Clinical Microbiology and Bacteremia/Septicemia, Gastroenteritis Notes 4
Recap and Examples
The goal is to align with the benchmark statement that everyone should have an awareness of all six clinical disciplines.
Two case studies: food poisoning (common, affects all ages) and bacterial septicaemia (serious, rare, more common in the elderly).
Food poisoning may not require medical attention, whereas septicaemia is more serious, with age being a risk factor.
Food poisoning occurs in a non-sterile environment (GI tract with normal flora), while septicaemia occurs when bacteria enter the (normally sterile) bloodstream.
One Health: human, animal, and environmental health are interconnected, especially relevant in antimicrobial resistance.
The UK's antimicrobial resistance strategy emphasizes the One Health approach.
Septicemia
Focus on bacterial septicaemia, acknowledging viremia, parasitism, and fungemia exist.
Transient bacteraemia (bacteria in the blood) is common and doesn't always cause illness.
Bacteraemia can result from daily activities (e.g., brushing teeth) or a leaky gut.
Bacterial Septicaemia: When bacteraemia causes illness. The existence of bacteria in the blood leads to an illness.
Blood contains components to fight bacteria; bacteria often don't want to be in the blood.
Blood is filtered by the kidneys and liver, detoxifying and removing non-self elements.
Blood also contains nutrients, proteins, carbs that microbes need, but also defense factors.
Whether bacterium in the blood causes illness depends on factors related to the host and the organism.
-aemia: Indicates something related to the blood.
Septicaemia: Implies the patient is ill; related to sepsis.
Sepsis: Large, out-of-control immune response, usually to a microbe.
In the UK, sepsis is usually bacterial, sometimes fungal (especially in immunocompromised patients).
Elevated white cell count and other blood markers (e.g., CRP) indicate infection.
White cell count may skew towards neutrophils (bacterial) or lymphocytes.
Sepsis is a spectrum of increasingly severe syndromes.
Sepsis can progress rapidly, from feeling well to critically ill within hours.
Sepsis Six: NHS guidelines for monitoring and responding to sepsis signs.
Sepsis is considered a preventable death if not treated promptly in hospital settings.
Signs and Symptoms of Septicemia
Raised temperature, significant debilitation.
Raised white cell count or, occasionally, a crash in white cell count (possibly due to overwhelming infection or localized infection).
Increased heart rate, increased breathing rate, shallow breathing.
Discoloration of fingernails and lips (signs of oxygen deprivation).
Systemic Inflammatory Response Syndrome (SIRS) can be non-infectious, but sepsis involves a confirmed or suspected infection.
Severe sepsis: Blood pressure drops dangerously low, leading to fainting, disorientation, and paleness.
Septic shock: Fluid replacement alone doesn't redress the balance; more aggressive intervention is needed.
Gram-negative bacteria can cause additional shock due to lipopolysaccharide (endotoxin) in their cell walls.
Multi-organ dysfunction syndrome (MODS) has a significant fatality rate, involving damage from the immune system.
Kidney failure occurs quickly, leading to toxic product buildup.
Death can result from renal failure or cardiac arrest.
In MODS, the immune response causes most of the damage.
Antibiotics may worsen the condition temporarily in gram-negative infections because they increase the surface area of endotoxin released from the bacteria.
Signs and Symptoms of Septicemia and Testing
High fever.
Samples often labeled "PUO" (pyrexia of unknown origin) require urgent testing.
Sepsis screening includes blood samples for haematology and clinical chemistry to check elevated markers of infection.
Urine samples are taken if possible; catheterization may be necessary.
Other body samples are taken if infection is suspected (e.g., knee fluid).
Blood samples for microbiology require culturing, so results aren't immediate.
The dilution effect in blood makes microscopic examination difficult.
Chills, shivering, elevated heart rate, slow breathing.
Fainting, confusion, disorientation.
Nausea and diarrhea. (toxins passing through may irritate the gut)
Cold, clammy skin, paling of extremities.
Disseminated intravascular coagulation (mini clots).
Sepsis is very serious and significant.
Gastroenteritis
Infectious gastroenteritis is the focus (not all diarrhea is infectious).
GI tract from mouth to rectum contains microbiota.
The small intestine has microbes per gram of fecal matter, but the stomach has lower microbial load due to acidity.
The stomach is not sterile; it has a normal microbiota living in close contact with the stomach lining protected by mucus.
Evidence from molecular biology shows a diverse range of organisms in the gut.
Helicobacter pylori is an acid-resistant microbe that can cause stomach ulcers. can proceed to be cancerous ulcers
The oral end shares a cavity with the respiratory tract, allowing organisms to end up in the wrong place.
Microbiota
Normal microbiota assists with digestion and is part of us.
We are transiently exposed to microbes all the time, through food and self-cleaning of the lungs.
Roughly 35,000 different species have been identified in the gut flora.
Individual humans probably have 200-300 different species.
