Flashcards in Microbiology Deck (260):
Why do we culture blood?
to look for bacteraemia - it is normally bacteria free without bacteria flora
How can blood be contaminated?
patient's skin, surface of the items used to take the culture, fingers of the person taking the blood, laboratory
How long does it take for a blood culture to identify an organism?
1 day to do gram stain and coccsu/bacillus
2-3 days to identify organism and assess whether this is likely to be a contaminant
Why are contaminants a problem?
give wrong treatment, waste of money, side effects for patients, unnecessary equipment, increased length of stay, mislead clinicians, not always able to identify whether it is a contaminant or not, don't meet contamination targets
What organism is resistant to all B lactams?
Disadvantage of using B lactam antibiotics?
can predispose to C.difficile and colonization with resistant bacteria e.g. MRSA, many people report allergies to this group, especially penicillin
What is the most widely used class of antibiotics and how do they work?
B lactams which includes penicillins, cephalosporins, carbapenems and combinations - bind to cell wall and inhibit cells wall sunthesis
Two main types of penicillins?
What antibiotic is used for enterococci and H.influenzae?
amoxcillin - but most enterobacteria are resistant to it
What is flucloxacillin used for?
anti staphylococcal agent as stability to penicillinase
What are B lactamase inhibitors used for?
bacteria resistance is through B lactamase production, so these antibiotics prevent this resistance, so use combinations e.g. co-amoxiclav, tazocin
What are monobactams used for?
e.g. Aztreonam, for gram negative bacilli, including pseudomonas and preferably aerobes, safer for C.diff
What are carbapenems used for?
e.g. imipenem for very broad spectrum hospital acquired infections
Disadvantages of carbapenems e.g. imipenem?
expensive, CI in CNS disorders and can predispose to C.diff
What are cephalosporins used for?
e.g. cefotaxime, ceftazidime for gram negative activity, good CNS penetration and good anti pseudomonal
What are glycopeptides used for?
e.g. vancomycin for gram positive only and reserved for serious, resistant ones e.g. MRSA (Iv only and toxic)
What are macrolides used for?
e.g. erythromysin, clarithromycin for staph and strep activity, used to soft tissue and throat infections if allergic to penicillins (no gram negative cover)
What are lincosamindes used for?
e.g. clindamycin for staph, strep and anaerobes and C.diff and PMC good bone concentrations and well absorbed orally
What are tetracyclines used for?
mild MRSA infections and chlamydias
What are aminoglycosides used for and how do they work?
e.g. gentamicin for enterobacteriaceae, pseudomonas and staphylococci, synergy with cell wall antibiotics against streptococci and enterococci - inhibit ribosomal activity and protein synthesis
Disadvantages of aminoglycosides?
more toxic than glycoproteins so nephro and oto toic levels must be monitored carefullly
What is fusidic acid used for?
serious anti staphylococcal agents e.g. osteomyelitis, only used in combination
What is oxazolidinone used for and how does it work?
grampositive including MRSA and VRE - inhibits bacterial protein synthesis and blocks initiatio complex formation
Disadvantages of oxazolidinone?
only 1 class e.g. linezolid and are expensive and can cause bone marrow suppression if used for >2 weeks
What are nuclei acids/quinolones used for and how do they work?
e.g. ciprofloxacin - UTIs, enterobacteriacease pseudomonas and staph - inhibitt DNA gyrase
What is rifampicin used for and how do they work?
TB and general Staph's and meningitis prophylaxis - must be used in combination - interfere with nuclei acid synthesis or function
What is metronidazole used for?
anti anaerobic for bacteria and protozoa
What likely organisms are seen in UTIs?
e coli, staph sparophyticus, enterococci
Antibiotics for UTIs?
trimethoprim, amoxicillin, clavulanate, cephalosporin
Likely organisms to cause COPD?
Hinfluenzae, pneumococcus, Moraxella catarrhalis
Treatment of COPD infection?
amoxicillin with clavulanate, tetracycline, trimethoprim
Likely organisms to cause pneumonia?
Treatment of pneumonia?
