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Introduction to Microbiology and infectious Disease (Bacterial genetic…
Introduction to Microbiology and infectious Disease
Bacterial genetic material transfer
transduction: bacterial DNA is packaged in phage particles and then transferred to new bacteria
lysogenic conversion: occurs when phage infection and lysogenic prophage integration changes the phenotype of a host bacterium
prophage carrying a gene encoding a virulence factor
conjugation: mediated by a transfer apparatus where a transient cytoplasmic bridge forms through which plasmid DNA can transfer from donor to recipient
transformation: mediated by naked DNA fragments through uptake and subsequent recombination
Mechanisms
antigenic variation: used by pathogens to vary the glycoproteins/components on the surface and attack host again
evasion of induction of the IFN-inducing pathways through viruses antagonism
bacteria
polysaccharide capsules is an anti-phagocytic virulence factor used for evasion of innate immunity
negative charge
concealment of cell wall ligands for recognition by the phagocyte
larger size
virulence factors
phenotypic traits allowing microbes to enter, survive, grow and cause damage in the host
encoded on chromosome, plasmids, or phages
Bacterial growth requirements
Temperature: most human pathogens are mesophiles
Oxygen level: where most human pathogens are facultative for oxygen so they can grow with or without oxygen
during the lag/log phase is where the bacteria experiences the state of maximal growth and constant division
log phase is the best phase to perform antibiotic susceptibility/resistance testing
Differences in gram and acid fast staining
Gram stain: thicker peptidoglycan cell wall of gram + cells blocks depolarization step
gram +: purple/blue because the initial wash doesn't wash out
gram -: should be pink because it does wash out
Acid fast stain: mycobacteria lack the outer membrane (Gram + feature) but have high lipid content in the cell wall, including mycelia acids
waxy cell wall prevents gram stain dye uptake which leads to gram-neutral blue status
acid-fast bacilli appear after the Ziehl- nelson staining as red