Kalmar "iyalin kwayoyin cuta" ba jumlar da aka saba amfani da ita ba ce a microbiology ko ilmin halitta. Duk da haka, kalmar “bakteriya” tana nufin wani babban rukuni na ƙananan ƙwayoyin cuta, kwayoyin halitta guda ɗaya waɗanda ke samuwa a cikin yanayi da yawa, ciki har da ƙasa, ruwa, iska, da rayayyun halittu.Bacteria sun rabu. zuwa kungiyoyi daban-daban dangane da halayensu, kamar siffarsu, girmansu, hanyoyin rayuwa, da sauran abubuwan. An rarraba waɗannan ƙungiyoyi zuwa matakan haraji daban-daban, kamar phylum, aji, tsari, iyali, jinsi, da nau'in. suna raba wasu halaye kuma an rarraba su a cikin iyali ɗaya bisa ga kamanceceniya ta kwayoyin halitta da yanayin halittarsu. Misalan iyalai na ƙwayoyin cuta sun haɗa da Enterobacteriaceae, Lactobacillaceae, da Streptococcaceae, da sauransu.