B lactams, erythromycin
Likely organisms in a wound?
staph aureus, strep pyogenes, anaerobes
Treatment of a wound?
flucloxacillin, erythromycin, co-amoxiclav
How can antibiotics be misused?
use broad spectrum when narrow are just as effective, treat for too long, treating with IV when oral is as effective, using combination when one is a effective, failure to use a dose appropriate for renal and hepatic function, using antibiotics for highly unlikely organisms, failure to step down organism once known
Dangers of antibiotic misuse?
adverse drug reactions which increases with multiple drug prescribing, harmful drug interactions, errors in prescribing monitoring, can cause super infection and antibiotic resistance
What is the difference between bacteriostatic and bactericidal?
bacteriostatic - prevents bacteria growth by inhibiting protein synthesis, DNA replication or metabolism, reduces toxin production
bactericidal - kills bacteria by inhibiting cell wall synthesis, good if poor penetration
Why do antimicrobials want a large MIC?
minimum inhibitory conc - to attach to more binding sites to inhibit bacteria
What factors must be considered in drug administration choice?
will it penetrate, pH of the site, is antimicrobial lipid soluble
How do bacteria resist antimicrobials?
change antimicrobial site by changing binding site configuration, destroy or inactivate the antimicrobal, prevent antimicrobial etery by modifying bacterial membrane porin channel site, numbers or selectivity, remove antimicrobial from bacterium using export pumps
How does bacterial resistance develop?
intrinsically naturally resistant so subpopulations can develop it too
acquired - not all subpopulations are equally resistant
Gram positive antimicrobial resistant bacteria?
Gram negative antimicrobial resistant bacteria?
B lactamases, ESBL, carbapenenases, AmpC B lactamase resistant
What methods can be used to test antimicrobial resistance?
antimicrobial sensitivity testing, chromogenic plates, mechanism specific tests, genotypic methods, breakpoint plates
What is a pathogen?
an organism that is capable of causing disease
What is a commensal?
an organism which colonises the host but causes disease in normal circumsatnces
What is an opportunist pathogen?
only causes disease if host defences are compromiseed
What is pathogenicity?
the degree to which an organism is pathogenic
What is asymptomatic carnage?
when a pathogen is carried harmlessly at a tissue site where it causes no disease
Components to a bacteria?
capsule, cell wall, outer and inner membrane, pili, chromosome, may also have plasmids
What is the function of a capsule on bacteria?
super coated so difficult for phagocytes to ingest
What is used to stain acid fast bacilli?
Ziehl Neelsen stain
What colour is a gram positive stain?
What colour is a gram negative stain?
What is the difference in gram positive and negative cell wall composition?
n = more lipopolysaccharide, with lipoprotein, less peptidoglycan with inner and out membrane
p = more peptidoglucan with lipoteichoic acid and cytoplasmic membrane
What is the idea bacterial environment?
What are the 4 stages of bacterial life?
lag, exponential (log), stationary, death
What is endotoxin?
component of outer membrane of bacteria produced by lipopolysaccharide gram negative, has non specific action, stable effect of heat, weak antigenicity and not convertable to toxoid
What is exotoxin?
secreted by gram positive (and negative), can be converted to toxoid, strong antigenicity, liable effect of heat and specific action
What is involved in a gram stain?
apply crystal violet stain to fix bacteria, add iodide to bind to crystal violet and help fix it to cell wall, decolourize with ethanol and counter stain with safranin (pink)
in gram negative, the decolourizze interacts with lipids and cells lose their lipopolysaccharide membrane and the crystal violet complex so appears pink
in positive, the decolourize dehydrate the cell wall and crustal violet is trapped in the multilayed peptidoglycan
Methods for infection control?
decontaminate medical equipment, single used items, manage peripheral and central IV lines, manage short term catheters, outbreak control plan, specific antimicrobial prescribing policies, personal protective equipment worn by all staff, dispose sharps into sharps bin, never res heath or bend needles or overfill sharps bin, hand hygeiene
What is an endogenous infection?
infection of a patient by their own flora, especially in hospitalised patients with invasive devices and surgical aptients
Prevention of endogenous infection?
good nutrition and hydration, antispepsis/skin prep where indicated, control underlying disease, remove linses and catheters as soon as clinically possible, reduce antibitotic pressue as much as clinically possible
What are protozoa?
