Microbicidal concentration

The processes described — transportation of the microbicide to the surface of the microbe cell, adsorption, diffusion, penetration and interaction at the target site, are not instantaneous. The time they take, the killing time, may well differ from microbicide to microbicide. The differences also depend on the mode of action, as well as on the chemical constitution and chemico-physical properties of the microbicide. As the latter characteristics may be very different among microbicides that share the same mode of action, one cannot say that a given mode of action corresponds to a short or long killing time. It will be understood that killing times decrease as the microbicide concentration and temperature rise but here, too, the influences depend on the microbicide concerned. 

Fig. 13. Dependence of the activity duration (Tgff) of a microbicide, whose reactivity is characterized by the slope a, on the microbicide concentration Q or C2.

Table 46. Microbicidal Concentrations within 10 min according to AO AC Use-Dilution Method (Block, 1983)...

The a.m. mixture of benzylphenols is used as an active ingredient in disinfectants, generally in combination with other active phenolics able to close the gap for Pseudomonades. The fact that the MICs are higher than the microbicidal concentrations demonstrates that the benzylphenols are sensitive to organic matter. As a preservative for material protection the mixture has not gained importance because of unfavourable solubility properties. 

PCMC is most effective between pH 4 and 8, where, in fact, contrary to other phenol derivatives only PCMC is sufficiently water soluble. By comparing the microbicidal concentrations of PCMC with those of PCMC-Na, solutions of which have pH values higher than 8, one notices a distinctive decrease in the activity of PCMC in alkaline media (Table 49). 

Table 50. Microbicidal Concentration of PCMC within 5 min — Use-Dilution Test...

Table 54. Microbicidal Concentrations of 4-Chloro-thymol — Use-Dilution...

Test organism Microbicidal concentration (g/litre) after 10 min exposure... 

Due to its higher degree of chlorination Bithionol shows in comparison to Fenti-chlor even more activity against gram-positive bacteria, but has the same gap for Pseudomonades in its activity spectrum. There is also for bisphenols a typical discrepancy between microbistatic and microbicidal concentrations, differing from 1 to 1000 mg/litre, e.g. for Staphylococcus aureus. 

R - ratio of total to free (not bound) microbicide concentration... 

The neutralizing effect of a microbicide binding to surface active agents above the critical micell concentration (CMC) can be overcome by diluting the mixture to or below the CMC or by increasing the microbicide concentration in the mixture to an amount such that the concentration of free microbicide reaches the effective level. 

The microbial efficacy and activity spectrum of CTAB is demonstrated by the microbicidal concentrations of CTAB for different species of bacteria, yeasts and fungi (Wallhausser, 1984) in Table 119. 

Table 119. Minimum Microbicidal Concentrations of CTAB (MMC) after 24 h at 22°C...

Doxycycline-loaded chitosan microspheres were developed using a novel water-inoil emulsion technique, involving oil phase ionic gelation. Assessment of antibacterial activity showed that doxycycline was able to exhibit a minimum microbicidal concentration (MIC) of 16.5,17.4,11.2 and 98.3 pg a gdinst Klebsiella pneumoniae (ATCC 15380), Escherichia coli (ATCC 25922), Staphylococcus aureus (ATCC 9144) and Pseudomonas aeruginosa (ATCC 25619), respectively. The scope of this investigation was the use of doxycycline-loaded chitosan microspheres for healing infected wounds [86]. 

Figure 19 Activity duration (Teff.) of microbicides in dependence of the slope a and the microbicide concentration Ci or C2 > Ceff.

Table 13 Minimum microbicidal concentration (%) of glutaraldehyde (50%) (with and without soiling —0.2% albumin -) at contact time (source THOR Biocides Division)...

Table 66 Microbicidal concentrations of 4-chloro-thymol - use-dilution test ...

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