Infection Flashcards
What are the main agents of infection?
Bacteria Viruses Parasites Fungi Prions
What are common tests used for viral detection?
PCR (ie molecular methods)
serology
antigen detection
What are common tests for bacterial detection?
Microscopy (+ or - staining)
Culture (selective or non-selective)
What are common bacterial features used for identification?
Morphological
Physiological
Biochemical
What common tests used for parasitic detection?
Microscopy of parasitic life stages
Serology
What are some of the basic infection control measures?
Handwashing
Decontamination (eg stethoscope, surfaces)
PPE
Isolation
List some of the common samples collected for culture
Faecal specimen Throat swab Wound swab Urine sample Sputum sample Blood sample
What are the main mechanisms of action of antibacterial drugs?
Inhibit cell wall synthesis
Affect protein synthesis
Affect nucleic acid synthesis
What are the main classes of drugs to affect cell wall synthesis in bacteria?
- beta lactams
- glycopeptides
What are the main types of beta lactams?
penicillins and cepharlosporins
What are the main classes of drugs that affect protein synthesis in bacteria?
- aminoglycosides
- macrolides
- tetracyclines
What are the properties and risks associated with cephalosporins?
broad spectrum antibiotics
can cause C. Difficile infections
What are some of the macrolide drugs used in bacterial infections and when are they often used?
clarythromycin, erythromycin
alternative for penicillin if allergic
What are the main classes of antibacterials which affect nuclear acid synthesis?
- trimethoprim and sulphamethoxazole (co-trimoxazole combined)
- fluoroquinolones
What are examples of fluoroquinolones and their limitations?
Ciprofloxacin, levofloxacin
Ciprofloxacin affects cartilage growth, can’t be used in children
What drug group is vancomycin part of, and what class of bacteria does it act on?
glycopeptide
Gram +ve bacteria
What drug group is gentamycin part of, and what class of bacteria does it act on?
aminoglycoside
Gram -ve bacteria
What are nitrofurantoin and nalidixic acid used for?
UTIs
What is the main advantage of nitrofurantoin over nalidixic acid?
It is effective on some gram +ve and -ve organisms
What class of bacteria does nalidixic acid act on?
gram -ve
What drugs are known to cause liver and renal toxicity?
Aminoglycosides (gentamycin) and glycopeptides (vancomycin)
What drugs are reserved for MRSA infections?
Linezolid and daptomycin
What antibacterials are safe to give to pregnant women?
penicillins, cephalosporins, nitrofurantoin
What are the main mechanisms of bacterial resistance?
- beta lactamase production
- PBP alteration
- vancomycin resistance (protein alteration)
What classes of drugs produce extended spectrum beta lactamases?
Gram -ve bacteria
What is the concern with carbapenemase producing bacteriaceae (CPE)
carbapenem is a broad spectrum antibiotic used for multi-drug resistant bacteria
if bacteria resistant to carbapenem, potentially no other drugs available to treat
What is the mechanism of action of penicillins?
they affect the synthesis of the peptidoglycan cell wall
What is the mechanism of action of glycopeptides?
they affect the synthesis at a stage prior to penicillins
What is the mechanism of action of nucleic acid inhibiting antibacterials, and give examples of drugs for each
- purine synthesis (trimethopriim, sulphamethoxaxole)
- DNA affected directly (fluoroquinolones eg ciprofloxacin))
What is a commonly used drug for anaerobic bacterial infections?
Metronidazole
What are the properties of piperacillin?
It is a broader spectrum version of penicillin which is also active against pseudomonas
What are the main types of antifungal drugs?
Polyenes
Azoles
Echinocandins
Allylamines
What are the main types of polyene drugs and their properties? (administration, when it’s used)
- Amphotericin B (toxic, IV for serious infections)
- Nystatin (topical, non-serious infections)
What are the main actions of antifungal drugs and what are examples of drug classes for them?
- target ergosterol (polyenes, allylamines, azoles)
- target glucan polysaccharide (echinocandins)
What is the mechanism of action of polyenes?
Target ergosterol on cell wall and make it permeable
What is the mechanism of action of allylamines and azoles?
Inhibit ergosterol synthesis
What is the effect of antiviral drugs on viruses?
