• gram negative
• obligate intracellular
• unique developmental cycle
• ubiquitous/small size

describe the intracellular developmental cycle of chlamydia.

• the dense, infectious spore-like EBs are taken up in vacuoles ("inclusion") and enter the cytosol of infected cell
• after internalization, EB differentiates into larger, less dense RB
  • nucleoid reorganizes into disperse config with permeable outer membrane allowing for nutrient uptake
• RB is metabolically active, multiplies intracellularly by binary fission; actively transports metabolites/precursors from cytosol of infected cell; multiplies while in contact with membranous vacuole wall
• late differentiation occurs 20-40hrs post infection when late expressed genes mediate outer membrane rigidification and condensation of chromosomal DNA
• fully mature condensation may have 100s-1000 EB; also may be >1 inclusion per cell; inclusions may be lobar
• cycle over when inclusion and host cell lyse and the progeny EB go on to infect neighboring cells in the same host or are transmitted to a new host

at any given time inside an inclusion, are bodies at the same stage of differentiation?

no. there is asynchronous differentiation.  during late stage differentiation in the mature inclusion there are many EBs and fewer RBs that have yet to convert to EBs.

describe some of the major differences between EB vs RB

• EB
  • smaller diameter
  • denser; compact DNA with histones
  • late stage of differentiation
  • strong cell wall (cysteine rich, lots of disulfides)
  • no metabolism, no replication
• RB
  • opposite of the above
  • made to replicate!!
  • not infectious
  • larger, less dense
  • pleitrophic cell walls (more diversity)
  • highly infectious

• small genome (1-1.2million base pairs) that is highly conserved among species (800/1000 genes shared)
• low G+C (~40%)
• no repeat sequences
• one of the easiest genomes for sequencing
• shattered dogmas:
  • chlamydia can make some ATP
  • chlamydia have peptidoglycan

what are some important chlamydia virulence factors?

• non specific adherence
• tryptophan synthase
• Type III secretion: molecular "syringes" that inject virulence factors directly into the cytosol of infected cells
• cytotoxins related to clostridial cytotoxins

• primary infection is usually localized to the site of infection; frequently asymptomatic or a mild nuisance; usually easily treated with broad spectrum antibiotics
• pathology results from inflammatory response (infected host cells release chemokines and proinflammatory cytokines that provoke inflamm cascade)
• severe disease from chronic infection & disease sequelae from extensive tissue remodeling and scarring, usually years post-primary infection, and at site remote from that of the initial one

what serovars cause the primary infection in trachoma?

• serovars: A, B, C
• trachoma: world's leading cause of blindness
• primary infection:
  • inclusion conjunctivitis (starts in babies w/in weeks of birth; spread from siblings or house flies)
• then more chronically (in teenage yrs):
  • follicular conjunctivitis
• corneal inflammation and scarring in adult years leads to:
  • pannus (scarring & neovascularization)
  • contraction of conjuctiva leads to in-turned eyelashes
  • continuous corneal abrasions from eyelashes leads to
    
    • trichiasis (corneal scarring)
    • blindness (in mid to late adulthood)

in what populations does inclusion conjunctivitis develop?

• infants: during passage through infected birth canal, demonstrating that serovars predominant in one tissue can infect another tissue type/site
• adults: with genital infection or infected partners

what are two potential chlamydial infections of the newborn?

1. ophthalmia neonatorum
   • incubation: 5-12 days post-natal
   • hospitals require antibiotic eyedrops immediately after delivery
2. pneumonia syndrome of newborn
   • incubation: 3-16 weeks
   • interstitial pneumonitis
   • chronic, if untreated

what is treatment for chlamydial infections of the newborn?

• erythromycin base 50mg/kg/day for 14 days

• macrolides, less data but probably equally effective

predominantly caused by serovars D-K

• most common bacterial STI in US
• 10% sexually active population is infected
• highest incidence in adolescents
• most often asymptomatic or mild, hence it being unreported or untreated
• men = reservoirs

• non-gonococcal urethritis (NGU)
• epididymitis
• men are more often asymptomatic, thusly functioning as reservoirs for bacteria

• urethritis
• cervicitis (majority asymptomatic)
• salpingitis
• pelvic inflammatory disease (PID)
• possible sequelae include:
  • infertility
  • life-threatening ectopic pregnancy

what are some sequelae of chronic C.pneumoniae infection?

• chronic bronchitis
• asthma
• exacerbation of COPD

what are some sequelae of *disseminated* chronic C.pneumoniae infection?

• reactive arthritis
• abdominal aortic aneurysm
• stroke
• MS, alzheimer disease
• strongest association with artherosclerosis

what is the relationship between CVD and C.pneumoniae?

