Bacterial Diseases in Human Body
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Throughout history, bacterial infections have been the cause of potentially fatal diseases. Bacteria are omnipresent; they can be present in the environment and the human body. Certain bacteria present within the stomach are good for gut health. These good bacteria keep the other harmful bacterial growth in check, preventing diseases.

The harmful bacteria often affect the various organ systems in the body by secreting toxins. These toxins hamper normal organ functions, resulting in diseases. In earlier times (before the discovery of antibiotics), these infectious diseases would also result in severe complications, including death.

Due to the vast antimicrobial agents available, bacterial diseases are more easily manageable. The only drawback is the resistance to these antimicrobial agents; it is a growing concern in the medical world. 

A bacterial infection in the human body depends on various factors such as the type of bacteria, mode of transmission, host immune response, and the environment.

Bacterial structure

Bacteria are prokaryotic organisms. A typical bacterial structure consists of circular DNA, ribosomes within the cytoplasm, cell membrane, and cell wall. Some bacteria may have additional features such as flagella, pili, or a capsule.

The cell wall is one of the common ways to differentiate bacteria into groups. Clinically, bacteria are classified into two main groups based on their cell wall properties. The gram staining technique can differentiate bacteria into gram-positive or gram-negative types. However, not every bacterial group fits this classification. Some bacteria like the mycobacterium group do not take up the stain. 

Another bacterial classification involves their growth potential in the presence of oxygen. 

  • Aerobic bacteria or aerobes thrive in an oxygen-rich environment. 
  • Anaerobic bacteria do not need oxygen. 

The structure of the bacteria often determines the development of infectious diseases in the human body and their response to various treatments.

Symptoms of bacterial infection in the human body

Bacteria can multiply rapidly through a process called binary fusion. Even a few bacteria can create an overwhelming infectious disease. If the human immune response is strong, they can check these bacterial infections. One may not even develop any signs or symptoms to recognize the presence of the bacterial infection in the body.

The clinical manifestation, if any, can present in a varied form depending on the bacterial species and its preference for the specific organic system. For example, Staphylococcus aureus typically causes skin infection, although it can affect the lungs, abdomen, heart valves, and almost any other site.

The most common signs and symptoms of a bacterial infection involves

  • Fever
  • Muscle aches
  • Headache
  • Fatigue and general weakness
  • Coughing
  • Diarrhoea
  • Nausea or vomiting
  • Rashes or skin lesions


The external environment plays a pivotal role in the interaction of the bacteria with the human host. Bacteria can take refuge in several sites before transmitting to the human body to cause an infection. Bacteria may be indigenous to specific geographic locations and not commonplace to other regions.


These are sites where the bacteria multiply and survive until they transmit to the human body to cause infectious disease. These reservoirs may be living or non-living sites.

Living reservoirs

Humans, animals, and insects are examples of living reservoirs. The bacteria grow in the living reservoirs, often without manifesting the symptoms and disease. They merely carry the infectious bacteria that transmit to the human host to cause disease.

  • Human reservoirs

Several bacterial types can grow and thrive within human reservoirs, some even exclusive to humans. When bacteria enter these human reservoirs, they can colonise and multiply. Also called carriers, they may or may not manifest the infectious disease.

  • A passive carrier bears the bacteria in the body but never gets infected. 
  • Convalescent carriers have a history of bacterial infection. They carry the bacteria during the recovery period and can transmit to others. 
  • Active carriers are ones with complete recovery but harbour the bacteria.
  • Animal reservoirs

Farm animals or pets are examples of animal reservoirs of bacterial infection in the human body. These animals harbour the bacteria and transmit them to their human counterparts through direct contact, consumption, or bites. Salmonella infection due to undercooked meat or eggs can infect the digestive tract.

  • Insect reservoir

The insects are involved in carrying the bacteria and transmitting the disease. The most common insect vector includes flies, mosquitoes, lice, and fleas. Arachnids such as mites and ticks can also be a reservoir.

Non-living reservoirs

The environmental components that allow bacterial growth are non-living reservoirs. It includes soil, water, air, and even food.

  • Soil

Some bacteria are present in the form of spores in the soil. Exposure to the contaminated soil through the wounds allows the bacteria entry into the bloodstream. Tetanus is a bacterial infection present in this reservoir. 

Often, the bacteria can survive in the spore form for several years within the soil. Disturbance of the soil layer due to heavy rains, excavation, or mining can cause bacterial exposure to humans.

