Question

Describe the correlation of the following cell structures or cellular processes with the establishment of microbial infections. Some of these may aid in the infection process, some of the host structures could be used by microbes to establish disease, and some of these could be used by the microbe to resist the immune system or antimicrobial chemotherapy.

A. Microbial Cell:

1) The Glycocalyx

2) Bacterial Cell Wall

3) Fimbriae and Pili

4) Flagella

5) Active transport (efflux pumps)

6) Plasmids

7) Ribosomes

8) Endospores

B. Host cell:

1) Plasma membrane

2) Cytoskeleton

3) Host ribosome

4) Nucleus

5) Endocytosis

Answer 1

A.

1) Glycocalyx helps the bacteria evade harmful phagocytes by creation of capsule. It also helps bacteria in attachment to host surface through biofilm formation. eg. Streptococcus pneumoniae attaches itself to lung cells via it's glycocalyx layer.

2) Cell wall components such as teichoic acids and O-specific polysaccharides can be used as adhesins by Gram-positive and Gram-negative bacteria, respectively [adhesins are used to attach or adhere to specific surfaces or tissues]. Other cell wall components can protect against phagocytic engulfment or digestion. Variations in the macromolecular structure of cell wall components is the basis of host resistance to pathogens.

3) Pili or fimbriae are often involved in adherence (attachment) of bacterial cells to surfaces. They allow pathogens to attach to tissues and, sometimes, to resist attack by phagocytic cells. eg. Neisseria gonorrhoeae utilizes its fimbriae in order to initially colonize the urethral or cervical epithelium.

4) For few pathogens, motility is a prerquisite for virulence and flagella provides motility to bacteria. In the case of Vibrio cholerae, the vibrios apparently swim (laterally) by the help of flagella into the intestinal mucosa to avoid being flushed out by the peristaltic action of the gut wall.

5) Active transport(efflux pumps) actively flush antibiotic molecules out of the bacterial cell.

6) Plasmids often contain genes that provide selective advantage to the bacteria. eg. genes for antibiotic resistance. They can help in increasing the pathogenic potential of bacteria.

7) Ribosomes are involved in protein synthesis and bacteria secrete different proteins that help to protect them from host immune response as well as help in making surfaces suitable for attachment.

8) Endospores are intracellular bacterial structures that are later released as free endospores. Endospores are highly resistant to environmental stresses. They are a survival mechanism of bacteria and under appropriate environmental conditions, they germinate back into vegetative cells. Endospores are formed mainly by two genera of bacteria: Bacillus and Clostridium. Both genera contain pathogens, and the endospores produced by these bacteria invariably play some role in the toxicity, transmission or survival of the pathogen.