MICROBIOLOGY 1

MICROBIOLOGY 1

1. Antimicrobial Rsistance

   • Susceptibility tested by a filter paper disc soaked with the test substance placed on the interface between bacterium and test
     • Exposing the bacterium to increasing concentrations
       • MIC - minimum inhibitory concentration
       • MBC - minimum bactericidal concentration
   • Bacteria may lack the target for the antibiotic
     • Chlamydia don't have peptidoglycan so not affected by cell wall inhibitors
   • The antibiotic target may be inaccessible
     • Peptidoglycan in Gram negative bacteria is inaccessible to penicillin's due to outer membrane
   • Efflux pumps actively pump out antibiotics
     • Gram negative bacteria resist tetracycline's by this mechanism
   • The antibiotic target may be modified
     • Trimethoprim resistance is manifested by alterations in the DHFR target enzyme
     • Quinolone resistance is effected by point mutations to DNA gyrase
   • The antibiotic may be chemically targeted or modified
     • Beta lactamases
     • Chloramphenicol resistance manifested by acetylation
   • Bacteria may elaborate alternative pathways
     • MRSA resistant to methicillin due to production of an alternative penicillin binding protein

2. Syphilis

   • Endemic in most coutries
   • Great pox - knowledge may have been increased by printing press development
   • Treatment
     • Originally treated with an arsenic derivative
     • Replaced with mercury treatment
     • Fever therapy - patients infected with malaria parasites as this produced high temperatures (fever)
     • Penicllin
     • Serology
       • VDRL test
         • Monitors therapy
       • TPI test
         • Tests for TP antigens
           • Also TPHA/TPPA
       • FTA (Abs) test
   • Treponema pallidum - motile, cant be cultured on lab medium
   • Transmission
     • Horizontal - sexual contact
     • Vertical - congenital and through blood transfusions
   • 9-90 days, more men affected
     • Primary stage
       • Penetrates skin/mucous membranes
       • Spreads via lymphatics to blood
       • Primary lesion appears at inoculation site
     • Secondary stage
       • Infection and rash
       • Enlarged lymph nodes
       • Ulcers, patchy baldness, eye problems
     • Latent stage - person appears well though still infected
     • Tertiary stage
       • Gummatous lesions everywhere

3. Food Poioning

   • Food poisoning can result from chemical contamination, the nature of the tissue or their by-products. Intoxication OR infection
     • Meats act as vectors for tapeworms, fluke or roundworm
       • Taenia sagginata is a tapeworm that causes infection of raw beef
       • Taenia solium is a tapeworm acquired from undercooked pork
       • Trichinosis is caused by a nematode worm sauced in pork
     • Puffer fish, Moray eel and shellfish can all cause food poisoning
       • Tryptophan in tuna breaks down to produce histamine when inadequately stored
     • Thermophilic campylobacters (Campylobacter jejuni) are the most prevalent food bourn infections in the developed world
       • Causes campylovacter enteritis - symptoms include profuse and watery diarrhoea with blood in the stools. Pain, cramping and nausea also occur
       • Campylobacters produce a toxin related to cholera
       • Poultry and unpasteurised milk are common sources of campylobacters. Wild birds act as a vector
   • Plants and their component parts may be poisnous
     • The stems of rhubarb plants are used in cooking but the leaves and roots causes vomiting and pain
     • Over soaking of dried pulses
   • Examples
     • Staphylococcus aureus is the most common in the UK. Causes vomiting
       • Part of commensal microbiota
       • Meat sandwiches, cold cooked meats, cream cakes, custards and food with high preparation (prawns)
       • Salt tolerant
     • Bacillus cereus - spore forming, aerobic, gram positive rod
       • Comtaminates rice - chinese restaurant syndrome
         • Bacillus spores produce a toxin in the cooling process of rice that survives the rice frying process
     • Clostridium perfringens - spore forming, anaerobic gram positive bacillus. Doesn't produce spores when cultivated in the lab
       • Poisoning is mild but causes diarrhoea and abdominal pain
       • Enterotoxin is produced as a secondary metabolite in situ - symptoms occur after a day
       • Associated with schools, hospitals and Halls (bulk prepared meat)
     • Botulin toxin causes botulism from contaminated sausages
       • Flaccid paralysis
       • Home canned food
     • E coli associated with children and travellers
       • Associated with haemolytic anaemia
     • Listeria monocytogenes associated with dairy, pate and soft cheeses

4. Food Spoilage

   • The process of rendering food unfit for consumption due to unpalatable taste, odour or texture
   • Meat and dairy provide many nutrents for spoilage organisms - perishable
     • Proteins broken down to amino acids
     • Fats are broken down to fatty acids and glycerol
     • Carbohydrates are fermented to acids, alcohols and gases
     • Joints of meat are less affected than mince (less surface area)
   • Milk is a growth media for bacteria and yeasts
     • Souring by lactobacilli
     • Bacillus species are proteolytic bacteria that degrade milk proteins
     • Clostridium infection may produce acid or alkali
       • Can also produce a stormy clot
   • Food preservation
     • Cooking
       • Pasteurisation - doesn't increase the shelf life of milk. UHT does
     • Chilling
       • Delays spoilage
     • Drying
       • Dried fruits and meat, powdered milk and soups
     • Osmotic protection
       • Salting or the addition of sugar
     • Filtration
       • Liquid foodstuffs
       • Appropriate filtration gaps
     • Irradiation
       • Gamma rays