| <table border="0" cellpadding="0" cellspacing="0"> <tr> <td valign="top" bgcolor="#ffffff">Bacteroides melaninogenicus. </td></tr></table> <table border="0" cellpadding="0" cellspacing="0"> <tr> <td valign="top" bgcolor="#ffffff">Haemophilus influenzae Diseases Sinusitis, otitis media, and pneumonia are common. Epiglottitis is uncommon, but H. influenzae is the most important cause. H. influenzae used to be a leading cause of meningitis, but the vaccine has greatly reduced the number of cases. Characteristics Small gram-negative (coccobacillary) rods. Requires factors X (hemin) and V (NAD) for growth. Of the six capsular polysaccharide types, type b causes 95% of invasive disease. Type b capsule is polyribitol phosphate. Habitat and Transmission Habitat is the upper respiratory tract. Transmission is via respiratory droplets. Pathogenesis Polysaccharide capsule is the most important determinant of virulence. Unencapsulated ("untypeable") strains cause mucosal infections but not invasive infections. IgA protease is produced. Most cases of meningitis occur in children younger than 2 years of age, because maternal antibody has waned and the immune response of the child to capsular polysaccharides can be inadequate. No exotoxins identified. Laboratory Diagnosis Gram-stained smear plus culture on chocolate agar. Growth requires both factors X and V. Determine serotype by using antiserum in various tests, e.g., latex agglutination. Capsular antigen can be detected in serum or cerebrospinal fluid. Serologic test for antibodies in patient's serum not useful. Treatment Ceftriaxone is the treatment of choice for meningitis. Approximately 25% of strains produce [ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذه الصورة]-lactamase. Prevention Vaccine containing the type b capsular polysaccharide conjugated to diphtheria toxoid or other protein is given between 2 and 18 months of age. Rifampin can prevent meningitis in close contacts. </td></tr></table> <table border="0" cellpadding="0" cellspacing="0"> <tr> <td valign="top" bgcolor="#ffffff">Bordetella pertussis Disease Whooping cough (pertussis). Characteristics Small gram-negative rods. Habitat and Transmission Habitat is the human respiratory tract. Transmission is via respiratory droplets. Pathogenesis Pertussis toxin stimulates adenylate cyclase by adding ADP-ribose onto the inhibitory G protein. Toxin has two components: subunit A, which has the ADP-ribosylating activity, and subunit B, which binds the toxin to cell surface receptors. Pertussis toxin causes lymphocytosis in the blood by inhibiting chemokine receptors. Inhibition of these receptors prevents lymphocytes from entering tissue, resulting in large numbers being retained in the blood. Inhibition of chemokine receptors occurs because pertussis toxin ADP-ribosylates the inhibitory G protein which prevents signal transduction within the cell. In addition, extracellular adenylate cyclase is produced, which can inhibit killing by phagocytes. Tracheal cytotoxin damages ciliated epithelium of respiratory tract. Laboratory Diagnosis Gram-stained smear plus culture on Bordet-Gengou agar. Identified by biochemical reactions and slide agglutination with known antisera. PCR tests, if available, are both sensitive and specific. Serologic tests for antibody in patient's serum not useful. Treatment Erythromycin. Prevention The acellular vaccine containing pertussis toxoid and four other purified proteins is recommended rather than the killed vaccine, which contains whole organisms. Usually given to children in combination with diphtheria and tetanus toxoids (DTaP). </td></tr></table> <table border="0" cellpadding="0" cellspacing="0"> <tr> <td valign="top" bgcolor="#ffffff">Legionella pneumophila Disease Legionnaires' disease ("atypical" pneumonia). Characteristics Gram-negative rods, but stain poorly with standard Gram stain. Require increased iron and cysteine for growth in culture. Habitat and Transmission Habitat is environmental water sources. Transmission is via aerosol from the water source. Person-to-person transmission does not occur. Pathogenesis Aside from endotoxin, no toxins, enzymes, or virulence factors are known. Predisposing factors include being older than 55 years of age, smoking, and having a high alcohol intake. Immunosuppressed patients, e.g., renal