eukaryotic organisms that consume bacteria, algae and microfungi
What are the 5 main protozoa?
flagellates - allows movement, reproduce by binary fision
amoebae - flow through cytoplasma, produced by pseudopodia
sporozoans - no locomotory extensions, most intracellular parasites and reproduce by multiple fission
ciliates - cilia beat rhythmically with macro and micro nuclei
microsporida - makes resistant spores, unique polar filament, coiled inside spore
What has malaria incidence increased?
parasite resistance, climate changes, increased travel to area
How do viruses cause disease?
virus causes invagination of the cell membrane and attaches to cell receptors and released into cell cytoplasm, carry nuclei acids and replicate using cells proteins and forms a defense mechanism
virus moves in vacuole and acidification causes a change in surface proteins of virus to release products, this replicates until the cell lysis or exocytosis so it can spread to other cells, budding causes parts of the virus to be pinched off
How does a virus cause damage?
direct destruction of host cells e.g. polio, modification of host cell structure or function e.g. rotavirus and HIV, damage through overreactivity of host in response to infection e.g. hepatitis B and C, damage through cell proliferation and immortalisation e.g. HPV, virus evasion of the host defences
What makes up a cell wall of fungi?
polysaccharides and chitin, most don't have a capsule, and the cell wall is the sterol rich cytoplasmic membrane
What are the different forms of fungi?
moulds, yeasts, dimorphic
Who are most at risk of getting a fungal infection?
immunocompromised, especially neutrophil deficient (those who are healthy only get superficial infections e.g. athletes foot)
What does the fungal cell wall stain with?
Gomorra methernamine silver of periodic acid schiff reagent as it is too weak for gram stain, KOH
How do yeasts and moulds repoduce?
yeasts - asexual budding
moulds - spore formation
Shape of yeasts and moulds?
yeasts - round/oval
moulds - tubular
How do yeasts and moulds grow?
yeasts - grow in tissue and bud as tubular forms as a pseudohyphae
moulds - grow by longitudinal extension and branch to form interwoven mycelium
What are the 3 types of fungal infection?
superficial mycoses - in skin, hair, nails, mucus membranes with yeast and ringworm
subcutaneous mycoses - pigmented fungi with septate dark brown cells singly or in clusters e.g. madura foot
systemic mycoses - primary or opportunist pathogens
Treatment of fungal infections?
drugs to target sterols in cell membrane, topical or systemic
antifungal therapy binds to serols in cell walls, destabalising it and inhibits RNA and DNA synthesis and inhibits ergosterol biosynthesis and mircotubule assembly
Examples of fungal infections?
candidasis - on mucous membranes of mouth and vagina, a commensal yeast that causes disease when microflora disturbed
ringworm - direct or indirect transfer of infection keratin e.g. athelets foot
aspergillois - spores in soils and ducts can be invasive, allergic or asperfillomia
cryptococcosis - capsulate yeast in immunosuppressed
Is microbacteria gram positive or negative?
weak gram positive with a high lipid ontent
How can mycobacteria cause infection
survive a long time in macrophages and are slow growing, so immunodeficient are susceptible
How does leprosy cause damage?
has granulomas formed as a response to try and contain mycobacteria, these can cause damage to nerves which means risk of tumour and burns and the nose can collapse
How do mycobacteria appear in a Ziehl Neelson stain?
turns red then destained to be blue
How long does it take to culture TB?
solid = 3-8weeks
liquid = 1-3 weeks - then can used mycobacteria growth indicator tube using flurometric detection
What does PCR do in TB culturing?
amplifies nucleic acids, purifies and concetratesTB, sonicates to release henomic material and performs PCR, rapid result and detects rifampicin resistance using fluorensence
What test is used to detect re-activity of T cells for TB
tuberculin skin test looks for cell mediated immune defense
Difference between lepromatous and tuberculoid leprosy?
LL - lesions full of bacilli, poorly formed granulomatus, extensive skin lesions, Th2 response
TL - tissue hypersensitivity and granulomatas, causing tissue damage, immune reaction, Th1 response and CD4+ T cell response, producing IFN-Y and TNF-a
4 drugs for TB treatment?
rifampicin, isoniazid, pyrazinamid, ethambutol for 2 months followed by INH and RIF for 4 months
Examples of gram positive cocci?
staphylococci, streptococci, enterococci
Examples of gram negative cocci?
neisseria and moraxella
Examples of gram positive bacilli?
actinomyces, bacillus, clostridia, diptheria, listeria monocytogenes
Examples of gram negative bacilli?
