Medical Microbiology

Yin Bingnan Department of Microbiology November, 2006 Chapter 3

Bacterial Growth and Metabolism What are the requirements for bacterial growth? Nutrients

• Water • Carbon source • Nitrogen source • Inorganic salts • Growth factors – organic compounds that a cell must have for growth but cannot synthesize itself Oxygen

• Obligate aerobe An organism that grows only in the presence of oxygen • Microaerophile An organism that requires a low concentration of oxygen for growth • Facultative anaerobe An organism that grows with or without oxygen • Oblige anaerobe An organism that grows only in the absence of oxygen Temperature

• Psychrophile (15～20℃) An organism that grows best at cold temperatures • Mesophile (30～37℃) An organism that grows best at moderate temperatures

An organism that • Thermophile (50～60℃) grows best at high temperatures pH

• Acidophile An organism that grows best at a pH below 6

• Neutrophile An organism that grows best at a pH between 6 and 8

• Alkalophile An organism that grows best at a pH above 8 How does a bacterium reproduce? Binary fission

Asexual reproduction in which a cell or an organism separates into two cells How often does a bacterium separate? For a single bacterium

• Majority – Escherichia coli: 20～30min • Exception – Mycobacterium tuberculosis: 18～20hrs For a population of bacteria What are the characteristics of bacteria in each phase? Lag phase

• No growth • Active metabolism Log phase

• Fast growth • Typical biological properties – Staining – Shapes – Chemical reactions – Sensitivity to antimicrobial agents Stationary phase

• Constant number of live cells • Atypical morphological properties • Spores, exotoxins and antibiotics produced Decline phase

• Decreased number of live cells • Collapse or atypical cells What are the medically important anabolic products of bacteria? Pyrogen a polysaccharide produced by bacteria that causes a rise in body temperature

Toxin

Exotoxin Endotoxin Invasive enzyme

Antibiotic a microbial product that inhibits or kills other microorganisms Bacteriocin an agent produced by a bacterium that inhibits or kills closely related species or even different strains of the same species

Vitamin Pigment The medical significance of these products?

Products Medical significance Pyrogen Pathogenicity of Toxin bacteria Invasive enzyme Antibiotic Treatment of Vitamin infectious diseases Bacteriocin Identification of Pigment bacteria Summary

• Definitions: pyrogen, antibiotic and bacteriocin • The requirements of bacterial growth • The mode of bacterial reproduction • The characteristics of growth curve • Seven medically important anabolic products of bacteria