A membrane filter technique for testing disinfectants.

Abstract

SYNOPSIS A membrane filter was used for assessing the surface disinfecting activity of phenolic disinfectants and a chloroxylenol disinfectant. The influence of the type of organism, inoculum size, and hardness of water was investigated. Pseudomonas aeruginosa was chosen for the standardized test. Disinfectant solutions were prepared in water of 300 ppm hardness and applied for two and a half minutes and eight minutes to the bacteria deposited from filtration of 1 ml of a suspension containing 106 bacteria. The membrane filter test has certain advantages over many tests, eg, all organisms surviving after treatment can be counted and residual disinfectant is easily removed.Membrane filtration has been used with considerable success in many branches of microbiology. The technique has been used for studying the activity of antimicrobial drugs (Meers and Churcher, 1974) and also for testing disinfectants (Prickett and Rawal, 1972). Its use offers more flexibility than most other suspension or surface tests, residual disinfectant is more readily removed, and it allows sampling of large volumes of mixtures of disinfectant and organisms.In this study, a test is described using membrane filters for assessing the activity of phenolic disinfectants and a chloroxylenol disinfectant. An attempt has been made to evaluate the influence of various factors, eg, time of exposure to the disinfectant, inoculum size, and hardness of water, on the performance of several disinfectants. Materials and Methods ORGANISMSThe following organisms were used in the experiments:-Staphylococcus aureus (NCTC 9717), Escherichia coli (NCTC 8196), Proteus vulgaris (NCTC 4635), Pseudomonas aeruginosa (NCTC 6749), and Klebsiella aerogenes (JP 1970

Microbiological Applications of the Inactivation of Antibiotics and Other Antimicrobial Agents

“…All three methods in Section 2 have been used to achieve this end, and additional practical details may be found in papers by Sykes (1965), Grossgebauer (1970) and Croshaw (1977). It must be stressed that in the membrane filtration technique the antimicrobial agent is washed out from the membrane before it is placed on the surface of an appropriate agar medium for enumerating survivors (Sykes 1970; Prickett & Rawal 1972;Meers 8c Churcher 1974; Prince et al 1975; see also Chiori et al 1965). (b) In the evaluation of antibiotics.…”

“…Although membrane filters may be employed for viable counting purposes, e.g. in disinfectant evaluation (Prince et al 1975) it is unlikely that they will find widespread use in the assessment of antibiotic activity.…”

“…1965), where it is essential that an appropriate antidote be used to wash the cells in situ or be incorporated into the agar medium on which the membrane filter is to be placed. Phenolic disinfectants are readily washed away by membrane filtration as no evidence of residual disinfectant activity has been found (Prince et al 1975).…”

A more accurate method for measurement of tuberculocidal activity of disinfectants

“…Based on the AOAC use dilution method, the current procedure has gone unchanged and has not kept pace with developments in technology. Several proposals have been made to go from carrier-based tests such as the AOAC tests to more quantitative procedures (10,12,13). A filtration method using a suspension of bacteria has several advantages over a carrier or surface method.…”

“…A case of cross-infection of patients through contamination of endoscopes by reused disinfectant has been reported (8). Suspension tests and other quantitative methods have been applied previously (4,5,13,14). Collins (7) reported a quantitative procedure for Mycobacterium tuberculosis.…”