E coli, campylobacter, pseudomonas, salmonella, shigella, proteus
What is the catalase test?
to see if the microbe has catalase which destroys H2O2 and produces O2, if O2 is produced it is positive and is staphlococcus and it has catalase, it no O2 it is negative and streptococcus
Purpose of catalase test?
distinguishes between staphylococcus and streptococcus
What test is used on gram positive cocci?
What test is used on staphylococci?
What is the coagulase test?
coagulase converts fibrinogen to fibrin and differentiates between staphylococcus aureus and staphylococcus epidemidis (positive is s.aureus and appears cream/yellow, negative is white)
How does s.aureus appear?
pigmented clusters, coagulated (solid), had DNAase
How does s.aureus cause disease?
high disease potential, pore forming toxin proteases. toxic shock syndrome toxin, spread by aerosal and touch and can colonize skin wounds
Treatment of s.aureus?
flucloxacillin (MRSA is resistant to B lactams though so needs vancomycin)
How does s.epidemidis appear?
non pigmented clusters, non coagulated, no DNAase
How does s.epidimidis causes disease?
low disease potential and s opportunistic and forms persistent biofilms
What test is done to distinguish streptococci?
haemolysis on blood agar
What are the 3 outcomes of haemolysis on blood agar and how do they appear?
beta haemolytic strep - clearing of agar around colonies due to strepolysin O and S production
alpha haemolytic strep (viridans strep) - greening of agar around the colonies due to H2O2 production
gamma haemolysis - no lysis
What test is done on beta haemolytic strep and how does it work?
The Lancefield test - serogroups antigenic gorup, differentiates according to surface antigens and their properties and the non coagulated one is the one to classify properties, producing A, B, C G
What is the likely diagnosis of group A Lancefield test?
s.pyogenes - causes tonsillitis, impetigo, scarlet fever, cellulitis
What test is done on alpha haemolytic strep?
What are the results of the optochin test?
Put the disc on the bacteria and if bacteria moves away from the disc then it is sensitive (s.pneumoniae) and if it doesn't it is resistant (s.viridans)
What does strep viridans cause and where does it occur?
in oral dental canes and deep organ abscess, caused infective endocarditis
Where does strep. pneumoniae act on and what does it cause?
in oropaharynx, it has capsule, inflammatory wall constituents and cytotoxins causing impaired mucus trapping, causes hypomnaglobinaemia and is dependent on antibody to capsule
What infections does step. pneumoniae cause?
pneumonia, sinusitis and meningitis
Where are the sterile parts of the body?
blood, peritoneal cavity, CSF, joint, pleural fluid, urinary tract, lower resp tract
Where can norma flora culture?
mouth, skin, urethra, large intestine, vagina
What test is used on gram negative bacillus?
the appearance on MacConkey or CLED or XLD
What are the outcomes of appearance on MacConkey agar?
white (non lactose fermenting - shigella, salmonella, pseudomonas, proteus)
pink (lactose fermenting - enterobacteriacae (coliforms)
What are the outcomes on XLD agar?
red with black dots (fermenting xylose)
red (non fermenting xylose)
What test is done on non lactose fermenting bacteria?
oxidase test using a redox indicator
What are the results of an oxidase test?
blue as produces cytochrome c oxidase from bacterial ECT (positive - pseudomonas aeruginosa)
no colour change (enterobacteriaceae - proteus and shigella)
What test is done on oxidase positive pseudomonas sp.?
anti pseudomonal sensitivity test
What is the treatment of pseudomonas sp?
