Lecture 5.1-5.2 - Microbiology Lecture Notes PDF

NEISSERIA MENINGITIDIS  1. MORPHOLOGICAL CHARACTERS  Gram negative cocci, kidney-shaped (in the form of ‘coffee beans’), laid ‘in diplo’.  In the pathological product (cerebrospinal fluid) they are located intracellular.  Newly isolated strains have a polysaccharide capsu...

NEISSERIA MENINGITIDIS  1. MORPHOLOGICAL CHARACTERS  Gram negative cocci, kidney-shaped (in the form of ‘coffee beans’), laid ‘in diplo’.  In the pathological product (cerebrospinal fluid) they are located intracellular.  Newly isolated strains have a polysaccharide capsule.  They are immobile, non-spore forming.  2. CULTURAL CHARACTERS  The colonies are smooth, small (1 mm diameter), transparent, light gray, without hemolysis.  The growth on culture medium is favoured by incubation in a atmosphere of CO2 5-10%.  3. METABOLIC CHARACTERS - Germs with large nutricious needs, the meningococci ferment glucose and maltose. - They are strictly anaerobes, it’s growth is facilitated by the presence of a atmosphere of carbon dioxide 5-10%.  4. ANTIGENIC CHARACTERS  Neisseria meningitidis have as antigens:  - a somatic nucleoprotein fraction (antigen P)  - a carbohydrate fraction - capsular polysaccharide antigens, causing specificity of the group  5. PATHOGENICITY CHARACTERS  5.1. VIRULENCE – Meningococcal capsule serves as anti- phagocyte structure.  5.2. TOXINOGENESYS  It was experimentally demonstrated that there is a meningococcal endotoxin, which injected in animals partially can reproduces the clinical picture of meningitis.  6. CLINICAL FEATURES  Epidemic cerebrospinal meningitis is an acute infectious disease caused by meningococcus.  The most common symptoms are a stiff neck, high fever, sensitivity to light, confusion, headaches and vomiting.  Even when the disease is diagnosed early and an adequate treatment is started, 5% to 10% of patients die, typically within 24 to 48 hours after the onset of the symptoms.  Bacterial meningitis may result in brain damage, hearing loss or a learning disability in 10% to 20% of survivors.  A less common but even more severe (often fatal) form of meningococcal disease is meningococcal septicemia, which is characterized by an hemorrhagic rash and rapid circulatory collapse.  Initial diagnosis of meningococcal meningitis can be made by clinical examination followed by a lumbar puncture showing a purulent spinal fluid.  A range of antibiotics can treat the infection, including penicillin, ampicillin, chloramphenicol and ceftriaxone. Neisseria gonorrhoeae   1. MORPHOLOGICAL CHARACTERS  They are Gram negative cocci, kidney- shaped (form of ‘coffee beans’), placed in ‘diplo’ predominantly intracellular (phagocyted by polymorphonuclears).  Are non-spore forming, immobile and may present a capsule in pathological products and in young cultures.  2. CULTURAL CHARACTERS  Neisseria gonorrhoeae develop colonies which are small, 1-2 mm in diameter, transparent, slightly gray, with shiny smooth edges (S type colonies).  3. METABOLIC CHARACTERS  They are aerobic germs, very demanding in terms of nutritional requirements.  It ferments glucose, but not maltose, which distinguishes it from meningococci.  4. ANTIGENIC CHARACTERS  - nucleoprotein antigen (antigen P)  - a common carbohydrate antigen (antigen K)  5. PATHOGENICITY CHARACTERS  It is a non-toxigenic virulent germ.  Virulence factors are:  - fimbriae – which are attached to the mucosa of genital tract and play an anti-phagocyte role.  - antigen K – with anti-phagocyte role, protecting the germ against intracellular digestion after incorporation in the phagocyte.  - protease – capable of cleaving the secretory IgA, resulting so the decrease of local antimicrobial activity.  6. CLINICAL FEATURES  Gonorrhea is a sexually transmitted infection.  Many people have no symptoms.  Men may have burning with urination, discharge from the penis or testicular pain.  Women may have burning with urination, vaginal discharge, vaginal bleeding between periods or pelvic pain.  