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Bacteria Compare with Other Microorganisms

Medical Review: No 
Date: 2017-11-07


Section 01: Introduction to Microbes

In this lecture educator presents the Bacteria Compared with other Microorganisms. In the first section of the lecture Introduction to Microbes is presented in detail. A microbe, or “microscopic organism” is a living thing that is too small to be seen with the naked eye. Microbes are living organisms that multiply frequently and spread rapidly.  A Microbe is used to describe many different types of life forms, with dramatically different sizes and characteristics: Bacteria, Archaea, Fungi, Protists, Viruses, Microscopic Animals and Microscopic Plants.

Important Features of Microbes are 1. Structure: Cells have a nucleus or nucleoid which contains DNA, surrounded by cytoplasm, within which proteins are synthesized and energy is generated, Viruses have an inner core of genetic material (either DNA or RNA) but no cytoplasm So they depend on host cells to provide the machinery for protein synthesis and energy generation. 2. Methods of Replication: Cells replicate either by binary fission or by mitosis, Prokaryotic cells (e.g., bacteria) replicate by binary fission, whereas eukaryotic cells replicate by mitosis & Viruses disassemble, produce many copies of their nucleic acid and protein, and then reassemble into multiple progeny viruses, With the exception of rickettsia and chlamydia, bacteria can replicate extracellularly. 3. Nature of the nucleic acid: Cells contain both DNA and RNA and Viruses contain either DNA or RNA but never both. 4. Motility: Most protozoa and some bacteria are motile, Fungi and viruses are nonmotile.


Section 02: Microbes that Cause Infections

In the second section of lecture Microbes that cause Infections are discussed. The agents of human infectious diseases belong to five major groups of organisms that are Bacteria, Fungi, Protozoa, Helminths and Viruses.

Bacteria: Autonomously replicating unicellular organisms lacking both an organized nucleus and organized intracellular organelles. They have only a single circular chromosome of double-stranded DNA (dsDNA), some extrachromosomal DNA, and most have a cell wall containing the polymer peptidoglycan. Bacteria are responsible for most food-borne illnesses. The cold-loving bacterium Listeria monocytes tends to colonize improperly processed meats, deli foods, hot dogs, milk, and soft cheeses leading to about 2500 cases of illness, most of which require hospitalization, and 500 deaths each year. They are also present in so-called biofilms that coat many ordinary surfaces.

Fungi: Fungi are free-living eukaryotic saprophytes consisting of yeasts and molds (also called filamentous fungi), Fungi can cause two broad classes of disease: superficial and deep.  The superficial diseases are either cutaneous, growing on the skin, or subcutaneous, growing just below the skin. The deep diseases are either systemic, they colonize most of the body, or opportunistic.

Protozoa: Protozoa can be subdivided into four groups Sarcodina, Sporozoa, Mastigophora and Ciliata. Protozoa are Grouped according to the location in the body: Within the intestinal tract (The ameba- Entamoeba histolytica, the flagellate- Giardia lamblia, and the sporozoan -Cryptosporidium hominis), In the urogenital tract (Flagellate -Trichomonas vaginalis), The blood and tissue protozoa (Flagellates -Trypanosoma and Leishmania and the sporozoans-Plasmodium and Toxoplasma).

Viruses: A virus is an obligate intracellular parasite. A virus is metabolically inert outside a cell, Viruses have no organized cellular structures but simply a protein coat, called the capsid, surrounding a nucleic acid core, called a genome. The capsid together with the genome is called the nucleocapsid. The nucleocapsid may be surrounded by an envelope that is composed of a lipid bilayer containing protein spike and an entire virus particle is called a virion.


Section 03: Characteristics of Prokaryotes

The word prokaryote comes from the Greek πρό (pro) "before" and κάρυον (karyon) "nut or kernel". Prokaryotes are divided into two domains, Archaea and Bacteria. The oldest known fossilized prokaryotes were laid down approximately 3.5 billion years ago, only about 1 billion years after the formation of the Earth's crust. 1938 American biologist Herbert Copeland proposed that unicellular organisms lacking nuclei be classified in their own kingdom, Monera, also called Kingdom Prokaryotae.

Characteristics of Prokaryotes: The genome in a prokaryote is held within a DNA/protein complex in the cytosol called the nucleoid, which lacks a nuclear envelope. Important genes of prokaryotes are stored in separate circular DNA structures called plasmids. Ribosomes in prokaryotes are smaller than in eukaryotes. Most prokaryotes have a rigid external cell wall that contains peptidoglycan, a polymer of amino acids and sugars, as its unique structural component. Processes such as oxidative phosphorylation and photosynthesis take place across the prokaryotic cell membrane. Prokaryotes have a larger surface-area-to-volume ratio, giving them a higher metabolic rate, a higher growth rate, and as a consequence, a shorter generation time than eukaryotes. Most protozoa and some bacteria are motile, whereas fungi and viruses are nonmotile.

