Medical Microbiology

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Who is susceptible to E.Coli?
Anyone exposed to contaminated food (i.e. undercooked ground beef, raw vegetables) and the young/elderly/unhealthy
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Where in the world/in the body does E.Coli effect?
Colonises at mucosal site (Nataro and Kaper, 1998), usually in the large intestine. Can come about anywhere in the world (e.g. outbreaks have occurred in Europe, USA, etc)
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When should E.Coli be Isolated?
Doesn't usually require a doctor. If in hospital, samples are taken if the patient has persistent diarrhoea; is traveller; children/elderly; immunocompromised; and during an outbreak. It is isolated from stool and sent to a qualified reference lab.
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Why does E.Coli cause illness? (Nguyen and Sperandio, 2012)
Enterohemorrhagic (EHEC) E.Coli colonises large intestine, releases Shiga Toxin, which has 2 subunints. B: pentamer, binds to GB3. A: mediates RNA N-glycosidase activity. Shiga binds to endothilia, expresses GB3, enters blood.
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Which organisms cause E.Coli infections?
According to CDC, 6 types are: Shiga producing (STEC); Enterotoxigenic (ETEC); Enteropathogenic (EPEC); Enteroaggregative (EAEC); Enteroinvasive (EIEC); and Diffusely Adherent (DAEC)
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What lab techniques are used to detect E.Coli?
Serotype enzyme immunoassays: directly from stool, 73-100% specificity, is expensive. Also, PCR assay for Shiga toxin, DNA Probes, and Multiplex PCR Assays (these are not widely available)
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How is E.Coli treated/cured?
Symptoms usually pass without treatment. Antibiotics aren't advised, as it reduces healthy microbiome. Rest + fluids at home recommended. If progressed to Hemolytic uremic syndrome, this requires IV fluids, blood transfusions, or even dialysis.
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Who is susceptible to Chlamydia trachomatis?
Anyone partaking in unprotected sex/sex acts. Young people tend to contract this more often: between ages 15-24
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Where in the world/on the body does Chlamydia trachomatis effect people most?
Anywhere in the world. On Women: in the cervix, rectum, and throat. On Men: in the urethra, rectum, and throat.
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When should Chlamydia trachomatis organisms be isolated?
Organisms can be isolated at any time during infection. Can also detect antigent, nucleic acids, or antibodies in the absence of infectious particles (Chernesky, 2005)
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Why does Chlamydia trachomatis cause infection?
According to CDC: are obligate, intracellular organisms with G- cell wall. After 8 hours, elementary bodies (EB) become reticulate bodies (RB) + multiply inside cell inclusion. 24 hours, RBs > EBs again, released, and infect new cells/host.
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What lab techniques are used to detect Chlamydia trachomatis?
Swab (no wood shaft) - e.g. cytobrush. Refrigerated (24hr+ = -70 frozen). Can be isolated, or antigens detected. Serum = not recommended. (Chernesky, 2005)
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How is Chlamydia trachomatis treated/cured?
If caught early, antibiotics can cure it. Azithromycin: 2/4 tablets at once; Doxycycline: 2 tablets a day for 7 days. (NHS)
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Who is susceptible to Wuchereria bancrofti?
People living in areas where mosquitos are prominent (e.g. Anopheles mosquitos). Also, there has been a proven mild genetic link - as the regulation of the infection depends on the patient's immune system.
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Where in the world/in the body does Wuchereria bancrofti cause illness?
It causes infections by entering the bloodstream and multiplying in the lymph system - causing leg and/or scrotum swelling. It is most commonly found to occur in Asia, Africa, and the Americas - due to heightened mosquito populations.
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When should Wuchereria bancrofti be isolated?
At the peak of microfilarial activity (22:00-02:00 for W. bancrofti)
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Why does Wuchereria bancrofti cause illness?
Lymphatic filariasis (bancroftian): downstream obstruction of lymph vessels by adult worms = blockage. Also causes Interstitial fibrosis: diffusible substances from live or dead worms (Dreyer et.al., 2000)
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Which organisms cause Wuchereria bancrofti infections?
The Wuchereria bancrofti nematode (worm), of which the adults cause lymphatic filariasis.
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What lab methods are used for detection and diagnosis of Wuchereria bancrofti?
The long-term used method: BinaxNOW filariasis card (10+ yrs). Weil et al, 2013 tested a new method: The Alere Filariasis Test ***** - and found it was more stable, more sensitive, and gave higher specificity.
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How is Wuchereria bancrofti treated/cured?
Can be treated using either Ivermectin (150-200mg) or Albendazole (400mg)
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Who is susceptible to MRSA?
It is nosocomial: any vulnerable patients (e.g. ICU or Surgical) or someone with broken skin. It is more likely if the person is already unwell (lower risk if healthy). E.g. Nursing home patients. (NHS)
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Where in the world/in the human body does MRSA cause illness?
If it enters the skin, it can affect all three layers of the skin: upper, middle, and lower dermis. Can enter the bloodstream and track around the body. Geographically: anywhere with high antibiotics use (e.g. USA or Europe)
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When should MRSA be isolated?
Some hospitals screen before admission as a selective patient, or on admission as an emergency patient. Patients are also screened regularly throughout stay. Screening is also done if a doctor suspects illness, or carrier.
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Why does MRSA cause illness?
Commensal opportunistic pathogen: enters via break in the skin/mucosal membrane. MSCRAMMS enable attachment (endocarditis); Biofilms enable persistence (relapsing infections, Cystic Fib.); Leukocidins enable defence evasion (Gordon and Lowy, 2008)
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Which organisms cause MRSA?
Staphylococcus aureus - strains that have become resistant to methicillin antibiotics.
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What lab techniques are used to detect and diagnose MRSA?
Baird-Parker medium with ciprofloxacin (BPC), which gives results within 24 hours. (Brown et al, 2005); there are also rapid, sensitive PCR methods as well as chromogenic agars.
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How is MRSA treated/cured?
Body washes and shampoo with chlorohexidine are given to carriers, as well as nostril ointment containing Mupirocin or Naseptin. Parenteral treatment (UK) involves Vancomysin; and cellulitis can be treated using Tetracylcines and/or co-Trimozadole.
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Card 2

Front

Where in the world/in the body does E.Coli effect?

Back

Colonises at mucosal site (Nataro and Kaper, 1998), usually in the large intestine. Can come about anywhere in the world (e.g. outbreaks have occurred in Europe, USA, etc)

Card 3

Front

When should E.Coli be Isolated?

Back

Preview of the front of card 3

Card 4

Front

Why does E.Coli cause illness? (Nguyen and Sperandio, 2012)

Back

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Card 5

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Which organisms cause E.Coli infections?

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