tailieunhanh - Environmental Pollution Control Microbiology - Chapter 3

Theo các điều kiện môi trường thích hợp, vi khuẩn theo mô hình xác định sự tăng trưởng cao tái sản xuất. Các kích thước nhỏ của vi khuẩn và đơn giản của quá trình trao đổi chất cho phép vi khuẩn sinh sản với tốc độ nhanh, so với các sinh vật bậc cao. Vi khuẩn phát triển tốt nhất là kiểm tra trong chất nền hòa tan hoàn toàn trong điều kiện môi trường tối ưu. Tăng trưởng có thể được đo bằng độ đục, bởi tính trực tiếp trên các phương tiện truyền thông chất lỏng, hoặc. | Chapter 3 BACTERIA GROWTH Under the proper environmental conditions bacteria follow definite patterns of growth that are highly reproducible. The small size of bacteria and their simplicity of metabolism allow bacteria to reproduce at a rapid rate compared to higher organisms. Bacterial growth is best examined in completely soluble substrates under optimum environmental conditions. Growth can be measured by turbidity by direct counts in liquid media or by plate counts on solid media. Turbidity is useful over a moderate range of bacteria growth. Turbidity can be determined as optical density at 600 nm in a single beam spectrophotometer. Turbidimetric measurements work best for growth studies in dilute nutrient media. As bacteria growth increases significantly the errors in turbidimetric measurements increase at a rapid rate. The primary error comes from several cells located along the same light path giving the impression of only a single cell in the turbidimetric measurement. Direct bacteria counts require dilution to reduce the number of bacteria to a reasonable level for accurate counting. Staining is normally used to permit easy observation of the cells. Fluorescent dyes have been used to permit direct counting of specific bacteria in mixed culture systems. Plate counts on solid media have proven to yield the best results and have been widely accepted for measuring bacteria growth. Experience has shown that serial dilutions to produce between 30 and 300 colonies per plate provide the best results. There is no single universal media that permits growth of all bacteria. Standardized protein and carbohydrate media have been used for isolation and growth of most common bacteria. Specialized bacteria require both specific nutrients and the proper envfronment. Membrane filters have been used for concentrating bacteria from dilute solutions for either direct counting or growth on specific media. Since the bacteria have definite masses the total mass of bacteria has .