Batterjee Medical College

Dr. Manal El Said Head of Microbiology Department Bacterial Introduction and Structure

Batterjee Medical College Medical microbiology deals with the study of microorganisms which are of medical importance and causing diseases in human beings. Microbiology Microbiology is the study of microorganisms, which are microscopic, unicellular, and cell-cluster organisms.

Batterjee Medical College Taxonomic Rank

Batterjee Medical College The agents of human infectious diseases belong to five major groups of organisms: 1-Bacteria : Prokaryote kingdom 2-Fungi : 3-Protozoa: 4-Helminths: Animal kingdom NB. Taken together, helminths and protozoa are commonly called parasites. 5-Viruses: they are not cells but can replicate only within cells Bacteria Compared with Other Microorganisms Protists kingdom

Batterjee Medical College Eukaryotes & Prokaryotes CharacteristicProkaryotic Bacterial Cells Eukaryotic DNA within a nuclear membraneNoYes Mitotic divisionNoYes DNA associated with histonesNoYes Chromosome numberOneMore than one Membrane-bound organelles, such as mitochondria and lysosomes NoYes Size of ribosome70S8OS Cell wall containing peptidoglycanYesNo Cells have evolved into two types: - Eukaryotic - Prokaryotic

Batterjee Medical College Bacteria have three shapes: - cocci (spheres) - bacilli (rods) - spirochetes (spirals) Cocci are arranged in three patterns: - Pairs (diplococci) - Chains (streptococci) - Clusters (staphylococci) The size of most bacteria ranges from 1 to 3 μm. Mycoplasma, smallest bacteria (smallest cells) are 0.2 μ m. Structure of Bacterial Cells Shape & Size

Batterjee Medical College All bacteria have a cell wall composed of peptidoglycan except Mycoplasma, which are surrounded only by a cell membrane. Gram-negative bacteria have a thin peptidoglycan covered by an outer lipid-containing membrane Gram-positive bacteria have a thick peptidoglycan & no outer membrane. These differences explain why: -Gram-negative bacteria lose the stain when exposed to a lipid solvent in the Gram stain process - Gram-positive bacteria retain the stain and remain purple. Structure of Bacterial Cells Bacterial Cell Wall

Batterjee Medical College It is found only in bacterial cells. It is a network that covers entire bacterium & gives organism its shape. It is composed of a sugar backbone (glycan) and peptide side chains (peptido). The side chains are cross-linked by transpeptidase (enzyme that is inhibited by penicillins & cephalosporins ) Peptidoglycan: Structure of Bacterial Cells The outer membrane of gram-negative bacteria

Batterjee Medical College Structure of Bacterial Cells Comparison of Cell Walls of Gram-Positive and Gram-Negative Bacteria

Batterjee Medical College Structure of Bacterial Cells Cell Walls of Acid-Fast Bacteria Mycobacteria are acid-fast because it resist decolorization with acid–alcohol after staining with carbolfuchsin. It is due to high concentration of lipids in cell wall. The dyes used in the Gram stain do not stain mycobacteria.

Batterjee Medical College The main inducer of septic shock. Endotoxin consists of: - lipid A fever & hypotension in septic shock - polysaccharide(O antigen) use in laboratory identification Endotoxin (lipopolysaccharide, LPS): It lies between inner cell membrane & outer membrane of gram-negative bacteria (It is the location of β –lactamases-the enzymes that degrade β - lactam antibiotics, such as penicillins and cephalosporins). Periplasmic space: Structure of Bacterial Cells The outer membrane of gram-negative bacteria

Batterjee Medical College It consists of phospholipid bilayer (without sterols) located just inside peptidoglycan. It regulates: - Active transport of nutrients into cell. - Secretion of toxins out of cell. Lysozymes They kill bacteria by cleaving glycan backbone of peptidoglycan. The cytoplasmic membrane of bacteria : Structure of Bacterial Cells The outer membrane of gram-negative bacteria

Batterjee Medical College Gram-positive bacteria stain purple, whereas gram-negative bacteria stain pink. Gram-positive bacteria has ability to retain crystal violet– iodine complex in presence of lipid solvent as alcohol. Gram-negative bacteria lose purple dye when treated with alcohol (have outer lipid-containing membrane & thin peptidoglycan) & become colorless & then stain pink when exposed to red dye such as safranin. Not all bacteria can be visualized using Gram stain. Structure of Bacterial Cells Gram stain

Batterjee Medical College Structure of Bacterial Cells Gram stain

Batterjee Medical College Structure of Bacterial Cells ZN stain

Batterjee Medical College They are small pieces of DNA that move between chromosomal DNA and plasmid DNA. They carry antibiotic-resistant genes. It consists of a single chromosome of circular DNA located in nucleoid. Plasmids Transposons They are extrachromosomal pieces of circular DNA that encode both exotoxins & enzymes antibiotic resistance Structure of Bacterial Cells Bacterial DNA The bacterial genome

Batterjee Medical College They are antiphagocytic, i.e., they limit ability of neutrophils to engulf bacteria. They are composed of polysaccharide (the polypeptide capsule of anthrax bacillus is exception). Capsules are antigens in several vaccines, such as pneumococcal vaccine. Antibodies against capsule neutralize antiphagocytic effect & allow bacteria to be engulfed by neutrophils. Opsonization is process by which antibodies enhance phagocytosis of bacteria. Capsules Structure of Bacterial Cells Structures External to the Cell Wall

Batterjee Medical College It is polysaccharide "slime layer" secreted by certain bacteria. It attaches bacteria firmly to: - Surface of human cells - Surface of catheters - Prosthetic heart valves & hip joints. The glycocalyx Structure of Bacterial Cells Structures External to the Cell Wall Pili They are filaments of protein that extend from bacterial surface & mediate attachment of bacteria to surface of human cells. A different kind of pilus, sex pilus, functions in conjugation.

Batterjee Medical College They are highly heat resistant & are not killed by many disinfectants. Boiling will not kill spores. They are formed by certain gram-positive rods, especially Bacillus & Clostridium species. They have a thick, keratinlike coat that allows them to survive for many years, especially in the soil. Spores are formed when nutrients are in short supply Spores germinate to form bacteria that can cause disease when nutrients are restored. They are metabolically inactive but contain DNA, ribosomes & other essential components. Spores Structure of Bacterial Cells Structures External to the Cell Wall

Batterjee Medical College Spores Structure of Bacterial Cells Structures External to the Cell Wall