Both Gram-positive and Gram-negative bacteria commonly have a surface layer called an S-layer. In Gram-positive bacteria, the S-layer is attached to the peptidoglycan layer. Gram-negative bacteria's S-layer is attached directly to the outer membrane). Specific to Gram-positive bacteria is the presence of teichoic acids in the cell wall
However, there are cases where the color may appear yellowish, sometimes referred to as âyellow spermâ or âyellow semenâ. The cause of yellow sperm is uncertain but it is believed that it can be caused by infection, or foods which are rich in sulfur such as garlic and onions.Another possible cause for yellow semen could be the natural thickening of semen; especially if you have not ejaculated for quite some time.he cause of yellow sperm is uncertain but it is believed that it can be caused by infection, or foods which are rich in sulfur such as garlic and onions.
Pink, red, or brown sperm may mean that a man has blood in his semen, and this can be the sign of an infection or injury. Semen color can change from day to day, and a sudden change or a change accompanied by discomfort or a foul odor should be checked by a physician.hen one refers to sperm color, he is usually referring to the color of semen. Usually, semen is white or grayish in color, due to the large amount of proteins present in the secretions. Yellow may also be a normal sperm color for some men.