Medically Important Prokaryotes: Diseases such as tuberculosis, gonorrhea, plague, whooping cough, pneumonia, syphilis, and botulism. Certain bacteria, including the soil bacteria Actinomycetes, produce antibiotics. Other bacteria are used industrially to synthesize vitamins, enzymes, organic acids, and food products and to produce drugs by the processes of genetic engineering.


Section 04: Characteristics of Eukaryotes

The concept of the eukaryote has been attributed to the French biologist Edouard Chatton. The terms prokaryote and eukaryote were more definitively reintroduced by the Canadian microbiologist Roger Stanier and the Dutch-American microbiologist C. B. van Niel in 1962. In his 1938 work Titres et Travaux Scientifiques. Chatton had proposed the two terms, calling the bacteria prokaryotes and organisms with nuclei in their cells eukaryotes. Knoll (2006) suggests they developed approximately 1.6–2.1 billion years ago. Some acritarch are known from at least 1.65 billion years ago, and the possible alga Grypania has been found as far back as 2.1 billion years ago. The Geosiphon-like fossil fungus Diskagma has been found in paleosols 2.2 billion years old.

Characteristics of Eukaryotes: The eukaryotic cell has a true nucleus with multiple chromosomes surrounded by a nuclear membrane and uses a mitotic apparatus to ensure equal allocation of the chromosomes to progeny cells. Eukaryotic cells contain organelles, such as mitochondria and lysosomes, and larger (80S) ribosomes. Either they are bound by a flexible cell membrane, or, in the case of fungi, they have a rigid cell wall with chitin, a homopolymer of N-acetylglucosamine. The eukaryotic cell membrane contains sterols, Sexual reproduction, typically involving an alternation between haploid and diploid generations, occurs through meiosis. The evolution of sexual reproduction may be a primordial and fundamental characteristic of eukaryotes. Medically Important Eukaryotes are Fungi: Athletes foot, Tinea cruris – ringworm infection, Blastomycosis, Candidiasis. Protozoa: Amoeboid protozoa – Brain infections, Flagellated protozoa – Giardiasis, Apicomplexan protozoa – Malaria. Helminths: Schistosoma japonicum, W. bancrofti – elephantiasis, Round worms.


Section 05: Terminology of Microbes

A host is any organism capable of supporting the nutritional and physical requirements of another. A microbe is a microscopic organism. The presence and multiplication of an organism on or within a host is called colonization or infection. We refer to the colonization of one organism by another as symbiosis. If the symbiotic relationship benefits both organisms, it is called mutualism. Commensalism is a symbiotic relation in which one organism benefits and the other is not harmed. Parasitism occurs when the infecting organism benefits and the host is harmed. If the host sustains injury or pathological changes in response to the parasite, the process is an infectious disease. Anything causing disease is said to be a pathogen.

Binomial nomenclature (also called binary nomenclature) is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, although they can be based on words from other languages. Two most important are the International Code of Zoological Nomenclature (ICZN) for animals and the International Code of Nomenclature for algae, fungi, and plants (ICN). Escherichia is the genus and coli is the species name. Yeast Candida albicans consists of Candida as the genus and albicans as the species. Viruses typically have a single name, such as poliovirus, measles virus, or rabies virus. Some viruses have names with two words, such as herpes simplex virus, but those do not represent genus and species.

Afridi, Maham
  • Academics: MS 
  • Specialization: Medical Genetics
  • Current: Research Scholar 
  • University: Quaid-e-Azam University
  • Location: Islamabad, Pakistan
  • Course: Biochemistry 
  • Clinical Years: 2
  • Teaching Years: 1

Ms. Maham Afridi joined Quaid-e-Azam University as a research scholar in 2017, Before that she served in Core lab of National University Science and Technology Islamabad. She also served in Armed Forces Institute of Pathology in their department of Immunology, where her major roles were detection of antibodies and other immunology tests, genetic counselling etc.

Ms. Maham has full command on Genotyping of human genes, Risk assessment of genetic disorders, Diagnostic tests (TyphiDot, ELISA, Allergy tests), HPLC, PCR, Immunohistochemistry, Cell and tissue staining, Bacterial culturing, Cell culturing, DNA extraction, SDS PAGE, Gel Electrophoresis, Spectrophotometry.

Ms. Maham was awarded by Pak China Business forum in Recognition for poster presentation.

10 lectures