Class notes on Bacteriology – Mycoplasma and Rickettsia
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Course
Bacteriology
Institution
Far Eastern University
Notes include a discussion on the clinically significant bacterial genera: Mycoplasma and Rickettsia. Information include its pathogenicity, diagnosis, vectors, diseases caused, pathogenic species, epidemiology, and treatment and prevention.
Mycoplasma & Rickettsia
Bacteriology
MYCOPLASMA CHARACTERISTICS
• Prokaryotes
• Relatively host specific
• Smallest (0.1 to 0.3um) free-living
pathogens of animals
• Viruses
• Normal flora of upper respiratory tract
o Reside extracellular in the
respiratory and urogenital tracts
• Rarely penetrate the submucosa, except
o In immunosuppression
o Instrumentation when they may
invade the bloodstream and
disseminate to organs and tissues
HISTORY • No cell walls
o Outer membrane – no
lipopolysaccharide layer
(endotoxin)
o Gram stain
o Giemsa stain
• Cross section of Mycoplasma
o Plasma membrane – outermost part
of the organism
o High content of sterols – prevent
osmotic lysis
o Highly pleomorphic
o May possess a capsule
o Although some are free living, most
are closely adapted parasite
• Edmond Nocard & Emile Roux (1898) • Non motile
• Contributed for mycoplasma discovery o otile by possible release and
• 1896 – Nocard & Roux reported the reattachment of terminal cell
cultivation of the causative agent of organelle
contagious bovine pleuropneumonia o No flagella
(CBPP) o Possess P1
o Grave and widespread disease in ▪ A protein attachment
cattle herds factor
o First isolation of a mycoplasma ▪ Interacts with a specific
species cellular receptor
ETYMOLOGY ▪ Allows adherence to
• Greek mykes (fungus) and plasma respiratory epithelium
(formed) • Strict aerobes
o Proposed in 1950s • Respiration
• Replaced the term pleuro pneumonia-like o Fermentation
organisms (PPLO) referring to organisms • Aerobic-anaerobic
like the causative agent of CBPP • Fastidious growth requirements
• Fungus-like growth pattern is unique to DIFFERENCE FROM OTHER BACTERIA
M. mycoides • Sterols in the cell membrane
BS BIOLOGY (MICROBIOLOGY TRACK) | 1
, Mycoplasma & Rickettsia
Bacteriology
• Does not share DNA homology with • Close phylogenetic relationship of these
known bacteria genera was measured by comparative
• Low guanine + cytosine content sequence analysis of the 5s and 16s
• Genome has a low molecular weight ribosomal RNA (rRNA)
• Exhibit no reversion to walled forms PATHOGENIC MYCOPLASMA & UREAPLASMA
CLASSIFICATION 5 species associated with human disease
• Order 1. Mycoplasma pneumonia
o Mycoplasmatales o Respiratory tract
o Mollicute 2. Mycoplasma hominis
• Family o Respiratory tract
o Mycoplasmataceae – require o Genitourinary tract
external cholesterol during growth 3. Mycoplasma genitalium
o Acholeplasmataceae – does not o Genitourinary tract
need external cholesterol during 4. Mycoplasma fermentans
growth o Respiratory tract
o Spiroplasmataceae – can form spiral o Genitourinary tract
structure 5. Ureaplasma urealyticum
• Genera o Respiratory tract
o Mycoplasma – utilize glucose or o Genitourinary tract
arginine but do not split urea VIRULENCE FACTOR
o Ureaplasma – hydrolyze urea • Not invasive
• Species • Colonize cell surfaces through specific
o M. pneumoniae binding
▪ Upper respiratory tract • Toxic metabolic products – damage to
disease host tissues
▪ Tracheobronchitis • Lack of cell wall
▪ Atypical pneumonia o Requires close contact between M.
o M. hominis pneumoniae and its host cell
▪ Pyelonephritis o Guarantees the exchange of
▪ Pelvic inflammatory disease compounds – support the growth of
▪ Postpartum fever the bacterium
o M. genitalium • Bacterial surface
▪ Nongonococcal urethritis o Parasitism
o M.penetraus o Host cell is severely damaged
o U. urealyticum • Adherence factors
▪ Nongonococcal urethritis o P1 Adhesin
CLASS MOLLICUTES ▪ Localizes at tips of the
• Five families bacterial cells
• 200 species ▪ Binds to sialic acid residues
o 16 species colonize humans on host epithelial cells
• Mycoplasma – any species included in the ▪ Nature is not established in
class Mollicutes other species
• Common characteristics ▪ Colonization of the
o Absence of bacterial cell wall respiratory tract by M.
o Osmotic fragility pneumoniae results in the
o Colony shape and filterability cessation of ciliary
through 450 nm pore diameter movement
membrane filters • Toxic metabolic products
BS BIOLOGY (MICROBIOLOGY TRACK) | 2
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