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81 Cards in this Set

  • Front
  • Back
Methods of Antibiotic Susceptibility Testing
Disc diffusion/ E test
Agar incorporation
Tube dilution
Molecular methods
Automation
Enzyme detection
Factors Affecting Antimicrobial Susceptibility Tests (1)
Inoculum size - biggest factor
Depth of agar
Culture media composition (free of antibiotic antagonists)
Carbohydrate content - change in pH during rowth which may affect the activity of the antibiotic
Aminoglycosides - more active in acid than alkaline, affected by divalent cations (calcium, sodium chloride, phosphates and magnesium) particularly when testing Psued spp
Factors Affecting Antimicrobial Susceptibility Tests (2)
Nitrofurantoin - less active in acid
Osmolarity - beta-lactam antibiotics rely on osmotic rupture of cells for their lethal effect
Antibiotic formulation - often antibiotics in clinical use will be slightly different
Esters of ampicillin and erythromycin inactive in vitro - active drug released in vitro
Chloramphenicol succinate
Factors Affecting Disc Diffusion Test
Zone size affected by solubility, ionic charge and molecular size of the antibiotic
Large molecules diffuse poorly - polymixins, vancomycin - small zones
Growth rate of organisms
Slow-growing - Large zones
Factors Affecting Disc Diffusion Test (2)
Prolonged storage at room temperature before incubation
if discs applied - large zones
Discs not applied - small zones
Disc content - commerciallt available discs have large tolerance
30 microgram discs could contain 20-45 micrograms
BSAC
Standardised inoculum
Standard Medium
Standard disc concentrations
Use of control strains
Provision of control values
Plotting of control values
Minimum inhibitor concentration (MIC) for control organisms
MIC breakpoint for test organisms
Disc content for test organisms
Zone size interpretation for test organisms
Urinary Tract Infection
Upper and lower - kidneys and bladder
Most infections from teh bowel
bacteria colonise the perineum and peri-urethral area
ascend urethra to the bladder
more common in women
Cystitis
inflammation of the bladder
Dysuria -painful urination
Frequency
suprapubic discomfort
mild temperature
haematuria, pyuria
Pyelonephritis
Kidney infection
Back pain
High temp
Rigors due to bacteraemia
cystitic symptoms may appear
permanent damage to teh kidneys causing fibrosis
repeat attacks can lead to kidney failure
UTI in children
consider in all unwell children
Bed-wetting
Proven UTI check for abnormalities
Vesico-ureteric reflux + chronic infection - premanent kindey damage
renal failure in early adulthood
UTI in elderly and catheterised patients
Symptoms of cystitis and pyelonephritis may be absent
Suspect UTI in elderly when unwell or confused
indwelling catheters put patients at increase risk of UTI
typical symptoms will be absent
UTI in pregnancy
Common
asymptomatic
physical abnormalities
regular screening is important
restricted antibiotic choice
Complications
Epididymo-orchitis - infection of the epididymis that may arise from UTI, can be distinguished from testicular torsion
ischemia of testies
clinical diagnosis with urine and blood culture
Bacteraemia, septicaemia, prostatitis, urethritis, renal abscess
Labrotory Diagnosis
Microscopy
WBC > 10/mm3
RBC > 5/mm3
epithelial cells - contamination
casts - signal kidney damage
Organisms
E.coli most common
77% of acute uncomplicated UTI
Renal tract abnormalities - stones
Staphylcoccus saprophyticus in women
20% urethritis and cystitis in sexually active young women
Complicated UTI - klebsiella, enterobacter, proteus, enterococcus
problems with contaminated samples
Treatment
High Fluid intake
Uncomplicated cystitis - treat empirically, trimethoprim, cephalexin and nitrofurantoin
complicated will need labratory results for guidance
