most bacteria are chemoorganotrophs

• carbon source: organic compounds
• energy source: redox rxns
• electron donors: organic compounds (glucose)

• water
  • reactant in metabolic processes
  • component of cytoplasm
• phosphate
  • ATP synthesis
  • phosphorylation
  • DNA/RNA
  • membrane phospholipids
• CO2
• mineral salts

what are the components of typical bacterial growth medium?

• [image]glucose
• ammonium chloride
• potassium phosphate (mono- and dibasic)
• magnesium sulfate
  
  • Mg2+ is a cofactor; essential ribosomal component
• ferric sulfate
• calcium chloride
  • among other things, Ca2+ in cell wall; endosome formation
• trace minerals

what are some key differences between bacterial and eukaryotic metabolism?

• increased diversity in types of metabolism that take place in bacteria (ie: types of substrates possible for growth...like sulfur, methane, etc)
• heavy dependence on fermentation reactions in bacteria
  • many pathogenic bacteria depend on fermentation vs oxidative phosphorylation for ATP synthesis

• molecular O2 absolutely required for growth
• energy via terminal respiration that involves cytochromes
• not many human pathogens, but DOES include:
  • PSEUDOMONAS
  • MYCOBACTERIA

• CANNOT grow in the presence of molecular O2
• require reducing conditions for growth
• energy from fermentation
• no hemoprotein enzymes

• no SOD (superoxide dismutase) to convert superoxide into molecular O2 + H202
• no catalase or peroxidase to convert H2O2 into water

both superoxide and hydrogen peroxide are TOXIC products that need to be eliminated

anaerobes may lack one or both of these enzymes

• grow under aerobic or anaerobic conditions
• cytochrome containing and so Pasteur effect is often observed
  
  • E.coli
  • staphylococci
• no functional respiratory system exhibiting oxidative phosphorylation (indifference to O2)
  • streptococci

the observation that some organisms switch between oxidative phosphorylation when in the presence of O2 and fermentation (when w/o O2) to synthesize ATP

• E. Coli
• Staphylococci

• requires or tolerates O2 only at concentrations lower than that found in air (<20%)
• example pathogen:
  • Neisseria meningitides
  • Neisseria gonorrhea (~5% oxygen)

what are the general methods of determining bacterial cell growth?

• cell mass
  • dry weight
  • turbidimetry (counting suspended cells with light beam)
• cell multiplication
  • counting chambers
  • viable cell count per ml of blood, urine, etc (other bodily fluid...)

a serial 10-fold dilution scheme used to determine number of bacteria in an unknown solution or culture flask (ie: CSF, blood, urine, bacterial culture, etc)

aiming for between 300 and 30 bacteria per plate; to obtain number in original sample, back track according to the number of dilutions...

on the bacterial growth phase, what does the lag phase represent?

the period of adjustment; the length of this phase is determined by the size and age of the starting inoculum and the generation (DOUBLING) time of the bacteria

on the bacterial growth phase, what does the exponential phase represent?

• period of balanced growth

• constant cell size

• exponential increase in bacterial numbers, cell organelles, and chemical constituents

reflects nature of the culture medium: in a minimum synthetic medium, the growth rate is relatively slow (slope would be smaller than that of bacteria growing in a more complex medium)

in a complex medium, bacteria are provided all essential nutrients needed for optimal growth, while in minimum synthetic medium, the bacteria have to synthesis most of what they need

what is a "shift up" vs a "shift down" on a bacterial growth curve?

• "shift up": when bacteria transferred from minimally required growth medium to complex growth medium

• "shift down": when bacteria transferred from a complex medium to a minimal medium

during exponential phase when cell components are being synthesized actively

what events are characterized by the slow growth phase?

one or both may occur in the stationary or "0 growth" phase:

decrease in the concentration of an essential nutrient

accumulation of toxic by-products of metabolism

use of a chemostat which removes toxic wastes and provides fresh culture medium

what pieces of information are necessary to calculate the generation time?

1. initial bacterial population (No)
2. final bacterial population (Nt)
3. time period of growth (T)

may be calculated as log base 2 or log base 10

they are inverses of each other

generation time (time/generation) is inverse of K (generations/time)

T = 1/K

what is knowing generation time essential when growing cultures?

it would be easy to discard a culture thinking that there is no bacteria present when it simply hasn't begun to grow to visible levels

ie: mycobacterium doubles in 18 hours, which is on the high end, while E.coli doubles in 20 mins, on the low end...very wide range of doubling times

how may bacteria be divided according to their temperature preference?

• thermophiles: high temps ~35-80 centigrade
• mesophiles: middling temps ~10-45 centigrade
  • majority of pathogenic bacteria grow between 30-45 centrigrade, covering human physiological temp range 
• pyschrophiles/cryophiles: capable of growth in cold temperatures
  
  • facultative: capable of growth but optimum closer to mesphile temp range
  • obligate: optimum is 15-18 centigrade, and killed above 20 centigrade

a tough dormant intracellular structure produced by gram positive bacteria (including, but not limited to: clostridium [tetanus; botulism] and bacillus[anthrax]); a thick internal wall that encloses DNA and cytoplasm

purpose: primary function of most endospores is to ensure the long-term survival of a bacterium through periods of environmental stress (can endure chemical, UV, lysozymes, temperature, starvation, etc)

• dipicolinic acid: used in cortex formation; enables refractility to high temperatures
• cysteine incorporation: during coat formation; enables chemical resistance

must increase the temperature to above 100 degrees centigrade by increasing the pressure to 15lbs (around 121 degrees centrigrade will kill spores)

must use autoclave or pressure cooker

*100 degrees centigrade will kill all bacteria but the spore formers*

how can you differentiate between bacteriocidal and bacteriostatic?

plot the log of cell count (viable cell number) over time

why does the plot of bacterial turbidity and viability differ in the presence of streptomycin?

the bacterial turbidity is a plateau while the viability shows a step drop in the presence of streptomycin

this difference in plots points to the mechanism of streptomycin's bacteriocidal action: it does not lyse the cell (which would show a decline in turbidity if it did) but rather it disrupts replication via inhibition of the ribosome (resulting in no cell number growth, or a decline in cell viability). so the turbidity can be flat with a bacteriocidal antibiotic; to tell how the antibiotic operates, you need to examine the log of viable cell plot