Microbiology Flashcards
Name 2 antibiotics that interfere with folic acid metabolism
. Trimethoprim
• sulfonamides
Name 2 antibiotics that interfere with cell wall synthesis
• Beta lactaMs
• glycopeptides
Also: lysozyme, cycloserine, bacitracin
Name 5 types beta lactaMs
• Penicillin
• beta lactam - beta/ lactamase inhibitor combinations
• cephalosporins
• carbapenems
• monobactams
Name 5 types penicillins with examples
• Natural penicillins: penicillin g, vk (narrow spectrum, primarily G +)
• beta lactamase resistant: methicillin, oxacillin, cloxacillin (staphylococci)
• amino penicillins semi synthetic: ampicillin, amoxicillin (broad spectrum)
• carboxy penicillins
• ureido penicillins: carbenicillin, piperacillin (pseudomonas)
How are bacteria resistant to penicillins? (2)
Enzymatic degradation
• G +: penicillinases
• G - : beta lactamases (tem-1 /shV-1)
Name 4 beta-lactam-beta /lactamase inhibitor combinations
• Augmentin: co- amoxicillin - clavulanic acid!
. PiperaCillin: tazobactam !
• ticarcillin: clavulanic
• ampicillin: sulbactam
Name 3 second generation cefalosporins
• Cefoxitin!
• cefuroxime
• cefamandole
Which antibiotics have the broadest antimicrobial spectrum and are beta lactamase stable
CarbapenemS
Name 2 glycopeptides antibiotics and moa
• Vancomycin
• teicoplanin
- Interfere with cell wall synthesis by binding to terminal d-ala-d-ala (only G + bc large molecules that they can’t penetrate )
Name a side effect of glycopepticles
Nephrotoxic
Which antibiotics are cell membrane inhibitors and what is their spectrum of activity
Polymyxin’s
Used as last resort for multi drug resistant bacteria (neuro and nephrotoxic): acinetobacter baumanii, pseudomonas aeruginosa, carbapenemase producing enterobacteriaçae (cre)
Nb no gram positive or anaerobic cover
Name 2 inhibitors of folate (nucleic acid) synthesis and use
• Sulfonamides: sulfamethoxazole (bacteriostatic, )
• trimethoprim
( usually used together for UTI, pneumocystis pneumonia, drug prophylax in HIV)
Name 3 side effects sulfonamides
• Fever, rashes! Photosensitive, bone narrow suppress
• Steven Johnson syndrome!,erythema multiforme
• toxic epidermal necrolysis
Name 2 antibiotic inhibitors of DNA (nucleic acid) synthesis
• Quinolones:
-1st gen- nalidixic acid (G-)
-2nd gen - fluoro quinolones: ciprofloxacin (G-, g+, excellent pseudomonas)
-3rd gen - levo floxacin
-4th gen: trovafloxaCin
• metronidazole
Name antibiotic inhibitors of m RNA (nucleic acid) synthesis
Rifampicin
Name 3 contraindications and side effects fluoroquinolones
Contraindications
• pregnancy
• children - damage growing bone and cartilage
Side effects
• tendinitis and tendon rupture in > 60 and corticosteroid use
Name 7 antibiotic inhibitors of protein synthesis with examples
• Aminoglycosides: gentamicin, neomycin, streptomycin (bactericide , prevent formation initiation complex) (g+, g-, pseudomonas)
• tetracyclines: doxycycline (bacteriostatic, block attach of charged amino acyl t rna to the A site on ribosome s.30) (mycoplasma, chlamydia, rickettsiae)
• chloramphenicol (bacteriostatic, bind to ribosome 50S to inhibit peptide transfer) (broad spec, good CSF penetration, reserved for severe haemophilus influenza bc bm suppression)
• Macrolide’s: ace azithro, clarithro, erythromycin (bacteriostatic, bind to ribosome 50s to prevent translocation) (broad spec, pseudomonas, but may aerobic G- enterobac resistant)
• lincosamides: clindamycin (bacteriostatic, ribosome 50s) ( g+ cocci, anaerobes!)
. Oxazolidinone’s: linezolid (bacterio static, 50s) (mrsa and other resistant enterococci and pneumococci)
• streptogramins: quinupristin-dalfopristin ( vancomycin resistant enterococci)
Name 2 side effects aminoglycosides
• Ototoxic
• nephrotoxic
Name 4 contraindications and side effects tetracyclines
Eg doxycycline
Contraindications,
• pregnancy
• children < 8: yellow staining developing teeth, effect bone development
Side effects
• suppress gut -flora: git upset
• resistance transmitted easily: superinfections
Which 3 antibiotics that inhibit protein synthesis share overlapping binding sites and why is this important
Macrolide’s (ace), lincosamides (clindamycin) and streptogramins (quinupristin - dalfopristin) bind to subunit 50S
Therefore if resistance to one group, resistance to all groups
Aerobic g- (esp enterobacteria) are intrinsically resistant to macrolides
Lincosamides may cause antibiotic associated pseudomenbranous colitis by removing normal anaerobic bowel flora, allowing C diff procreation
Describe the components of the chain of infection (6)
Infectious agents: bacteria prions etc →
Reservoir: people, water food →
Portal of exits: blood, secretions etc →
Mode of transmission: physical contacts, droplets, airborne (try to stop here usually)
Portal of entry: mucous membrane, broken skin etc →
Susceptible host: immune deficiency, diabetes, burns, surgery, age →.
