Community and Hospital Acquired Bacterial Infection Flashcards
what are the examples of virulence factors?
- flagella (movement and attachment)
- pili (adherence)
- capsule (protect against phagocytosis)
- endospores (metabolically dormant forms of bacteria.)
- biofilms (aggregates of bacteria embedded in polysaccharide-matrix resistant)
- secretion systems
- exotoxins
- endotoxins
examples of bacteria using capsule
Streptococcus pneumoniae.
examples of bacteria using endospores
Bacillus sp. And Clostridium sp.
examples of bacteria using biofilms
Pseudomonas aeruginosa and Staphylococcus epidermidis
what are the exotoxins?
- neurotoxins (act on nerves or motor-end-plates)
- enterotoxins (act on GIT)
- pyrogenic exotoxins (stimulate release of cytokines)
- tissue invasive exotoxins (enzymes that allow bacteria to tunnel through tissue)
- miscellaneous exotoxins (specific to certain bacteria, function not well understood)
examples of neurotoxins
Tetanus
Botulinum toxins.
what are the two effects of enterotoxins? what bacteria cause them?
Infectious diarrhoea
– Vibrio cholera, E. coli, Shigella dysenteriae, Campylobacter jejuni.
Food poisoning
– Bacillus cereus, Staph. aureus.
examples of bacteria that release pyrogenic exotoxins
Staph. aureus
Strep. pyogenes.
examples of bacteria that release tissue invasive exotoxins
Staph. aureus,
Strep. pyogenes
Clostridium perfringens.
examples of bacteria that use specific exotoxins
Bacillus anthracis
Corynebacterium diphtheriae.
where are endotoxins found?
only GRAM NEG
Lipid A domain of LPS , only from gram -ve bacteria, shed constantly by living bacteria
it is not a protein, but a lipid
what effect does treating someone with a gram -ve infection with Abx have?
make them worse:
Bacteria lyses –> release large quantities of LPS/endotoxins –> septic shock.
what is an outbreak?
a sudden increase in the incidence of a disease in a particular place at a particular time.
what is the triad of Haemolytic-uraemic syndrome? what caused this?
- triad of acute renal failure, haemolytic anaemia and thrombocytopenia
- caused by entero-aggregative E. coli (EAEC) using the Shiga-Toxin that is acquired from another strain EHEC
- Reservoir is usually in cattle.
- result of the fusion of Enterohaemorrhagic E. coli and Enteroaggregative E. coli.
what is a possible epidemic case?
Any person that has developed the symptoms AND has met a laboratory criteria (e.g. isolation of agent).
what is a probable epidemic case?
Any person that has met the case criteria AND has been in epidemic country, consumed possibly contaminated food, been in close contact with a confirmed epidemic case.
what is a confirmed epidemic case?
Any person meeting criteria for a possible case AND has had strain isolated.
how can isolates in an outbreak be screened?
by multiplex PCR, can be done on stool samples, determine if the strain is the outbreak strain or not
what does PCR reveal about the strains EHEC and EAEC?
- EHEC : prophage encoding the Shiga toxin
- EAEC:
1) pAA-type plasmids - contain aggregative adhesion fimbrial operon.
2) ESBL plasmids – gene encoding for extended-spectrum beta-lactamases.
what are the components of the Shiga Toxin?
o StxA is the enzymatic portion
– cleaves RNA so inhibits protein synthesis and might affect gut commensal bacteria
o StxB is the pentamer that binds to host cell receptors.
what encode the Shiga toxins? enables horizontal transfer
bacteriophages and contribute to horizontal gene transfer meaning they can be given to other bacteria types in phages.
what is the virulence factor of EAEC? what effect does this factor have?
Aggregative Adherence Fimbriae (AAF):
o AFF required for adhesion to enterocytes and stimulates IL-8 response.
o AFF also allows a biofilm formation.
how is an outbreak effectively identified?
o Surveillance.
o Good and timely reporting systems.
o PCR.
examples of respiratory tract infections and the bacteria that cause them
1) Legionnaire’s disease – Legionella pneumophilia (gram-ve)
- inhalation of aerosols
2) Tuberculosis – Mycobacterium tuberculosis
- 77% success of first treatment and 54% success of second treatment
- cell wall and slow growth makes it resistant to antimicrobials
what is the virulence factor of Legionella pneumophilia?
type IV secretion systems – legionella replicates in legionella containing vacuoles (LCVs) inside cells.
what is the virulence factor of Mycobacterium tuberculosis?
has an extra lipid layer & can enter a dormant state for reactivation.
examples of STIs
1) Chlamydia
– Chlamydia trachomatis (gram-ve obligate intracellular parasite)
- causes blindness outside of Europe
- not cultured outside host cell
2) Gonorrhoea
– Neisseria gonorrhoeae (gram-ve)
- Urogenital tract infection infecting non-ciliated epithelial cells.
what are the virulence factors of Chlamydia trachomatis and Neisseria gonorrhoeae?
pili, antigenic variation mechanisms
examples of food and waterborne diseases?
