Gram +ve Pathogens

Gram +ve pathogens .gram + cell wall. Bacterial cell envelope- cell wall & cytoplasmic membrane. Thick layer of peptidoglycan staining purple in gram staining. Composed of peptidoglycan, trichroic acid - charged attracting cations for cell wall stability, lipoteichoic acid & proteins for interaction with environment. Peptidoglycan layer: Glycan- sugar of alternating NAG & NAM Layers connected by peptide chains consisting 3-5 amino acids long which all link together creating a mesh around 15 layers thick Gram staining: differential staining by Hans Christian Gram 1884. Primary stain fixed within peptidoglycan layer Characteristics to classify: Differentiated on biochemistry, guanine to cytosine ratio high (50%+) actinomyces, bifidobacterium, streptomyces etc. low (50%-) lactobacillus, enterococcus, clostridium etc. based on cell shape, cocci (spheres), bacilli (rods). Based on ability to form spores Sporulating +ve bacteria: Endospore formation begins with asymmetrical division Bacillus: Rod-shaped, aerobic/ facultatively anaerobic, catalase positive (enzyme containing to hydrolyse H202), able to form endospores I.e. B. Subtilise (cloning), B. Megatherium, B. Cyrus, B. Anthracis Clostridiae: Rod-shaped, anaerobic, catalase negative, able to form endospores I.e.- C. Difficult- colon infection, C. Tetan- tetanus, C. Botulinum, C. Prefringens- gas gangrene Streptomyces: Filamentous-fungi like, aerobic, able to form exospores, found commonly in soil & sometimes aquatic Antibiotic producers I.e. streptomycin, linked to sporulation as secondary metabolites Non-sporulating gram +ve bacteria: Staphylococci: bunch of grape shape Facultatively anaerobic, catalase positive, resistant to drying & high salt concentration, pigmented I.e. S. epidermis- skin flora is, S. aureus S. Aureus: normal flora of skin and upper respiratory track. Have virulence3 factors of coagulate, clumping factors, protein A & toxins Toxins may include alpha-hemolysin- blood cell lysis, enter toxin B- food poisoning, Toxic shock syndrome Pathogenic strains may be treated with penicillin but with MDR strain emergence, methicillin may treat some strains also MRSA methicillin-resistance S. aureus Streptococci: twisted shape Facultatively anaerobic, catalase negative, multiple classifications based on: haemolytic pattern & serology grouping based on polysaccharide & teichoic acid cell wall antigens -alpha-haemolytic:incomplete hemolysis greenish zone around colonies, beta-hemolytic complete haemolysis, gamma-hemolytic no hemolysis non-pathogenic commonly S. Pyogenes: part of upper respiratory track, normal flora -streptococcal pharyngitis, strep throat mild fever swollen tonsils tender lymph nodes, middle ear infections impetigo mammary gland infections -scarlet fever: caused by pyrogenic exotoxins, strawberry tongue sore throat fever rash, necrotising fasciitis, rheumatic fever, acute glomerulonephritis S. Pneumoniae: causing pneumonia -lung infections, thick capsules protects the cell from phagocytosis, accumulation of fluids & phagocytes cells in lungs Usually treated with penicillin but some are now resistant Corynebacterium diphtheriae: -club shaped anaerobic, causes infections of throat/ tonsils, pathogenic strains carry corynephage beta encoding diphtheria exotoxin inhibiting protein synthesis and causes cell damage Throat tissues forms lesions pseudo membrane containing damaged cellls & C. Diphtheria mostly affecting children Listeria: Coco bacillus abundant in soil & water, killed in radiation/ heat, facultatively aerobic, food industry presence such as cold meats, pasteurised dairy I.e. L. Monocytogenes may lead to meningitis Mycobacterium: Rod-shaped, aerobic cells coated with thick waxy capsule with polysaccharide, acid fast staining used, slow-growing tuberculin skin test intradermal injection of soluble cell extracts Gram +ve bacteria without cell wall: Mycoplasmas: Differentiated between mycoplasma & spiroplasma -cell wall not required as always within host cell, mycoplasma in mammals whereas spiroplasma plants Sterols contained for classification tools Lipoglychans resembling lipopolysaccharide used to attach to surface receptors of host cells I.e. M. Pneumoniae