Bacterial toxins Bacterial toxins Bacterial toxins Poisonous substances

Bacterial toxins

Bacterial toxins

Bacterial toxins Poisonous substances produced by bacteria 220 known bacterial toxins 40% cause disease by damaging the eukaryotic cell membrane Toxemia ﺗﺴﻤﻢ ﺍﻟﺪﻡ : Toxins in the bloodstream

Types of toxins 1. Exotoxins: Exotoxins are generated by the bacteria and actively secreted outside the bacterial cell. 2. Endotoxins: Part of the outer cell wall of Gram (-) bacteria. The body’s response to endotoxin can involve severe inflammation.

Exotoxins Mostly seen in Gram (+) Bacteria Heat labile, can be inactivated by heating at 60 -80⁰C. Excreted (secreted) from the microbial cells into the surrounding. i. e. culture media or circulatory system. Don’t require bacterial death or cell lysis for their release.

Types of Exotoxins 1. Cytotoxins Kill cells – Shigella, Vibrio 2. Neurotoxins Interfere with normal nerve impulses Clostridium botulinum Clostridium tetani 3. Enterotoxins Effect cells lining the G. I. tract E. coli Salmonella

Response to Toxins The body responds to exotoxins by producing special antibodies called antitoxins, When toxins and antitoxins molecules combine with each other, the toxin is neutralize. Exotoxins inactivated (heat, formalin or phenol) no longer cause disease, but stimulate the production of antitoxins.

Toxoids Altered exotoxins – Toxoids: a chemically modified toxin from a pathogenic microorganism, which is no longer toxic. Toxoids: is a detoxified toxin by treated exotoxin to be (inactive form) by using chemical treatment such as formalin, iodine, ketones for using in vaccines and is no longer damage to tissue. Toxoids – injected to stimulate the production of antitoxins and provide immunity.

Endotoxins Part of the Gram (-) Bacterial cell wall. Biological activity or toxicity of endotoxin is largely due to lipid A. Relatively heat stable can withstand heat over 60⁰C for many hours. Released upon cell lysis or death. Less potent than exotoxins, active in large doses only. Often produce fever in hosts. Salmonella, Shigella, Escherichia, Neisseria.

Bacteriocins were first discovered by A. Gratia in 1925. He called first discovery a colicine because it killed E. coli. Bacteriocins are proteinaceous toxins produced by bacteria to inhibit the growth of similar or closely related bacterial strain(s).

Medical significance Bacteriocins are of interest in medicine because they are made by non-pathogenic bacteria that normally colonize the human body. Loss of these harmless bacteria following antibiotic use may allow opportunistic pathogenic bacteria to invade the human body.

Microbial Mechanisms of pathogenesis

Pathogenesis The word comes from the Greek Pathos, “disease”, and genesis, creation. The term pathogenesis means step by step development of a disease. Caused by a microbial, chemical or physical agent.

Pathogenicity – ability to cause disease Virulence– degree of pathogenicity Pathogenicity – the ability to cause disease by overcoming the defenses of the host Virulence – the degree or extent of pathogenicity Many properties that determine a microbe’s pathogenicity or virulence are unclear or unknown But, when a microbe overpowers the hosts defences, disease results.

Portals of entry 1. Mucus membranes 2. Skin 3. Parenteral

1. Mucus Membrane A. Respiratory tract

Common diseases contracted via the respiratory tract Common cold Flu Tuberculosis ﺍﻟﺴﻞ Whooping cough ﺍﻟﺴﻌﺎﻝ ﺍﻟﺪﻳﻜﻲ Pneumonia ﺍﻻﻟﺘﻬﺎﺏ ﺍﻟﺮﺋﻮﻱ Measles ﺍﻟﺤﺼﺒﺔ Strep throat ﺑﻜﺘﻴﺮﻳﺎ ﺍﻟﺤﻠﻖ Diphtheria ﺍﻟﺨﻨﺎﻕ

Mucus membranes B. Gastrointestinal tract Microbes gain entrance thru contaminated food & water or fingers and hands. Most microbes that enter the G. I. tract are destroyed by HCl & enzymes of stomach or bile & enzymes of small intestine.

Common disease contracted via the G. I. tract Cholera Vibrio cholorea Ulcers Helicobacter pylori Salmonellosis Salmonella sp. Shigellosis Shigella sp. Botulism ﺍﻟﺘﺴﻤﻢ ﺍﻟﻐﺬﺍﺋﻰ Clostridium botulinum

Fecal – Oral diseases These pathogens enter the G. I. tract at one end and exit at the other end. spread by contaminated hands & fingers or contaminated food & water. Poor personal hygiene.

Mucus membranes of the Genitourinary system Gonorrhea ﻣﺮﺽ ﺍﻟﺴﻴﻼﻥ Neisseria gonorrhoeae Syphilis ﺍﻟﺰﻫﺮﻱ Treponema pallidum Chlamydia trachomatis

Mucus Membrane D. Conjunctiva ﺍﻟﻤﻠﺘﺤﻤﺔ Lacrymal secretion ﺇﻓﺮﺍﺯ ﺩﻣﻌﻲ Lysozyme Trachoma Chlamydia trachomatis

2. Skin – the largest organ of the body. Sebaceous ﺩﻫﻨﻰ secretion – containing fatty acids. Resident flora. When unbroken is an effective barrier ﺣﺎﺟﺰ for most microorganisms. Some microbes can gain entrance thru openings in the skin: hair follicles ﺑﺼﻴﻼﺕ and sweat glands ﺍﻟﻐﺪﺩ ﺍﻟﻌﺮﻗﻴﺔ.

3. Parenteral Microorganisms are deposited into the tissues below the skin or mucus membranes. Punctures ﺛﻘﻮﺏ Injections Bites ﻟﺪﻏﺎﺕ Scratches Surgery Splitting of skin due to swelling or dryness

Number of invading microbes LD 50 – Lethal Dose of a microbes toxin that will kill 50% of experimentally inoculated test animal. ID 50 – Infectious Dose required to cause disease in 50% of inoculated test animals. Examples: ID 50 – for Vibrio cholerea 108 cells (100, 000 cells). ID 50 – for inhalation ﺍﺳﺘﻨﺸﺎﻕ Anthrax – 5, 000 to 10, 000 spores.

BACTERIAL PROTEIN TOXINS A + B Subunit Arrangement of Protein Toxins Many protein toxins, consist of two components: 1. Subunit A: responsible for the enzymatic activity of the toxin. 2. Subunit B: concerned with binding to a specific receptor on the host cell membrane and transferring the enzyme across the membrane. The enzymatic component is not active until it is released from the native toxin. Isolated A subunits are enzymatically active and but lack binding and cell entry capability. Isolated B subunits may bind to target cells (and even block the binding of the native A+B toxin), but they are nontoxic.