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UNIVERSITY OF J01

DR.: AS'''' A L S H ' H A ~ '

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~ ) \ ~ ) \ ~ \ ~In order to classify bacteria into genres or int.ospecies, we have to know how bacteria grow (bothin vitro & in vivo) and how they obtain energy.According to the source of energy, bacteria can bedivided into major groups:

' ) H e t e r o t r o ~ derive their energy frombreaking down complex organic compounds proteins, sugars, fat ...

N.B.: bacteria that reside on human tissue i.e: oralcavity, intestines, urethra, vagina ... without causingdisease are called commensal bacteria. Howeverduring injury- oral or intestinal or others- thesecommensal bacteria become pathogenic and maycause disease.N.B.: all pathogens are heterotrophs.

~ Autotrophs: survive and live in the nature,where they fix COr to make their own foodsource. According to their source of energy theyare divided into types:i) photoautotrophs: using light energy

Iii) chemoautotrophs: oxidation of nitrogen orsulfur

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") Saprophytes: like commensal bacteria, theyare nonpathogenic. They produce energy byfermentation or by respiration. Responsibie.for decay and rot of food, dead organisms ...

According to O consumption:, ) Microaerophillic : bacteria that grow inenvironments with low O concentration high C O , 0%_ , % (normal concentration is '. ' f %)example: nisseria, this pathogen is responsible for" diseases - gonorrhea and meningitis-") Obligate anaerobes: cannot tolerate O ~ because O deactivates enzymes in theirmembrane responsible for transport thus leadingto death of the bacteria. They obtain their energyby the breakdown of organic compounds and use inorganic compounds as end recipients of electrons.This is done by fermentation. This bacteria makesup to "0%_" "% of the bacteria in our intestines andup to " % of the bacteria in the mouth and vagina.N.B.: obligate anaerobes establish equilibrium andcontribute to the digestion of foo'd in the

Iintestines. Aiso bateriode fragil help detoxifytoxins.

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i) Obligate aerobes: bacteria that grow using Oras the end recipient of electrons by respiration.These bacteria usually reside in the respiratorytract.Example: M. tuberculosisThey survive in the atmospheric Or level due to ienzymes:- Peroxidase: during oxidative phosphorylationthe bacteria produce HrOr which inhibits sometransport proteins. This enzyme oxidizes HrOrinto HrO and NAD.

- Superoxiase dismutase: reduces active Or (negatively charged) into HrOr and molecular Or

- Catalase: reduces HrOr into HrO and OrN.B: these enzymes are found only in obligateanaerobe and facultive aerobes. Thus obligateanaerobes cannot get rid of HrOrCulture Mediain order to study any type of bacteria we have touse a cuture media, a media that contains all thenecessary nutrients and minerals for bacterialgrowth.

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Culture media can be in " forms:' ) Solic:J: called gggr and is usually

placed in a Petri dish.We can see spots in the dish, each one'represents a colony d e r i v e ~ from ,bacterial cell

") Fluid: called broth and is formed in testtubes. Notice the turbidity (actually hebacteria)

For the growth of bacteria we do not only neednutrients but we also need the correct physicalenvironment.Classification according to pH:

, ) neutrophils: pH v-v." , most pathogens arethis type") acidophils:

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') mesophiles:" c_ i c but optimum is iV c,pathogens are of this type.

") Psychrophiles: \. c, non-pathogenic exept

fo r ' type called M.thermophillia whichcauses lung infection.

N.B.: generation time is the time it takes onenewly formed bacteria cell to divide into" cells.Bacteria divide by binary fission, where" equalsize cells are formed. During the processelongation of chromosomes occurs and a septum orcell wall is formed in the middle of the dividingcell. In the rapidly dividing bacteria, usuallyfacultive anaerobes, the generation time is ". min.however, this can be slowed down due to manyfactors i.e: depletion of nutrients.

o

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Bact 1;141 Gl'owth u r v ~Lag Log DeathPhase Phase Stationary Phase PhaseI

enQ). 0o...... '" '-o.....Q).0E::JZ

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Time-La9.....Phase: ,s t adaptation, "nd activation ofenzymes, , rd replication. In this stage there is afew hundred cells and there is no turbidity in thetest tubes.-monential growth: rapid growth + turbidity inthe test tube.-Stationary phase: due to the presence of limitednutrients bacteria cannot grow forever andeventually some start to die equilibrium,growth=death. It stays approx. " i hrs-Death phase: death>growthN.B.: in industry, to grow bacteria we keep aconstant supply of nutrientsNB.: In the human body, there is an equilibriumbetween growth and d e a t h ~ stationary phase.

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