What tests are done on oxidase negative enterobacteriacae?
biochemical identification (API strip) and sensitivity strips
What test is done on lactose fermenting bacteria?
biochemical identification (API strip) and sensitivity strips
Which is the least selective agar?
blood agar so good for many bacteria
What is chocolate agar?
blood agar heated to 80c for 5 minutes to release nutrients into agar - means certain organisms dont grow as well
What is MacConkey agar used for?
to grow and differentiate gram negative bacilli with bile salts to inhibit positive, contains lactose and neutral red dye to strain fermenting and non fermenting
What is gonococcus agar used for?
contains growth factors to promote Neisseria and has antibiotics and antifungal agents to inhibit other growth
What is CLED agar used for?
non inhibitory growth medium to differentiate microoganisms in urine, classifying fermenting and non fermenting
What is Sabouraud's agar used for?
cultures fungi and uses bacteria with antibiotics
What is XLD agar used for?
very selective for salmonella and shigella with phenol red indicator so bright red at pH 7.4 and then turns yello
How can pathogens be distinguished from norma flora?
restrict it using plates in different atmospheres and temperatures with range of nutrients and using selective media
What does shigella cause?
4 types that lead to diarrhea
What does salmonella cause?
gastroenteritis and enteric fever and bacteraemia
What is the most common faculative anaerobe in the gut?
What does E.coli cause?
cystitis, UTI, wounds infections
What the main forms of Neisseria?
Neisseria meningitidis and Neisseria gonorrhoea
What are the main bacteria that cause UTI?
E coli, klebsiella, pseudomonas
What is a common gram positive bacilli that is in neonates and elderly?
Are staphylococci and streptococci chains or clusters?
staph = clusters
strep = chains
What is another name for s.pyogenes?
group A streptococci
What organism is oxidase test negative and causes dysentry?
What are the 2 methods of viral diagnosis?
virus detection or serology
What methods are used for virus detection?
electron microscopy, cytopathic effect and PCR (preferred)
What is and advantage and disadvantage of ECM and cytopathic effect for virus detection?
time consuming and a lot of effort and cannot be be used in modern labs, but are good for new viruses
What happens in PCR?
enzymes unzip DNA and RNA chains, make complementary copies with flourescent tags, and is then replicated and then the DNA can be measured by the flourescence which is only activated when bound to the chain
Advantages and disadvantages of PCR in virus detection?
very sensitive and quick, but liable to contamination and false positives, so you must have suspected the virus in the first place, making it difficult for novel viruses
What is serology?
the study and detection of antibody responses in the serum
What antibodies are seen after an acute infection??
IgM for up to 12 weeks after, then IgG later and is responsible for immunity
What different serology techniques are there?
complement fixation test, haemagglutination (inhibition), enzyme linked immunosorbent assay (ELISA), radioimmuo assay, immunofluoresence
rhinovirus, echovirus, coxsackie a and b
Common respiratory viruses?
influenza A/B, parainfluenza, RSV, coronavirus, rhinovirus, measle, rubella, metapneumonvirus, parvovirus, adenovirus
What samples can be used for diagnosis?
green viral swab, black charcoal swab, CSF, stool
What tests count WCC quickly?
What blood tests can be done?
FBC, blood film and yellow top for EBV serology
How long does it take for blood results to be available?
film - hours
pcr - next day
acute EBV serology - 1-2 days
Management of glandular fever?
supportive therapy, avoid contact sport for 6 weeks to avoid splenic rupture
What 3 markers can HIV tests detect in the blood?
antibody, antigen p24, HIV RNA
What happens if HIV test is negative?
may not be in window period, so screen again after window period
What happens in HIV test is positive?
confirm test inn the lab with a different assay
Treatment of CMV?
Causes of UTI?
sexual intercourse, catheterisation, enlarged prostate, renal tract tumours, renal stones
What investigations are need in UTI?
mid stream urine, direct microscopy for pyuria, culture (which can show significant bacteriuria, doubtful significance or a contaminant), sensitivity testing (to find appropriate antibiotics)
What is a skin organisms that can colonise the perineium and seen in UTI?
staphylococcus saprophyticus (gram positive cocci)
What do leucocytes and nitrates in urine sample suggest?