transplant recipients, are highly susceptible. The organism replicates intracellularly, therefore cell-mediated immunity is an important host defense. Smoking damages alveolar macrophages, which explains why it predisposes to pneumonia. Laboratory Diagnosis Microscopy with silver impregnation stain or fluorescent antibody. Culture on charcoal yeast extract agar containing increased amounts of iron and cysteine. Urinary antigen provides rapid diagnosis. Diagnosis can be made serologically by detecting rise in antibody titer in patient's serum. Treatment Azithromycin or erythromycin. Rifampin can be added in severe cases. Prevention No vaccine or prophylactic drug is available. </td></tr></table> <table border="0" cellpadding="0" cellspacing="0"> <tr> <td valign="top" bgcolor="#ffffff">Brucella Species (e.g., B. abortus, B. suis, B. melitensis) Disease Brucellosis (undulant fever). Characteristics Small gram-negative rods. Habitat and Transmission Reservoir is domestic livestock. Transmission is via unpasteurized milk and cheese or direct contact with the infected animal. Pathogenesis Organisms localize in reticuloendothelial cells, especially the liver and spleen. Able to survive and replicate intracellularly. No exotoxins. Predisposing factors include consuming unpasteurized dairy products and working in an abattoir. Laboratory Diagnosis Gram-stained smear plus culture on blood agar plate. Identified by biochemical reactions and by agglutination with known antiserum. Diagnosis may be made serologically by detecting antibodies in patient's serum. Treatment Tetracycline plus rifampin. Prevention Pasteurize milk; vaccinate cattle. No human vaccine is available. </td></tr></table> <table border="0" cellpadding="0" cellspacing="0"> <tr> <td valign="top" bgcolor="#ffffff">Francisella tularensis Disease Tularemia. Characteristics Small gram-negative rods. Habitat and Transmission Reservoir is many species of wild animals, especially rabbits, deer, and rodents. Transmission is by ticks (e.g., Dermacentor), aerosols, contact, and ingestion. Pathogenesis Organisms localize in reticuloendothelial cells. No exotoxins. Laboratory Diagnosis Culture is rarely done, because special media are required and there is a high risk of infection of laboratory personnel. Diagnosis is usually made by serologic tests that detect antibodies in patient's serum. Treatment Streptomycin. Prevention Live, attenuated vaccine for persons in high-risk occupations. Protect against tick bites. </td></tr></table> <table border="0" cellpadding="0" cellspacing="0"> <tr> <td valign="top" bgcolor="#ffffff">Pasteurella multocida Disease Wound infection, e.g., cellulitis. Characteristics Small gram-negative rods. Habitat and Transmission Reservoir is the mouth of many animals, especially cats and dogs. Transmission is by animal bites. Pathogenesis Spreads rapidly in skin and subcutaneous tissue. No exotoxins. Laboratory Diagnosis Gram-stained smear and culture. Treatment Penicillin G. Prevention Ampicillin should be given to individuals with cat bites. There is no vaccine. </td></tr></table> <table border="0" cellpadding="0" cellspacing="0"> <tr> <td valign="top" bgcolor="#ffffff">Yersinia pestis Disease Bubonic and pneumonic plague. Characteristics Small gram-negative rods with bipolar ("safety pin") staining. One of the most virulent organisms, i.e., very low ID50. Habitat and Transmission Reservoir is wild rodents, e.g., rats, prairie dogs, and squirrels. Transmission is by flea bite. Pathogenesis Virulence factors include endotoxin, an exotoxin, two antigens (V and W), and an envelope (capsular) antigen that protects against phagocytosis. V and W proteins allow organism to grow within cells. Bubo is a swollen inflamed lymph node, usually located in the region of the flea bite. Laboratory Diagnosis Gram-stained smear. Other stains, e.g., Wayson's, show typical "safety-pin" appearance more clearly. Cultures are hazardous and should be done only in specially equipped laboratories. Organism is identified by immunofluorescence. Diagnosis can be made by serologic tests that detect antibody in patient's serum. Treatment Streptomycin either alone or in combination with tetracycline. Strict quarantine for 72 hours. Prevention Control rodent population and avoid contact with dead rodents. Killed vaccine