Bacteria (38) - Microbiology Notes PDF

Chapter (20): MYCOPLASMA cholesterol → A�er several days of incuba�on, mycoplasmas produce minute colonies whichhave characteris�c “fried-egg” appearance that can be only visualized microscopically • Diagnosis of mycoplasma infec�on is based on serology because: 1- Direct microscopical detec�on is...

Chapter (20): MYCOPLASMA cholesterol → A�er several days of incuba�on, mycoplasmas produce minute colonies whichhave characteris�c “fried-egg” appearance that can be only visualized microscopically • Diagnosis of mycoplasma infec�on is based on serology because: 1- Direct microscopical detec�on is of limited value 2- Cul�va�on is difficult & requires prolonged incuba�on (up to 3 weeks in case of M. pneumoniae) 3- PCR, although rapid and highly sensi�ve, does not dis�nguish between coloniza�on & infec�on • The serological tests used are: 1- Specific tests: → detec�on of IgM or four-fold rise in IgG an�body �tre by EIA is diagnos�c 2- Non-specific test: * Detec�on of cold agglu�nins → which are IgM an�bodies that agglu�nate red cells at 4°C but not at 37°C Lab diagnosis *Titre of >/= 1:128 of cold agglu�nins is indica�ve of recent infec�on Mycoplasma species, diseases & modes of transmission 1- Ischaemia & even necrosis of hands & feet → because of in vivo clumping of RBCs when the pa�ent is exposed to cold temperature . r D Small Extracellular Metabolically inert particles Represent the infectious form Larger Intracellular Metabolically active particles Represent the replicating form 1 Chlamydia trachomatis: has several serotypes 1 Chlamydia trachomatis 2-The EBs • Bind to specific host cell receptors by protein adhesins & enter cells by endocytosis (sexually transmi�ed diseases) Females may present with • urethri�s &/or cervici�s, which may progress to salpingi�s & pelvic inflammatory disease (PID). → condi�on may be complicated by infer�lity or ectopic pregnancy 1- Non-gonococcal urethri�s Caused by Serotypes D-K Males present with urethri�s, which may progress to epididymi�s, prosta��s or proc��s • More than 50% of infected females are asymptoma�c Ocular infec�ons 1- Trachoma Caused by Transmission Trachoma manifests as Serotypes A, B or C Commonly occurs by Chronic keratoconjunc�vi�s fingers, fomites & flies with scarring mostly during which may lead to blindness hot & dry climates Caused by serotypes D-K (sexually transmi�ed diseases) 3- Once inside the cell • EB reorganizes within hours into larger RB which divides repeatedly by binary fission & produces new infec�ous EBs. 2 Chlamydia pneumonia 3 Chlamydophila psittaci * Laboratory diagnosis: 2- Lymphogranuloma venereum (LGV) Caused by Serotypes L1, L2 or L3 Manifests as Ini�al genital papule accompanied by suppura�ve inguinal lymphadenopathy 2- Inclusion conjunc�vi�s Caused by Serotypes D-K Trachoma is ancient disease which was well described in Egyp�an wri�ngs around 3800 B.C. Neonatal pneumonia • Their cell wall structure resembles that of Gram-nega�ve bacteria but lacks typical pep�doglycan layer • Site of replica�on appears as an intra-cytoplasmic inclusion body, which can be stained & visualized microscopically * Chlamydiae that infect humans are divided into three species Genital tract infec�ons • Chlamydia have unique biphasic life cycle 4- EBs are then released by lysis of host cell N.B N.B s e H m s E • Erythromycin & tetracycline are the drugs of choice for all mycoplasmas • Although chlamydia are similar to viruses in being small obligate intracellular organism, they are considered bacteria 1-There are two morphological forms of Chlamydia Life cycle • In lab, they can be grown on �ssue culture Sexual t a Treatment 2- Mild haemoly�c anaemia → due to in vivo destruc�on of RBCs throughout the body m a h • Gram stain is not useful; but organism can readily be stained by Giemsa stain Inhalation of respiratory droplets Bacteria (38) • Some pa�ents develop very high �tres of cold agglu�nins → this may result in: Chapter (21): CHLAMYDIA • Chlamydia is genus of very small obligate intracellular bacteria. → they lack ability to produce sufficient energy to grow independently &, therefore, can grow only inside host cells v Pharyngitis, bronchitis & otitis media u Non-gonococcal urethritis v Pelvic inflammatory disease (PID) w Post-abortal or postpartum fever N.B • However: * Posi�ve results may occur in some viral infec�ons, malaria, haemoly�c anaemia and liver disorders → most of these diseases have symptoms that easily dis�nguish them from those of primary atypical pneumonia * Nega�ve results may occur in about 50% of cases of M. pneumoniae infec�ons Characteristic features u Atypical pneumonia (20% of pneumonia cases) Transmission occurs: In neonates During passage through infected birth canal It is the most common In adults cause of neonatal As a result of transfer of organisms from conjunc�vi�s genitals to eye (as auto-infec�on) or through a vehicle (e.g. swimming pools) Infec�on occurs during passage through infected birth canal 1 Specimens 3 Cultivation • Specimens are inoculated onto �ssue culture Taken from urethra, cervix, conjunc�va, ........etc → intra-cytoplasmic inclusion bodies can be detected by Giemsa stain or immunofluorescence 2 Direct detection • Microscopic examina�on of Giemsa-stained smears For detec�on of intra-cytoplasmic basophilic inclusion bodies → This method is insensi�ve, non-specific & requires good experience • An�gen detec�on by immunofluorescence or by ELISA This method is more specific, reliable & rapid • Nucleic acid detec�on by DNA probes or PCR * Treatment & prevention 4 Serological tests • Are not helpful except in LGV infec�on 5 Frei skin test • It is similar to tuberculin test → rarely used for diagnosis of LGV infec�on An�bio�c of choice is Chlamydia are not sensi�ve to ß-lactam Erythromycin or an�bio�cs due to lack of typical pep�doglycan layer tetracycline in adults Detec�on & treatment of asymptoma�c Erythromycin is recommended for neonates & pregnant individuals are important preven�ve measures women because of effect of tetracycline on teeth & bones N.B Characteristic features 1- Mycoplasmas are bacteria without cell wall → lack of cell wall renders these organisms: 1- Unstainable by Gram stain 2- Resistant to an�bio�cs which inhibit cell wall synthesis (e.g. beta-lactam an�bio�cs) 3- Variable in shape (pleomorphic) 2- Their contents are enveloped by cell membrane 3- They are the only bacteria that contain sterol (in the form of cholesterol) in the cell membrane 4- They are the smallest bacteria that can be grown on cell free media → They require serum-enriched medium containing • It is recommended that pa�ents receiving treatment for gonorrhoea also be treated with tetracycline for possible concurrent Chlamydia infec�on