Healthy flora consists mainly of Bacteroidetes and Firmicutes.
Ratios of bacteria vary in different parts of the body, depending on oxygen levels.
Hormonal shifts during puberty and menopause can alter the flora.
Dietary preferences influence flora composition; protein vs. carbohydrate.
Slight seasonal shifts in flora due to changes in eating habits.
Antibiotic consumption can disrupt gut flora, causing diarrhea.
Probiotics and prebiotics may help redress the balance; prebiotics have stronger evidence. designed to promote good bacteria in the gut and support overall digestive health, thereby reducing the incidence of gastrointestinal disturbances.
Acquisition
Microbes are involved in the metabolism of carbohydrates and proteins, as well as the synthesis of B vitamins and vitamin K.
They produce bacteriocins, which are small chemicals that suppress other bacteria (e.g., colicin).
They support immune system development in the gut, particularly gut-associated lymphoid tissue and T cell development.
Multi-biotic animals (sterile animals) have underdeveloped immune systems. create challenges cause they dont replicate us
Gut microbiota blocks binding sites, preventing invading organisms from taking hold.
The stomach's acidic pH (pH 1.5-2.5) kills many microbes, but some survive in food boluses.
Our cells produce antimicrobial polypeptides, which are short chemicals found in mucous membranes.
Antimicrobial polypeptides hese are short, sometimes as small as 12 amino acid long chemicals that our body produces, anywhere we have a mucous membrane you will find anti-microbial polypeptides in your cavity, we find them in the gut, genital tack specifically in females and they are unique to the site. They were hoped to be a new source of antibiotics.
Peristalsis the act of moving things along.
bile salts: made in liver then stored in gall bladder
Infections
Campylobacter spp is the most numerous bacterium in the UK, followed by Salmonella spp, Shigella spp, and E. coli O157. (the abbreviation "spp." means “species” in the plural form)
The sample sent to the lab is feces, containing broken down food, bacteria, fungi, and cells.
Bristol Stool Chart
The Bristol stool chart is based on observation of the British population.
It ranges from hard, compacted matter to almost entirely liquid diarrhea.
Consistency depends on diet, exposure, and intake.
Feces samples should be a good spoonful, unless for parasitology, which requires about 10 grams.
Not all diarrhea is infectious; it can be caused by stimulation, alcohol, or hydration level.
Diarrhea is an imbalance of water flowing through the body vs. the amount being reabsorbed.
Microbes in bacterial diarrhea can either cause the body to pump out liquid (e.g., cholera actively interacts with the cells of the lining, changes the cyclic AMP pathway and pushes more water into the gut.) or reduce resorption surface area (e.g., Cryptosporidium can actually cause those villi to be, blunted and flattened down so you lose resorption surface area.). Both of them lead to a net result of a higher concentration of water in the final output.
Sometimes, the microorganism never gets to the gut and it's a toxin that does all the damage.
Comparing and Contrasting Two Diseases
Focus on UK-specific factors.
Bloodstream infections are usually normal flora-derived, from sites like urinary tract infections.
Traumatic injuries, gardening accidents, car accidents can introduce bacteria.
Intravenous drug abuse and medical procedures increase risk.
Infections can spread from other sites in the body (e.g., pneumonia leading to secondary septicaemia).
Gastroenteritis in the UK is primarily foodborne, although Shigella can be transmitted person-to-person.
C. difficile can be part of the normal flora or acquired of the patient survives because it's a spore forming organism that can survive antibiotics in its spore form, is associated with hospital-acquired infections due to spore formation. hospital associated infection
Normal flora has a role in both conditions.
Replication
Bloodstream has nutrients for replication, but the inoculum size matters.
Capsules protect some bacteria from opsonization and phagocytosis, promoting septicaemia.
Gastroenteritis requires attachment to the gut wall to get a foothold.
The immune response is not as strong in gastroenteritis as in sepsis.
Some organisms need a large initial dose to establish infection, while others (e.g., Shigella) can cause disease with as few as ten bacteria.
Conditions
Bloodstream infections lead to immune reactions that damage organ systems.
Toxins produced by bacteria, drive damage elsewhere like Staph aureus which produces toxins that can kill white blood cells.
Some bacteria produce hemolysis, causing anemia; others produce leukocidins, killing white blood cells.
Toxic shock syndrome toxin leads to another form of shock.
In the GI tract, organisms produce toxins that cause damage, such as cholera toxin that disrupts normal cell activity; E. coli O157 toxins damage the gut and renal system.
Secondary infections such as arthritis can occur.
Autoimmune conditions like Guillain-Barre syndrome can result from Campylobacter infections due to molecular mimicry, leading to demyelination of neurons. (you've got molecular mimicry, where the cell of the compylobacter triggers antibodies that are similar enough to someones neurones therfore the antibodies stick to them and start attacking the patient's own neurones and they cause demyelination.)
Bloodstream infections can have high fatality rates, whereas gastroenteritis is usually less severe.