Resistance is futile ? – antibiotic
resistance in Scottish pneumococci
Andrew Smith
Professor of Clinical Bacteriology
Acknowledgements
Ben Cooke
Mathew Diggle
Karen Lamb
Christopher Robertson
Donald Inverarity
Johanna Jefferies
Giles Edwards
Stuart Clarke
Jim McMenamin
Tim Mitchell
All staff at SHLMPRL
Prof T Mitchell Pneumococcal
Research Group
Resistance is futile?
Defining resistance
• Resistance may be defined from a clinical
perspective
High breakpoint
Low breakpoint
% of isolates
Likely to respond
Sensitive
Indeterminate response
Intermediate
Not likely to respond
Resistant
Antibiotic concentration ug/ml
• Clinical resistance: When infection is highly unlikely
to respond even to maximum doses of antibiotic
(EUCAST)
Defining resistance
• Resistance may be defined from a biological
perspective
– National variations in breakpoints
• Resistance definitions usually based on in-vitro
quantitative testing of bacterial suspensions to
antibacterial agents
Minimum inhibitory
concentration
Defining resistance
% of isolates
Microbiological resistance
Resistant
Sensitive
Breakpoint
Antibiotic concentration ug/ml
• Microbiological resistance: bacteria that possess any
resistance mechanism demonstrated either phenotypically or
genotypically (EUCAST)
Confounding variables
• Laboratory
– Inoculum size, growth phase, planktonic, pH, atmosphere…
• Clinical
– Co-morbidities, pus collections, foreign bodies, site of
infection ………..
– Pharmacokinetics
– Pharmacodynamics
Mechanisms of resistance in pneumococci
• Penicillin resistance: Pencillin binding proteins (PBPs)
• 6 PBP’s described in the pneumococcus
• Alterations in PBP’s = resistance
• Resistance= mosiacism in PBP 2b, 2x and 1a
Mechanisms of resistance in pneumococci
• Erythromycin resistance
• Methylation Erm(B) MLSb
• Macrolide efflux Mef(A)
• Other mechanisms (less prevalent)
Penicillin resistance in pneumococcus
1st Reported in 1967 (Hansman & Bullen 1967)
Serotype 23 Pen MIC = 0.6ug/ml
Subsequent reports from Papua New Guinea
1974 12% - 1980 30% resistant
1974-1984
Foci with >10% include New Guinea, Israel, Spain, Poland, South
Africa & USA (states)
Klugman Clin Micro Rev 1990 171
Penicillin resistance in pneumococcus (1990’s)
Rates 5-80% (Forward Sem Resp Infect 1999 243-254, Thornberg
et al AAC 199943: 2612; Song et al CID 1999 28: 1206)
USA 2/3 of PRP’s have MICs of 2ug/ml & others = 4ug/ml
(Doern et al EID 1999; 5: 757)
MIC values of 8ug/ml reported from Spain (Baquero et al AAC
1999; 43: 357) & USA (Doern et al AAC 1996; 40: 1208)
MIC of 16ug/ml reported from Eastern Europe & USA
(Applebaum CID 1992; 15:77; Gross et al AAC 1996; 39: 116668)
Prevalence of penicillin non-susceptible
pneumococcus in Europe (EARS 2008)
• 1-5% UK, Germany , Austria, Norway & Sweden
• 10-25% Portugal, Ireland, Finland & Turkey
• 25-50% Spain, France, Greece & Israel
Prevalence of erythromycin resistant
pneumococci in Europe (EARS 2008)
• 1-5% Latvia & Sweden
• 10-25% UK, Spain, Portugal,
Germany, Poland, Norway & Finland
• 25-50% France, Italy & Greece
Aims
• Identify susceptibility profiles (1999-2007) to
• Penicillin & erythromycin
• Establish contribution that different serogroups and
sequence types make to the burden of antibiotic
resistance.
• Explore extent to which internationally recognised
PMEN (Pneumococcal molecular epidemiology
Network) clones are seen in Scotland
Methods
• Isolates obtained from SHLMPRL
• Received from diagnostic labs in Scotland from all
invasive isolates
• Typing & antimicrobial testing as part of Electronic
Communication of Surveillance in Scotland (ECOSS)
• 4,727 isolates available covering 1999 - 2007
Methods
• Susceptibility testing
• Using E-tests
• Breakpoints derived from BSAC
• Typing of isolates
– Serogrouping 1999-2002
– Serotyping 2003-2007
– MLST 2003-2007
Multi-Locus Sequence Typing (MLST):



Based on sequences from 7 housekeeping genes
7 sequences assigned a number - barcode
Each barcode assigned a number - sequence type
(ST)
Strain
aroe
gdh
gki
recP
spi
xpt
ddl
ST
01-2696
12
5
13
5
17
4
20
227
01-1956
12
8
13
5
16
4
20
306
IPD Serotypes (2001-2006) total
PCV7
Sero
4
6B
9V
14
18C
19F
23F
ST
205
138
162
9
113
162
37
Sequence types (2001-2006) total
PCV7
Sero
4
6B
9V
14
18C
19F
23F
ST
205
138
162
9
113
162
37
2001 serogroups Blood /CSF under 5
PCV7
Sero
4
6B
9V
14
18C
19F
23F
ST
205
138
162
9
113
162
37
2001 serogroups Blood /CSF over 65
PCV7
Sero
4
6B
9V
14
18C
19F
23F
ST
205
138
162
9
113
162
37
Results
Penicillin non-susceptibility
I=0.12-1mg/L
R=≥2mg/L
Results
Penicillin non-susceptibility
I=0.12-1mg/L
R=≥2mg/L
• Pneumococcal penicillin resistance is rare
• MIC ≥ 2mgl-1
• Highest MIC found = 2mgl-1
• N=7 (0.15%)
• Mainly represented by serogroup 14
• Pneumococcal penicillin intermediate sensitivity
• MIC 0.12-1mgl-1
• N=148 (3%)
• Mainly represented by serogroup 14
• Pneumococcal penicillin non-susceptible
• MIC >0.12mgl-1
• N=155 (3%)
• N=87 (56%) from >65yrs
• N=22 (14%) from <16 years
• N=13 (8%) from <2yrs
• Pneumococcal penicillin non-susceptible
• MIC >0.12mgl-1
• Varied with age (P=0.01)
• 4.1 % >65yrs (95% CI 3.3-5.0%)
• 2.4% 16-64 yrs (95% CI 1.8-3.2%)
• 3.1% <16 yrs (95% CI 2.1-4.7%)
• Pneumococcal blood culture isolates
• N=4531 (96%)
• N= 143 (3%) were pen non-susceptible (MIC >0.12mgl1)
• Pneumococcal CSF isolates
• N=171 (4%)
• N=6 were pen non-susceptible (MIC >0.12mgl-1)
Total CSF isolates & MIC >0.12
All invasive isolates
Serogroup contribution: penicillin intermediate & resistant
PCV7
Sero
4
6B
9V
14
18C
19F
23F
ST
205
138
162
9
113
162
37
Clinical significance of intermediate sensitivity?
