Ampicillin-dextrin agar medium for the enumeration of Aeromonas species in water by membrane filtration

Published selective media were evaluated for the isolation of Aeromonas spp. from environmental samples by membrane filtration. Satisfactory recoveries were obtained only with mA agar (Rippey & Cabelli) and dextrin-fuchsin-sulphite agar (Schubert), but neither was sufficiently selective. The positive aspects of these two media were combined in a new medium, ampicillin-dextrin agar. Recovery from pure cultures and environmental samples was optimal at an ampicillin concentration of 10 mg/l and incubation for 24 h at 30 degrees C under aerobic conditions, and specificity was high (i.e. confirmation rate usually greater than 90%, no false negative colonies encountered). The medium can also be used for isolation of Aeromonas spp. from sea water provided that the vibriostatic agent 0/129 is added at 50 mg/l.     

An evaluation of media for the membrane filtration enumeration of Aeromonas from drinking water

Two laboratory-prepared media (Ampicillin Dextrin Agar, ADA, and Xylose Ampicillin Agar, XAA) were compared with two commercially-available media (Ryan's Aeromonas Medium and Bile Salt-Irgasan-Brilliant Green Agar, BIBA) for the enumeration of Aeromonas spp. from drinking water. Ryan's medium and ADA were superior for both recovery of Aeromonas and selectivity, with 95+% of typical colonies from both media confirming as Aeromonas . Colony characteristics were more consistent on Ryan's medium.     

A note on a selective agar medium for the enumeration of Flavobacterium species in water

A selective nutrient agar medium containing kanamycin at 50 micrograms/ml was developed for the isolation and enumeration of yellow-pigmented colonies from the River Sowe, Coventry. Such organisms were shown to be members of the heterogeneous genus Flavobacterium. Typically, yellow pigmented colonies constituted less than 10% of the colonies on nutrient agar alone but up to 70% on nutrient agar plus kanamycin. This medium is a useful addition to the range of media available for the isolation and further ecological study of particular species of this important group of micro-organisms.     

A note on a selective agar medium for the enumeration of Flavobacterium species in water

A selective nutrient agar medium containing kanamycin at 50 μg/ml was developed for the isolation and enumeration of yellow-pigmented colonies from the River Sowe, Coventry. Such organisms were shown to be members of the heterogeneous genus Flavobacterium . Typically, yellow pigmented colonies constituted less than 10% of the colonies on nutrient agar alone but up to 70% on nutrient agar plus kanamycin. This medium is a useful addition to the range of media available for the isolation and further ecological study of particular species of this important group of micro-organisms.     

The preparation of ampicillin dextrin agar for the enumeration of Aeromonas in water

Introduction of ampicillin dextrin agar (ADA) has revealed problems in details of the preparation. The final pH of the medium varied substantially between different laboratories. Measuring temperature has a pronounced effect on the pH (0·7 units lower at 50°C than at 6°C). Addition of agar during medium preparation resulted in a fall in pH of 0·5 units. If poured plates were stored in the refrigerator, the pH was reduced by 0·1–0·4 units, in particular during the first day. Recovery of Aeromonas from pure cultures and naturally polluted samples was unaffected by variation in pH between 7·1 and 8·3 but colony differentiation was optimal at a higher pH. The use of ADA at a final pH of 7·8 ± 0·2 (at 25°C) is recommended. Different types of dextrin differed in respect of solubility, fermentability and colony differentiation. Optimal results were obtained with Difco 161 and Merck 3006.     

A note on a modified membrane-Bovis agar for the enumeration of Streptococcus bovis by membrane filtration

The effect of dilution and temperature on the antibacterial properties of potassium sorbate was determined. The time taken to kill a standard inoculum of Escherichia coli was increased considerably after either dilution of the preservative or lowering of the temperature. The value for the concentration exponent, eta, was approximately 3 and that for the temperature coefficient, Q10, was 2.3.     

Model studies on a membrane filtration method for the enumeration of coagulase-positive staphylococci in swimming-pool water using rabbit plasma-bovine fibrinogen agar

The recovery of Staphylococcus aureus from swimming-pool water by membrane filtration was studied in model experiments. On the nonselective medium tryptone soya agar (TSA) there was no difference in counts of noninjured S. aureus with all membrane filters tested and with pour plates. Chlorine-injured S. aureus was enumerated most efficiently on TSA by Gelman Tuffryn HT-450 and Sartorius SM 13806 filters. Tuffryn filters were also most productive when used in combination with the selective medium rabbit plasma - bovine fibrinogen agar (RPFA). Other filters, particularly Gelman GN-6 and Millipore HAWP, when used on RPFA were shown to have a synergistic inhibitory effect on both noninjured and chlorine-injured S. aureus. This effect was not found on Baird-Parker agar. Using Tuffryn filters, counts on RPFA were equal to those on TSA for noninjured S. aureus and 0.1-2.0 log units less for chlorine-injured S. aureus. Despite this, the possibility for reading the in situ coagulase reaction for individual colonies on RPFA is considered such an advantage of this medium that its general use for enumeration of S. aureus in swimming pools is recommended. Further studies should be carried out to allow better resuscitation.     

