Question

Compare and contrast pathogenesis between bacteria with its human (Eukaryotic) host and bacteriaphage with its bacterial host. How are their processes similar in terms of the infection process? How are they different? How do they choose their hosts? How could or do these relationships change over time?

Answer 1

Bacteria can cause different infection and this capacity of a bacterium to cause disease is called its pathogenicity. Bacteria multiplies in the tissue fluid rather to cause disease. Bacteria like Rickettsia sp.can grow only in eukaryotic cells whereas others invade cells but do not require host for growth, eg. Salmonella sp. Virulence is the measure of the pathogenicity of an organism and it helps the bacteria in different ways. Virulence factors help bacteria to enter the host, cause diseases and evade host differences. Some of the virulence factors are Adherence Factors, Invasion Factors, Capsules, endotoxins and exotoxins. Infection is the entering of microorganisms into the host tissue. The degree of virulence depends on the ability of the organism to cause disease and it is affected by  numerous variables such as the number of infecting bacteria, route of entry into the body, specific and nonspecific host defense mechanisms, and virulence factors of the bacterium. Pathogenesis is the mechanism of both infection and disease develops. Bacterial infections are susceptible to host and increased amounts of specific antibodies or T cells are formed in response to invading bacterial pathogens, and defend the host against the microbes with the mechanism of host resistance. Bacteria which enter eukaryotic host have specialized mechanisms to protect themselves from the effects of the lysosomal enzymes encountered within the cell. Bacteria have cell wall adhesive proteins which can attach to different host cell receptor.

Bacterial virulence factors may be encoded on chromosomal, plasmid, transposon, or temperate bacteriophage DNA; virulence factor genes on transposons or temperate bacteriophage DNA may integrate into the bacterial chromosome.

On the other hand, Bacteriophage are the viruses that infect bacteria. Two groups of phages are found i.e. the somatic coliphage, which infect E coli host strains through cell wall receptors, and the F-specific RNA coliphage, which infect strains E. coli and related bacteria through conjugation tubes. A phage consist of a head and a tail held together by a connector, but cubic, spindle, filamentous or pleomorphic are also found. Bacteriophages has two major cycles of viral reproduction (i) the lytic cycle consists of infection, replication and lysis of their bacterial hosts and (ii) the lysogenic cycle consists of integration of the bacteriophage genome. This genome is a called a prophage.  Lytic or virulent phages redirect the host metabolism toward the production of new phages which are released as the host cell lyses. Phages nucleic acid material of the temperate or lysogenic phage remains dormant within the host and prophage are replicated along with the host until the lytic cycle is induced.  Virulence factors are often produced during lysogeny, when most phage-encoded genes are not efficiently transcribed. Many phage-encoded virulence genes are located near the attachment sites of their respective phages and, many phage-encoded virulence genes are regulated by chromosome-encoded transcription factors. Bacteriophages involved in  bacterial pathogenesis- including adhesion and invasion, evasion of immunity, and exotoxin production.