How can gram negative bacilli appear on a CLED agar?
yellow (lactose fermenting)
white (non lactose fermenting)
What antibitoics is E.coli pyelonephritis resistant and sensitive to?
r = amoxicillin
s = co amoxiclav
Why can't catheter bag urine be used for urinalysis results?
because all catheters have bacteria and white cells in, even without an infection
Benefits of CLED agar?
promotes UTI pathogens
distinguished lactose and non lactose fermenting
prevents proteus swarming
When should you treat asymptomatic bactriuria?
in pregnant women
What is erysipela?
intradermal skin infection
What causes erysipela?
group A beta haemolytic streptococcus and staphylococcus aureus
What is cellulitis?
a subcutaneous skin infection
What causes cellulitis?
group A beta haemolytic streptococcus (occasionally B, C, G) and staphylococcus aureus
In who are atypical organisms causing skin infections common?
IV drug users and immunocompromised
What organisms commonly cause skin soft tissue abscess?
What organisms commonly causes lung abscesses?
staphylococcus aureus, kelbiella pneumoniae, anaerobic organisms, mycobacterium tuberculosis
What organisms commonly cause liver abscesses?
gram negative, strep.milleri, anaerobes, entamoeba histolytica in tropic
What organisms commonly cause kidney abscesses?
e.coli and klebsiella
What organisms commonly cause bowel abscesses?
gram negative, anaerobes, strep.milleri
How does impetigo present?
itchy, growing in size spot on the face, it weeps and crusts
Treatment of impetigo?
What swab is most appropriate for impetigo?
black charcoal swab
What is impetigo commonly caused by?
How does celluilitis present?
erythematous, hot and tender skin, commonly of leg, fever, painful
What investigations should be done for cellulitis?
take blood from more than one sire on more than one occasion
Treatment of s.pyogenes?
What organism commonly causes cellulitis?
What does MRSA stand for?
methicillin resistant staphylococcus aureus
How is MRSA carriage identified?
chromogenic MRSA plate on swabs from the axillae and groin
What kind of antibiotic is vancomycin?
Treatment of community acquired pneumonia?
What pathogens atypically cause community acquired pneumonia?
How does pneumonia present?
increased HR and RR but low BP, cough, confusion
Treatment of legionella pneumophilia and why?
clarithrimycin or ciprofloxacin as atypical pathogens that cause pneumonia are not sensitive to amoxicillin
What investigation in done in chronic bronchitis?
What does gram negative with white colonies of chocolate agar suggest?
What is the treatment of H.influenzae
amoxicillin and doxycycline
What agars is H.influenzae testing on?
blood agar and chocolate agar
Why is chocolate agar needed for H.influenzae?
the heating of the agar causes release of nutrients that H.influenzae needs for its fastiduous growth, X and V plates have been added too and it only colonies around the XV disc as both are needed, confirming H.influenzae
What 2 stains are used to detect mycobacteria?
ziehl neelsen stain and auramine phenol flourescent stains
Why does TB not show anything on gram stain?
has a different cell wall from other bacteria
What culture medium is used in TB and why?
Lowenstein Jensen Slope - as MTB divides very slow and may take up to 6 weeks to grow
What is seen on TB biopsy?
How can sputum be obtained?
induced or bronchoalveolar lavage
What will sputum show in HIV?
cysts of P.jiroveci
Treatment of P.jireoveci?
prednisolone if significant type 1 resp failure
CD4 count in HIV?
Treatment of pseudomonas in bronchietasis exacerbatio?
antipseudomonal beta lactam or fluroquinolone
What medium are fungus grown on?
Examples of fungus infections?
aspergillus fumigatus and candida albicans
What are the main bacterial causes of meningitis in neonates?
e.coli, group b streptococcus and listeria monocytogenes
What are the main bacterial causes of meningitis in infants?
neisseria mengitidis, H.influenzae, Streptococcus pneumoniae
What are the main bacterial causes of meningitis in young adults?
neisseria meningitidis, streptococcus pneumoniae
What are the main bacterial causes of meningitis in elderly?
streptococcus pneumoniae, neisseria meningitidis and listeria
What are the main viral causes of meningitis?
mumps, echo, coxsackie, enteroviruses, HSV, lymphocytic chorio meningitis virus, poliovirus
Symptoms of meningitis?
stiff neck, photophobia, headache, rash
Investigations in meningitis?
CSF, bloods, nose and throat swabs, stool, serology
Symptoms of encephalitis?
lethargy, fatigue, decreased consciousness, fever
Main viruses that cause encephalitis?
HSV, varicella zoster virus, parvovirus, HIV, mumps, measles
Investigations in encephalitis?
