These are the smallest, cell wall-less organisms. Classification Based on their existence. 1. Common pathogen- Mycoplasma pneumonia 2. Less pathogen- M. hominis, Ureaplasma urealyticum 3. Non pathogen- M. orale, M. salivarum
M. pneumoniae – also known as
Eaton agent Pleuropneumonia like organism (PPLO) It causes pharyngitis bronchitis primary “atypical” pneumonia
Atypical pneumonia is a pneumonia that does not respond to the usual antibiotic treatment.
It can be caused by bacteria: Mycoplasma pneumoniae Chlamydia pneumoniae Legionella pneumophila Bordatella pertussis Viruses
Normally, these infections are not as severe as typical pneumonia, but legionella causes legionnaire’s disease, which kills up to 50% of its victims if left untreated.
The deadly SARS virus, which appeared only last year, is a new coronavirus that causes atypical pneumonia.
Characteristics: Mycoplsma are pleomorphic organisms.
They do not possess cell-wall, this makes them resistant to cell-wall active antibiotics like- penicillin & cephalosporins.
They are slow growing, highly fastidious, facultative anaerobes. They require complex media containing cholesterol and fatty acids for growth.
Important exception include aerobic M. pneumoniae and more rapidly growing M. hominis.
The mycoplasmas grow slowly by binary fission and produce "fried egg" colonies on agar plates; the colonies of M. pneumoniae have a granular appearance.
The colonies may take up to 3 weeks to develop and are usually very small.
A. Adherence factors – The mycoplasmas are extracellular pathogens that adhere to epithelial cell surfaces. The adherence protein in M. pneumoniae is P1. The P1 Adhesin localizes at tips of the bacterial cells and binds to sialic acid residues on host epithelial cells
B. Toxic Metabolic Products – Both hydrogen peroxide and superoxide, which are products of mycoplasma metabolism, have been implicated in pathogenesis since oxidized host lipids have been found in infected tissues.
C. Immunopathogenesis Mycoplasmas can activate macrophages and stimulate cytokine production and lymphocyte activation . M. pneumoniae is a superantigen.
Thus, it is has been suggested that host factors also contribute to pathogenesis.
Mycoplasma causes two types of diseases in manAtypical Pneumonia Genital infections
Mycoplasma pneumoniae causes “atypical” pneumonia.
The term atypical means that the causative bacteria cannot be isolated on routine media in diagnosis or the disease does not resemble pneumococcal pneumonia.
Mode of transmission: respiratory droplets Incubation period: 2-3 wks In lungs the organism is rod shaped.
The respiratory mucosa is not invaded but the ciliary motion is inhibited and necrosis of the epithelium occurs. It produces hydrogen peroxide, which contributes to the damage to the respiratory tract cells.
The infection occurs world wide, with increased incidence in the winter. It is more frequent cause of pneumonia in young adults and is responsible for outbreaks in groups with close contacts. It accounts for 5-10% of all community acquired pneumonia.
Pathogenesis: During M. pneumoniae infection autoantibodies are produced against red cells (cold agglutinins) and brain, lungs, and liver cells. These antibodies may be the source of the extrapulmonary manifestations of infection.
Clinical findings: The onset is gradual begins with a nonproductive cough, sore throat or ear ache.
Sputum is produced in small amounts , it is non bloody and whitish in color.
Symptoms like fever, headache, malaise and myalgias are pronounced.
Extrapulmonary complications- including cardiovascular, Central nervous system, dermatologic and gastrointestinal problems are rare occurrences.
M. pneumoniae has been implicated as a co-infection or
co-factor in epidemic group A meningococcal meningitis and infant pneumoniitis.
Erythema multiforme rash (Stevens-Johnson syndrome) associated with Mycoplasma pneumoniae infection in a preadolescent girl.
M. hominis & Ureaplasma urealyticum: These are associated with the urogenital tract.
They are opportunistic pathogens, the immune status is an important factor in the occurrence and severity of disease.
It has also been studied that among sexually active individuals the rate of colonization is directly related to the number of sexual partners.
Higher rate of colonization have been noted in adults of lower socioeconomic status.
M. hominis is found in the lower genitourinary tracts of approximately 50% of healthy adults and causes nongonococcal urethritis (NGU).
The organism invade upper genitourinary tract and cause salpingitis, pyelonephritis, pelvic inflammatory disease (PID) postpartum fevers.
