Determination of decimal reduction time (D value) of chemical agents used in hospitals for disinfection purposes.
BACKGROUND
Prior to the selection of disinfectants for low, intermediate and high (sterilizing) levels, the decimal reduction time, D-value, for the most common and persistent bacteria identified at a health care facility should be determined.


METHODS
The D-value was determined by inoculating 100 mL of disinfecting solution with 1 mL of a bacterial suspension (10(4)-10(5) CFU/mL for vegetative and spore forms). At regular intervals, 1 mL aliquots of this mixture were transferred to 8 mL of growth media containing a neutralizing agent, and incubated at optimal conditions for the microorganism.


RESULTS
The highest D-values for various bacteria were determined for the following solutions: (i) 0.1% sodium dichloroisocyanurate (pH 7.0)--E. coli and A. calcoaceticus (D = 5.9 min); (ii) sodium hypochlorite (pH 7.0) at 0.025% for B. stearothermophilus (D = 24 min), E. coli and E. cloacae (D = 7.5 min); at 0.05% for B. stearothermophilus (D = 9.4 min) and E. coli (D = 6.1 min) and 0.1% for B. stearothermophilus (D = 3.5 min) and B. subtilis (D = 3.2 min); (iii) 2.0% glutaraldehyde (pH 7.4)--B. stearothermophilus, B. subtilis (D = 25 min) and E. coli (D = 7.1 min); (iv) 0.5% formaldehyde (pH 6.5)--B. subtilis (D = 11.8 min), B. stearothermophilus (D = 10.9 min) and A. calcoaceticus (D = 5.2 min); (v) 2.0% chlorhexidine (pH 6.2)--B. stearothermophilus (D = 9.1 min), and at 0.4% for E. cloacae (D = 8.3 min); (vi) 1.0% Minncare (peracetic acid and hydrogen peroxide, pH 2.3)--B. stearothermophilus (D = 9.1 min) and E. coli (D = 6.7 min).


CONCLUSIONS
The suspension studies were an indication of the disinfectant efficacy on a surface. The data in this study reflect the formulations used and may vary from product to product. The expected effectiveness from the studied formulations showed that the tested agents can be recommended for surface disinfection as stated in present guidelines and emphasizes the importance and need to develop routine and novel programs to evaluate product utility.
Mazzola
Priscila Gava
PG
Department of Biochemical and Pharmaceutical Technology, School of Pharmaceutical Sciences, University of São Paulo, São Paulo, Brazil. pmazzola@usp.br
Penna
Thereza Christina Vessoni
TC
Martins
Alzira M da S
AM
D001412:Bacillus subtilis / Q000187:drug effects; D001419:Bacteria / Q000187:drug effects*; D004202:Disinfectants / Q000737:chemistry / Q000494:pharmacology*; D004203:Disinfection; D004926:Escherichia coli / Q000187:drug effects; D001411:Geobacillus stearothermophilus / Q000187:drug effects; D008826:Microbial Sensitivity Tests; D013211:Staphylococcus aureus / Q000187:drug effects
D004202:Disinfectants