1) Campylobacteriosis – Campylobacter sp. (mostly C. jejuni - GI disease, high risk in kids - uncooked poultry - sporadic cases, no outbreaks
2) Salmonellosis – Salmonella sp. (gram-ve) - GI disease - uncooked poultry - can cause outbreaks
3) Cholera
– Vibrio cholera (gram-ve)
- acure severe diarrhoea
4) Listeriosis
– Listeria monocytogenes (gram+ve)
- the elderly, immunocompromised, and pregnant at risk
- capable of crossing tight barrier like the materno-foetal barrier
what are the virulence factors of Campylobacter sp.?
T4 secretion systems,
adhesion, invasion factors, flagella motility, toxins
what is the virulence factor in Salmonella sp?
T3 secretion systems encoded on pathogenicity islands
what is the virulence factor in vibrio cholera?
T4 fimbria, cholera toxin (increased cAMP –> opening of Cl- channels and expulsion of water from cells), carried on phages.
what is the virulence factor of listeria monocytogenes?
actin-based cell motility
ActA and VASP
examples of emerging and vector borne disease
1) Plague
– Yersina pestis (gram-ve).
2) Q fever
– Coxiella burnetti (gram-ve).
3) Smallpox (A VIRUS) – eradicated.
examples of vaccine preventable disease and the bacteria that cause them?
1) Diphtheria
– Clostridium diphtheriae (gram+ve).
2) Invasive HA disease
– Haemophilus influenzae (gram-ve).
3) Invasive meningococcal disease
– Neisseria meningitides (gram-ve).
4) Invasive pneumococcal disease
– Streptococcus pneumoniae (gram+ve)
5) Pertussis
– Bordetella pertussis (gram-ve).
6) Tetanus
– Clostridium tetani (gram+ve).
what are antimicrobials?
interferes with growth & reproduction of a ‘microbe’.
what are antibacterials?
describes agents that reduce or eliminate harmful bacteria
antibiotics are a type of antimicrobial
what are the most frequent HAIs?
surgical site infections, UTIs, pneumonia, bacteraemias, GI infections
what is the burden of HAIs?
- 3.2m a year get an HAI, 37,000 of those die of them.
- increases the length of stay
- HAIs cost an ~£1b extra a year.
what are the 3 categories of causes of HAIs?
- interventions
- dissemination
- concentration
what interventions cause HAIs?
- catheters
- intubation
- chemotherapy
- prosthetics
- lines
- prophylactic antibiotics
- inappropriate prescribing.
how is dissemination a cause of HAIs?
carriers of the infection from person to person e.g. from staff
how is concentration a cause of HAIs?
a high number of sick people in one place
how is a HAI defined?
an infection acquired in a hospital setting after 48 hours from admission
what are the “ESC(/K)APE” pathogens that cause HAIs?
o Enterococcus faecium (+ve) - Vancomycin resistant. o Staph. aureus (+ve) - MRSA. o Klebsiella pneumoniae [K] o Acinetobacter baumanii (-ve) - Highly drug resistant. o Pseudomonas aeruginosa (-ve) - MDR o Enterobacteriaceae (-ve) - MDR – all the sub-types.
- Pa thogenic e coli - Enterobacter species [ Clostridium difficile(+ve) - Can infect due to previous AB treatment]
what is pathogenic E.coli resistant to? how?
resistant to cephalosporins:
due to the presence of the ESBL (Extended Spectrum Beta Lactamase)
gene that produces the lactamase cleaves the cephalosporin to inactivate it
what are cephalosporins? what is their mechanism of action?
class of beta-lactams: that inhibit peptidoglycan synthesis by inhibiting the activity of penicillin binding protein (PBPs)
what other antibiotic apart from cephalosporins target PBPs and therefore pathogenic e.coli?
carbapenems (beta lactam)
- this differs in structure and is cleaved by a different enzyme: carbapenemase (not ESBL)
pathogenic E.coli is still sensitive to carbapenems
however K.pneumonia is resistant to carbapenems
what bacteria is the most common cause of community and HAI UTIs? what can it also cause?
pathogenic e.coli
also the most frequent cause of bacteraemia by g-ve bacteria
which bacteria is resistant to carbapenems?
Klebsiella pneumoniae
CRKP – Carbapenem-Resistant Klebsiella pneumoniae
what does Klebsiella pneumoniae cause and who are at risk?
- UTIs and respiratory tract infections.
- immunocompromised.
what is staphylococcus aureus resistant to? how is this resistance mediated?
methicillin
- MRSA expresses a different PBP (PBP2A) gene so bypasses inhibition of peptidoglycan synthesis and therefore survives as the beta lactam methicillin can’t bind
summary: PBP2A has a low affinity to methicillin so Staph aureus can still function
who is at risk of Pseudomonas aeruginosa?
immunocompromised
- resistant to several antimicrobials
which bacteria is resistant to vancomycin? how is this mediated?
enterococcus faecium
- VRE synthesises a different peptidoglycan precursor that is not targeted by the vancomycin.
vancoymin is a glycopeptide that will bind to the pentapeptide used in peptidoglycan synthesis
what effect does drug resistance having on treatment options?
Clinicians are forced to use older, previously discarded drugs (e.g. colistin) that are associated with higher toxicities and for which there is less data on guides in dosage and duration of therapy.
gram negative antibiotic resistance infections in the UK
- pseudominas aeriginosa
e. g. UTI, HA pneumonia - ESBL
e. g. ecoli - Acinetobacter baumanii
gram positive antibiotic resistant infections in the uK
- MRSA
- enterococcus faecium
