Factors influencing a suspension test method for antimicrobial activity of disinfectants

Abstract

s LANGSRUD AND G. SUNDHEIM. 1998. Factors influencing the numbers of Escherichza coli DShI 682 and Staph.ylococcus aureus ATCC 6538 surviving exposure to disinfectants were evaluated by factorial design. Aerobic conditions during precultivation rendered E. coli more resistant to the lethal activity of benzalkonium chloride (BC) and a disinfectant containing grape fruit extract (GSE), whereas Staph. aureus became more sensitive. The degree of shaking and the pre-growth medium (tryptone soy broth or hlueller-Hinton broth) did not influence the result of the bactericidal test. The number of E. coli surviving BC treatment was significantly lower if the neutralizing broth contained thiosulphate, plate pouring was used instead of plate spreading, or the plates were incubated at 37 instead of 30 "C. The negative effect of plate pouring was also found with Staph. aureus. The use of filtration without prior neutralization of the disinfectant decreased the numbers of chlorinetreated, but not BC-treated, E. coli. The results showed that rigorous standardization is necessary to obtain good reproducibility of bactericidal suspension tests.

Evaluation by Conductance Assay of Shiga Toxin-Producing Escherichia coli (STEC) O157 and O26 and teir Sensitivity to Selected Disinfectants

“…Most authors drew attention to this fact (e.g. Evans et al 1990;Russel et al 1993;Brown et al 1994;Bloofield et al 1995;Langsrud and Sundheim 1998). Specific growth demands of individual tested strains should be taken in consideration in terms of methodical procedures used.…”

Emergence of resistance to antibacterial agents: the role of quaternary ammonium compounds—a critical review

“…Like other antibacterial agents, susceptibility to QACs may be based on the ability of QACs to kill microorganisms and/or to inhibit growth, depending on the purpose. The testing conditions can highly influence the results; thus, it is difficult to compare results between investigations and to extrapolate from laboratory to practical conditions [21][22][23][24][25]. The most influential test conditions include temperature, time of exposure, amount of organic material, growth conditions and growth phase of the microorganism to be tested.…”

Residential Bacteria on Surfaces in the Food Industry and Their Implications for Food Safety and Quality

“…Bacteria protected from disinfectants through biofilm formation may die once they are released from the biofilm and subjected to the antibacterial agent, whereas bacteria with higher resistance will survive. However, using neutralizers is not straightforward, as different types of disinfectants need different neutralizers (Russell 2004), and their components themselves may be harmful to some bacteria, especially for those sublethally injured (Langsrud and Sundheim 1998;Sutton and others 2002), leading to both a potential underestimation of the bacterial level and a biased composition of the bacteriota. The negative effects of neutralizers on the viability of bacteria are small; in most cases, not using them would result in a larger bias.…”