Comparative study of selective media for enumeration of Pseudomonas aeruginosa from water by membrane filtration

In the present study, mPA-D and mPA-E agar, modifications of mPA-C agar that reduce background fecal streptococci that interfere with the differentiation and enumeration of the Pseudomonas aeruginosa colonies grown in other mPA media, are proposed for use in analyzing natural water samples. In addition, the efficiencies of several culture media for the recovery of P. aeruginosa in water after membrane filtration and multiple-tube techniques are compared. The degree of selectivity, precision, efficiency, and sensitivity achieved with the proposed media exceeded that achieved by current methods. Furthermore, they yielded equal rates of accuracy and specificity. Incubation at 36 degrees C resulted in an improved recovery of stressed P. aeruginosa. In conclusion, we propose the use of mPA-D and mPA-E agar, both incubated at 36 degrees C for 24 to 48 h, for analyzing river water and seawater, respectively.     

Evaluation of two media for the membrane filtration enumeration of Clostridium perfringens from water

Two media (mCP medium and Tryptose Sulphite Cycloserine (TSC) agar) were evaluated for recovery of Clostridium perfringens in environmental and part-treated drinking water. For laboratory strains of Clostridium , mCP was more selective and specific for Cl. perfringens than TSC, but was markedly less efficient for the enumeration of both vegetative cells and spores. For samples of river water and part-treated drinking water, TSC recovered significantly greater numbers of Cl. perfringens than mCP. In contrast to previous reports, there was a significant number of false presumptive positive and negative isolates on mCP. TSC is a more suitable medium for the routine monitoring of water supplies for the presence of Cl. perfringens .     

A medium detecting β-glucuronidase for the simultaneous membrane filtration enumeration of Escherichia coli and coliforms from drinking water

A medium for the single membrane enumeration of Escherichia coli and coliforms from potable water was developed by the modification of the standard UK membrane filtration medium. The medium, membrane-Lactose Glucuronide Agar (m-LGA), employs a chromogenic substrate for the detection of β-glucuronidase activity and sodium pyruvate to enhance recovery of chlorine-stressed coliforms. Escherichia coli identification was significantly improved on m-LGA with 98.6% of presumptive isolates confirming. Recovery of coliforms from drinking water samples was also significantly improved.     

Comparative study of selective media for enumeration of Pseudomonas aeruginosa from water by membrane filtration.

In the present study, mPA-D and mPA-E agar, modifications of mPA-C agar that reduce background fecal streptococci that interfere with the differentiation and enumeration of the Pseudomonas aeruginosa colonies grown in other mPA media, are proposed for use in analyzing natural water samples. In addition, the efficiencies of several culture media for the recovery of P. aeruginosa in water after membrane filtration and multiple-tube techniques are compared. The degree of selectivity, precision, efficiency, and sensitivity achieved with the proposed media exceeded that achieved by current methods. Furthermore, they yielded equal rates of accuracy and specificity. Incubation at 36 degrees C resulted in an improved recovery of stressed P. aeruginosa. In conclusion, we propose the use of mPA-D and mPA-E agar, both incubated at 36 degrees C for 24 to 48 h, for analyzing river water and seawater, respectively.     

Modified Pseudomonas agar: new differential medium for the detection/enumeration of Pseudomonas aeruginosa in mineral water.

Pseudomonas aeruginosa has been implicated as a foodborne and waterborne pathogen and is now considered a primary infectious agent. In the present study, the survival of P. aeruginosa inoculated in mineral water was evaluated by drop counts on Pseudomonas Agar Base (PAB), PAB with CN supplement X107, PAB with cetrimide, PAB with nalidixic acid, and these media with added FeSO(4). Initial counts, before starvation, were the same in all media tested. Following this period, P. aeruginosa became sensitive to PAB with added cetrimide. The addition of FeSO(4) did not improve the recovery of stressed P. aeruginosa but gave colonies a typical dark brown colour being easily differentiated from other species that can grow at 42 degrees C. The modified Pseudomonas agar medium was also tested with several P. aeruginosa strains, other species of Pseudomonas, and other genera. Only P. aeruginosa strains (pyocyanin positive) produced the typical colonies. Our results demonstrate that Pseudomonas agar with ferrous sulphate, used for the differentiation of P. aeruginosa colonies, and nalidixic acid, used as an inhibitor of Gram-positive bacteria, might be a useful medium for the detection of injured P. aeruginosa in mineral water.     

