Gram Positive Rods PDF

Medical Bacteriology Gram positive rods Bacillus, Clostridia, Listeria, Corynebacterium  Sporigeneous rods Non sporigeneous rods BACILLUS CLOSTRIDIA LISTERIA CORYNEBACTERIA B. a...

Medical Bacteriology Gram positive rods Bacillus, Clostridia, Listeria, Corynebacterium  Sporigeneous rods Non sporigeneous rods BACILLUS CLOSTRIDIA LISTERIA CORYNEBACTERIA B. anthracis C. tetani C. botulinum L. monocytogenes C. perfringens C. difficile C. diphteriae bacterial spore  BACILLUS o Gram positive rods, large organisms arranged singly or in long serpentine chains o endospore-formers and toxin-producers o aerobic or facultative anaerobic, nonmotile/motile, nonhemolytic rods o ubiquitous in nature (vegetation, water, or soil), throughout the world, and invoved in the biological cycles of carbon/nitrogen o the family Bacillaceae consists of a diverse collection of genera and species; some are commensal of herbivors, some can infect the human host o the clinically relevant strains for humans are: Bacillus anthracis Bacillus cereus In members of genus Bacillus, the diameter of the spore does not exceed that of the bacterial cell  Bacillus anthracis Gram positive rod, spore-forming Virulent strains have a prominent polypeptide capsule (of poly-D-glutamic acid) encoded by a plasmid, pXO2 Virulent strains carry genes for three toxic protein components on a large plasmid, pXO1 o PA (protective antigen) o EF (edema factor) o LF (lethal factor)  Anthrax (charcoil) Anthrax is a zoonotic disease that primarily affects herbivores such as cattle, sheep, goats, and deer → infected by ingesting contaminated vegetation, water, or soil Humans are infected (accidental hosts) through exposure to contaminated animals (their carcasses) or animal products including meat, wool, or items made with those products, such as wool clothing.  Transmission Human disease is acquired by one of three routes: o inoculation of spores through exposed skin from contaminated soil or infected animal products (95% of cases) o ingestion of spores (rare for humans, frequent in grass- eating animals) o inhalation of spores leads to human infections (only), however, it is the most likely route of infection with biological weapons. Ingestion anthrax Cutaneous anthracis B. anthracis soft-tissue infections in intravenous Inhalation anthrax drug users  Cutaneous anthrax Gastrointestinal anthrax Typically, cutaneous anthrax starts with the Ulcers form at the site of invasion (mouth, development of a painless papule at the esophagus, intestine), leading to regional site of inoculation that rapidly progresses to lymphadenopathy, edema, and sepsis. an ulcer and then to a necrotic eschar. First symptoms are nausea, vomiting, and An eschar with extensive surrounding malaise, which rapidly progress to edema/inflammation is the hallmark of systemic disease. cutaneous anthrax Virtually 100% fatal in absence of Case-fatality: 20% in absence of treatment; treatment 4 days) Inhalation botulism: o major concern in the era of bioterrorism o aerosolization of the neurotoxin as a biological weapon o rapid onset and potentially high mortality  Diagnosis, Treatment & Prevention CLINICAL DIAGNOSIS is confirmed by toxin detection in the implicated food, or patient’s serum and feces. o cultures of heated specimens (to kill all non spore-forming bacteria) on nutritionally enriched anaerobic media allow spore to germinate. TREATMENT: o adequate ventilatory support o elimination of the organism from the gastrointestinal tract o the use of penicillin or metronidazole to kill the bacteria and reduce toxin production o passive immunization with trivalent botulinum antitoxins (A, B and E) to neutralize unbound toxin PREVENTION o destroy the spores in food (virtually impossible) o prevent spores germination o destroy the preformed toxin by heating food at 60-100°C for 10 minutes  Clostridium perfringens Gram positive rod C. perfringens is a large, rectangular rod with spores rarely observed C. perfringens inhabits the intestinal tract of humans and animals and is widely distributed in nature, particularly in soil and water contaminated with feces. Virulence