Mycoplasmas: Investigating the Intriguing World of Minimalist Microorganisms and their Distinctive Organic Traits
Mycoplasmas are a bunch of very small, wall-less organisms, of
which Mycoplasma pneumoniae is the foremost pathogen.
Further info relating to the scientific elements of
infections attributable to the organisms on this chapter is offered
in Half IX entitled Infectious Illnesses starting on web page 589
Mycoplasma pneumoniae causes “atypical” pneumonia.
Mycoplasmas are the smallest free-living organisms; many are
as small as 0.3 μm in diameter. Their most hanging characteristic is the
absence of a cell wall.
Consequently, mycoplasmas stain poorly with Gram stain,
and antibiotics that inhibit cell wall (peptidoglycan) synthesis
(e.g., penicillins and cephalosporins) are ineffective. Their
outer floor is a versatile cell membrane; therefore, these organisms
can assume quite a lot of shapes. It’s the solely bacterial membrane
that comprises ldl cholesterol, a sterol normally present in eukaryotic
Mycoplasmas may be grown within the laboratory on synthetic
media, however they’ve advanced dietary necessities, includ-
ing a number of lipids. They develop slowly and require a minimum of 1 week
to kind a visual colony. The colony regularly has a character-
istic “fried-egg” form, with a raised middle and a thinner outer
Pathogenesis & Epidemiology
Mycoplasma pneumoniae, a pathogen just for people, is
transmitted by respiratory droplets. Within the lungs, the organ-
ism is rod-shaped, with a tapered tip that comprises particular
proteins that function the purpose of attachment to the respiratory
epithelium. The respiratory mucosa shouldn’t be invaded, however ciliary
movement is inhibited and necrosis of the epithelium happens. The
mechanism by which M. pneumoniae causes irritation is
unsure. It does produce hydrogen peroxide, which contrib-
utes to the harm to the respiratory tract cells.
Mycoplasma pneumoniae has just one serotype and is anti-
genically distinct from different species of Mycoplasma. Immunity
is incomplete, and second episodes of illness can happen. Throughout
M. pneumoniae an infection, autoantibodies are produced in opposition to
purple cells (chilly agglutinins) and mind, lung, and liver cells.
These antibodies could also be concerned in a few of the extrapulmo-
nary manifestations of an infection.
Mycoplasma pneumoniae infections happen worldwide, with
an elevated incidence within the winter. This organism is the
commonest reason behind pneumonia in younger adults and is
accountable for outbreaks in teams with shut contacts akin to
households, navy personnel, and school college students. It’s estimated
that solely 10% of contaminated people really get pneumonia.
Mycoplasma pneumonia accounts for about 5% to 10% of all
Mycoplasma pneumonia is the commonest kind of atypical
pneumonia. It was previously known as major atypical pneu-
monia. (Atypical pneumonia can also be attributable to Legionella
pneumophila [Legionnaires’ disease], Chlamydia pneumoniae,
Chlamydia psittaci [psittacosis], Coxiella burnetii [Q fever],
and viruses akin to akin to influenza virus and adenovirus.
The time period atypical implies that a causative bacterium can’t be
remoted on routine media within the diagnostic laboratory or that
the illness doesn’t resemble pneumococcal pneumonia.) The
onset of Mycoplasma pneumonia is gradual, normally starting
with a nonproductive cough, sore throat, or earache. Small
quantities of whitish, nonbloody sputum are produced. Consti-
tutional signs of fever, headache, malaise, and myalgias are
pronounced. The paucity of findings on chest examination is
in marked distinction to the prominence of the infiltrates seen on
the affected person’s chest X-ray. The illness resolves spontaneously in
10 to 14 days. Along with pneumonia, M. pneumoniae additionally
The extrapulmonary manifestations embody Stevens-Johnson
syndrome, erythema multiforme, Raynaud’s phenomenon,
cardiac arrhythmias, arthralgias, hemolytic anemia, and neuro-
logic manifestations akin to Guillain-Barré syndrome.
Prognosis is normally not made by culturing sputum samples; it
takes a minimum of 1 week for colonies to seem on particular media.
Tradition on common media reveals solely regular flora.
Presently, a polymerase chain response (PCR) assay that
detects M. pneumoniae-specific nucleic acids in sputum or in
respiratory secretions is the very best diagnostic process.
Serologic testing for the presence of antibodies within the
affected person’s serum might also be helpful. A chilly-agglutinin titer of
1:128 or increased is indicative of latest an infection. Chilly aggluti-
nins are IgM autoantibodies in opposition to kind O purple blood cells that
agglutinate these cells at 4°C however not at 37°C. Nevertheless, solely half
of sufferers with Mycoplasma pneumonia will probably be constructive for chilly
agglutinins. The check is nonspecific; false-positive outcomes happen
in influenza virus and adenovirus infections. The analysis of
M. pneumoniae an infection may be confirmed by a fourfold or
higher rise in particular antibody titer in both a complement fix-
ation or an enzyme-linked immunosorbent assay (ELISA) check.
The remedy of alternative is both a macrolide, akin to erythro-
mycin or azithromycin, or a tetracycline, akin to doxycycline.
The fluoroquinolone levofloxacin can also be efficient. These medicine
can shorten the period of signs, though, as talked about
earlier, the illness resolves spontaneously. Penicillins and ceph-
alosporins are inactive as a result of the organism has no cell wall.
There isn’t any vaccine or different particular safety measure.
Mycoplasma hominis has been implicated as an rare trigger
of pelvic inflammatory illness.
Mycoplasma genitalium causes urethritis, predominantly in
males. It’s estimated to trigger roughly 20% of nongono-
coccal urethritis (NGU). Infections in ladies are sometimes
Ureaplasma urealyticum might trigger roughly 20% of
circumstances of NGU. Ureaplasmas may be distinguished from myco-
plasmas by their capacity to supply the enzyme urease, which
degrades urea to ammonia and carbon dioxide.
1. Mycoplasma pneumoniae is a crucial reason behind atypical pneu-
monia. Relating to this organism, which one of many following is the
(A) Amoxicillin is the drug of alternative for pneumonia attributable to this
(B) Antibody in a affected person’s serum will agglutinate human purple
blood cells at 4°C, however not at 37°C.
(C) Gram stain of the sputum reveals small gram-negative rods.
(D) It’s an obligate intracellular parasite that may solely develop inside
human cells within the scientific laboratory.
(E) Folks with cystic fibrosis are predisposed to pneumonia
attributable to this organism.
2. Which one of many following is the drug of alternative for atypical
pneumonia attributable to M. pneumoniae?
SUMMARIES OF ORGANISMS
Transient summaries of the organisms described on this chapter
start on web page 653. Please seek the advice of these summaries for a speedy
evaluate of the important materials.
PRACTICE QUESTIONS: USMLE &
Questions on the matters mentioned on this chapter may be discovered
within the Medical Bacteriology part of Half XIII: USMLE
(Nationwide Board) Apply Questions beginning on web page 715. Additionally
see Half XIV: USMLE (Nationwide Board) Apply Examination