Mycoplasma & Ureaplasma (2024-2025) - PDF

Medical Microbiology-Term-1 Academic Level: 3rd Year 2024-2025 MI.9.1 Mycoplasma and Ureaplasma Objectives: Discuss the common medically important Mycoplasma spp. Describe the morphology, mode of infection , pathogenesis, clinical course, discuss prevention and treatment of M...

Medical Microbiology-Term-1 Academic Level: 3rd Year 2024-2025 MI.9.1 Mycoplasma and Ureaplasma Objectives: Discuss the common medically important Mycoplasma spp. Describe the morphology, mode of infection , pathogenesis, clinical course, discuss prevention and treatment of Mycoplasma and ureaplasma Mycoplasmas Morphology: pleomorphic shape (neither rods nor cocci). Not seen with Gram stain because it lacks peptidoglycan cell walls. Cell membrane is a sterol-containing lipid bilayer in their cell membranes.  Small organisms (diameter 0.2-0.3 μm )  Lacking cell walls, mycoplasmas are insensitive to antibiotics that inhibit cell division by preventing cell wall synthesis.  They are enclosed in a single plasma membrane. Species: Mycoplasma species are widely distributed in nature and include several commensals commonly found in the mouth and genitourinary (GU) tracts of humans and other mammals. Three Mycoplasma species are definitively associated with human disease, namely. 1-Respiratory Mycoplasma include; Mycoplasma pneumoniae, which is the cause of an atypical pneumonia. 2-Genital Mycoplasma include; Mycoplasma hominis, Mycoplasma genitalium and Ureaplasma species. Mycoplasma pneumoniae It is transmitted by respiratory droplets and causes a lower respiratory tract infection (atypical pneumonia, so named because the signs and symptoms are unlike typical lobar pneumonia). The organism accounts for -20% of pneumonia cases as well as causing milder infections such as bronchitis, pharyngitis, and nonpurulent otitis media. Infections occur worldwide and year round, with increased incidence in late summer and early fall. Pathogenesis: It possesses a membrane-associated protein, P1, which functions as cytoadhesin, which binds sialic acid rich glycolipids found on certain host cell membranes. Among susceptible cell types are ciliated bronchial epithelial cells. The organisms grow closely attached to the host cell luminal surface and inhibit ciliary action. Eventually, 1  Medical Microbiology-Term-1 Academic Level: 3rd Year 2024-2025 ‫ﺑﻘﻊ‬ ‫ﺗﺘﻘﺸﺮ‬ patches of affected mucosa desquamate, and an inflammatory response develops in bronchial and adjacent tissues involving lymphocytes and other mononuclear cells. M. pneumoniae produces an exotoxin that is similar to pertussis toxin. The toxin is an adenosine diphosphate-ribosylase and results in extensive vacuolization and death of host cells. In infected individuals, organisms are shed in saliva for several days before onset of clinical illness. Reinfection is common, and symptoms are more severe in older children and young adults who have previously encountered the organism. Clinical significance:  Atypical pneumonia is the best-known form of M. pneumoniae infection.  upper respiratory tract and ear infection being much more frequent.  Atypical pneumonia clinically resembles pneumonia caused by a number of viruses and bacteria such as Chlamydia species.  The incubation period averages 3 weeks. Onset is usually gradual, beginning with nonspecific symptoms such as unrelenting headache, accompanied by fever, chills, and malaise. After 2-4 days, a dry or scantily productive cough develops. Earache is sometimes an accompanying complaint.  Chest radiographs reveal a patchy, diffuse bronchopneumonia involving one or more lobes.  Patients often remain ambulatory throughout the illness (hence, "walking pneumonia").  In the absence of pre-existing compromise (eg, immunodeficiency or emphysema), the disease remits after 3-10 days without specific treatment.  X-ray abnormalities resolve more slowly in 2 weeks to 2 months.  