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|Logo image © Jeffrey Nelson, Rush University, Chicago, Illinois and The MicrobeLibrary|
6th edition Chapter 42 (Spirochetes)
Figure 1. Congenital syphilis, primary and secondary syphilis rates, by year -- United States, 1992-1998. Epidemiology, surveillance. CDC/Dr. Demetri Vacalis email@example.com
The most important genera of spirochetes are Treponema, Borrelia and Leptospira. These are are Gram negative bacteria that are long, thin, helical and motile. Axial filaments (a form of flagella) found between the peptidoglycan layer and outer membrane and running parallel to them, are the locomotory organelles.
|Figure 3 Primary Syphilis Bristol Biomedical Archive © University of Bristol. Used with permission||Figure 4 Primary syphilis. Primary chancre on the glans The University of Texas Medical Branch Figure 6 Primary syphilis. A vulvar chancre and condylomata acuminata The University of Texas Medical Branch|
Borrelia burgdorferi and Lyme disease
Lyme disease is caused by Borrelia burgdorferi
(figure 8 and 13) and is a relatively newly recognized
disease. It is found widely in the United States (figure 9 and 10). Although clinically first described in 1975, the role of a tick-borne
spirochete was not proven until 1983. These ticks (figure 12 and 14) infect a large array of wild
life, particularly white footed mice. A tick bite leads to transmission of B.
burgdorferi causing an erythematous skin rash (figure 11) in a few days along with a
transient bacteremia leading to (weeks or months later) severe neurologic
symptoms or polyarthritis. Cardiac problems may occur in a minority of cases. If
antibiotic therapy is initiated early, a cure is usually achieved. However, late
antibiotic administration (penicillin or tetracycline) is often ineffective.
|Figure 8 Histopathology showing Borrelia burgdorferi spirochetes in Lyme disease. Dieterle silver stain. CDC/Dr. Edwin P. Ewing, Jr. firstname.lastname@example.org||Figure 9 Reported cases of Lyme disease in the United States 1998 CDC Figure 11 Lyme disease rash CDC|
Figure 13 Morphology of Borrelia burgdorferi. Dark
field image ©
Jeffrey Nelson, Rush University, Chicago, Illinois
and The MicrobeLibrary
There are less than 100 cases of relapsing fever per year in US. Relapsing fever (with associated bacteremia) is caused by other species of Borrelia which are transmitted by tick (B. hermsii, rodent host) and lice (B. recurrentis, human host) bites. The term relapsing fever is derived from the following repeating cycle. As an immune response develops the disease relapses. However, the antigens expressed change and the disease reappears. The organism is extremely difficult to culture and there is no serological test. The organism is generally detected by blood smear.
|Figure 15 Scanning electron micrograph of Leptospira interrogans strain RGA. Two spirochetes bound to a 0.2 µm filter. Strain RGA was isolated in 1915 by Uhlenhuth and Fromme from the blood of a soldier in Belgium. CDC/NCID/Rob Weyant email@example.com||
There are less than 100 cases per year in US. This flu-like or severe systemic disease is also a zoonotic infection. Leptospira (figure 15) are transmitted in water contaminated with infected urine from wild animals (including rodents) and farm animals and can be taken in through broken skin (e.g. bathing). Leptospira particularly infect the kidney (figure 16), brain and eye. They are the most readily culturable of the pathogenic spirochetes; but this is not routine and diagnosis is usually by serology.
|Figure 17 Positive FA test for Neisseria gonorrhoeae. This strain was penicillin-resistant. CDC||
are Gram negative diplococci (pairs of cocci). These bacteria grow best on
chocolate agar (so-called because it contains heated blood, brown in color); a
modified (selective) chocolate agar commonly used is Thayer Martin. The colonies
are oxidase positive (i.e. produce cytochrome oxidase) which is demonstrated by
flooding the plate with a dye which on oxidation changes color.
