The survival benefit of short-chain organic acids and the inducible arginine and lysine decarboxylase genes for Escherichia coli.

The short-chain organic acids (SCOAs), acetic and propionic acids, are used widely as food preservatives. The production of these two acids plus butyric acid in the colon by anaerobes serves as a mechanism for controlling the numbers of enterobacteria (which can be pathogens) in this organ. It has been found in this study that the acid tolerance of cells initially grown at near neutral pH (6.5) to a lethal pH of 3.5 is enhanced by their exposure to 0.1% propionate or butyrate. The data also indicate that the inducible arginine and lysine decarboxylases are important for the survival of Escherichia coli exposed to a combination of mildly acidic pH (5.5) and 0.5% butyrate. This study suggests that the presence of SCOAs could trigger an adaptive survival response which may be important in the survival of food-borne pathogens.

An evaluation of preservative adsorption onto nylon membrane filters.

Pharmaceutical drug products often contain antimicrobial agents as a preservative in their formulation. These excipients are required to destroy or impede the growth of microorganisms that inadvertently enter the product during manufacturing. Unfortunately, these preservatives may also interfere with microbiological assays used to determine product sterility or bioburden levels. The extent of interference by these preservatives can be quite significant, but varies depending on the method used. The most frequently used method for testing parenteral drug products is the membrane filtration technique. Membrane filters are composed of a wide variety of materials such as cellulose, polycarbonate, acrylic polypropylene, Teflon, and nylon. This study evaluated the adsorption characteristics that nylon filters, obtained from five different manufacturers, had on the filtration of solutions of four different antimicrobial compounds (phenol, methylparaben, propylparaben, and benzalkonium chloride). The adsorption properties were determined using both HPLC and microbiological assay techniques. The data revealed that there was a wide range in the amounts of antimicrobial agent (2.3 to 94.1%) bound to the membrane filters when direct product filtration was used without a subsequent rinse step. However, when a rinse step is included, only propylparaben showed any significant "true" adsorption (less than 1 to 33.3%), but showed only marginal bacterial inhibition. Interestingly, the microbiological assays indicated that with a saline rinse step, only benzalkonium chloride was lethal for the two challenge organisms even though the percent adsorbed as measured by HPLC was below 1%. This discrepancy is significant because it demonstrates the analytical limitation when using HPLC to detect minimal concentrations of benzalkonium chloride that may be deleterious to microorganisms.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of refrigeration and mixing on detection of endotoxin in parenteral drugs using the Limulus Amebocyte Lysate (LAL) test.

Prior to testing for the presence of bacterial endotoxin, parenteral products are handled and stored in a variety of ways. Two incidents, detected by the U.S. Food and Drug Administration, revealed that differences in product handling and storage may have played a role in causing analytical discrepancies in the testing of identical samples. The testing procedure was the USP Bacterial Endotoxin test using Limulus Amebocyte Lysate (LAL) reagent. Consequently, an evaluation was made at the two principal factors that contributed to the suspected analytical anomaly. The factors were sample storage and the degree of agitation prior to sample analysis. Additional variables such as bacterial growth medium and adsorption potential of endotoxin by rubber stoppers were also evaluated. It was found that neither the medium employed to grow the E. coli endotoxin nor the storage temperature of the spiked solutions were problematic. However, it was shown that 20-40% of the spiked endotoxin was lost due to non-agitation of solution in vials in which the solution was in contact with the rubber stoppers. A suggested remedy for this problem is to store intact product containers in an upright position and to establish a uniform mixing procedure prior to endotoxin assay.

Survey of infant foods for Clostridium botulinum spores.

A total of 236 samples of infant foods, including honey, dry cereal, nonfat dry milk, evaporated milk, canned formula, and canned baby food, were collected in the New York City area and tested for the presence of Clostridium botulinum spores. Methods for recovery of spores were validated using foods spiked with 4 spores/mL or g. None of the products contained C. botulinum spores, indicating that their incidence in these commercial foods is not widespread. This limited study did not identify any food types that could be suspected of being involved in the transmission of infant botulism.

Problems encountered with the capillary tube immunodiffusion method for detection of botulinal toxin.

By using antitoxin specific for the neurotoxin molecule, the capillary tube immunodiffusion method did not detect low levels of crystalline toxin. Reactions described earlier with crude toxin and less specific antitoxin were probably due to nontoxigenic botulinal antigens.

Development of culture vessel for sterility testing of bandages and other medical devices.

A cylindrical glass culture vessel equipped with a vented nylon closure was developed and evaluated for sterility testing. The sterility testing cylinder (STC), made in 2 sizes, accommodates 250 or 400 mL culture broth. A tight-fitting, skirted nylon cap protects the upper part of the cylinder, and a membrane filter in a recessed opening allows venting during autoclaving and ensures sterility during removal and replacement of the cap. The configuration of the vessel in terms of the opening size and ratio of the horizontal to vertical cross section provides depths desirable for testing many shapes of medical devices, including elongated and narrow ones, without excessive waste of medium. They are easy to charge with medium, and to autoclave, store, inoculate, and observe for growth.