Always virustatic, there are no virocidal drugs
What is the main drug for Herpes Simplex Virus?
Aciclovir
Famciclovir
What is aciclovir used for?
Herpes simplex virus
varicella zoster virus
What are the aciclovir analogues used to treat?
Ganciclovir - CMV
Famciclovir - HSV and shingles
How is aciclovir activated, and what type of molecule is it?
Nucleoside analogue
Prodrug - activated by thymidine kinase
What is the mechanism of action of Zidovudine?
Nucleoside analogue - acts on reverse transcriptase
What is Zidovudine used to treat?
HIV
What is commonly used to treat HIV?
A combination of different reverse transcriptase inhibitors
nucleoside reverse transcriptase inhibitors
non-nucleoside reverse transcriptase inhibitors
protease inhibitors
When is Foscarnet used?
Treating CMV, HSV, VZV infections resistant to aciclovir/ganciclovir/famciclovir
Foscarnet toxic for kidneys, only IV
What are examples of drugs used to treat Hepatitis B and C?
Interferon alpha
Lamivudine
What are examples of Herpes viruses?
Cytomegalovirus
Herpes Zoster virus
Varicella Zoster virus
Epstein-Barr virus
What are the main classes of viruses treated with drugs?
Severe/life threatening viral infections
- HIV
- chronic hepatitis B/C
- Herpes viruses
What is lamivudine used for?
chronic hepatitis B
What is interferon alpha used for?
Hepatitis B and C
What is the combination of drugs often used for treating chronic hepatitis infections?
Interferon alpha + ribavarin
What is ribavarin used for?
combination with interferon alpha for chronic hep C
may be used for respiratory RSV infection
What can be used to treat Influenza A or B in early stages?
Zanamavir
What is Zanamavir used for?
Treating Influenza A or B in early stages
What are the most common methods used to analyse the sensitivity of an organism to an antibiotic?
- automated methods
- E test
How do trimethoprim, suxamethoxazole and co-trimoxazole act?
Affect purine synthesis
How do fluoroquinolones act and when are they used?
Directly affect nucleic acid synehtsis
Pseudomonas infection, strep pneumoniae LRTI
What class of bacteria are always resistant to which type of drug?
Gram +ve streptotoccus - always resistant to gentamycin (aminoglycoside)
Gram -ve bacteria - always resistant to vancomycin (glycopeptide)
What are the main genetic mechanisms which allow bacteria to become resistant?
- spontaneous mutation of genetic code
- spread of resistance (through transposons or plasmids)
How do cephalosporins change in properties with generations?
Newer generations have
- better gram -ve action
- worse gram +ve action
Can someone with a penicillin allergy also be allergic to cephalosporins?
Yes, about 10% of those allergic to penicillin
What antibiotic is associated with pseudomembranous colitis?
Clindamycin
Cephalosporins
Fluoroquinolones
What can pseudomembranous colitis be caused by?
A drug induced increase of C Difficile in the colon
What can be used to treat early stages of Influenza A and B
Zanamavir
Oseltamivir
What are azoles often used for?
Yeast infections and some filamentous infections
What are allylamines often used for?
Dermatophytic infections
What are polyenes used for?
Amphoterycin B - serious infections (IV)
Nystatin - yeast
What are echinocandins used for?
Serious fungal infections - expert advice only
What is flucloxacillin mostly used for?
Staphylococcal infections
What class of bacteria is amoxycillin most effective for?
Gram -ve
What is the main difference between Gram +ve and Gram -ve bacteria?
Gram +ve: thick peptidoglycan layer + inner membrane (2 layers)
Gram -ve: lipopolysaccharide layer + thin peptidoglycan layer + inner membrane (3 layers)
What is the main function of the bacterial capsule, what is its structure and what is it made of?
Stops the bacterium from being phagocytosed and digested.
slimy, forms biofilm
made of glycosaminoglycans (GAG)
What are the different terms for flagella and what ist their function?
Monotrichous
Amphitrichous
Lothotrichous
Peritrichous
used for motility
What is the purpose of fimbriae on a bacterium?
Stickiness - helps to adhere to surfaces
What is a plasmid?
A piece of bacterial DNA which can be injected into other bacteria
What is normal genetic division in bacteria called, and what does it result in?