  • Water

Water reservoirs become contaminated with bacteria due to improper faecal and waste disposal. If one consumes the contaminated water, the bacteria can transmit to the human body and cause infectious disease.

  • Food reservoirs

Eating contaminated food is a common cause of most gastrointestinal bacterial infections. Untreated milk, undercooked meat, and faecal contamination are typical bacterial reservoirs. Salmonella and E.coli are bacteria commonly present in food reservoirs.

  • Fomites

These are inanimate objects that can carry bacteria on their surface. These bacteria can infect through direct contact. 

Fomites can be found on any surfaces in frequent contact by human hands, such as doorknobs, switches, pens, and keyboards among others.

Mode of transmission

Bacteria can transmit to the human host through any of these five modes of transmission:

  • Direct contact through skin, mucus membrane, or body fluids such as blood, saliva, or semen.
  • Airborne 
  • Droplet spread following a cough or sneeze by an infected individual
  • Vehicular transmission (food, water, and fomites)
  • Vectors such as ticks, mosquitoes, or flies

Preventing bacterial infection in human

Prevention of bacterial infections is easy. Following certain precautions can lessen the transmission of the bacteria.

  • Practice hygiene behaviours

Handwashing, reducing frequent touching of the face, nose, and eyes can prevent the bacteria from entering the body.

  • Food preparations

Undercooked meat allows the bacteria to remain in the food. Ingesting such infected food can increase the risk of bacterial infection. Cooking at the right temperature kills the bacteria present in the meat. Also, store the food properly in a refrigerator. Clean the food, cooking utensils, and countertops to avoid bacteria.

  • Vaccinations

Vaccines can help develop the natural immune response against bacteria. It can drastically reduce the risk and extent of infection. Regular vaccinations are essential for both adults and children.

  • Distancing when ill

Social distancing can reduce the transmission risk. Also, avoid sharing personal items such as toothbrushes, combs, razors during the illness and recovery period to reduce the risk of fomite transmission.

  • Travel precautions

When travelling to other countries, always follow the health guidelines. Ensure to vaccinate before travelling and drink clean and potable water.

Diagnosis of bacterial infections

Diagnosis of bacterial infections largely depends on the patient history and lab testing. Exposure to bacterial reservoirs can give a definitive direction that needs further confirmation with tests to start the treatment.

Lab tests

CBC – complete blood count shows the white blood cell count in the body. White blood cells fight against the infection and destroy the bacteria. An increase in the cell count will appear in the CBC during bacterial infections.

Urine and stool samples will detect any bacterial presence or abnormalities. Throat swabs in case of respiratory infection will help detect bacterial infection. 

Other diagnostic tests

Imaging through X-ray, MRI, or CT scan can detect the location of the infective lesions. It can help comprehend the extent of infection.

A biopsy may be advisable in some cases. A small sample of the infected tissue is cultured to understand the type and characteristics of the bacteria causing infection. Additionally, the doctor may also advise for culture studies. A culture study can shed light on the susceptibility and resistance of the bacteria to various antibacterial agents. The study can help guide the future line of treatment.

Treatment of bacterial infections in the human body

The bacterial strain and characteristics dictate the treatment for these infectious diseases. Antibacterial agents (antibiotics) are the first line of treatment for managing bacterial infections. These agents target the bacterial cell structure while sparing the human host cells.

Some bacteria are susceptible to specific antibiotics. Knowledge of the infecting bacterial strain can help with the appropriate treatment. However, overuse of these antibiotics can result in the growth of resistant strains of the bacteria. It can make the bacteria more difficult to treat.


  1. What are the most diseases caused by bacteria in the human body?

Some of the most deadly diseases caused by bacteria in the human body include Tuberculosis, Anthrax, Tetanus, Pneumonia, Cholera.

  1. Who is at risk of developing a bacterial infection?

A weakened immune system can allow the bacteria to infiltrate, causing increased fatality risk and disease severity. Weak immunity is present in 

  • Someone undergoing immunosuppressant therapy
  • Underwent a surgery or medical procedure
  • A chronic disease affecting the organs
  • Already have an infectious disease such as AIDS
  • Elderly or children and infants
  • Under or malnourished individuals
  1. Which is the strongest antibiotic for bacterial infection?

Vancomycin is one of the strong antibiotics available for treating bacterial infections.

  1. How long does it take for antibiotics to work in bacterial infections?

Antibiotics typically require one to three days to act against the bacteria.

  1. Can bacterial infections recover without antibiotics?

A healthy immune system is often strong enough to fight against common bacterial infections. Severe bacterial infections may require antibiotic support of early and complete recovery.

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