DEVELOPMENT OF KESISTANCE TO MERCURIALS 



983 



DEVELOPMENT OF RESISTANCE TO MERCURIALS 



Most types of microorganism appear to be able to adapt to the presence 

 of mercurials, but usually not as readily or to such a degree as to arseni- 

 cals, sulfonamides, or antibiotics. Some resistance factors are given in the 

 accompanying tabulation, but it is likely that greater tolerance could have 



Organism 



Mercurial 



Resistance 

 factor 



Reference 



been developed in some instances if training had been prolonged. There are 

 also naturally occurring resistant strains and species. An interesting exam- 

 ple is the relative tolerance of Penicillium roqueforti to PM. and this has 

 bearing on the preservation of groundwood pulp (Russell, 1955). Most fungi 

 fail to grow in 0.006-0.030 mM PM, but this species grows well in a con- 

 centration of 0.06 mM and furthermore accumulates sufficient mercurial 

 to allow the less resistant organisms to grow. The number of serial cultures 

 in increasing mercurial concentrations required to produce tolerance varies 

 with the organism: It was 20 transfers for the fungi in the above table 

 (Partridge and Rich, 1962), 70-100 transfers for the species of Salmonella 

 (Severens and Tanner, 1945), and up to 500 transfers for yeast (Imshenetsky 

 and Perova, 1957). Occasionally no transfers are required and the organism 

 begins to grow normally after a prolonged lag period, as is the case with 

 Aspergillus glaucus where hyphal inoculations fail to grow for periods of 

 up to 14 days in 0.033 mM Hg++, and then proliferate without loss of vigor 

 (Briault, 1956). This indicates that resistance can develop in nonprolif crat- 

 ing organisms. 



Inasmuch as we do not understand how the mercurials depress growth, 

 it is clear that we cannot immediately postulate logical mechanisms for the 

 developed resistance. However, some interesting observations may contrib- 

 ute to the elucidation of the mechanisms of inhibition. The resistance is 

 apparently not due to a reduction of permeability to the mercurials, as 