Binary fission - two identical copies
What is a bacteriophage?
It’s a virus that kills bacteria by injecting its DNA into them
What are the methods of DNA transfer among bacteria?
- Conjugation
- Transformation
- Transduction
What is the function of spores in bacteria?
they are produced by bacteria to survive in difficult environments
How are bacteria classified?
Genus - staphylococcus, streptococcus etc
Species - aureus, epidirmidis, pneumoniae etc
What are the possible structures of a virus?
helical
icosahedral (20 sides)
complex
What are the ideal factors for eradication of a virus?
easy method for virus detection effective treatment effective prophylaxis (vaccines) remove possible hosts economical/political support
What are the aspects of a virus used to identify it?
mode of replication
shape/size
genome structure
envelope
What are the outcomes of a viral infection?
Resolution (plus or minus immunity)
latency
chronic infection
genetic changes (eg cancer)
What is the mode of replication of viruses?
Infect host cell
inject own DNA in host cell nucleus to make viral proteins and new viral nucleic acid strands
new viral nucleic acid/proteins assembled and leave the cell
Do all viruses have a lipid envelope?
No
What is a viral capsid?
a membrane that contains the viral genome
What are spike projections on viral lipid envelopes used for?
target for treatment
What is viral latency?
it’s a stage after the initial infection during which the virus is dormant but can reactivate to cause disease
Does viral infection resolution always result in immunity?
no
what can be the result of genetic changes from a viral infection?
cancer (eg cervical from HPV)
How can a virus induce cancer in cells?
- induced cell proliferation
- reduced apoptotic measures
- damage from reactive oxygen species
How are viral infections prevented?
vaccination prophylactic and post-exposure treatment infection control antenatal screening blood/tissue/organ screening
What are the main three classes of fungi?
mushrooms
yeasts
moulds
What is the main difference between yeasts and moulds?
Yeasts grow as uni-cellular organisms
Moulds have hyphae and are filamentous
What is dermatophytosis and what can it also be called?
ringworm infection
tenia
what are examples of opportunistic fungal pathogens?
candida spp
aspergillus spp
dermatophytes
cryptococcus neoformans
which fungal infections are normally more serious?
candida infections
aspergillus infections
what host factors contribute to fungal growth?
moist/warm environment
low immune system
broad spectrum antibiotic use
Are candida spp moulds or yeasts?
Yeasts
What is a unique feature of candida albicans?
it can grow hyphae in some environments
are aspergillus spp moulds or yeasts?
Moulds
Are cryptococci yeasts or moulds?
Yeasts
What are the main types of cryptococcus?
cryptococcus neoformans
cryptococcus gattii
which main types of fungi are moulds?
aspergillus spp
dermatophytes
Which main types of fungi are yeasts?
candida spp
cryptococcus spp
Are dermatophytes moulds or yeasts?
moulds
What is a unique feature of aspergillus spp?
can invade blood vessels
What is a unique feature of cryptococcus?
it has a capsule
What is a unique feature of dermatophytes?
use skin keratin for nutrition
What is pityriasis versicolor caused by and what kind of fungus is it?
Malassezia spp - yeast
What are the main classes of parasites?
Protozoa
Helminths
Arthropods
What are the types of protozoa?
malaria
amebae
flagellates
What are the types of helminths?
Flatworm
roundworm
tapeworm
What are the types of arthropods?
mites
ticks
lice
What causes malaria?
Plasmodium spp
Which type of plasmodium is most fatal?
plasmodium falciparum
What is the lifecycle of the plasmodium spp?
sexual reproduction in mosquito gut
injected in human blood, mature in liver, multiply in RBC
What are the most common protozoal infections?
malaria
amoebic dysentery
leishmaniasis
What is schistosomiasis caused by?
schistosomes that penetrate through skin
Where is schistosomiasis contracted?
swimming in fresh water
What immune reaction can helminth infections cause?
Eosinophilia
elevated IgE
What is microscopy used for in diagnosing helminth infections?
identifying PCO (parasites, cysts, ova) in faeces
What causes an infection of leishmaniasis?
Sandfly bite
What does schistosomiasis affect?
Skin, urinary tract and intestine
What can leishmaniasis affect in terms of where in the body it can cause damage?
skin
internal organs
Which type of bacteria are haemolytic?
