1、Lecture 14BIOL 5331LegionellaBIOL 533Lecture 14Medical MicrobiologyLecture 14BIOL 5332History American Legion Convention in 1976 in Philadelphia hotel Respiratory distress and fever 200 affected 34 died Lecture 14BIOL 5333History Six months after outbreak,CDC isolated bacteria from post-mortum lung
2、tissue Inoculated lung tissue into peritoneal cavity of guinea pigs After animal became ill,removed its spleen and injected tissue into fertilized chicken eggs(rickettsial methodology)Lecture 14BIOL 5334History Organism was thought to be unique,given new genus and species name:Legionella pneumophila
3、 Epidemiological search revealed outbreak in same hotel two years earlier Culture problems because organisms:Do not grow on common laboratory media Do not readily stainLecture 14BIOL 5335Microbial Physiology and Structure Family Legionellaceae One genus:Legionella 25 species and 42 serotypesLegionel
4、la pneumophila responsible for 85%of infections(serotype 1 most common)Lecture 14BIOL 5336Microbial Physiology and Structure Species can be differentiated by:DNA homology Cell wall fatty acids Biochemical testing Immunological serotypingLecture 14BIOL 5337Microbial Physiology and Structure Morpholog
5、y Gram rods(pleomorphic on artificial media)Do not stain well except with special silver stain Culture:do not grow in ordinary lab media,even though they are aerobic organisms Require high concentration of cysteine and are inhibited by sodium ions and aromatic compoundsLecture 14BIOL 5338Microbial P
6、hysiology and Structure Media developed have:Charcoal to absorb aromatic compounds Non-sodium ion buffer Antibiotics to suppress other organisms Dyes to make colonies visible on solid mediaLecture 14BIOL 5339Pathogenesis Encounter:aquatic;found in lakes and streams Large numbers in polluted water ar
7、ound power stations Can live in chlorinated drinking water Normally found in hot water tanks of buildings Get into pipes and multiply in sediment and accumulate over period of years Do not spread from person to person Sediment provides shelter as well as nutrition for other bacteria that can supply
8、cysteineLecture 14BIOL 53310Pathogenesis Entry,spread,and multiplication Entry:inhalation of organisms Incubation period:2-10 days Initial host response:acute inflammatory response of aveoli and then bronchioles(similar to pneumococcal infection)Neutrophils accumulate followed by macrophageLecture 1
9、4BIOL 53311Pathogenesis Different from pneumococcal infection Organisms located inside of macrophage Inhibit lysosomal fusion and acidification of phagocyteLecture 14BIOL 53312Damage Organism possesses several exotoxins Proteases,hemolysins,and other cytotoxins One inhibits oxidative killing of neut
10、rophils May also damage tissue directly Spread rapidly in lung tissue Symptoms resulting from inflammatory disease in lung Cough,chest pains,abnormal breathing sounds,and feverLecture 14BIOL 53313Damage Other target sites:heart,kidney,lymph nodes,spleen,liver,and brain Neurological symptoms and diff
11、use metabolic abnormalities result from bloodstream invasion:confusion,delirium Some patients have gastrointestinal symptoms,including diarrheaLecture 14BIOL 53314Disease Syndromes In general,healthy people rarely get disease Immunosuppressed patients and heavy smokers with a history of respiratory
12、problemsLecture 14BIOL 53315Disease Syndromes Pontiac fever(flu-like illness)Pontiac,Michigan in 1968 Symptoms:fever,chills,muscle aches,malaise,headache Develops over 12-hour period,persists for 2-5 days,then spontaneously resolves Minimal morbidity and no mortalityLecture 14BIOL 53316Disease Syndr
13、omes Legionaires disease Much more severe,with high mortality unless promptly treated Overall mortality is 15-20%Symptoms reviewed in Pathogenesis sectionLecture 14BIOL 53317Epidemiology Incidence is poorly understood because disease documentation is difficult Pneumonias due to organism:less than 1%
14、to greater than 30%Estimated that 25,000 to 50,000 cases occur annuallyLecture 14BIOL 53318Epidemiology Time of year Sporadic infections throughout year Epidemic infections occur in late summer and fall Elderly with decreased pulmonary function and cellular immunity are at increased riskLecture 14BI
15、OL 53319Laboratory Diagnosis Microscopy Difficult because of lack of staining intracellular nature Require large number of organisms to detect Best test:direct fluorescent antibody Test is very specific False positives observed rarely with Pseudomonas,Bacteriodes,and other organismsLecture 14BIOL 53
16、320Laboratory Diagnosis Culture:buffered charcoal yeast extract(BCYE)Grow after 3-5 days Appear as small colonies with ground glass appearanceLecture 14BIOL 53321Laboratory Diagnosis Detection of Ag in respiratory secretions or urine Can be detected immunologically or by hybridization Excretion in u
17、rine can occur for as long as a yearLecture 14BIOL 53322Laboratory Diagnosis Serology:indirect fluorescent antibody test Four-fold or greater increase in antibody titer Response can be delayed as long as eight weeksLecture 14BIOL 53323Laboratory Diagnosis Identification Demonstration of typical morp
18、hology and growth requirements Gram bacteria(pleomorphic and weakly straining)Growth on BCYE with cysteine but no BCYE Confirmation by fluorescent antibodyLecture 14BIOL 53324Treatment Erythromycin is antibiotic of choice Can penetrate white blood cells Most strains possess-lactamasesLecture 14BIOL 53325Prevention Complete elimination of organism from water supplies is almost impossible Decrease in numbers normally effective Normally,healthy people not at risk Hyperchlorination and heating of water frequently employedLecture 14BIOL 53326Lecture 14 Questions?Comments?Assignments.
