Mollicutes mollis = soft; cutis = skin “soft skin” Bacteria lack a rigid cell wall, they only have atrilaminar outer membrane Small size 0.2-0.3 µm Small genome Members of the order Mycoplasmatales, classMollicutes Some are free living but most are parasitic
MollicutesOnly two genera, Mycoplasmaand Ureaplasma are important inmedicine.
These groups of microorganisms, previouslydescribed under the general title ofpleuropneumonia-like organisms (PPLO), aresmall procaryotic cells (200-250 nm indiameter). They resemble larger procaryotic cells (e.g.bacteria) in their ability to grow in cell-freemedia although some are exacting in theirgrowth requirements and grow slowly.
They have no rigid cell wall. There is atrilaminar cytoplasmic membrane, butunlike that of bacteria, it containscholesterol or carotenol in addition to theusual phospholipids.The mycoplasma cannot synthesize theirown cholesterol and require it as a growthfactor in the culture medium.
The absence of a rigid cell wall is reflectedin branched and other unusualmorphological forms of the mycoplasmacell.Cells of some species have a coccobacillarymorphology, other are filamentous, somehave specialized processses for attachmentto host cells that are probably also related tothe capacity for gliding motion.
In line with absence of a cell wall thesemicroorganisms are not inhibited bymembers of the beta-lactam antibiotics.In general they are sensitive totetracyclines, macrolides,fluoroquinolones and chloramphenicol.
Mycoplasma are grown in soft agarmedium with a high (10-20%)concentration of serum or other proteinsuch as ascitic fluid.The function of the serum or other proteinThe function of the serum or other proteinis to provide a source of cholesterol, fattyacids, or urea in the case of theureaplasmas, and to regulate theiravailability to the organisms.
Some mycoplasma species are aerobes orfacultative anaerobes, other grow better inhydrogen or nitrogen with 10% CO 2 .The colonies looks like "fried egg" on thesolid agar.Colony size varies from 200-500 µm forthe large colony mycoplasmas to 15-30µm for the ureaplasmas.
The established human mycoplasma floracomprises:– M. pneumoniae– M. hominis– M. salivarium– M. orale– M. buccale– M. faucium– M. fermentans– M. genitalium Of these mycoplasmas M. pneumoniae is thepredominant pathogen. M. hominis, M. fermentans, M. genitalium have avariable importance.
MycoplasmaHistory: PPLO and pneumonia.–PleuroPneumonia-Like Organisms(PPLO): term first used to describemicroorganism now known asMycoplasma pneumoniae, responsiblefor 10-30% of lower respiratoryinfections (acute bronchitis andpneumonia in adult humans).–Initiated by conditions of crowding.
Clinical associations are: M. pneumoniae with pharyngitis, sinusitis, febrilebronchitis or pneumonia. In recent years extrapulmonary manifestations suchas arthritis, hepatitis have been reported. M. hominis, M. fermentans or U. urealyticum withsome cases of salpingitis, tuboovarian abscess,pelvic abscess, septic abortion and fever. An association of U. urealyticum (and perhaps nowM. genitalium) with non-gonococcal (NGU) orpostgonococcal urethritis or cervicitis.
Despite some colonial similarities,mycoplasmas are quite distinct fromL-phase variants of bacteria and donot revert to bacteria when cultured inmedia free of inhibitors of bacterialcell wall synthesis or other L-phaseinducers.
The ureaplasma (Ureaplasmaurealyticum) were previously known asT mycoplasma, T for tiny colony - areference to the size difference of theircolonies compared with those of themycoplasmas.As the name implies, they have the abilityto split urea to amoniac, unlike themycoplasma.
Mycoplasma hominis and Ureaplasma urealyticum arefrequently found colonizing the genital tracts of normal,sexually active man and women. They are less common insexually inactive populations, which supports the view thatthey may be sexually transmitted. M. hominis may cause pelvic inflammatory disease, post-abortal and post-partum fevers. Ureaplasma urealyticum has been associated with urethritisand prostatitis in man. Fortunatelly, both M. hominis and U. urealyticum aresusceptible to tetracycline which is also the treatment ofchoice for chlamydial infections.
Infections, vhich can be causedby Chlamydophila pneumoniae: pharyngitis 2 - 5 % sinusitis 5 - 10 % bronchitis 5 - 10 % acute exacerbation ofchronic bronchitis 4 - 5 % community-acquired pneumonia 6 - 25 %
Infections, vhich can be causedby Mycoplasma pneumoniae:pneumoniapharyngitistracheobronchitisbronchitisbronchiolitisotitis media
Laboratory diagnosisof mycoplasma infections M. pneumoniae infection of the respiratorytract:– diagnosis may most easily be made by detectionof specific IgM antibody. Serodiagnosis may be supported bydemonstration of antigen or specificnucleotide sequences, or by culture of themicroorganism.