pyelonephritis may need iv antibiotics
Prevention
prophylaxis - low dose daily
Investifate for abnormalities - children and young men
urinary catheters are major risk factors
keep use to a minimum and aseptic technique
Staphylococci
Gram positive Cocci in clusters
skin, skin glands and mucous membranes
resistant to dry, acid and salt
facultative anaerobe
non-spore forming
Catalase positive - can survive in oxygen
coagulase (enzyme which clots blood plasma) positive or negative
S.aureus
Main human pathogen
coagulase positive
commonly associated with a number of infections
major cause of morbidity and mortality as a nosocomial pathogen (hospital acquired infection)
S.aureus: inflammator pathogen
Often acute and pyogenic (make pus)
furuncles (boil) and carbuncles (larger than boil)
Cellulitis (local severe inflammation of dermal and subsequent layers of skin)
Impetigo - sores and blisters on skin, common in children
post operative/trauma wound infections
Pneumonia
Endocarditis - inner lining of heart (endocardium) infected
osteomyelitis - infection of bone, most are S.aureus
S.aureus Toxin based pathology
Scaled Skin Syndrome: epidermolyitic toxin A or B
Food Poisoning: Enterotoxins heat resistant (100*C for a few mins) up to 65% of strains produce them
Toxic shock Syndrome: 70% mortality rate - toxin assoiated with enterotoxins in general
TSST and enterotoxins are known as superantigens, highly immunogenic, antigen interacts with 0.01% of available T cells, super antigen interacts with up to 25%
S.aureus Identification
Appearance of plates, Golden, use media high in NaCl
Coagulases causes fibrin shield around bacteria stopping host immune cells getting contact
Nucleases
Gram-stain
Clumping factor
PCR for specific antibiotic resistances
Staphylococcus Treatment
methicillin (a penicillin) sensitive usually
Methicillin resistant Staphylococcus aureus (MRSA)
longer to treat
Not associated with other virulence factor
S. epidermidis
Most common coagulase negative staphylococci (75%)
very common, care as can be skin contaminant
opportunistic pathogen
skin breached, immunocompromised
location of skin breach denotes severity
associated with prostheses
endocarditis
joint replacements
CAPD fluid (peritoneal dialysis)
post operative meningitis
S.saprophyticus
Coagulase negative
novobiocin resistance DNA gyrase
UTI second most common after E.coli in sexually active women
S. lugdunensis
Coagulase negative
Haemolytic andyellow in appearence like S. aureus
Endocarditis
Aggressive infection
High mortality
Valve replacement
Streptococci
Gram positive cocci in chain
facultative anaerobe
catalase negative
fermenters
beta, alpha or non haemolytic on blood agar
beta may be identified using lancefield groups - cell wall polysccharide
21 groups A-H and K-W
alph beta or no haemolysis on blood agar
beta haemolysis is complete lysis of RBCs, often the pyogenic organisms
alpha haemolysis is oxidation of haemoglobin by bacteria derivatived hydrogen peroxide
Gamma - no haemolysis
Groups
Mutans - teeth, plaque, non haemolytic
bovis - colonic alpha or non haemolytic occasional cancer
Saliivarius and anginosus - mouth and upper respiratory tract, none or alpha haemolytic
Mitis - all alpha haemolytic
Pyogenic - most pathogenic, all beta haemolyti
S. pyogenes
Beta haemolytic lancefield group A
Pyogenic, purulent, suppurative (pus) the attraction of neutrophils to site of infection
Diseases non-invasive inflammatory
Pharyngitis, tonsilitis (strep-throat) about 20-30% of all pharyngitis
scarlet fever caused by pyrogenic exotoxin strains. rash of skin and mucus membranes after initial pharyngitis
skin infections often with S. aureus impetigo, spread through scratching
Invasive illnesses
Cellulitisis and Necrotizing fascitis, damage to skin acts as breach, destroys fat and tissue and connective tissue
