polymyxin
noun
poly·myx·in ˌpä-lē-ˈmik-sən 
: any of several toxic antibiotics obtained from a soil bacterium (Bacillus polymyxa) and active against gram-negative bacteria
Example Sentences
Recent Examples on the Web After 30 days of exposure, the bacteria could tolerate doses of polymyxin B that were 256 times higher than the original amount, but the SCUBs remained effective at the same dose. 
Max G. Levy, Wired, 30 Nov. 2021 Instead, antibiotics commonly used in flu vaccine manufacturing include neomycin, kanamycin, polymyxin B and gentamicin. Anne P. Kim, The Conversation, 13 Nov. 2020
Max G. Levy, Wired, 30 Nov. 2021 Instead, antibiotics commonly used in flu vaccine manufacturing include neomycin, kanamycin, polymyxin B and gentamicin. Anne P. Kim, The Conversation, 13 Nov. 2020 Word History
Etymology
International Scientific Vocabulary, from New Latin polymyxa, from poly- + Greek myxa mucus — more at mucus
First Known Use
1947, in the meaning defined above
Medical Definition
polymyxin
noun
poly·myx·in ˌpäl-i-ˈmik-sən
: any of several toxic antibiotics obtained from a soil bacterium of the genus Bacillus (B. polymyxa) and active against gram-negative bacteria