Bacteriology Lecture Notes 2024-2025 PDF

Bacteriology B. Gram positive rods B. Gram positive rods There are 4 medically important genera of gram-positive rods: Bacillus, Clostridium, Corynebacterium, and Listeria B. Gram positive rods Bacillus and Clostridium form spores, whereas Corynebacterium and Listeria do not....

Bacteriology B. Gram positive rods B. Gram positive rods There are 4 medically important genera of gram-positive rods: Bacillus, Clostridium, Corynebacterium, and Listeria B. Gram positive rods Bacillus and Clostridium form spores, whereas Corynebacterium and Listeria do not. Members of the genus Bacillus are aerobic, whereas those of the genus Clostridium are anaerobic B. Gram positive rods I. Spore-Forming Gram-Positive Rods BACILLUS : There are 2 medically important Bacillus species: Bacillus anthracis and Bacillus cereues.  I. Spore-Forming Gram- Positive Rods CLOSTRIDIUM There are 4 medically important Clostridium species: C tetani, C botulinum, C perfringens (which causes either gas gangrene or food poisoning), and C difficile. All clostridia are anaerobic, sporeforming, gram- positive rods. II. Non-Spore Forming Gram-Positive Rods There are 2 important pathogens in this group: Corynebacterium diphtheriae and Listeria monocytogenes. II. Non-Spore Forming Gram-Positive Rods CORYNEBACTERIUM DIPHTHERIAE : Disease : C diphtheria causes diphtheria. Other Corynebacterium species (diphtheroids) are implicated in opportunistic infections.  II. Non-Spore Forming Gram-Positive Rods CORYNEBACTERIUM DIPHTHERIAE : Important Properties : Corynebacteria are gram-positive rods that appear club-shaped (tapered at one end) and are arranged in palisades or in V- or L-shaped formations. The rods have a beaded appearance. II. Non-Spore Forming Gram-Positive Rods  II. Non-Spore Forming Gram-Positive Rods CORYNEBACTERIUM DIPHTHERIAE : Transmission : Humans are the only natural host of C diphtheriae. Both toxigenic and non toxigenic organisms reside in the upper respiratory tract and are transmitted by airborne droplets. The organism can also infect the skin at the site of a preexisting skin lesion.  II. Non-Spore Forming Gram-Positive Rods CORYNEBACTERIUM DIPHTHERIAE : Pathogenesis : Although exotoxin production is essential for pathogenesis, invasiveness is also necessary because the organism must first establish and maintain itself in the throat.  II. Non-Spore Forming Gram-Positive Rods CORYNEBACTERIUM DIPHTHERIAE Pathogenesis : Diphtheria toxin inhibits protein synthesis by ADP ribosylation of elongation factor 2 (EF-2). II. Non-Spore Forming Gram-Positive Rods CORYNEBACTERIUM DIPHTHERIAE Pathogenesis : The host response to C diphtheriae consists of (1) local inflammation in the throat with a fibrinous exudate that forms the tough, adherent, gray “pseudomembrane” characteristic of the disease; and  II. Non-Spore Forming Gram-Positive Rods CORYNEBACTERIUM DIPHTHERIAE Pathogenesis : The host response to C diphtheriae consists of (2) antibody that can neutralize exotoxin activity by blocking the interaction of fragment B with the receptors, thereby preventing entry into the cell.  II. Non-Spore Forming Gram-Positive Rods CORYNEBACTERIUM DIPHTHERIAE Pathogenesis : The immune status of a person can be assessed by Schick’s test. performed by intradermal injection of 0.1 mL of purified standardized toxin. If the patient has no antitoxin, the toxin will cause inflammation at the site 4-7 days later. If no inflammation occurs, antitoxin is present and the patient is immune.  II. Non-Spore Forming Gram-Positive Rods CORYNEBACTERIUM DIPHTHERIAE Clinical Findings : most prominent sign, the thick, gray, adherent membrane over the tonsils and throat. The other aspects are nonspecific : fever, sore throat, and cervical adenopathy.  II. Non-Spore Forming Gram-Positive Rods CORYNEBACTERIUM DIPHTHERIAE Clinical Findings : There are 3 prominent complications: (1) extension of the membrane into the larynx and trachea, causing airway obstruction; (2) myocarditis accompanied by arrhythmias and circulatory collapse; (3) recurrent laryngeal nerve palsy.  II. Non-Spore Forming Gram-Positive Rods CORYNEBACTERIUM DIPHTHERIAE Clinical Findings : Cutaneous diphtheria causes ulcerating skin lesions and does not cause systemic symptoms.  II. Non-Spore Forming Gram-Positive Rods CORYNEBACTERIUM DIPHTHERIAE Laboratory Diagnosis : involves both isolating the organism and demonstrating toxin production. It should be emphasized that the decision to treat with antitoxin is a clinical one and cannot wait for the laboratory results.  