Is Listeria a virus or bacteria? And could you elaborate on the key differences between viruses and bacteria in terms of their cellular structure, mode of reproduction, and how they generally cause illness in humans? I’m trying to understand the fundamental distinction between these two types of microorganisms to better grasp the nature of Listeria infections.
Answer
Listeria is a bacterium. Specifically, it’s a genus of bacteria, and the most well-known species is Listeria monocytogenes, which is a pathogenic bacterium that can cause listeriosis, a serious infection.
Bacteria are single-celled microorganisms that lack a nucleus and other complex organelles. They reproduce through binary fission, a process where one cell divides into two identical daughter cells. They possess a cell wall, cytoplasm, ribosomes, and a nucleoid region containing their DNA.
Viruses, on the other hand, are much smaller than bacteria and are not considered living organisms. They consist of genetic material (DNA or RNA) enclosed in a protein coat called a capsid. Viruses require a host cell to replicate. They invade host cells and use the host’s cellular machinery to produce more virus particles. Unlike bacteria, viruses do not have cell walls, ribosomes, or the ability to reproduce independently.
Listeria monocytogenes is a gram-positive, rod-shaped bacterium that is motile via flagella. It is a facultative anaerobe, meaning it can grow in both the presence and absence of oxygen. It’s also capable of growing at refrigerator temperatures (psychrotolerant), which is a key factor in its ability to contaminate refrigerated foods and cause illness.