Chlamydiae, Rickettsiae and Mycoplasmas
a miscellaneous group with Properties common to bacteria & viruses they differ from each other . visible with light microscopy free growth (only mycoplasma) both DNA ,RNA present Rigid cell wall (except mycoplasma) suscptible to tetracyclin reproduce by binary fissionChlamydia spp.
Related to Gram –ve bacteriaBUT unlike bacteria ,obligate intracellular growthLarger than viruses (visible by light microscopy)Both DNA &RNA are present.Complex growth cycle Sensitive : tetrac., erythrom., sulphanomides3 species
Ch. Trachomatis (many diseases) Ch. Pneumoniae (acute respiratory tract infection) Ch.psittaci (psittacosis in birds ,also known as psittacosis in human)chlamydia
Chlamydia trachomatis cause1-Ocular infection: Neonatal conjuctivitis,keratoconjuctivitis ,blindness(trachoma)in the developing word. 2-Genital infection-non specific urethritis(the most common sexually transmitted disease in the UK. 3-Pneumonia-in neonates
Culture and diagnosis
Tissue culture ……Why???Serology (complement fixation test) .Fluorescent Ab staining of smears from the Lesion.Antibiotic sensitivity: Tetracyclin is effective for all Chlamydia l infection.
Rickettsia
1-Pleomorphic m.o.2-Coccobacilli3-Smaller than bacteria, but resembling them structurally & metabolically including cell wall formation ,visible by L.M.(by Giemsa stain)4-They like Chlamydia & viru ses (Obligate intracellular parasites ,which replicate by binary fission.5-Have cell wall(resemble gram –ve)6-Like viruses :obligate intra cellular parasite7-The best –known human rickettsial disease is typhus.8-Sensitive to tetracycline and chloramphenicol 9-Infect birds & mammals 10-Transmitted to man via bites of arthropods
There are 2 genera within the Rickettsieae: 1-Rckettsia 2-Coxiella
Rickettsial diseases include:1-Typhus :Acute febrile illness ,transmitted by rat flea 2-Spotted fevers-Rocky Mountain spotted fever
Coxiella
Coxiella burnetii An organism closely resembling Rickettsiae ,causes Q fever (atyphus like illness) Q fever usually present as the non bacterial pneumonia ,the lesions may be seen in the brain ,heart with resultant endocarditis.Culture & identification
Guinea inoculation Serology reactionGeneral Characteristics of Mycoplasma
$ Are the smallest prokaryotes capable of binary fission. $Pleomorphic morphologic forms (as they lack p.G. cell wall) $Wall less bacteria ,no P.G.cell wall but bound by plasma memb.consisting of lipids and sterols,hence they are highly pleomorphic Bacteria with No cell wall Outer membrane No lipopolysaccharide layer (endotoxin) Weak gram negative stain Normal flora of upper respiratory tract
Pleomorphism of mycoplasma
Mycoplasma speciesMycoplasma pneumoniae causes:• Atypical pneumonia•Mucocutaneous eruptions ,including the oral mucosa•Haemolytic anaemia
Mucocutaneous eruptions: M.Pneumonia may cause skin rashes &ulcerations of both the oral & vaginal mucosa
Oral Mycoplasma M.buccale M.oral M.salivarium Have been isolated from saliva,oral mucosa & dental plaque . But their significance in either health or disease is unclear.
Culture and identification:Can be cultured in special media (slow ,about 10 days)The colony have a characteristics (fried –egg)appearance.Serology is useful as the culture result s are delayed.Immunofluorescence of colonies transferred to glass slides(as they do not take gram stain well) Complement fixation test for M.pneumoniae Antibodies.