is available for persons in high-risk occupations. Close contacts should be given tetracycline. </td></tr></table> <table border="0" cellpadding="0" cellspacing="0"> <tr> <td valign="top" bgcolor="#ffffff">Mycobacterium tuberculosis Diseases Tuberculosis. Characteristics Aerobic, acid-fast rods. High lipid content of cell wall, which prevents dyes used in Gram stain from staining organism. Lipids include mycolic acids and wax D. Grows very slowly, which requires that drugs be present for long periods (months). Produces catalase, which is required to activate isoniazid to the active drug. Habitat and Transmission Habitat is the human lungs. Transmission is via respiratory droplets produced by coughing. Pathogenesis Granulomas and caseation mediated by cellular immunity, i.e., macrophages and CD4-positive T cells (delayed hypersensitivity). Cord factor (trehalose mycolate) correlates with virulence. No exotoxins or endotoxin. Immunosuppression increases risk of reactivation and dissemination. Laboratory Diagnosis Acid-fast rods seen with Ziehl-Neelsen (or Kinyoun) stain. Slow-growing (3–6 weeks) colony on Löwenstein-Jensen medium. Organisms produce niacin and are catalase-positive. Serologic tests for antibody in patient's serum not useful. Skin Test PPD skin test is positive if induration measuring 10 mm or more appears 48 hours after inoculation. Induration is caused by a delayed hypersensitivity response. Positive skin test indicates that the person has been infected but not necessarily that the person has the disease tuberculosis. Treatment Long-term therapy (6–9 months) with three drugs, isoniazid, rifampin, and pyrazinamide. A fourth drug, ethambutol, is used in severe cases (e.g., meningitis), in immunocompromised patients (e.g., those with AIDS), and where the chance of isoniazid-resistant organisms is high, as in Southeast Asians. Most patients become noninfectious within 2 weeks of adequate therapy. Treatment of latent (asymptomatic) infections consists of isoniazid taken for 6–9 months. Multidrug-resistant (MDR) strains have emerged and require other drug combinations. Prevention BCG vaccine containing live, attenuated Mycobacterium bovis organisms may prevent or limit extent of disease but does not prevent infection with M. tuberculosis. Vaccine used rarely in the United States but widely used in parts of Europe and Asia. </td></tr></table> <table border="0" cellpadding="0" cellspacing="0"> <tr> <td valign="top" bgcolor="#ffffff">Atypical Mycobacteria These mycobacteria are called atypical because they differ from M. tuberculosis in various ways. The most important difference is that the atypicals are found in the environment, whereas M. tuberculosis is found only in humans. The atypicals are also called "Mycobacteria other than M. tuberculosis," or MOTTS. The atypicals are subdivided into slow growers and rapid growers based on whether they form colonies in more than or less than 7 days. (Pigment production by the slow growers need not concern us here.) The following are important slow growers:
The important rapid grower is Mycobacterium fortuitum-chelonei complex, which causes infections of prosthetic joints and indwelling catheters. It also causes skin and soft tissue infections at the site of puncture wounds. The organisms are usually resistant to most antituberculosis drugs. </td></tr></table> <table border="0" cellpadding="0" cellspacing="0"> <tr> <td valign="top" bgcolor="#ffffff">Mycobacterium leprae Disease Leprosy. Characteristics Aerobic, acid-fast rods. Cannot be cultured in vitro. Optimal growth at less than body temperature, so lesions are on cooler parts of the body, such as skin, nose, and superficial nerves. Habitat and Transmission Humans are the reservoir. Also found in armadillos, but it's uncertain whether they are a source of infections for humans. Most important mode of transmission is probably nasal secretions of patients with the lepromatous form. Patients with the lepromatous form are more likely to transmit than those with the tuberculoid form because they have much higher numbers of organisms than those with tuberculoid leprosy. Prolonged exposure is usually necessary. Pathogenesis Lesions usually occur in the cooler parts of the body, e.g., skin and peripheral nerves. In tuberculoid leprosy, destructive lesions are due