Attention is drawn to the confused epidemiological picture experienced in investigating outbreaks of salmonellosis due to multiple serotypes. Public Health Laboratories are often faced with the examination of specimens containing several serotypes and in this paper six techniques are described which have been found useful in dealing with this problem. The choice of technique depends on the time available for the examination and the epidemiological importance of obtaining an accurate result. A preference is expressed for an immuno-isolation technique, in which the bacteriologist is in technical control of the isolation of specific serotypes. The method is possibly open to objection on the grounds of serological induction of new serotypes, but we should regard this danger as slight in the majority of samples examined.
SUMMARYThree enrichment broths, selenite F, Muller-Kauffmann tetrathionate and Rappaport, were examined for their efficiency in salmonella isolation. The three media, prepared from single ingredients in the laboratory, were compared with their commercial equivalents. Laboratory-prepared media were more efficient for isolating salmonellas from sewage-polluted natural water samples. A pre-enrichment stage using buffered peptone water was employed throughout the investigation. The size of inoculum from the pre-enrichment medium was relevant to successful salmonella isolation. Inocula studied were 1 ml and one loopful (3 mm diameter loop). The smaller inoculum gave better results with Rappaport, the larger with selenite and tetrathionate. Using the optimal inocula, Rappaport was the most efficient enrichment broth of the three fluid media in this study.
SummaryIn three separate series, samples were examined for salmonellas by culture in selenite F broths incubated at 37 and 43° C. The samples used were:(1) Gauze swabs placed in sewage.(2) Gauze swabs placed in drains in abattoirs.(3) Sewage-polluted river water.In each series the higher temperature gave better results.The modification of tetrathionate broth for incubation at 43° C. and the adjustment of the incubation temperature to suit more inhibitory enrichment broths is discussed. The medium of Rappaport, Konforti & Navon (1956) is not suited to incubation at 43° C.We should like to acknowledge the help of Prof. Scott Thomson in the preparation of this paper, and the capable technical assistance of Mr T. R. Liddington and Mr John Morgan. We are also indebted to Dr H. Campbell, Senior Lecturer in Medical Statistics in the Welsh National School of Medicine, for his advice and to Mr M. C. Finniear, Deputy Public Analyst of the Glamorgan County Public Health Laboratory, for the calculation of molar tetrathionate in Rolfe's tetrathionate broth.
The ability of malachite green/magnesium chloride broth (Rappaport's medium) to isolate salmonellas from 25 ml quantities of sewage-polluted natural water was investigated. Samples were first pre-enriched in buffered peptone water and varying volumes of inoculum from the pre-enrichment culture were inoculated into Rappaport's broth. Inoculum ratios in the range 1:2000 to 1:10 were examined. The inoculum ratio denotes the ratio of the volume of inoculum to the volume of fluid medium into which it is introduced. Optimum results were obtained with the 1:2000 ratio, although the salmonella isolation rate was only slightly less with the 1:500 and 1:100 ratios. The 1:2000 inoculum ratio was obtained with a graduated loop holding approximately 0.005 ml of fluid. Use of a loop for inoculation has advantages in speed of performance and safety of manipulation.
1. Moore's gauze swabs have, in our hands, been shown to be a reliable instrument for the survey of salmonella infection in the environment of two food premises.2. A large bakery was demonstrated to be regularly contaminated with salmonellae. Thirty-one floor gully swabs out of 111 (27·9%) were positive for salmonellae. Little spread of infection to the general public was experienced.3. Staff infection with salmonellae was shown to occur in this bakery. Fifteen positive specimens of staff sewage out of 93 were obtained (16·1%). There was little evidence of prolonged contamination of the sewers with salmonellae. Staff infections were probably, therefore, of short duration. The staff probably became infected from contaminated goods in the bakehouse. Rat contamination of sewers was excluded by water trapping.4. It is not thought that regular examination of staff excreta would be a profitable means of discovering carriers or of preventing contamination of the products. The frequency with which such examinations would have to be performed to discover short-term excreters would be administratively impossible.5. Of 274 swabs from gullies in abattoirs, 111 were positive for salmonellac (40·5%). Twenty-one different serotypes were isolated. Seventeen of these serotypes are known to occur in animal feedingstuffs.6. Parallel examination of abattoir swabs and excreta from human infections for S. typhimurium, coupled with phage-typing of the strains, provided information of the geographically local nature of much sporadic illness due to this serotype. Of a total of 30 typable strains, 23 belonged to phage-types found in the abattoirs, or on local farms. Sporadic incidents were represented by 25 of these cultures, 18 of which corresponded in phage-type to those found in the abattoirs or in local farm animals. The phage-types of S. typhimurium isolated from the slaughter houses not infrequently corresponded in timing with the strains isolated from human infections.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.