Medicinally Important Bacteria PDF

Medicinally important bacteria pt1 Gram negatives Peptidoglycan is outside of cell wall. - Gram positive bacteria à purple, has thick peptidoglycan - Gram negative bacteria à pink, has thin peptidoglycan, more likely to be pathogenic. How are bacteria classified? - Phenetic (phenot...

Medicinally important bacteria pt1 Gram negatives Peptidoglycan is outside of cell wall. - Gram positive bacteria à purple, has thick peptidoglycan - Gram negative bacteria à pink, has thin peptidoglycan, more likely to be pathogenic. How are bacteria classified? - Phenetic (phenotype): o Gram reaction and morphology. o Carbon sources, energy sources. o Electron acceptors (e.g. aerobic/anaerobic) o You classify bacteria based on what you can see, like sizes and shapes. - Phylogenetic (genotype): o Ribosomal RNA sequence. o Other DNA, RNA, protein sequence. Phylogenetic tree of bacteria Diverse Gram-negative bacteria can cause disease - Proteobacteria (contains lots of pathogenic bacteria) o Escherichia o Salmonella o Vibrio o Pseudomonas o Neisseria o Rickettsia - Bacteroidetes o Bacteroides - Spirochaetes o Treponema Escherichia - Facultative anaerobic (can survive with or without oxygen), heterotrophic, G-ve rods. - Found in gut of humans and animals. - Part of family Enterobacteriaceae: contains many other pathogens: salmonella, klebsiella, Yersinia à cause food poisoning) - Widely used in microbiology as a model organism (E.coli 대장균) - Motile by peritrichous flage. E coli - Most strains are normal flora, and beneficial o E.g. E coli biosynthesizes vitamin K. - Some strains are pathogenic; these are food or water borne pathogens. - O157 – infection by animal food, O111 - Symptoms-diarrhoea, fever. - Virulence factors: endotoxin (present in all G-ve), enterotoxin (something that can be secreted by the bacteria. Mostly spilled out of the bacteria rather than stay inside the membrane.) (produced by some E Coli) Salmonella - Facultative anaerobic, heterotrophic, G-ve rods. - Normal flora in animal gut, pathogenic to humans. - S. enterica: food-borne infection, self-limiting diarrhoea. à uncooked egg, chicken. àself- limiting. - S. typhi: water-borne, typhoid fever, potentially fatal. - Virulence factors: endotoxin, enterotoxin, cytotoxin. Salmonella - Identifying Enterobacteriaceae - Selective + di]erential agars for identifying Enterobacteriaceae. - E coli is capable with breaking down the lactose. Breaking down the lactose will make pH acidic. - Black on salmonella’s agar plate, it’s due to iron precipitate. Salmonella produce iron precipitate. Vibrio - Facultative anaerobic, heterotrophic, G-ve curved rods. - Motile, various flagella arrangements. - Habitat is primarily marine but can cause gut infection. à e.g. due to seafood, drinking contaminated water. - V. cholerae o The most pathogenic vibrio species. o Causes cholera: severe diarrhoea à transmission. o Virulence factor à cholera toxin (an exotoxin) § Cholera toxin will cause intestinal epithelial cell to secrete all sodium and calcium into the cavity. à diarrhoea. o Common in sewage contamination. Vibrio (V. Cholerae) - Transmission usually by faecal contamination of water. - How do the symptoms of cholera help its transmission? - V. cholerae is more rarely a food-borne disease (seafood). Pseudomonas - Aerobic, heterotrophic G-ve rods, motile (polar flag), can survive many environments. - Ubiquitous in soil and water, opportunistic pathogens. - Large genome (6 Mb) à metabolically versatile. - P. aeruginosa o Nosocomial infection (hospital acquired) – especially burns. o Virulence factors: § innate antibiotic resistance (low membrane permeability), § haemolysin, à can break down the enzyme, red blood cell § proteases. o E.g. Nosocomial infection: § P. aeruginosa transmitted from nurse’s fingernail to many heart surgery patients. § Metabolic versatility helps P. aeruginosa to colonise diverse niches. (e.g. fingernail, heart) § P. aeruginosa infections are common, but person to person transmission is rare. Neisseria - Aerobic, heterotrophic, G-ve diplococci - Habitat: mammalian mucous membranes. - Carrier – back of throat, nose. - Virulence factors o Capsule: evasion of immune response. o Fimbriae: adhesion to tissues - Pathogenic species o N. gonorrhoeae à gonorrhoea (hairy Neisseria) o N. meningitidis à meningitis (meningococcal disease) (smooth Neisseria) N. meningitidis - Meningitis: inflammation of meninges (membrane around brain) à fever, rash, headache, confusion, death. - Serious, rapidly progressing disease à needs rapid diagnosis and treatment (antibiotics) - Analysis: microscopic examination CSF - Crystal violet stain: both white blood cell nuclei and Neisseria cells appear purple. N. gonorrhoeae - Gonorrhoea: a sexually transmitted disease. - Diagnose by microscopic examination. - Safranin: epithelial cells and Neisseria appear pink. - Note adherence of Neisseria cells to the epithelial cells. Rickettsia - Aerobic, heterotrophic, G-ve, coccobacilli - Cannot be grown in vitro – only in tissue culture. - Bacteria are very dependent on host metabolism. - Intracellular parasites of arthropods – e.g. fleas, lice, ticks. - Small degenerate genome (1Mb) à specialised lifestyle. - Related to mitochondrion – significance? - Zoonotic. (transmitted by animal) - Transmissions to humans occurs via bites or faeces of arthropods à various fever diseases. - R. prowazekii → epidemic typhus o headache, fever, rash (up to 50% mortality) o overcrowded conditions → transmitted by body louse o virulence factors: adhesin, phospholipase Bacteroides - Obligate anaerobe, heterotrophic, G-ve rods. - Normal flora but can be opportunistic pathogens. - Bacteroides are most abundant cells in human body - Several beneficial species: digestion of carbohydrates, exclude pathogens by competition (Salmonella) - Very abundant in our body, usually not cause harm and beneficial. - B. fragilis o Opportunistic pathogen: cause infection if it escapes the gut eg. abcesses, septicemia, appendicitis o Virulence factors: capsule, antibiotic resistance - Easy to transmit antibiotic resistance. Treponema - Anaerobic, heterotrophic, G-ve, spirochaetes. - Obligate parasites, require animal cells for growth. - Rely on host (human) in order to provide the nutrients. - - - Use axial filament for structure and corkscrew motility. - Great to move through viscous fluid. - T. pallidum o Causes Syphilis: a sexually transmitted disease (STD) o E]ects: 1 0: chancres, 2 0: rash, 3 0: nervous system damage o Can’t be grown in standard media. Degenerate small genome (1 Mb) Medicinally important bacteria Pt2 Diversity of bacteria – Gram positives Both Gram + and – bacteria are medically-important Chlamydia - Aerobic, heterotrophic, G-ve cocci. - Obligate intracellular parasites of humans & animals. - Cause sexually transmitted disease and eye infection. - Cannot be grown on agar, small genome (1 Mb) consistent with host-dependence. - An ‘energy parasite’ – dependent on host cells for ATP and other metabolites. (cannot live outside of host cell) - Virulence factors: o unusual cell wall allows growth inside phagocytes o has no peptidoglycan → intrinsic resistance to all antibiotics targeting PG. - Chlamydia - C. trachomatis o Causes urethritis (STD) and trachoma (eye infection). o Chlamydia is serious pathogen for koalas. Rank of the STIs - Chlamydia - Gonorrhoea - Syphilis à very severe but not prevalent why? à due to its symptoms. - Chlamydia 50-90% asymptomatic. Gram positive bacteria - Phylum Firmicutes, phylum Actinobacteria. - Distinguished from gram negatives by thicker peptidoglycan and lack of outer membrane. - Divided into firmicutes (low GC) and actinobacteria (high GC) groups. o GC means % GC content of DNA. - Firmicutes o Facultative anaerobic rods or cocci. o Some make endospores. - Actinobacteria o Aerobic rods or filaments. à tend to live outside of human body. o Some make exospores. (e.g. Streptomyces) Bacillus - Facultative anaerobic, heterotrophic, G+ve rods. - Ubiquitous in environment, especially soil. - Transient flora on skin. - Older/ starving / stressed cells make endospores. - - Bacillus spore stain shows endospores (green) and vegetative cells (red) Firmicutes: Gram positive rods. - May be facultative anaerobic or strictly anaerobic. - Contain both normal flora and pathogenic species. - Normal flora o Lactobacillus à can colonise mouth, vaginal area, not often but also gut. - Primarily soil organisms, some are pathogens. o Bacillus o Clostridium Bacillus - B. anthracis o Causes anthrax: highly infectious and deadly disease. o