1975 Dr. E. Arum; Dr. N. Jacobs  This photograph depicts a number of Gram-negative Mycoplasma hominis, and T-strain Mycoplasma isolates, which had been grown on agar medium,  Members of the genus Mycoplasma lack a cell wall, and are therefore, difficult to treat with many antibiotics, which have a negative affect on bacterial cell-wall synthesis such as penicillin.