10 Taxonomia 2

Infection of the upper respiratory track

• Grey-green pseudomembrane forms in the nasopharyngeal region

• Hard to swallow and breathe

elementary body (EB)

reticulate body (RB)

• Distinct developmental cycle → two phases

• Infectious extracellular form is called the elementary body

(EB)

• bind to host cell receptors

• followed by chlamydia-induced actin remodeling that facilitates entry into the cytoplasm

• EBs become internalised into endocytic vacuoles → intracytoplasmic

inclusion

• EBs transform into non-infectious replicative form of the organism called the reticulate body (RB)

• RB utilises nutrients within host cytoplasm and replicates

• When RB-filled inclusion reaches a critical volume → conversion of RBs back to EBs occurs

• EBs released into extracellular milieu via host cell lysis or extrusion of the cytoplasmic inclusion

• Released EBs attach to adjacent host cells where they initiate another round of infection

C. difficle infection (CDI)

Requires a tick vector

• human infection is a ‘mistake’

• not a natural reservoir of disease

ETEC is one of the most common causes of bacterial diarrheal disease in developing countries

• ~840 million cases annually

• ~ 30% of travelers diarrhea

• Causes acute watery diarrheoa in infants and adults

• Infections via consumption of fecally contaminated food or water Escherichia coli (2) - ETEC

• Pathogenesis involves attachment to the intestinal mucosa

• mediated by fimbrial protein called CFA (colonisation factor antigen)

• Next is elaboration of enterotoxins → diarrhea

• ETEC produces two classes of enterotoxins

• heat-stable toxins (STa and STb)

• heat-labile toxins (LT-I, LT-II)

EPEC frequently causes infant-associated diarrheoa (outbreaks)

• also causes sporadic diarrheoa in adults

• Disease is transmitted by faecal-oral exposure to contaminated surfaces or food products

• EPEC is non-toxigenic and non-invasive

Pathogenesis → adhesion to intestinal mucosa

• mediated by plasmid coded bundle-forming pili

• form cup-like projections called pedestals

• A/E lesions (attaching and effacing lesions) are produced on the intestinal epithelium

• encoded by chromosomal LEE gene (locus for enterocyte effacement)

• → leads to disruption of brush border epithelium causing increased secretion and watery diarrhea

• Disease onset is very rapid (although most infections resolve after 2-3 days)

EAEC are a heterogeneous collection of strains

• characterised by their autoagglutination in a “stacked-brick” arrangement over the intestinal epithelium

• Prevalence unclear because a single molecular marker for these bacteria has not been discovered

• Genes encoding adhesins, toxins (including Shiga toxin), and other virulence proteins are highly variable among EAEC

• Intestinal colonisation mediated by aggregative adhesion fimbriae I (regulated by aggR gene)

• also produces EAST l toxin (entero-aggregative heat stable enterotoxin l)

• Symptoms include persistent and acute diarrhea

• especially in low to middle income countries (LMICs)

• E. coli 0104: H4 is an EAEC strain that caused major outbreaks in Germany in 2011

• produces Shiga-like toxin and can cause HUS (haemolytic-uremic syndrome) – like EHEC

• fenugreek sprouts were identified as most likely vehicle of infection!

Nomenclature is confusing!

• Shiga toxin–producing E. coli (STEC), verocytotoxin-producing E. coli (VTEC), and enterohemorrhagic E. coli (EHEC)

• All members are defined by presence of Shiga toxin 1 (Stx1) or 2 (Stx2)

• Some, but not all EHEC strains are LEE positive and form A/E cytopathology, resembling EPEC strains

• Most infections associated with consumption of undercooked ground beef or other meat products, water, unpasteurised milk or fruit juices or uncooked vegetables

Ingestion of fewer than 100 bacteria can result in disease (remember ID50)!

• Disease caused by STEC ranges from mild uncomplicated diarrheoa to hemorrhagic colitis → severe abdominal pain and bloody diarrhea

• more commonly associated with STEC O157:H7

• outbreak in Scotland (1996) – 280 ill and 5 deaths… • Hemolytic uremic syndrome (HUS) complication in 5-10% children <10 years

• acute renal failure, thrombocytopenia, and microangiopathic hemolytic anemia

• 3-5% mortality rate

• BUT also long term issues (renal impairment, hypertension, CNS manifestations) in 30% of HUS patients

EIEC strains are rare in both high and LMICs

• Strains are closely related by phenotype and pathogenic properties to Shigella

• Can invade and destroy the colonic epithelium

• disease characterised initially by watery diarrhea

• minority of patients progress to dysenteric form of disease → fever, abdominal cramps, and blood and leukocytes in stool

• Plasmid encoded genes (pInv) mediate bacterial invasion into colonic epithelium

• Bacteria then lyse phagocytic vacuole and replicate in the cell cytoplasm

• Movement within cytoplasm and into adjacent epithelial cells regulated by formation of actin tails (like Listeria)

• Process of epithelial cell destruction with inflammatory infiltration can progress to colonic ulceration

DAEC strains recently recognised as the sixth class of diarrheoagoenic E. coli

• heterogeneous group

• Characterised by ability to adhere in a diffuse pattern → bacteria uniformly cover the entire cell surface

• Express diffuse adherence fimbriae which contribute to pathogenesis

• Strains can cause diarrheoa in children

• primarily in children aged 2-6 years

• do not appear to cause diarrheoa in adults

• can also be asymptomatic intestinal microbiota strains in children and adults

• Pathogenesis and pathogenicity to be determined!

Facultative intracellular pathogen naturally found in fresh water

• invade and replicate inside amoebae in the environment → reservoir

• can contaminate hot water tanks, hot tubs, and cooling towers of large air conditioners

• Causes atypical pneumonia

• survives inside immune cells (macrophages)

• being elderly and having impaired lung function are risk factors

• Disease named after the outbreak where it was first identified

• 1976 American Legion convention in Philadelphia