Usually zoonotic: transmitted from animals (cattle, sheep) o Possible bioterrorism agent due to stable endospores. o Plasmid-encoded virulence factor: exotoxin. - - Anthrax exotoxin – three secreted proteins work together to kill cells. - Anthrax can present in three diZerent ways: o Cutaneous: common, ~20% mortality o Gastrointestinal: rare, ~50% mortality o Pulmonary: rare, ~80% mortality o All potentially treatable with antibiotics: eg. ciprofloxacin Clostridium - Anaerobic, heterotrophic, G+ve rods with endospores. - Habitat: soil, human and animal gut. - Some species are normal flora, some are pathogens. - Pathogenic clostridia make potent exotoxins. o C. tetani → tetanus o C. botulinum → botulism - C. tetani o Tetanus: muscle rigidity, death die to respiratory failure. o Virulence factor: tetanospasmin, an exotoxin. o Requires deep wounds to multiply (NB. Anaerobic) o Common-source disease, not a contagious disease source: soil/manure, inoculated into puncture wound. o Tetanospasmin is a neurotoxin: blocks transmission of ‘relaxation’ signal to muscles → body rigidity, death from respiratory paralysis - C. botulinum o Causes botulism, a dangerous type of food poisoning (common-source disease). o Lives in soil. Spores enter food chain. Persist through processing, germinate in food (anaerobic, neutral pH) o Virulence factor: botulinum toxin (Botox) – the most deadly poison known, lethal dose ~1microgram. Lactobacillus - L. acidophilus o Facultative anaerobic, heterotroph, G+ve non-sporing rods. o Normal flora of mouth, gut, vaginal; non-pathogenic. o Probiotic e]ect? – competition with pathogens in gut. o Cheese + yoghurt production: lactic acid fermentation. Gram-positive cocci - All are non-motile, and either aerobic or facultative. - Contain both normal flora and pathogenic species. - Medically important genera: o Staphylococcus, streptococcus § Normal flora/potential pathogens. Staphylococcus - Facultative anaerobic, heterotrophic, G+ cocci - clumps. - Habitat: human-associated, either as normal flora (skin/nose) or as pathogens (wound infection) - Tough cell wall makes Staph. Resistant to physical stress. (e.g. desiccation) à long survival in environment. - Resistant to salt – trait needed to survive on skin & nose. - Staphylococci on mannitol-salt agar: o S. epidermidis: non-mannitol fermenting (red) o S. aureus: mannitol-fermenting (yellow) S. aureus “Golden Staph - Opportunistic pathogen. - Infections: wound infections, boils, impetigo, toxic shock. - Nosocomial spread – hospital strains antibiotic resistant. - Morphology arrangement – Staph vs Strep o Closely related. - - Virulence factors: coagulase, exotoxins. - Coagulase as a diagnostic test. - From clot around bacteria à helps hide from immune system. Streptococcus - Facultative anaerobic, heterotrophic, G+ve cocci in chains. - Habitat: mouth and gut of animals and humans. - Beneficial streptococci: o S. thermophilus: yoghurt + cheese production, normal flora - Harmful streptococci: o S. pyogenes: scarlet fever – contagious, mostly a]ects young children. o S. pneumoniae: pneumonia. - - Gram stain of sputum from pneumonia case: note G+ve cocci in pairs and short chains. S. pneumoniae - Can cause pneumonia and meningitis. - Characteristic alpha-haemolysis reaction on blood agar. - Virulence factors: capsule, haemolysis. o Encapsulated strains are 100,000 times more virulent. - o Breakdown the blood to get iron. Actinobacteria: Streptomyces, Mycobacterium - Aerobic - Gram positive filaments or rods. o Streptomyces – makes antibiotics § Streptomyces colonies à powdery surface, di]usible pigments. o Mycobacterium – causes tuberculosis. Mycobacterium - Aerobic, heterotrophic, G+ve rods. - Mycolic acids in cell wall à waxy layer à acid fast stain. - Wax protects against stresses, including immune system. - Pathogenic species o M. tuberculosis: tuberculosis (TB) o M. leprae: leprosy M. tuberculosis - Obligate pathogen of humans – no environmental reservoir. - One of the Big 3 killer disease of humanity. - Chronic infection of lungs: fever, coughing weight loss. - Can be grown in vitro, but slow-growing and fastidious - Virulence factors: o Waxy cell wall gives resistance to many stresses. o E.g. antibiotics, macrophage. - Wrinkly colonies of M. tuberculosis on Lowenstein – Jensen agar.