Formaldehyde bacterial resistance

Mechanism of action In order to act, methenamine [meth EN a meen] must decompose at an acidic pH of 5.5 or less in the urine, thus producing formaldehyde, which is toxic to most bacteria (Figure 32.5). The reaction is slow, requiring 3 hours to reach 90% decomposition. Methenamine should not be used in patients with indwelling catheters. Bacterial resistance to formaldehyde does not develop. [Note Methenamine is frequently formulated with a weak acid such as mandelic acid, which lowers the pH of the urine thus aiding decomposition of the drug.]... 

Sterilization of a membrane system is also required to control bacterial growth. For cellulose acetate membranes, chlorination of the feed water is sufficient to control bacteria. Feed water to polyamide or interfacial composite membranes need not be sterile, because these membranes are usually fairly resistant to biological attack. Periodic shock disinfection using formaldehyde, peroxide or peracetic acid solutions as part of a regular cleaning schedule is usually enough to prevent biofouling. 

Mycobacteria are generally considered to be of intermediate resistance to biocides, including aldehydes, between bacterial spores and other vegetative cells [90], Formalin, aqueous formaldehyde solution and glutaraldehyde are mycobactericidal, although some mycobacterial strains show increased resistance [90, 101, 236]. 

Yakima and Shivrina report that woolen te.vtiles may be rendered resistant to bacterial degradation by soakir in aqueous formaldehyde, washing and d.rying. Wool treated in this w-ay stands up well on use in paper machines. R istance of treated samples was measured by treating with 0.4 per cent solution of trypsin in a solution buffered to pH 8.3-S.5. 

---