is mediated by the production of several toxins (α, β, ε, iota, and enterotoxin): o α-toxin, a phospholipase C that lyses erythrocytes, platelets, leukocytes, and endothelial cells→hemolysis, increased vascular permeability and bleeding, tissue destruction, hepatic toxicity, myocardial dysfunction o enterotoxin, produced during the phase transition from vegetative cells to spores in the small intestine →food poisoning  Soft tissue infections caused by C. perfringens C. perfringens is responsible for soft-tissue infections including cellulitis, fasciitis or suppurative myositis, and myonecrosis with gas formation in the soft tissue (gas gangrene). Pathogenesis: o clostridial spores or vegetative organisms can be introduced into tissue during surgery or by a traumatic injury (wound contamination with soil) o onset of the disease generally within a week o symptoms are intense pain, skin becomes discolored, bullae and necrosis develop, and subcutaneous gas are present o then muscle necrosis, shock, renal failure and death often within 2 days of initial onset (mortality range 40-100%)  Laboratory diagnosis and Treatment MICROSCOPY o Gram stain in clinical specimens: detection of the bacteria with a characteristic morphology (Gram positive rectangular rods) o Colonies grow on agar media or blood culture broths. TREATMENT FOR SOFT-TISSUE INFECTIONS o surgical debridement o high dose of penicillin o hyperbaric oxygen treatment (inconclusive results) TREATMENT FOR FOOD POISONING o oral rehydration, intravenous fluids and electrolytes o antibiotic therapy is not recommended  Clostridium difficile Gram positive rod C. difficile is a large, anaerobic rod that freely form spores in vivo and in culture C. difficile is part of the normal intestinal flora in a small number of healthy and hospitalized patients, however, in some situations it is the agent of endogenous infections The bacteria is responsible for 15-25% of AAD cases (antibiotic- associated diarrhea). The disease occurs as a complication after antibacterial therapy. Symptoms are mild watery diarrhea → fever, abdominal cramps and diarrhea → bloody mucous diarrhea, in the most severe forms: pseudomembranous colitis Pathogenesis is mediated by toxins: o Toxin A: cholera-like enterotoxin o Toxin B: potent cytotoxin (protein synthesis inhibition)  Diagnosis and Treatment DIAGNOSIS Isolation of the C. difficile in stool culture documents colonization, but not disease. The diagnosis of disease is confirmed by demonstration of the toxins in a stool specimen from a patient with compatible clinical symptoms (antigen detection) or detection of the C. difficile toxin genes in clinical specimens by nucleic acid amplification techniques (molecular tests). TREATMENT o discontinuation of the implicated antibiotic is generally sufficient to alleviate mild disease o metronidazole or vancomycin is necessary for the management of severe diarrhea and colitis  Sporigeneous rods Non sporigeneous rods BACILLUS CLOSTRIDIA LISTERIA CORYNEBACTERIA B. anthracis C. tetani C. botulinum L. monocytogenes C. perfringens C. difficile C. diphteriae bacterial spore  LISTERIA Lysteria monocytogenes o facultatively anaerobic Gram positive rod with flagella o short rod (coccobacillus), sometimes in pairs or in short chains o growth in a wide range of temperature, pH and high salt concentration o facultative intracellular pathogen o ubiquitous in nature (soil, vegetation, water, and in the gastrointestinal tract of animals, but NO HUMANS) Human disease is uncommon and restricted to: o pregnant women/neonates o elderly o patients with defective cellular immunity THE PRIMARY SOURCE OF INFECTION IS CONSUMPTION OF CONTAMINATED FOOD, undercooked processed meat, unpasteurized or contaminated milk or soft cheese, and unwashed raw vegetables  Listeria monocytogenes The bacteria: o enter through the gastrointestinal tract after ingestion of contaminated food o adhere to epithelial cells via the action of a cell wall surface protein, internalin A, which induces phagocytosis of the bacteria o (inside the infected cells) produce listeriolysin O and two phospholipase C enzymes → the