• viable C.pneumoniae has been found in atherosclerotic plaque of CHD patients
• large antibiotic intervention studies aimed to demonstrate a causal role of C.pneumoniae infection in the devt of CHD=  in humans INCONCLUSIVE
• animal models (mice, rabbits) show C.pneumoniae does contribute to devt of atherosclerotic plaques and that it can be recovered in pure culture from diseased arteries
  

how is diagnosis and treatment of C.pneumoniae handled?

• diagnosis
  • not usually attempted because organism if fragile and difficult to culture
• treatment
  • doxycycline or erythromycin for at least 10 - 14 days
  • quinolones (ie: levofloxacin)
• no vaccine

what strain of chlamydia is an occupational hazard to people exposed to exotic birds, poultry farm workers, and BGE engineers & what is the treatment?

• avian Chlamydia psittaci

psittacosis (ornithosis): zoonotic infection caused by C.psittaci EBs in feces of infected animals

flu-like illness --> severe pneumonia-like syndrome

treatment: DOXYCYCLINE, TETRACYCLINE

30-95% infection rate in pigeons in Sarajevo, chicken in Beijing

outbreaks in "foie gras" duck farms in France, poultry in Germany

• wall-less pleiomorphic bacteria, evolved from Gram-positive by mutational loss
• able to grow outside of host cell
• broad group, few pathogenic to humans
• fastidious organisms, difficult to manipulate in vitro

what species of Mycoplasma cause disease in humans?

•    Mycoplasma pneumoniae
•   Mycoplasma hominis
•   Mycoplasma genitalium
•   Mycoplasma fermentens
  
• Ureaplasma urealyticum
  

what cellular characteristics led to mycoplasma's being mistaken for a virus?

• small size and plasticity of mycoplasma (since it doesnt have a cell wall) allow these to pass through verrrry  small pores
• "filtrability" along w/ poor biochemical and electron microscopy data led to their wrong characterisation as viruses
• also- they are difficult to manipulate in vitro (complex nutritional requirements), grow at slow rates (2-8 hour generation time), and usually yield tiny colonies on agar that are visible in 3-10 days

how do mycoplasmas replicate and what is their colony morphology?

1) binary fission to form chains

or

2) cell elongation to eventually split into multiple cells

colony morphology: "fried egg" for most mycoplasmas; an important exception is M.pneumoniae, which forms mulberry colonies

what are some potential mycoplasma virulence determinants?

• hemolysins
  • alpha or beta
  • M.pneumoniae makes beta
  • all other human mycoplasmas make alpha
• surface structures
  • attachment organelles (M.pneumoniae) that mediate attachment to the surface of ciliated epithelial cells of resp. tract
• capsule
  • some species make polysaccharide capsule that may be involved in attachment or may have toxic effects

primary, atypical pneumonia may be of multiple etiologies. name some causative agents.

• Legionella pneumophila
• adenovirus
• influenza A and B viruses
• parainfluenza type 3
• RSV
• M.pneumoniae *** only agent causing primary atypical pneumonia that is associated with cold aglutinins
  

what is the epidemiology and clinical presentation of M.pneumoniae?

• 2 million cases/yr in US
• leading cause of pneumonia in school-age children and young adults
• clinical presentation:
  • persistant dry cough
  • "scratchy" sore throat
  • malaise
  • low fever
  • community acquired
  • frequently referred to as "walking pneumonia"
• diagnose via serology and PCR

what are the beneficial and deleterious immune responses in M.pneumoniae infection?

beneficial

• early on IgM Abs
• later in infection IgG Abs
• no long lasting protection (IgM, IgG)
• IgA in resp secretions and CMI play a role in host resistance

deleterious

• 1/2 half pts develop "cold agglutinins": IgM Abs agglutinate RBCs at 4 degrees C, but not at 37 degrees C
• these IgM are specific to one host RBC antigen thats on surface of 97% folks' RBCs
• theory: during infection some RBC Ags damaged, self recognition is lost, and so they are readily attacked by IgMs --> autoimmune response
• human brain glycolipids cross-react with Abs to M.pneumoniae --> CNS complications

• round mulberry colonies
• serology is method of choice
  • cold agglutinins (old test, poor sensitivity)
  • IgG or IgM by ELISA
• culturing is SLOW (~20 days) and requires a complex isolation medium

• doxycycline
• ciproflaxin
• erythromycin
• azithromycin
• levoflaxin

no vaccine

what mycoplasma are present in the genital tract of a large proportion of sexually active adults?

HIV grows better in vitro when host cells are already infected with what species of Mycoplasma?