Microbiology Flashcards
why is chocolate agar useful
easier to grow organism not easily grown
why is MacConkey agar useful
contains bile salts = inhibit gram positive growth
stains lactose = lactose fermenters pink, nonlactose fermenters white
why is CLED agar useful
differentiate microorganisms in urine
classify lacotse/nonlactose fermenters in gram negative bacilli
why is gonoccocus agar useful
promote growth of neisseria gonorrhoea and other neisserias
contains antibiotics/antifungals to inhibit growth of other organisms
why is XLD agar useful
very selective isolates salmonella red at pH 7.4 shigella/salmonella = red other gut bacteria = yellow
why is sabouraud agar useful
grows funghi inhibits bacteria
what is a pathogen
organism capable of causing disease
what is a commensal
organism which colonises the host but normally causes no disease
what is an opportunistic pathogen
microbe that only causes disease if host defence are compromised
what is pathogenicity/virulence
degree to which a given organism is pathogenic/damage causing
virulence factor = product or strategy which contributes to virulence
what is an asymptomatic carriage
when a pathogen is carried harmlessly at a tissue site where it causes no disease
what is a gram stain
method to determine bacteria type between gram positive and gram negative
what is a capsule
peptigoglycan layer that surrounds some bacteria = allows it to hide from immune system and is antiphagocytic
what are funghi
eurokaryotic cells with chitinous cell walls
heterotrophic and generate spores
name 3 common fungal infection
nappy rash
vulvovaginal candidiasis
athletes foot
what are the 3 common life threatening fungal infections
candida line infections
intra-abdominal infections
fungal asthma
infectivity definition
ability to become established in the host (adherence and immune defence)
invasiveness definition
ability to penetrate mucosal surfaces to reach sterile sites
what is chronic carrier state
steady state between virus replication in host cells and virus death through host responses
what is an endotoxin
component of outer membrane of bacterium from gram negative bacteria ONLY = LPS based
what is an exotoxin
secreted proteins of gram negative and gram positive bacteria which causes harm to the host = protein based
how does bacteria directly cause harm
destroy phagocytes/cells
endo/exooxins
how does bacteria indirectly cause harm
inflammation
immune pathology
diorrhoea
name a gram positive coagulase positive bacteria
staphylococcus aureus
name a gram positive catalase positive coagulase negative bacteria
staphylococcus epidermidis
staphylococcus saproplyticus
what is the difference between staphylococcus and streptococcus
staphylococcus = catalase positive streptococcus = catalase negative
describe alpha haemolytic streptococcus
greening on agar
viridans group strep
how to determine if bacteria is strep pneumoniae
optochonin test
if sensitive to optochonin disc = positive
describe beta haemolytic streptococcus
clearing on agar
different groups A,B,C, G
what is lancefield grouping
bacteria have carb cell surface antigens e.g. A, B etc
antiserum for each group added to a suspension of bacteria
agglutination = recognition
give examples of each group of streptococcus
A = tonsilitis B = sepsis, meningitis C = UTI
what are the features of enterobacter
rods with flagella
facultatively anaerobic
what does the outer layer of gram negative bacteria contain
lipid A = toxic
core antigens
somatic antigens
name 5 important enterobacter
escherichia coli shigella salmonella proteus mirabilis klebsiella pneumoniae
how do allylamines work
= fungicidal
inhibit biosynthesis pathway of ergosterol metabolism = affect membrane = kills fungus
high first pass metabolism
how do azoles work
= fungistatic
inhibit ergosterol synthesis
used for more invasive fungus
high doses = hepatitis
how do polyenes work
= fungicidal
affect activity of membrane bound proteins = disrupt insertion of molecules into membrane
cause nephrotoxicity
what are the 4 main features of antifungals
- poor bioavailability
- poor penetration to difficult areas
- have few drug interactions
- limited drug toxicity
name 2 gram negative bacillus that ferments lactose
E.coli
klebsiella
name 2 gram negative bacillus that does not ferment lactose
Shigella
salmonella
what are the sterile sites in the body
blood CSF lower respiratory tract pleural fluid peritoneal cavity joints urinary tract
which sites would you be able to culture normal flora
mouth skin vagina urethra large intestine
the HIV envelope contains
RNA
capsid
reverse transcriptase
describe antimicrobial resistance in MRSA
s.aureus is resistant to vancomycin
what are the clinical signs of sepsis
temp = above 38.3 or below 36 heart rate above 90 WBC above 12 hypoxia low BP
definition of antibiotic
molecule that binds to bacteria target site and affects reactions critical to bacterial survival
what are beta lactams and how do they work
penicillins, cephalosporins, carbapenems
bind to peptidoglycan PBP on gram positive bacteria = inhibit cell wall synthesis = bactericidal
how does metronizadole and rifampicin work on bacteria
interfere with nucleic acid synthesis and function
how do flouroquinolones work on bacteria
inhibit DNA gyrase
how do sulphonamides and trimethoprim work on bacteria
inhibit folate synthesis and carbon metabolism
how do macrolides and tetracyclines work
inhibit 30S ribosome = inhibit protein metabolism
what does is mean if an antibiotic is bacteriostatic
inhibits bacterial growth by inhibiting protein synth, DNA replication + metabolism = reduce endotoxin production
= will eventually kill 90%
minimum inhibitory concentration required MIC
what does bactericidal mean
inhibit cell wall synthesis = kills bacteria = good for hard to treat infections
minimum bactericidal conc required MBC
what should the ratio of MIC to MBC be
MIC:MBC > 4
why is the concentration of antibiotic important
drug must occupy adequate number of binding sites
why is the time of action of an antibiotic important?
