Mycoplasmas: Investigating the Intriguing World of Minimalist Microorganisms and their Distinctive Organic Traits

Mycoplasmas: Investigating the Intriguing World of Minimalist Microorganisms and their Distinctive Organic Traits

 

INTRODUCTION

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

Illness

Mycoplasma pneumoniae causes “atypical” pneumonia.

Essential Properties

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.

1

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

cell membranes.

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

edge.

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

community-acquired pneumonia.

Medical Findings

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

causes bronchitis.

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.

Laboratory Prognosis

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.

Remedy

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.

Prevention

There isn’t any vaccine or different particular safety measure.

Different Mycoplasmas

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

asymptomatic.

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.

SELF-ASSESSMENT QUESTIONS

1. Mycoplasma pneumoniae is a crucial reason behind atypical pneu-

monia. Relating to this organism, which one of many following is the

most correct?

(A) Amoxicillin is the drug of alternative for pneumonia attributable to this

organism.

(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?

(A) Amoxicillin

(B) Azithromycin

(C) Ceftriaxone

(D) Gentamicin

(E) Vancomycin

ANSWERS

(1) (B)

(2) (B)

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 &

COURSE EXAMINATIONS

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