• Exoenzymes released by bacteria include: Necrotizing enzymes Coagulase Kinases Hyaluronidase Collagenase Hemolysins Lecithinase
Copyright © 2015 Wolters Kluwer • All Rights Reserved Mechanisms by Which Pathogens Escape Immune Responses • Antigenic Variation – Some pathogens evade the immune system by changing their surface antigens – antigenic variation ; examples, Neisseria gonorrhoeae and Borrelia recurrentis . • Camouflage and Molecular Mimicry – Some organisms conceal their foreign nature by coating themselves with host proteins – like camouflage (e.g., adult schistosomes). • Destruction of Antibodies – Some pathogens produce IgA protease, an enzyme that destroys some of the host’s antibodies; example, Haemophilus influenzae .
Copyright © 2015 Wolters Kluwer • All Rights Reserved Intracellular pathogens
Copyright © 2015 Wolters Kluwer • All Rights Reserved Obligate Intracellular Pathogens • Pathogens that must live within host cells in order to survive and multiply are referred to as obligate intracellular pathogens (examples: Rickettsia and Chlamydia spp.). – Intraleukocytic pathogens ( e.g., Ehrlichia spp. and Anaplasma phagocytophilum ) live within white blood cells, causing diseases known as ehrlichiosis and anaplasmosis. – Plasmodium spp. (which cause malaria) and Babesia spp. (which cause babesiosis) are examples of intraerythrocytic pathogens; they live within red blood cells .
Copyright © 2015 Wolters Kluwer • All Rights Reserved Facultative Intracellular Pathogens • Facultative intracellular pathogens are capable of both an intracellular and extracellular existence. • Intracellular Survival Mechanisms – Possess a cell wall composition that resists digestion (e.g., Mycobacterium tuberculosis ) – Fusion of lysosomes with phagosomes is prevented – Production of phospholipases that destroy the phagosome membrane, thereby preventing lysosome-phagosome fusion – Other unknown mechanisms
Copyright © 2015 Wolters Kluwer • All Rights Reserved Burton's Microbiology for the Health Sciences Chapter 8. Controlling Microbial Growth in Vitro
Copyright © 2015 Wolters Kluwer • All Rights Reserved What you absolutely must know…. • Definition of microbial growth and the 8 factors that affect microbial growth • Definitions of sterilization and disinfection and examples of each method • The 5 most common mechanisms of action of antimicrobial agents • The difference between bacteriostatic and bactericidal agents • The six major categories of antibacterial agents and their mechanisms of action • Mechanisms of antibiotic resistance
Copyright © 2015 Wolters Kluwer • All Rights Reserved Chapter 8 Outline • Introduction • Factors that Affect Microbial Growth • Encouraging the Growth of Microbes in Vitro • Inhibiting the Growth of Microbes in Vitro
Copyright © 2015 Wolters Kluwer • All Rights Reserved Factors That Affect Microbial Growth 1. Availability of Nutrients All living organisms require nutrients to sustain life.