Healthy Living

Pathogens that Cause Pneumonia

Pathogens that Cause Pneumonia

The pathogens involved in pneumonia are bacteria, virus, fungus, rare parasites, and other microorganisms. Virus is the most common cause of pneumonia among babies and children. Adults with weak immune systems are vulnerable to bacterial pneumonia.

Pneumonia Causing pathogens:

The pathogens that cause pneumonia are broadly classified into the following three categories:

  1. Common pathogens
  2. Drug-resistant pathogens
  3. Atypical pathogens

Most common pathogens:

Streptococcus pneumoniae (pneumococcus)
Mycoplasma pneumoniae
Chlamydophila pneumoniae

Respiratory viruses:

Hemophilus influenzae
Legionella pneumophila
Moraxella catarrhalis

Streptococcus pneumoniae, also known as pneumococcus, is one of the common pathogens that cause community-acquired pneumonia (CAP).

Atypical CAP pathogens include mycoplasma, chlamydophila, and legionella. These pathogens cause one third of community-acquired pneumonia. While legionella is the reason behind severe CAP, mycoplasma and chlamydophila are the cause for mild pneumonia. These bacteriae are not clearly visible during a sputum Gram stain test. These atypical bacteriae survive even when penicillin or other types of beta-lactam antibiotics are administered.

The common reason behind CAP is influenza respiratory virus. Influenza infection predisposes an individual to the subsequent progress of bacterial CAP known as “post-influenza pneumonia.”

Moraxella and hemophilus are responsible for infection in patients suffering from a chronic obstructive pulmonary disease (COPD) or intrinsic lung disease.

Drug-resistant pneumococcus:

One of the commonly identified reasons behind CAP is drug-resistant streptococcus pneumoniae (DRSP).

Resistance to beta-lactam antibiotics

Drug-resistant microorganisms are the germs that do not get eliminated by the medicine used to treat the disease. These microorganisms equip themselves to survive the attack of drugs used to cure the infections they cause.

Drug-resistant streptococcus pneumoniae (DRSP) has late developed resistance to beta-lactam antibiotics, cephalosporin antibiotics, and penicillins by avoiding antibiotic binding agent of beta-lactam to the bacterial enzymes. This bacterial enzyme is involved in the production of bacterial peptidoglycan.

Less Common CAP Pathogens:

Enteric Gram negative bacilli

Pseudomonas aeruginosa

Group A Streptococcus

Endemic fungi

Staphylococcus aureus

Pneumonia Causing Viruses: 

Nearly one-third of pneumonia is because of viruses, this pneumonia virus affects more often children less than 5 years of age.

Respiratory syncytial virus (RSV):

A respiratory virus is considered to be one of the major reasons for pneumonia and bronchiolitis infection in children.

Human rhinovirus:

Human rhinovirus is one of the reasons behind lower respiratory infection and generally followed by common cold and it usually affects people with weak immunity.

Herpes Simplex Virus (HSV):

This virus is strong enough to affect people with good or weak immunity.


Pneumonia Causing Fungus:

The fungus that causes pneumonia infection is usually found in the soil. In addition, whenever your body's immune system becomes weak, the fungi present in your body will multiply, spread, and start attacking your system - which then leads to infection.           


This is a type of pneumonia-causing fungus that often thrive in warm and arid regions. Whenever a person inhales spores of fungus present in the air, the infection start.


This kind of fungus is present in the droppings of bats and birds. They grow in humid areas, contaminating the soil and air around it. People get infected whenever the fungus reaches the lungs through inhalation of the contaminated air or through soil contact. This infection can become fatal if it starts spreading outside the lungs.


This type of fungus is also present in bat and other bird droppings. It grows as yeast. Once the fungus reaches the lungs of the person through inhalation or soil contact, the infection starts.


Who is at risk of developing pneumonia?

People of any age can get affected by pneumonia since it affects individuals who have a weak immune system. People who have a high risk of getting infected by pneumonia fall under the following three categories: 

a.) Children less than 5 years of age: Pneumonia or other respiratory infection is the main cause of mortality in children under the age of five. This is because the immune system of children is not yet fully developed to fight against infection, which makes them vulnerable to any disease. Therefore, pneumonia affects children very easily. The presence of pneumonia in children can be identified when they have difficulty in breathing, continuous cough, and a raised temperature. The chest wall may start drawing in and breathing can become faster than usual.

b.) People above 65 years of age: After an individual crosses 65 years of age, the body becomes weak and susceptible to various diseases. The advancing age gradually suppresses the immune system, and the body becomes easily vulnerable to infection. When they get infected with pneumonia, the suppressed immune system of the body, compounded by other diseases, easily allow pneumonia to take over and develop rapidly. Therefore, elderly people have a very high risk of developing pneumonia.

c.) Individuals with other medical conditions: There is a certain category of adults who have a higher chance of developing pneumonia and these include:

● Malnourished individuals: Due to inadequate food intake, the body does not receive enough nutrition, which leads to the weakness of multiple organs. Your body and its immune system will become weak, making you more vulnerable to any kind of infection.

Respiratory diseases: People with lung diseases - including cystic fibrosis, infection of upper respiratory tract, asthma, or other chronic obstructive pulmonary diseases - have a weak immune system, making them highly susceptible to pneumonia-causing germs, viruses, and bacteria.

Diabetes: People with type 2 diabetes suffer from a compromised immune system. The sugar levels in the body will be high, providing a more suitable environment for pathogens to grow. These individuals can easily catch a cold, flu, or fever compared to normal people. They also take a longer time to recover from these diseases.

● Immune deficiency disorders: There are many diseases and medical conditions that can suppress the immunity of the body. Some of these conditions include HIV, organ transplant, chemotherapy, or prolonged use of steroids.

 Smoking: Smoking cigarettes increases your risk of getting infected with pneumonia, lung disease, and asthma.

 Alcoholism: Consuming large amounts of alcohol reduces the white blood count in your bloodstream. White blood cells are necessary to fight against any infection in the body. Lack of white blood cells decreases the body's immunity level, making it more prone to contracting pneumonia and other infections.

Hospital-acquired pneumonia

This happens more often to patients and individuals who are hospitalized for other diseases, who visit hospitals regularly, or those people who work in the hospitals. These individuals will have more exposure to pneumonia-causing bacteria, viruses, and other pathogens.

The common symptoms include a sore throat and a cough, often accompanied by sputum. As the infection advances, chest pain, fever, chills, difficulty breathing, and shortness of breath may also develop.

Patients suffering from pneumonia should wear a mask covering the nose and mouth to avoid cough droplets from spreading into the air and thus to other individuals. Also, people visiting and working in the hospitals should always wear protective masks to avoid infection.