Streptococci
What are the differences in haemolytic bacteria?
Alpha haemolytics - partially lyse blood
beta haemolytics - fully lyse blood
What is the main feature to distinguish between staphylococci?
Coagulase test
Are coagulase negative bacteria harmful, are there exceptions?
No, but staph ludgunensis can cause infections if it gets into cannulas
What is the difference between staphylococcus and streptococcus?
Staphylo - clusters
strepto - chains
What are the main shapes of gram positive bacteria?
Cocci
Bacilli
What differentiates clostridium difficile from streptococci and staphylococci?
bacillus
anaerobic
Which bacillus has a drumstick appearance?
clostridium tetanii
What are examples of bacteria which can’t be identified from Gram stains?
AAFB
spirochaetes
What is the only anaerobic Gram +ve bacterium?
Clostridium spp
Where can Staph aureus be found as a commensal?
Nose
Axilla
Genitaln/anal area
How can Staph aureus be identified?
Gram staining
Coagulase test
What bacterium forms blue chains and creates a green hue in culture?
Strep pneumoniae
partial (alpha) haemolytic
What bacterium forms blue chains and creates a seethrough area in culture?
Strep pyogenes
total (beta) haemolytic
Which bacteria Gram -ve and also coagulase -ve?
Staph epidirmidis, staph lugdunensis
Where is staph lugdunensis normally found?
skin
What beta hemolytic group of bacteria does strep pyogenes class under?
Group A
What beta hemolytic group of bacteria does strep agalactiae class under?
Group B
What classes as Group D streptococci, but have now been renamed?
Enterococci
What is strep pneumoniae also known as?
Pneumococcus
What is strep viridans and what does it cause?
alpha hemolitic Gram +ve
infective endocarditis
What is strep agalactiae known for?
serious neonatal infections
Where is clostridium difficile normally found?
In gut
Why is it called that, and why is that?
Difficile - difficult to culture
because it’s anaerobic
How do clostridium difficile and clostridium tetani cause damage?
Through toxin release
Where can clostridium perfringens be found normally and where can it be pathogenic?
Normally in gut
can cause wound infections and gastroenteritis
Is clostridium spore forming?
Yes
What do neisseria spp, campylobacter, salmonella and pseudomonas aeruginosa have in common?
All gram -ve
What does neisseria meningitidis cause?
Meningitis
What does moraxella catarrhalis cause?
RTI
What do neisseria and moraxella have in common?
Gram -ve cocci
What are examples of gram negative bacilli?
Salmonella E Coli Shigella Krebsiella Pseudomonas
What are examples of curved bacilli?
Campylobacter
Helicobacter
What does campylobacter cause and why?
Main cause of diarrhoea
Found in chickens
What is the appearance of haemophylus influenzae?
mixed appearance (cocco-bacilli)
What can be used as a preliminary test for gram negative bacilli?
Lactose fermentation
Is E Coli a lactose fermenter?
Yes
Is Salmonella a lactose fermenter?
No
What is another name for gram negative bacilli?
Coliforms
What diseases can spirochaetes cause?
Leptospirosis
Lyme disease
Syphilis
can chlamydia spp be cultured?
no
what is the method used to identify chlamydia?
serology
where is porphorymonas found and what are its properties?
dental/periodontal abscess
anaerobic gram -ve bacillus
How are mycobacteria identified?
ZN/auramine stain
culture
How are spirochaetes identified?
serology
nucleic acid amplification
What are some of the symptoms of malaria?
Flu-like
fever
rigors
What can be a symptom of entamoeba histolytica?
GI infections
Liver abscess
What are some symptoms of leishmaniasis?
Skin/mucocutaneous lesions
Visceral: fever, malaise, weight loss, enlarged spleen and liver
What can schistosomiasis cause?
itching urinary and gastrointestinal infections bladder cancer haematuria delayed fever
where in the body are nematodes found?
intestine and lungs
What are potential symptoms of nematode infection?
asymtomatic
some respiratory symptoms
What type of worms are ascaris lumbricoides?
Nematodes
What is an exotoxin?
A toxin produced and released outside of the bacterium
What is an enterotoxin?
A toxin which is produced by a bacterium and is released into the GI tract
What is an endotoxin and where can it be found?
