chapter 1 a brief history of microbiology azeem ahmad, ph.d des moines area community college...

Chapter 1

A Brief History of Microbiology

Azeem Ahmad, Ph.DDes Moines Area Community College

(DMACC-URBAN)

Learning Objectives

• Invisible world• Six classes of microorganisms• Prokaryotes, Archaea and Eukaryotes• Viruses• Spontaneous generation• Koch postulates• Gram stain• Infection and disease• Genetics• Modern microbiology

The Early Years of Microbiology

• What Does Life Really Look Like?– Antoni van Leeuwenhoek (Dutch)

– Began making and using simple microscopes– Often made a new microscope for each specimen– Examined water and visualized tiny animals, fungi,

algae, and single-celled protozoa: “animalcules”

– By end of 19th century, these organisms were called microorganisms

© 2012 Pearson Education Inc.

Figure 1.2 Reproduction of Leeuwenhoek’s microscope

Specimen holderLens

Figure 1.3 The microbial world


• How Can Microbes Be Classified?– Carolus Linnaeus developed taxonomic system

for grouping similar organisms together– Leeuwenhoek’s microorganisms grouped into six

categories: – Bacteria– Archaea– Fungi– Protozoa– Algae– Small multicellular animals



• Bacteria and Archaea– Unicellular and lack nuclei– Much smaller than eukaryotes– Found everywhere there is sufficient

moisture– Reproduce asexually– Two kinds

– Bacteria – cell walls contain peptidoglycan– Archaea – cell walls composed of polymers

other than peptidoglycan


Figure 1.4 Cells of the bacterium Streptococcus

Nucleus ofeukaryotic cheek cell

Prokaryoticbacterial cells


• Fungi– Eukaryotic (have membrane-bound nucleus)– Obtain food from other organisms– Possess cell walls– Include

– Molds – multicellular; grow as long filaments; reproduce by sexual and asexual spores

– Yeasts – unicellular; reproduce by budding or sexual spores


Figure 1.5 Fungi-overview


• Protozoa– Single-celled eukaryotes– Similar to animals in nutrient needs and cellular

structure– Live freely in water; some live in animal hosts– Asexual (most) and sexual reproduction– Most are capable of locomotion by

– Pseudopodia – Cilia – Flagella


Figure 1.6 Locomotive structures of protozoa-overview


• Algae– Unicellular or multicellular

– Photosynthetic

– Simple reproductive structures

– Categorized on the basis of pigmentation, storage products, and composition of cell wall


Figure 1.7 Algae-overview

Figure 1.9 Viruses infecting a bacterium

Virus

Bacterium

Virusesassemblinginside cell

The Golden Age of Microbiology

• Scientists searched for answers to four questions

– Is spontaneous generation of microbial life possible?

– What causes fermentation?

– What causes disease?

– How can we prevent infection and disease?



• Some thought living things arose from three processes

– Asexual reproduction

– Sexual reproduction

– Nonliving matter

• Aristotle proposed spontaneous generation

– Living things can arise from nonliving matter



• Pasteur’s Experiments– When the “swan-necked” flasks remained

upright, no microbial growth appeared

– When the flask was tilted, dust from the bend in the neck seeped back into the flask and made the infusion cloudy with microbes within a day


Figure 1.11 Louis Pasteur

Figure 1.12 Pasteur’s experiments with “swan-necked” flasks

Steam escapesfrom open endof flask.

Infusionis heated.

Infusion sits;no microbes appear.

Months

Air moves inand out of flask.

Infusion remainssterile indefinitely.

Dust fromair settlesin bend.


• The Scientific Method– Spontaneous generation debate led in part to

scientific method– Observation leads to question– Question generates hypothesis– Hypothesis is tested through experiment(s)– Results prove or disprove hypothesis

– Accepted hypothesis leads to theory/law– Reject or modify hypothesis


Figure 1.13 The scientific method

Observations

Question

Hypothesis

Repeat

Experiment,includingcontrol groups

Modifiedhypothesis

Observations

Experimentaldata supporthypothesis

Experimentaldata do notsupporthypothesis

Accepthypothesis

Rejecthypothesis

Modifyhypothesis

Theoryor law

Figure 1.14 Pasteur's application of the scientific method

Observation:

Hypothesis Experiment Observation Conclusion

Fermentinggrape juice

Microscopic analysisshows juice containsyeasts and bacteria.

Day 1: Flasks of grapejuice are heated sufficientlyto kill all microbes.

Day 2

I. Spontaneousfermentationoccurs.

II. Air fermentsgrape juice.

III. Bacteria fermentgrape juiceinto alcohol.

IV. Yeasts fermentgrape juiceinto alcohol.

Juice in flask is inoculated withyeast and sealed.

Juice in flask is inoculated withbacteria and sealed.

Flask remainsopen to airvia curved neck.

Flask is sealed.

No fermentation;juice remainsfree of microbes

No fermentation;juice remainsfree of microbes

Bacteria reproduce;acids are produced.

