Bacterial Infections

Bacteria are microscopic, single-celled organisms and are among the earliest forms of life on Earth¹. Thousands of bacterial species exist, and they live in almost every environment – air, water, soil, plants, animals and humans. Most bacteria are harmless or beneficial. For example, certain intestinal bacteria contribute to digestion and the production of important vitamins. Fewer than 1% of all bacteria are pathogenic, but those that are can cause serious conditions such as salmonellosis, pneumonia and meningitis².

Bacterial infections

Bacterial infections represent a global health challenge with major consequences for public health. Although bacterial infections are generally easier to treat than viral infections because of the wide range of antimicrobial agents available, the rapid development of antibiotic resistance is a serious threat with potentially catastrophic consequences³. The world's deadliest bacterial disease is tuberculosis, caused by Mycobacterium tuberculosis, which causes more than 1.7 million deaths annually. Around 13% of cases are resistant to most antibiotics, and 6% are considered nearly untreatable².

Bacterial Structure and Reproduction

Bacteria are prokaryotic organisms, and their genetic material is stored in a circular, double-stranded DNA structure. Many species also contain plasmids – small circular DNA units carrying additional information. Bacteria have ribosomes in the cytoplasm, a cell membrane and a complex cell wall (except Mycoplasma). Outside the cell wall, they may have capsules, flagella or pili. Reproduction usually occurs through binary fission, in which one cell divides into two. Under favorable conditions, bacteria can reproduce very rapidly, and some infections therefore require only a small number of organisms to cause severe disease.

Classification of Bacteria

Bacteria can be classified according to several criteria:

• Gram staining: Gram-positive and gram-negative bacteria are distinguished by differences in cell-wall structure using a method developed by Hans Christian Gram in 1882. Gram-negative bacteria have an outer membrane containing endotoxins that can cause tissue damage, circulatory failure and death. Gram-positive and gram-negative bacteria also respond differently to antibiotics, so treatment depends on the bacterial group involved.

• Oxygen requirements: Aerobic bacteria require oxygen to grow, while anaerobic bacteria thrive in oxygen-free environments³.

• Scientific nomenclature: Bacteria are named according to genus and species, for example Clostridium botulinum. Within a species, different strains may have genetic variations that affect how the bacterium responds to medications and vaccines.

• Shape: Bacteria have three main shapes: cocci (spherical), bacilli (rod-shaped) and spirochetes (spiral-shaped)¹.

Mechanisms of Disease

Different bacterial species target specific organs. For example, Neisseria meningitidis commonly infects the meninges but rarely causes skin infection.

Disease may result from:

• Direct cell destruction caused by the bacterium

• Immune response to the infection, which can itself damage the body. Severe bacterial infections may trigger a systemic inflammatory response syndrome (SIRS), which can progress to sepsis and organ failure. Once this cascade has been triggered, even the strongest antibiotics may be insufficient³.

Bacterial Defense MechanismsBacteria use several strategies to protect themselves:

• Capsule: An external protective layer that prevents phagocytosis by white blood cells in encapsulated bacteria.

• Outer membrane: Gram-negative bacteria have a membrane that protects against certain antibiotics and releases endotoxins when damaged.

• Spores: Dormant forms that tolerate extreme conditions. When the environment becomes favorable, they reactivate and reproduce.

• Flagella: Long structures that enable movement. Bacteria without flagella have limited motility.

• Antibiotic resistance: Some bacteria are naturally resistant, while others develop resistance through gene mutations or transfer of genes from other bacteria. Resistance genes can be passed to the next generation or transferred to other species¹.

The Deadliest Bacterial Infections

• Tuberculosis

• Anthrax

• Tetanus

• Leptospirosis

• Pneumonia

• Cholera

• Botulism

• Pseudomonas infection

• MRSA infection

• E. coli infection

• Meningitis

• Gonorrhea

• Plague (Yersinia pestis)

• Syphilis⁴

Prevention of Bacterial Infections

Preventive measures substantially reduce morbidity and mortality. This is especially important in the era of antibiotic resistance, where treatment options are becoming more limited. There are three main principles for controlling bacterial infections:

1. Eliminate or control the source of infection

2. Break the chain of transmission

3. Protect the individual from disease

Primary prevention (vaccination), secondary prevention (treatment to prevent symptoms) and tertiary prevention (treatment to prevent transmission) are all important approaches³.

An example of failed prevention occurred in China in 2019, when thousands were exposed to brucellosis after bacteria leaked from a pharmaceutical facility. The factory used expired disinfectants, and bacteria-containing aerosols spread by wind to nearby institutions. At least 181 people were infected before the outbreak was identified⁵.

Antibiotic Resistance

Antibiotic resistance is now one of the greatest threats to global health, food security and societal development⁶. It affects everyone regardless of age or place of residence. Although resistance can arise naturally, overuse and misuse of antibiotics in both human and veterinary medicine accelerate the problem.

A growing number of infections – including pneumonia, tuberculosis, gonorrhea and salmonellosis – are becoming more difficult to treat. Consequences include longer hospital stays, higher costs and increased mortality⁶.

Sources:

1. MSD manual Bacteria ;https://www.msdmanuals.com/home/infections/bacterial-infections-overview/overview-of-bacteria

2. World Atlas What's The Deadliest Bacterial Disease? :https://www.worldatlas.com/articles/what-s-the-deadliest-bacterial-disease.html

3. Doron S, Gorbach SL. Bacterial Infections: Overview. International Encyclopedia of Public Health. 2008:273.:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7149789/

4. "Top 14 Most Infectious and Deadliest Diseases Caused By Bacteria," in Bio Explorer, November 10, 2020, :https://www.bioexplorer.net/bacterial-diseases.html/

5. CNN world News Bacterial outbreak in China :https://edition.cnn.com/2020/09/17/asia/china-brucellosis-outbreak-intl-hnk/index.html

6. WHO Antibiotic resistance :https://www.who.int/en/news-room/fact-sheets/detail/antibiotic-resistance