Bactericidal Effect of Ultraviolet Rays on Microorganisms on Restaurant Glass-Ware

Abstract

52S~~l z n z n v y .The results secured in these investigations show that the initial nuniber of cells influelices survival o f niicroijrg-anisnis exposed to ultraviolet light. Dilute suspensions are destroyed more quickly than heavy ones. The order of decreasing-resistance for the species used was : Staphylococciis (xiireus, Escherichia coli ( Frank strain), Escherichin coli (American Type Collection No. 4338 1, and Serrntin W Z~I ' C~S C E I Z S .For the niold-spores studied the orderof decreasing resistance was : AsPcrgilliis ghiiciis, As/u?rgillus iziycr, Penicillium, and PviIucor.Cardboard strips, which had been inoculated by immersion in 3 suspension of niold-spores, were not as thoroughly sterilized as were the suspensions themselves, when exposed to ultraviolet light in Petri dishes. On many of the strips it was possible to determine that the colonies originated from the under side of the strip more frequently than from the upper side. This was interpreted as indicating that indirect irradiation is much less effective than direct irradiation.To study the bactericidal effect of irradiation with the Sterilamp on drinking glasses which had been used at soda fountains, it was necessary to select or devise a method of sampling the bacteriological contamination of the glasses. The multiple glass test proposed by the American Public Health Association' was used whenever a series o f glasses from a soda fountain was examined. Other procedures were followed including the method used by Speck and In addition, a supplementary method was devised which permitted examination of the entire inner surface of the glass as well as the rims and proved to be sinipler than that of Speck and Black. About 5 ml of a 25 ml water blank were poured into the drinking glass to be sampled and the entire inner surface of the glass was wetted and rubbed by means of a sterile cotton swab. The swab was then broken 1