Title: Microbiology Nuts
1Microbiology Nuts BoltsSession 4
- Dr David Garner
- Consultant Microbiologist
- Frimley Park Hospital NHS Foundation Trust
2Aims 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
3Gladys
- 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?
4Differential Diagnosis
- Immediately life-threatening
- Common
- Uncommon
- Examination and investigations explore the
differential diagnosis - What would be your differential diagnosis for
Gladys?
5Differential 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?
8How to interpret a wound swab result?
- Appearance
- Not available
- Microscopy
- Not available
- Culture
- Is the organism consistent with the clinical
picture?
9Culture 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
10Culture classification of bacteria
11Classification of Gram-positive cocci
12Group 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
13Community Normal Flora
14Factors 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
15Back 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?
16Types 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
17Types 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
18Necrotising Fasciitis Treatment
- Surgical
- Remove all dead or diseased tissue
- Antibiotics
- Combination of b-lactam plus Clindamycin
- Adjuncts
- Immunoglobulin
19How 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?
20In reality
you look at empirical guidelines
21How antibiotics work
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23Antibiotic resistance
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25Other 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
26Next 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?
27Gladys
- 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?
28Reasons 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?
29Intravenous 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.
30Gladys
- 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
31Conclusions
- 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
32Any Questions?