Selective Enrichment Media Research Articles

Laboratory studies on salmonella-contaminated cheese involved in a major outbreak of gastroenteritis.

A major outbreak of gastroenteritis was traced to Cheddar cheese contaminated with Salmonella typhimurium. There were no significant differences in pH values of the contaminated (mean pH 5.31) and non-contaminated (mean pH 5.39) cheese. The isolation rates of Salm. typhimurium were about the same when cheese samples were homogenized in lactose broth, lactose broth containing 1% Tween 80, or in aqueous 2% sodium citrate. Salmonella typhimurium was isolated regardless of preenrichment in lactose broth, but required selective enrichment in selenite cystine or tetrathionate brilliant green broth. There were no marked differences in the isolation rates obtained with different selective enrichment media, or after incubation at 36 degrees and 43 degrees C for 24 or 48 h. Contaminated samples of cheese failed to yield Salm. typhimurium consistently despite large and multiple samplings; samples from the interior of cheese blocks yielded positive results more frequently than the samples from the exterior. The number of Salm. typhimurium in factory sealed blocks as well as in samples obtained from the homes of known cases of salmonellosis was found to range from less than 3/100 g to 9/100 g of cheese. The infective dose of Salm. typhimurium in contaminated cheese was probably no greater than 10(4) organisms, and a rapid decline in numbers of Salm. typhimurium must have occurred subsequent to the outbreak.

Studies on a new selective enrichment medium for the isolation of beta-hemolytic streptococci

Studies on a new selective enrichment medium for the isolation of beta-hemolytic streptococci

Comparison of two methods for assessing the bacteriological condition of the water supply in slaughter houses

One hundred and five water samples of drinking water quality used in slaughter houses were examined according to The Netherlands' Standard N 3043 (1956) and by the new ‘Differential Hydrobacteriogramme’ (DHB) technique. The latter procedure allows for resuscitation of debilitated cells, uses one single selective enrichment medium and various isolation media and includes confirmation of isolates. Identification of isolates demonstrated that false positives as well as false negatives were frequently obtained by the N 3043 method. Rejection rate of samples by the N 3043 and DHB methods, respectively, was 63 vs. 72 for 81 samples taken from taps, and 4 vs. 10 for 24 samples drawn from wells and mains, Based on these results the DHB technique seems particularly suitable for the monitoring of re-used waters, because it provides more information and has a higher accuracy.

A new type of histamine-forming bacteria - III. Seasonal variations in numbers of psychrophilic and halophilic histamine-forming bacteria (N-group bacteria) in seawater and on marine fishes.

In the previous papers, the authors repored that a new type of histamine-forming bacteria (tentatively named N-group bacteria) was isolated from a common a mackerel, and that this group of bacteria were also found in Pacific saury and sardine, and gew well at 2.5 storage of thee fish samples. The present study was undertaken to obtain more information as to seasonal variation in the mumber of N-group bacteria in seawater and on the fisher skins and intesines. N-group bacteria werre found most abundantly in the sewater during the late autumn and winter, and it is considered that this group of bacteria strikingly decreased in number when the water temperature rose above 22°C. The majouity of the fresh fish samples had less than 100 organisms of organisms of N-group bacteria per cm2 of skin; and especially in the summer samples, they were below 10 orgainisms. The number of this group of bacteria increased at 2.5storage of the fish samples and eached to 107-108 level in a few samples. This group of bacteria were found in all of the intesine amples, where their number ranged from 103 to 108 per gram. A selective enrichment medium with PH 4.5 was devised for detection and isolation of N-group bacteria.

Effect of Various Media and Incubation Conditions on Recovery of Inoculated Salmonella from Poultry Feed

