Different Bacteria Types: Harmful, Beneficial and Gram Staining

Bacteria are classified under a distinct kingdom because of its peculiar cellular and morphological characteristics that makes it different and distinct from all other kingdoms like fungi, animal and virus. Bacteria are microscopic, unicellular (single celled) ancient organisms that are responsible for a number of lethal diseases. There are different types of bacteria that shares classic morphological characteristics of the kingdom but are classified differently in 5 major groups on the basis of their habitat, laboratory characteristics, staining methods, requirement of certain nutrients for the generation of energy and presence of certain cytoplasmic extensions like flagella or cilia (that are helpful in the motility of bacteria).

This article will discuss some major characteristics that are helpful in the determination of different types of bacteria.

Watch an overview of good bacteria vs. bad bacteria, then refer to more details of the classification:

5 Types of Harmful Bacteria

Bacteria Type


Streptococcus Pyogenes

Streptococcus Pyogenes is the causative agent of mild sore throat and skin infections that may worsen in certain situations to lead to life threatening infections like toxic shock syndrome and septicemia (when bacteria gain access to the blood stream). It is classified as gram positive coccus that grows mainly in chains.

Escherichia Coli

E- Coli is a gram negative bacillis as discussed previously and is considered as a causative agent of traveler’s diarrhea; however some pathogenic strains can also lead to bloody diarrhea and circulatory shock.

Vibrio Cholerae

Vibrio cholerae is the causative agent of cholera and is associated with intake of improperly cooked food or poor sanitary conditions. Vibrio Cholerae is linked to hundreds and thousands of deaths worldwide (mostly in under- developed countries) due to cholera outbreak.

Enteritis Salmonella

The most common causative agent of food poisoning throughout the world is Enteritis salmonella and can lead to serious and life threatening food poisoning, diarrhea, circulatory shock and dehydration in children. Infection can be controlled by timely intake of proper antibiotics and circulatory support.

Salmonella Typhi

Salmonella Typhi is a gram negative organism that is the causative agent of typhoid fever. It is associated with a high mortality rate after initial infection and characterized by blood diarrhea, vomiting, dehydration, fever and may lead to death if proper treatment is not instituted at the right time.

5 Types of Beneficial Bacteria

Not all the bacteria are bad for human survival. Our body is loaded with hundreds and thousands of bacteria that serve to colonize our body in order to prevent overgrowth of pathogenic elements. In addition these bacteria also serve a variety of functions. Examples of beneficial bacteria are:

Bacteria Type


Lactobacillus acidophilus

Lactobacillus acidophilus exists in different parts of human body like intestine, vagina and oral cavity. It is responsible for slightly acidic pH of vagina that is helpful in preventing overgrowth of other microorganisms. In addition it is also known to boost immunity.

Due to its beneficial properties, it is used in a variety of dietary products like tempeh, yogurt, miso and probiotics supplements.

Bacillus subtilis

Bacillus subtilis occurs independently in the environment around us and was first used by Nazi army to manage diarrheal illness. It helps in normalizing gut motility and metabolic functioning.

It is fortified in products like yogurt, cheese, milk, ice cream and fermented soybeans.

Bifidobacterium animalis

Bifidobacterium animalis is found in the intestine of animals and humans as a normal commensal that aid in digestive process. In addition it can also be consumed in supplemental doses to improve the symptoms of constipation or irritable bowel syndrome.

Streptococcus thermophilus

Streptococcus thermophilus is classified under coccus and it has the ability to withstand a temperature of about 212 degrees Fahrenheit. Streptococcus thermophilus strengthen immunity and improves the functioning of gut. It can be obtained from cheese and other dairy products.

Lactobacillus reuteri

Lactobacillus reuteri is one of the probiotics agents that are present in maternal breast milk and becomes a permanent part of gut flora. It is also present in dietary sources like yogurt and cheese.

Types of Bacteria According to Gram Staining

Since bacterial organisms are so minute, it is impossible to view the organisms without compound microscope. In order to visualize the cellular components and to differentiate bacteria from other microbial agents, staining techniques are used by scientists to categorize different bacteria.

Gram staining is a special method that involves dying the outer covering of the bacterial cell wall that prevents it from physical and environmental trauma. On the basis of gram staining, bacteria are widely classified as gram positive (bacteria with the cell wall) and gram negative (bacteria without cell- wall).

There are a number of structural and functional variations in the bacteria of one group that helps in adapting these bacterial agents to survive in one environment where other bacteria cannot.

Bacteria Type



Coccus is rounded or spherical in shape and may occur in chains or clusters. These occurs abundantely in the environment and also as normal commensal on the human body (in nostrils, skin, oral cavity and genitals).

If these pathogens grow excessively, diseases like impetigo, food poisoning and tonsillitis may occur

Examples are: Staphylococcus aureus, Streptococcus pyogenes


Bacilli are rod shaped and may be gram positive or negative on staining. Most popular species are salmonella (the causative agent of typhoid) and E- Col (causative agent for hemorrhagic diarrhea). Gram negative as well as gram positive bacilli are well known causative agents for gastroenterological, pulmonary and cutaneous infections.


Rickettsia is considered unique bacteria since it is incapable of surviving outside living organisms. Due to unstable morphological features, it is transmitted by different vector sources like ticks, fleas and mites to cause life threatening infectious diseases like Rocky mountain spotted fever and typhus.


All bacteria are characterized by a cell wall outside cell-membrane; however, mycoplasma is unique as it lacks a cell wall that is also considered a protective mechanism that makes it easier for bacteria to evade antibiotic therapies. It is causative agent for life threatening pulmonary infections and some strains may cause pelvic disease.


Spirillum is different from other bacterial agents as it is cork-screw shaped. It includes causative agent of Lyme’s disease (transmitted by tick bites) and syphilis.

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