Measurements were made of the rates at which continuously cultured Streptococcus sanguis NCTC 7868 cells accumulated on the inside surfaces of narrow glass capillaries from suspensions of the bacteria flowing down the capillaries at different velocities. Initially, the rate of accumulation of bacteria on the clean walls of the capillary was rapid. The deposition rate decreased with time, however, resulting in a saturation coverage of the glass surface which was considerably less than a monolayer. Multilayer coverage of the tube surface by bacteria was only achieved when fresh nutrient was pumped over deposited cells. This was attributed to cell growth. Although theoretical considerations of the deposition of small particles on to the walls of a tube suggest that the initial deposition rate should increase with flow rate, this was not the case with cells grown at dilution rates of 0.2 and 0.5 h-1. It is suggested that this can be explained by a polymer bridging mechanism of attachment.

We have shown that an alcoholic lotion containing ethyl lactate when applied topically to rat skin under occlusion became localized in the follicles and sebaceous glands. When applied to human facial skin the ethyl lactate was hydrolysed to ethanol and lactic acid, and thereby lowered the skin pH. Under such conditions the growth of recoverable skin bacteria, in particular the anaerobe Propionibacterium acnes, was inhibited, and the hydrolysis of sebum to free fatty acids by lipase derived from the bacteria was greatly impaired. These effects of ethyl lactate would account for its observed clinical efficacy in acne vulgaris.

The feasibility of using traditional growth media for biological testing of metal species, for example as potential microbiocides, was investigated. Significant interactions between both of the representative metal species studied, Cu2+ and FeEDTA, and the test media were found. It is recommended that the use of growth media for tests on metal species should be avoided.

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