NU BIOL 1121 - Chapter 22: Respiratory System infections

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Chapter 22: Respiratory System infectionsIntroduction- Rebecca Lancefield, graduate of Wesley and later Columbia - Studied groups of surface antigens on strep on b-hemolytic speciesAnatomy and Physiology - Enormous variety of diseases from minor to fatal- Upper respiratory - head and necko generally not life threatening but frequento otitis (ear infection- can be ecternal or internal)o nasal cavity, nasopharynx and pharynx  colonized by numerous bacteria of many classes aerobes, anaerobes pharyngitic (throat infection) sinusitis and mastiodis (infection of the air passages in the skull)- rhinitis (nose infection)o conjunctiva (eye, eyelid membranes) usually no bacteria organisms swept into the nasolacrimal duct (tear duct) and nasopharynx- Tonsils: lymphoid organso Inflammation due to tonsillitis causes enlargement of the adenoid, or tonsils interfere with the draining of eustachain tubes, causing ear infection  These tubes equalized pressure in the middle ear and drain mucous secretions- Lower respiratory – chesto Normally sterileo more serious, can be life threateningo particularly in the immuno-compromisedo laryngitis, bronchitis, pneumonitis (results in infection of the alveoli if pus and fluid is pneumonia)o pneumonia, pertussis, tuberculosis- Muscociliary escalator**Normal Microbiota- Nasal cavity, nasopharynx (alpha and non hemolytic strep and dipheriods) and pharynx are the only structures that are lined with all types of bacteria- The eye is normally sterile due to lysozyme secretions with every blink- Nasopharynx has opportunistic bacteriaBacterial Infections of The Upper Respiratory System- Strep Throato Symptoms difficulty swallowing swollen tonsils fever red throat with pus patches enlarged tender lymph nodes in neck [not typical: red eyes, runny nose, cough.. = viral pharyngitis]  most patients recover uneventfully in about a week, many don’t have symptoms at allo Causative AgentStreptococcus pyogenes- Gram-positive, coccus in variable chains- β-hemolytic: complete hemolysis of RBC a.k.a. “group A streptococcus”- due to Lancefield Group A carbohydrate in cell wall- basis for rapid pyogenes species identification using antibodies- or DNA test probeso Streptococcal pathogenesis Streptococcus pyogenes arsenal of virulence factors Has many superantigens that cause fleshing eating disease, tissue damage, and strep shock C5a peptidase- Inhibits attraction of phagocytes by destroying c5a Hyaluronic and capsule- Inhibits phagocytosis; aids in penetration of epithetlium M Protien- Interferes with phagocytosis by causing breakdown of C3b opsonin Protien F- Responsible for attachment to host cells  Protien G- Interferes with phagocytosis by binding Fc segment of IgG Streptococcul pyrogenic exotoxins (SPE)- Spuperantigens responsible for scarlet fever, toxic shock, etc - Streptolysin O and So Lyse leukocytes and erthrocytes- Tissue degrading enzymes o Enchance spread of bacteria by breaking down DNA, proteins, blood clots, tissue hyaluronic acid - Scarlet Fevero Erythrogenic toxinoo Complications of Strep Throat in acute phase of strep throat: scarlet fever- rash due to the SPE systemic erythrogenic toxin - red skin rash, “strawberry” tongue sequelae = complications days to months later - 1. acute glomerulonephritis o abrupt fever, fluid retention, bloody urineo kidney damage due to inflammation from presence of immune complexes in the glomeruli- 2. acute rheumatic fever (~3 weeks later)o behavior changes, uncontrolled body movementso often damage to heart valves => leakage => heart failure in later lifeo susceptibility to subacute bacterial endocarditis when damaged valves are infected with normal micrbiotao Epidemiology Only humans because reacts specially with a human clotting factor o Streptococcal Pharyngitis Prevention - No vaccine availableo genome sequence of S.pyogenes may reveal new epitopes- Adequate ventilation- Avoid crowds- A sore throat with fever should be cultured for prompt treatmento to avoid complications Treatment- Confirmed strep throat treated with 10 days of penicillin or erythromycino Eliminates organisms in 90% of cases- Diphtheriao Symptoms mild sore throat, slight fever, fatigue and malaise and often dramatic neck swelling (“bull neck”) whitish membrane forms on tonsils, or in nasal cavity heart and kidney failure can followo Causative Agent Corynebacterium diphtheriae variably shaped, arranged in palasades  Gram-positive non-spore forming certain strains make diphtheria toxino Diptheria toxin tox gene provided by a bacteriophage = lysogenic conversion phage integrates the C. diptheriae chromosome (= forms a lysogen) Toxin production from the tox gene is controlled by iron (Fe) concentration- when Fe binds tox repressor (protein) => toxin production is repressed (turned off)- when available Fe is low => Fe dissociates from tox repressor and toxin genes is expressed (turned on)o Pathogenesis- C. diptheriae cells not very invasive- exotoxin -> bloodstream => damage to heart, nerves and kidneys Diphtheria toxin = A-B type exotoxin- inactive protein cut into A and B chains- B binds host cell membrane and A-B enters by endocytosis- free A chain becomes active enzyme => inactivates EF2 => stops protein synthesis in host cells- enzyme (re-used) inactivates large population of cells => explains potency of diptheria toxino Epidemiology Humans are primary reservoir , present in chronic skin infections like cutaneous dipheria  Spread by air - acquired through inhalation Sources of infection include- Carriers who recovered from infection- Asymptomatic cases- People with active disease- Contaminated fomites (inanimate objects)o Prevention DPT trivalent vaccine- diptheria-pertussis-tetanus- antibodies to diptheria toxoid neutralize the toxin- vaccination often neglected Immunity wanes after childhood- booster immunization every 10 yearso Treatment Effectiveness depends on early antiserum treatment- Delay in treatment may be fatal Antibiotics (penicillin and erythromycin) eliminate C.diptheriae but…  transmission of disease stopped but no effect on absorbed toxin Even with antibiotic therapy 1 in 10 patients die- Sinus, Earache and eye infectionso Pinkeye- Symptoms  increased tears and redness swollen eyelids sensitivity to bright light large amounts of puso Symptoms –


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NU BIOL 1121 - Chapter 22: Respiratory System infections

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