Medically Important Microbes Flashcards
What are the ways in which we can categorise bacteria?
- Gram staining: positive vs. negative
- Morphology: cocci vs. bacilli
- Growth: anaerobic vs. aerobic
- Gram-stainable vs. non gram-stainable
- Extracellular vs. intracellular
- Culturable vs. non-culturable
- Fermenters vs. non-fermenters
Why is gram staining helpful?
- It proves there are bacteria present in the sample
- It allows us to target certain bacteria groups
- It gives us some more clues to help identify which bacteria is causing the infection
- Cheap, simple and quick
Which bacteria will stain with counter stain safranin?
Gram negative
Why does a gram negative bacteria stain with safranin, whereas a gram positive bacteria will not?
This is due to differences in peptidoglycan thickness difference. Gram +ve bacteria have a thick peptidoglycan layer where as G-ve do not.
What colour does a G+ve bacteria look under the microscope?
Purple due to the retention of crystal violet stain due to the thick peptidoglycan content
Define the following growth requirement: Obligate aerobe
This type of bacteria will only grow in the presence of oxygen.
Define the following growth requirement: Obligate anaerobes
These bacteria will only grow in the absence of oxygen
Define the following growth requirement: facultative anaerobes and facultative aerobes
These bacteria grow well in the presence and absence of oxygen. Most human pathogens have this characteristic.
Define the following growth requirement: Microaerophilic
This type of bacteria prefer lower oxygen concentrations
Describe the following morphology: cocci
Round bacteria that can appear in chains, pairs or clusters
Define the following morphology: Rods (bacilli)
Elongated looking bacteria
Define the following morphology: coccobacilli
An intermediate shape between rods and cocci
Define the following morphology: Spiral
Look like a twirl
How do Beta-lactam (penicillin) Abx work?
They inhibit peptidoglycan synthesis in bacterial cell walls therefore are bactericidal
Why do we sometimes have to give beta-lactamase inhibitors with a penicillin (beta-lactam antibiotic)?
Some bacteria can neutralise the effect of beta-lactam antibiotics and use beta-lactamase enzymes to break down the beta-lactam ring. The combination of penicillin and a beta-lactamase inhibitor should allow the penicillin to be effective.
Give an example of a beta-lactamase inhibitor
Tazobactam
What bacteria commonly cause traveller’s diarrhoea?
- Shigella Salmonella
- Yersinia enterocolitica
- Campylobacter
- E.Coli O157:H7
Which parasites can cause traveller’s diarrhoea?
- Entamoeba histolytica
- Isospora belli
When does traveller’s diarrhoea normally present?
Within the first few days of travel
What is the most common route for Traveller’s Diarrhoea?
Faecal-oral
What is the most important piece of advice to give to someone with Traveller’s diarrhoea?
Keep hydrated as lots of insensible fluid losses will occur from the diarrhoea
When would someone with traveller’s diarrhoea need treatment with antibiotics and admission?
- Bacteraemia - bacteria present in the blood culture
- Dysentery - infection of the intestines
What neurological syndrome can be related to infective diarrhoea?
Guillan-Barre syndrome
What is the potential long-term complication of bacterial traveller’s diarrhoea?
Reative arthritis
What is the most common cause of bacterial pneumonia?
Streptococcus pneumoniae
What is the morphology of S.Pneumoniae?
Gram +ve coccus
What is the mortality rate in association with candidaemia?
40-50%
Is candidaemia a medical emergency?
YES
This carries a very significant mortality rate and should be treated as quickly as possible.
IV antifungal treatment for 2 weeks will be required
What is the most common source for candidaemia?
From gut flora - microscopic or macroscopic bowel damage allows the gut flora to pass into the blood stream
What are the 3 categories of fungal infection?
- Superficial
- Subcutaneous
- Deep
List some superficial fungal infections
- Oral and vaginal thrush
- Tinea
- Fungal nail infection
- Pityriasis versicolor
Who can get superficial fungal infections?