Complications in women include pelvic inflammatory disease and in men include inflammation of the epididymis.  If untreated gonorrhea can occasionally spread affecting joints or heart valves.  Gonorrhea is spread through sexual contact with an infected person. This includes oral, anal and vaginal sex.  It can also spread from a mother to a child during birth - ophthalmia neonatorum – signs are:  - Pain and tenderness in the eyeball.  - Conjunctive discharge: purulent  - Conjunctiva shows hyperemia and chemosis (the swelling or edema of the conjunctiva). Eyelids are usually swollen. May lead to blindness.  Prevention:  - at birth we can do instillation with solution 1% of silver nitrate into child eyes. MORAXELLA (brahmanella) CATARRHALIS  1. MORPHOLOGICAL CHARACTERS  Is a gram-negative diplococcus with a tendency to resist decolorizing.  Non-spore forming, non capsulate and non motile.  The size of the microorganism varies; it is often larger than the meningococcus or gonococcus.  2. CULTURAL CHARACTERS  On blood agar - forms small, opaque, gray-white colonies, 1-3 mm in diameter, circular and non-hemolytic.  They can be pushed over the surface of the agar like a hockey puck on ice.  3. METABOLIC CHARACTERS  - They grow in basic agar media at 35°C.  - Does not ferment sugars and do not produce indole or urease.  - Catalase and oxidase reactions are positive.  - Hydrolysis of DNA and tributyrin are valuable differentiating tests for Moraxella catarrhalis.  4. CLINICAL FEATURES  These bacteria are known to cause otitis media, bronchitis, sinusitis and laryngitis.  Elderly patients and long-term heavy smokers with chronic pulmonary disease should be aware that Moraxella catarrhalis is associated with bronchopneumonia and exacerbations of existing chronic obstructive pulmonary disease (COPD).  Additionally, it causes bacterial pneumonia, especially in adults with a compromised immune system.  It is an important cause in maxillary sinusitis, bacteremia, meningitis, conjunctivitis, acute purulent irritation of chronic bronchitis, urethritis, septicemia (although this is rare) and septic arthritis (which is also a rare occurrence). corynebacterium diphteriae  1. MORPHOLOGICAL CHARACTERS  Gram positive bacilli, with swollen ends and ‘Chinese letters’ arrangement of cells.  They are non-spore forming, don’t have cilia and are capsulated.  In the heads can be observed metachromatic particles (Babes-Ernst) in Del Vecchio stain.  2. CULTURAL CHARACTERS  For growing we can use several media as:  - the enrichment medium OCST (egg, cysteine, serum, potassium tellurite)  - elective Löffler's medium (with ox coagulated serum)  - solid selective media with blood and potassium tellurite - Tinsdale and Gundel-Tietz  - blood-agar medium.  - on Löeffler's medium : white, convex colonies.  - on Tinsdale medium: black colonies with a brown halo around them  - on solid media containing potassium tellurite and blood there are three types of colonies, which allow splitting diphtheria bacilli into three types: gravis, mitis, intermedius. - ‘gravis’ type – large colonies of black or dark grey, with rough surface, irregular margins – R colonies which are pathogenic – with an appearance like a ‘daisy flower’  - ‘mitis’ type – colonies are smaller in diameter, black, with smooth surface and circular outline – S colonies  - ‘intermedius’ type – grey-black colonies, usually with rough surface, but with irregular margins  - on blood-agar medium: the colonies are grey, like pearls.  3. METABOLIC CHARACTERS  Ferments glucose and maltose with acidification of the medium, without gas production.  Some strains of ‘gravis’ type can ferment sucrose.  Urease is negative.  4. ANTIGENIC CHARACTERS  - Diphtheria toxin, highly immunogenic, is the most important antigen of Corynebacterium diphtheriae.  - Corpuscular antigens from the surface of germs with carbohydrate and protein nature.  5. PATHOGENICITY CHARACTERS  DIPHTHERIA TOXIN  The germ remains at the entrance gate and secretes an exotoxin = diphtheria toxin which diffuses from the entrance gate in the body.  