Infection S2 (Done) Flashcards
What are the mechanisms by which a human may become infected with pathogenic organisms?
For each mechanism, include an example of how it might occur or an example of an infection that occurs due to this mechanism
Contiguous:
Anus to vagina spread of faeces (UTI)
Peritonitis secondary to burst appendix
Inoculation:
Bite/Stabbing (Tetanus, Rabies)
Haematogenous:
Vascular transmission of bacteria from mouth to heart (Endocarditis)
Ingestion:
Faeco-oral transmission (Food poisoning)
Inhalation:
Aerosols (TB, Chickenpox)
Vector:
Insects (Mosquitos and Malaria)
Vertical transmission:
In utero or during birth (Syphilis, HIV)
What are the major patient factors that influence suseptibility to infection?
Person:
Age
Gender
Physiological state
Pathological state
Social factors
Time:
Calendar time
Relative time
Place:
Current
Recent
Give some ways in which age can affect infection
Early life:
0-3 months protection provided by mother’s antibodies
3mnths to 3yrs High risk
Sexual activity:
Rise in STDs after mid teens until 30s
Old age:
Infections steadily rise post 50
Give examples of how physiological state can affect infection
Puberty, Pregnancy and menstrual cycle affect pH of vagina, raising suseptibility to vaginal infection
During pregnancy it is theorised that that colonic microbiota can affect gestational diabetes development
Give examples of how pathological state can affect infection
HIV caused immunocompromised patients to pick up additional infections
Cancer, bone marrow transplant and haemotology patients immunocompromised, can cause physiological aspergillus colonies becoming pathological
Give an example of how social factors may affect infection
Young school children can pick up infections such as chickenpox from classmates (association with specific groups can increase risk of infection)
How does calendar time affect infection?
Certain infections more likely in certain seasons
Eg. Norovirus and influenza spread during winter
What is meant by ‘relative time’ in regards to infection and how does it affect infection?
Refers mainly to differences in time scales of infections
E.g. Length of incubation period if known can guide how long we quarantine possible cases of severe pathogenic infection
How does the patient’s recent travel and current location affect our management of infection?
Both can guide the physican to possible micro-organisms that are causing infection based on where those micro-organisms are found
What are the two major modes of host damage caused by infection?
Direct damage from toxins
OR
Interaction with host defenses leading to direct damage or inflammation (which in turn causes damage)
What are the 3 things that must be done to make a diagnoses in a patiet with suspected infection?
History taking
Examinations
Investigations
What are the differences between specific and supportive treatment of infection?
Give specific examples
Supportive:
Focused on symptom relief and restoring normal physiological state
E.g. Fluid replacement
Specific:
Targeted treatments at specific micro-organisms or body systems
E.g.
Antimicrobials
Surgery (drainage, debridement, dead space removal)
Where does infection prevention occur and why is it important?
Occurs in hiospital and community
Important because it prevents transmission to other patients, healthcare workers etc.
Explain the different outcomes of infection
Cure:
Infection completely removed
Chronic:
Chronic infection can persist
Can cause disability
Death
What are the different broad types of anti-microbial?
Antibacterial
Antifungal
Antivarial
Antiprotozoal
What are the different ways of classifying antibacterial agents?
Bacteriocidal or bacteriostatic
Broad or narrow spectrum
Target site (mechanism of action)
Chemical structure (antibacterial class)
What ae the ideal features of an antimicrobial agent?
Selectively toxic
Few adverse effects
Reach site of infection
Both oral and IV formulations
Long half life (infrequent dosing)
No interference with other drugs
What are the 4 major targets of antibacterial action?
Give examples of classes of each
Cell wall synthesis
Beta lactams
Glycopeptides
Protein synthesis
Tetracyclines
Aminoglycosides
Macrolides
Cell membrane function
Polymixin
Nucleic acid synthesis
Quinolones
Rifampicins
Give the two mechanisms of inhibition of bacterial cell wall synthesis and an example of an antibacterial that utilises this method
Penicillin:
Inhibits penicillin binding protein, which creates crosslinks between cell wall proteoglycans
Vancomycin:
Stops cell wall cross linking enzyme from binding to preoteoglycans and cross linking them
What is the mechanism of antibacterial action of fluoroquinolones?
Binds to 2 nuclear enzymes, DNA gyrase and Topoisomerase IV (one or both depending on organism) to prevent them from coiling bacterial DNA, thereby limiting space available for further DNA synthesis
Outline the 3 mechanisms of bacterial resistance
Drug inactivating enzymes:
B-lactams, aminoglycoside enzymes
Altered Target:
Target has lowered affinity for antibacterials thereby decreasing effectiveness (E.g. Meticillin resistance in MRSA)
Altered Uptake:
Decreased permeability
Increased efflux
What are two methods by which an organism might gain antibiotic resistance?
