Lesson+16.+Gram+positive+bacilli.pdf

Lesson 16 Bacteria of dental interest: Gram-positive bacilli Microbiology Dra. Sara Mª Martínez Sánchez Dra. Ana Isabel García Guillén Bachelor´s degree in Dentistry INDEX CONTENTS 1. Lactobacilli 5. Bacilli 2. Corynebacteria Corynebacterium diphtheriae Bacillus anthracis B. cereus 3. Propio...

Lesson 16 Bacteria of dental interest: Gram-positive bacilli Microbiology Dra. Sara Mª Martínez Sánchez Dra. Ana Isabel García Guillén Bachelor´s degree in Dentistry INDEX CONTENTS 1. Lactobacilli 5. Bacilli 2. Corynebacteria Corynebacterium diphtheriae Bacillus anthracis B. cereus 3. Propionibacteria 4. Actinomycetes Actinomyces Nocardia 4. Clostridia Clostridium perfringens C. tetani C. difficile C. botulinum 2 Gram negative 3 Gram positive 4 Lactobacillus Characteristics of the genus Saprophytes in vegetable and animal material (e.g. milk) Commensals Food industry (probiotic) 5 Lactobacillus Taxonomy Complex taxonomy • Homofermenters (lactic acid from glucose fermentation) • • Lactobacillus casei Heterofermenters (lactic acid as well as acetate, ethanol and carbon dioxide) • L. fermentum • L. casei, L. rhamnosus, L. acidophilus and the newly described species L. oris are common in the oral cavity L. rhamnosus 6 Lactobacillus Habitat and transmission ◦ Oral cavity (less than 1% of total micobiota) ◦ Female genital and gastrointestinal tract ◦ Unknown transmision routes ◦ When S. mutans colonizes (acid environment) L. rhamnosus 7 Lactobacillus Characteristics ◦ Gram-positive coccobacillary forms (mostly bacillary) ◦ α or non-haemolytic ◦ Facultative anaerobes, microaerophilic ◦ Acidogenic and aciduric ◦ Vaginal flora (maintain low pH equilibrium) ◦ Gram-positive coccobacillary forms (mostly bacillary) Homeostasis of intestinal microbiota 8 Lactobacillus Pathogeneicity • Deep carious lesions (acid pH) • First bacteria related to caries in 40’s (20th century) Lactobacillus count indication of caries activity Not very reliable • But useful for monitoring dietary profile • Kids: coronal caries • Adults: radicular caries and pulpitis 9 Corynebacterium Generalities • Demonstrate pleomorphism (i.e. coccobacillary appearance • Are non-sporing, non-capsule and non-motile • In common with Mycobacterium and Nocardia 10 Corynebacterium diphteriae Habitat and transmission • Human throat and nose • Occasionally skin • Carriers up to 3 months after infection Transmission is via respiratory droplets • C. diphtheriae (childhood diphtheria) 11 Corynebacterium diphteriae Characteristics • Gram-positive club-shaped or in palisades 2-5 µm in length • Facultative anaerobe (Blood agar) at 37ºC C. diphteriae 12 Corynebacterium diphteriae Virulence • Exotoxin • Gel precipitation test, ELISA and immunochromographic strips • Inhibits protein biosynthesis in eukaryotic cells • Grey, adherent pseudomembrane comprising bacteria, fibrin and epithelial and phagocytic cells • Patient may die of asphyxiation • Into the blood stream affects motor nerves of myocardium and nervous system 13 Elek test for toxin-producing Corynebacterium Other species • C. ulcerans • diphtheria-like throat lesions not cause toxaemia • C. matruchotti • True coryneform organism in oral cavity • Resembles a whip (’whip-handle cell) short, fat body and a long filament at one end 15 C. matruchotti Corynebacterium Diphteroids • Bacilli that morphologically resemble diphtheria • C. hofmannii, C. xerosis • Inhabitants of the skin and conjunctiva Occasional opportunistic pathogens • e.g. endocarditis in prosthetic valves 16 Propionibacterium Generalities • Obligate anaerobes • P. acnes • Normal skin flora • May also be isolated from dental plaque • P. propionica (Arachnia propionica) production of propionic acid from glucose 17 Actinomycetes Generalities • Thought to be fungi • Two important genera: • Actinomyces • Nocardia 18 The genus Actinomyces Generalities • Soil organisms • Microaerophilic or