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 AgentStreptococcus 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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