Chromosomal gene transfer
Horizontal gene transfer
Outline the 3 methods of Horizontal gene transfer
Conjugation
Transfer of bacterial DNA (Plasmid or transposon) via direct cell to cell contact through a bridge
Transduction
Delivery of DNA into a bacterium through a viral vector (bacteriophage) (normally from another bacterium)
Transformation
Uptake of exogenous DNA by a bacterial cell through the cell membrane from its surroundings
Outline the Disk sensitivity test for antibiotics (aka. Agar diffusion test)
Antibiotic impregnated wafers are places on an agar plate where bacteria have been placed. The disk is then left to incubate
If an antibiotic prevents growth or kills bacteria a circle will be left around the wafer where no bacteria have been grown (zone of inhibition)
The larger the circle indicates relative effectiveness of different antibiotics
Describe minimum inhibitory concentration tests
Bacteria are grown in a series of solutions or plated on agar
Antibiotic is added at varying known concentrations
The lowest concentration found to inhibit bacteria growth determines the minimum inhibitory concentration
Controls can be used, one sample is free from antibiotic administration, the other free from bacteria
What are the major categories of beta-lactam antibiotics?
Penicillins
Cephalosporins
Carbapenems
Monobactams
What are the Penicillins we must know?
Benzylpenicillin
amoxicillin
flucloxacillin
Co-amoxiclav
Tazocin (piperacillin + tazobactam)
Give a short description of Carbapenems (3 points)
Give an example of a carbapenem
Carbapenems:
Very broad spectrum (aerobes and anaerobes)
Active against **most **G-negs
Generally safe in penicillin allergy if anaphylaxis is not a risk
E.g. Meropenem
What is penicillin mainly active against?
Streptococci
What is amoxicillin mainly effective against?
Streptococci and some gram-neg bacteria
What is flucloxacillin mainly effective against?
Streptococci and staphylococci
What is Co-amoxiclav and what is effective against?
Co-amoxiclav is a mix of antibiotic amoxicillin and Beta-lactamase enzyme inhibitor clavulanic acid
Effective against Strep, staphylococci anaerobes and Gram negative bacteria
What is tazocin and what is it effective against?
A mix of antibiotic piperacillin and beta-lactamase enzyme inhibitor tazobactam
Effective against Strep and staphylococci and anaerobes
Highly effective against Gram negative bacteria including pseudomonas spp
Give a short description of cephalosporin drugs (3 points)
Give an example and why that drug is useful in treatment of meningitis
Cephalosporins:
Multiple generations with increasing effectiveness against G-neg and often reduced G-pos activity.
Broad spectrum
No anaerobe activity
E.g. Cetriaxone:
Good activity in the CSF
Give a list of antibacterial drugs types we need to know about that are not Beta-lactams
Glycopeptides
Tetracyclines
Aminoglycosides
Macrolides
Quinolones
Sulphonamides
Give an example of a Glyocopeptide drug
Describe it (5 points)
Hint: Activity? Resistance? Administration?
Vancomycin
Active against most Gpos (not Gnegs)
Some enterococci are resistant (VRE)
Resistance in staphylococci is rare
Not absorbed orally (Oral use for C.difficile only)
Therapeutic drug monitoring required (narrow therapeutic window
Give a description of Tetracyclines (4 points)
Give an example
Oral only
Broad spectrum (specific use in penicillin allergy, usually for Gpos)
Active against atypical pathogens in pneumonia, chlamydia, some protozoa
Shouldn’t be given to children under 12
E.g. Doxycycline
Give a description of Aminoglycoside antibiotics (5 points)
Give an example
Profound activity against Gnegs
Good activity in blood/urine
Potentially nephrotic/ototoxic
Therapeutic drug monitoring required
Generally reserved for sever Gneg sepsis
E.g. Gentamicin
Give a short description of Macrolide antibiotics (3 points)
Well distributed through body (even intercellularly)
Alternative to penicillin for mild Gpos infections
Also active against atypical respiratory pathogens
E.g. Erythromycin
Give a short description of Quinolone antibiotics (4 points)
Give an example
Inhibit DNA gyrase
Very active against Gnegs
Also active against atypical pathogens
Increasing resistance and risk of C.diff infection
E.g. Ciprofloxacin
Give the method of action of sophonamides and trimethoprim
Inhibitors of folic acid synthesis
What is trimethoprim used to treat in the UK?
UTI
Give a description of the drug Co-trimoxazole
Combination of Trimethoprim and sulphamethoxazole
Used to treat Pneumocystis pneumonia
Has activity against MRSA
Give two groups of antifungal drugs
Azoles
Polyenes
Give a short description of Azole drugs
Give an example and it’s specific use
Active against yeasts, less effective against molds
Inhibit cell memebrane synthesis
Fluconazole used to treat Candida spp
Give a short description of Polyene drugs
Give 2 examples and their specific uses
Inhibits cell membrane function
Nystatin:
Topical treatment of Candida spp
Amphotericin:
IV treatment of systemic fungal infections (E.g. Aspergillus)
Give 2 examples of Antiviral drugs and their uses
Aciclovir:
When phosphorylated inhibits viral DNA polymerase
Treats Herpes Simplex (genital herpes, encephalitis)
Treats Varicella zoster (Chickenpox and shingles)
Oseltamivir (Tamiflu):
Inhibits viral neuraminidase
Influenza A and B
Give a short description of metronidazole
Antibacterial and antiprotozoal agent
Active against anaerobic bacteria
Active against protozoa:
**- **Amoebae (dysentery and systemic)
**- **Giardia (Diarrhoea)
**- **Trichomonas (Vaginitis
