Bacteria and viruses are different types of microorganisms. Not all of them cause illness and disease, but bacterial and viral pathogens have the potential to do so.

This article describes the differences between bacterial and viral infections, and gives examples of each.

We also outline the different treatment options for bacterial and viral infections and provide tips on how to prevent infections in general.

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Pathogens are micrcoorganisms that cause illness and disease.

Bacteria, viruses, and fungi are different types of microorganisms.

Pathogens are microorganisms that have the potential to cause illness or disease.

Bacterial pathogens cause bacterial infections, whereas viral pathogens cause viral infections.

Sometimes, both bacteria and viruses can cause illness. Examples include pneumonia and meningitis.

Bacteria are living organisms that have just one cell. There are many different species of bacteria. Some live inside the human body and carry out functions, such as:

  • helping people to digest food
  • providing vitamins
  • getting rid of cells that could cause disease

Less than 1% of bacterial species can cause bacterial infections. Such infections occur when the bacteria enter the body and invade the body’s immune system, where they quickly multiply and produce harmful toxins.

We outline some common types of bacterial infection below.

Streptococcal infections

Streptococcus or strep is a group of bacteria. There are two main types: alpha (α)-hemolytic streptococci, and beta (β)-hemolytic streptococci.

Alpha-hemolytic streptococci

Alpha-hemolytic streptococci includes the bacterial species Streptococcus pneumoniae (S. pneumoniae), as well as Viridans group streptococci.

S. pneumoniae

S. pneumoniae usually exist on the skin and inside the throat. This bacterial species can cause minor infections, such as sinus infections and middle ear infections. More severe infections include:

Viridans group streptococci

Viridans group streptococci most commonly exist in the mouth, gut, and genital region. Severe infections can occur if the bacteria enter other parts of the body.

A Viridans group streptococci infection that enters the bloodstream can infect the inner lining of the heart. The medical term for this is endocarditis. It is a serious condition that requires prompt medical treatment.

Beta-hemolytic streptococci

There are two types of Beta-hemolytic streptococci: Group A and Group B streptococci.

Group A strep

An infection by group A strep, or Streptococcus pyogenes, can be invasive or non-invasive. Invasive infections are those that spread to the bloodstream.

The most common non-invasive Group A strep infections include:

Invasive Group A strep infections are much rarer. They may lead to the following conditions:

Group B strep

Group B strep, such as Streptococcus agalactiae usually live harmlessly inside the digestive system and female genital tract.

Group B strep most commonly affects newborns. This is because the bacteria can pass from mother to fetus in the womb. According to one article, most people develop a natural immunity to Group B strep as they get older.

A newborn who has a Group B strep infection may display the following signs and symptoms:

  • floppiness and unresponsiveness
  • poor feeding
  • unusually low or high body temperature
  • unusually slow or fast heart rate

Without treatment, a Group B Strep infection may lead to serious conditions, such as meningitis and pneumonia.

Staphylococcal infections

There are more than 30 types of Staphylococcus, or staph, bacteria. Most staph infections are due to the species Staphylococcus aureus (S. aureus). This bacteria lives on the skin or inside the nose and can enter the body through an open wound.

Staph bacteria can cause various types of infections, including:

Escherichia coli infections

Escherichia coli (E. coli) is a type of bacteria that live inside the gut. According to the Centers for Disease Control and Prevention (CDC), most types are harmless. However, some types live in or on certain foods and cause food poisoning.

The CDC indicate the following as sources of E. coli infection:

  • contaminated meats
  • unwashed fruits and vegetables
  • unpasteurized milk and juices

Once inside the body, the bacteria can cause the following symptoms:

Viruses are tiny pathogens made up of genetic material. In order to replicate, they must enter the cells of a living organism, such as a human or an animal.

A viral infection happens when a virus gets into the body and invades healthy cells. The virus then uses the cell’s machinery to make copies of itself. This process can kill, damage, or change the cells.

There are many different types of viral infections. We outline some examples below.


According to the CDC, there are many different types of coronavirus. Some cause minor cold-like symptoms, while others may cause severe health complications.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a new type of coronavirus. People exposed to the SARS-CoV-2 virus may go on to develop the novel coronavirus disease (COVID-19).

Coronaviruses spread via the following means:

  • through inhaling tiny droplets, or aerosols, from the cough or sneeze of a person who has the virus
  • through touching items that have come into contact with the virus, and then touching the mouth, nose, or eyes

Influenza viruses

Influenza viruses cause influenza, or the flu. The CDC indicate that people who get flu will experience symptoms such as:

However, people who have a weakened immune system may experience severe symptoms and potentially serious flu complications.

According to the CDC, other people at risk of developing severe complications from the flu include:

  • older people
  • young children
  • pregnant women
  • people with underlying health conditions


HIV attacks the body’s immune cells, which ordinarily help to fight off infection. This makes people vulnerable to other infections and diseases.

Although there is no cure for HIV, antiretroviral medications help to keep the virus under control. Without such treatment, HIV leads to AIDS.

HIV spreads through bodily fluids, such as:

  • the blood
  • semen
  • pre-seminal fluid, or pre-cum
  • vaginal fluids
  • rectal fluids
  • breast milk

According to the CDC, most HIV transmission occurs due to sex without using barrier contraception or sharing needles to inject drugs.

In order to diagnose a bacterial or viral infection, a doctor will ask a person about their medical history and symptoms.

The doctor may then order tests to look for signs of bacteria or viruses in the person’s blood or urine, or from a throat or nasal swab.

Treatment will depend on whether the illness is due to a virus or bacteria.


Antibiotics are medicines that either kill bacteria or make it hard for the bacteria to replicate.

Different types of antibiotics work for different types of bacterial infections. Antibiotics are not effective against viral infections.

Antibiotics are available in the following forms:

  • oral forms, such as pills, capsules, and liquids
  • ear drops and eye drops
  • topical forms, such as creams, ointments, and sprays

If the infection is more severe, a doctor may recommend an antibiotic injection or intravenous infusion or drip.

Antiviral drugs are medicines that make it hard for the virus to multiply. Each antiviral medication usually works on one specific virus or group of viruses.

There is currently no approved antiviral medication for the SARS-CoV-2 virus (although research trials are ongoing) or for viral infections that cause the common cold.

Anyone worried about a viral infection should speak to a doctor.

The best way to reduce the risk of contracting and transmitting a virus is to follow good hygiene practices, including:

  • washing the hands thoroughly and often
  • using a tissue when coughing or sneezing, then throwing the tissue away
  • coughing or sneezing into the crook of the elbow if there is no tissue available
  • avoiding picking wounds or squeezing spots
  • washing and dressing any cuts or wounds
  • avoiding sharing personal items, such as towels, bedding, and cutlery
  • never sharing needles if injecting drugs
  • always use condoms or another barrier contraception when having sex

People can also protect themselves from some viruses and bacteria by getting vaccines. These are preventive therapies that prepare the body to fight off specific infections in the future.

According to the CDC, the United States Government recommends that children receive vaccinations to protect them against the following diseases:

Bacteria and viruses are different types of microorganisms. Some bacteria and viruses can cause infection and disease.

Doctors use antibiotics to treat certain bacterial infections, and antivirals to treat certain viral infections. However, some infections are untreatable.

The best way to prevent infection is to practice good hygiene. Vaccines are an effective method for preventing certain viruses, such as measles, mumps, and polio.

A person should visit their doctor if they suspect they may have an infection. A doctor may recommend tests to check for bacteria or viruses in the person’s blood or urine.