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Advances in the antimicrobial action of Usnic acid

Oct 08, 2019

       Many lichens, such as Usnea ,contain antimicrobial substances, among which the antimicrobial effect of Usnic acid is prominent.

     Usnic acid’s antibacterial spectrum is mainly Gram-positive bacteria and Mycobacterium tuberculosis. In vitro, Usnic acid has a strong bacteriostatic effect on pneumococci, Streptococcus haemolyticus, diphtheria and Mycobacterium tuberculosis. The bacteriostatic concentration is 1 μ 5 μ g / ml, and 50 μ g / ml ,which could completely inhibit the growth of bacteria. The inhibition of Staphylococcus aureus is slightly weaker than that of the above bacteria, but stronger than that of Gram-negative bacteria. There was no significant difference in antibacterial effect between right-handed type and left-handed type.However, it has also been reported that it is not effective against Gram-negative pertussis, Bacillus subtilis, pneumoniae and even Escherichia coli, Proteus, Shigella dysenteriae and typhoid bacillus.In vitro studies, Usnic acid has a significant inhibitory effect on human tuberculosis bacillus. 20 ≤ 50 μ g / ml could be completely suppressed, and the serum can slightly reduce its efficacy.In vivo studies (the treatment of experimental tuberculosis in guinea pigs), it is generally believed that oral or intraabdominal injection has a better effect and can limit the development of tuberculosis lesions.It has also been reported that Usnic acid alone has no effect on experimental tuberculosis in guinea pigs, but can enhance the effect of streptomycin.


Usnic acid

      In vitro, Usnic acid also has a slight synergistic effect with streptomycin or isoniazid. For human lung and intestinal tuberculosis, oral administration of 0.1 × 1.0 g sodium Usnic acid or Evosin (a preparation containing Usnic acid and reduced ovalic acid) 0.1 g / 0.5g ,which can improve some symptoms of tuberculosis, such as cough, anorexia, fever or intestinal tuberculosis diarrhea, and even make the microscopic examination of tuberculosis negative, but the observation is not perfect , final conclusion can not be drawn. The improvement of these symptoms does not seem to have a direct influence on tuberculosis, because after oral administration, the blood does not reach the level of bacteriostatic concentration. Some people think that it has no obvious effect on human tuberculosis.  use of Usnic acid in the treatment of pulmonary tuberculosis, has been observed to have a certain effect in China.

        Many studies have been carried out on the bacteriostatic principle of Usnic acid. Some people think that it can inhibit the synthesis of proteins, and some think that it is related to the repulsive combination of oxidative phosphorylation. 

      Looking forward to a better study of Usnic acid in science in the future