A note on a membrane filtration method for the concentration and enumeration of bacteriophages from water

A membrane filtration method is described for the recovery and enumeration of bacteriophage from water. The method is conveniently used in the field and requires no complex or expensive equipment.     

A new membrane filtration medium for simultaneous detection and enumeration of Escherichia coli and total coliforms.

Recovery of total coliforms and Escherichia coli on a new membrane filtration (MF) medium was evaluated with 25 water samples from seven states. Testing of the new medium, m-ColiBlue24 broth, was conducted according to a U.S. Environmental Protection Agency protocol. For comparison, this same protocol was used to measure recovery of total coliforms and E. coli with two standard MF media, m-Endo broth and mTEC broth. E. coli recovery on the new medium was also compared to recovery on nutrient agar supplemented with 4-methylumbelliferyl-beta-D-glucuronide. Comparison of specificity, sensitivity, false positive error, undetected target error, and overall agreement indicated E. coli recovery on m-ColiBlue24 was superior to recovery on mTEC for all five parameters. Recovery of total coliforms on the new medium was comparable to recovery on m-Endo.     

Comparison of plate count agar and R2A medium for enumeration of heterotrophic bacteria in natural mineral water

In order to recover as many viable bacteria as possible from natural mineral water, in this study we have compared the counts obtained with the standard method (pour plate procedure with Plate Count Agar (PCA)) and counts with alternative test methods (PCA/spread plates, R2A medium/pour plates and R2A medium/spread plates). The results showed that counts with R2A medium/spread plates at 22°C and after a 7-day incubation period were more than 343% higher than those obtained with PCA/pour plate method. At 37°C and after a 3-day incubation period, the R2A pour plate technique gave counts about 368% greater than for the standard method. Moreover, while Pseudomonas, Comamonas and Acinetobacter species were isolated both from PCA and R2A medium, Flavobacterium spp. and Arthrobacter spp. were isolated only from R2A medium. For its higher productivity, R2A medium should be recommended for heterotrophic plate counts in natural mineral water.     

Improved medium for recovery and enumeration of Pseudomonas aeruginosa from water using membrane filters.

A modified mPA medium, designated mPA-C, was shown to recover Pseudomonas aeruginosa from a variety of water sources with results comparable to those with mPA-B and within the confidence limits of a most-probable-number technique. Enumeration of P. aeruginosa on mPA-C was possible after only 24 h of incubation at 41.5 degrees C, compared with 72 h of incubation required for mPA-B and 96 h of incubation for a presumptive most probable number.     

Improved medium for recovery and enumeration of Pseudomonas aeruginosa from water using membrane filters.

A modified mPA medium, designated mPA-C, was shown to recover Pseudomonas aeruginosa from a variety of water sources with results comparable to those with mPA-B and within the confidence limits of a most-probable-number technique. Enumeration of P. aeruginosa on mPA-C was possible after only 24 h of incubation at 41.5 degrees C, compared with 72 h of incubation required for mPA-B and 96 h of incubation for a presumptive most probable number.     

Bifidobacterium-selective isolation and enumeration from chicken caeca by a modified oligosaccharide antibiotic-selective agar medium

AIMS: To determine the efficacy and selectivity of an acidified, antibiotic-selective, oligosaccharide-containing media for enumerating Bifidobacterium spp. from chicken caeca samples. METHODS AND RESULTS: Transoligosaccharide propionate agar medium (TOS) modified by addition of mupirocin (50 microg ml-1) and glacial acetic acid (1%, v/v), did not inhibit the growth of bifidobacteria compared with the control media yet inhibited the growth of Lactobacillus acidophilus, Lactobacillus gallinarum, Lactobacillus helveticus and Streptococcus gordonii. CONCLUSIONS: Addition of mupirocin (50 microg ml-1) and glacial acetic acid (1%, v/v) to TOS (TOS-AM50), is an effective selective medium for isolation and enumeration of Bifidobacterium spp. from chicken caeca samples. SIGNIFICANCE AND IMPACT OF THE STUDY: The development of an intestinal bifidobacteria-selective media contributes to the study of probiotics and prebiotics in poultry and potentially other species.