• Non-meningeal pneumococcal infections
• Doubtful (Choi & Lee 1998)
• Drug levels usually >MIC (Heiber & Nelson 1977)
• Pharmacodynamics: T>40% MIC
• Meningeal pneumococcal infections
• Impact of blood brain barrier
• Lower levels of resistance associated with failure
(Friedland 1992)
• Increased failure of monotherapy if MIC>1
Results
Erythromycin resistance
• Macrolide resistance (>0.5mgl-1)
• N=585 (12.3%)
• 95% recovered from blood cultures
• Significant reduction over
the study period
• (P<0.0001)
• Macrolide resistance & serogroup
• 22 different serogroups
• Serotype 14 = 467 (80%)
PMEN clones identified in
Scottish invasive pneumococcal isolates (2003-2007)
• PMEN clones
• Internationally distributed clones identified by
serotype and MLST
• should have wide geographic distribution (isolated
on at least 2 continents)
• Can be resistant to one or more antibiotics that are
in wide clinical use; or a global susceptible clone
known to be important in disease
http://www.sph.emory.edu/PMEN/pmen_ww_spread_clones.html
PMEN clones identified in
Scottish invasive pneumococcal isolates (2003-2007)
• 1,124 identified (37% of 3073 isolates)
• PMEN Clones accounted for 28 penicillin nonsusceptible isolates (35% 28/81)
• Spain 9v ST156 N=14
• Utah 35B ST377 N=6
• Spain 6B ST90 N=2
PMEN clones identified in
Scottish invasive pneumococcal isolates (2003-2007)
• 1,124 identified (37% of 3073 isolates)
• PMEN Clones accounted for 248 of the macrolide
resistant isolates (75% 248/330)
• England 14 ST9 N=230
PMEN clones identified in
Scottish invasive pneumococcal isolates (2003-2007)
• Frequency of PMEN clones
• England 14 ST9 n= 239
• Sweden 1 ST306 = 225
• Netherlands 8 ST53 = 154
• Netherlands 7F ST 191 = 136
• Netherlands 3 ST180 = 126
Multi-drug resistant pneumococci?
• Overlap between macrolide and pencillin nonsusceptibility was 0.9% (n=44)
• France and Spain 40% of pneumococci = multidrug
resistance (Reinert Clin Micro Infect 2009)
Antimicrobial use in Scotland
• Ab use in primary care increased by 18.4% between
2004-2008
• Amoxicillin accounted for 24% of ab used
• Phenoxymethyl penicillin accounted for 4%
Is Ab resist associated with a fitness cost?
• Yes
• Adult pneumonia with PRSP = milder clinical
manifestations (Einarsson et al SCJID 1998)
• ICU admin No sig diff pen MIC>25 vs lower (Moroney
et al CID 2001)
• Adult pneumococcal pneumonia (10.5% isolates
MIC>1 no signif diff (N=465 adults) (Bedas et al 2001)
• In vitro (mice) virulent phenotype was predictive of
pen susceptibility (Azoulay-Dupuis et al AAC 2000)
Is Ab resist associated with a fitness cost?
• NO (i.e. increased mortality)
• Adult pneumonia with PRSP (>4) (Feiken et al AJPH
2000)
• Pen MIC>2 independent predictor of mortality
(bacteraemia) (Turett et al CID 1999 )
• But
• Old age remains biggest predictor of mortality
(Mufson et al AJM 1999)
• Also chronic renal failure
• APACHE II score predict prognosis of bacteraemic
disease (Kalin et al 1999)
Conclusions
• Relatively low levels of ab resist in invasive
pneumococci from Scotland 1999-2007
• Most common penicillin non-susceptible clone is
serogroup 9 MLST 156 clone (PMEN Spain 9v)
• Most common macrolide resistant clone is the
serotype 14 MLST 9 clone (PMEN England 14)
• Non-susceptibility was rare among non vaccine
(PCV7) serogroups
• Pen non-susceptible serotype not covered by PCV7
or PCV13 is 35B ST377