Ureaplasma spp. do not cause disease in female lower genital tract but have been associated with approximately 10% of cases of NGU in men as well as with upper female genitourinary tract disorders.
U. urealyticum has been associated with reproduction disorders- chorioamnionitis congenital pneumonia development of chronic lung disease in premature infants.
M. hominis and U. urealyticum can be transmitted to the fetus at delivery and cause meningitis.
It has been recommended that culture for these organisms be attempted when CSF is negative for both Gram stain and routine bacteriology culture.
In immunocompromised individuals, U. urealyticum causes chronic inflammatory disease such as arthritis and cystitis in hypogammaglobulinemic patients.
Other mycoplasma species:
M. genitalium has been associated with NGU & PID in
M. fermentans is a oppurtunistic respiratory pathogen. It ha
been also recovered from adult patients with respiratory illness and those with acquired immunodeficiency syndrome (AIDS).
M. penetrans has been demonstrated in urine of homosexual
male patients with HIV- associated diseases.
Specimen collected: Primary atypical pneumoniaSputum Throat swab Blood for serology. Genital infection: Urethral discharge Endocervical swabs.
Direct microscopy: direct immunoflurescent method is useful. Culture: media usedMycoplasma agar PPLO agar New York City (NYC) agar It takes at least one week for colonies to appear on special media.
A direct plate immunofluorescent method also can be used.
Fluorescent – labelled anti M. pneumoniae antibody is flooded on colonies on the plate. The plate is then washed and observed for immunofluorescence.
Serologic testing: CFT – 4 fold or greater rise in specific antibody titer.
Cold agglutination test: A titer of 1:128 or higher is indicative of recent infection.
Cold agglutinins are IgM autoantibodies against type O red blood cells that agglutinate these cells at 4°C. the test is non specific and false positive results occur in influenza virus and adenovirus infection. ELISA
Treatment: The treatment of choice is either a macrolide likeerythromycin or azithromycin Tetracycline like doxycycline.
Prevention: There is no specific vaccine.
Points to remember: Mycoplasma organisms do not possess a cellwall
M.pneumoniae is an important cause of community
M. hominis & Ureaplasma spp. Are genital mycoplasma
commonly diagnosed by culture, although PCR is available.
Mycoplasmas have all of the following characteristics except Possession of both DNA and RNA. Capability for cell-free growth Susceptibility to penicillin G Extracellular parasitism in vivo
A. B. C. D.
2. A 25-yr old medical student has contact with a patient who has pneumonia with fever and cough. Four days later, the medical student develops fever and cough, chest x-ray shows consolidation of the right lower lobe. Routine bacterial sputum cultures are negative. Pneumonia caused by Mycoplasma pneumoniae is considered. Which of the following is an appropriate way to confirm this diagnosis? A. PCR amplification of M.pneumoniae DNA in sputum B. Culture of sputum for M.pneumoniae C. Gram stain of sputum smear D. Culture of a lung aspirate for M.pneumoniae E. Complement fixation test of acute and convalescent sera
3. A 25-yr old woman is reffered to the sexually transmitted diseases clinic because of contact with a male partner with gonorrhea. The woman has had 15 male sex partners since becoming sexually active. The likelihood that she also has genital Mycoplasma hominis infection is A. 1% B. 5% C. 15% D. 40% E. 90%
4. Which one of the following types of organisms is NOT an obligate intracellular parasite and therefore can replicate on bacteriologic media? A. Chlamydia B. Mycoplasma C. Adenovirus D. Rickettsia
5. Which one of the following organisms is MOST likely to be the cause of pneumonia in an immunocompetent patient? A. Nocardia asteroides B. Serratia marcescens C. Mycoplasma pneumoniae D. Legionella pneumophila
6. A 19-year-old college student presents to the student health clinic complaining of weakness, malaise, and a chronic cough. He has a fever of 100 degrees F and a dry cough; no sputum can be obtained for laboratory analysis, so a bronchial lavage is performed and the washings are submitted to the laboratory. The laboratory reports that the Organism is "slow-growing." Serodiagnosis reveals Strep MG agglutinins in the patient's serum. Which of the following organisms is the most likely cause of this student's illness?
A. Klebsiella pneumoniae
B. Mycoplasma pneumoniae C. Parainfluenza virus D. Respiratory syncytial virus E. Streptococcus pneumoniae
Jawetz: 23rd edition- 26 Levinson: 7th edition-23