Difference Between Parasites and Bacteria

Main Difference – Parasites vs Bacteria

Parasites and bacteria are microbes which live in plants, animals or environment. Some parasites and bacteria may create pathogenic effects in both plants and animals separately. Parasites are multicellular organisms, usually visible to the naked eye. They are always pathogens. Bacteria are unicellular, microscopic organisms which form colonies. Bacteria are either beneficial or sometimes harmful. The key difference between parasites and bacteria is that parasites are considered as ‘true life’ forms living in/on a host, even in a single stage of their life cycle whereas bacteria, found everywhere, consist of the mere basics which constitute ‘life’.

This article contains,

1. What are Parasites
      – Characteristics, Classifications
2. What are Bacteria
     – Classification, Cellular Structure, Metabolism
3. What is the difference between Parasites and Bacteria

Difference Between Parasites and Bacteria - Comparison Summary

What are Parasites

Parasites are multicellular creatures who live in/on a host. Some parasites such as helminths are macroparasites, and are visible to the naked eye whereas some such as protozoa are microparasites and are smaller. Plants, such as Cuscuta and mistletoe are parasites. Animals like hookworms are also parasites. Parasites do not kill their host. They reduce the biological fitness of the host. They also reproduce faster than their hosts.

Classification of Parasites

Based on their life cycles, parasites can be divided into two groups: obligate parasites and facultative parasites. Obligate parasites depend on the host throughout their entire life cycle. Facultative parasites, on the other, depend on their host for only one or more stages of their life cycle. Single host species is invaded by direct parasites whereas indirect parasites invade multiple host species.

Based on the interactions with their hosts, parasites can be divided into six groups: ectoparasites, endoparasites, mesoparasites, epiparasites, social parasites and adelpho-parsites. Ectoparasites, such as lice, fleas, and some mites live on the outside of the host’s body. A human louse is shown in figure 1.

Main Difference - Parasites vs Bacteria

Figure 1: A human head louse

Endoparasites, such as parasitic worms live inside the host. Endoparasites can be divided into two groups: intercellular parasites and intracellular parasites. Intercellular parasites live in the spaces of the host’s body. Intracellular parasites live inside the cells. Intracellular parasites such as protozoa, bacteria and viruses consist of a carrier or vector as the third organism in order to invade the host. Mesoparasites live in an intermediate position in the host’s body. Social parasites take benefits from the interactions between social organisms such as ants. Adelpho-parasites’s hosts are closely related to their parasites, bot parasite and the host belong to the same family or genus. 

What are Bacteria

Bacteria are simple unicellular microorganisms found everywhere. They are considered as one of the first life forms evolved on Earth. Bacteria can be found in most habitats such as soil, water, acidic hot springs, deep portions of Earth’s crust and radioactive waste. They live in either symbiotic or parasitic relationships with plants and animals. Bacteria form dense aggregations like a mat by attaching to surfaces. These bacterial mats are called as biofilms.  

Classification of Bacteria

Bacteria can be categorized depending on their morphology. Cocci are the spherical-shaped bacteria. Bacillus is the rod shaped bacteria. Comma-shaped bacteria are called vibrio, and spiral-shaped bacteria are spirilla or tightly coiled ones are called spirochaetes. Some bacteria live as single cells. But, some of them live in pairs called diploids. Streptococcus are the bacterial chains. Staphylococcus form ‘bunch of grapes’ like clusters. Filaments are the elongated bacteria like Actinobacteria. Some are branched filaments such as Nocardia. A rod-shaped E. coli bacteria is shown in figure 2.

Difference Between Parasites and Bacteria

Figure 2: E. coli

Cellular Structure of Bacteria

Bacterial cells are surrounded by a cell membrane. The membrane-enclosed cytoplasm contains nutrients, proteins, DNA and other essential components of the cell. Bacteria are prokaryotes which lack membrane-bound organelles. Protein localization is carried out by their cytoskeleton. A single, circular chromosome is found in the nucleoid. This simple arrangement of bacteria is referred to as ‘bacterial hyperstructures’.

Murein forms a cell wall outside the bacterial cell membrane. The thicker cell wall is classified as gram-positive, and the thinner cell wall is classified as gram-negative in the gram staining of bacteria. Flagella are used for the mobility. Fimbriae are the attachment pili. They are used in the sexual reproduction of bacteria, which is known as conjugation. The entire cell is covered by glycocalyx which forms the capsule. 

Some genera of gram-positive bacteria form a resistant, dormant structures called as endospores. Endospores contain little cytoplasm, DNA, and ribosomes, covered by a cortex. They are resistant to radiation, detergents, disinfectants, heat, freezing, pressure and desiccation. 


Depending on the carbon source, bacteria can be divided into two groups: heterotrophs and autotrophs. The carbon source in organic compounds in heterotrophs whereas the carbon source is carbon dioxide in autotrophs. Depending on the energy source, bacteria can be divided into three groups: phototrophs, lithotrophs or organotrophs. In phototrophs, the energy source is sunlight. Organic compounds are used as the energy source in organotrophs. In lithotrophs, the energy source is inorganic compounds.

Difference Between Parasites and Bacteria


Parasites: Parasites are considered as the ‘true life’.

Bacteria: Bacteria are considered as the mere basic which constitute ‘life’.


Parasites: Parasites are multicellular organisms, visible to the naked eye.

Bacteria: Bacteria are unicellular, microscopic organisms.


Parasites: Parasites are complex; cells contain membrane-bound organelles including nucleus.

Bacteria: Bacteria are simple. Cells contain a ring of DNA and no organelles.

Nutritional Type

Parasites: Parasites depend on the host.

Bacteria: Bacteria can be phototrophs, lithotrophs or organotrophs.


Parasites: Parasites are classified into coccus, bacillus, rickettsia, mycoplasma and spirillum depending on size and shape.

Bacteria: Bacteria are classified into obligatory parasites, temporary parasites and facultative parasites.


Parasites: Both sexual and asexual reproduction are used.

Bacteria: Bacteria are asexually reproduced by binary fission and sexually reproduced by conjugation.


Parasites: Anisakiasis, giardiasis, cryptosporidiosis, trichinosis, taeniasis, etc. are caused by parasites.

Bacteria: Cholera, tuberculosis, Lyme disease, pertussis, salmonella, staph infections, strep throat, leprosy, tetanus, diphtheria, etc. are caused by bacteria.


Parasites: Tapeworms, lice, fleas, and barnacles are examples of parasites.

Bacteria: Lactobacillus, nitrogen-fixing bacteria, Helicobacter pylori, and Staphylococcus are examples of bacteria.


Bacteria are unicellular microbes which live either as symbioses or parasites. Parasites are multicellular organisms which grow, feed and shelter in/on different organisms. They can be either bacteria, viruses, protozoa, plants or animals. Both parasites and bacteria can cause diseases. The main difference between parasites and bacteria is their cellular organization and pathogenic nature.

1.“Parasitism”. Wikipedia, the free encyclopedia, 2017. Accessed 28 Feb 2017
2.“Bacteria”. Wikipedia, the free encyclopedia, 2017. Accessed 28 Feb 2017

Image Courtesy:
1. “Male human head louse” By Gilles San Martin – originally posted to Flickr as Male human head louse (CC BY-SA 2.0) via Commons Wikimedia
2. “E. coli Bacteria (16578744517)” By NIAID – E. coli Bacteria (CC BY 2.0) via Commons Wikimedia

About the Author: Lakna

Lakna, a graduate in Molecular Biology & Biochemistry, is a Molecular Biologist and has a broad and keen interest in the discovery of nature related things

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