Module 6 - Microbiology Flashcards
Microbe
Microbes are tiny living organisms that are found all around us and are too small to be seen by the naked eye (microscopic). They include bacteria, archaea, single-cell eukaryotes, and viruses
Commensalism
one benefits one not harmed
Mutualism
both benefit and depend on each other
Parasitism
one benefits, one adversely affected
Opportunism
a change in living relationship resulting in parasitism
Outbreak
relatively high number of infections are observed where no cases or only sporadic cases occurred in the past
epidemic
sudden rapid rise in the incidence of a disease in a particular population
Pandemic
global epidemic
endemic
disease that is always present in a given population. there is a permanent reservoir (human or other animals).
Identify Koch’s 4 postulates
- suspected pathogen must be present in all cases of disease and absent from health animals
- suspected pathogen must be grown in pure culture
- cells from pure culture of suspected pathogen must cause disease in health animal
- suspected pathogen must be reisolated and shown to be the same as the original
Infection
when microorganisms invade host tissue and multiply
subclinical infection
no symptoms apparent but immune response is induced
localised infection
confined to one area of the body
systemic infection
infection spreads to other organ systems
disease
harmful alteration to the host
pathogen
microorganism capable of causing disease
pathogenesis
process of disease arising
pathogenicity
measure of ability of a pathogen to cause disease
pathogenic determinant/virulence factor
feature of a pathogen that influences how well it can cause disease
Gram positive bacteria
thick peptidoglycan layer and has a plasma membrane
purple colour
Gram negative bacteria
thin peptidoglycan layer
has outer membrane and inner membrane
red in colour
why it is important to know about the bacterial characteristics particularly in the health care setting
- Accurate ID of bacteria needed for choosing treatment
- In general, the Gram status, morphology and functional characteristics would be sufficient information for the appropriate treatment
More information to narrow down to species level - Ultimate knowledge: DNA sequencing; expensive; slow (but improving)
Macroscopy
- Colony morphology & phenotype (seen with the naked eye)
- Bacterial colony morphology: size, shape, pigmentation, elevation, margin, opacity, surface texture
- Requires culture on solid media & isolating single colonies (16 streak technique)
Microscopy
Examination of bacterial cells by their morphology (cell shape)
Problem: bacteria (often) colourless
Only visible in phase-contrast microscope
Staining of the bacteria may help
Why do bacteria like living together
Bacteria rarely live as single cells
They form colonies with other individuals (often from the same species)
They can also form biofilms (single or mixed species)
Significant for infection control & treatment
The steps of infection
- attachement and entry into body
- local or general spread in body
- multiplication
- evasion of host defenses
- shedding
- cause damage in host
Bacterial Reproduction
Bacterial cells undergo Binary Fission to reproduce a cell into two parts which involves:
* DNA replication to get two copies
* Moving of the DNA strands to opposite ends of the cell
* Splitting of the cell in the middle into two separate bacteria that has the same genetic material
Generation Time
is time taken for one cell to reproduce itself
Bacterial Reproduction: Growth Phases
Replication results in an exponential increase in cell number
- Lag Phase
Initial adaptation to conditions - Logarithmic Phase
Exponential increase in cells - Stationary Phase
Rate of cell division equals cell death - Death Phase
Decrease in cell numbers
How do we measure bacterial growth
Turbidity which can be measured using a spectrophotometer
- Increased turbidity is directly related to the number of cells * Can be seen by the eye
- Can be measured using optical density (OD)
- More cells = more scatter = higher OD
Viruses
Are not living organisms because they:
* Consist only of DNA or RNA and protein
* Are incapable of independent reproduction * Are smaller than any cell (~0.1 𝜇m)
* Have no cell membrane
* Do not have ribosomes
* Have few enzymes for metabolism
Properties of Viruses
- Infect bacterial, plant and animal cells
- Are large, inert systems consisting of nucleic acid (DNA or RNA) and protein
- No cell wall, ribosomes, mitochondria or nucleus
Thus, cannot produce energy or synthesize proteins - Incapable of independent replication and require living host— they are “obligate intracellular parasites”
Classification of Viruses
- Type of nucleic acid
DNAorRNA - Arrangement of nucleic acid
*Double-stranded or single-stranded
Linear or circular - Structure of the virus particle Enveloped/“naked”
- Symmetry of capsid Icosahedral
Helical
complex
The viral lifecycle
- Attachment to host cell surface
- Penetration into host cell cytoplasm
- Uncoating to release viral genome
- Replication of viral genomes, mRNA and proteins
- Assembly of viral components
- Maturation and release of progeny viruses through host membranes
Key process: Attachment
Interaction between viral surface protein:
* Capsid component
* Viral attachment protein
And host cell surface protein (receptor)
Tropism
Viruses target specific cells
* Cellular tropism
* Tissue tropism
* Host tropism
Events in virus replication
- early viral protein synthesis
- late viral protein synthesis
General patterns of viral infections
- Acute infection
- non-productive latent infection
- productive chronic infection
- transformation
Immunopathology
antibodies and immune cells destroy
infected cells → tissue damage
Fever
- Stimulates the immune response
- Inhibits virus replication–most viruses very temperature
sensitive
*Inflammation
- Redness
- Localized heat
- Swelling
- Pain
- Loss of function (e.g., eye infection)
Human papillomavirus (HPV)
DNA virus
common cold of sexual activity
SARS-CoV-2
RNA virus
Transmission: droplet spread, airborne, faecal-oral
Fungi
Fungi are eukaryotic multicellular (in many cases
multinucleate) organisms with thick carbohydrate cell walls
Three major groups:
1. Macroscopic filamentous fungi with large fruiting body (Eg. Mushrooms)
2.Multicellular filamentous moulds
3.Single-celled yeasts
Basic fungal structure
- Thick carbohydrate cell wall serves a few functions: 1. Protection from the environment
2. Acquisition of nutrients
3. Cell recognition & Mating - Similar to the plasma membrane to other eukaryotes
- Therefore, finding a drug target is difficult as it would target
human cells as well
List 3 types of fungal innfections (aka mycoses)
- Superficial mycoses (most common)
* Fungus grows on body surfaces e.g., Skin, hair, nails, mouth
* Example: Athlete’s foot, thrush, ringworm - Subcutaneous mycoses
* Fungus grows in the deeper layers of the skin * Example: Madura foot - Systemic mycoses
* Fungus grows/spreads into internal organs
* Example: histoplasmosis, systemic candidiasis
List the three types of parasites
- Helminths (worms)
- Protozoa
- Arothropods
Helminths (worms)
- Enterobius vermicularis (AKA pinworm)
- The most common type of human worm infection
- Faecal-oral transmission (ingestion of eggs)
- Symptoms include: pruritus (itchy skin), irritability, insomnia
- Reinfection is very common
Medically Relevant Protozoa: Plasmodium spp.
