Microbial Nutrition and Growth Ch 6 Microbial Nutrition and Growth

SLOs Define five terms used to express a microbe’s optimal growth temperature. Explain how microbes are classified on the basis of O2 needs. Identify 2 ways in which aerobes avoid damage by toxic forms of O2. Identify three important environmental factors (other than temperature and oxygen) with which microorganisms must cope. List and describe the five types of associations microbes can have with their hosts. Explain biofilms, describe their formation and their potential for causing infection. Summarize the steps of cell division used by most bacteria. Explain doubling time, and how it leads to exponential growth. Outline the 4 growth phases in a bacterial growth curve. Review some direct and indirect methods of measuring bacterial cell growth.

6.1 Microbial Nutrition Review 6.1 in the textbook on your own if necessary (pages 142-148). Compare it to what you have learned in BIO 30

6.2 Environmental Factors that Influence Microbes Temperature Gases pH Osmotic Pressure Other Organisms Microbial growth = increase in cell number, not cell size

1. Temperature Minimum, optimum, and maximum growth temperatures Five groups based on optimum growth temperature Psychrophiles Psychrotrophs Mesophiles Thermophiles Extreme thermophiles

2. Gases O2 and CO2 influence microbial growth As O2 enters cellular reactions, it is transformed into several toxic products Microbes fall into one of three categories: Those that use oxygen and detoxify it. Those that can neither use oxygen nor detoxify it. Those that do not use oxygen but can detoxify it.

Toxic Oxygen Products Superoxide ion (also known as superoxide anion) Hydrogen Peroxide Superoxide ion (also known as superoxide anion) Hydrogen Peroxide 2 ·

Oxygen Usage and Tolerance Patterns O2 requirements vary greatly Compare to Table 6.5

Capnophiles Aerobic bacteria that grow better in high ______ and low oxygen In human body, these conditions found in __________________ Examples: Campylobacter jejuni, N. meningitides, S. pneumonieae Use candle jar, CO2-generator packets, or CO2 incubators Candle jar

3. pH and 4. Osmotic Pressure Most bacteria, the so-called ______________ , grow best between pH 6.5 and 7.5. Some bacteria prefer a pH range 1 to 5. These are the __________________ What bacterium lives in the stomach? Some bacteria do well in hypertonic (?) environments: Obligate vs. facultative __________________ S. aureus can grow on NaCl media ranging from 0.1% to 20%.

What happens to a bacterium in a high salt environment if it is not salt tolerant?

5. Other Organisms Symbioses Microbes generally live in shared habitats. Major types of microbial associations: Symbioses Mutualism: Mutually beneficial relationship Commensalism: Commensal benefits, partner doesn’t (but is not harmed) Parasitism: Parasite benefits, host suffers. All microbes that cause disease.

Associations But Not Partnerships Antagonism: Members of a community compete Antibiosis: Production of inhibitory compounds such as antibiotics to inhibit or destroy another microbe in the same habitat In soil, mixed communities compete for space and food In gut, normal microbiota prevents transient potential pathogens to take hold Synergism: Benefits but not necessary for survival Participants cooperate to produce result that none of them could do alone E.g.: Mixed infections such as gum disease, dental caries, and some bloodstream infections

Biofilm: Epitome of Synergy Mixed communities attached to each other and to a surface. Formation of a biofilm: Attachment of planctonic bacteria (pioneer colonizers) to surface structures. Other microbes attach to those bacteria or a polymeric sugar or protein substance secreted by the microbial colonizers. Attached cells are stimulated to release chemicals as the cell population grows.

Cause of most nosocomial infections, i.e.: Indwelling catheters Bacteria communicate by chemicals via quorum sensing “The secret social lives of bacteria” TED talk by Bonnie Bassler Bacteria in biofilm behave differently and are sheltered from harmful factors (disinfectants etc.) Cause of most nosocomial infections, i.e.: Indwelling catheters Fig 6.7

Study of Bacterial Growth Binary fission – exponential grow Generation time – time required for a complete fission cycle (also known as doubling time) Ranges from 10 min (___________) to many days (_____________) Average 30 – 60 mins. Fig 6.8

Consider reproductive potential of E. coli! Type of curve? Compare to Fig 6.9

The Mathematics of Population Growth The size of a population can be calculated by the following equation: Nt = (Ni)2n Nt is the total number of cells in the population, t denotes “at some point in time” Ni represents the starting number of cells The exponent n denotes the generation number. 2n represents the number of cells in that generation.

Fig 6.11

Practical Importance of Growth Curve Chemostat Automatic growth chamber Admits steady stream of new nutrients Siphons off used media and old bacterial cells Stabilizes growth rate and cell number Used in research and industrial applications

Direct Count Methods: Viable Plate Count Fig 6.10 CFUs =__________________________

Additional Direct Counts Direct microscopic count: Counting chambers (slides) for microscope Fig 6.13 Coulter counter: electronically scans a fluid as it passes through a tiny pipette Flow cytometer: similar to Coulter counter, but can measure cell size and differentiate between live and dead cells Fig 6.14

Indirect Count: Spectrophotometry measures turbidity as an indicator of growth Compare to Fig 6.12 OD (Absorbance) is function of cell number

The End Inside the Clinic: Fever – To treat or not to treat? Case File: Wound Care Inside the Clinic: Fever – To treat or not to treat? Who will present? The End