drug must stay at binding site for long enough time to interfere with bacteria
what is conc dependent killing
depends on height of conc above MIC = aminoglycosides have high conc dependent killing
what is time dependent killing
depends on time that conc stays above MIC = beta lactams, macrolides have high time dependent killing
what are cephalosporins used for
= beta lactams
used in penicillin allergies
resistant bugs
hard to reach places e.g. meningitis
what antibiotics are used for gram positive bacteria
beta lactams
what is vancomycin used for
gram positive bacteria
MRSA
penicillin allergy
what are macrolides used for
e.g. clarithromycin, erythromycin
gram +ve bacteria
atypical pneumonias
what are lincosamides used for
e.g. clindamycin
gram +ve
anaerobic cellulitis
what are tetracyclines used for
e.g. doxycycline
cellulitis
chest infection
penicillin allergy
what is ciprofloxacin used for
gram -ve specific
UTI
gallbladder/abdominal infections
what is trimethoprim used for
gram -ve UTI
what is nitrofurantoin used for
gram -ve UTI
what is the significance of beta lactamases
= enzymes produced by bacteria that provide resistance to beta lactam antibiotics
what are beta lactamase inhibitors
class of medicine that block the activity of beta lactamases = prevent degradation of beta lactams
what antibiotics are protected against beta lactamases
co-amoxiclav
cephalexin
cefuroxime
where can nematodes be found in the body
= roundworms
intestinal
under skin
tissue
where can trematodes be found in the body
= flatworms
intestinal
blood
liver
what is the pre-patent period (PPP)
interval between infection and presence of eggs in stool
what is the largest and most common worm
ascaris lumbricoides
what are the symptoms of loaffler’s syndrome
= larvae in lungs cough wheeze fever eosinophilia positive chest XR
what conditions can E.coli be responsible for
wound infections UTI gastroenteritis traveller's diarrhoea bactereamia
describe entero-toxigenic ecoli ETEC
virulence factors = toxin and pili/fimbriae
act in small intestine = watery diarrhoea in tourists
describe entero-pathogenic ecoli EPEC
virulence factor = pedestal formation (lumps on epithelium)
acts in small intestine = watery diarrhoea less than 1 year
describe entero-haemorrhagic ecoli EHEC
virulence factor = pedestal formation and shiga like toxin
acts in large intestine = bloody diarrhoea and HUS = food borne
describe entero-invasive ecoli EIEC
virulence factors = invasins leading to inflammation/ulceration
acts in large intestine = bloody diarrhoea/dysentry (in children)
describe entero-aggregative ecoli EAEC
virulence factors = pili and cytotoxin = shorter villi + mucus production
acts in large intestine = chronic diarrhoea in children
describe uro-pathogenic ecoli UPEC
virulence factors = haemolysin = inflammation
acts in urinary tract = UTI in women
describe the pathogenicity of entero-toxigenic ecoli
- toxins cause G protein modification = locking in ON state
2. increased cAMP production = loss of Cl and H2O§
describe the pathogenicity of pedestal formation and which forms of ecoli does this occur with
- pathogen adheres to microvilli with pathogenic pilli
- T3SS acts like syringe = disrupts tight junctions and ion activity (diarrhoea)
- microvilli reform into pedestal holding pathogen
= in entero-pathogenic and entero-haemorrhagic
which bacteria are obligate intracellular
rickettsia
chlamydia
coxellia
which bacteria have no cell wall
mycoplasma pneumoniae
which bacteria has filament growth
actinomyces
nocardia
streptomyces
which bacteria are spirochaetes
leptospira
treponema
borrelia
describe the growth cycle of chlamydia
elementary bodies = infectious stage enters cell inhibits phagosome function become reticulate bodies
reticulate bodies = not infectious stage intracellular replication convert back to EB cell lysis and EB release
name the 3 most important types of chlamydia
C.trachomatis = most common STD, conjunctivitis C.pneumoniae = atypical CAP pathogen C.psittaci = severe pneumonia
name 6 typical bacteria that commonly cause CAP
strep. pneumoniae hameophilus influenzae staph. aureus group A strep moraxella catarrhalis aerobic gram negative bacteria e/g/ klebsiella/e.coli
