Dear Sayan

Most strains of Morexella are colistin-sensitive; some strains are colistin-resistant.

Thanks

Most strains are are Colistin sensitive but if you have any doubt about the sensitivity ask for a disk diffusion technique.

We are mostly studying Moraxella catarrhalis on human subjects..

Here I quote  Harkirat singh in Indian J Crit Care Med. 2010 Jul-Sep; 14(3): 161–162, in  the article Management with colistin. He says  " Notably, Proteus spp., Moraxella catarrhalis, Providencia spp., Serratia marcescens, Morganella morganii, gram-negative cocci, and all gram-positive bacteria are resistant to colistin. " So I think it is resistant to Colistin 

Sir, Also if i am right disc diffusion testing for colistin is available only for P. aeruginosa and no other bacteria, so better to to go for MIC.

Most erfernces cite that Colistin resistance in mORAXELLA IS VARIABLE..

tHAT IS WHY THEY ARE  different from Neisseria (even commensal ones) because Neisseria sp. are always resistant to colistin,.,.,

The occasional finding of colistin-resistant Moraxella isolates is well known, but there is scant information about the mechanisms of resistance. Because of the characteristics of colistin and its mechanism of action, is not feasible a significant role for impermeability or efflux pumps. In P. aeruginosa, the overproduction of  H1 protein displaces the Mg ions from the LPS, thus inhibiting binding of the antibiotic and leading to low level resistance. High level resistance has also been described, associated to the activation of a two- components system (PmrA-PmrB), that finally reduce the negative charge of the LPS, decreasing affinity and binding of polimyxins to the outer membrane..

Moraxella catarrhalis is usually susceptible to colistin, but some strains can be resistant. You can set up a disk diffusion susceptibility test to colistin. Colistin is not one of the recommended antibiotics to treat M. catarrhalis infections.

The question arising here is that why you are going to treat your patient with 

Always resistant to Colistin