Question

2. a)Frances Redi disproved spontaneous generation by designing a controlled experiment where he placed raw meat in six (6) jars. He covered three jars with a fine net and left three jars open. After a short period, maggots appeared in the open jars while the covered jars had no maggots. In your opinion, what additional controls and measurements could Frances Redi have done to prove that rotting of raw meat is caused by live bacteria?

b)Microorganisms were inoculated on two agar plates and incubated for 24 hours. After incubation, no microbial colonies were seen on the spread plate agar, but three microbial colonies were seen in the pour plate agar. What may account for this observation and how can growth of this microorganism be enhanced?

c)Discuss three importance of glycocalyx to microorganisms with specific examples.

Answer 1

Answer 2. a):

Francesco Redi's experiment with meat jars to disprove spontaneous generation was well coordinated. In the experiment, meat in side the jars that were covered with cloth to restrict the entry of flies did not show maggots, though outside the cloth where flies descended, maggots were seen.

But the meat eventually rot, maggots or no maggots, was due to bacteria already present in the meat or the jar. This could have been shown by Redi by sterilizing the jars and boiling the meat for more than 30 minutes and sealing it with cork or other sealant so as to avoid further contamination. This meat would have survived for longer time without getting rotten as all bacteria and their spores would have destroyed by heat. This could have further supported his experiment disproving agenesis and would have given additional conclusion of presence of bacteria and their role in decomposing organic matter.

Answer 2. b):

The biggest disadvantage of spread plate method is that it can detect only aerobically growing bacteria. In contrast the pour plate agar method can give chance to grow for both aerobes and anaerobes. The presence of 3 colonies in the pour plate agar and no growth on spread plate show that these bacteria growing are microaerophilic or anaerobes. By providing proper anaerobic conditions, in an anaerobic jar, the growth of these anaerobic bacteria could be enhanced considerably.

Answer 2. c):

Glycocalyx literally means sugar coat. It is a network of polysaccharides that project from the cell wall of bacteria. In some bacteria it is present as capsule which is firmly attached to the cell wall of the bacterium, In bacteria where it is loosely attached to the cell wall, it is known as slime layer. Some microorganisms forma biofilm where in the capsules of individual bacteria merge to give a protective cover to the hole colony.

Primary functions of Glycocalyx include:

• It protects bacteria from phagocytosis by hiding them from host immune cells.
• It forms a protective layer that protects from extraneous chemicals and desiccation
• It contributes to virulence in some bacteria
• It helps organisms to attach to inert surfaces.

Pathogens that are encapsulated include: Klebsiella pneumoniae, Neisseria meningitidis, Hemophilus influenzae, Bacillus anthracis, Streptococcus pneumoniae and more.