Name 5 Tb tests
• Tb microscopy eg auramine fluorescence microscopy
• X pert mtb/rif and Xpert mtb/ rif ultra (real time pcr) (mycobacterium tuberculosis bacilli From sputum,identify rifampicin resistance, < 2 hours )
• line probe assay (genotype mtbdrplus [ ID MTB complex and detect rifampicin and isoniazid resistance ] + genotype mtbdrs/ [also detect fluoroquinolone and second line injectable drug resistances ] by HAIN life sciences)
• X pert xdr cartridge
• liquid culture (take 15 -42 days)
Name 2 limitations Gene X pert mtb/rif and Xpert mtb/ rif ultra
•Low specificity (false negatives)
• can’t determine response to treatment
Approach to Tb GXP positive and rifampicin sensitive? (2)
• Treat as tb, start on regimen 1 ripe
• send one specimen for microscopy
Approach to Tb suspect with GXP positive and rifampicin resistant? (2)
• Treat as mdr-tb and refer to unit
• collect one specimen for culture and DST for rifampiCIN, isoniazid, fluoroqunolone, aminoglycoside
Approach to Tb suspect with GXP positive and rifampicin unsuccessful? (2)
• Treat as tb: start on regimen 1
• collect one specimen for microscopy and LPA (line probe assay)
Approach to Tb suspect with GXP negative? (8)
• Do HIV test!
If HIV positive,
. collect one specimen for culture and LPA or DST (for r and H )
• chest xray
• treat with antibiotics and review after 5 days
-if poor response to antibiotics or clinically Tb on Cxr, treat as Tb and start on regimen 1 ,
-if LPA / DST results show resistant to r and h or r only, treat as mdr-tb and refer to unit
If HIV negative, treat with antibiotics
• good response: no further follow up, advise to returnwhen symptoms recur
• poor response: consider other diagnosis and refer
Approach to Tb suspect with GXP unsuccessful?
Repeat
Approach to Tb suspect with X pert ultra “mtb trace detected”? (3)
• Clinical assessment and collect sputum for Tb culture and DST
. If asymptomatic or clinical findings don’t suggest tb, follow up culture and DST results
. If clinical presentation consistent with tb, commence ds -tb treatment and follow up
Approach to positive Tb fluorescence microscopy smear?
Do line probe assay
Approach to negative Tb fluorescence microscopy smear?
Do culture
Approach to positive Tb culture?
Do ziehl Nielsen microscopy
- if cords, mtbdr plus
- if no cords, Cm
Type specimen needed for anaerobic cultures?
Tissue and fluids
Swabs not acceptable
What is anal sellotape used for
Enterobius threadworms
Which 2 genes cause isoniazid resistance
- Kat G
- inhA
(Also fab G1, oxyr-ahpc intergenic region)
Detected in mtbdr plus line probe assay
What gene detects rifampicin resistance
81bp rpoB gene
What is line probe assay
- Molecular assay based on DNA amplification and reverse hybridisation
- ID MTB complex and rifampicin and isoniazid resistance
- MTBDR plus assay
Name 3 macrolides and moa
- Erythromycin
- azithromycin
- clarithromycin
(Ace)
Broad spectrum but many G - resistant
Bind to 505 bacterial ribosomal unit to prevent translocation
Bacteriostatic
What caused acquired resistance to macrolides?
Loss of binding affinity caused by plasmid-mediated methylation of 23S rRNA
Name 2 lincosamides and moa
- Clindamycin
- lincomycin
Broad spec, esp anaerobes!
Ae = antibiotic associated pseudo-membranous colitis ( C diff )
Name a streptogramin and moa
Quinupristin - dalfopristin
Act synergistically against g+
Disrupt translation mRNA into protein
Mainly to treat vancomycin resistant enterococci
Name antibiotic susceptibility testing methods (5)
- Kirby - Bauer disc diffusion method (qualitative)
- broth microdilution (quantitative) ( test tubes)
- Gradient diffusion e test (quantitative) (strip)
- automated methods: vital, phoenix, microscan
- molecular methods: Gene expert, mtbdr plus LPA, gene sequencing
How report antibiotic susceptibility testing results? (4)
- Categorical reporting (intermediate/ sensitive/ resistant)
- MIC data
- cascade reporting (based on principle of antimicrobial stewardship)
- antibiograms
Name 7 high risk microbiology specimens
- Blood borne virus infection or carrier: hepatitis b/c, HIV /AIDS
- Tb
- brucellosis
- typhoid / paratyphoid
- prion disease
- e coli 0157
- viral haemorrhagic fivers
How transport high risk microbiology specimens (4)
- Label container properly
- biohazard plastic bag
- laboratory request form
- transport immediately and inform lab
