CLASSIFICATION & STRUCTURE OF BACTERIA Assistant Professor Microbiology

OBJECTIVES Classify Bacteria Identify Unicellular nature of Bacterial cell Review selective toxicity of antimicrobials

CLASSIFICATION OF BACTERIA Nomenclature Binomial Linnean System Genus species Italicize Example Escherichia coli Used for bacteria, fungi and parasites Not used for viruses(single name e.g. Poliovirus)

CLASSIFICATION OF BACTERIA Criteria for classification Growth requirement O2 requirements e.g. Aerobe, Anaerobe, Facultative anaerobe, Strict anaerobe, Strict aerobe CO2 requirements e.g. Carboxyphilic Salt requirements e.g. Halophilics (Salt loving) Microscopy Gram staining e.g. Gram Pos & Gram Neg due to cell wall differences

CLASSIFICATION OF BACTERIA Biochemical Reactions Oxidase test, Catalase test Serology Strep pyogenes –Rheumatic fever nephritogenic strain, M types 2, 42, 49, 56, 57, and 60 DNA-DNA Similarity Ribosomal RNA analysis

CLASSIFICATION OF BACTERIA Bergey's Manual of Systematic Bacteriology Classification of medically imp bacteria based upon criteria like Gram reaction, motility, cell structure, etc

CLASSIFICATION OF BACTERIA I. Gram-negative eubacteria that have cell walls Group 1: The spirochetes Treponema, Borrelia, Leptospira Group 2: Aerobic/microaerophilic, motile helical/vibroid gram-negative bacteria Campylobacter , Helicobacter, Spirillum, Group 4: Gram-negative aerobic/microaerophilic rods and cocci Bordetella, Brucella, Legionella, Neisseria, Pseudomonas Group 5: Facultatively anaerobic gram-negative rods Escherichia (and related coliform bacteria) Klebsiella, Proteus, Salmonella, Shigella, Vibrio Group 6: Gram-negative, anaerobic, straight, curved, and helical rods Bacteroides, Fusobacterium Group 9: The rickettsiae and chlamydiae Rickettsia, Coxiella, Chlamydia

CLASSIFICATION OF BACTERIA II. Gram-positive bacteria that have cell walls Group 17: Gram-positive cocci Enterococcus, Staphylococcus, Streptococcus Group 18: Endospore-forming gram-positive rods and cocci Bacillus,Clostridium Group 19: Regular, nonsporing gram-positive rods Listeria Group 20: Irregular, nonsporing gram-positive rods Actinomyces, Corynebacterium Group 21: The mycobacteria Mycobacterium Group 22–29: Actinomycetes Nocardia III. Cell wall-less eubacteria: The mycoplasmas or mollicutes Group 30: Mycoplasmas Mycoplasma, Ureaplasma

STRUCTURE OF BACTERIAL CELL Shape, Arrangement, Color & Size Three basic shapes- Cocci (round), Bacilli (rod), Spirochetes (spiral) Pleomorphism Shape due to cell wall Arrangement is due to orientation at cell division Pairs-Diplococci Chains-Streptococci Clusters-Staphylococci

STRUCTURE OF BACTERIAL CELL Shape, Arrangement, Color & Size Color-Gram Staining gives purple or red color to bacteria Staining reaction-cell wall differences Size-0.2 to 5µ Clinical importance Above parameters help us identify certain bacteria

BASIC STRUCTURE OF PROKARYOTE

Unicellular nature of Bacterial cell Prokaryotic cell is a unicellular structure It has nucleoid, cytoplasm and outer covering called Cell envelop Prokaryotic cell lacks nuclear membrane- DNA is present loosely in area called Nucleoid Cytoplasm contains ribosome- smaller size 70S with 30S & 50Ssubunits Insoluble granules stores-e.g. metachromatic granules of Corynaebacterium diphtheriae Metachromatic granules

CELL ENVELOPE Structure that surrounds the cytoplasm of bacteria In Gram positive, two components:- Cytoplasmic membrane Thick peptidoglycan layer (Cell wall) In Gram negative, three components:- Cytoplasmic membrane (Also called Inner membrane) Thin peptidoglycan layer Outer membrane Gram + cell envelope

CELL ENVELOPE IN GRAM +ve AND GRAM –ve BACTERIA

BACTERIAL CELL STRUCTURE Teichoic Acid Outer layer of Gram +ve bacteria Can induce septic shock like Endotoxin of Gram –ve Attach Staphylococci to mucosal surface

BACTERIAL CELL STRUCTURE LIPOPOLYSACCHARIDE LPS of outer membrane of Gram –ve is Endotoxin Produce hypotension, fever, shock Three components Lipid A is toxic component Core polysaccharide of 5 sugars Outer polysaccharide of up to 25 sugar- O somatic Ag

BACTERIAL CELL STRUCTURE Outside Cell Wall Capsule Layer covering entire bacterium Polysaccharide except Bacillus anthracis-polypeptide capsule Determine sero-type e.g. Strep pneumoniae 84 serotypes Virulence factor- Negative charge resist phagocytosis. Bacteria that lose capsule-become avirulent

BACTERIAL CELL STRUCTURE Outside Cell Wall Pili (Fimbrae) Hair-like filament extend from cell surface Mainly in Gram –ve Two functions Attachment of bacterium to specific receptor in human tissue (Mutant Ns lose pili-avirulent) Sex pili form attachment during conjugation

BACTERIAL CELL STRUCTURE Outside Cell Wall Flagella Long whip-like appendage-motility Subunit-flagellin Energy provided by ATP Spirochetes have flagellum like-axial filament Importance for two reasons UTI causing bacteria move up in bladder Lab identification using anti-sera e.g. Salmonella

BACTERIAL CELL STRUCTURE Outside Cell Wall Glycocalyx (Slime Layer) polysaccharide coating allows the bacteria to adhere firmly to various structures e.g. skin, heart valves, and catheters Pseudomonas aeruginosa- cystic fibrosis Staphylococcus epidermidis- endocarditis Streptococcus mutans-dental plaque and caries

BACTERIAL CELL STRUCTURE Spores Highly resistant structures In response to adverse conditions Sporulation occurs when sources of carbon and nitrogen are depleted Inside the cell bacterial DNA, a small amount of cytoplasm, cell membrane, peptidoglycan, very little water a thick, keratin-like coat -dipicolinic acid

Selective toxicity of antimicrobials Antimicrobials used with aim to target structures and functions of bacteria not present in Eukaryote human cells Cell Wall Ribosome Metabolic pathways

Selective toxicity of antimicrobials Penicillin target the Cell wall not present in Eukaryote cells Tetracyclin, Macrolides target 30S & 50S subunits of ribosome Co-trimoxazole attacks Folic acid synthesis pathway unique to Bacteria Quinolones inhibit Topoisomerase IV enzyme of bacteria

MCQs GEN BACTERIOLOGY You have isolated a cell with a peptidoglycan cell wall. What other structure can you safely assume the cell has?     a mitochondrion   a Nuclear membrane a plasma membrane   a nucleus Ans: c

MCQs GEN BACTERIOLOGY A young boy is suffering from acute pharyngitis. You perform a throat swab and isolate a Gram positive cocci β- hemolytic colonies on blood agar. This bacterium protects itself from osmotic lysis by which of following structures? Cell membrane Peptidoglycan layer Hydrolytic enzymes Ribosomes DNA Ans: B

MCQs GEN BACTERIOLOGY All of the following are found in the cell walls of Gram positive bacteria except:     Lipid A   Peptidoglycan N-acetylglucosamine Lipoteichoic acid   Teichoic acid Ans: A