anaerobic • Potentially pathogenic species are commensals of the mouth • Actinomyces israelii human actinomycosis • Actinomyces odontolyticus earliest stages of enamel demineralization • Major component of dental plaque and gingivitis • Association on root surface caries • Female genital tract • Tonsillar crypts (throat) 19 Actinomyces israelii Habitat and transmission • Gram-positive filamentous branching rods • Non-motile, non-sporing and non-acid-fast • Yellowish ‘sulphur granules’ in pus (sinus tracts) • Serotype II is now a separate specie: A. gerencseriae • Common but minor component of healthy gingival microbiota Molar tooth-shaped colonies of A. israelii on blood agar 20 Actinomyces israelii Pathogenicity • Most (70-80%) chronic, granulomatosus, endogenus infections of the orofacial region • Usually a history of trauma (e.g., tooth extraction) • Also associated with intrauterine devices • 10-20% ileocaecal, lung or skin • Could be polymicrobial associated with Aggregatibacter actinomycetemcomitans Haemophilus spp. • anaerobes acting as co-infecting agents A histopathological section from an actinomycetic lesion of the mandible showing a branching filamentous mass of Actinomyces spp. infiltrating the bony cortex. 21 The genus Nocardia Generalities • Soil saprophytes • Cause nocardiosis in human (immunocompromised patients) • Aerobic • N. asteroides common form of human nocardiosis pulmonary infection that progresses to form abscesses and sinus tracts N. asteroides 22 The genus Clostridium Generalities • Anaerobic spore-forming bacilli • Spores are not found in infected tissues • Important group of pathogens • Widely distributed in soil • Gut of humans and animals • Significant morbidity and mortality, in developing countries 23 The genus Clostridium Diseases Clostridium spp.c C. perfringens Disease gas gangrene food poisoning C. tetani Tetanus C. botulinum Botulism C. difficile Pseudomembranous colitis C. septicum C. ramosum C. novyi C. bifermentans bacteraemia gas gangrene soft tissue infections 24 The genus Clostridium habitat • Soil • Water • Decaying animal and plant matter • Human and animal intestines 25 The genus Clostridium Characteristics • Gram-positive rods, but older cultures may stain irregularly • Endospores, which create a bulge in the bacterial body drumstick-shaped C.tetani (laboratory identification) • Some species are motile with peritrichous flagella (e.g. C. tetani) • Others have a capsule (e.g. C. perfringens) 26 The genus Clostridium Culture and identification • Grow anaerobically on blood agar or Robertson’s cooked meat medium (liquid culture) • C. tetani and C. novyi, strict anaerobes • C. histolyticum and C. perfringens, aerotolerant Saccharolytic*, proteolytic and toxigenic potentials are useful in identification • *Sacharolytic: able to use completely complex carbohydrate 27 Clostridium perfringens Habitat and transmission • Spores are found in the soil • Vegetative cells are normal microbiota of the colon and vagina • Exogenous or endogenous infections: • Gas gangrene (myonecrosis) • infection of dirty ischaemic wounds (e.g. war injuries) • Food poisoning ingestion of food contaminated with enterotoxin-producing strains 28 Clostridium perfringens characteristics • Short, fat bacillus • Spores are not usually found (formed under nutritionally deficient conditions) • More tolerant oxygen than other clostridia • Blood agar under anaerobic conditions • β-haemolytic and non-haemolytic • Ferments litmus milk (’stormy-clot’ reaction) “Stormy clot” reaction 29 Clostridium perfringens Exotoxins • At least 12 toxins • Collagenase, proteinase and hyaluronidase • α-toxin lyses the phospholipids of eukaryotic cell membranes • Species divided into five types (A-E) based on toxins Type A is the human pathogen Nagler`s reaction 30 Clostridium perfringens Exotoxins Neutralization of the α-toxin • On agar plate containing egg yolk (phospholipase) Half