Microbiology (Infectious Disease) Flashcards

•They can be acquired by different routes: –Respiratory tract –Oral cavity and digestive system –Skin and genitourinary tract

Free of microbes due to the constant removal of foreign particles due to cilia

Upper RT, is inhabited by: streptococci, staphylococci, neisseriae, diphtheroids and yeasts. Some of these are potentially pathogenic but are normally controlled by the presence of other microbes and host antibodies.

•Upper RT: More than 90% of these infections are caused by viruses. Strep throat caused by, Streptococcus pyogenes is the most common bacterial infection. These Group A strep are called pyogenic cocci, “associated with pus formation”. Symptoms include, fever, inflammation of the mucous membrane of the throat, glandular swelling. Usually self limiting however if all three symptoms are seen treatment is recommended. Infections can lead to scarlet fever, rheumatic fever and acute glomerulonephritis.

•Scarlet fever, is caused by lysogenic strains of S. pyogenes that synthesize an exotoxin called, erythrogenic toxin,which causes a red rash throughout the body. Strawberry tongue is also a characteristic of this illness. This toxin is under the control of a temperate bacteriophage. Penicillin is the treatment.

•Rheumatic fever and acute glomerulonephritis are nonsuppurative (non pus forming) sequelae of strep throat. Rheumatic fever is characterized by lesions that appear in the heart, joints and skin that appear 2-3 wks post strep throat. These people have a high anti-streptolysin O titer. Streptolysin O is a hemolysin produced by these bacteria. Acute glomerulonephritis, is often seen in children following strep throat or a cutaneous strep infection; edema, hypotension blood in urine are symptoms.

•Necrotizing fasciitis, rapid destruction of fibrous tissuethat encloses and separates muscle, caused by S. pyogenes, aka “flesh eating bacteria”.

•Gram positive cocci in chains, catalase negative. On blood agar three different types of hemolysis are observed, S. pyogenes, Group A produces β hemolysis, or complete lysis of sheep’s blood. This strain is also bacitracin sensitive. Confirmatory test coagglutination.

•This bacterium is also known as pneumococcus. Bacterial pneumonia is often a secondary infection that follows viral infections of the upper respiratory tract. Bacteria ends up in the lung, fluid accumulates in lungs to produce edema. Complications of this illness lead to meningitis, pleurisy (inflammation of the pleura), abscess formation, septicemia.

•Gram positive, encapsulated , lancet shaped diplococci that are seen in the patient’s sputum. These species are α hemolytic, optochin sensitive and bile soluble. Optochin is ethylhydrocupreine hydrocholoride, it inhibits the growth of S. pneumoniae. This strain also produces an autolytic enzyme, N-acetyl-muramyl-L-alanine amidase, that solubilizes the cell wall peptidoglycan and results in cell lysis. This is the basis of bile solubility, pneumococcal cells are incubated in sodium deoxycholate and lysis is observed. Quellung reation, capsular swelling in the presence of antisera directed against capsular antigens.

•Form of pneumonia caused by Legionella pneumophila, aerobic, Gram negative rod, first isolated in 1976. This microbe has an incubation period of 2-10 days, headache, fever 104-105 F, chills, muscle aches, dry cough, chest pain, abdominal pain, diarrhea. This is usually describes as a bronchopneumonia. Grows on medium containing L-cysteine and iron salts, charcoal yeast extract and Mueller Hinton agar base with L-cysteine and iron. Colonies visible after 4-5 days, incubation 35 C under CO2 tension. Several ways to confirm identity, immunofluorescence, DNA probe, ELISA. Mortality in untreated cases 15 to 25 %, high with immunocompromised patients. 1,000 cases / yr in US, a milder form of the disease is called Pontiac Fever.

•Bordetella pertussis, Gram negative, coccobacillus bacterium that causes an acute respiratory disease. Bacterium is transmitted through infected droplets in the air, highly contagious. Severe coughing, gasps for air between coughing aka “whoops”. A heat sensitive exotoxin as well as an extracytoplasmic adenylate cyclase that increases cAMP levels contribute to the pathogenesis. Isolated on Bordet Gengou agar. Mild cases no treatment necessary, serious require Er, children immunized with DPT vaccine.

•Corynebacterium diphtheriae is the causative agent. Gram positive, pleomorphic rod shaped bacterium, obligate aerobe. It produces Babes-Ernst bodies, polyphosphate intracellular granules. Strains with the lysogenic bearing prophage produce the diphtheria exotoxin, which when cleaved into components fragment A & B. Fragment A inhibits eukaryotic protein synthesis by modifying EF2, inhibiting protein synthesis. In the throat a grayish pseudomembrane forms, necrosis, inflammation result is suffocation. Identification /isolation on the basis of tellurite containing agar, colonies appear black-grey. Exotoxin assayed using Guinea pigs or Elek gel diffusion test.

•TB is caused by Mycobacterium tuberculosis an acid fast organism, cell wall has a high lipid content, mycolic acids. The cell wall is thus impermeable to stains and nutrients thus accounting for its slow growth. This causes a lung disease and is transmitted by droplets from coughs, causes a characteristic lesion in the lung “tubercule”, Grows slowly on Lowenstein-Jensen medium. 2 to 6 weeks in 5 to 10 % CO2. •Screen for exposure using the tuberculin skin test. Injected into the forearm, examined at 48 hrs, look for zone of induration. Treatment, Sm, Rif, isoniazid. In Europe a vaccine bacile-Calmette-Guerin (BCG) is used. It contains live, attenuated M. bovis, gives immunity to TB.

•An infection of the membranes that surround the brain and spinal cord, can be caused by a variety of bacteria. Hib vaccine, prevents H.influenzae type b. Before this vaccine 20,000 cases/ yr in the US.