Complications are rare but include central nervous system (CNS) disturbances; a rash (erythema multiforme); and mild, hemolytic anemia. Lab.diagnosis: -Sputum samples or throat swabs can be cultured on special media, but, because isolation of the organism usually requires 8-15 days, they cannot aid in early treatment decisions. -M. pneumoniae grows under both aerobic and anaerobic conditions and can be isolated on specialized media supplemented with serum. However, the organism is ، ‫ﺣﺴﺎس‬ fastidious, and -isolation is not commonly performed in clinical laboratories. Mycoplasmas produce minute colonies on specialized agar after several days or weeks of incubation. For some species, the central portion of the colony penetrates the agar, whereas the periphery spreads over the adjacent surface, in some cases giving the colony a characteristic "fried egg" appearance. However, because of their fastidious growth requirements, these organisms are not routinely cultured in the clinical laboratory. 2 Medical Microbiology-Term-1 Academic Level: 3rd Year 2024-2025 -Serologic tests are the most widely used for establishing a diagnosis of atypical pneumonia because of M. pneumoniae. Specific antibody can be detected by ELISA Treatment: M. pneumoniae is sensitive to doxycycline, azithromycin, or levofloxacin Genital Mvcoplasmas: Three Mycoplasma species: M. genitalium, M. hominis, and U. urealyticum, are human urogenital pathogens. They are often associated with sexually transmitted infections, such as NGU or puerperal infections (ie, infections connected with or occurring during childbirth or the period immediately following childbirth). associated with a variety of GU diseases, such as urethritis, pelvic inflammatory disease (PID). However, M. hominis and Ureaplasma species are also frequently isolated from genital tracts of healthy individuals. Mycoplasma genitalium is a recently recognized sexually transmitted pathogen that causes nongonococcal urethritis (NGU). Mycoplasma hominis and U. urealyticum are common inhabitants of the GU tract, particularly in sexually active adults. Because colonization rates in some populations are in excess of 50%, it is difficult to establish an unequivocal causal role in various disease states with which the organisms are associated. Both agents can be cultured. They grow more rapidly than M. pneumoniae and can be distinguished by their carbon utilization patterns: M. hominis degrades arginine, whereas U. urealyticum hydrolyses urea. The major clinical condition associated with M. hominis is postpartum or postabortal fever. Ureaplasma urealyticum is a common cause of urethritis, particularly in men. In women, the organism has been isolated from the endometrium of patients with endometritis and from vaginal secretions of women who undergo premature labor or deliver low-birth weight babies. The infants are often colonized, and U. urealyticum has been isolated from the infant's lower respiratory tract and CNS both with and without evidence of inflammatory response. Mycoplasma genitalium has been recognized as a sexually transmitted pathogen, resulting in a series of syndromes similar to those caused by Neisseria gonorrhoeae and Chlamydia trachomatis. M. genitalium causes NGU in males and is associated with cervicitis and PID in women. The organisms appear to be resistant to doxycycline, which is the treatment of choice for NGU caused by C. trachomatis. 3 Medical Microbiology-Term-1 Academic Level: 3rd Year 2024-2025 Therefore, recommendations for testing for M. genitalium include cases in which the patient fails to respond to doxycycline treatment. Nucleic acid amplification testing is recommended for specific diagnosis of M. genitalium infections. Treatment: Azithromycin is often recommended for treating M. genitalium infections; however, increasing macrolide resistance and emerging quinolone resistance threaten the continued utility of these antimicrobial agents. Case Senaero: A 30-year-old woman complained of unrelenting headache, accompanied by fever, chills, and malaise. After 2-4 days, a dry cough developed. Chest x-rays reveal a patchy, diffuse bronchopneumonia involving both lobes. Her white cell count was normal. Which of the following is the most likely diagnosis? A. Legionellosis B. Infection with parainfluenza virus C. Infection with Streptococcus pneumoniae D. Infection with Haemophilus influenzae E. Infection with Mycoplasma pneumoniae 4