Download SNP Antibiogram – Respiratory Pathogens 2004 – 2010 comparison

SNP Antibiogram – Respiratory Pathogens 2004 – 2010 comparison
Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis
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The trend for nonsusceptibility (Intermediate + Resistant)
to penicillin for S pneumoniae has increased since
2004. 9.4% of isolates are resistant i.e. the minimum
inhibitory concentration (MIC) is ≥ 2 mg/L, compared
to 2.4% in 2004. Approximately 23.4% of isolates have
intermediate susceptibility, i.e. MIC. of 0.12mg/L to 1
mg/L. Although infections with isolates of intermediate
susceptibility will generally respond to higher doses
of conventional beta-lactam antibiotics (penicillin,
amoxycillin), treatment failures have occurred when
such organisms have caused meningitis. Pneumonia
caused by S pneumoniae and treated with parenteral
penicillin can generally be successfully treated when the
penicillin MIC is as high as 2 mg/L (see Table 1).
Susceptibility testing of the third generation
cephalosporins (ceftriaxone, cefotaxime) is only
routinely performed on penicillin intermediate or
resistant S pneumoniae. The 10.2% resistance and
26.9% intermediate susceptibility for ceftriaxone refers
to this subset of isolates only. The few multiresistant
S pneumoniae isolates tested against the newer
generation quinolone, moxifloxacin, (n = 26) were all
susceptible.
Macrolide resistance (erythromycin, clarithromycin)
for S pneumoniae has also increased from 19%
to 27.4%. The corresponding resistance rates for
clindamycin in 2004 and 2010 are 14.5% and 24%
respectively. Clindamycin resistance is only slightly
less than that of erythromycin, indicating that most
erythromycin/clindamycin resistance is mediated by
the same erm gene that encodes for erythromycin
ribosome methylase, rather than an independent efflux
method. Erythromycin is unsuitable for treatment
of H influenzae infections. There are proponents for
treatment of H influenzae with the related macrolides
(roxithromycin, clarithromycin). In this series, 88.4%
tested susceptible. This has been an increase since
2004. Most M catarrhalis are susceptible in vitro to
the macrolides, erythromycin and clarithromycin
(99.1%), and these can be used effectively to treat these
infections.
Cotrimoxazole is not recommended for treatment of
respiratory tract infections. 26.6% of S pneumoniae
isolates (n = 1296), 30.9% of H influenzae (n = 3932)
and 1.9% of M catarrhalis isolates (n = 976) are resistant.
Tetracycline (including doxycycline) is generally not
effective for empiric therapy of S pneumoniae (n = 1296)
showing 21.8% resistance and increase from 2004 when
the rate was 12.8%. H influenzae (n = 3932) resistance
rates for tetracycline are 0.2% (a suprising decrease
from 14.6% in 2004), and 0.3% for M catarrhalis
isolates (n = 976) which is not significantly different from
resistance rates of 0.9% in 2004.
Beta-lactamase production by H influenzae (n = 3932),
and consequent resistance to amoxycillin/ampicillin,
occurs in 23.2% of isolates in 2010, in contrast to 21.4% in
2004. Alternative treatment is co-amoxyclav, although
there is a small number of beta-lactamase negative
amoxicillin/ampicillin resistant isolates (BLNAR). 1.0%
of a total number of 3893 H influenzae isolates would
not be effectively treated by the addition of clavulanate
as in co-amoxyclav in 2010. In contrast, in 2004 the rate
was 2.6%. Beta-lactamase production is very common
in M catarrhalis isolates (96.95%). Infections with this
organism can be effectively treated with co-amoxyclav.
Fluoroquinolone resistance (moxifloxacin) remains
rare and is the treatment of choice for multidrug resistant
pneumococcus.
Table 1
Penicillin susceptibility definitions for S pneumoniae
Susceptible Penicillin parenteral
(Meningitis)
≤ 0.06 mg/L
Intermediate
-
Resistant
≥ 0.12 mg/L
Penicillin parenteral
(non Meningitis)
≤ 2 mg/L
4 mg/L
Penicillin oral
≥ 0.12 – 1 mg/L ≥ 2 mg/L
≤ 0.06 mg/L
≥ 8 mg/L
SNP Antibiogram – Respiratory Pathogens 2004 – 2010 comparison
Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis cont...
Dr Jenny Robson FRCPA FRACP FACTM
Dr Jenny Robson graduated from The University of Queensland and has worked at Sullivan Nicolaides Pathology since 1989. She is
interested in all things infectious, but particularly zoonoses, immunisation, tropical and travel medicine, antibiotic resistance, infection
control, and the molecular diagnosis of infectious diseases.
Dr Robson is available for consultation.
T: (07) 3377 8506
E: [email protected]
Dr Sarah Cherian FRCPA
Dr Sarah Cherian graduated from The University of Queensland and worked with the Brisbane Southside Public Health Unit before joining
Sullivan Nicolaides Pathology in 2001. Sarah’s interests include public health, microbiology, hepatitis testing, and molecular diagnosis of
infectious diseases.
Dr Cherian is available for consultation.
T: (07) 3377 8628
E: [email protected]
Item 05816
Correct at time of printing – reviewed July 2011
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