81 (± 0.07)% for 50 nm particles, 0.26 (± 0.03)% for 100 nm particles, and 0.12 (± 0.00)% for 200 nm particles. Compositional analyses indicate that SPP contain carbohydrates and proteins. The SPP contribution to global CCN is uncertain but could be important depending on pollen concentrations outside the surface layer and the number of SPP generated from a single pollen grain. The production of hygroscopic SPP from pollen represents a novel, biologically driven cloud formation pathway that may influence cloud optical properties and lifetimes, thereby influencing climate.

Descriptions of melissopalynological methods involving centrifugation should include data for calculating Relative Centrifugal Force (RCF) or should express data in units of RCF or gravities (g)

Techniques of pollen recovery involving centrifugation of honey pollen (melissopalynology) described in certain publications are difficult to 1) reproduce and 2) compare to other melissopalynological methods because dimensions of the centrifuge rotor were not described. Centrifugation data should be stated either in units of Relative Centrifugal Force (RCF) or gravities (g), or the data should be stated so RCF can be calculated using revolutions per minute (RPM) and the dimensions of the centrifuge rotor.

Comparison of Morphology of Sorghum Grain to Resistance to Maize Weevil Sitophilus zeamais

The maize weevil, Sitophilus zeamais Motschulsky, is one of most damaging insect pests of stored grain, including sorghum, Sorghum bicolor (L.) Moench [1]. Maize weevils infest kernels in the field, deposit eggs in stored kernels, and the larva feeds inside and damages the kernel. While the use of sorghum resistant to weevils is an alternative to insecticide, resistance to maize weevils in different sorghum genotypes has not been evaluated for more than 20 years. The first goal of this research was to evaluate the resistance of 20 genotypes of stored sorghum grain to maize weevil. The second goal was to examine the relationship between resistance to weevils and the morphology of the seed coat observed using light microscopy (LM) and scanning electron microscopy (SEM).

Scanning Electron Microscope Aided Wood Identification of a Bronze Age Wooden Diptych

A broken wooden diptych was found in 1986 on the 14th century B.C. Ulu Burun, Turkey, shipwreck, with only minute fragments available for anatomical study using scanning electron microscopy. Previously, the earliest known diptychs, considered the oldest books in existence, had been found at Assyrian Nimrud and were constructed of walnut. Using observed features from the wood fragments a computerised wood identification program generated Buxus as a probable candidate. Boxwood (Buxus) is frequently mentioned in historical references, including Assyrian texts, as a wood used for small, durable objects. Comparison of the diptych wood features with those of Buxus sempervirens convinces us that the diptych was constructed from boxwood (Buxus sp.).

Detecting Iron-based Pigments on Ruthenium-coated Archaeological Pottery by SEM-EDS and by Micro-XRF-SEM

1 Microscopy and Imaging Center, Interdisciplinary Life Sciences Building, Mail Stop 2257, Texas A&M University, College Station, TX 77843-2257. 2 American Section, University Museum, University of Pennsylvania, Philadelphia, PA 19104. 3 Microscopy Consulting Technologist, P.O. Box 6124, Thomasville, GA 31758. 4 Department of Agricultural Sciences, West Texas A&M University, Box 60998, Canyon, TX 79016-0001.

Ship Components, Cargo, or Contamination: Determining the Origin of Wood Fragments Recovered from an Underwater Shipwreck Site

The characteristics of two wood samples (labeled A and B) recovered in August 1991 from an underwater shipwreck site (fig. 1) near the town of Dodos Greece are described using images obtained by scanning electron microscopy (SEM). This underwater site was located in the Bay of Skindos in the Aegean Sea and was dated to 2200 B.C. The wood samples were analyzed to determine if they were associated with the wreck structure, or the wreck cargo, or were modern debris brought into the site by ocean current activity.

Analysis of Minute and Priceless Artifacts Using Scanning Electron Microscopy

Analyzing minute remains, delicate objects, or components of priceless artifacts is often difficult. An example of the difficulties encountered in analyzing these types of artifacts is seen in the wood analysis of a wooden writing tablet (diptych), recovered from a 14th century B.C. submerged shipwreck. Because only minute fragments of the diptych were available for analysis, we utilized a scanning electron microscope (SEM) to obtain high resolution images of the fragments at high magnifications. The similarity of the diptych wood to a reference sample of Boxwood (Buxus sempervirens) suggested it is the probable wood used for the diptychs construction. This study presents an example of why SEM is occasionally necessary as a tool in archaeology.