The effects of biocides on microbial respiration (oxygen uptake) by E. coli demonstrated that all of the isothiazolone biocides rapidly shut down consumption of oxygen using glucose within 6 min of contact (Figure 5). Biocides were added at equal molar amounts (134 M). CMIT (20 mg•kg) and OIT (29 mg•kg) showed the most rapid rate of inhibition, followed by MIT (15 mg•kg), with DCOIT (38 mg•kg) the slowest of the four tested. These data are in good agreement with previous studies showing 2 mg•kg of CMIT/MIT producing immediate inhibition of respiration within 5 min of addition to a mixed culture of bacteria in synthetic cooling water [1]. Additional studies confirmed the same effect was observed in cooling tower water with native bacteria. Similar results have been observed for DCOIT (data not shown).
The effect of shutting down respiration on microorganisms means that no oxygen is consumed to produce energy for growth and metabolism. Thus all aerobic processes cease to function. Anaerobic processes do not rely on oxygen, yet isothiazolone affects growth, energy (ATP), and enzymes, all of which are critically disabled.