of the plate with antitoxin • An opaque reaction surrounding the growth in the untreated half of the plate Nagler`s reaction 31 Clostridium perfringens Pathogenicity Gas gangrene (myonecrosis) • Wounds associated with traumatized tissue (especially muscle) • Life-threatening spreading infection • Activity results in toxin and enzyme production, allowing multiplication in the wounds • Pain, oedema and crepitation produced by gas 32 Clostridium perfringens Pathogenicity Food poissoning • Enterotoxin • Ingestion of large numbers of vegetative cells • Sporulate in the gut and release enterotoxin • Watery diarrhoea with little vomiting 33 Clostridium tetani Habitat and transmission • Intestinal tract of herbivores • Spores are widespread in soil • Germination promoted by poor blood supply and necrotic tissue and debris 34 Clostridium tetani Characteristics • Long, thin bacilli • Terminal spores (’drumstick’) • Tetanospasmin (extremely potent neurotoxin) Vegetative cells at the wound • Tetanolysin (haemolytic) • Toxin genes are plasmid-coded 35 Clostridium tetani Culture and Identification • Blood agar • Anaerobic • Fine spreading colony • Identification in vitro by a toxin neutralization test on blood agar or in vivo by inoculation of culture filtrate into mice 36 Clostridium tetani Pathogeneicity 37 Clostridium difficile Generalities • Faeces of 3-6% adults and almost all healthy infants • Antibiotic-associated colitis (lethal pseudomembranous colitis) • Clindamycin and ampicillin • 25% common antibiotic-associated diarrhoea 38 Clostridium botulinum Generalities • Botulism, a form of food poisoning • Powerful toxins used in warfare • Minute doses popular in beauty therapy (minimize wrinkles) 39 The genus Bacillus Generalities • Nearly 50 species • Sporing, Gram-positive, chain-forming bacilli • Soil saprophytes 40 Bacillus anthracis Generalities • Spores survive in soil for years Humans are accidental hosts • Infection (anthrax) is acquired when spores enter abrasions on the skin or are inhaled • Septicaemia and death • Pulmonary anthrax (woolsorters’ disease) • Life-threatening pneumonia • Polyglutamic acid capsule of the organism is antiphagocytic • Much attention due to biological warfare 41 Bacillus cereus Generalities • Food poisoning • Reheated, contaminated rice 42 The genus Bacillus Other species • B. stearothermophilus • B. subtilis • Biological indicators to sterilization test efficacy of autoclaves, ethylene oxide and ionizing radiation 43 Remember • Actinomyces spp. are potentially pathogenic commensals and are frequent isolates from dental plaque. They cause cervicofacial (most common), ileocaecal and thoracic actinomycoses, which are essentially chronic, granulomatous infections. • Clostridia are Gram-positive, anaerobic, spore-forming bacilli, though spores are not found in infected tissues. • Pathogenic clostridia produce powerful exotoxins that are responsible for most disease symptoms. • Spore-bearing Clostridium tetani cells are characterized by their drumstick shape. • Tetanospasmin and tetanolysin are toxins produced by C. tetani, the agent of tetanus. • Tetanus causes sustained muscle spasm (including the masticatory muscles) resulting in lockjaw (trismus), risus sardonicus and arching of the body (opisthotonos). • Tetanus toxin (tetanospasmin) can be attenuated to form a toxoid. The latter is a component of the diphtheria–tetanus–pertussis (DTP) vaccine. • The spores of Bacillus stearothermophilus and Bacillus subtilis are used as biological indicators to test the sterilization efficacy of autoclaves, ethylene oxide and ionizing radiation. 44 BIBLIOGRAPHIC REFERENCES Kumar , S. (2016). Essentials of Microbiology. Jaypee Brothers Medical Publishers (P) Ltd. Samaranayake, L. (2012)Essential Microbiology for dentistry .Fourth Edition. Elsevier Ltd. 45 Ana Isabel García Guillén [email protected] UCAM Universidad Católica de Murcia © © UCAM UCAM