Micro Bio

REVISION

COMMON TYPES OF MICROBES

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BACTERIA
Difference between Gram Positive and Gram Negative Shapes of bacteria and examples
What shapes have you learnt? GRAM STAIN: The process! You should work on your lab notes. LECTURE 2

GRAM STAIN
Developed by a Danish called Christian Gram in 1884 Stain a heat-fixed smear with a dye like crystal violet and fix with Iodine Then wash with ethanol or acetone Finally counterstain with a dye of different colour such as safranin (what is its colour? You have used it before!)

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Gram positive

Gram negative

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GRAM POSITIVE CELL WALL
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Consists of a thick, homogenous sheath of peptidoglycan 20-80 nm thick tightly bound acidic polysaccharides, including teichoic acid and lipoteichoic acid cell membrane

Retain crystal violet and stain purple

GRAM POSITIVE WALL

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GRAM NEGATIVE CELL WALL
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Consists of an outer membrane containing lipopolysaccharide (LPS) thin shell of peptidoglycan periplasmic space inner membrane

Lose crystal violet and stain red from safranin counterstain

GRAM NEGATIVE CELL WALL

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ENDOSPORES
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Resting, dormant cells produced by some G+ genera: Clostridium, Bacillus & Sporosarcina Have a 2-phase life cycle – vegetative cell & an endospore

sporulation -formation of endospores germination- return to vegetative growth hardiest of all life forms withstand extremes in heat, drying, freezing, radiation & chemicals not a means of reproduction

ENDOSPORES
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resistance linked to high levels of calcium & dipicolinic acid dehydrated, metabolically inactive thick coat longevity verges on immortality 25, 250 million years. pressurized steam at 120oC for 20-30 minutes will destroy.

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ENDOSPORES

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LABORATORY SESSIONS
Making of culture medium 2. Recall your investigations on Culturing Effectiveness of Soaps and Alcohols What kind of culture medium did you use? Milks What did you do to investigate the effect on “temperature” treatment to milk?
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PHYSICAL AND CHEMICAL
MICROBIAL CONTROLS

PHYSICAL AND CHEMICAL
MICROBIAL CONTROLS

DEFINITIONS:
Sterilization Disinfection Sanitization Antiseptic Pasteurization

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NOSOCOMIAL INFECTIONS
Definition Universal/ Standard Precautions Use of disinfectants Vincent’s Lecture

PRIONS
Prof Maxwell’s notes and this lecture! Definitions What are the common infectious diseases by prions? Any treatments? Epidemiology, aetiology,…….

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TAPEWORMS
Prof Maxwell’s notes What is the disease that is caused by “tapeworm”? Aetiology, epidemiology, sign and symptoms, pathogenesis, prevention and control

MRSA
Methicillin-resistant Staphylococcus aureus (MRSA) infections Control of infection in health care settings: 1. Control the reservoir 2. Interrupt the transmission 3. Prevent access of agent to new host 4. Increase resistance of new host

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MRSA
Major reservoir: humans • S. aureus can be normal flora - Nares - Pharynx - Skin - Axilla - Perineum

MRSA-TRANSMISSION
Patient-to-patient via transient carriage on hands of Health Care Workers (HCW) HCW-to-patient through chronic HCW carrier Via devices or environmental surface

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MRSA- CONTROL
Infection control measures: Contact precautions -Hand hygiene -Protective barriers - Patient placement - Environmental cleaning - Patient education - Patient transport - Dedicated patient care equipment Appropriate use of antibiotics

CHAIN OF INFECTION

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CHAIN OF INFECTION
I. Infection cycle is well defined A. Infective agent: pathogen such as a bacteria or virus B. Reservoir 1. Place where causative agent can live 2. Common reservoirs include human body, animals, environment, and fomites or objects contaminated with infectious material that contains the pathogens

CHAIN OF INFECTION
C. Portal of exit 1. Way for causative agent to escape from the reservoir 2. Pathogens can leave the body through urine, feces, saliva, blood, tears, mucous discharge, sexual secretions, and draining wounds

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CHAIN OF INFECTION
D. Means of transmission 1. Pathogen must be transmitted to another reservoir or host where it can live 2.Can be transmitted in different ways a. Direct Contact 1. Person-to-person spread by physical contact 2. Contact with the body secretions containing pathogen b. Indirect contact 1. Pathogen is transmitted from contaminated substances (i.e. food, air, soil, insects, feces, clothing, instruments, and equipment) 2. Touching contaminated equipment 3. Breathing in droplets carrying airborne pathogens 4. Receiving the bite of an insect carrying pathogen

CHAIN OF INFECTION
E. 1. 2. a. b. c. d. e. Portal of entry Way to enter a new reservoir or host Means of entry Breaks in the skin or mucous membrane Respiratory tract Digestive tract Genitourinary tract Circulatory system

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CHAIN OF INFECTION
F. Susceptible host 1. Individual who can contract the disease 2. Humans may fight off causative agents and do not contract disease if a. Defense mechanisms of body are intact b. Immune system functioning 3. Human becomes susceptible host in some instances a. Large numbers of the pathogen invade the body b. Body defenses are weak

II.

THE CYCLE OF INFECTION CAN BE BROKEN AT

ANY LINK OF THE CHAIN

A. The infectious agent can be neutralized or destroyed by treatment B. The reservoir host must maintain personal hygiene C. The portal of exit is closed by the use of proper attire (gowns, gloves, other clothing), control of body secretions, and proper handwashing D. The route of transmission is minimized through proper handwashing, disinfection and sterilization and proper disposal of contaminated materials. E. The portal of entry is blocked by asepsis, disinfection, and sterilization procedures. F. Host susceptibility is broken when the health and wellness of an individual is maintained.

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ASEPSIS IS THE ABSENCE OF INFECTION.
A. Medical asepsis: practices and techniques that are designed to protect individuals from the spread of disease 1. Antiseptic: substances that inhibit the growth of bacteria. Some of these substances can be used on the skin. 2. Disinfectant: substances or practices that cannot be used on the skin. This includes chemicals and boiling. 3. Sterile: absence of all microorganisms

B. Surgical asepsis: the use of sterile technique to handle equipment, maintain sterile fields, change dressings and dispose of contaminated materials without introducing harmful microorganisms

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V. Epidemiology: tracing the occurrence of health related events in society VI. Nosocomial infections: infections acquired while receiving treatment in a health care facility

EPIDEMIOLOGY DEFINITIONS OF
Endemic Pandemic

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The Concept of Immunity
Susceptibility: Lack of resistance to a disease. Immunity: Ability to ward off disease. Innate immunity: Defenses against any pathogen. Adaptive immunity: Immunity, resistance to a specific pathogen.

Fig 16.1

IMMUNITY

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IMMUNITY

FEVER
Mechanism if triggered by Gram-ve bacteria

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ANTIBODY-ANTIGEN REACTIONS
The antibody-antigen reactions in the body: 1. Agglutination: clumps pathogens; prevents spreading; reduce the number of units that phagocytes need to engulf 2. Opsonisation: phagocytosis is easier because phagocytes have receptors for binding antibody

ANTIBODY-ANTIGEN REACTIONS
The antibody-antigen reactions in the body: 3. Inflammation: activation of complement by the classical pathway leads to formation of the membrane attack complex and enhancement of inflammation 4. Neutralisation: bacteria, viruses and toxins are prevented from binding to host cells 5. Antigen-dependent cell-mediated cytotoxicity: naturally killer cells recognize bound antibody, cause them to release perforins and lytic enzymes

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