- 5 different species of Plasmodium are of medical
importance and causes malaria - P. falciparum causes the most deaths
- Malaria is a severe global problem (> 1.5 million deaths/year)
- Transmitted via the Anopheles mosquito
- In humans, it results in infection of blood and liver
Arthropod
- Ectoparasites (eg. Lives outsides the host but feeds on host tissue/blood)
- Two main groups:
- Arachnids (2 segments, 8 legs) – ticks, mites * Insects (3 segments, 6 legs) – fleas, lice
- They also serve as vectors and transmit pathogens
Describe how the healthcare environment contributes to the incidence of infectious disease
Of particular concern:
* Concentration of vulnerable and/or infective persons
* Repeated contact with equipment, carers/therapists/other staff * Reservoir of non-typical pathogens/highly resistant organisms
Can lead to:
* Nosocomial ( = hospital) acquired infections
* More recently — HCAI ( = health care associated infections)
Describe what is meant by MRSA, its key virulence factors and pathophysiology
MRSA is a type of bacteria that is resistant to many antibiotics, making it difficult to treat.
Produces a number of virulence factors;
- PVL
- alpha-toxin
- exotoxins.
- MRSA strains are capable of forming biofilms, which are communities of bacteria that are embedded in a self-produced extracellular matrix.
- Can occur in both community and healthcare settings
- Can be transmitted through direct contact with an infected person or contaminated surfaces.
- MRSA infections can cause a range of symptoms, from mild skin infections to life-threatening infections such as sepsis.
Describe other significant bacterial HCAIs
healthcare-associated infections (HCAIs) are infections that patients acquire while receiving medical treatment in healthcare settings. Some significant bacterial HCAIs;
- Enterococcus species
- E. coli
- C. difficile
- CRE
- Acinetobacter baumannii
- Klebsiella pneumoniae
- Pseudomonas aeruginosa.
These bacteria can cause a range of infections, from mild to severe, and can be difficult to treat due to antibiotic resistance.
Understand basic antibiotic modes of action
antibiotics are drugs that are used to treat bacterial infections by targeting specific bacterial structures or processes
Modes of action of antibiotics;
- inhibition of cell wall synthesis
- inhibition of protein synthesis
- interference with nucleic acid synthesis
- inhibition of a metabolic pathway
- inhibition of membrane function
- inhibition of ATP synthase
Different classes of antibiotics target different bacterial structures or processes, and the choice of antibiotic depends on the type of infection and the susceptibility of the bacteria causing the infection.
Describe bacterial antibiotic resistance mechanisms
- Production of enzymes
- Alteration in the bacterial cell binding sites
- Change in membrane permeability
- Producing alternate metabolic pathways/drug efflux pump
- Biofilm formation
Describe what human practices can lead to antibiotic resistance and what can be done to prevent it
human practices that can lead to antibiotic resistance:
- overuse and misuse of antibiotics
- failure to complete a full course of antibiotics
- use of antibiotics in animal feed
- poor infection prevention and control
To prevent antibiotic resistance;
- only use when necessary
- the full course of antibiotics should be completed
- good hygiene practices
- vaccination should be practiced
- the use of antibiotics in animal feed should be reduced
- prevention and control practices should be implemented in healthcare facilities
Infection control measures
Standard precautions
*Hand hygiene
* Use of PPE where appropriate
* Includes environmental controls—waste management; routine cleaning; spill management
Additional precautions
* Contact precautions
PPE, avoid patient contact, single use equipment
* Droplet precautions
Contact precautions,+surgical mask for carer and patient
* Airborne precautions
Contact precautions,+single occupancy room (neg pressure),patient respirator during transfer
Sterilisation vs. Disinfection
Sterilisation—the killing or removal of all viable organisms,
including spores
* Heat (wet/dry autoclave)
* Irradiation (Gamma vs UV irradiation)
Disinfection—the killing of many but not all microorganisms
* Pasteurisation (Heat & rapid cooling)
* Filtration (0.22 uM filter)
* Chemical disinfectant (chlorohexidine, ethanol)
Describe how antimicrobial resistance can be transferred (gene transfer)
- Transformation
- Transduction
- via bacteriophage *
- Conjugation
- Bacterial “mating”
- Transposition
- Through transposons
