UTS - Microbiology Flashcards
Child presents with sores on face.
(A) What is it? After being Swabbed, the plate shows the below (left) and gram status (what would it be).
(B) What infection is this? Also given Horse Blood Agar plate like below.
(C) What kind of haemolysis?
(D) Precautions needed to limit spread?
(A) What is it? = Impetigo (also called school sores)
(B) What infection is this? = Streptococcus pyrogenes (single chain cocci) – Gram positive cocci
(C) What kind of haemolysis? = Beta-Haemolysis (breaks down haemoglobin completely leaving clear zone around growth). Alpha (partial break down leaving green zone around growth).
(D) Precautions needed to limit spread? = Isolation until 24 hours after antiobiotics (penicillin or amoxycillin as gram positive)
Pertussis
(A) What can do you do test for it?
(B) How does this manifest differently in children vs adults?
(C) What antibiotic would you use to treat it?
(D) What additional steps can you take to limit spread?
Bordetella pertussis (Whooping Cough)
(A) What can do you do test for it? = Nasopharyngeal Swab (NPS), Microscopy, Culture and Sensitivity (MCS), PCR, Blood Test (IgA/G Serology)
(B) How does this manifest differently in Children vs Adults? = More serious in children. <6 months may not show signs of classic Pertussis, instead have pause in breathing (Apnoea). Adults: coughing, sneezing, nasal discharge, fever
(C) What antibiotic would you use to treat it? (D) What additional steps can you take to limit spread? = Macrolides, such as Clarithromycin, Erythromycin and Azithromycin
(D) What additional steps can you take to limit spread? = Vaccination, Isolation
Define Sterilisation and Disinfection
Disinfection – a process which eliminates most or all disease-causing organisms from a surface – usually inanimate surfaces, and typically uses a chemical disinfectant. This reduces the likelihood of transmission.
Sterilisation – the process of complete destruction or removal of all viable microorganisms from a surface, liquid or object. Examples are steam autoclaves, hot air ovens, γ (gamma) irradiation, UV irradiation and chemical sterilization.
E. coli is cultured in solutions of 70% ethanol, 70% ethanol + soil, bleach, bleach + soil.
Which solutions would have growth and why?
Solutions with organic matter (soil) will have growth because they act as food and protectant barrier.
Sonidet (neutral liquid detergent) – not effective unless used in conjunction with vinegar.
Spores can only be killed by autoclaving.
Staphylococcus aureus and Bacillus subtilis are both heated up to different temperatures. Staph dies at 100 whereas Bacillus survives after 5 minutes at 112. Why?
• Bacillus forms endospores which can survive at higher heat
Briefly explain Disc-diffusion method of antibiotic sensitivity testing
- Agar cultured with pathogen
- Several discs of antibiotics placed on plate and incubated
- As organism grows, the antibiotics diffuse
- If sensitive to antibiotic, there will be a zone of no growth
- >6mm is cut off for sensitivity
Why treat with bacteriostatic antibiotics, if they don’t kill bacteria?
Prevent growth of bacteria allowing for immune system and other physiological processes (e.g. urination, mucociliary clearance) to remove the bacteria
Two isolated organisms are cultured for sensitivity using the Disc-diffusion method. Questions on following slides
Sensitive (S) or Resistant (R)?
If both organisms are Staphylococcus aureus, what is the significance of the result on plate B?
• Plate B indicates Methicillin-Resistance S. aureus (MRSA)
Woman is taking multiple Antibiotics for sepsis and for UTIs and has been in hospital for a week. She now suffers from severe diarrhoea with no fever
- What Pathogen?
- What mechanism (how)?
- What is the management for this type of infection? 3 things
- What tests would you perform?
- What Pathogen? = Clostridium difficile (C. diff).
- What mechanism (how)? = Multiple antibiotics eradicates normal flora creating vulnerability to opportunistic infection
- What is the management for this type of infection? 3 things = IV fluids (fluids lost due to diarrhoea), Cease current antibiotics, Give Metronidazole then Vancomycin (if severe), Supportive care
- What tests would you perform? = Stool culture, PCR, FBC (for WBC)
Is it normal to have growth in a culture from urine? What does the below culture signify? What antibiotic would you use?
Scenario: Child comes into surgery with these lesions on his face. You suspect that it might be ‘school sores’, impetigo.
- What pathogens will be responsible for this infection?
- How can you confirm your suspicion of this diagnosis?
- How would you treat this infection?
The results of the culture come back as shown:
- Describe the gram stain:
- How does this change or confirm your diagnosis?
- Is there anything that you could do immediately that would distinguish the suspected diagnosis?
- How will you now treat the infection?
Give the most appropriate b-lactam antibiotic to treat isolate A.
Give the most appropriate glycopeptide antibiotic to treat isolate B.
Cefoxitin disks are used to determine methicillin susceptibility or resistance in staphylococci. The identity of isolate B therefore is….
If a hospital in-patient was colonised with isolate B, what would be some appropriate management strategies to minimise the spread of infection?
Disc diffusion:
Q: Why there is a change in shape – the key shape with B-lactamase and what this signifies?
- Extended spectrum B-lactamases (EBSL) confer resistance in vivo to almost all beta lactams. They attack b-lactam rings – leads to keyholes or champagne corks
- Augmentin in a combination of amoxicillin and clavulanic acid. Clav acid inhibits the ESBL and enhances activity of cefotaxime and cefepime in the picture – hence the keyhole effect
- Inducible AmpC B-lactamases lead to a “flattening effect” (of the circle on the agar plate). These also confer resistance to almost all b-lactams. Their presence is detected by switching-on gene expression by inducers such as imipenem and can render other antibiotics (e.g. cefoxitin) to be resistant
