Microbiological characterisation of southern African medicinal and cosmetic clays.

The effects of traditionally used medicinal and cosmetic clays in southern Africa on selected microorganisms were studied using microbiological media. The clay pH, microchemical composition, kind of associated microorganisms and antimicrobial activity of clays against test microorganisms were determined. The clays contained varying numbers of microorganisms which ranged from 0 up to 105 CFU/g. Clay pH ranged from 2.3-8.9. Neither Escherichia coli, nor other faecal coliforms were detected. Clays of pH value of <4 displayed antimicrobial activities. Clays which were active against test microorganisms had Na(2)O, Al(2)O(3), SiO(2), SO(3), CuO or Cl(2)O as major components. Microbial activity of clays was attributed mainly to low pH but cations such as Cu, Al, S or Cl and various anions might have contributed to the microbicidal effects. No antimicrobial activity was established for many of the clays commonly used in the treatment of common ailments of microbial origin.

Low pressure mode combined with OsO4 vapor fixation and sputter-coating for the preservation of delicate aerial hyphae and conidia in the ESEM.

The newer generation of environmental scanning electron microscopes (ESEMs) allows samples to be viewed under a range of different vacuum conditions. No specific sample preparation protocols are required with the ESEMs, as fresh, unfixed samples are used and discarded later. We have worked out a method that preserves aerial hyphae on biltong that closely resemble fresh specimens and may be stored for viewing at a later date. Another advantage is that fixed samples are more resilient to the variable vacuum encountered in the ESEM. When biltong samples with fungal growth were first studied, we observed that vacuum-related artifacts were induced unless vacuum conditions and changes in pressure were carefully controlled. Damage readily occured in conidia and its delicate hyphae. Fresh, unfixed samples are very vulnerable to these artifacts. In addition, biltong proved to be a problematic study sample because of its high salt content, its hygroscopic nature as well as being laden with spices. To eliminate these artifacts, the preservation of specimens by OsO4 vapor fixation combined with a special sputter-coating technique is described. Previous studies confirmed that OsO4 vapor fixation is superior to traditional immersion fixation methods for the examination of hyphae and conidia of various fungi in a conventional SEM. However, both preparation methods induce sample shrinkage. We observed that OsO4 vapor fixation followed by Au coating under strictly controlled vacuum conditions induced fewer artifacts and gave the best images with minimum distortion in low pressure (LP) mode. The proposed method allows samples to be viewed both in ESEM and LP mode. There are however some disadvantages inherent to ESEM mode. Even when viewing fixed, coated samples, care should be taken to maintain a pressure of not lower than 0.2 Torr in the specimen chamber. It is critical that different samples have the same vacuum exposure history, as shrinkage and collapse were found to be directly related to the lowest pressure the samples were subjected to, both in the sputter coater chamber and in the electron microscope specimen chamber.

Presence of Bacillus cereus in street foods in Gaborone, Botswana.

The purpose of this study was to evaluate the microbiological safety and quality of street foods sold in Gaborone, Botswana. A total of 148 point-of-sale composite street food samples were bought and analyzed between June 2001 and May 2002. The analysis focused on the level of contamination of various street foods with Bacillus cereus. The B. cereus (vegetative and spores), total spore, and total viable counts were determined on all the samples. Also B. cereus isolates from 444 individual point-of-sale food samples were characterized with respect to their biochemical profiles and enterotoxigenic properties. The B. cereus contamination rate for point-of-sale foods was 65%. The B. cereus counts ranged from not detectable to levels as high as 9.1 log CFU/g. Despite the high rate of contamination of some samples, generally, most samples had B. cereus counts of less than 4 log CFU/g; hence, they were of acceptable microbiological quality. Bacillus diarrheal enterotoxin was detected from 52 isolates from individual portions of meals using the B. cereus enterotoxin reversed passive latex agglutination kit. Results of the assay revealed that 59.6% of the B. cereus isolates were enterotoxigenic. Most of the enterotoxigenic isolates were obtained from vegetable samples.

The Microbiology of Phane, an Edible Caterpillar of the Emperor Moth, Imbrasia belina.

The larvae of Imbrasia belina (Westwood) are cooked and sun dried to make a product known as phane, which is consumed as a delicacy. A study was conducted to determine the sanitary quality of phane and the kinds of microorganisms associated with it. It also looked into the potential for the existence of health risk associated with its consumption. Laboratory- and field-processed phane and that from open markets were subjected to microbiological analyses. The total microbial population for the larvae was in the range of 3 × 105 to 2 × 107 CFU/g. Species belonging to seven genera of bacteria and five genera of fungi were isolated from the larvae. About 50% of the identified bacteria were gram-positive, yet their combined population was much lower than that of the gram-negative bacteria. Cooking (89 to 93°C) under both sets of conditions (laboratory and field) reduced the microbial population to less than 9 × 103 CFU/g. The survivors were mostly sporeformers. Laboratory-processed phane was contaminated during drying, but none of the isolates were coliforms and the population increment was marginal. Field-processed phane, on the other hand, had a population of 4 × 104 to 1 ×108 CFU/g after 24 h of drying. The high moisture content of phane (55%) and a high degree of contamination from the soil and air appeared to have contributed to the increased population. Aspergilli including A. flavus and phycomycetes were frequently isolated from the samples. Coliforms were present in 30% and 50% of the phane processed in the field and in market phane, respectively. Escherichia coli and Klebsiella pneumoniae were found in 33% and 21%, respectively, of samples acquired from the market. The presence of K. pneumoniae . E. coli , a toxin-producing sporeformer ( Bacillus cereus ), and mycotoxin-producing fungi ( A. flavus , Penicillium sp., and Fusarium sp.) all point to the possible existence of health risks associated with its consumption.