Definition of retain. transitive verb. 1a : to keep in possession or useb : to keep in one's pay or service; specifically : to employ by paying a retainerc : to keep in mind or memory : remember.
However, some gram- positive bacteria may also have capsules. Examples for gram-negative bacteria with capsules: Escherichia â¦coli, Klebsiella pneumoniae, Salmonella. Examples for gram-positive bacteria with capsules : Bacillus megaterium, Streptococcus pyogenes, Sterptococcus pneumoniae.
The capsule is found most commonly among Gram-negative bacteria: 1  Escherichia coli (in some strains) 2  Neisseria meningitidis. 3  Klebsiella pneumoniae. 4  Haemophilus influenzae. 5  Pseudomonas aeruginosa. 6  Salmonella.