Bacterial

google

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mid 19th century: modern Latin, from Greek baktērion, diminutive of baktēria ‘staff, cane’ (because the first ones to be discovered were rod-shaped). Compare with bacillus.

wiktionary

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bacteria +‎  -al

etymonline

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bacterial (adj.)

"of or pertaining to bacteria," 1869, from bacteria + -al (1).