to the cell-mediated response to the organism. Damage to fingers is due to burns and other trauma, because nerve damage causes loss of sensation. In lepromatous leprosy, the cell-mediated response to M. leprae is lost and large numbers of organisms appear in the lesions and blood. No toxins or virulence factors are known. Laboratory Diagnosis Acid-fast rods are abundant in lepromatous leprosy, but few are found in the tuberculoid form. Cultures and serologic tests not done. Lepromin skin test is positive in the tuberculoid but not in the lepromatous form. Treatment Dapsone plus rifampin for the tuberculoid form. Clofazamine is added to that regimen for the lepromatous form or if the organism is resistant to dapsone. Treatment is for at least 2 years. Prevention Dapsone for close family contacts. No vaccine is available. </td></tr></table> <table border="0" cellpadding="0" cellspacing="0"> <tr> <td valign="top" bgcolor="#ffffff">Actinomyces israelii Disease Actinomycosis (abscesses with draining sinus tracts). Characteristics Anaerobic, gram-positive filamentous, branching rods. Habitat and Transmission Habitat is human mouth, especially anaerobic crevices around the teeth. Transmission into tissues occurs during dental disease or trauma. Organism also aspirated into lungs, causing thoracic actinomycosis. Retained intrauterine device (IUD) predisposes to pelvic actinomycosis. Pathogenesis No toxins or virulence factors known. Organism forms sinus tracts that open onto skin and contain "sulfur granules," which are mats of intertwined filaments of bacteria. Laboratory Diagnosis Gram-stained smear plus anaerobic culture on blood agar plate. "Sulfur granules" visible in the pus. No serologic tests. Treatment Penicillin G and surgical drainage. Prevention No vaccine or drug is available. </td></tr></table> <table border="0" cellpadding="0" cellspacing="0"> <tr> <td valign="top" bgcolor="#ffffff">Nocardia asteroides Disease Nocardiosis (especially lung and brain abscesses). Characteristics Aerobic, gram-positive filamentous, branching rods. Weakly acid-fast. Habitat and Transmission Habitat is the soil. Transmission is via airborne particles, which are inhaled into the lungs. Pathogenesis No toxins or virulence factors known. Immunosuppression and cancer predispose to infection. Laboratory Diagnosis Gram-stained smear and modified Ziehl-Neelsen stain. Aerobic culture on blood agar plate. No serologic tests. Treatment Sulfonamides. Prevention No vaccine or drug is available. </td></tr></table> <table border="0" cellpadding="0" cellspacing="0"> <tr> <td valign="top" bgcolor="#ffffff">Mycoplasma pneumoniae Disease "Atypical" pneumonia. Characteristics Smallest free-living organisms. Not seen on Gram-stained smear because they have no cell wall, so dyes are not retained. The only bacteria with cholesterol in cell membrane. Can be cultured in vitro. Habitat and Transmission Habitat is the human respiratory tract. Transmission is via respiratory droplets. Pathogenesis No exotoxins produced. No endotoxin because there is no cell wall. Produces hydrogen peroxide, which may damage the respiratory tract. Laboratory Diagnosis Gram stain not useful. Can be cultured on special bacteriologic media but takes at least 10 days to grow, which is too long to be clinically useful. Positive cold-agglutinin test is presumptive evidence. Complement fixation test for antibodies to Mycoplasma pneumoniae is more specific. Treatment Erythromycin or tetracycline. Prevention No vaccine or drug is available. </td></tr></table> <table border="0" cellpadding="0" cellspacing="0"> <tr> <td valign="top" bgcolor="#ffffff">Treponema pallidum Disease Syphilis. Characteristics Spirochetes. Not seen on Gram-stained smear because organism is too thin. Not cultured in vitro. Habitat and Transmission Habitat is the human genital tract. Transmission is by sexual contact and from mother to fetus across the placenta. Pathogenesis Organism multiplies at site of inoculation and then spreads widely via the bloodstream. Many features of syphilis are attributed to blood vessel involvement causing vasculitis. Primary (chancre) and secondary lesions heal spontaneously. Tertiary lesions consist of gummas (granulomas in bone, muscle, and skin), aortitis, or central nervous system inflammation. No toxins or virulence