Microbiology Flashcards
Where do antibiotics target?
Cell wall Ribosomes DNA replication DNA gyrases Metabolic pathways
What are the two types of bacteria and how are they different?
Gram positive - has a double layered cell wall
Gram negative - has a single layered cell wall
Which antibiotics act on the cell wall?
Penicillins
Cephalosporins
Glycopeptides
How do penicillins and cephalosporins (beta-lactams) work?
They are bacteriocidal and blocks synthesis of the cell wall
What are the types of penicillins and what type of bacteria do they act on (+ve or -ve)?
Flucloxacillin - Gm +ve Amoxicillin - Gm +ve and -ve Co-amoxiclav - Gm +ve and -ve Temocillin - Gm-ve (Piperacillin/tazobactam) - Gm +ve and -ve
What are the 4 C’s you should avoid using?
Cephalosporins
Co-amoxiclav
Ciprofloxacin
Clindamycin
Why should you avoid using the 4 C’s?
They are broad spectrum antibiotics so have a higher risk of c. Difficile infection
Protozoa is a eukaryote. True or false?
True
What type of microorganism can undergo haemolysis?
Streptococci
What are some microbiological tests?
Blood culture Urine culture Faeces culture Swab of pus PCR
What does exogenous microorganisms mean?
Not normal flora
What does virulence mean?
The ability of a microbe to cause damage to a host
What is a pathogen?
A harmful organism producing a pathology
Commensal bacteria is part of your normal flora, ture or false?
True
Where would an opportunistic pathogen be found?
In an immunocompromised patient
Give examples of some gram negative bacteria.
Neisseria
Escherichia
Salmonella
Shigella
Give examples of gram positive bacteria.
Streptococcus
Staphylococcus
Enterococcus
Give examples of fungi
Candida spp. (Yeast)
Aspergillus (mould)
Give examples of protozoa
Malaria
Toxoplasma
How do viruses work?
Attach Enter (non-enveloped enter via endocytosis, enveloped ones fuse their membrane and the cells membrane) Uncoat Nucleic acid and protein synthesis Assembly Release (exocytosis)
What is a coliform?
Species of GM-ve bacilli that look like Escherichia coli on gram film and when cultured on blood agar
Note many are part of normal gut flora
What is the first line antibiotic used to treat coliform infections?
Gentamicin
Why is haemolysis of streptococci used?
To help classify the streptococci
What happens in alpha-haemolysis?
Partial haemolysis- causes a greenish decolourisation around the colony
What happens in beta-haemolysis?
Complete haemolysis - there is a complete clearing around the colony (looks like its glowing)
What happens in gamma-haemolysis?
No haemolysis
What are the most pathogenic streptococci?
Beta-haemolytic group A
What causes scarlet fever?
Streptococci in group A
Enterococci is non-haemolytic, true or false?
True
Give examples of staphylococcus bacterium.
S. Aureus (+ve)
S. Epidermidis (-ve)
What does neisseria spp cause?
STD/STI
Meningitis
Where does escherichia coli effect?
GI tract
What are the 5 i’s of infection?
Inhalation Ingestion Inoculation Mother to infant Intercourse
What genus does a gram positive sample belong to if it is cocci in clusters?
Staphylococcus
What is haemolysis?
The ability of the bacterium to break down the red blood cells
How can you physically tell the difference between streptococci and staphylococcus?
Streptococci = chains
Staphylococcus = clusters
What does MRSA stand for?
Methicillin resistant staph aureus
What categaries does streptococci subdivide into?
Alpha beta and gamma haemolytics
What bacteria is alpha haemolytic?
Strep. Pneumoniae
Strep. Viridans
What bacteria is beta haemolytic?
Group A strep. (Strep pyogens)
Group B strep (neonatal meningitis)
What does non-haemolytic bacteria called?
Enterococcus sp.
What is c. Difficile?
Anaerobic bacilli
Are coliforms gram positive or negative?
Gram negative
What is virulence?
degree of pathogenicity (ability of pathogen to cause disease) of an organism
what are the 3 types of atmostphere that bacteria can grow in?
Aerobic
Microaerophilic (reduced O2 and more CO2)
Anaerobic
What type of bacteria release exotoxins?
Gram positive
what type of bacteria release endotoxin?
Gram negative
what is an exotoxin?
Toxin produced inside gram positive bacterial cells that is exported out
what is an endotoxin?
Toxin found in gram negative bacterial cell wall.
Give examples of fungi.
Mould (aspergillus)
Yeasts (candida)
what are the different types of gram positive cocci?