Anyone, they are common. E.g. ringworm, athletes foot etc
Who is more at risk of developing superficial fungal infection?
Those who are immunocompromised - HIV or diabetic patients
Where in the world do subcutaneous fungal infections occur most commonly?
In tropical countries
Who is at risk of deep fungal infections?
Those who are immunocompromised in some way
Name some deep fungal infections
- Invasive candida sp. : Central line infection
- Invasive Aspergillus fumigatus: transplant and chemo patients
- Pneumocystis jirovecii pneumonia
- Cryptococcal meningitis
What is the clinical term for chickenpox?
Primary varicella zoster infection
What sort of rash is common in chickenpox?
Widespread, itchy, vesicular rash
What are some severe complications of chickenpox?
- Pneumonitis
- Bacterial infection of the skin
- Encephalitis
- Hepatitis
- Myocarditis
What treatment should be used in an immunocompromised patient for chickenpox?
Aciclovir
What is the route of chickenpox infection?
Mucosa of the upper respiratory tract or conjunctiva
What are the prodromal symptoms of a chickenpox infection?
- Fever
- Lethargy
There are dermatological changes in chickenpox. What does it originally present as and develop into?
Macules and papules which go on to become vesicles which burst and then crust
What are the 4 most important herpes viruses to know?
- Herpes simplex-1 (HSV1)
- Herpes simplex-2 (HSV2)
- Epstein-Barr virus (EBV)
- Cytomegalovirus (CMV)
What was the MMR vaccine said to be related to developing in the early 2010s?
Autism
What are the prodromal features of measles?
- Fever
- Malaise
- Conjunctivitis
- Cough
What is a distinguishing feature of measles?
Koplik spots in the buccal cavity mucosa - blue/grey/white spots
What sort of rash is present in measles?
Morbilliform rash (maculopapular) beginning on the face then spreading down the body
What are the potential complications of measles?
- Bacterial pneumonitis
- Otitis media
- Acute encephalitis
What are some of the key features of a HIV infection?
- Generalised rash
- Pharyngitis
- Generalised lymphadenopathy
- Headache
- Mouth ulcers
- Flu-like symptoms
What does HSV-1 commonly cause?
Oral or ocular disease
What does HSV-2 commonly cause?
Genital lesions
What are the symptoms of Glandular fever?
- Fever
- Sore throat
- Lymphadenopathy
Which drug can precipitate glandular fever?
Amoxicillin
Define the following; Endoparasites
Parasites that live on the skin and hair
Define the following; Endoparasites
Parasites that live on the mucosal surfaces such as the gut and in tissue
What are helminth parasites?
Worm-like parasites, mostly visible to the naked eye
What are protozoan parasites?
Single-celled eukaryotic organisms that are usually motile
What is a definitive host?
The animal that hosts the adult stage of a parasite
What is an intermediate/secondary host?
The animal that hosts the developmental stage of the parasites life
What is an accidental host?
A host that the parasite cannot use to complete its life-cycle. This host is a dead end for the parasite.
What is a vector?
A parasite that can transmit other diseases such as bacterial infection e.g. some ticks are vectors for Lyme disease
What are mosquitos the vector for?
Malaria
What is the recommended chemoprophylaxis against Malaria?
Doxycycline
What is the commonest cause of eosinophilia in clinical practice?
Atopic disease - asthma, hayfever, eczema
What parasite causes pinworm?
Enterobius vermicularis
How does the lifecycle of the pinworm carry out?
An adult worm lives in the gut of the child. During the night the worm ventures out of the anus and lays eggs at the perineum. The child gets an itchy bottom and then transfers the eggs from perineum to mouth or others’ mouths.
Where can Diphyllobothrium latum be caught from?
Eating undercooked fish or sashimi
Which organisms does metronidazole treat?
Obligate anaerobes (G+ve or G-ve) Giardia
