Colistin antimicrobial activity

Synergistic action of colistin and polymyxin in combination with other antibiotics in vitro and in vivo has been reported by several investigators " . In clinical application the effect of these combinations seems to be more a broadening of the antimicrobial spectrum than a synergistic interaction. Several salts and derivatives of both colistin and polymyxin have been reported. Commercially available are the sulphates and also recently the sodium sulphomethyl derivatives which are prepared by treatment of the free bases of polymyxin and colistin with formaldehyde and sodium bisulphite . These derivatives have a lower toxicity than the sulphates, however, and their in vitro antimicrobial activity is also reduced. 

It is still premature to give a clear correlation between structure and activity in the polymyxin group, because most published data on antimicrobial activity have been obtained either with impure material or with mixtures of the different individuals. Also the definition of potency differs for those antibiotics which were considered to be different up to now. But the synthesis " of the four compounds originally proposed by Hausmann with a D-a,y-diaminobutyric acid adjacent to the fatty acid and the synthesis of polymyxin Bj and colistin A have given some clues in these respects Table 1.12). 

Colistin (polymyxin E) is available as colistin sulfate for oral use and as colistimethate sodium for parenteral administration (not recommended). The antimicrobial activities of polymyxin B and colistin are restricted to gram-negative bacteria. 

Carbenicillin has a broader range of antimicrobial activity than any other known penicillin. It is not absorbed orally and must be given by injection. Carbenicillin is synergistic with gentamicin colistin and streptomycin. ... 

Pamp, S.J., Gjermansen, M., Johansen, H.K., Talker-Nielsen, T. Tolerance to the antimicrobial peptide colistin in Pseudomonas aeruginosa biofilms is linked to metabolically active cells, and depends on the pmr and mexAB-oprM genes. Mol Microbiol 68 (2008) 223-240. 

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