1-Biology of Microbes I

Biology of

MicroorganismsBy

Prof.Dr Nehal Yousef

Biology of Microorganisms Microbiology:Study of tiny living organisms of microscopic size

Medical Microbiology: Study the causative agents of infectious diseases of man

The response generated by man against infectious agents Methods of diagnosis Treatment and prevention

Prokaryotic and Eukaryotic Cells

Prokaryotes Eukaryotes

Cell structure Simple Complex

Cell wall Present except Mycoplasma Absent except Fungi & Algae Cytopl. membrane Sterols absent Sterols Present

Nucleus Primitive nucleus True nucleus

Nuclear membrane Absent Present

Nucleoli Absent Present

Mitochondria Absent Present

Chromosome Single Multiple

Ribosomes Sediment. Coeff. 70 S Sediment. Coeff. 80 S

Multiplication Binary fission Mitosis

Examples Bacteria, Rickettsia Fungi, Protozoa, Algae

Eukaryotic cell Prokaryotic cell

Gram +

Gram -

Cell wall

Cell (inner) membrane Outer membrane

Ribosomes

Rough endoplasmic reticulum

Mitochondria

Granule

(e.g. animal)

Cell wall

Nucleoid

Nucleus

Cell membrane

Capsule

Cytoplasm

Flagellum

Pili

Similarity between eu- and pro- karyotics

Medically Important Organisms * Bacteria : * Fungi *Viruses: *Prions:

Infectious proteins devoid of nucleic acid

.

Morphology of Bacteria

Size : 0.2-14 um

Shape : Spherical (cocci) Rod- shaped (bacilli) Curved rods Spiral (flexuous spiral) Variable in shape (pleomorphic)Arrangement: Pairs or diplos Tetrad Chains Grape-like clustres

Structure of Bacterial Cell

Chapter 4

Bacterial Structures Flagella Pili Capsule Cell Wall Plasma Membrane Mesosome Cytoplasm Nuclear material Inclusions Spores Ribosome

Cell structures Functions Cell wall Maintain the Shape , Protect the cell Responsible

for Gm stain reactionContain somatic O antigen. Responsible for endotoxic activity of Gm negative. Plays a role in cell division

Cell membrane Selective permeability, transport .Secretion& excretion of toxins

Nucleus Genetic information, Control Growth and Metabolism

Flagella Locomotion

Fimbria Plasmid

Attachment, conjugationExtrachromosomdouble stranded circular DNA molecule

Cell structures Functions ( Cont.) Ribosomes

Protein synthesisComposed of RNA and proteins.

Mesosomes

EnergyPlay a role in cell division (Origin of cross walls), Play a role in cell respiration (site of electron transport)

Capsule Anti- phagocytic

Spore Protection against unfavorable conditions.

Structure of Bacterial Cell1- Cell wall: Basal structure murine base. Outer most rigid structure. Surrounding the plasma membrane

a- in gram positive bacteria. Peptidoglycan (mucopeptide) - very thick. Teichoic acid (somatic O antigen)

b- in gram negative bacteria. Inner layer of peptidglycan - thin layer. Outer layer of lipopolysaccharides (LPS). The periplasmic space in between filled with gel

thick, dense peptidoglycan layer

preduced peptidoglycan layer coverd outer membrane,}

Gm +ve and Gm –ve cell wall

Bacteria

Growth And Metabolism

Growth Requirement Of Bacteria

* Growth of bacteria depends on: . adequate supply of food• Food is essential for : . Build up of protoplasm . Production of energy* Metabolic activities are brought about: . Various enzymes

* Enzyme activity is conditioned by: . Moisture . Temperature . pH

1- Bacterial Nutrition

1- Autotrophic bacteria:- Free living, non parasitic (No medical

importance)

- Utilize simple inorganic substances as: . CO2 as a source of carbon . Ammonium salts as a source of nitrogen

- Energy needed is obtained from: . Light . Oxidation of organic substances

Bacterial Nutrition (cont.)2-Heterotrophic bacteria: . Most bacteria of medical importance

. Require complex preformed organic substance . Obtained food from plant or animal source

. Live in or on animal body (parasitic bacteria)

. Many grow on simple media

. Some require complex organic material (Blood,serum)

ıı- Gaseous Requirements 1- Oxygen requirements: 4 groups a- Obligatory aerobes: Only grow in presence of free oxygen Energy system depends on O2 as H2 acceptor

b- Facultative anaerobes: Bacteria that grow in presence or absence of O2 Use O2 to generate energy by aerobic respiration

if present Use anaerobic respiration in absence of O2 c- Obligate Anaerobes: Grow only in complete absence of O2 In presence of O2, toxic molecules are produced (H2O2) Anaerobic bacteria lack enzymes that breakdown toxic molec.

d- Microaerophilic bacteria:Organisms grow best in presence of minimal

amount of O2

2- Carbon dioxide (CO2) requirement:

. Bacteria require CO2 minute quantities as in air

. Some require higher CO2 concentration (carboxyphilic)

e.g. Pathogenic Neisseria (5 % CO2) Brucella abortus (20 % CO2)

Physical Requirements Of Bacteria

1- Temperature requirements:

Temperature range Optimum temperature Mesophilic bacteria 18 – 42 °C 37 °C Psychrophilic bacteria 5 – 30 °C 15- 20 °C Thermophilic bacteria 25 – 80 °C 50- 60 °C

. Most medically important bacteria grow at 25-40 C (Mesophilic)

. Optimum growth at 37 °C . Non pathogenic bacteria grow at temperature lower than 20 °C Higher than 55 °C (Thermophilic bacteria)

2- Hydrogen ion concentration (pH): . Pathogenic bacteria grow at a narrow range of pH (7.2 - 7.6) . Few species require an alkaline pH (Vibrio cholerae, pH 8) . Some prefer an acid pH (Lactobacilli, pH 4)

Bacterial Growth Curve Lag phase: Logarithmic phase: Stationary phase: Decline phase

Bacterial Growth Curve Number of viable bacteria/ml calculated at regular time interval A growth curve (divided into 4 stages) is obtained

1- Lag phase: . Period from inoculation to beginning multiplication . No or little cell division occurs . Bacteria adapt to the new environment . Clinically corresponds to incub. peroid of disease

2- Logarithmic (Exponential ) phase: .Rapid cell division (most active phase) .Number of bacteria increase steadily . Clinically corresponds to clinical signs & symptoms of disease . This phase continues until: . Exhaustion of nutrients and/or accumulation of toxic waste prod.

Bacterial Growth Curve (CONT.)

3- Stationary phase: . Number of dying cells equals newly formed cells . Number of living bacteria remains constant . Total number of bacteria (living + dead) increases . Slow growth due to: . Nutrient depletion , waste product accumulation or pH change . Clinically corresponds to recovery stage of disease

Stationary

Log Decline

Lag cell number

4- Decline phase: Time in hours

. Number of living bacteria decreases steadily . Death rate exceeds multiplication rate . Exhaustion of nutrients and accumulation toxic products

Clinical Significance of Growth curve

Correlation of 4 stages of growth curve to stages of disease

Phases of growth curve Stages of disease In vitro In vivo

- lag phase Incubation period of disease

- Logarithmic & Stationary phase Clinical signs & symptoms

- Decline phase Recovery & convalescence

Bacterial Reproduction

* Bacterial cell division is a sexual

* Bacteria multiply by simple binary fission

* Start by duplication of chromosome

* Each copy attach to cytoplasmic membrane at mesozome

* Cytoplas. Membr. forms a transverse membr. growing inwards

* A new transverse cell wall grows inwards

* A complete transverse septum separate two daughter cells