II. Non-Spore Forming Gram-Positive Rods CORYNEBACTERIUM DIPHTHERIAE Treatment : The treatment of choice is antitoxin, which should be given immediately on basis of clinical impression because there is a delay in laboratory diagnostic procedures. The toxin binds rapidly and irreversibly to cells and, once bound, cannot be neutralized by antitoxin. The function of antitoxin is therefore to neutralize unbound toxin in the blood.  II. Non-Spore Forming Gram-Positive Rods CORYNEBACTERIUM DIPHTHERIAE Treatment : Treatment with penicillin or erythromycin is recommended also, but neither is a substitute for antitoxin. Antibiotics inhibit growth of the organism, reduce toxin production, and decrease the incidence of chronic carriers.  II. Non-Spore Forming Gram-Positive Rods CORYNEBACTERIUM DIPHTHERIAE Prevention : immunization of children with diphtheria toxoid (usually given as a combination of diphtheria toxoid, tetanus toxoid, and killed perutussis ogranisms).  II. Non-Spore Forming Gram-Positive Rods CORYNEBACTERIUM DIPHTHERIAE Prevention : Diphtheria toxoid is prepared by treating the exotoxin with formaldehyde. This treatment inactivates the toxic effect but leaves the antigenicity intact. Immunization consists of 3 doses given at 2, 4, and 6 months of age, with a booster at 1 and 6 years of age.  II. Non-Spore Forming Gram-Positive Rods LISTERIA MONOCYTOGENES: Diseases: L monocytogenes causes meningitis and sepsis in newborns and immunosuppressed adults.  II. Non-Spore Forming Gram-Positive Rods LISTERIA MONOCYTOGENES: Important Properties: L monocytogenes is a small gram-positive rod arranged in V-or L-shaped fromations similar to corynebacteria. The organism exhibits an unusual tumbling movement that distinguishes it from the corynebacteria, which are nonmotile. Colonies on a blood agar plate produce a narrow zone of beta- hemolysis that resembles the hemolysis of some streptococci.  II. Non-Spore Forming Gram-Positive Rods LISTERIA MONOCYTOGENES: Pathogenesis: Listeria infections occur primarily in 2 clinical settings : (1) in the fetus or newborn as a result of transmission across the placenta or during delivery; and (2) in immunosuppressed adults, especially renal transplant patients.  II. Non-Spore Forming Gram-Positive Rods LISTERIA MONOCYTOGENES: Pathogenesis: The organism is distributed worldwide in animals, plants, and soil. From these reservoirs, it is transmitted to humans by contact with animals or their feces, by unpasteurized milk, and by contaminated vegetables.  II. Non-Spore Forming Gram-Positive Rods LISTERIA MONOCYTOGENES: Pathogenesis: listeriosis is primarily a food-borne disease associated with eating unpasteurized cheese.  II. Non-Spore Forming Gram-Positive Rods LISTERIA MONOCYTOGENES: Pathogenesis: The pathogenesis of Listeria is dependent upon the organism’s ability to invade mononuclear phagocytic cells. Because Listeria preferentially grows intracellularly, cell-mediated immunity is a more important to Listeria infections.  II. Non-Spore Forming Gram-Positive Rods LISTERIA MONOCYTOGENES: Pathogenesis: The organism produces listeriolysin O, a hemolysin similar to streptolysin O. it acts by producing holes in cell membranes.  II. Non-Spore Forming Gram-Positive Rods LISTERIA MONOCYTOGENES: Clinical Findings : Infection during pregnancy can cause abortion, Premature delivery, or sepsis during the peripartum period.  II. Non-Spore Forming Gram-Positive Rods LISTERIA MONOCYTOGENES: Clinical Findings : Newborns infected at the time of delivery can have acute meningitis 1-4 weeks later. The infected mother is either asymptomatic or has an influenza-like illness,  II. Non-Spore Forming Gram-Positive Rods LISTERIA MONOCYTOGENES: Clinical Findings : L monocytogenes infections in immunocompromised adults can either be sepsis or meningitis.  II. Non-Spore Forming Gram-Positive Rods LISTERIA MONOCYTOGENES: Laboratory Diagnosis : primarily by Gram stain and culture. Identification of the organism as L monocytogenes is made by sugar fermentation tests.  II. Non-Spore Forming Gram-Positive Rods LISTERIA MONOCYTOGENES: Treatment : Treatment consists of ampicillin with or without gentamicin. Trimethoprim-sulfamethoxazole is also effective. Resistant strains are rare.  II. Non-Spore Forming Gram-Positive Rods LISTERIA MONOCYTOGENES: Prevention : Prevention is difficult because there is no immunization. Limiting the exposure of immunosuppressed patients to potential sources such as infected animals and their products and contaminated vegetables is recommended. The End