Kwayar cuta kwayoyin cuta ce da ake dasu an yi amannar cewa shine sifar rai kawai a Duniya tsawon shekaru biliyan 2.000. Binciken shi an yaba wa Anton van Leeuwenhoek, masanin kimiyyar Holan na ƙarni na XNUMX.
Prokaryotes ne, wato, basu da cikakkiyar kwayar halitta, kuma girman sa ya kasance tsakanin 0,5 zuwa 5 micrometers, kodayake godiya ga microscopes ana iya lura da shi dalla-dalla, da kuma nau'ikan siffofin da yake ɗauka: fannoni, sanduna, kayan kwalliya da masu talla.
Sun taɓa kasancewa cikin masarautar dabbobi, amma daga baya aka sanya su a cikin masarauta mai zaman kanta, da ake kira monera. Nazarinsa ya dace da kwayoyin cuta, kimiyyar da ta fara haɓaka a ƙarshen karni na sha tara sakamakon bincike na likitanci da ƙosarwar ruwa, musamman na Louis Pasteur da Robert Koch.
Kwayar cuta rayuwa a cikin dukkan kwayoyin halitta, haka kuma ga dukkan sassan duniya, daga zurfin teku zuwa tsauni mafi tsayi, saboda cewa sun saba cikin sauki ga duk wani yanayin muhalli. An kiyasta cewa akwai wasu kwayoyin cuta a Duniya fiye da kowane nau'in kwayoyin halitta. A cikin gram ɗaya kawai na ƙasa mai ni'ima, za a iya isa zuwa kofi biliyan 2,5 da rabi.
Mutane kuma suna da ƙwayoyin cuta da ke zaune a cikinmu, musamman a kan fata da kuma hanyar narkewar abinci. Wasu suna da fa'ida kuma wadanda ba haka ba yawanci ana lalata su ta hanyar kariya ta tsarin garkuwar jiki. Koyaya ba koyaushe haka bane. Wasu ƙwayoyin cuta masu cuta suna iya haifar da cuta cuta mai haɗari ga lafiya, kamar kwalara ko kuturta.