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Legionella responsible for respiratory disease (pneumonia) in persons attending an American
legion convention in Philadelphia. It is caused legionnaireʼs disease which is sever respiratory
illness first recognized in 1976. there are several species(50 spp and 70 serogroups) have a
medical importance.
Legionella spp
1- L. pneumophila caused pneumonia, several serotypes
2- L. micdadei
3- L.gormanii
4- L. jordanis and other species all which are caused respiratory diseases.
Typical organisms
Legionella are fastidious aerobic gram- negative bacteria, they are stained poorly by gram stain
(G-ve), therefore used carbol fuchsin as counterstain
Poorly gram negative of Legionellae Gram stain for Legionellae
Legionella and unusual G-ve bacilli
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Elecctron photography for Legionella
Culture
It is cannot growth on ordinary media therefore needed to specific culturing media
supplemented with iron and cystein, example of this media is buffered charcoal-yeast
extract(BCYE), at PH 6.9. Temperature 35 c and 90% humidity, antibiotic can be added to make
the medium selective for legionella, colonies usually appear after 3 days. Leg in blood cultures
usually require 2 wks or more to grow.
Legionellae on BCYE medium Legionellae on BCYE medium
Growth characteristics
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Legionellae r catalase positive, L . Pneumophila r oxidase positive while other spp are variable in
oxidase activity. L. pneumophila hydrolyze hippurate, other spp do not.
Most spp produce gelatinase and beta lactamase, while L. micdadei do not.
Enzymes and antigenic sturctures
There are more than 10 of L. pneumophila, serotype 1 responsible about legionnaries disease. L.
produce several enzymes like, proteases, phosphatases, lipases, Dnase, RNase and major
secretory protein which is metaloprotease, has hemolytic and cytotoxic activity.
Pathogenesis
Infection of debilitated or immunocompromised human commonly follows inhalation of the
bacterium from infected aerosoles generated from contaminated air conditioning systems,
shower heads and similar sources.
L.pneumophila produce a lobar, segmental, or patchy pulmonary infiltration
L. pneumophila enters and grows within human alveolar macrophages and monocytes and is
not effectively killed by PMN leukocytes.
The bacteria multiply within the phagosome vacuoles until they are numerous, the cells are
destroyed then bacteria are released and infection other macrophages.
The presence of iron is essential for the process of intracellular growth of the bacteria
Clinical finding
Asymptomatic infection is common in all age groups, as shown by elevated titer of specific
antibodies.
The disease well recognized in human over age 55 years.
Factors associated with high risk include smoking, chronic bronchitis and emphesema, steroid
and other immunosuppressive treatments , cancer chemotherapy and diabetes mellitus . So
when pneumonia occur in patients with these risk factors Legionella should be investigated as
the cause.
Infection may result in nondescript febrile illness of short duration or in a severe, rapidly
progressive illness with high fever, chills, malaise, nonproductive cough, hypoxia, diarrhea, and
chest X- ray reveal patchy, often multilobar consolidation
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Diagnosis
1- specimens : the organisms can be recovered bronchial washing, pleural fluid, lung biopsy or
blood. From sputum the isolation is more difficult.
2- smear: poorly stained by gram stain, but direct flourescent antibody test, but this test has low
sensitivity compared with culture.
3- specimens are cultured on BCYE agar.
4- serological test: levels of antibodies against Legionella rise slowly during the illness.
Serological tests have a sensitivity of 60-80% and a specificity of 95-99%.
Treatment
1- Legionella are susceptible to Erythromycin, some strain respond to rifampin.
2- Assisted ventilation may be necessary
Gardnerella vaginalis
G. vaginalis formerly called Hemophilus vaginalis is an organism isolated from female
genitourinary tract in percentage 30-90%and also associated with vaginitis. In wet smear, this
nonspecific vaginitis, or bacterial vaginosis, yeilds clue cells which are vaginal epithelial cells
covered with many tiny rod. Vaginal discharge often has a distinct fishy odour.
Treatment: Metronidazole is the drug of choice oral or intervaginal cream
Gardnerella vaginalis
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Streptobacillus moniliformis
Is an aerobic, gram negative highly pleomorphic organism that form irregular chains of bacilli. Its
grow is best at 37 C,°in medium containing serum, protein, egg yolk, or starch.
S. moniliformis is a normal inhabitant of throats of rats and humans can be infected by the rat
bites.
Clinical signs
Human disease (rat- bite fever) is characterized by 7 days fever, petechial rashes and
polyarthritis.
Diagnosis:
1-depend on cultures of blood, joint fluid, or pus.
2-mouse inoculation
3-serum agglutination test
rat- bite fever
Treatment
Penicillin is theraptically effective and other newly broad spectrum antimicrobial can be used.
Bacteroids
It is gram negative anaerobic bacilli, it is the most important group of anaerobes that cause
human infection. They are non-spore forming.
Morphology
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The most commonly encountered species is B.fragilis, a G-ve, non-motile, non-capsulate and
non- spore forming and appear as filamentous bacilli.
Cultural reqirements: strictly anaerobic optimum temperature is 37 c, incorporation of 20% bile
in the media enhances growth of all B.fragilis.
Growth is slow even under optimal conditions and on blood agar colonies appear after 48 hours
incubation. Hemolysis is rare.
Biochemical reactions
B.fragilis can be differentiated from other spp e.g. B. oralis and B. melaninogenicus on the basis
of varying patterns of sugar fermentation reactions
Pathogenicity
Bacteroides are commonsals in the buccal cavity and gastrointestinal tract. B. fragilis is the most
common of all bacteroides involved in abdominal, and gynaecological sepsis.
B. melaninogenicus and B. oralis an important role in dental caries
Treatment
Metronidazole is the drug of choice and many species are also sensitive to the lincomycin