CSF, PCR, serology of blood to detect antibodies
Treatment of H.influenzae in babies?
IV cefotaxime or ceftrixone
What are 25% of women at childbearing age asymptomatically carrying in their genital tract?
group b streptococcus
Who is at risk of listeria monocytogenes (group B strep)?
pregnant women, neonates, elderly, immunodeficient, chronic glucocorticosteroid use, DM
If at risk of listeria monocytogenes, what additional antibiotic therapy should be used with cefotaxime in meningitis treatment?
Which organism that causes meningitis grows better on chocolate agar than blood agar?
Who needs to be informed of a meningitis outbreak?
public health england, close contacts for prophylaxis
What is used for meningitis prophylaxis?
single dose of oral ciporflaxcin or 2 day course of oral rifampicin
What does a predominantly lymphocytic CSF suggest in CNS diagnosis?
viral meningitis or encephalitis
Treatment of herpes simplex encephalitis?
IV antibiotics and IV acyclovir
What is the most common cause of encephalitis?
herpes simplex virus
How can you confirm a herpes simplex virus?
Bacterial causes of diarrhea?
e.coli, v.cholerae, s.sonnei (dysenteriae)
Organisms from food poisoning causing diarrhea?
salmonella, campylobacter, cl.perfringens, B.cereus, St.aureus
Antibiotic causes of diarrhea?
cl.difficile, st.aureua, c.albicans
Viral causes of diarrhea?
Systemic infections causing diarrhea?
s.typhi, s.paratyphi, h.pylori
How can salmonella be further classified?
presence of different O (oligosaccharide) and H (flagellar) surface antigens, using agglutination tests and are classified using the Kauffman White scheme
What investigations are done on stool samples for persistent diarrhea?
wet prep and staining with fluorescent antibodies
What organism are young children and immunocompromised at risk of that causes watery diarrhea?
c.parvum (detected in stool sample)
What pathogens can be detected in a stool sample?
c.parvum, entamoeba histolytica, giardia lamblia, helminths
Treatment of rota virus gastroenteritis?
supportive, and isolation
How do antibiotics cause diarrhea?
increased risk of infection from PPI acid suppression
Treatment of antibiotic associated diarrhea caused by C.diff?
stop the antibiotics, oral vancomycin or metronidazole, isolationg
Antibiotics for ruptured appendicitis?
CoAmoxiclav or cefuroxime and metronidazole
What is the purpose of an Mz disc?
it contains metronidazole which confirms the presence of anaerobic bacteria if it prevents growth
Antibiotics for anaerobic bacterioides?
Antibiotics for ascending cholangitis?
What is dysentery?
inflammatory disorder of GI tract with blood and pus in the faeces with pain, fever, abdominal cramps, usually caused from disease of the large intestine
Gram negative bacilli organisms in the GI tract?
salmonella, shigella, e.coli, campylobacter jejuni, helicobacter pylori
What is infectivity?
the ability to become established in a host
What is virulence?
the ability to cause disease
What is invasiveness?
capacity to penetrate mucosal surface to reach normally sterile sites
What is a microbiome?
the totality of microorganisms, gentic elements and enviromental interactions
the use of genetics to describe microoragnisms diversity
What are the different types of adhesions that help bacteria bind to mucosal surfaces?
fimbriae, non fimbrial proteins, lipid, glycosaminoglycans, lectins of viruses and parasites, miscellaneous viral capsids
Virulent factors in bacteria?
pili for adherance to mucosal surface
motility to reach mucosal surfaces
IgA protease for IgA cleavage
iron binding proteins to trap iron
capsule to prevent phagocytosis and complement deposition
antigenic variation for evasion of antibodies
Types of toxins?
ADP ribosylating, adenylate cyclase, RNA gangliosidase, metalloproteiniase, cholesterol dependent
What are superantigens?
bacteria and viruses can produce antigens that bind outside the peptide groove of the T cell receptor to stimulate a large number of T cells e.g. EBV
Where are the 2 places that toxins can be?
chromosomal or on plasmids
What is C.diphtheriae?
a toxin spread by droples that inhibits protein synthesis and toxin recognition on Elek plate, preventing with vaccination