Control of Microbial Growth

1. Control of Microbial Growth Chapter 7 Siti Sarah Jumali 06-4832123 www.slideshare.net/sarah_jumali

2. Terminology • Sepsis refers to microbial contamination. • Asepsis is the absence of significant contamination. • Antisepsis: Removal of pathogens from living tissue • Degerming: Removal of microbes from a limited area • Sanitization: Lower microbial counts on eating utensils

3. Terminology cont’d • Decontaminated - item that has been treated to reduce # of disease causing organisms • Preservation - delaying spoilage of foods • Sterilization, Disinfection, Antiseptic, Bacteriocidal, Bacteriostatic

4. Terms used: Sterilization vs. Disinfection • Sterilization: destroying all forms of life • Disinfection: destroying pathogens or unwanted organisms • Disinfectant vs. Antiseptic • Disinfectant: antimicrobial agent used on inanimate objects • Antiseptic : antimicrobial agent used on living tissue

6. cidal vs. static • Biocide/Germicide: Kills microbes • Bacteriostasis: Inhibiting, not killing, microbes • Examples: - Bactericidal - kills bacteria - Bacteriostasis (Bacteriostatic)- inhibits bacterial growth - Fungicidal - Fungistatic - Algacidal - Algastatic

7. Methods of control • Physical or chemical? • physical control includes heat, irradiation, filtration and mechanical removal • Chemical control involves the use of microbial chemicals • Depends on the situation • degree of control required

8. Methods of control cont’d • Daily life - Cooking - refrigeration - cleaning - soap water mechanical Mechanical and chemical

9. Methods of control cont’d • Hospitals • Important to minimize nosocomial infection (hospital acquired infection) due to - weakened patients’ condition - breaching of intact skin - high concentration of pathogens from patients and workers • Sterile condition

10. Methods of control cont’d • Microbiology lab utilizes • Sterile equipment • Aseptic technique • And possesses workers who takes care of the nature of of microbiologists (GLP)

11. Methods of control cont’d • Foods/food production industry - physical removal - adding chemicals - may result in toxicity - clean surface/ machinery

12. Selection of Control Method • Antimicrobial procedure used for control of microbial growth is based on • Types of microbe • Extent of contamination • Environmental conditions • Potential risk

13. Selection of Control Method cont’d • Types of microorganism - some organisms are more resistant and require stronger measures for control - endospores require chemical treatment for 10 hours - Mycobacterium’s waxy cells are resistant to chemicals Mycobacterial cell wall: 1-outer lipids, 2-mycolic acid, 3-polysaccharides (arabinogalactan), 4-peptidoglycan, 5-plasma membrane, 6-lipoarabinomannan (LAM), 7-phosphatidylinositol mannoside, 8-cell wall skeleton

14. Selection of Control Method cont’d • Extent of microbial population - larger population take more time to destroy - usually 90% of the population is destroyed in a given period e.g if in 1st 3 minutes 90% of the population is destroyed, then 90% of the remaining population gets destroyed in the next 3 minutes and so on

16. Selection of Control Method cont’d • Environmental conditions - pH, temperature - presence of - organics: blood - dirt - grease - the potential risk of transmitting infectious agents - critical items - semicritical items - non-critical items Must be cleaned first, then controlled

17. Selection of Control cont’d • Critical items have - indirect contact with body tissues - needles, scalpels • Semicritical items have contact with - mucous membranes but it does not penetrate endoscopes, endotrachial tubes

18. Selection of Control cont’d • Non-critical items have - indirect contact with unbroken skin - countertops, stethoscopes

19. Methods to Control Microbial Growth

20. Physical Microbial Controls: Heat • Heat as a microbial control - fast, reliable, inexpensive - does not introduce potential toxic substances • Types of heat control include - moist heat - pasteurization - pressurized steam - dry heat

21. Physical Microbial Controls: Heat cont’d • Moist heat - causes irreversible coagulation of proteins found in microorganisms - 10 minutes of boiling - most microbes and viruses will be destroyed except endospores and few others which can survives hours of boiling

22. Physical Microbial Controls: Heat cont’d • Pasteurization - reduces number of heat sensitive organisms - widely used in milk and juices increases shelf life and does not alter quality - original pasteurization was 62ºC, 30 mins - now: UHT-shorter time 72ºC, 15 secs

