Ma'anar "kwayoyin cuta" ita ce:"Kowace yanki (Bacteria) na musamman zagaye, karkace, ko sanduna masu siffa guda ɗaya na prokaryotic microorganisms waɗanda yawanci ke rayuwa a cikin ƙasa, ruwa, kwayoyin halitta. kwayoyin halitta, ko jikin tsirrai da dabbobi, wadanda suke yin nasu abincin musamman daga hasken rana ko kuma masu saprophytic ko parasitic, sau da yawa suna motsa jiki ta hanyar flagella, suna haifuwa musamman ta hanyar fission na binary, kuma sun haɗa da yawancin cututtuka masu mahimmanci."