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. Microbial cell:

1. Glycocalyx: It is composed of carbohydrate coating and covers the eukaryotic cell as well as the  bacterial cell. On the microbial cell the presence of glycocalyx is associated with its ability to infect the host cell. It plays 2 roles:

• Protection- the presence of glycocalyx protect the bacteria against the immune cells such as phagocytes by increasing the effective size of the bacteria and also by concealing the recognition sites of the bacterium.This makes the bacteria difficult to engulf.
• Adhesion- With the help of biofilm (glycocalyx enclosed) the bacterial cell have the ability of attaching itself to the inert surfaces such as teeth  or tissues of the host cell and cause infection.

2. Bacterial cell wall: Generally the bacterial cell wall have an additional glycoprotein attached to the surface which is known as S-layer. This surface component contribute to the pathogenicity as the cell associated proteins adhesins are utilized by the pathogens (bacteria). It also protects the bacterium against the attack of complement system and phagocytes and also against enzymes.

3. Pili and fimbrae: These are short hair like structures present on the surface of the bacterial cell. It is involved in the attachment of the pathogen on the tissues and colonize and contribute to the bacterial virulence.

4. Flagella: The mucosal surfaces are the main sites of infections where the host and pathogens interact. These pathogenic bacteria produce flagella to promote the colonization and invasion of the mucosa . Here it is required for motility(chemotaxis), adhesion, invasion through secretion of virulence factors. The flagella's main motive is motility which combined with the chemotaxis helps in the targeting the mucosal tissues thus increasing the occurrence of host pathogen interaction and hence contributing to the pathogenicity.

5. Active transport: Gram negative bacteria consists of the drug efflux system which provides it resistance against the drugs or antimicrobial agent.Thus these system aid the virulence of the pathogen by  pumping the solutes out of the cells which includes toxins (drugs, antimicrobial agents or metabolites). Through this efflux system these microbes regulate their internal homeostasis.

6. Plasmids: These extra chromosomal material contains genes which contribute or encode for virulence factors (proteins). These virulence plasmids are responsible for the invasion of the pathogens in the host tissues. These plasmids are also involved in the regulation or survival within the host as they contain genes encoding for antibiotic resistance.

7. Ribosomes:

8. Endospores: The endospores are produced by the bacteria during stress to survive in unfavourable conditions, so these structures are very durable and can resist the conditions in the host's body. These endospores are also capable of secretion of toxins which can resut in host cell damage and also paly a role in the survival of the pathogen.

B. Host cell:

1. Plasma membrane: Pathogens infect the host cell by adhering to the cell membrane of the host cell through protei-protein interaction which is mediated by adhesins present on the bacterial surfaces. Another protein known as integrins are used by bacterias to interact with the host directly or indirectly through fibronectins (bridging molecule).

2. Cytoskeleton: During the pathogenic infection the microbe exploit the actin cytoskeleton of the host cell and thus invade the cell to colonize. They colonize between the infected tissues to prevent their uptake by pahgocytic cells. The disruption of the cytoskeleton also promotes the adherence of pathogens to the cell surfaces of the host.

4. Nucleus: The pathogenic proteins are capable of controlling or mimicking  the transcription factors or chromatin regulatory factors and thus hijack the host defences by directly interfering in the functions of the nucleus (transcription, chromatin remodelling, RNA splicing or DNA relication and repair).

5. Endocytosis: The pathogens enter the cell through endocytosis and may include the 3 mechanism shown: they may either escape the endosome or prevent the fusion with the lysosomes or survive in phagolysosome.