Bacteria as Pathogens

General Properties of Bacteria

Bacteria are unicellular organisms.
They fall into three primary shapes: cocci (spherical), bacilli (rod-shaped), and spirochetes (spiral-shaped).
Some bacteria exist as individuals, others exist in chains or clusters.
Bacteria can survive in different environments due to their varied metabolic capabilities, some of them cause disease in humans and other organisms.

Pathogenic bacteria have physical or biochemical characteristics that enable them to penetrate host barriers and cause disease.
The pathogenicity of bacteria can be associated with their capacity to adhere to surfaces, invade tissues, and produce toxins.
Adherence can be facilitated by bacterial capsules, pili and fimbriae. Capsules also protect bacteria from host immune defenses.
Bacterial toxins are categorised into two groups: endotoxins and exotoxins. Endotoxins are released when bacteria die and break down. Exotoxins are toxins released by living bacteria.

Bacteria can enter the body through natural openings like the mouth or nose, or through wounds.
Once in the body, they may multiply rapidly, release toxins, and cause a range of infections, such as strep throat, urinary tract infections, and pneumonia.
The severity of bacterial infections depends on the virulence of the bacteria and the strength of the host’s immune response.

The human immune system is typically quite capable of fighting off bacterial infections.
The lymphatic system is particularly geared towards fighting bacteria, with lymphocytes producing antibodies while macrophages and neutrophils consume bacteria.
However, some bacteria have evolved mechanisms to avoid or resist these defenses.

Antibiotic resistance occurs when bacteria evolve in a way that enables them to survive in the presence of antibiotics.
Mechanisms of resistance include bacteria altering their own proteins, producing enzymes that destroy antibiotics, or developing ‘pumps’ to remove the antibiotic from the bacterial cell.
Misuse and overuse of antibiotics greatly contributes to the issue of antibiotic resistance.