Toxigenic strains of Corynebacterium diphtheriae are all lysogenic – carrying the beta temperate bacteriophage.  This phenomenon have a great practical importance: strains which are present in the pharynx of healthy children, may become toxigenic (diphtheria toxin production) after the contact with beta bacteriophages.  At the entrance gate where the germ remains, the toxin can produce characteristic necrotic lesions.  In the body diphtheria toxin produces toxic injury to myocardium and peripheral nerve (cardiotoxic and neurotoxic action).  By treating diphtheria toxin with formalin, we can obtain diphtheria anatoxin, an non-toxic product, which have lost its pathogenic capability, but retained immunogenic properties. Diphtheria anatoxin is the diphtheria vaccine.  6. CLINICAL FEATURES  A. Diphtheritic angina  Locally – at pharyngeal pillars, tonsils, tongue, pseudomembranes appear: white-grey film, very adherent, composed of fibrin clots, leukocytes, dead epithelial cells and microorganisms.  B. Nasopharyngeal diphtheria – the pseudomembranes are both in the throat and in the nasal cavity mucosa surface.  C. Conjunctival diphtheria – is a very rare disease, usually secondary to a nasopharyngeal diphtheria advancing through the lachrymal canals.  D. Cutaneous diphtheria - the lesions consist of skin ulcerations without spontaneous healing tendency.  E. Laryngeal diphtheria (croup) – the extension of the pseudomembranes into the larynx and trachea can lead to obstruction of the airway with subsequent suffocation and death. Required emergency treatment is tracheotomy for airway clearance. listeria 1. MORPHOLOGICAL CHARACTERS  Gram positive bacilli, non-spore forming, facultative anaerobic rods.  Can vary in size (0.4–0.5 in diameter by 1–2 µm long), with rounded ends and not encapsulated.  They are motile by means of a few peritrichous flagella, with motility typically manifesting itself at ≤30°C but not at 37°C. 2. CULTURAL CHARACTERS  Listeria species are able to grow at temperatures ranging from 0–45°C.  Growth can also occur between pH 6 and pH 9, or in nutrient broth supplemented with up to 10% NaCl.  On blood agar sometimes produces beta- hemolysis with small, grey, translucent drop- like colonies.  On tryptose agar - green-blue colonies.  3. METABOLIC CHARACTERS  The genus Listeria is characterized by its catalase activity, its lack of hydrogen sulfide production, and its production of acid from glucose.  They are oxidase negative.  It has a positive methyl red reaction and a positive Voges– Proskauer reaction.  It does not produce indole, utilize citrate or possess urease activity.  4. CLINICAL FEATURES  Two species are of human pathogenic significance: L. monocytogenes and L. ivanovii.  In particular, L. monocytogenes causes meningitis and sepsis in newborns and accounts for 10% of community-acquired bacterial meningitis in adults.  Listeria is also diarrheagenic in humans, with those infected having vomiting, nausea and diarrhea.  Ingestion of Listeria from unpasteurized milk products can lead to bacteremia and septicemia with meningoencephalitis.  When transmitted across the placenta to the fetus, infection can lead to placentitis, neonatal septicemia and possible abortion.  Individuals at particular risk for listeriosis include newborns, pregnant women and their fetuses, the elderly and persons lacking a healthy immune system.  The bacterium usually causes septicemia and meningitis in patients with suppressed immune function.  Antibiotics are recommended for treatment of infection because most strains of Listeria are sensitive to ampicillin with an aminoglycoside. BACILLUS ANTHRACIS  1. MORPHOLOGICAL CHARACTERS  Is a Gram positive, non-motile, rectangular, aerobic, rod-shaped bacterium with square ends, capsulated.  Chain formation is common.  After discharge from an infected animal, or when bacilli from an open carcass are exposed to free oxygen, spores are formed which are resistant to extremes of temperature, chemical disinfectants, and desiccation.  