Infectious Disease Flashcards
Shapes of Bacteria: rods
Bacillus
Salmonella tiphimurium
Bacillus anthracis
Shapes of bacteria: spheres
Coccus (sphere)
Ex: Streptococcus pneumoniae
Coccobacillus (between rod/sphere)
Ex: Yersinia pestis
Shapes of bacteria: others
Spirillum (rigid spirals)
Spirochete (undulating spirals)
Vibrio (comma shape)
Vibrio cholerae
Bacterial arrangements: cocci
Single
Diplococcus (pair)
Ex. Streptococcus pneumoniae, neisseria meningitidis
Streptococcus (chain)
Ex. Streptococcus pneumoniaeNeisseria meningitidis
Tetrad
Ex. Micrococcus luteus
Staphylococcus
Ex. Staphylococcus aureus
Bacterial staining
Gram-positive: stain blue
Gram-negative: stain red
Specialized stains:
Most useful is acid-fast stain
Bacterial Reproduction
Reproduce by binary fission
One circular chromosome per cell which doubles and the bacteria then splits to produce 2 bacteria
Bacteria: nucleoid
DNA has a large amount of DNA that must be packed into the bacteria’s small body without the presence of a nucleus
Some unknown protein helps to condense DNA w/in bacteria
Bacterial cytoskeleton
Have cytoskeletal components similar to eukaryotes and some unique proteins
MreB (homolog to actin) FtsZ (homolog to tubulin) Crescentin (Homolg to Intermediate filaments) MinD/ParA RhlB / RNase E
This is important for antimicrobial design (create a drug that target these structural proteins)
Bacterial exoskeleton
Normally referred to as the murein sacculus
Other names: peptidoglycan, cell wall, or rigid layer
Function:
Giant molecule that envelopes the bacteria and protects from stress
Importance:
Environment is generally hypertonic, without exoskeleton the cell will swell –> lysis
Common anti-microbial targets of bacterial exoskeleton
Murein synthesis (penicillin) Ribosomal proteins (gentamycin) DNA gyrase (ciprofloxacin)
Only bacteria that doesn’t have an exoskeleton
Mycoplasma:
Do not have necessary proteins to form the exoskeleton and are therefore amorphous
Gram-positive bacteria
Have a much thicker murein sacculus (stain gets trapped in this layer)
Contain specific polysaccharides in envelope
Teichoic acids polysaccharide:
covalently linked to the peptidoglycan layer or to the lipids of the cytoplasmic membrane
Difference between gram positive bacteria is based on the antigenicity of the teichoic acid **
Contain wall associated exoproteins:
Varies types
Function as a type-specific antigencity and virulence (important for host defense invasion)
Levels of bacterial classification
Morphology, Metabolism, Antigenicity, Genetics
Bacterial classification: Morphology
Staining: gram stain positive vs. negative
Then,
Shape: coccus, bacillus, spirillum, coccobacillus, spirochete, vibrio
Bacterial classification: Metabolism
Anaerobic (fermentation) vs. aerobic (Respiration)
Can be facultative or obligate
Specific nutrients (e.g. fermenter of specific carbohydrates)
Production of certain metabolic products (e.g. acid, alcohols)
Specific enzymes (e.g. catalase
Bacterial classification: Antigenicity
Use of antibodies that are particular to certain bacteria
Bacterial classification: Genetics
Most commonly we use ribosomal DNA to look for highly conserved sequences particular to a family or genus
Virulence factors
Genetic traits that enhance the ability of bacteria to cause disease
Pathogenicity island
Large chromosomal regions that contain sets of genes that encode for virulence factors
Possible outcomes of new exposure
Transient colonization & clearance
Permanent Colonization
Disease
Strict Pathogens
Virulent bacteria that promote their growth at the expense of their host
Ex: mycobacterium TB
Neisseria gonorrhoeae
Plasmodium spp. (Malaria)
Rabies virus
Opportunistic bacteria
an organism capable of infecting only when host defense are breached or compromised (some commensals are opportunistic)
Ex. Staph aureus
E. coli
Pseudomonas aeruginosa
Candida albicans
Commensal bacteria
Bacteria that does not harm nor benefit their host
Natural defense mechanisms for bacterial entry
skin, mucus, ciliated epithelium, and antibacterial secretions