Lecture 4 Introduction to microbial pathogens Flashcards by Deepu pras

What is a pathogenic microorganism?

Agent capable of causing disease in a host

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What is a disease?

Disorder of structure or function producing symtoms and signs

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Example of it being possible to be infected by pathogen without disease being produced:

Pathogen in NW of Aus called Murray Valley encephalitis (MVE) but only 1:800-1000 of infected people develop significant disease

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What types of microorganisms can be found on host?

Commensal

Pathogen

Opportunistic pathogen

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What are commensals?

Bacteria primarily

Colonise many body sites

Referred to as commensal flora/normal flora or microbiome

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How much of faeces are bacteria?

60% of dry weight

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What is lactobacillus useful for?

Maintains vaginal pH at 3.8 - 4.5 this pH protects from other harmful bacteria.

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Are commensals all over the body?

No they are in heavily colonized body sites (such as the oral cavity, oropharynx, nasopharynx, bowel, vagina, skin)

They are not present on sterile body sites (Bloodstream, cerebrospinal fluid, bladder, peritoneal space, and joint space)

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What are the types of sources that pathogens can come from?

Exogenous sources (external source)

Endogenous sources (microbiome)

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What is the carrier state of commensals?

When pathogens are found in normal flora without causing disease

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What is another way of carrying disease?

Some pathogens can remain carried for months after recovery from disease

Salmonella typhi

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Can asymptomatic carriers be a source of infection of others?

Yes

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What are opportunistic pathogens?

Pathogens very low in virulence so don’t cause disease

Opportunistic diseases cause infection when they can bypass the host’s innate immune defences.

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What is toxoplasma gondii?

Protozoan parasite definitively hosted by cats and can infect humans and other mammals

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How is toxoplasma gondii infection acquired?

Uncooked meat or cat faeces

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Is infection of toxoplasma gondii common in humans?

Yes with 15 - 70% of people infected but it is asymptomatic

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How does toxoplasma gondii affect humans?

It remains dormant in various tissues in what are known as pseudocysts.

If immune system fails the cysts can become active and cause damage to brain and other host tissue

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What is candida albicans?

A fungal yeast that colonizes humans and causes diseases like vaginal thrush

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What are the harms associated with candida albicans?

It can bypass innate defences when immunocompromised and infect many internal organs

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How can people be susceptible to candida albicans?

Intravenous cannulas

Broad spectrum antibiotics

Urinary catheters

Surgical procedures

Corticosteroid therapy

Neutropenia

Severe burns

Parenteral nutrition

Superficial infection elsewhere

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What are virulence factors?

Properties that microbes have that enable them to cause disease.

Disease can be caused by the microbe or the host’s reaction to it

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What is a good example of a virulence factor?

Cholera toxin enables vibrio cholera to cause disease

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How does cholera toxin kill people?

Causes lots of fluid loss and hypotension

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What types of organisms can be pathogenic?

Bacteria (unicellular prokaryotes that can live and replicate outside the host)

Viruses (not cellular and can only replicate in living cells)

Fungi are eukoryotic multicellular organisms that can live or replicate outside of host

Protozoa are unicellular eukaryotes that can live and replicate outside of human host

Helminths are non0microorganisms with complex life cycles within or without host (eg. gineaworm)

Pions non organisms that are just proteins that cause disease

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What system of classification is important with bacteria?

Genus and species

What does the name tell doctors?

Specific disease potential How it was acquired How it can be transmitted The drugs that are likely to effectively treat it

What differences can we see within species?

Population Strains Clones Genotypes Serotypes, serogroups

What does the cytoplasmic membrane of a bacterium typically consist of?

Phospholipid bilayer An osmotic barrier Performs organelle like functions such as active transport of nutrients and ions Synthesis of lipids, peptidoglycan precursors, lipopolysaccharides, and capsular polysaccharide Protein secretion Electron transport Flagellar movement and chemotaxis

What does the nucleoid consist of?

single continuous DNA double strand

What do both prokaryotes and eukaryotes contain?

ribosomes (E.coli can have 1500 per cell)

What are plasmids?

circular DNA that can be transferred between cells

Where are genes for virulence factors and antibiotic resistance typically contained?

Genes for virulence factors Antibiotic resistance

What is the cell wall made up of?

crosslinked peptidoglycan

What does cell wall do?

Provides rigidity to bacterial cells

What enzymes create cross linkages?

Transpeptidases (if this is interfered with we have no cell wall = easy to burst bacterium)

What organisms posses an outer membrane?

Only gram negative-bacteria

What is the function of the outer membrane?

Main function is osmoregulation and contains important embedded molecules such as Lipopolysaccharide (virulence factor causing toxic shock) LPS is antigenic

What are some proteins that are found in bacterial outer membranes?

Porin proteins (trimeric proteins that control ingress and egress of molecules including antibiotics) Outer membrane proteins (OMPs) with numerous important functions such as survival in macrophages.

What do OMPs do?

Survival in macrophages Resistance to complement Attachment to host cells Efflux pumps Iron acquisitions

What is the capsule "slime layer"?

Present in some bacteria Usually made of polysaccharide

What does the capsule do?

Antiphagocytic Adhesin function Antigen Component of biofilm

What is the implication of the adhesivity of the capsule on prosthetics?

If there is any sign of infection the prosthetics must be removed

What are fimbriae?

Hair-like projections that are also important for horizontal gene transfer.

What are flagella?

Whip-like structures that confer motility (possible virulence factor)

Are flagella always the same arrangement?

No different arrangements can be often seen

What is the difference between gram positive and gram negative bacteria?

Gram positive: Purple when stained with crystal violet due to presence of thick cell wall Gram negative: Stains red when dyed with crystal violet due to presence of thin cell wall Has outer membrane Has thinner cell wall

How is a gram stain done?

Specimen from patient added to glass slide then flooded with crystal violet which gets among peptidoglycan cell wall The slide is then flooded with Lugol's iodine for 30 seconds. Iodine fixes crystal violet onto peptidoglycan. The slide is then rinsed with H2O. Crystal violet is then decolourized with the alcohol in everything but gram positive bacteria. Thick cell wall retain the crystal violet but thin wall don't. The slide is then flooded with carbol fuchsin counterstain to show the invisible bacteria that was decolourised as a result of lower retention of crystal violet

What are the types of morphology we can observe in bacteria?

Cocci (round balls) Bacilli (rods) Comma shaped (vibrio) Helical (campylobacter) Spirochaetes

What are the types of arrangements observed in coccus bacteria?

clumps Chains diplococcous

What are clumped balls typically?

Staphylococcus

What are stringed balls typically?

Streptococcus

What are diplococci?

double ball shape

What is irregular arrangement called?

diptheroids or coryneforms

Which bacteria do not take up gram stain?

spirochaetes and mycobacterium

What is done to bacteria that don't take up gram stains?

A special stain is used for them. Acid-fast stain or ziehl-Neelsen stain

What is the clinical significance of the gram stain?

It is the first piece of information clinicians gather about bacteria It allows early management decisions

What information is achieved from a gram stain?

Whether it is gram negative or positive Colour Morphology

Summary

Not all microorganisms found on the body are pathogens Not all pathogens cause disease The gram stain appearance (colour and morphology) of a bacterium is very important. Name of microorganism carries important information

Name an example of a gram-negative curved or comma shaped rods called?

Vibrio

Name a gram negative helical rod:

Campylobacter

Name a gram positive filamentous or branching rod:

Nocardia