Streptococcus
Enterococcus
Staphylococcus
how do you differentiate between staphylococcus?
coagulase test
How do you distinguish between streptococcus and enterococcus and why?
Haemolysis as strep will either be alpha or beta, enterococcus will be gamma
if gram positive cocci are found in clusters what does this suggest?
Staphylococcus
How do you identify staph aureus?
Gram positive cocci, in cluster, that is coagulase positive, appearing golden
what is the antibiotic of choice to treat staph aureus infection?
Flucloxacillin
what would coagulase negative staphylococcus suggest (including common cause of infection), and what is this?
Staph epidermidis
normal skin commensal, can be found in IV line infections
why does the immune system give rise to fever?
Growth of pathogens is slow if temp increases
How are gram negative cocci orientated?
Diplococci
Give examples of gram negative cocci bacterium (2)
Neisseria gonorrhoea
Nisseria meningitidis
What are coliforms?
Gram negative bacilli
which can be aerobic or anaerobic
Give examples of coliforms both commensals and pathogens.
Gut commensals: - E coli - Klebsiella - Proteus Gut pahtogens: - Salmonella - Shigella - E coli 0157
give examples of strict aerobes.
Gram negative bacilli:
pseudomonas aeruginosa
Legionella pneumophilia
What type of bacterium is campylobacter and what does it cause?
Spiral or curved gram negative bacilli causing food poisoning
what group of bacterium is haemophilus influenzae caused by?
small gram negative bacillus
what is clostridium spp. and where is it normally found
gram positive anaerobic bacilli that is part of normal bowel flora
what is the first line antibiotic used to treat coliforms?
Gentamicin
what is the first line treatment for infections caused by anaerobes?
metronidazole
what type of bacteria is TB
Microbacteria characterised by thick waxy outer coat
what are the different ways of bacterial gene transfer and how do they work?
Transformation (DNA from dead bacteria taken up)
Conjugation (fimbria to transfer plasmid DNA - sex)
Transduction (viruses infecting bacteria can transfer from one to the other)
give an example of a narrow and broad spectrum antibiotic.
Narrow = penicillin Broad = tetracycline
what type of cell wall do gram positive organisms have?
Thick layer of peptidoglycan and single phospholipid bilayer
What type of cell wall do gram negative organisms have?
Thin layer of peptidoglycan and two phospholipid bilayers
why are cephalosporins limited to hospital?
May induce clostridium difficile infection
what type of antibiotic is vancomycin and what does it act on?
Glycopeptide which acts on gram positive cell walls
which groups of antibiotics inhibit protein synthesis?
Macrolides
Tetracyclines
Aminoglycosides
What group is erthromycin in?
Macrolides
Give an example of a tetracycline.
doxycycline
What group is gentamicin in?
Aminoglycosides
How do macrolides and tetracyclines work?
Bacteriostatic attaching to bacterial ribosomes to prevent protein synthesis
How do aminoglycerides work?
Bactericidal binding to ribosomes so kill that protein.
what are the side effects of gentamicin?
Kidney damage
Damage of CN VIII resulting in deafness and dizziness
which antibiotics act on bacterial DNA?
Metronidazole
Trimethoprim
Fluoroquinolones
How does metronidazole work and what is it used to treat?
Causes strand breakage of bacterial DNA
Treats true anaerobic infections
How does trimethoprim work and what does it treat?
Inhibits bacterial folic acid synthesis
Works against gram positivie and negative bacteria
Give examples of fluoroquinolones.
Ciprofloxacin, levofloxacin
how do fluoroquinolones work?
Bactericidal and prevent supercoiling of bacterial DNA
why should you avoid broad spectrum antibiotics?
increase risk of C. difficile
which antibiotics should you avoid in pregnancy?
Gentamicin, tetracycline, fluoroquinolones (avoid trimethoprim and metronidazole in first 3 months)
how do viruses replicate?
Attachment
Entry
Uncoating
Nucleic acid and protein synthesis (using host ribosomes)
Assembly
Release (budding - released in envelope - or lysis - cell burst, and virus escapes)
which antibodies neutralise viruses and how do they do this?
IgG and IgM, prevent virus binding to cellular receptors
how do you detect viruses clinically?
PCR and antigen detection
which groups of antibiotics act by inhibiting protein synthesis?
macrolides, aminoglycerides, clindamycin, tetracylines
which groups of antibiotics act on bacterial DNA?
metronidazole, trimethoprim/co-trimoxazole, fluroquinolones
