Controlling Pathogens

How can we control pathogens to prevent disease?  Hygienic measures/Antiseptic Technique  Treatment of infections  Defence at the organism level

Hygienic Measures  simple hygienic measures such as washing hands or covering your mouth when you sneeze can impact on the spread of pathogens.  Above and beyond this, the use of antiseptics and disinfectants have an important role in preventing infection.

Antiseptics and Disinfectants Antiseptics: used on skin to kill pathogens  alcohol (70% ethanol) – breaks down lipids and denatures protein  hydrogen peroxide – oxidizing agent  detergents – disrupt cell membranes  iodine – binds to proteins Disinfectants: used to kill pathogens on objects  chlorine – oxidizing agent  phenols – denature proteins  ammonium compounds – interact with phospholipids in membranes  copper sulfate – precipitates protein

Levels of cleanliness???  Sterilization  is the complete destruction or elimination of all viable organisms.  procedures involve the use of heat, radiation or chemicals, or physical removal of cells.  Disinfection  reducing the number of viable microorganisms present in a sample.  Sanitization  cleaning of pathogenic microorganisms from public eating utensils and objects.  Sanitizer – an agent that reduces, but may not eliminate, microbial numbers to a safe level.  Decontamination  Decontamination is the treatment of an object or inanimate surface to make it safe to handle.

Treatment of Infections  Antibiotics and antimicrobials  Fungicides and antifungals  Antivirals  Antiprotozoan and antihelminthic drugs

Antibiotics and antimicrobials Antibiotics  Substances naturally produced by microorganisms, that are active against other microorganism.  First antibiotic was penicillin which is produced by the fungus Penicillium notatum. Antimicrobial agents  Chemicals that can be used to inhibit microbial growth, including antibiotics.  Key requirement for a antimicrobial is selectivity – the ability to kill microorganisms but not cells of the host.  Antimicrobials may be broad-range (kill many types of bacteria) or narrow- range (only kill one or two types).  Sensitivity tests are often carried out in a clinical setting to determine which drug is most effective against infecting bacteria.

Types of antibiotics DrugSpectrumMode Possible side effects ErythromycinNarrow (Gram +) Inhibit protein synthesis GI upset Liver damage PenicillinNarrow (Gram +) Inhibit cell wall synthesis so bacteria can’t reproduce Allergic response sulfonamidesBroad (Gram + and -) Compete against against bacteria (inhibit folic acid production) Allergic response Kidney and liver damage tetracyclinesBroad (Gram + and -, rickettsia and Chlamydia) Inhibit protein synthesis GI upset Teeth discolouration Kidney and liver damage

Fungicides and antifungals Fungicides  Used to kill fungi.  Bordeaux mixture (developed in 1870s) – a mixture of copper sulfate and lime prevents mildew and fungal disease in plants). Antifungals  Very few available for treatment of humans (with the exception of topical creams).  Major difficulty is that fungi and human cells are both eukaryotic and therefore have similar properties.  Ergosterol is a major target of antifungal drugs as it is found in fungal but not human cell membranes. Problem is that there is still some interference with similar substances in human cells.

Antivirals  Viral infections are difficult to treat as it is difficult to attack a virus without harming its host cell.  Viruses don’t have the structures that are the usual targets for antibiotics, so drugs need to target specific steps in the viral reproduction pathway, for example:  Interfering with the uncoating of coated viruses such as influenza  Preventing nucleic acid synthesis (herpes virus and HIV)  Preventing the assembly and release of viral particles (influenza and HIV)  Interferons are a group of antiviral agents produced by virus-infected tissues. They preparing neighbouring cells to shut down protein synthesis in the vent the become infected.

Example of an antiviral  The most effective HIV drugs at the moment are those that target step 2.  Nucleoside inhibitors prevent reverse transcription which means that ds viral DNA can’t be made and viral protein can’t be produced.  Not 100% effective.

Antiprotozoan and antihelminthic drugs  Antihelminthics are use to treat infection with hookworm, pinworm, threadworm, whipworm and tapeworm. Some kill the worms on contact. Others starve or paralyse the worms, which then pass out of the body in the faeces. Think Combantrin!  Antiprotozoal drugs are used to treat protozoal infections, for example malaria, trypanosomiasis and leishmaniasis. In general these drugs are inadequate.  Unfortunately, these are largely diseases of third world countries and very little research is being done in regards to further drug development.

Defence at the organism level  Organisms must continually defend themselves against pathogens of many kinds  A variety of defence mechanisms have evolved to increase the chances of survival in the face of these external challenges  Defence mechanisms operate at all levels – external and internal, and involve molecules, cells and organ systems.  The ways that organisms protect themselves against pathogens fall into two categories: non-specific and specific.