For this reason, the carcass of an animal that died from anthrax should not be necropsied.  2. CULTURAL CHARACTERS  In broth growth occurs as flocular deposit.  3. METABOLIC CHARACTERS  - catalase positive  - hemolysis negative  - indole positive  - motility negative  - oxidase negative  - urease negative  - glucose, maltose, sucrose, trehalose fermented  4. PATHOGENICITY CHARACTERS  The toxins and the capsule are the primary virulence factors of the anthrax bacillus.  The anthrax toxin is complex, consisting of three protein components: I, II, and III.  Component I is the edema factor (EF), component II is the protective factor (PA) and component III is the lethal factor (LF).  These three components act synergistically to produce the toxic effects seen in anthrax.  Components I and II cause edema with low mortality, but, when component III is included, there is maximum lethality.  5. CLINICAL FEATURES  There are 4 forms of naturally occurring human anthrax infection:  Cutaneous anthrax is the result of spores entering the body through small breaks in the skin.  Is characterized by a sore at the point of infection that develops into a painless ulcer covered by a black scab (eschar).  Gastrointestinal anthrax - result of eating the meat of animals infected with B. anthracis.  The intestinal tract, mouth, or throat (oropharyngeal anthrax) may be infected.  GI anthrax is normally thought to occur as a result of ingestion of vegetative bacteria rather than spores; therefore, GI anthrax is not expected to result from exposure to aerosolized spores.  Inhalational anthrax is the result of breathing B. anthracis spores into the lungs.  Injection related anthrax is a newly recognized entity.  A number of cases have occurred recently in Europe in intravenous drug users.  This is believed to be caused by injecting heroin that is contaminated with material containing B. anthracis spores. clostridium  Species  - Clostridium tetani: Tetanus  - Clostridium perfringens: Gas gangrene  - Clostridium botulinum: Botulism  - Clostridium difficile: Pseudomembranous colitis  They are obligate anaerobes capable of producing endospores.  The genus Clostridium formerly included an important cause of diarrhea, Clostridioides difficile, which was reclassified into the Clostridiodies genus in 2016.   1.MORPHOLOGICAL CHARACTERS  Under the microscope, they appear as long, irregular (often drumstick- or spindle-shaped) cells with a bulge at their terminal ends (forms subterminal spores).  Under Gram staining, Clostridium cells are Gram-positive.  2. CULTURAL CHARACTERS  Show optimum growth on blood agar at human body temperatures in the absence of oxygen.  Clostridium difficile on blood agar – it is non hemolytic and form large and flat colonies.  3. CLINICAL FEATURES FOR CLOSTRIDIUM DIFFICILE  C. difficile is catalase- and superoxide dismutase-negative, and produces two types of toxins: enterotoxin A and cytotoxin B.  Clostridium difficile infection (CDI) occurs as a disease with a spectrum of severity ranging from mild, self-limiting diarrhoea to a severe colitis, pseudomembraneous colitis or toxic megacolon.  The disease arises as a major complication of antibiotic therapy and is most commonly acquired in hospital.  Currently the mainstay of diagnosis is the demonstration of C. difficile toxins in a diarrhoeal sample; only a few laboratories set up cultures for the microorganism. ENTEROBACTERIACEAE (ENTERIC BACTERIA)  Some enteric bacteria are always pathogenic as they cause disease : some strains of Escherichia coli, Salmonella, Shigella.  Other enteric bacteria are saprophytic and are included in the normal intestinal flora, where contribute to the food digestion.  These can become pathogenic in certain conditions, if they leave their intestinal habitat and colonize other sites.  Conditionally pathogenic bacteria include Escherichia coli, Klebsiella, Proteus, Pseudomonas.  