Chapter 2 Physiology of

Bacteria

Section 1 and section 2(study by yourself)

Ⅳ.the bacterial metabolic products of biosynthesis(p31)

A.pyrogen:It is polysaccharide in nature ,resistant to high heat even at 120℃/20min ， usually use distill

B.Exotoxin:secrete toxic subtance

C.Endotoxin: G-,toxic component from the cell wall

D.Pigments:

E.antibiotic:A few of bacteria produce some bactericidal or bacteristasis substances that are known as antibiotics

F.Bacteriocin

G.Vitamin

Section3 Bacterial growth and multiplication

Bacteria replicate by binary fission and undergo exponential growth

Number of cells 1 2 4 8 16Exponential 20 21 22 23 24

Definitions: Binary fission: process in which one bacterium splits into two

cells.

Generation time: The time it takes a population of bacteria

to double in number.

Requirements for bacterial growth

Nutritional requirements

Water

Carbon source: CO2, glucose, sucrose, etc.

Nitrogen source: N2, nitrates, ammonia, etc

Inorganic salts: S, P, K, Mg, Ca, etc.

Growth factors: organic compounds that a cell must have for growth but cannot synthesize itself.

pH

1. Many bacteria grow best at neutral pH.

2. Some specialized bacteria can survive and even grow in acid or alkaline conditions.

TemperatureTemperature

Bacteria may grow at a variety of temperatures fromclose to freezing (pyschrophile) to near to the boilingpoint of water (thermophiles).

Mesophiles: grow best at human body temperature(includes all human pathogens and opportunists)

Requirements for bacterial growth

Gas requirementsOxygen (O2)

Obligate aerobes: organisms that grow only in the presence of

oxygen.Microaerophiles: organisms that require a low concentration of

oxygen (about 4%) for growth, but higher concentrations are inhibitory.

meningitides

Obligate anaerobes: organisms that grow only in the absence of

oxygen and, in fact, are often inhibited or killed by its presence.

Facultative anaerobes: organisms that grow with or without oxygen,

but generally better with oxygen.

Carbon dioxide (CO2): e.g., Neissria

Measuring bacterial mass in liquid cultures.

Common methods include:

Turbidity

1. The cloudiness of a liquid culture of bacteria.

2. A measure of total bacteria [live and dead].

3. This is usually quantitated with a spectrophotometer.

Determination of the number of viable bacteria in a culture.Usually assessed by counting the number of colonies that grow after streaking a known volume on a plate ("plate counting" of colony forming units).

Bacterial growth-Standard growth curve Lag phase: The number does not increase; Metabolism is active;Lasts for a few minutes to several hours.

Exponential phase / log (logarithmic) phaseDivide at their most rapid rate;

Size, shapes, biochemical activation, and sensitivity to antimicrobial agents of

bacteria are typical.

Lasts for 8-18hrs

Bacterial growth-Standard growth curve

Stationary phaseThe number of live cells is constant.Spores, exotoxins, and antibiotics are produced.

Decline phaseThe number of live cells decreases.

Media for laboratory studies

Basal mediumEnriched mediunSynthetic mediumDifferential mediumSelective mediumAnaerobic medium

Media for laboratory studies

Liquid medium

solid medium

semi-solid medium

triangular flask

inoculating loopalcohol lamp

Blood Agar PlateBlood Agar Plate

Some question

What is the growth curve?why?

The enviromental factors effecting growth include?