Myositis rare, throat infection leading to bacteraemia and muscle degradation, no skin breach
TSS
Puerperal sepsis, infection after childbirth
bacteraemia once in blood, doubling time is 18 min, huge numbers often heart failure
Complications
Rheumatic fever inflamation of joints, heart or CNS, cause of heart failure in teh young, may cause life long damage to valves. Autoimmune
Acute Post-Strep Glomerulonephritis is an immune based disease. rare as it requires an untreated streptococcus infection elsewhere for several weeks
Virulence factors of S. pyogenes
M proteins fibrils protruding from bacteria, antibodies generated against them. ends very variable allows resistance to phagocytosis
M proteins can also bind to parts of the immune system and mask the bacteria
Capsule hyaluronic acid, mimics connective tissue of the host, anti-immunogenic as well as preventing phagocytosis
C5a peptidase attack the complement system - principle phagocyte attractor
Other beta haemolytic streptococci
S. agalactiae lancfield grooup B
Similar virulence factors to S. pyogenes
Colonise maternal genital tract
Causes serious neonatal infection
Neonatal sepsis and meningitis
lancefield group C and G, similar infections to S. Aureus, not as virulent, can be present in a commensal role (mutualistic relationship)
Strptococcus anginosus group
also known as strep milleri
Occasionally Beta haemolytic but usually non haemolytic
Form small dry colonies with a characteristic caramel aroma on blood agar
pyogenic infections - abscesses
S. pneumoniae
present in up to 70% of population
alpha haemolytic draftsmen shaped or mucoid colonies
lancet shaped diplococci often capsulate - associated with disease
Pneumolysin - a virulence factor which forms pores to lyse host cells and interfere with soluble molecules of the immune system
S. pneumoniae (2)
Pneumonia 0.1 - 0.3% of population with 5% fatality rate
can lead to bacteraemia and meningitis 20-30% fatality
Sinusitis
Endocarditis
Viridians group streptococci
Alpha haemolytic normally found in mouth
often inhibit the growth of pathogens by bacteriocins and hydrogen peroxide
S. sanguis/salivarius/mitis/oralis
endocarditis if predisposing condition
dental caries
strep bovis - GI cancer
Identification
Blood agar, permits growth and allows quick haemolytic activity check.
catalase negative when linked with gram stain diploid or chains
S.pneumoniae are optochin sensitive
Upper respiratory infections
Above Trachea
Common Cold
nasal discharge
Rhinovirus - most common cause (30%) many different serotypes
Parainfluenza viruses (1-4)
Coronaviruses (15% adult colds)
Respiratory syncytial virus, adenovirus, coxsacki and echovirsues (10%)
Influenza virus (A+B)
may lead to secondary bacterial infection
Pharyngitis and tonsilitis
Epstein-barr virus-glandular fever,malaise, lymphadenopathy
Cytomegalovirus - glandular fever-like illness
Human immunodeficiency virus as part of seroconversion illness
Bacterial and Fungal Pharyngitis and Tonsillitis
S.pyogenes most common
Borrellia cincenti and Fusobacterium species - vincents angina ulcers
Corynebacterium diphtheriae - diphtheria
C ulcerans and Arcanobacterium haemolyticum - very rare pharyngitis
Neisseria gonorrhoeae - pharyngitis
Treponema pallidum - 1ary and 2ary syphilis
Candida albicans - thrush
Why is it important to distinguish between viral and bacterial pharyngitis?
bacterial can lead to arthritis and kidney damage, virus leads to not much else
Otitus media and Otitis externa
Media: infection of middle ear in young children, pain and fever, D+V due to antibiotics. S.pyogenes, S.pneumoniae, S.aureus
Externa: Infection of external auditory canal, pain and discharge, S. aureus, Pseudomonas aeruginosa, proteus and candida species.
