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Microbiology Nuts

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Microbiology Nuts & Bolts Session 4 Dr David Garner Consultant Microbiologist Frimley Park Hospital NHS Foundation Trust – PowerPoint PPT presentation

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Title: Microbiology Nuts


1
Microbiology Nuts BoltsSession 4
  • Dr David Garner
  • Consultant Microbiologist
  • Frimley Park Hospital NHS Foundation Trust

2
Aims Objectives
  • To know how to diagnose and manage
    life-threatening infections
  • To know how to diagnose and manage common
    infections
  • To understand how to interpret basic microbiology
    results
  • To have a working knowledge of how antibiotics
    work
  • To understand the basics of infection control

3
Gladys
  • 71 years old
  • Presents with painful swollen left leg
  • On examination
  • Temperature 38.5 oC
  • Erythema overlying left lower leg
  • Unable to weight bear
  • How should Gladys be managed?

4
Differential Diagnosis
  • Immediately life-threatening
  • Common
  • Uncommon
  • Examination and investigations explore the
    differential diagnosis
  • What would be your differential diagnosis for
    Gladys?

5
Differential Diagnosis
  • Immediately life-threatening
  • Sepsis
  • Common
  • Osteomyelitis, cellulitis, varicose eczema
  • Uncommon
  • Inflammatory?
  • How would you investigate this differential
    diagnosis?

6
  • Full history and examination
  • Bloods
  • FBC, CRP, UEs
  • Clotting
  • Blood culture
  • Wound swabs

7
  • Bloods
  • WBC 25 x 109/L
  • CRP 457
  • UEs Urea 9, Creat 113
  • INR 1.5
  • How are you going to manage Gladys now?

8
How to interpret a wound swab result?
  • Appearance
  • Not available
  • Microscopy
  • Not available
  • Culture
  • Is the organism consistent with the clinical
    picture?

9
Culture how are wound swabs processed?
  • Cannot do a Gram-stain
  • Pus is always better!
  • Mixture of selective and non-selective agar
    plates
  • Culture 24-48 hours
  • Sensitivities 24-48 hours
  • Swab total time 48-96 hours
  • A swab cannot diagnose an infection, that is a
    clinical judgement, it tells you what might be
    causing the infection

10
Culture classification of bacteria
11
Classification of Gram-positive cocci
12
Group Names Flora Clinical
A S. pyogenes Mucus membranes? Tonsillitis, cellulitis, septic arthritis, necrotising fasciitis
B S. agalactiae Bowel, genital tract (females) Neonatal sepsis, septic arthritis, infective endocarditis, association with malignancy?
C S. dysgalactiae S. equi S. equisimilis S. zooepidemicus Mucus membranes, animals? Tonsillitis, cellulitis, septic arthritis
D Enterococcus faecalis Enterococcus faecium Bowel Infective endocarditis, IV catheter associated bacteraemia
F Milleri group S. intermedius S. anginosus S. constellatus Bowel Empyema (pleural and biliary), bowel inflammation and perforation
G S. dysgalactiae Mucus membranes, bowel? Tonsillitis, cellulitis, septic arthritis, association with malignancy?
B-haemolytic Streptococci
13
Community Normal Flora
14
Factors Affecting Normal Flora
  • Exposure to antibiotics provides a selective
    pressure
  • e.g. previous b-lactams may select out MRSA
  • Increased antimicrobial resistant organisms in
    the environment
  • e.g. Meticillin Resistant Staphylococcus aureus
    (MRSA)
  • Easily transmissible organisms
  • e.g. Skin flora such as Coagulase-negative
    Staphylococci
  • Immunosuppressants
  • e.g. Steroids, chemotherapy, prosthetic joints etc

15
Back to Gladys
  • Bloods
  • WBC 25 x 109/L
  • CRP 457
  • UEs Urea 9, Creat 113
  • INR 1.5
  • Erythema spreads within the 30 minutes after she
    was examined
  • What is the probable diagnosis?
  • How would you manage Gladys now?

