lab 7 the effect of physical factors on microbial growth

HIGH TEMP- bactericidal (kills bacteria) what are two heat methods?

- dry heat (hot air oven- 2 hrs at 160-180 C): oxidation of cellular molecules & desiccating (drying) of bacteria. * used to sterilize material that could be damaged by moist heat (ex: corrosive metals) * require longer time and higher temp. it's less penerating than moist heat methods. - moist heat: denatures nucleic acids and enzymes in bacteria. Ex) boiling, pasteurization, and autoclaving. 1. Boiling- does not guarantee sterilization. kills vegetative cells but no spores. 2. Pasteurization- controls microbial growth in food like milk or fruit juices. * HOLDING method- low heat (63C) for 30 mins. Kills Escherichia coli, Mycobacterium tuberculosis, Salmonella species. * FLASH pasteurization (71.6 C for 15 sec) * ULTRA-HIGH temp (140 C for 3 sec) CAN STERILIZE w/ proper aseptic conditions. 3. AUTOCLAVE- use steam under pressure (15 lbs/in^2 of pressure) 121.5 C. STERILIZATION- kills all forms of life, viruses and spores. Ex) used in laboratory to sterilize glassware, growth media, hospital settings to sterilize bedding.

65 C (Determination of the Thermal Death Time) for 15 mins, 20 mins, 30 mins, and 0 min for control. E. coli- take 30 mins to kill S. aureus- 30 mins to kill M. roseus (is sensitive)- takes 15 mins to kill G. stearothermophilus (spores)- didn't die.

80 C (Determination of the Thermal Death Time) for 15 mins, 20 mins, 30 mins, and 0 min for control. Escherichia coli- 15 mins Staphylococcus aureus- 20 mins Micrococcus roseus- 15 mins Geobacillus stearothermophilus- 30 mins to kill ***At a higher temperature, the thermal death time was shorter.

Why would we need to expose the two bacteria to UV radiation for different amounts of time to achieve sterilization?

Because bacteria differ in their range of exposure since they are time dependent. Some are more resistant and can be exposed to UV light longer before there's significant damage. While others die fast from the exposure.

Bacteria are affected in diff ways by their physical environment. EFFECT of temp. Psychrophiles Mesophiles Thermophiles Hyperthermophiles

Psychrophile: thrives at very low temperatures (0º-25ºc) Mesophile: they grow at room temp but they thrive at 37 degrees celsius. Typically Pathogens and they can survive at room temp 25 degrees celsius and human body temp 37 degrees celsius. Thermophile: They are going to survive above 40 degrees celsius up to 80 degrees celsius. Thermophiles love heat so it's above human body temp up to 80 degrees celsius Hyperthermophile : thrives in extremely hot environments they can survive from 80 degrees celsius up to 110 degrees celsius and those are going to be Arkea

what bacteria survived drying conditions in our experiment?

Staphlyococcus aureus (endospores) and Mycobacterium phlei (acid fast-thick lipid layer prevents drying) both very resistant.

Serratia marcescens (sensitive)- more time under the UV light with lid off, significant decrease in bacteria growth. Bacillus subtilis (spores)- always a lot of growth but as it was exposed to UV lid off for a longer period of time, you can see less colonies than the beginning.

* Organisms have different sensitivity to UV light. --Serratia marcescens are very sensitive to UV light and mutation can occur quickly causing cell death. --Bacillus has endospores, therefore it needs to be exposed to UV light for an extended period of time to see any effect. Endospores are very resistant.

Effect of UV radiation

* damages DNA molecules (to prevent replication&transcription) by causing the formation of pyrimidine dimers- unnatural bonds between adjacent thymine and cytosine nucleotides. * have repair mechanism but UV can cause mutations. * long term exposure to UV light= cell death

Effect of temperature: 4 C (psychrophile), 25 C (room temperature), 37 C (tray), 55 C (thermophile). What bacterium is a psychrophile? What bacteria are mesophiles? room temp 25C to tray 37 C What bacterium is a thermophile? 55 C

*** inoculated small streak of four bacteria, then incubated them at 4 different temperatures. TESTS TO DETERMINE WHICH TEMPERATURES ARE APPROPIATE FOR THE GROWTH OF THESE SPECIES. psychrophile-Micrococcus roseus mesophiles- Escherichia coli and Serratia marcescens (changes in pigment at different temps: red) thermophile: Geobacillus stearothermophilus

What did we do for UV radiation experiment? What was the purpose of this experiment?

**We put Serratia mercescens and Bacillus subtilis in different conditions: UV lid off for 5 sec, 10 sec, 1 min, 10 mins. Also Visible Light- complete light, there's no UV (serves as a control in the absence of UV) Lid on- UV doesn't penetrate the lid (control) Has to be direct to work.

Effect of moisture what bacteria can survive on dry conditions?

- Transferred bacteria that's in broth with a swab and placed on the bottom of an empty tube (make sure not to transfer too much moisture) * endospores and when the cells finds itself a moist environment, it will germinate, turning into vegetative cells * other non-spore bacteria can persist in his environment based on cell wall properties & the amount of glycocalyx they produce.

Where is UV radiation used and what's the purpose of it.

* "used to control microbial growth" in operating rooms, sterile hoods, & areas when not in use b.c. it's damaging to our skin cells. ** the purpose was to determine the effect of UV light on two different bacterial species.

Temperature can control bacterial growth LOW TEMP- bacteriostatic (NOT permanent if temp increases) Low temps are commonly used to prevent what?

bacteriostatic- Inhibit bacterial growth and/or reduce the total # of bacteria. * Inhibit enzyme activity- biochemical reactions are slowed- rate of metabolizing & reproducing reduced. * Prevents food from spoiling (but can't be used to sterilize materials)

thermoduric what is thermoduric?

can survive short bursts of heat but will only grow at lower temperatures. **(endospores are because they are resistant to short bursts of heat)

Thermal Death Point

lowest temperature that is required to kill a population of microbes when applied for a specific time.

Autoclave experiment

one side was autoclaved, the other side was not. Geobacillus stearothermophilus used, * used to see if autoclave kills thermophile, endospores, and all forms of life. *Result: complete sterilization when autoclaved (no growth)

What is the purpose of the Thermal Death Time experiment?

to determine how much time it takes to kill the organism. -minimum time it takes to kill a population of microbes at a specific temperature.