Malignant otitis externa, bone and cartilage at base of skull, P. aeruginosa
Acute epiglottitis and croup
Epiglottitis - life threatening, haemophilus influenzae tybe b most common cause
Croup - young children, affects larynx and epiglottits - narrows airway, respiratory syncytial virus most common
treatment of upper respiratory tract infections
Common cold - paracetamol and tissues
viral aetiology - none, bacterial - penicillin, fungal - antifungal lozenges
sinusitis - antibiotics and surgery
otitis media - antibiotics not recomended
otitis externa - aural toilet, drops with steroid and antibiotics (care)
croup - none
whooping cough, a childhood disease
gram negative fastidious bacteria with humans the only host.
initial symptoms similar to croup, a cough to clear mucus brought on by toxin paralysing cilia when bound, leading to pneumonia and secondary infection
lack of breath
ampicillin, tetracycline, erythromycin
vaccination best
acute tracheobronchitis
dry cough and chest tightness
occurs in minority of viral upper respiratory tract infection
influenza, parainfluenza, rhinovirus and RSV
secondary bacterial infection - productive cough
Infective exacerbation of chronic obstructive pulmonary disease (COPD)
long term smoking, foreign objects in lungs cause inflammation
S.pneumoniae and H. influenzae colonise in damaged lung
frequent cause of emergency medical admission
many infective exacerbation are viral - influenza, parainfluenza, rhinovirus, coronavirus and RSV
pneumonia: inflammation of the lung
fever, cough, breathlessness, pleuritic pain when breathing in one area
consolidation liquid instead of gas around bronchioles
Treatment of lower respiratory tract infections
Antibiotics
antivirals
physiotherapy
Clostridal infections
Gram positive bacilli
anaerobic
spore forming
toxin production - often major factor in the disease
normal bowel flora
contaminant of human and animal excreta
C. perfringens
double zone of haemolysis on blood agar
spores raresly seen in gram film
nagler positive: phospholipase
lactose positive: ferments as has no electron transport chain
usually grows in 24 hours
5 types A-E
4 lethal toxins - Alpha, Beta, Epsilon and Iota related to disease process
C. perfringens (2)
a-toxin - phospholipase C
most important produced by all 5 types
Lyses RBC, platelets, WBC and endothelial cells
Gan Gangrene
C. perfringens treatment
Amputation
Surgical debridement (removal of dead material)
Large doses of penicillin
Other clostridia causing Gas Gangrene
Clostridium novyii type A: profound toxaemia
Clostridium septicum: not as strict an anaerobe, typhlitis - rapid fatal ileal infection and septicaemia if gut integrity impaired or if host is immunocompromised
gas gangrene is polymicrobial - other abcteria produce anoxic conditions that allow spores to germinate
Clostridium tetani
very strict anaerobe
fine spreading growth 48-72hrs
terminal spores
asaccharolytic, cannot break down sugars
proteolytic
spores can be highly resistant
C. tetani
Produces 2 toxins
Tetanolysin - oxygen labile haemolysin, clinical significance unknown.
Tetanospasmin - plasmid-encoded heat labile neurotoxin, released when the cell is lysed, non toxic if taken orally
Tetanospasmin
Inactivates proteins that regulate the release of inhibitory neurotransmitters - glycine and gamma-aminobutyric acid
unregulated excitatory response in motor neurones
binding is irreversible - new terminal - muscles cant relax
treatment
sedation and constant nursing
ventilation
immunoglobulin
penicillin or metronidazole
1 million deaths/year - 1/2 neonatal
Clostridium botulinum
Strict anaerobe
widely distributed in teh environment
produces spores resistant to heat and radiation
7 types A-G
A,B and E most common human disease
Toxins
Potent neurotoxin
among most poisonous natural substances known
doesnt need to infect, only small amount of toxin needed
antigenically different from types A-G
if administered in emergency, only specific antitoxin will work
inactivates proteins that regulate release of ACH
blocking neurotransmission at synapses
ACH is req for muscle excitation
lack of stimulation
Clinical
severe often fatal form of food poisoning
Insufficient heating of food
Preserved foods