N. gonorrhoeae (the "gonococcus")
N. gonorrhoeae (figure 20 and 21), found only in man, is the causative agent of gonorrhea, the second most common venereal disease. The organism often causes an effusion of polymorphonuclear cells. A smear (figure 17, 18, 19) may show the presence of Gram negative cocci present in cells. However, culture is essential for definitive diagnosis.
A common feature of disseminated gonoccocal disease is arthritis. Although commonly considered a form of septic arthritis, in many cases gonococci cannot be isolated from the joint (i.e. they are "reactive" in nature). Dermatitis is also common.
Penicillin therapy is still usually effective. However, resistant strains producing beta lactamases are sufficiently common that alternatives are recommended for all gonococcal infections; this includes ceftriaxone (a beta lactamase-resistant cephalosporin). There is no vaccine since strains are highly variable in their external antigens (both outer membrane and pili). Both are involved in the initial adhesion of the organism to genital epithelium.
IgA proteases (also produced by N. meningitidis) are involved in successful colonization. As for many other bacterial infections, a role for both the lipopolysaccharide and peptidoglycan in tissue injury have been suggested. Exotoxins are not believed to be of importance in pathogenesis.
of Neisseria gonorrhoeae
Figure 18 Neisseria gonorrhoeae Gram stained urethral discharge. The image shows many polymorphonuclear leukocytes (PMNs) and gram-negative extra- and intra-cellular diplococci.
(1,000X oil) © J. Michael Miller
Centers for Disease Control and Prevention Atlanta, Georgia and The MicrobeLibrary
Figure 19 Gram Stain from Neisseria gonorrheae Infection Urethral discharge from a male patient.
Stain shows gram-negative diplococci both intracellular and extracellular to a polymorphonuclear leukocyte or puss cell. In a symptomatic male patient, this Gram stain finding is considered diagnostic of the sexually transmitted disease caused by Neisseria gonorrheae. In female patients, one cannot use this type of finding as diagnostic of N. gonorrheae infection because the female genital tract may contain commensal Neisseria species.
© Gloria J. Delisle and Lewis Tomalty, Queens University, Kingston, Ontario
Figure 20 Scanning electorn micrograph of Neisseria gonorrheae © Margaret Ketterer, University of Iowa, Iowa City, Iowa USA and The MicrobeLibraryFigure 21 Neisseria gonorrhoeae - coccoid prokaryote (dividing); causes gonorrhea (SEM x 40,000) © Dennis Kunkel Microscopy, Inc. Used with permission
Figure 22 Neisseria meningitidis, group C, in spinal fluid.
CDC/Dr. M.S. Mitchell
Figure 23 Neisseria meningitidis - coccoid prokaryote (dividing); causes meningitis and Waterhouse-Friderichson syndrome (a fulminating meningococcal infection occurring mainly in children under ten years old) © Dennis Kunkel Microscopy, Inc. Used with permission
N. meningitidis (the "meningococcus")
This organism (figure 22 and 23) resides only in man. The majority of cases are sporadic cases most commonly seen among young children. Outbreaks occur usually among adults living in confined and crowded conditions (e.g. army barracks). Initial infection of the upper respiratory tract (involving binding by pili) leads to invasion into the bloodstream and from there to the brain. Indeed, it is the second most common cause of meningitis (pneumococcus is the most common). It is usually fatal if untreated but responds well to antibiotic therapy. Thus, rapid diagnosis is important. The organism is often detectable in spinal fluid (Gram negative diplococci within polymorphonuclear cells) or antigenically. Culture on Thayer Martin (or similar) agar is essential for definitive diagnosis. Penicillin is the drug of choice.
Meningococci vary antigenically and can be serogrouped with anti-capsular antibodies. The capsule is an important pathogenesis factor allowing inhibition of phagocytosis. A vaccine against these capsular antigens is available. However, effective immunization against the most common group B has not been achieved.
Non-pathogenic species morphologically resembling Neisseria are found in the normal flora of the oropharynx but can be differentiated from the pathogenic Neisseria readily. These occasionally cause opportunistic human disease (including pneumonia).