What Are the Most Common Bacterial Infections in Humans?

A bacterial infection is the invasion and multiplication of bacteria in the body tissues causing damage and immune reactions [1]. The most common bacterial infections are:

• Cellulitis
• Pertussis
• Tuberculosis
• Pneumonia
• Impetigo
• Tetanus
• Chlamydia
• Meningitis
• Lyme Disease
• Otitis Media
• Erysipelas
• Botulism
• Boil
• Necrotising Fasciitis
• Staphylococcal Infections
• Carbuncle

1. What Are Bacteria?

Bacteria are unicellular microorganisms, and therefore, cannot be seen by the naked eye [2]. They are also known as prokaryotes and are found everywhere around us, including water, air, and soil.

They also inhabit the surface of the skin and are an important part of the gastrointestinal system.

Although bacteria can cause severe and tissue-damaging infections, not all bacteria are bad.

The best example of good bacteria is the microbiota or gut flora (microbiome) that are essential for the breakdown of food during digestion which provides essential nutrients for the body.

1.1. What Are the Types of Bacteria?

Bacteria are classified according to their shape, composition of their cell wall, mode of their nutrition, and their mode of respiration.

• Classification based on shape

Bacteria are classified as rod-shaped or bacillus (e.g., Escherichia Coli), sphere or coccus (e.g., streptococcus pneumoniae), spiral or spirilla (spirochete) such as Spirillum volutans, and comma-shaped or vibrio (e.g., Vibrio cholerae).

• Classification based on the composition of the cell wall

Bacteria are classified as Gram-positive (Peptidoglycan cell wall) and Gram-negative (Lipopolysaccharide cell wall).

• Classification based on nutrition mode

Autotrophic bacteria (Cyanobacteria) and heterotrophic bacteria (All disease-causing bacteria).

Autotrophic bacteria are bacteria that make their own food, while heterotrophic bacteria cannot make their own food and require food from their environment.

• Classification based on respiration mode

Bacteria are classified as aerobic which requires oxygen for survival (e.g., Mycobacterium), and anaerobic bacteria which do not require oxygen (e.g., Actinomyces).

1.2. How Does Bacteria Reproduce?

Each bacterium (single of bacteria) divides into two bacteria through a division process known as binary fission.

This process of multiplication is controlled by many factors including temperature and availability of nutrients (food).

2. Cellulitis

Cellulitis is a bacterial infection of the dermis and hypodermis layers of the skin by the bacteria streptococcus and Staphylococcus aureus.

Cellulitis manifests with localized pain, redness, and heat with potential complications such as abscess, inflammation of surrounding tissues, and sepsis.

The treatment of cellulitis involves antibiotics such as amoxicillin, cephalexin, or cloxacillin.

2. Pertussis

Pertussis or whooping cough is a bacterial infection of the lung and respiratory tubes by the bacteria Bordetella pertussis.

It manifests with symptoms such as runny nose, fever, vomiting, extreme fatigue, and coughing which become severe after weeks.

Although vaccines exist for this pertussis, antibiotics such as erythromycin, azithromycin, or clarithromycin are used for treatment.

3. Tuberculosis

Tuberculosis (TB) is a bacterial infection that mainly targets the lung (pulmonary tuberculosis) but can also affect another part of the body such as the neck, urogenital system, and central nervous system.

It is caused by Mycobacterium tuberculosis and manifests with symptoms such as fatigue, fever, sweating, chills, loss of appetite, chest pain.

Although vaccines exist for tuberculosis, treatment with multiple antibiotics is used for patients.

4. Pneumonia

Pneumonia is an infection of the alveoli of the lung by Streptococcus pneumoniae causing chest inflammation.

Alveoli are small air sacs found at the end of pulmonary airways and involved in gas exchange by providing oxygen to the blood and collecting carbon dioxide from the blood.

Bacterial infection is not the only cause of pneumonia as it can also be caused by viral infection.

Pneumonia manifests with symptoms such as fever, dry coughing, chest pain, difficulty breathing.

If the pneumonia is caused by a bacterial infection, antibiotics are used for treatment.

5. Impetigo

Impetigo is a bacterial infection of the skin dermis by Staphylococcus aureus or Streptococcus pyogenes.

Impetigo manifests with yellowish crusts on the face, arms, legs, and between the waist and neck. The lesions may be itchy and painful.

The treatment of impetigo involves topical (skin) application of antibiotics such as mupirocin.

6. Tetanus

Tetanus is an acute bacterial infection of the nervous system by Clostridium tetani found in soil, manure, dust, and saliva.

The most common symptoms are severe spasms, headache, fever, difficulty swallowing, tachycardia, and hypertension.