Preformed toxin in teh food
no sign of spoilage, you need that little toxin
1-2 days after ingestion
drooping eyelids, blurred vision with fixed dilated pupils
dry mouth, speech and swallowing difficulties
progressive descending bilateral weakness of teh muscles
flaccid paralysis
no loss of consciousness or sensation
death due to respiratory or cardiac failure
was 70% mortality now 10%
Tretment
Remove unabsorbed toxin from teh stomach
Polyvalent antitoxin to neutralise infixed toxin
intensive care
complete recovery may take months or years, regrow nerve endings
Clostridium difficile
part of a normal healthy bowel flora in 3-5% of humans
harmless as cannot compete with resident flora
administration of broad spectrum antibiotics allow the organism to grow
vulnerable patients - particularly the elderly
antibiotics remove competitive barrier
organism grows and produces toxins
antibiotic associated colitis
treat by witholding antibiotics, replace body fluids
patient to patient spread (spores)
Lab Diagnosis
Culture the organism - selective or enrichment media
detect toxin
toxin A - enterotoxin
toxin B - cytotoxin
Enterobacteriacae
Gram negative bacilli, no spores, motile and non motile
MacConkey agar (bile salts to kill gram +ve and show lactose +ve/-ve
aerobic and anaerobic
ferment glucose and other sugars with gas production
catalase positive can grow in oxygen
oxidase negative cant use oxygen in oxidative phosphorylation
Reduce nitrate to nitrite as part of anaerobic respiration
contain a G + C content 39 - 59%
Chemical Tests with ecoli as example
MacConkey agar
Lactose fermenters go red as pH drops with acid prod. E+
Indole released when tryptophan is cleaved to release pyruvate as a source of energy. E+
Citrate produces alkaline media by producing citrase blue green and gorwth E-
Gas from glucose often CO2 or H2 E+
Clinically important species
Salmonella enterica, Citrobacter freindii, diversus, koseri (neonatal meningitis): gas from glucose, motile, indole -ve, citrate +ve
E.coli: Gas from glucose, Motile, Indole +ve, Citate -ve
Shigella sonnei, flexneri, dysenteriae, boydii: no gas from glucose, non motile indole -ve, citrate -ve similar to E.coli toxin
Identification of different species
compare profiles of biochemical reactions, complete identification isnt always possible due to very similar species.
bacteria may switch on or off enzymes which will effect results
Antigen detection
DNA-DNA hybridisation studies
PCR for antibiotic resistances
Treatment
Ampicillin, Amoxycillin: betalactams, most (80-90%) resistance (klebsiella 99%)
Trimethoprim
Nitrofurantoin
Cephalexin, Cefuroxime, Cefotaxime
Pseudomonas and Acinetobacter
Environmental gram negative bacilli
Non-fermentative
Often isolated in clinical specimens
Persist in the hospital environment
An important cause of nosocomial infection, Opportunistic
resistant to antibiotics
Pseudomonas
Oxidase and catalase positive non fermentative gram negative bacilli, Motile
found in water, soil and plants
survive in distilled water for days
most common clinical isolate P. aeruginosa
often colonise hospital environment, sink traps
Green pigment and aroma
exopolisaccharide called biofilm
Pseudomonas infections
otitus externa
eye infections
pneumonia respirator infections via community
bacteraemia
UTI
Joints
CAPD after kidney failure
Virulence factors
Proteinases
flagella and adhesins massive inflammation which can shed to reduce immune response for providing nutrients
Acinetobacter
Oxidase negative, non motile, non fermentative gram negative bacilli
survives in moist and dry environment
most common clinical isolate A. baumannii (hospital)
ICU fully disinfected then 6 months later same strain returns
with MRSE there is a ratio of 2:1 colonised vs infected
Infections and Risk factors
infect debilitated and immunocompromised patients
RTI and UTI, Bacteraemia, meningitis
Risk factos: mechanical ventilation, catheter (invasive procedure), age, hospital stay, antibiotic resisstance
Virulence factors
still at early stage
siderophores
fimbriae and pili
resistance due to living in soil and out competing organisms with the same weapons as us,
Isolation and identification
simple culture media
P. aeroginosa if producing pigment