bacteria are released into the cytosol of infected cells o replicate into epithelial cells of the gastrointestinal tract and move from cell to cell by pushing the formation of protrusion (filopod) without being exposed to immune system o entry into macrophages after passage through the intestinal lining, dissemination to the liver and spleen → disseminated disease (immunoevasion mechanism) intracellular pathogen Life Cycle of L. monocytogenes in Host Cells  Who are at higher risk? o Pregnant women: nonspecific influenza-like symptoms o Newborn: if listeriosis is acquired during pregnancy (early-onset disease) → abortion, stillbirth, premature birth or formation of abscesses and granulomas in multiple organs (granulomatosis infantiseptica, high mortality rate without treatment); if listeriosis is acquired at or soon after birth (late-onset disease) → meningitis or meningoencephalitis with septicemia o elderly and immunocompromised patients: invasive infections, such as sepsis, meningitis, and meningoencephalitis. Listeria infections in healthy adults are mainly asymptomatic or occur in the form of a mild influenza-like illness (acute self-limited gastroenteritis, headache, myalgias, and arthralgias).  Laboratory diagnosis & Therapy MICROSCOPY Gram stain (short rods → coccobacillus) CULTURE Colonies grow on most conventional media, with small colonies and β-hemolysis when grown on blood agar plate (difficulty in distinguishing from streptococci) →cold enrichment for culture from food TREATMENT o gentamicin with either penicillin or ampicillin for serious infections (septicemia and meningitis) o trimethoprim-sulfamethoxazole  Corynebacterium spp. The genus Corynebacterium includes > 100 species of: o Gram positive bacteria with irregular shape arranged in clumps or short chains o aerobic or facultatively anaerobic o nonmotile, non-spore forming, and club shaped o widely distributed in nature: they are commonly found in soil and water, as well as on human skin and respiratory tract o the most important is C. diphtheriae, the etiologic agent of diphtheria and humans are the only known reservoir Corinebacteria frequently present metachromatic granules containing phosphates, lipids, RNA, arranged at the ends of the bacterial cell Club shaped cells “Chinese letters” appearance on microscopy  C. diphtheriae The major virulence factor is the diphteria toxin. The tox gene is introduced by a lysogenic bacteriophage, β-phage The receptor for the toxin is heparin-binding epidermal growth factor, which is present in many cell types, particularly on heart and nerve cells  Diphteria RESPIRATORY INFECTION The bacteria: o enter through the respiratory tract and multiply locally on epithelial cells in the pharinx and cause localized damage → malaise, sore throat, exudative pharyngitis, and a low- grade fever. The exudate evolves into a thick pseudomembrane composed of bacteria, lymphocytes, plasma cells, fibrin, and dead cells o produce the toxin that spreads in the blood and non-contiguous anatomical sites with severe disease primarily involving the heart (myocarditis) and nervous system (neuropathy, dysphagia, paralysis). Pseudomembrane  Diphteria CUTANEOUS INFECTION Cutaneous diphtheria occurs from invasion of the organism from the patient’s skin into the subcutaneous tissue. A papule develops at the site of contact that later becomes covered by a grayish membrane. As in the respiratory disease, the toxin elicits a systemic response with fever and it can also have effects on the heart and nervous system. Cutaneous diphtheria  Laboratory diagnosis, therapy and prevention MICROSCOPY Gram stain preparation on pseudomembrane, respiratory swabs, cutaneous lesions CULTURE Bacteria from clinical specimens are cultured on Loffler medium (horse serum) and on selective agar plates (cystein-tellurite blood agar, colistin-nalidixic agar). TREATMENT o penicillin or erythromycin is used to eliminate C. diphtheriae and terminate toxin production o early administration of diphtheria antitoxin to specifically neutralize the exotoxin before it binds the epithelial cells Vaccination is the best way to prevent diphtheria