Question

List and describe the phases of the bacteria growth with regards to: a) Number of cells; b)”Tooling”; c) generation time; d) viability; e) mortality, f) pH changes in media; g) waste production

List three (3) instruments often used to detect the growth of bacteria. How are these instruments used to estimate the growth of microorganisms?

Discuss the techniques that are frequently employed to detect/estimate bacteria growth. Explain the advantages and weaknesses of these methods.

Answer 1

Answers;

When a bacterium is inoculated into a suitable liquid medium and incubated,its growth follows a defined course.the population size of the bacteria increases showing a classical pattern.when plotted on a graph a distinct curve is obtained referred to as the bacterial growth curve.The curve shows four phases.

1.Lag phases : Immediately following the inoculation of a culture ,edium,the cells do not increase in number but may increase in size.The initial period is the time required for adaptation to the new environment,during which the organisms starts building up sufficient quantities of necessary enzymes and substances for multiplication to proceed.The duration of the lag phase varies with the species,size of the inoculum,pH,composition of the culture medium and environmental factors such as temperature.                                                 

2.Log phase : Following the lag phase the cells start dividing and their numbers increases exponentially with time.

3.Stationary phase : After a varying period of exponential growth,cell division stops due to nutrients being used up during growth and accumulation of toxic products.The number of daughter cells formed is just enough to replace the number of cells that die.The viable count remains the same as a balance exists between the dying cells and the newly formed cells.

4.Phase of Decline : This is the phase when the population decreases due to cell death.Besides lack of nutrients in the medium and accumulation of toxic products, cell death may also be caused by lytic enzymes within the cells.

Bacterial nutrients : for growth and multiplication of bacteria the minimum nutritional requirements are water,a source of carbon ,nitrogen and some inorganic salt.Bacteria can be classified nutritionally based on their energy requirements and their ability to synthesise essential metabolites; phototrops,chemotrops,autotrops,heterotrops.                                              Oxygen requirement and metabolism : Depending on the influence on growth and viability bacteria are divided into aerobes and anaerobes.aerobic require oxygen for growth and anaerobic grow in the absence of oxygen.                              pH : Each species of bacteria has an optimum pH at which it grows best.The majority of pathogenic bacteria grow best at neutral or slightly alkaline pH (7.2-7.6).                                                                                                              Light : Bacteria grow well in the dark.they are sensitive to ultraviolet light and other radiation.

Moisture and drying : Water is an essential ingredient of bacterial protoplasm and hence,drying is lethal to cells.spores are resistant to desiccation and may survive in the dry state for several decades.

* Microscopy and Staining methodsare the main instrumental method that used to detect growth of the bacteria . microscopes are required to study the morphology of becteria. Diffrent types of microscopes are used they are optical or light microscope,fluorescence microscope,phase contrast microscope,dark field microscope,electron microscope.    Different types of staining methods are simple stains,negative staining,impregnation method,gram staining method,acid fast staining.

1.Optical or Light microscope : Bacteria may be examined under the compound microscope,either in the living state or after fixation and staining.Examination of wet films or hanging drop indicates the shape,arragements,motility,and approximate size of the cells.The disadvantage of this type of microscopy is that due to lack of contrast details cannot be easily seen.

2.Fluorescence microscope : Fluorescence microscopy makes use of fluorescent labels,which when illuminated by the correct wavelength of light,appear fluorescent.This property can be used to highlight features of microbes and makes this technique easier for the microscopist.

3.Simple stain : Dyes such as methylene blue or basic fuchsin are used for simple staining.they provide colour contrast,but result in all bacteria having the same colour

In a preparations of live bacteria,it is not possible to see much structural detail under the light microscope due to lack of contrast.Hence it is customary to use staining techniques to produce colour contrast.in some cases some stains can penetrate cell walls and highlight cell components.this can help to visualize metabolic process.also the stains also help distinguish between the live cells and dead ones.staining allows scientists count the number of cells of a particular type within a certain biomass.                                                                       The microscopic method is rapid,simple and also very easy method that requring minimum equipment.the bacterial morphology can be observed as they counted and very dense suspensions can be counted if they are diluted appropriately.although rapid, a direct count has the disadvantages that both living and dead cells are counted.small cells are difficult to see under the microscope and some cells are probably missed.in the microscopic method the precision is difficult to achieve.