1. MORPHOLOGICAL CHARACTERS  Gram negative bacilli, with rounded heads, non-spore forming, without capsule (with one exception: Klebsiella), mobile (with two exceptions: Shigella, Klebsiella). General aspect of Klebsiella Enterobacteriaceae family  2. CULTURAL CHARACTERS  ESCHERICHIA COLI:  On Istrate-Meitert medium or Drigalski medium the colonies are yellow (lactose positive), round, convex, with medium size.  SHIGELLA:  On selective medium the colonies are transparent, bright, in the colour of the medium (green), also are lactose negative (don’t produce the fermentation of lactose from the medium).  SALMONELLA:  On selective medium with bile, lactose and pH indicator (bromothymol blue), the colonies of Salmonella are small, lactose-negative (don’t change the colour of the medium), semi-transparent, with blue tint. Some of strains can have a black dot in the center given by the production of hydrogen sulfide.  PROTEUS:  On simple agar or blood agar media due to enhanced mobility it is present a phenomenon called “swarming”: from the initial growth concentric waves emerge, which invade the medium in a few hours.  On selective medium for enteric bacteria like Istrate - Meitert, Proteus develops lactose – negative colonies, round, green with a black center due to production of hydrogen sulfide (aspect named “cat's eye”).  KLEBSIELLA:  On simple agar medium after 24 hours at 37ºC, the colonies of Klebsiella are large, round, convex, moist with mucous appearance. After 48 hours the colonies increase in diameter and tend to confluence.  The colonies on lactose medium are big, yellow, convex, round with irregular edges, glossy, wet look, mucous like a "drop of honey" flowing on the surface plate.  PSEUDOMONAS:  On Istrate-Meitert medium: small, blue colonies, adherent to the medium.  On blood-agar medium: gray, shiny colonies, surrounded by β-hemolysis.  The culture of Pseudomonas aeruginosa releases a smell of ‘linden’.  3. CLINICAL FEATURES  A. DIGESTIVE INFECTIONS  ESCHERICHIA COLI  - Enteric infections – by pathogenic serotypes - malignant epidemic diarrhea of newborns, enterocolitis in adults (travellers’ diarrhea).  - Food poisoning  SHIGELLA  - BACILLARY DYSENTERY  - cramps, diarrhea, with slimy-consistent stools, fever, blood or mucus in stools  - rectal tenesmus = a clinical symptom, where there is a feeling of constantly needing to pass stools, despite an empty colon.  B. URINARY INFECTIONS - ESCHERICHIA COLI, KLEBSIELLA, ENTEROBACTER, PROTEUS MIRABILIS, CITOBACTER  C. RESPIRATORY INFECTIONS AND ENT (EAR NOSE THROAT) - KLEBSIELLA, PROTEUS, ESCHERICHIA COLI  D. GENITAL INFECTIONS - ESCHERICHIA COLI, KLEBSIELLA  E. PURULENT INFECTIONS - KLEBSIELLA, ENTEROBACTER, ESCHERICHIA, PROTEUS  F. INVASIVE INFECTIONS  SALMONELLA – TYPHOID FEVER  G. NOSOCOMIALE INFECTIONS – ESCHERICHIA COLI, SERRATIA, ENTEROBACTER, PROTEUS HAEMOPHILUS  Haemophilus spp. are small, pleomorphic, nonmotile, nonsporing Gram-negative rods or coccobacilli.  They are aerobic and facultatively anaerobic.  Growth is often enhanced by the addition of 5–10% carbon dioxide to the incubation atmosphere.  The oxidase and catalase reactions vary among the species.  Haemophilus spp. require one or both of two accessory growth factors (X and V).  X factor can be provided by hemin, protoporphyrin IX or other iron-containing porphyrins.  V factor is nicotinamide adenine dinucleotide (NAD) or NAD phosphate or certain unidentified precursors of these compounds. It is essential for oxidation–reduction processes.  Haemophilus influenzae is the major human pathogen in the group.  Some strains of H. influenzae have a polysaccharide capsule, of which there are six distinct antigenic types, designated a–f.  The most important is type b commonly causing bloodstream invasion and meningitis in children younger than 2 years.  Other Haemophilus species cause disease less frequently.  Haemophilus parainfluenzae - pneumonia or bacterial endocarditis.  Haemophilus ducreyi – chancroid - a venereal infection causing ulceration of the lymph nodes in the groin.  Haemophilus aphrophilus is a member of the normal flora of the mouth and occasionally causes bacterial endocarditis.  Haemophilus aegyptius - conjunctivitis.