name 3 atypical bacteria that commonly cause CAP
legionella
mycoplasma pneumoniae
chlamydia pneumoniae
name 4 viruses that commonly cause CAP
influenza A and B
parainfluenza virus
rhinovirus
adenovirus
describe a spirochete bacterium
has endoflagellum between outer membrane and peptodoglycan = allows corkscrew movement
describe borrelia burgdorferi
= lyme disease
tick-borne
cause rash/flu-like symptoms
spreads through extracellular matrix to bloodstream and other organs
descrive leptospira interrogans
spread from animal urine to human through mucous membrane
cause flu-like symptoms - Weil’s disease in severe cases
describe treponema pallidum
= syphilis
primary stage = localised infection v. infectious
secondary stage = systemic infection lymph nodes, skin, joints, vessels
tertiary stage = granuloma in soft tissue = cardio/neurosyphilis
treat with flucloxacillin
name 3 important mycobacteria
M. tuberculosis = TB
M. leprae = leorosy
M. avium complex (MAC) = infection in AIDS and chronic lung disease
what are the 4 types of protozoa and give an example for each
flagellates - trypanosoma (sleeping sickness), trichromonas vaginalis (STI), GIARDIA LAMBLIA
sporozoans - plasmodium, toxoplasma gondii (toxoplasmosis)
amoebae - entamoeba histolytica (amoebic dysentery)
ciliates - balatidium coli (colonic ulceration)
what is significant to remember about trichomonas vaginalis
dont confuse it with chlamydia
name the 4 disease causing plasmodium
p. falciparum
p. ovale
p. vivax
p. malariae
what is the vector for malaria
female anopheles mosquito around stagnant water = 3-4 week infected lifecycle
what is the hypnozoite stage in the malaria life cycle
after schizonts rupture in hepatocyte releasing merozoites into the bloodstream = p.ovale and p.vivax can lie dormant in the liver and reactivate
what are most protozoa treated with
metronizadole
what is giardia lamblia
parasitic microorganism that infects the small intestine
causes giardiasis = diarrhoea/bloating/cramps
foecal oral spread
travel associated
stool microscopy diagnosis
metronizadole treatment
describe the process of a gram stain
- fixation
- crystal violet
- iodine
- decolorisation using ethanol
- application of safranin as counter stain
- gram positive bacteria not decolourised by ethanol = purple
gram negative is decolourised so retain pink of safranin counterstain
describe zeihl-neelson staining for mycobacteria
- cells stained using carbol fuchsin = red
- washing with acid alcohol = removes carbol fuschin from background cells = mycobacterium remain red because it is acid-fast (holds fast to the dye)
- slide stained with methylene blue
- mycobacterium stained purple = identified
need 10,000 acid fast bacilli per ml
name 3 methods of culturing mycobacteria
- soft culture
- liquid culture
- nucleic acid detection
what are cytopathic effects
viruses have to be grown in cells so cannot be cultured
CPE = effects observed when viruses are cultured inside living cells
what is serology
study/detection of antibodies in serum
mainly IgM/IgG
IgM appears within a week of infection and remains in blood up to 12 weeks
IgG appears later but remains within blood for years for immunity
what swabs are used for bacterial and viral infection
green = viral black/charcoal = bacterial
how do mycobacteria cause disease in the body
- mycobacteria engulfed by macrophage = phagolysosome = APC
- CD4 T cells recognise APC = interferons and interleukins stimulate macrophage activity
granuloma formation
describe granuloma formation as part of mycobacterial disease
- highly stimulated macrophages = become epithelioid cells = fuse to become Langhans giant cells = fibroblasts laid down around granuloma
- central tissue necrosis = caseating necrosis = cavity in tissues e.g. in the lungs in TB
describe the immunology of tuberculoid leprosy
Th1 response (IFN+TNF) = tissue hypersensitivity and granulomas = tissue damage
describe the immunology of lepromatous leprosy
Th2 response (IL 4,5,10) = lesions full of bacilli and NO granuloma = skin lesions
what 4 drugs are used to treat TB
RIPE rifampicin isoniazid pyrazinamide ethambutol
name 3 viruses that cause direct host cell destruction
hip!