factors known. Laboratory Diagnosis Seen by dark-field microscopy or immunofluorescence. Serologic tests important: VDRL (or RPR) is nontreponemal (nonspecific) test used for screening; FTA-ABS is the most widely used specific test for Treponema pallidum. Antigen in VDRL is beef heart cardiolipin; antigen in FTA-ABS is killed T. pallidum. VDRL declines with treatment, whereas FTA-ABS remains positive for life. Treatment Penicillin is effective in the treatment of all stages of syphilis. In primary and secondary syphilis, use benzathine penicillin G (a depot preparation) because T. pallidum grows slowly, so drug must be present for a long time. There is no resistance. Prevention Benzathine penicillin given to contacts. No vaccine is available. </td></tr></table> <table border="0" cellpadding="0" cellspacing="0"> <tr> <td valign="top" bgcolor="#ffffff">Borrelia burgdorferi Disease Lyme disease. Characteristics Spirochetes. Gram stain not useful. Can be cultured in vitro, but not usually done. Habitat and Transmission The main reservoir is the white-footed mouse. Transmitted by the bite of ixodid ticks, especially in three areas in the United States: Northeast (e.g., Connecticut), Midwest (e.g., Wisconsin), and West Coast (e.g., California). Eighty percent of cases are in the Northeastern states of Connecticut, New York, and New Jersey. Very small nymph stage of ixodid tick (deer tick) is most common vector. Tick must feed for at least 24 hours to deliver an infectious dose of B. burgdorferi. Pathogenesis Organism invades skin, causing a rash called erythema migrans. It then spreads via the bloodstream to involve primarily the heart, joints, and central nervous system. No toxins or virulence factors identified. Laboratory Diagnosis Diagnosis usually made serologically, i.e., by detecting IgM antibody. Confirm positive serologic test with Western blot assay. Treatment Doxycycline for early stages; penicillin G for late stages. Prevention Vaccine containing outer membrane protein of the organism was available but has been withdrawn. Avoid tick bite. Can give doxycycline or amoxicillin to people who are bitten by a tick in endemic areas. </td></tr></table> <table border="0" cellpadding="0" cellspacing="0"> <tr> <td valign="top" bgcolor="#ffffff">Leptospira interrogans Disease Leptospirosis. Characteristics Spirochetes that can be seen on dark-field microscopy but not light microscopy. Can be cultured in vitro. Habitat and Transmission Habitat is wild and domestic animals. Transmission is via animal urine. In the United States, transmission is chiefly via dog, livestock, and rat urine. Pathogenesis Two phases: an initial bacteremic phase and a subsequent immunopathologic phase with meningitis. No toxins or virulence factors known. Laboratory Diagnosis Dark-field microscopy and culture in vitro are available but not usually done. Diagnosis usually made by serologic testing for antibodies in patient's serum. Treatment Penicillin G. There is no significant antibiotic resistance. Prevention Doxycycline effective for short-term exposure. Vaccination of domestic livestock and pets. Rat control. </td></tr></table> <table border="0" cellpadding="0" cellspacing="0"> <tr> <td valign="top" bgcolor="#ffffff">Borrelia recurrentis Causes relapsing fever. Transmitted by human body louse. Organism well known for its rapid antigenic changes, which account for the relapsing nature of disease. Antigenic changes are due to programmed rearrangements of bacterial DNA encoding surface proteins. </td></tr></table> <table border="0" cellpadding="0" cellspacing="0"> <tr> <td valign="top" bgcolor="#ffffff">Chlamydia trachomatis Diseases Nongonococcal urethritis, cervicitis, inclusion conjunctivitis, lymphogranuloma venereum, and trachoma. Also pneumonia in infants. Characteristics Obligate intracellular parasites. Not seen on Gram-stained smear. Exists as inactive elementary body extracellularly and as metabolically active, dividing reticulate body intracellularly. Habitat and Transmission Habitat is the human genital tract and eyes. Transmission is by sexual contact and during passage of neonate through birth canal. Transmission in trachoma is chiefly by hand-to-eye contact. Pathogenesis No toxins or virulence factors known. Laboratory Diagnosis Cytoplasmic inclusions seen on Giemsa-stained or