16
Types Causes of Bacterial Skin Infections
  • Ulcers
  • Staphylococcus aureus, b-haemolytic Streptococcii
  • Become colonised with bacteria, especially
    Enterobacteriaceae that DO NOT need treating in
    most patients
  • Take samples from healthy base after debriding
    slough
  • Only treat if increasing pain, erythema or
    purulent discharge
  • Cellulitis
  • Staphylococcus aureus, b-haemolytic Streptococcii
  • Necrotising Fasciitis
  • Beta-haemolytic Streptococcii, Clostridium
    perfringens, Synergistic gangrene

17
Types Causes of Bacterial Skin Infections
  • Ulcers
  • Staphylococcus aureus, b-haemolytic Streptococcii
  • Become colonised with bacteria, especially
    Enterobacteriaceae that DO NOT need treating in
    most patients
  • Take samples from healthy base after debriding
    slough
  • Only treat if increasing pain, erythema or
    purulent discharge
  • Cellulitis
  • Staphylococcus aureus, b-haemolytic Streptococcii
  • Necrotising Fasciitis
  • Beta-haemolytic Streptococcii, Clostridium
    perfringens, Synergistic gangrene

18
Necrotising Fasciitis Treatment
  • Surgical
  • Remove all dead or diseased tissue
  • Antibiotics
  • Combination of b-lactam plus Clindamycin
  • Adjuncts
  • Immunoglobulin

19
How do you choose an antibiotic?
  • What are the common bacteria causing the
    infection?
  • Is the antibiotic active against the common
    bacteria?
  • Do I need a bactericidal antibiotic rather than
    bacteriostatic?
  • Does the antibiotic get into the site of
    infection in adequate amounts?
  • How much antibiotic do I need to give?
  • What route do I need to use to give the
    antibiotic?

20
In reality
you look at empirical guidelines
21
How antibiotics work
22
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23
Antibiotic resistance
24
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25
Other considerations
  • Are there any contraindications and cautions?
  • e.g. Clostridium difficile and clindamycin
  • Is your patient allergic to any antibiotics?
  • e.g. b-lactam allergy
  • What are the potential side effects of the
    antibiotic?
  • e.g. Vancomycin and red man syndrome if infusion
    too fast
  • What monitoring of your patient do you have to
    do?
  • e.g. Teicoplanin levels and full blood count

26
Next Day
  • Still cardiovascularly unstable
  • Bloods
  • WBC 27 x 109/L
  • CRP 411
  • UEs Urea 18, Creat 178
  • INR 1.6
  • Blood Culture
  • Gram-positive coccus in chains
  • What would you do for Gladys now?

27
Gladys
  • After multiple extensive surgical debridements
    and IV Benzylpenicillin and Clindamycin Gladys
    starts to make a slow recovery
  • 2 weeks into admission PICC line becomes
    erythematous
  • IV Flucloxacillin 2g QDS started
  • 2 days later erythema is still spreading
  • Why might Gladys not be responding to antibiotics?

28
Reasons for failing antibiotics treatment
  • Does the antibiotic cover the normal causes of
    this type of infection?
  • Is the patient compliant?
  • Is the patient receiving the antibiotics?
  • If on oral antibiotics is the patient able to
    absorb oral antibiotics?
  • Is the antibiotic appropriate for the patients
    weight?
  • Does the patient have prosthetic material that
    needs removing to allow recovery e.g. IV access,
    urinary catheters etc?
  • Does the patient have a resistant bacteria
    causing the infection e.g. MRSA?

29
Intravenous catheter infections
  • IV lines breach the bodys main barrier to
    infection, the skin
  • The most common causes of infection are skin
    bacteria e.g. Staphylococci
  • Gram-negative bacteria are unusual and normally
    occur in immunosuppressed patients or those on
    antibiotics that cause changes in skin flora
  • The main treatment of an IV line infection is to
    remove the line
  • Essential with Staphylococcus aureus, Pseudomonas
    sp. and Klebsiella sp.

30
Gladys
  • Line site swab grew Staphylococcus aureus
    resistant to Flucloxacillin, i.e. MRSA
  • PICC line removed
  • Antibiotics switched to IV Teicoplanin 6mg/kg as
    body weight over 70kg
  • Erythema settled in 7 days and antibiotics
    stopped
  • Gladys eventually recovered

31
Conclusions
  • Most skin infections are caused by Gram-positive
    cocci e.g. Staphylococci and Streptococci
  • Necrotising fasciitis is an emergency for which
    the main treatment is surgery
  • Antibiotics are chosen to treat the likely
    bacteria
  • All of the microbiology report is important and
    helps with interpretation of the result
  • MRSA is commonly selected by the use of b-lactam
    and quinolone antibiotics and is not treatable by
    either class

32
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