Understanding bacterial pathogenicity: a closer look at the journey of harmful microbes

Abstract

Bacteria are the most prevalent form of microorganisms and are classified into two categories based on their mode of existence: intracellular and extracellular. While most bacteria are beneficial to human health, others are pathogenic and can cause mild to severe infections. These bacteria use various mechanisms to evade host immunity and cause diseases in humans. The susceptibility of a host to bacterial infection depends on the effectiveness of the immune system, overall health, and genetic factors. Malnutrition, chronic illnesses, and age-related vulnerabilities are the additional confounders to disease severity phenotypes. The impact of bacterial pathogens on public health includes the transmission of these pathogens from healthcare facilities, which contributes to increased morbidity and mortality. To identify the most significant threats to public health, it is crucial to understand the global burden of common bacterial pathogens and their pathogenicity. This knowledge is required to improve immunization rates, improve the effectiveness of vaccines, and consider the impact of antimicrobial resistance when assessing the situation. Many bacteria have developed antimicrobial resistance, which has significant implications for infectious diseases and favors the survival of resilient microorganisms. This review emphasizes the significance of understanding the bacterial pathogens that cause this health threat on a global scale.

Keywords: AMR; bacteria; disease severity; host susceptibility; immune response.

Figure 1

Basic structure of bacteria and their associated environmental reservoirs. Bacteria possess a simple body structure without a true nucleus or membrane-bound organelles. Their basic structure comprises the cell wall, which offers structural support and protection, and the plasma membrane, which surrounds the cytoplasm and distinguishes it from the external environment. In addition, some bacteria possess a protective outer layer known as the capsule, which aids them in evading the host's immune system. Bacteria are commonly found in various environments, such as animals, food, humans, air, water, soil, and plants.

Figure 2

Bacterial classification based on Gram staining and lifestyle. It provides insights into their structural characteristics and interactions with host environments.

Figure 3

Steps of bacterial pathogenesis: (1) Bacterial exposure to host through air, food, infected person, and environment, (2) Colonization of the bacteria inside host within specific organs, tissues, and cells, (3) Evasion of immune response through diverse strategies, and (4) generating negative impact on host by causing infection.

Figure 4

Host factors affecting the growth and pathogenesis of bacteria. The disease outcome is heavily influenced by the interactions between the host and the microbes. This interaction can be determined by several factors, such as the host's immune system, genetic makeup, age, natural microbiota, co-existing asymptomatic infections, pathogen virulence, and antimicrobial resistance.

Figure 5

Consequences of bacterial infection. (1) Bacterial elimination by host cell, (2) Partial digestion of bacteria, and (3) bacterial escape and survival.