Gram Positive Rods Non-Spore Forming Bacteria PDF

True bacteria – Rods - Gram positive rods Non-spore forming bacteria Corynebacterium, Listeria, Propionibacterium Corynebacterium The genus Corynebacterium includes C. diphtheria: the cause of the diphtheria, and Diphthe...

True bacteria – Rods - Gram positive rods Non-spore forming bacteria Corynebacterium, Listeria, Propionibacterium Corynebacterium The genus Corynebacterium includes C. diphtheria: the cause of the diphtheria, and Diphtheriodes: as normal flora (the skin, the conjunctival sac, the mouth, the vagina). Corynebacterium diphtheriae The caused of diphtheria. The vaccination protocols and widespread immunization beginning in early childhood has made the disease rare in developed countries. Epidemiology C. diphtheriae is found in the throat and nasopharynx of carriers and in patients with diphtheria. The disease is a local infection, so the organism is primarily spread by: 1- Respiratory droplets by carriers. 2-Direct contact with an infected individual 3-Contaminated waste. Pathogenesis Diphtheria is caused by the effects of a exotoxin that inhibits protein synthesis. The toxin is composed of two fragments A and B(Figure 1). Fragment B binds to the receptor in cell membranes and then mediates the delivery of fragment A.  Inside the cell, fragment A separates from fragment B, and catalyzes the transfer of adenosine diphosphate ribose (ADPR) from nicotine adenine dinucleotid (NAD+) to polypeptide chain elongation factor EF-2 ,then the complex(ADPR+EP-2)is inactivated and peptide synthesis stops. Clinical Significance 1-Respiratory diphtheria Diphtheria consist of : (1) Local infection of the throat, produces a thick, grayish, adherent exudate (pseudomembrane) (Figure 2), coats the throat and may extend into the nasal passages or down ward in the respiratory tract, leading to suffocation. (2) Generalized symptoms occur as the disease progresses (marked swelling of the lymph nodes in the neck), involve the heart and peripheral nerves, lead to congestive heart failure and permanent heart damage and paralysis of muscle groups are seen late in the disease. 2- Cutaneous diphtheria A puncture wound or cut in the skin can result in introduction of C. diphtheriae into the subcutaneous tissue, leading to a chronic non healing ulcer with a gray membrane. Diagnostic laboratory tests Clinical observation → Diphtheria should be considered in patients with = pharyngitis, low –grade fever,cervical adenopathy (swelling of the neck),erythema of the pharynx and adherent gray pseudomembranes. Microscopic examination: Gram stain: G+ rods , pleomorphic,that tend to stain unevenly,form clumps that look like Chinese characters , nonmotile, noncapsulated and nonspore forming.  Albert’s stain is important to diagnostic it because its contain volutin granules (contains phosphate granules, metachromatic granules) that stain deeply give rod a beaded appearance beside the bacilli looks like bipolar (see figure 3) and arranged in pairs or groups and from various angles with each other like L, V, X, Y, Z thus called Chinese letter arrangement. Macroscopic examination: Culture = a selective medium such as Tinsdale’s agar (Figure 2) which contains potassium tellurite, an inhibitor of other respiratory flora, and on which C. produces black colonies (to reduction of tellurite salt). On rich media (blood, serum or egg) colonies are small, granular, moist, glistening irregular edges. Biochemical reaction = Catalas +, oxidase - , gelatin- , Urase - , phosphatase -, ferment glucose and maltose with acid production only.  Fermentation of starch, glycogen and dextrin, is useful to differentiate between the 3 types of C. diphtheriae (on selective media containing tellurite, 3 types of C. diphtheriae : Gravis, Mitis, Intermedius). Gravis ferments starch, glycogen and dextrin, while the two other types don’t ferment starch and glycogen,ferment only dextrin. Treatment 1. Neutralization of toxin: by antitoxin inactivates any circulating toxin, not bound toxin to a cell-surface receptor. 2. Eradication of the organism: by several antibiotics, such as erythromycin or penicillin (Figure 2). Prevention By DTP vaccine (Diphtheria + Tetanus + Pertussis )which neutralize unbound toxin preventing the disease from progressing,should be started in children (2 years ). Booster injections of DT vaccine should be given at 10 year intervals throughout life. Diphtheroids Other Corynebacterium spp., that morphologically resemble to C. diphtheriae , are common commensals of the nose, throat, nasopharynx, skin, urinary tract and conjunctiva, and are generally unable to produce exotoxin, but a few cause disease in immunosuppressed individuals.  Listeria Listeria species are intracellular parasites that may be seen within host cells in tissue samples (Figure 1). Listeria monocytogenes is the only species that infects humans, other species are widespread among animals. Epidemiology Listeria infections are usually food borne (ice cream , cheese, ground meats and poultry) (growth at 4°C in food). 1 – 15 % of healthy humans are asymptomatic intestinal carriers of the organism. Listeria infections are most common in pregnant women + fetuses or newborns + immunocompromised individuals, such as the elderly or patients receiving corticosteroids. Antigenic classification Three serotypes are present isolates from humans , Ia , Ib , Irb. Irb causes an epidemic associated with cheese made from anpasteurized milk, cause meningitis between birth 3 week of life with high mortality rate. Pathogenesis It’s a facultative intracellular parasite, attaches to and enters a macrophage by phagocytosis and incorporated into a phagolysosome (see figure). It escapes from the phagolysosome by elaborating a toxin called Listeriolysin O as virulent factors.. L. monocytogenes grows in the cytosol, and assembles an actin filament tail that pushes the bacterium to the surface of the macrophage. A pseudopod extension forms , facilitating transfer of the Listeria into a neighboring phagocyte. Listeria produced phospholipases mediate the passage of the organism directly to a neighboring cell, allowing avoidance of cells of the immune system. Clinical significance Septicemia and meningitis are the most commonly reported forms of L. monocytogenes infection (listeriosis). Pregnant women, in the third trimester, may have a milder illness as well as in asymptomatic vaginal colonizaition, the organism can be transmitted to a newborn (cause of newborn meningitis) or to the fetus and initiate abortion. Immunocompromised individuals are susceptible to serious generalized infections, as meningocephalitis and bacteremia. Diagnostic laboratory tests Specimens = blood, cerebrospinal fluid, and other. Microscopic examination = Gram stain :G+ rods, occur as diplobacilli or in short chains, nonspore forming and may be seen within host cells in tissue samples. Its motile with tumbling motility by light microscopy in liquid medium after growth at 25°C , distinguish it from Corynebacterium (nonmotile) which may be confused morphologically with Listeria. Macroscopic examination = On blood agar, produces a small colony with β- hemolysis( figure 1).  Biochemical reaction = catalase + distinguish it from Streptococci (catalase - ) which may be confused morphologically with Listeria. Treatment Ampicillin and trimethoprim /sulfamethoxazole are used (Figure 1). Ampicillin and gentamicin also used after therapy. Prevention By proper food preparation and handling. Propionibacterium Propionibacterium acnes is classified as a Corynebacterium anaerobic diphtherods, form part of the normal flora of the skin. They cause acne by produce lipase which split off fatty acids from skin ,then produce tissue inflammation which contribute to acnes. Sometimes associated with endocarditis or infections of plastic implants. It's name come from produce propione acid from carbohydrate fermentation. Its G+ rods , nonspore forming , anaerobic microaerophilic rods.