Samples of commercially pelleted poultry feed (30 g) were inoculated with nalidixic acid-resistant marker strains of Salmonella heidelberg or S. montevideo at levels of 1 (low), 20 (medium), or 40 (high) cells/g of feed, then 100 ml of either a nonselective preenrichment medium (lactose broth) or a selective enrichment medium [selenite cystine (SC) or tetrathionate brilliant green (TT) broth] was added and incubated at either 37 or 43 C for 24 or 48 hr in different experiments. Four selective plating media [MacConkey with 100 ppm nalidixic acid, brilliant green (BG) sulfa, modified BG, bismuth sulfite] were then streaked. MacConkey agar with nalidixic acid served as a control to which the other three plating media were compared. After 24 hr incubation at 37 C, colonies with characteristics typical of Salmonella were selected from the plates and examined biochemically and serologically to determine if they were the marker organism.In this study, preenrichment was counterproductive, because the marker organisms were recovered much more often with direct enrichment in SC or TT broth than with preenrichment in lactose broth. The TT broth produced 135 positive recoveries, whereas only 88 positive recoveries were made with SC. No differences were observed between 37 and 43 C or 24 and 48 hr incubation of the selective enrichment media. Overall efficiency of the plating media for Salmonella recovery from feed, when compared to the control (MacConkey), was BG sulfa, 65%; modified BG, 64%; and bismuth sulfite, 40%. The most effective enrichment broth-plating medium combination was TT-BG sulfa, yielding 86% positive recoveries when compared to the control.

Transport Media forcampylobacter Fetus Venerealis

Abstract Sir. — Cultural confirmation of venereal campylobacteriosis in cattle can only be achieved if samples arc cultured on the day of collection or a suitable transport medium is used. Clark et al.(3) have developed a selective enrichment medium for Campylobacter fetus venerealis which is also an effective transport medium (8). However, this transport medium is very cumbersome to prepare in that it requires a special gas mixture and large quantities of fresh bovine serum. This letter reports on the evaluation of Clark’s (8), cooked meat medium with antibiotics (CMMA), Weybridge (4), modified EMJH (5), Stuart’s (Oxford) and Cairy Blair (Oxoid) media, as transport media for C. fetus veneralis.

Sampling of Broiler Carcasses for Salmonella with Low Volume Water Rinse

The uneven distribution and low numbers of salmonella usually present on broiler carcasses make whole carcass rinsing the most sensitive sampling procedure for detecting this organism on the raw product. However, 270 ml of water or medium has been the smallest volume used in past published research. We found that 100 ml was adequate to recover Salmonella typhimurium, S. California, or S. montevideo from freshly processed broiler carcasses that had been inoculated with the organism at the rate of 50 cells/carcass. When carcasses were inoculated with 20 cells of S. heidelberg, then stored at −23 C for 3 or 6 months, sampling with 100 ml was adequate to detect the organism on all carcasses. The advantages of using the smallest volume of rinsing medium that will consistently lead to detection of salmonella present are: 1) less enrichment medium is required, 2) less incubator space is required, and 3) the concentration of cells in the selective enrichment medium at the end of incubation is greater; hence, the greater are the chances of salmonella detection when a drop is subsequently transferred to the selective plating medium.

Variability in gas production by Escherichia coli in enrichment media and its relationship to pH.

Variability in gas production in multiple subcultures of Escherichia coli was assessed in two selective enrichment media and in lactose peptone water. Considerable variability occurred with all media at 37 and 44 degrees C. Addition of buffer increased gas production and decreased variability. The relationships between pH, growth, and gas production were complex. In buffered media, viable counts increased by 269 x 10(6) to 382 x 10(6)/U of pH fall, whereas in unbuffered media, they increased by 9.45 x 10(6) to 30.37 x 10(6)/U of pH fall. In buffered and unbuffered media, pH fell as gas production rose. However, variability in gas production among individual subcultures was not associated with changes in pH.

RECOVERY OF Salmonella FROM MILK CHOCOLATE USING A CHEMICALLY DEFINED MEDIUM AND FIVE NONDEFINED BROTHS

ABSTRACTThe efficiency of various pre‐enrichment media for recovering Salmonella from milk chocolate was determined for the minimal, chemically defined M‐9 medium and for nonfat dry milk with brilliant green dye (NFDM‐BG), NFDM with crystal violet dye, lactose broth, trypticase soy broth and buffered peptone water (BPW). Pre‐enrichment in NFDM‐BG or BPW, incubated at 35°C, consistently gave the highest Salmonella MPNs, However, incubation of these pre‐enrichment media or the two selective enrichment media, selenite cystine and tetrathionate, at 43°C resulted in lower Salmonella recoveries. Use of the optimal enrichment and incubation conditions established for recovering Salmonella from milk chocolate resulted in more effective recovery of nonstressed cells than heat‐stressed cells from a variety of chocolate and chocolate‐substitute products.