Yeasts reproduce;alcohol is produced.

Reject hypothesis I.

Reject hypothesis II.

Modify hypothesis III; bacteria fermentgrape juice intoacids.

Accept hypothesis IV; yeasts fermentgrape juice intoalcohol.

Table 1.1 Some Industrial Uses of Microbes


• What Causes Disease?– Pasteur developed germ theory of disease

– Robert Koch studied causative agents of disease

– Anthrax– Examined colonies of microorganisms


Figure 1.15 Robert Koch


• Koch’s Contributions– Simple staining techniques– First photomicrograph of bacteria– First photomicrograph of bacteria in diseased

tissue– Techniques for estimating CFU/ml– Use of steam to sterilize media– Use of Petri dishes– Techniques to transfer bacteria– Bacteria as distinct species


Figure 1.16 Bacterial colonies on agar

Bacterium 1

Bacterium 2

Bacterium 3

Bacterium 4

Bacterium 5

Bacterium 6 Bacterium 7Bacterium 8

Bacterium 9

Bacterium 10

Bacterium 11

Bacterium 12


• Koch’s Postulates– Suspected causative agent must be found in

every case of the disease and be absent from healthy hosts

– Agent must be isolated and grown outside the host

– When agent is introduced into a healthy, susceptible host, the host must get the disease

– Same agent must be found in the diseased experimental host



• Gram’s Stain– Danish scientist Hans Christian Gram developed

more important staining technique than Koch’s in 1884

– Involves the applications of a series of dyes– Some microbes are left purple, now labeled

Gram-positive– Other microbes are left pink, now labeled Gram-

negative– Gram procedure used to separate into two

groups


Figure 1.17 Results of Gram staining

Gram-positive Gram-negative

Figure 1.19 Some scientific disciplines and applicationsBIOLOGISTS MODERN DISCIPLINES

Pre-1857

The Golden Age ofMicrobiology (1857–1907)

Leeuwenhoek

Linnaeus

SemmelweissSnow

Bacteriology (bacteria)Protozoology (protozoa)Mycology (fungi)Parasitology (protozoa andanimals)Phycology (algae)

Taxonomy

Infection controlEpidemiology

PasteurPasteurization

Industrial microbiology

Food and beverage technology

Buchner

Koch Koch’s postulates

Ivanowski

BeijerinckWinogradsky

Gram

ListerNightingale

Jennervon BehringKitasato

Ehrlich

Fleming

Microbial metabolismGeneticsGenetic engineering

Etiology

Virology

Environmental microbiologyEcological microbiology

Microbial morphology

Antiseptic medical techniquesHospital microbiology

SerologyImmunology

Chemotherapy

Pharmaceutical microbiology

Table 1.3 Fields of Microbiology

The Modern Age of Microbiology

• What Are the Basic Chemical Reactions of Life? – Biochemistry

– Began with Pasteur’s and Buchner’s works– Microbes used as model systems for biochemical

reactions– Practical applications

– Design of herbicides and pesticides

– Diagnosis of illness and monitoring responses to treatment

– Treatment of metabolic diseases

– Drug design



• How Do Genes Work?– Microbial genetics

– Molecular biology

– Recombinant DNA technology

– Gene therapy



• Microbial Genetics– Avery, MacLeod, and McCarty: genes are

contained in molecules of DNA

– Beadle and Tatum: a gene’s activity is related to protein function

– Translation of genetic information into protein explained

– Rates and mechanisms of genetic mutation investigated

– Control of genetic expression by cells described



• Molecular Biology– Explanation of cell function at the molecular level

– Pauling proposed that gene sequences could– Provide understanding of evolutionary

relationships/processes– Establish taxonomic categories– Identify microbes that have never been cultured

– Woese determined cells belong to bacteria, archaea, or eukaryotes

– Cat scratch disease caused by unculturable organism



• Recombinant DNA Technology– Genes in microbes, plants, and animals

manipulated for practical applications

– Production of human blood-clotting factor by E. coli to aid hemophiliacs

• Gene Therapy– Inserting a missing gene or repairing a defective

one in humans by inserting desired gene into host cells



• What Roles Do Microorganisms Play in the Environment?

– Bioremediation uses living bacteria, fungi, and algae to detoxify polluted environments

– Recycling of chemicals such as carbon, nitrogen, and sulfur



• How Do We Defend Against Disease?– Serology

– The study of blood serum– Blood contains chemicals and cells that fight

infection– Immunology

– The study of the body’s defense against specific pathogens

– Chemotherapy– Fleming discovered penicillin– Domagk discovered sulfa drugs


Figure 1.20 Effects of penicillin on a bacterial “lawn” in a petri dish

Fungus colony(Penicillium)

Zone of inhibition

Bacterial colonies(Staphylococcus)


• What Will the Future Hold?– Microbiology is built on asking and answering

questions

– The more questions we answer, the more questions we have


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