23. Physical Microbial Controls: Heat cont’d • Pressurized steam - pressure cooker or autoclave - higher air pressure increases the temperature at which steam forms - 15 psi (lbs/square inch) at 121ºC for 15 mins -effective to kill endospores

24. The autoclave: Moist heat and pressure • 15psi, 121ºC, 15 minutes • Thermal death point (TDP): Lowest temperature at which all cells in a culture get killed in 10 mins • Thermal death time (TDT): time to kill all cells in a culture • Decimal reduction time (DRT): Minutes to kill 90% of a population at a given temperature

25. The autoclaving machine

26. Temperature of steam and Pressure at sea level

27. The autoclaving machine

28. Physical Microbial Controls: Heat cont’d • Dry heat - without moisture e.g. flaming - burns cell constituents - object is oxidized to ash - irreversibly denatures proteins - takes longer (200ºC, 1.5 hrs dry=121ºC, 15 min moist) - advantages are for powders, does not corrode metals and blunt sharps - e.g flasks, tubes, pipettes in microbiological laboratories.

29. Physical Microbial Controls: Filtration • Used for heat sensitive fluids • air

30. Physical Microbial Controls: Filtration cont’d • Fluids • solutions of antibiotics, vitamins, tissue extracts, animal serum, etc. • Depth filters –able to retain microorganisms while allowing fluids to pass through • Membrane Filter - The use of graded pore size 0.2-0.4µm

31. Physical Microbial Controls: Filtration cont’d • Air - HEPA (High Efficient Particulate Air) filter and laminar air flow are commonly used - filter incoming air and outgoing air respectively - HEPA filter prevents the income of 0.3µm and large size particles to enter.

32. Physical Microbial Controls: Radiation • “Cold sterilization“ for disposable materials made up of plastics, wool, cotton, etc without altering the material. • Radiation damages DNA • Ionizing radiation (X-rays, gamma rays, electron beams) • Non-ionizing radiation - UV - Microwaves kill by heat not especially antimicrobial

34. Physical Microbial Controls: Radiation cont’d • Gamma irradiation - penetrate deeply - for heat sensitive materials - causes biological damage to microorganisms - does not alter food flavor (meat)

35. Physical Microbial Controls: Radiation cont’d • UV light • damages the structure and function of nucleic acids • Penetrate poorly- cannot penetrate even into liquid. • Used to disinfect surfaces • Can cause damage to human cells • Germicidal lamps -kill or reduce the number of viable microorganisms to sterilize microbiological laboratories hospital operating rooms, and specific filling rooms in various industries

36. Physical Microbial Controls: Radiation cont’d • Microwave • Kills by heat • Does not affect microorganisms directly

37. Physical Methods used to control Microbial growth

42. Chemical Microbial Control

44. Chemical Microbial Control cont’d • Grouped according to potency • Sterilants • High-level • Intermediate level • Low level

45. Chemical Control sterilants • destroy microorganisms, endospores and viruses • used for critical equipment-scalpels

46. chemical control cont'd • high level - destroy viruses and  vegetative microorganisms (no endospores) - used for semicritical equipment: endoscopes • intermediate level - destroy vegetative microorganisms, some viruses - used for non-critical equipment: sthetoscopes • low level -destroy fungi, vegetative microorganisms - used for general purpose disinfectants

47. Selecting Germicidal Chemical • Germicide: An agent capable of killing pathogens and non-pathogens but not necessarily endospores • toxicity to human or environment? - weigh the benefits vs the risks • presence of organic material - hypochlotrite is inactivated by the presence of organic matter • compatibility -electrical equipment with a liquid?? • residue - some have to be rinsed with sterile water • cost and availability

48. Selecting germicidal Chemical cont'd • storage and stability - may come in concentrated form for ease in storing - those have to be mixed • environmental risk - is neutralization necessary before disposal?

49. Classes of Germicidal Chemicals • alcohols alcohols • aldehydes • biguanides • ethylene oxide  • halogens: oxidize proteins

50. Classes of Germicidal Chemicals • alcohols - coagulated enzymes and proteins - damage lipid membranes - on-toxic - inexpensive - no residue