A toxin which makes up part of the bacterial structure (eg LPS complex in Gram -ve bacteria)
What are the two properties a pathogen needs to cause disease?
Infectivity
Virulence
What is meant by bacterial infectivity and how is it achieved?
The ability to settle in an organism
“stickiness”
resistance to acid (capsule)
What is meant by bacterial virulence, and what are some factors which contribute to it?
the ability to cause disease once settled into a host
invasiveness
toxin production
ability to evade immune system
Which class of bacteria contains endotoxins?
Gram -ve bacteria
What are the main ways viruses cause disease?
- killing the cells they infect
- changing the cells they infect (eg tumour inducing)
- causing an immune reaction
Why is Staph aureus a likely secondary bacterial RTI after a viral infection?
Because it’s a nose commensal, and viral infections can destroy respiratory epithelium allowing S aureus to get into the airways
What is an enterovirus and what can it cause?
A virus that only gets in through GI tract but can spread to any organ, causing infections in other parts of the body
Where does Herpes virus stay during its latency period?
Ganglia
How can viruses get into the body?
skin respiratory arthropod GI genital urinary
What are the roles of complement and when is it activated?
activated by combination of IgM with IgG
- opsonization
- kill gram -ve bacteria
- chemotaxis
What is the role of antibodies?
destroy bacteria/viruses
opsonization
stops organisms from attaching
Where does humoral immunity occur?
extracellularly
Where does cell mediated immunity occur?
intracellularly
What is the difference between T4 and T8 cells?
- T4 are helper cells
- T8 are cytotoxic cells
What are the subtypes of adaptive immunity and what lymphocytes do they involve?
Humoral immunity (B cells) cell-mediated immunity (T cells)
What types of infections is the humoral immune system good for?
Bacterial infections
extra-cellular infections
What types of infections is the cell-mediated immune system good for?
viral/fungal infections
intra-cellular infections
What is antigenic drift and shift?
Drift - slow changes to virus strain
Shift - sudden change in virus strain
What is the principle of giving passive immunity?
Giving someone premade antibodies/immunoglobulins to fight infection
What is the principle of giving active immunity?
Giving someone mild version of antigen, so the body will produce their own antibodies/immunoglobulins against it
What is an advantage of giving passive immunity?
Immediate effect
What is a disadvantage of giving passive immunity?
body may cause immune reaction to the injected foreign antibodies (serum sickness or arthus reaction)
What are the types of vaccine available?
live attenuated
killed
toxoid
subunit
What is a subunit vaccine and what are available examples?
particles from virus or resembling virus
- HPV vaccine
- Hep B surface antigen vaccine
How is an attenuated vaccine made?
Grown in animals so that when it’s injected back into humans it doesn’t thrive as well
What is a toxoid vaccine?
It’s a toxin that has been treated with formalin so it’s not toxic anymore
What are some contraindications to vaccines?
immunocompromised
fever
pregnancy (no live vaccine)
allergy
What is the concept of herd immunity?
individuals who cannot be vaccinated will benefit from the immunity of others around them
In which vaccine are T cells essential?
BCG (anti TB)
What are checkpoint inhibitors and why could they be targeted in cancer?
proteins that stop T cells from attacking other cells
they could be used for the body to elicit an immune response against cancer cells
What is POCT and what is it useful for? What are examples of POCT?
Point of care Testing
Useful for immediate test results (eg glucose, blood gas, urine tests)
What is the disadvantage of POCT?
Not always accurate
What are some of the common methods of identification which can help to determine the identity of a body?
Sex Age Height Medical/dental records Tattoos/scars Finger prints DNA Hair/eye colour, facial hair
What is rigor mortis and when does it occur?
Stiffening of muscles after death 5-12 hours after death
What is hypostasis and what causes it?
Areas of pallor with bruising around them
Caused after death by blood pooling with gravity
What is saponification and what is it caused by?
Adipoceres formation by fat cells invading tissue after death
What are the different types of decomposition?
Putrefaction Saponification Mummification Maceration Skeletonisation
What can putrefaction be caused by?
Bacterial infestation
Autolysis
What is a general rule of thumb which can be used to estimate time of death?
Temperature drop - 1C per hour