HIV
influenza
polio
name 2 viruses that cause modification of host cell function/structure
HIV
rotavirus
name 3 viruses that cause an over-reactive host response
Hep B
Hep C
HIV
name a virus that causes cell proliferation and immortalisation
HPV
describe 3 ways viruses evade host cell defence
persistence (measles)
variability (flu)
host defence modulation (all viruses)
describe a rotavirus infection
- acid resistant rotavirus invades jejunal epithelial cells = cause villi and microvilli to atrophy
- reduced SA and enzyme conc = no sugar absorption = hyperosmosis = diarrhoea
describe a Hepatitis B infection
- HBV infection causes antibody and cytotoxic T lymphocyte response = hepatocyte destruction = liver damage
- steady state reached between hepatocyte destruction and viral replication = no spread
describe cervical carcinoma development
- HPV infects superbasal layer of genital tract = replicates as mucosal cells move up
- HPV and host cell genome integration = p53 suppression = carcinogenesis
what is wuncheria bancroftii
human parasitic worm = filariworm
causes lymphatic filariasis = lymphoedema
what disease do schistosome flatworms cause
schistosomiasis which can cause bladder cancer
what disease is associated with the hookworm
iron deficient anaemia
describe the humoural response to viruses
IgA and IgM block viral binding and aid agglutination
complement and GB antibody = opsonisation and cell lysis
describe the cell mediated response to viruses
interferon prevents infection of non-infected cells
cytotoxic T lymphocytes directly kill infected cells and activate antibody dependent cell destruction
which viruses virulence factors include direct cell cytotoxicity
flu = respiratory epithelium shingles = skin cells HIV = T cells
which viruses show antigenic variation
rhinovirus
influenza
HIV
which viruses cause immune suppression
MMR
EBV
HIV
CMV
name 3 ways protozoa evade host defence
surface antigen variability
intracellular phase
shed outer coat
describe a delayed type hypersensitivity reaction (type 4) for example in TB
- intracellular infection (TB) = Tdth cells stimulated = influx of inflammatory cells
- second contact = Tcth secretes IFN TNF IL = macrophage recruitment
- prolongued DTH = granuloma formation = lytic enzymes cause tissue damage
name 3 ways bacteria can resist phagocytosis
polysaccharide capsule
M protein
phagolysosome escape
what is an API strip
card with self contained series of biochemical reaction tubes which identify bacteria based on metabolic and enzymatic properties
what is B.fragilis
anareobic gram negative bacteria lives naturally in the colon
is usually commensal but can cause infection after surgery/trauma or if displaced into bloodstream
what is a Mz disc
contains metronidazole
confirms presence of anaerobic bacteria if prevents bacteria growth
what number of bacteria cultured indicate significant bacteriuria
10^5 bacteria/ml
what number of bacteria cultured suggests doubtful significance of bacteriuria
between 10^4-10^5 bacteria/ml
(simply) how does HIV cause immune dysfunction
- CD4 cell death =
- direct cytotoxicity
- impaired homeostasis
- premature apoptosis
- reduce T cell production - CD8 CTL increased activation but decreased cytotoxic function
- B cells increased activation but antibodies non specific
- decreased function of
- natural killer cells
- macrophages
- neutrophils
describe the progression of an HIV infection
- acute primary infection = low then high CD4 count
- asymptomatic phase = progressive loss of CD4
- early symptomatic phase = manifestation of clinical features
(roughly 5-10 years later) - AIDS = CD4 < 200
what are the HIV infection markers
CD4 count
HIV viral load = RNA concentration
how is malaria treated
non p.falciparum: chloroquine primaquine to prevent relapse p.falciparum: complicated = quinine + IV artesunate non-complicated = oral quinine + riamet
