BSAC recommendations for interpreting the susceptibility of urinary tract isolates

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BSAC recommendations for interpreting the
susceptibility of urinary tract isolates

• Jenny Andrews

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UTIs

• Frequency of micturition
• Dysuria
• Urgency
• Suprapubic pain
• Pyrexia
• Pyelonephritis

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Bacterial causes of UTIs
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Non-bacterial causes of UTIs
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Simple UTIs

• Women of child-bearing age
• E. coli
• P. mirabilis
• Klebsiellae
• Enterococci
• S. saprophyticus
• Group B Streptococci

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Prevalence of organisms isolated from samples
taken in the community (female)
City Hospital data
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Complicated UTIs

• Male patients
• Abnormal anatomy
• Catheterisation
• Children
• Immunocompromised patients
• Elderly

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Microbial causes

• Enterobacteriaceae
• Non-fermenters
• Staphylococci
• Enterococci
• Antibiotic-resistant strains frequently isolated

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UTI in men
Wallach, 2001 McMurdo and Gillespie, 2000
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Conditions associated with or predisposing to
lower UTI in men

• Prostatitis/Prostate enlargement
  (common in older men)
• Abnormal urinary tract, anatomical
  changes,calculi and tumours
• Impaired host defences
• Impaired renal function

Bailey 1996
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UTI in men organisms associated with infection

• E.coli the most common pathogen in acute and
  chronic prostatitis
• Klebsiella spp. and P. mirabilis isolated less
  frequently
• Hospital acute cases may involve staphylococci
  and occasionally enterococci or Pseudomonas spp

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Prevalence of organisms isolated from samples
taken in the community (male)
City Hospital data
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Laboratory diagnosis

• Mid Stream Urine
• Low epithelial cell count
• Pyuria/haematuria
• Semi-quantitative culture
• 105 cfu/ml bacteria considered significant
• Identification (some laboratories do not ID urine
  isolates) and susceptibility testing

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BSAC Systemic recommendationsNon-species
specific
Table 6 MIC and zone breakpoints for
Enterobacteriaceae (including Salmonella and
Shigella spp.).
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BSAC Species specific breakpoints for simple UTIs
NB. These recommendations are for organisms
associated with uncomplicated urinary tract
infections. For complicated infections systemic
recommendations should be used.
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BSAC Species specific breakpoints for simple UTIs
NB. These recommendations are for organisms
associated with uncomplicated urinary tract
infections. For complicated infections and
infections caused by Staphylococcus aureus and
Staphylococcus epidermidis, which are associated
with more serious infections, systemic
recommendations should be used.
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Organism Identification

• Essential for interpretation of susceptibility
• Chromogenic media

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Chromogenic agar (6570 UTI)
Klebsiella-Enterobacter-Serratia
28.6
Proteus-Morganella-Providencia
6.9
72.5
Data presented by Trevor Winstanley at User
Group meetings in 2005 (Power Point presentation
available on the BSAC web site (www.bsac.org.uk)
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Footnotes to the UTI tables
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BSAC recommendations

• The recommendations are for organisms associated
  with uncomplicated urinary tract infections
• For complicated infections systemic
  recommendations should be used
• For infections caused by S. aureus and S.
  epidermidis, which are associated with more
  serious infections, systemic recommendations
  should be used

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BSAC recommendations

• If an organism is isolated from multiple sites,
  for example from blood and urine, interpretation
  of susceptibility should be made with regard to
  the systemic site.
• Direct susceptibility tests on urine may be
  performed as long as the inoculum gives
  semi-confluent growth.

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BSAC recommendations

• In the absence of definitive organism
  identification, use the recommendations most
  appropriate for the presumptive identification,
  accepting that on some occasions the
  interpretation may be incorrect. A more cautious
  approach is to use systemic recommendations

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BSAC recommendations

• The identification of Enterobacteriaceae to
  species level is essential before applying expert
  rule for the interpretation of susceptibility
  e.g. recommendations for ampicillin/amoxicillin
  are for E. coli and P. mirabilis not for species
  that have chromosomal penicillinase (Klebsiella
  spp.) or those that typically have inducible AmpC
  enzymes (e.g. Enterobacter spp., Citrobacter spp.
  and Serratia spp.)

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Under review by EUCAST/BSAC

• Use of trimethoprim for the treatment of
  enterococci
• The clinical efficacy of mecillinam in the
  treatment of ESBL infections

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Gaps in the Coliform recommendations

• Coliform means like an E. coli, the
  recommendations should not be used for
  Enterobacter spp. etc.
• ID to species level is essential for the correct
  interpretation

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Should nalidixic acid be used to detect FQ
resistance?

• Using nalidixic acid alone 25-40 of isolates
  with LLR will be reported resistant to
  ciprofloxacin
• Organisms with LLR are probably susceptible in
  uncomplicated infections because of the high
  concentration of drug in urine

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Summary

• BSAC urinary breakpoints are for simple UTIs
• For complicated infections systemic
  recommendations should be used
• ID is necessary for the interpretation of
  susceptibility and the application of expert
  rules (see the Power Point presentation on the
  BSAC web site for the User Group Meeting in 2005
  Trevor Winstanley Expert rules and inexpensive
  identification methods)
• EUCAST are preparing a document on expert rules
  that should be available at the end of the year