Spasms are caused by the effect of Clostridium tetani toxins on muscle contraction.

Although vaccines exist for tetanus, treatment involves tetanus antibodies to inactivate the toxins and antibiotics to target Clostridium tetani

7. Chlamydia

Chlamydia is a common sexually transmitted bacterial infection caused by Chlamydia trachomatis. Transmission can also happen during childbirth.

It manifests with urogenital symptoms such as vaginal discharge, penis discharge, and burning feeling when urinating.

If untreated it can lead to complications such as infertility, pelvic inflammation, or ectopic pregnancy.

Chlamydia is treated using antibiotics such as doxycycline or erythromycin.

8. Meningitis

Meningitis is the infection of the membranes covering the brain and spinal cord, known as meninges, causing inflammation.

Meningitis is mostly viral but can be bacterial caused by meningococcal bacteria such as Neisseria meningitis, pneumococcal bacteria such as Pneumococcus pneumoniae, Hemophilus influenzae type b (HIB) bacteria.

Meningitis caused by Listeria monocytogenes can be due to the consumption of foods that are not properly prepared.

Meningitis manifests with symptoms such as headache, fever, stiffness of the neck, vomiting, confusion, joint and muscle pain, seizures, feeling sleepy, and skin rash.

The treatment of bacterial meningitis involves antibiotics and corticosteroids.

9. Lyme Disease

Lyme disease is a bacterial infection caused by Borrelia burgdorferi which is transmitted to humans by infected ticks.

It manifests with redness of the site of the bite, headache, fever, and tiredness. Complications may include facial nerve paralysis and joint pain.

Although vaccines exist for Lyme disease, the treatment involves antibiotics such as doxycycline.

10. Otitis Media

Otitis media is an inflammation of the middle ear caused by a viral or bacterial infection with Staphylococcus aureus, Streptococcus pneumoniae, Hemophilus influenzae, or Moraxella catarrhalis [3].

It manifests with symptoms such as fever, ear pain, and loss of hearing.

The treatment of otitis media caused by bacterial infections involves antibiotics and pain relievers.

11. Erysipelas

Erysipelas is a bacterial infection of the skin upper dermis by Streptococcus pyogenes causing skin rash on the face and legs.

Erysipelas can also manifest with fever, fatigue, headaches, vomiting, and shivering.

The treatment also involves antibiotics such as erythromycin or penicillin.

12. Botulism

Botulism is a rare bacterial infection that affects the neurotransmission of acetylcholine by toxins produced by Clostridium botulinum.

Symptoms include muscle weakness, blurred vision, double vision, speech difficulty, difficulty swallowing, and breathing difficulties. If intreated respiratory failure may occur.

Treatment involves the use of botulinum antitoxin and intensive care to restore vital functions.

13. Boil

Boil or furuncle is a bacterial infection of the hair follicle by Staphylococcus aureus leading to hard and painful lumps on the skin that can develop an abscess.

Most of the time a boil goes away on its own and rarely leads to complications.

14. Necrotising Fasciitis

Necrotizing fasciitis or flesh-eating disease is a bacterial infection of the under skin soft tissue that surrounds organs and muscle by a mixture of bacteria such as gram-positive bacteria, gram-negative bacteria, clostridium bacteria, and Bacteroides.

It mostly develops from cuts or burns that affect the arms, legs, and perineum resulting in swelling, redness, intense pain, fever, diarrhea and vomiting, and dark blisters.

Treatments of Necrotising fasciitis involve surgery to remove the dead tissue or amputation and several antibiotics due to the different types of bacteria involved.

15. Carbuncle

Carbuncle is a bacterial infection of the back of the neck skin by Staphylococcus aureus or Streptococcus pyogenes resulting in a cluster of boils that causes fever and chills.

A carbuncle can lead to complications such as sepsis, osteomyelitis, and endocarditis.

16. Staphylococcal Infections

Staphylococcus infections are due to staphylococcus bacteria that can take advantage of cuts and bruises on the skin to invade different tissues and organs in the body.

Staphylococcus bacteria can cause skin diseases, asthma, rhinitis (nose tissue inflammation), sinusitis, gastroenteritis, sepsis, endocarditis (inflammation of the endocardium), and toxic shock syndrome.

Treatment of staphylococcal infections involves antibiotics and wound cleaning depending on the tissue or organ affected.

Conclusion

Although bacterial infections are efficiently treated with antibiotics, bacteria resistance to antibiotics is becoming an issue in the treatment of infections, and therefore, new anti-bacteria therapeutic agents are required to overcome this serious health problem.