Studies on Selective Enrichment Media for Isolation of Salmonella from Milk and Dairy Products

Studies on Selective Enrichment Media for Isolation of Salmonella from Milk and Dairy Products

Presence and Distribution of Salmonella Species in some Local Foods from Baghdad City, Iraq

A total of 353 local food samples were cultured for Salmonella species using mannitol broth and two selective enrichment media, tetrathionate brilliant green bile broth and selenite cystine broth. Fifteen Salmonella species and serotypes were isolated: Salmonella paratyphi B. Salmonella typhimurium, Salmonella 4,5,12:-:-. Salmonella muenchen, Salmonella senftenberg, Salmonella lille, Salmonella alachua, Salmonella 6,7:-:-. Salmonella anatum, Salmonella enteritidis, Salmonella havana, Salmonella eppendorf, Salmonella emek, Salmonella california, and Salmonella 1.3.19:-:-. Salmonella was recovered from 27% of food samples examined. The occurrence of some species was as high as 11% of the samples. S. lille and S. alachua were isolated and are reported for the first time in Iraq. Seventy food samples (19.8%) harbored one type of Salmonella. 11 (5.9%) harbored two types and four (1.1%) harbored three types. Isolation of Salmonella from foods is affected by types of enrichment media. Tetrathionate brilliant green bile broth was superior to selenite cystine for Salmonella recovery from most foods. Some species prefer certain enrichment media for growth and multiplication. Use of more than one type of selective medium increases the chance of isolation of more Salmonella species and serotypes.

Secondary selective enrichment of salmonellae from naturally contaminated specimens by using a selective motility system

A selective motility medium was used as a secondary selective enrichment medium to examine specimens naturally contaminated with salmonellae. The medium, incubated at 37 degrees C, was inoculated from either selenite brilliant green sulfa enrichment broth or Müller-Kauffman tetrathionate broth, both of which had been incubated at 42 degrees C. The use of the selective motility medium resulted in an increase in the number of positive specimens from 65 and 74% to 80 and 82%, when inoculated at 24 and 48 h, respectively, from tetrathionate broth. Tetrathionate broth, when used singly, was significantly better than selenite brilliant green sulfa broth, which detected 55% of positive specimens at both 24 and 48 h. The use of the selective motility medium of Harper and Shortridge (J. Hyg. 67: 181--186, 1969) for the further examination of specimens culturally negative on primary selective enrichment is advocated.

Method for the Detection of Injured Vibrio parahaemolyticus in Seafoods

The sensitivity of Vibrio parahaemolyticus cells to refrigeration and frozen storage and the development of a method for detecting injured and uninjured V. parahaemolyticus cells were studied. Cell suspensions in different kinds of seafood homogenates were either regrigerated (4 degrees C) or frozen (-20 degrees C), stored, and examined for cell survival during storage. V. parahaemolyticus cells were sensitive to both storage temperatures. Many cells died, and many survivors were sublethally injured. In general, refrigeration storage appeared to be more injurious than frozen storage. The initial recovery of the sublethally injured cells was highest in a nutritionally rich, nonselective liquid medium such as Trypticase soy broth, whereas maximum cell multiplication was observed in Trypticase soy broth containing 3% NaCl. The sublethally injured V. parahaemolyticus cells demonstrated sensitivity to the selective enrichment medium, glucose salt teepol broth. From these findings, a new method (designated as the "repair-detection" method) was developed for the isolation and enumeration of V. parahaemolyticus. Comparative studies between the recommended and the repair-detection methods showed that injured V. parahaemolyticus cells were present in commercial seafoods and that the repair-detection method was definitely more effective for the detection of total numbers of V. parahaemolyticus cells.

Reliability of Enrichment and Selective Media for the Estimation of Salmonella typhimurium

Selective media are normally used for the enumeration or the enrichment of salmonellae in foods. The advantages of enriching injured salmonellae in nonselective media is known. Results of this study indicate that in the nonselective cooked meat medium resuscitation can be achieved in 5-6 hours, before growth of salmonellae or other contaminating microorganisms has occurred. Thereafter, the salmonellae could be transferred to a selective enrichment medium. However, the reliability of the dehydrated selective enrichment media appeared to be further complicated by brand and lot differences.