Medical Microbiology Dr. Oruba lec.3

Microbial Metabolism

Metabolism Metabolism: Is the sum of all chemical reactions in the body. metabolism is divided into two types of classes: catabolism and anabolism.

Metabolism; It includes all the chemical reactions that occur in the cell, which include two processes; 1- Anabolism; all the chemical reactions that building up of cell structures and constituents where these reactions require energy. 2- Catabolism; all the chemical reactions that lead to the breaking down of macromolecules in to small and simpler ones where it leads to production of energy.Oxidation of carbohydrates to form carbon and energy source………………….. Hexoses and pentoses are the major monosaccharides sources……… Funneling into the major pathways…….. Degradation of bigger molecules into smaller ones……….. Formation of end products……  

Assimulation (anabolism): energy-requiring Dissimulation (catabolism): energy-acquiring Glycolysis Pentose phosphate pathway TCA cycle Respiration (aerobic and anaerobic) Fermentation Focal metabolites: metabolic intermediates that link anabolic and catabolic pathways. Microbiology Dr Saleh

The Requirements for Growth: Chemical Requirements Carbon Structural organic molecules, energy source Chemoheterotrophs use organic carbon sources Autotrophs use CO2

*According to the source of energy, organisms are divided into two groups; Phototrophs; convert radiant energy from sunlight into chemical energy….. Chemotrophs; transfer energy from organic or inorganic molecules into specific energy molecules……… *According to the source of carbon, organisms are divided into two groups; Heterotrophs; use organic or inorganic chemicals( other than CO2) as a source of carbon… Lithotrophs (autotrophs); their source of carbon is by fixation of CO2 from the atmosphere….  

Therefore, organisms in general, are divided into four groups;   Nutritional group Carbon source Energy source Examples 1- 2- 3- 4- Chemolithotrophs Chemoheterotrophs Photolithotrophs photoheterotrophs CO2 Org.comp. Org. comp. Chemicals Light Sulfur bact., iron bact.,…. Higher animals including human, most eukaryotic organisms,…. Green plants, most algae….. Some cyanobact., some algae.

On the basis of the kind of electron acceptor, energy, in the form of ATP, in microorganisms is produced by 3 ways; Fermentation; it is an oxidation-reduction process for the production of energy, where the electron donors and electron acceptors both are organic compounds….and the amount of energy produced is only 2 ATP. Aerobic respiration; it is an oxidation-reduction process for production of energy where the electron donors are either organic or inorganic compounds, and the final electron acceptor is oxygen….and the amount of energy produce is 36 ATP. Anaerobic respiration; it is an oxidation-reduction process, where the electron donors are either organic or inorganic compounds, and the electron acceptor is inorganic molecules, such as; NO-3, NO-2, SO4- -, CO2, H2S, …….etc. The amount of energy produced is only 1 or 2 ATP.  

*Mechanism of electron transport and oxidative phosphorylation is basically the same in aerobic and anaerobic respiration, but differs in the followings: Type of the electron acceptor.. Amount of the energy produced The terminal enzyme component in electron transport system in anaerobes is not cytochrome oxidase but other enzymes such as reductases…

The Requirements for Growth: Chemical Requirements Nitrogen In amino acids, proteins Most bacteria decompose proteins Some bacteria use NH4+ or NO3 A few bacteria use N2 in nitrogen fixation Sulfur In amino acids, thiamine, biotin Some bacteria use SO42 or H2S Phosphorus In DNA, RNA, ATP, and membranes PO43 is a source of phosphorus

The Requirements for Growth: Chemical Requirements Trace Elements Inorganic elements required in small amounts Usually as enzyme cofactors

The Requirements for Growth: Chemical Requirements Organic Growth Factors Organic compounds obtained from the environment Vitamins, amino acids, purines, pyrimidines

Agar Complex polysaccharide Used as solidifying agent for culture media in Petri plates, slants, and deeps Generally not metabolized by microbes Liquefies at 100°C Solidifies ~40°C

Culture Media Culture Medium: Nutrients prepared for microbial growth Sterile: No living microbes Inoculum: Introducing of microbes into medium Culture: Microbes growing in/on culture medium

Sterile Mannitol Salt Agar

Streak Plate Figure 6.10a, b

Nasal swab sample on Mannitol Salt Agar (MSA) Nasal swab sample on Mannitol Salt Agar (MSA). Non-mannitol fermenter on left. Mannitol fermenter on right, viewed from bottom

References: 1- Jawetz, Melnick, & Adelberg’s.( 2013). Medical Microbiology (Twenty-Sixth Edition). 2- Kenneth Todar. (2008).Todar’s Online Textbook of Bacteriology ,University of Wisconsin.

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