fluorescent-antibody-stained smear. Glycogen-filled cytoplasmic inclusions can be visualized with iodine. Organism grows in cell culture and embryonated eggs, but these are not often used. PCR-based assay and an ELISA using patient's urine are available. Treatment A tetracycline (such as doxycycline) or a macrolide (such as azithromycin). Prevention Erythromycin effective in infected mother to prevent neonatal disease. No vaccine is available. </td></tr></table> <table border="0" cellpadding="0" cellspacing="0"> <tr> <td valign="top" bgcolor="#ffffff">Chlamydia pneumoniae Disease Atypical pneumonia. Characteristics Same as C. trachomatis. Habitat and Transmission Habitat is human respiratory tract. Transmission is by respiratory aerosol. Pathogenesis No toxins or virulence factors known. Laboratory Diagnosis Serologic tests for antibody in patient's serum. Treatment A tetracycline, such as doxycycline. Prevention No vaccine or drug is available. </td></tr></table> <table border="0" cellpadding="0" cellspacing="0"> <tr> <td valign="top" bgcolor="#ffffff">Chlamydia psittaci Disease Psittacosis. Characteristics Same as C. trachomatis. Habitat and Transmission Habitat is birds, both psittacine and others. Transmission is via aerosol of dried bird feces. Pathogenesis No toxins or virulence factors known. Laboratory Diagnosis Diagnosis usually made by testing for antibodies in patient's serum. Cytoplasmic inclusion seen by Giemsa or fluorescent-antibody staining. Organism can be isolated from sputum, but this is rarely done. Treatment Tetracycline. Prevention No vaccine or drug is available. </td></tr></table> <table border="0" cellpadding="0" cellspacing="0"> <tr> <td valign="top" bgcolor="#ffffff">Rickettsia rickettsii Disease Rocky Mountain spotted fever. Characteristics Obligate intracellular parasites. Not seen well on Gram-stained smear. Antigens cross-react with OX strains of Proteus vulgaris (Weil-Felix reaction). Habitat and Transmission Dermacentor (dog) ticks are both the vector and the main reservoir. Transmission is via tick bite. Dogs and rodents can be reservoirs as well. Pathogenesis Organism invades endothelial lining of capillaries, causing vasculitis. No toxins or virulence factors identified. Laboratory Diagnosis Diagnosis made by detecting antibody in serologic tests such as the ELISA test. Weil-Felix test is no longer used. Stain and culture rarely done. Treatment Tetracycline. Prevention Protective clothing and prompt removal of ticks. Tetracycline effective in exposed persons. No vaccine is available. </td></tr></table> <table border="0" cellpadding="0" cellspacing="0"> <tr> <td valign="top" bgcolor="#ffffff">Rickettsia prowazekii Disease Typhus. Characteristics Same as R. rickettsii. Habitat and Transmission Humans are the reservoir, and transmission is via the bite of the human body louse. Pathogenesis No toxins or virulence factors known. Laboratory Diagnosis Serologic tests for antibody in patient's serum. Treatment A tetracycline, such as doxycycline. Prevention A killed vaccine is used in the military but is not available for civilian use. </td></tr></table> <table border="0" cellpadding="0" cellspacing="0"> <tr> <td valign="top" bgcolor="#ffffff">Coxiella burnetii Disease Q fever. Characteristics Obligate intracellular parasites. Not seen well on Gram-stained smear. Habitat and Transmission Habitat is domestic livestock. Transmission is by inhalation of aerosols of urine, feces, amniotic fluid, or placental tissue. The only rickettsia not transmitted to humans by an arthropod. Pathogenesis No toxins or virulence factors known. Laboratory Diagnosis Diagnosis usually made by serologic tests. Weil-Felix test is negative. Stain and culture rarely done. Treatment Tetracycline. Prevention Killed vaccine for persons in high-risk occupations. No drug is available. </td></tr></table> <table border="0" cellpadding="0" cellspacing="0"> <tr> <td valign="top" bgcolor="#ffffff">Note Only the more important of the minor bacterial pathogens are summarized in this section. </td></tr></table> <table border="0" cellpadding="0" cellspacing="0"> <tr> <td valign="top" bgcolor="#ffffff">Bartonella henselae </td></tr></table> // |
بعض اختصارات الميكروبيولوجي-2
admin- Admin
- المساهمات : 2533
تاريخ التسجيل : 22/03/2010
العمر : 63
الموقع : O.KATTAB@YAHOO.COM
