Lecture 10 Microbiology Anaerobic Bacteria PDF

Lecture 10 Microbiology: Anaerobic Bacteria  Content 1. Overview: Clostridia , non-spore forming anaerobes The main biological characteristics of Clostridia (C. tetani, C. botulinum and C. perfringens). Infection and Pathogenesis of Clostridia (tetanospasimin, and Bo...

Lecture 10 Microbiology: Anaerobic Bacteria  Content 1. Overview: Clostridia , non-spore forming anaerobes The main biological characteristics of Clostridia (C. tetani, C. botulinum and C. perfringens). Infection and Pathogenesis of Clostridia (tetanospasimin, and Botulinum toxin, toxin of C. perfringens ) and immunity Diagnostic laboratory tests for the diseases cause by Clostridia Treatment and prevention of Clostridia 2. Infection caused by non-spore forming anaerobes  Anaerobic bacteria: Bacteria that do not use oxygen for growth and metabolism but obtain their energy from fermentation reactions. A functional definition of anaerobes is that they require reduced oxygen tension for growth and fail to grow on the surface of solid medium in 10% CO2 in ambient air. Bacteroides and Clostridium species are the examples of anaerobes.  Anaerobes Anaerobes fail to grow in presence of 10% of oxygen. Some are sensitive to oxigen concentration as low as 0.5%. Oxygen tolerance is variable and many of anaerobes can survive briefly in the presence of 2-8% of oxygen, including most of the species pathogenic for humans. MOST ANAEROBES LACK EZNYMES: CATALASE AND SUPEROXYDASE DISMUTASE (SOD - WHICH NEUTRALISES THE TOXIC EFFECT OF OXYGEN) THUS THIS FACT MAKES THEM SUSEPTIBLE TO OXYGEN. Anaerobes lack the cytochromes required to use oxygen as a terminal electron acceptor.  Spore forming and nonspore forming anaerobes Spore-forming: rod, Gram Nonspore-forming: Rod, Gram (+) Propionibacterium (+) Bifidobacterium Clostridium Lactobacillus Eubacterium Actinomyces Rod, Gram (-) Bacteroides Fusobacterium Campylobacter Cl. perfringens Cocci, Gram (+) Peptococcus Peptostreptococcus Cocci, Gram (-) Veillonella  SOD Most bacteria of the Bacteroides fragilis group have small amounts of both catalase and SOD. There appear to be multiple mechanisms for oxygen toxicity. Presumably, when anaerobes have SOD or catalase (or both), they are able to negate the toxic effects of oxygen radicals and hydrogen peroxide and thus tolerate oxygen. Obligate anaerobes usually lack SOD and catalase and are susceptible to the lethal effects of oxygen; such strict obligate anaerobes are infrequently isolated from human infections, and most anaerobic infections of humans are caused by “moderately obligate anaerobes.”  B. fragilis Opportunistic pathogen, bile-resistant Slim, pale staining, capsulate, Gram negative rods, has adhesive surface pili Most strains produce superoxide dismutase and are tolerant to oxygen Major disease causing strict anaerobic after abdominal surgery Non-spore-former Anti-phagocytic abscess formation Endotoxin low toxicity structure different than other lipolysaccharide Many species previously included in the genus Bacteroides have been reclassified into the genus Prevotella or the genus Porphyromonas.  Bacteroides (cont) Bacteroides species are normal inhabitants of the bowel and other sites. Normal stools contain 10^11 B. fragilis organisms per gram (compared with 10^8 /g for facultative anaerobes). Other commonly isolated members of the B. fragilis group include: Bacteroides ovatus, Bacteroides distasonis, Bacteroides vulgatus, Bacteroides thetaiotaomicron. Bacteroides species are most often implicated in intra-abdominal infections, usually under circumstances of disruption of the intestinal wall as occurs in perforations related to surgery or trauma, acute appendicitis, and diverticulitis. These infections are often polymicrobial. Both B. fragilis and B. thetaiotaomicron are implicated in serious intrapelvic infections, such as pelvic inflammatory disease and ovarian abscesses. B. fragilis group species are the most common species recovered in some series of anaerobic bacteremia, and these organisms are associated with a very high mortality rate.  Epidemiology Endogenous infection mixed with other intestinal bacteria, e.g. E.coli Human-to-human transmission is not known and seems unlikely  Pathogenesis B. fragilis cells can withstand up to 3 days exposure to atmospheric levels of oxygen due to activation of an oxidative stress response Capsule is involved into abscess formation Diarrheal enterotoxin is possible  Manifestation and treatment Abdominal pain and fever may evolve to peritonitis Abscess combined with anaerobes and Enterobacteriaceae Treatment: Resistant to cephalosporin and tetracyclin, susceptible to metronidozole and clindamicyn  Prevotella Prevotella species are Gram-negative bacilli and may appear as slender rods or coccobacilli. Most commonly isolated are: P. melaninogenica, Prevotella bivia, and Prevotella disiens. P. melaninogenica and similar species are found in infections associated with the upper respiratory tract. P. bivia and P. disiens occur in the female genital tract. Prevotella species are found in brain and lung abscesses, in empyema, and in pelvic inflammatory disease and tubo-ovarian abscesses. In these infections, the Prevotella species are often associated with other anaerobic organisms that are part of the normal microbiota.  Porphyromonas The Porphyromonas species also are Gram-negative bacilli that are part of the normal oral microbiota and occur at other anatomic sites as well. Porphyromonas species can be cultured from gingival and periapical tooth infections and, more commonly, breast, axillary, perianal, and male genital infections  Fusobacteria There are approximately 13 Fusobacterium species, but most human infections are caused by Fusobacterium necrophorum and Fusobacterium nucleatum. Both species differ in morphology and habitat as well as the range of associated infections. F. necrophorum is a very pleomorphic, long rod with round ends and tends to make bizarre forms. It is not a component of the healthy oral cavity. F. necrophorum is quite virulent, causing severe infections of the head and neck that can progress to a complicated infection called Lemierre’s disease. The latter is characterized by acute jugular vein septic thrombophlebitis that progresses to sepsis with metastatic abscesses of the lungs, mediastinum, pleural space, and liver. Lemierre’s disease is most common among older children and young adults and often occurs in association with infectious mononucleosis. F. necrophorum is also seen in polymicrobial, intra-abdominal infections.  F. nucleatum F. nucleatum is a thin rod with tapered ends (needle-shaped morphology) and is a significant component of the gingival microbiota as well as the genital, gastrointestinal, and upper respiratory tracts.  GARDNERELLA VAGINALIS G. vaginalis is a serologically distinct organism isolated from the normal female genitourinary tract and also associated with vaginosis, so named because inflammatory cells are not present. In wet smears, this “nonspecific” vaginitis, or bacterial vaginosis, yields “clue cells,” which are vaginal epithelial cells covered with many Gram-variable bacilli, and there is an absence of other common causes of vaginitis such as trichomonads or yeasts. Vaginal discharge often has a distinct “fishy” odor and contains many anaerobes in addition to G. vaginalis. The pH of the vaginal secretions is greater than 4.5 (normal pH is