Hot topic: Geographical distribution and strain diversity of Lactobacillus wasatchensis isolated from cheese with unwanted gas formation

Lactobacillus wasatchensis, an obligate heterofermentative nonstarter lactic acid bacteria (NSLAB) implicated in causing gas defects in aged cheeses, was originally isolated from an aged Cheddar produced in Logan, Utah. To determine the geographical distribution of this organism, we isolated slow-growing NSLAB from cheeses collected in different regions of the United States, Australia, New Zealand, and Ireland. Seven of the cheeses showed significant gas defects and 12 did not. Nonstarter lactic acid bacteria were isolated from these cheeses on de Man, Rogosa, and Sharpe medium supplemented with ribose, a preferred substrate for Lb. wasatchensis. Identification was confirmed with 16S rRNA gene sequencing and the API50CH (bioMérieux, Marcy l'Etoile, France) carbohydrate panel. Isolates were also compared with one another by using repetitive element sequence-based PCR (rep-PCR). Lactobacillus wasatchensis was isolated only from cheeses demonstrating late-gas development and was found in samples from 6 of the 7 cheeses. This supports laboratory evidence that this organism is a causative agent of late gas production defects. The rep-PCR analysis produced distinct genetic fingerprints for isolates from each cheese, indicating that Lb. wasatchensis is found in several regions across the United States and is not a local phenomenon.     

Selecting a heating system for FRP and plastic tanks and vessels

Tank heating system design considerations such as temperature differentials and limits, thermal resistance components, and power requirements are reviewed, and the merits of two heater styles are analyzed in terms of efficiency, safety, and economy of operation. The two heater styles considered are self-limiting and low-watt-density constant wattage. Both styles are available as panel or strip heaters. The benefits and drawbacks of each design are noted with respect to a particular design example, while neither style is preferred overall, it is noted that for safe operation the self-limiting heater should be used with a thermostatic control     

Recent advances in the production

Emphasis has been directed toward consistent and reproducible fiber characteristics, among them optical attenuation, dispersion, dimensional tolerances, numerical aperture and strength. Actual performance of an optical communication system will depend upon control and reproducibility of these properties to small tolerances fiber-to-fiber. Strength considerations also have received increased emphasis because of the need for long length, strong fibers. Average tensile strength in excess of 1.4 × 10⁴ N/mm² can be routinely obtained as measured by short gage length test samples. However, the useful strength of a fiber is determined by the rare flaw distribution for the fiber. Improvements in the long length strength value will be realized through process improvements and control, as well as new coatings to preserve the inherent fiber strength through subsequent processing operations. Continuous in-line screen tests insure minimum tensile strength values for all fibers. Typical properties and tolerances for commercially available step and graded index fibers are presented and discussed relative to the significances of the properties.