Transcript Temperature - IS MU - Masaryk University

Institute for Microbiology, Medical Faculty of Masaryk University
and St. Anna Faculty Hospital, Brno
MUDr. Lenka Černohorská, Ph.D.
Microbes and their
environment
Lecture for 2nd-year students
March 13th, 2010
Environmental factors
1.
2.
3.
4.
5.
6.
7.
8.
water
nutrients
temperature
osmotic pressure
pH
redox potential
radiation
toxic substances
1. Water
80 % of bacterial cell weight. 15 % of spore live
weight
Hygrophile organisms (most of bacteria):
require freely accessible water
Resistance to drying
• Low: gonococci
• More resistant: skin flora – staphylococci,
acidoresistant (mycobacteria)
• Resistant: actinomycetes, moulds, parasite cysts,
helminth eggs
• Highly resistant: bacterial spores
Water availability
Degree of water availability = water activity of the
environment (aw)
aw of pure water = 1,0
aw is inversely related to osmotic pressure (higher
osmotic pressure, the lower aw)
aw levels tolerated by different microbes:
G– bacteria
G+ bacteria‚ most of yeasts
moulds and yeasts
aw ≥ 0,95 (meat)
aw ≥ 0,9 (ham)
aw ≥ 0,6 (chocolate)
Lowering of water activity is useful for food conservation
•
•
•
•
drying – meat, mushrooms, fruit
concentration – preparing jam
salting – meat, fish, butter
adding sugar – syrup, jam, candied fruit
2. Nutrients
• Most microbes do not grow in pure water
• The problem lies in keeping the water pure
• In distilled water Pseudomonas aeruginosa
multiply
• In shower outlets: Legionella pneumophila
More about nutrients in previous + practical
lectures (liquid, solid media…)
3. Temperature
Minimum – sometimes <0 °C
Optimum – psychrophiles: 0 – 20 °C
mesophiles: 20 – 45 °C
thermophiles: 45 – 80 °C
hyperthermophiles: >80 °C
Maximum – sometimes
>110 °C
Growth temperature range:
narrow (gonococci 30 – 38,5 °C)
wide (salmonellae 8 – 42 °C)
Impact of the temperature on
bacterial growth
ex. is theoretical
bacteria do
not grow, but
growth interval
can alive
12
lower killing
temperature
32
bacteria do not
grow, but alive
35-37,5 39
growth optimum
growth minimum
growth maximum
60°C
upper killing
temperature
Impact of cold
• Cold shock: gonococci on cold media from
refrigerator die
• Low minimum growth temperature: 5 °C
survive yersiniae, listeriae
• Slow ordinary freezing and repeated thawing
damages microbes
• Lyofilization – dry and freeze quickly – is used
for longterm storage
Impact of higher temperature
Higher temperature → shock and
gradual killing of cells. Number of
killed cells depends on the duration
of higher temperature
Relation between the number of surviving cells
and the duration of temperature effect is
logarithmic one
Time needed for killing the whole population
depends on the original number of microbes
Temperature – important
parameters I
Relation between the duration of heating
and the number of surviving microbes
log10 number of
surviving
microbes
6
5
4
3
2
1
D = decimal reduction time =
= time required to reduce the
number of microbes to 1/10 =
= time required to kill 90 % of
the microbes
D
1
2
3
4
5
6
(min)
Temperature – important
parameters II
Thermal death point = the lowest temperature
at which a microbe is killed in a certain time
(cca 10 minutes). It depends on the kind of
microbe,on its conditions, number and the
effect of environment
Thermal death time = the shortest time to kill
the given number of microbes. For most
bacteria - 10-15 min at 60-65 °C
4. Osmotic pressure (OP)
Hypotonicity – protection by the cell wall
Hypertonicity – mostly harmful (salting meat,
candying fruits)
high OP is tolerated by: Halophiles
• halotolerant: enterococci, staphylococci
• obligate: halophilic vibrios
moulds tolerate contents of saccharose (jam)
5. pH
Neutrophiles: growth optimum pH 6 - 8
Alcalophiles: Vibrio cholerae (pH 7,4 – 9,6)
alcalotolerant: Proteus (splits urea)
Enterococcus (large pH range 4,8 – 11)
Acidophiles:
facultative: yeasts, lactobacilli (>3),
coxiellae (low pH in a phagosome)
obligate: Thiobacillus thiooxidans (pH <1)
6.Redox potential (rH)
depends on the composition of environment and atmosphere
Aerobes – rH>200 mV. Strict aerobes1 require oxygen to grow
Anaerobes – rH≤0 mV. Strict anaerobes2 cannot grow in the presence of
oxygen. In nature as well as in our body prosper owing to the
cooperation with aerobes and facultative anaerobes. Anaerobes in our
body: large intestine (99 % of intestinal microorganisms)‚ vagina‚ oral
cavity (sulci gingivales)
Facultative anaerobes3 – can grow in both environments
Microaerophiles4 - grow best at a low oxygen concentration
Capnophiles5 – grow best at CO2 enriched atmosphere
co2
1
2
3
4
5
7. Radiation
UV radiation (max. at 260 nm)
• In nature: airborne bacteria are protected by
pigments
• Artificially: is used for surface or air disinfecting and
for destroying traces of DNA in PCR laboratories
Ionizing radiation (X rays‚ gamma rays)
For sterilization of disposable syringes, infusion sets,
sutures, tissue grafts…
!Very resistant: bacterial spores
8. Toxic substances
• The impact increases with concentration and
c
duration of action
t
• Resistance of different types of microbes
against various toxic substances differs
!!G- bacteria are more resistant than G+ ones
Sterilization x disinfection
Sterilization = removing all microorganisms
from objects/environment
Disinfection = removing agents of infection
from objects/environment/a bodily surface
Disinfection interrupts the spread of infection
Types of disinfectants
1.
2.
3.
4.
5.
6.
7.
8.
9.
Oxidizing agents
Halogens
Alkylating agents (aldehydes)
Cyclic substances (phenols)
Acids and alkali
Heavy-metal derivatives
Alcohols
Surface-active agents (QACs)
Others (more in practise…)
Thank you for your attention