Microbiology 1- Bacterial properties Flashcards
Describe some of the properties of bacteria
Bacteria are small and unicellular
They have no internal organelles (no chloroplasts, nucleus, ER, mitochondria)
Haploid
Some have flagella
What are the three forms of bacteria
Cocci- spherical
bacilli - rod
Spirilla- helical or spiral shape
Other than gram positive and gram negative what other types of bacteria exist
Most of the bacterial pathogens of humans are classified as Gram-positive or Gram-negative, but some notable exceptions include the mycoplasmas, chlamydiae, spirochetes and the mycobacteria.
How are bacteria classified
Although we organize bacterial pathogens into natural groups for discussion based on bacteriological criteria, rather than on the basis of affected organ, mode of transmission, or type of disease
Describe the gram stain
Gram stain: developed by a Danish physician in the late 1800s.
Distinguishes between two different kinds of bacterial cell walls.
Bacteria are stained with a violet dye and iodine, rinsed in alcohol, and then stained with a red dye.
Stain indicates whether or not you have Gram-negative or Gram-positive bacteria.
How do gram positive bacteria appear under the microscope
Peptidoglycan in cell wall retains dye.
High peptidoglycan = deep violet
How do gram negative bacteria appear under the microscope
Dye is lost from thinner peptidoglcan
The cells absorb counterstain making them appear pink.
Describe the structure of the cell wall in gram negative bacteria
Outer membrane
Peptidoglycan cell wall
Plasma membrane
Describe the structure of the outer membrane in gram negative bacteria
For the bacterium, the outer membrane is first and foremost a permeability barrier, but primarily due to its lipopolysaccharide content, it possesses many interesting and important characteristics of Gram-negative bacteria. The outer membrane is a lipid bilayer intercalated with proteins, superficially resembling the plasma membrane. The inner face of the outer membrane is composed of phospholipids similar to the phosphoglycerides that compose the plasma membrane. The outer face of the outer membrane may contain some phospholipid, but mainly it is formed by a different type of amphiphilic molecule which is composed of lipopolysaccharide (LPS). Outer membrane proteins usually traverse the membrane and in one case, anchor the outer membrane to the underlying peptidoglycan sheet.
Low techionic acid content.
What is the role of LPS
Bacterial lipopolysaccharides are toxic to animals. When injected in small amounts LPS or endotoxin activates macrophages to produce pyrogens, activates the complement cascade causing inflammation, and activates blood factors resulting in intravascular coagulation and hemorrhage. Endotoxins may play a role in infection by any Gram-negative bacterium. The toxic component of endotoxin (LPS) is Lipid A. The O-specific polysaccharide may provide ligands for bacterial attachment and confer some resistance to phagocytosis. Variation in the exact sugar content of the O polysaccharide (also referred to as the O antigen) accounts for multiple antigenic types (serotypes) among Gram-negative bacterial pathogens. Therefore. even though Lipid A is the toxic component in LPS, the polysaccharides nonetheless contribute to virulence of Gram-negative bacteria.
What can be done after gram staining
Culture and microscopy
Biochemical and serological tests
Sensitivities to antibiotics
DNA techniques: PCR, sequencing
Describe the difference in sensitivities to penicillin and lysozymes in gram positive and gram negative bacteria.
A few Gram-negative bacteria are sensitive to natural penicillins. Many Gram-negative bacteria are sensitive to some type of penicillin, especially semisynthetic penicillins. Gram-negative bacteria, including E. coli, can be made sensitive to natural penicillin by procedures that disrupt the permeability characteristics of the outer membrane.
(2) Gram-negative bacteria are sensitive to lysozyme if pretreated by some procedure that removes the outer membrane and exposes the peptidoglycan directly to the enzyme.
Are the vast majority of bacteria commensal or pathogenic
Commensal
List some gram positive pathogenic bacteria
Staphylococcus aureus (skin diseases, endocarditis, bacteraemia, joint diseases, pneumonia)
Streptococcus pneumoniae (pneumonia, meningitis, otitis media)
Streptococcus pyogenes (tonsilitis, necrotizing fasciitis, bacteremia, scarlet fever)List some gram negative phatogenic bacteria
Escherichia coli (EPEC - diarrhea, EHEC - produces toxin, dysentry and kidney failure)
Salmonella (typhimurium - food poisoning, typhi - typhoid)
Shigella (dysentery)
Vibrio cholerae (cholera)
Neisseria (meningitidis- meningitis, gonorrhoeae- gonorrhea)
