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81 Cards in this Set
- Front
- Back
Methods of Antibiotic Susceptibility Testing
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Disc diffusion/ E test
Agar incorporation Tube dilution Molecular methods Automation Enzyme detection |
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Factors Affecting Antimicrobial Susceptibility Tests (1)
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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 |
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Factors Affecting Antimicrobial Susceptibility Tests (2)
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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 |
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Factors Affecting Disc Diffusion Test
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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 |
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Factors Affecting Disc Diffusion Test (2)
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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 |
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BSAC
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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 |
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Urinary Tract Infection
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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 |
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Cystitis
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inflammation of the bladder
Dysuria -painful urination Frequency suprapubic discomfort mild temperature haematuria, pyuria |
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Pyelonephritis
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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 |
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UTI in children
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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 |
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UTI in elderly and catheterised patients
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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 |
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UTI in pregnancy
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Common
asymptomatic physical abnormalities regular screening is important restricted antibiotic choice |
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Complications
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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 |
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Labrotory Diagnosis
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Microscopy
WBC > 10/mm3 RBC > 5/mm3 epithelial cells - contamination casts - signal kidney damage |
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Organisms
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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 |
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Treatment
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High Fluid intake
Uncomplicated cystitis - treat empirically, trimethoprim, cephalexin and nitrofurantoin complicated will need labratory results for guidance pyelonephritis may need iv antibiotics |
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Prevention
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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 |
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Staphylococci
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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 |
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S.aureus
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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) |
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S.aureus: inflammator pathogen
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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 |
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S.aureus Toxin based pathology
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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% |
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S.aureus Identification
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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 |
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Staphylococcus Treatment
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methicillin (a penicillin) sensitive usually
Methicillin resistant Staphylococcus aureus (MRSA) longer to treat Not associated with other virulence factor |
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S. epidermidis
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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 |
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S.saprophyticus
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Coagulase negative
novobiocin resistance DNA gyrase UTI second most common after E.coli in sexually active women |
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S. lugdunensis
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Coagulase negative
Haemolytic andyellow in appearence like S. aureus Endocarditis Aggressive infection High mortality Valve replacement |
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Streptococci
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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 |
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alph beta or no haemolysis on blood agar
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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 |
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Groups
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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 |
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S. pyogenes
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Beta haemolytic lancefield group A
Pyogenic, purulent, suppurative (pus) the attraction of neutrophils to site of infection |
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Diseases non-invasive inflammatory
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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 |
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Invasive illnesses
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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 |
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Complications
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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 |
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Virulence factors of S. pyogenes
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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 |
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Other beta haemolytic streptococci
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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) |
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Strptococcus anginosus group
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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 |
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S. pneumoniae
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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 |
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S. pneumoniae (2)
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Pneumonia 0.1 - 0.3% of population with 5% fatality rate
can lead to bacteraemia and meningitis 20-30% fatality Sinusitis Endocarditis |
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Viridians group streptococci
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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 |
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Identification
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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 |
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Upper respiratory infections
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Above Trachea
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Common Cold
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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 |
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Pharyngitis and tonsilitis
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Epstein-barr virus-glandular fever,malaise, lymphadenopathy
Cytomegalovirus - glandular fever-like illness Human immunodeficiency virus as part of seroconversion illness |
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Bacterial and Fungal Pharyngitis and Tonsillitis
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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 |
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Why is it important to distinguish between viral and bacterial pharyngitis?
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bacterial can lead to arthritis and kidney damage, virus leads to not much else
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Otitus media and Otitis externa
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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 |
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Acute epiglottitis and croup
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Epiglottitis - life threatening, haemophilus influenzae tybe b most common cause
Croup - young children, affects larynx and epiglottits - narrows airway, respiratory syncytial virus most common |
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treatment of upper respiratory tract infections
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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 |
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whooping cough, a childhood disease
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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 |
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acute tracheobronchitis
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dry cough and chest tightness
occurs in minority of viral upper respiratory tract infection influenza, parainfluenza, rhinovirus and RSV secondary bacterial infection - productive cough |
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Infective exacerbation of chronic obstructive pulmonary disease (COPD)
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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 |
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pneumonia: inflammation of the lung
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fever, cough, breathlessness, pleuritic pain when breathing in one area
consolidation liquid instead of gas around bronchioles |
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Treatment of lower respiratory tract infections
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Antibiotics
antivirals physiotherapy |
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Clostridal infections
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Gram positive bacilli
anaerobic spore forming toxin production - often major factor in the disease normal bowel flora contaminant of human and animal excreta |
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C. perfringens
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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 |
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C. perfringens (2)
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a-toxin - phospholipase C
most important produced by all 5 types Lyses RBC, platelets, WBC and endothelial cells Gan Gangrene |
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C. perfringens treatment
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Amputation
Surgical debridement (removal of dead material) Large doses of penicillin |
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Other clostridia causing Gas Gangrene
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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 |
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Clostridium tetani
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very strict anaerobe
fine spreading growth 48-72hrs terminal spores asaccharolytic, cannot break down sugars proteolytic spores can be highly resistant |
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C. tetani
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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 |
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Tetanospasmin
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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 |
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treatment
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sedation and constant nursing
ventilation immunoglobulin penicillin or metronidazole 1 million deaths/year - 1/2 neonatal |
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Clostridium botulinum
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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 |
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Toxins
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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 |
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Clinical
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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% |
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Tretment
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Remove unabsorbed toxin from teh stomach
Polyvalent antitoxin to neutralise infixed toxin intensive care complete recovery may take months or years, regrow nerve endings |
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Clostridium difficile
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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) |
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Lab Diagnosis
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Culture the organism - selective or enrichment media
detect toxin toxin A - enterotoxin toxin B - cytotoxin |
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Enterobacteriacae
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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% |
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Chemical Tests with ecoli as example
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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+ |
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Clinically important species
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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 |
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Identification of different species
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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 |
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Treatment
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Ampicillin, Amoxycillin: betalactams, most (80-90%) resistance (klebsiella 99%)
Trimethoprim Nitrofurantoin Cephalexin, Cefuroxime, Cefotaxime |
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Pseudomonas and Acinetobacter
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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 |
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Pseudomonas
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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 |
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Pseudomonas infections
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otitus externa
eye infections pneumonia respirator infections via community bacteraemia UTI Joints CAPD after kidney failure |
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Virulence factors
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Proteinases
flagella and adhesins massive inflammation which can shed to reduce immune response for providing nutrients |
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Acinetobacter
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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 |
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Infections and Risk factors
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infect debilitated and immunocompromised patients
RTI and UTI, Bacteraemia, meningitis Risk factos: mechanical ventilation, catheter (invasive procedure), age, hospital stay, antibiotic resisstance |
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Virulence factors
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still at early stage
siderophores fimbriae and pili resistance due to living in soil and out competing organisms with the same weapons as us, |
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Isolation and identification
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simple culture media
P. aeroginosa if producing pigment |