Download “Infections caused by group C and G streptococci” Kristina Trell MD

“Infections caused by group C and G streptococci”
Kristina Trell
MD, PhD student
Division of Infection Medicine
Department of Clinical Sciences Lund
Lund University
Supervisor:
Magnus Rasmussen
Co-supervisor:
Bo Nilson
Malin Inghammar
Opponents:
Fredrik Resman
Mattias Collin
Date of mid-term assessment:
2016-10-11
Summary of thesis for mid-term assessment
This thesis investigates infections caused by beta-hemolytic streptococci group C (GCS) and G (GGS). Isolates
of GCS and GGS were collected prospectively or retrospectively at the Department of Clinical Microbiology in
Region Skåne and examined to determine species and emm-type. Subjects with recurrent bacteremia with GCS
and GGS were identified and compared to controls with only one episode of bacteremia to detect risk factors for
recurrent bacteremia. Isolates of GGS and GCS from different sites of isolation (throat, wound, and blood) were
species determined and emm-typed to investigate differences in preference of different types to cause certain
types of infections. Patients with bacteremia with isolates of GCS identified as Streptococcus equi were also
described and the isolates were typed through sequencing of the gene encoding SzP.
The thesis comprises three works (I-III below). At mid-term assessment paper I-III are completed. Paper I is
published and paper II is accepted for publication in Diagnostic Microbiology & Infectious Diseases. Paper III is
under review for submission in Diagnostic Microbiology & Infectious Diseases.
Invasive disease caused by GCS and GGS is increasing (18-20). In a previous project (4), we demonstrated that
GGS is an important cause of erysipelas. In a fourth project we aim to compare microbiological and clinical
aspects of invasive disease caused by GCS and GGS to GAS. This will be a retrospective study with systematical
review of the medical records for data on morbidity and mortality. Furthermore statistical interpretation of
microbiological findings, patient demographics and clinical presentations is planned.
•
Paper I: Recurrent bacteremia with Streptococcus dysgalactiae: a case-control study.
By: Kristina Trell, Parham Sendi and Magnus Rasmussen
Published in: Diagnostic Microbiology & Infectious Disease, January 22, 2016.
•
Paper II: Species and emm-type distribution of group C and G streptococci from different sites of
isolation.
By: Kristina Trell, Bo Nilson and Magnus Rasmussen
Accepted for publication in: Diagnostic Microbiology & Infectious Disease
•
Paper III: Clinical and microbiological features of bacteremia with Streptococcus equi.
By: Kristina Trell, Bo Nilson, Ann-Cathrine Petersson and Magnus Rasmussen.
Under review for submission in Diagnostic Microbiology & Infectious Diseases.
Introduction
Beta-hemolytic streptococci group C (GCS) and G (GGS) are important causes of human infections (1-3, 7).
GCS and GGS can colonize the upper respiratory tract, the gastrointestinal tract, vagina and skin. The spectrum
of diseases caused by GCS and GGS includes pharyngitis, skin infections, bacteremia, endocarditis, septic
arthritis and meningitis (4-6). Most GCS and GGS belong to the species Streptococcus dysgalactiae (SD), which
can be further subdivided into the subspecies Streptococcus dysgalactiae subsp equisimilis (SDSE) and
Streptococcus dysgalactiae subsp dysgalactiae (SDSD) (8-9).
The vast majority of clinical isolates associated with human infection that are identified as GCS and GGS belong
to the subspecies Streptococcus dysgalactiae subsp equisimilis (SDSE), but species determination is difficult and
has not routinely been performed (8-9). Sequencing of the16SrRNA gene can determine subspecies in most
cases (10), but is time-consuming. Matrix-assisted laser desorption/ionization time of flight spectrometry
(MALDI-TOF MS) has been shown to be able to differentiate GGS and GCS to a species level (11) and is now
implemented in routine practice.
Species determination has made it possible to identify suspected zoonotic infections. Among GCS causing
human infections isolates of Streptococcus equi have been found and some isolates of GGS are streptococcus
canis, both with animal origin (12). Infections in humans caused by streptococcus equi have been related to
contact with horses or consumption of unpasteurized milk products and can present as bacteremia of unknown
focus, arthritis, aortitis and endocarditis (13-17).
Several studies have shown an increase of invasive infections caused by GCS and GGS and clinical disease
similar to beta-hemolytic streptococcus group A (GAS) (18-20). GCS and GGS exhibit the M-protein, expressed
by the emm-gene, a known virulence factor in GAS infections (21-22). Temporal associations of emm-types and
their connections to clinical disease in infections caused by GCS and GGS is not as well-studied as in GAS
infections. In recent years several studies have investigated both what emm-types are present in infections caused
by SDSE and their correlation to invasive disease (23-30).
SDSE has a propensity to recur and recurrence rates of between 3 and 9 % has been reported (7, 19, 31-33).
Some studies have tried to link the tendency of SDSE to recur to certain emm-types (3, 19, 31). Furthermore
underlying clinical condition predisposing for reappearance of SDSE have been examined (19, 31).
Increased understanding of human infections caused by GCS and GGS is the aim of this thesis. Paper I
comprises a case-control study to describe the clinical and molecular risk factors for recurrence of Streptococcus
dysgalactiae (SD) bacteremia. In paper II the species and emm-types of GCS and GGS from different sites of
isolations are determined. In paper III the clinical and microbiological features of bacteremia with Streptococcus
equi is described. The present plan for work IV is to compare clinical and microbiological aspects of bacteremia
caused by GCS and GGS with GAS.
Paper I:
Recurrent bacteremia with Streptococcus dysgalactiae: a case-control study
Kristina Trell, Parham Sendi and Magnus Rasmussen.
Background
GCS and GGS can cause recurrent infections and is typed according to the expression of emm-genes
(3, 7, 19, 31-33). The purpose of this retrospective study was to evaluate the rate of recurrence and the
relationship to emm-types and clinical factors.
Methodology
Cases of recurrent bacteremia with GCS and GGS in the period 2003-2013 were identified in the databank of the
Department of Clinical Microbiology in Malmö/Lund and compared to controls with bacteremia with SD of the
same streptococcal group. MALDI-TOF MS was used for species determination and type was determined by
sequencing of the emm-gene. Data on clinical presentation were taken from medical records. Statistical analyses
were made using the Prism 6 software.
Results
Among a total of 593 episode, 23 episodes of recurrent bacteremia with GCS and GGS were found in 20032013. 22 cases were caused by SD and one was identified as S. canis. The distribution of emm-types in the
isolates causing recurrence paralleled the isolates causing single episodes. In 19 patients the recurrence was
caused by the same emm-type. Erysipelas was the most frequent clinical manifestation, seen in 50% of the
recurrent cases and 38% of those with a single episode. Demographics and Charlson comorbidity scores were
similar in both groups.
Conclusion
In our study 23 patients with recurrent episodes of SD bacteremia were seen. Most recurrences were caused by
the same emm-type, which might suggest host-specific colonization. Furthermore, in our study no specific emmtypes were associated with recurrences. We argue that information to patients about the risk of recurrence and in
some cases antibiotic prophylaxis can be warranted.
Paper II:
Species and emm-type distribution of group C and G streptococci from different sites of
isolation
Kristina Trell, Bo Nilson and Magnus Rasmussen.
Background
Infections caused by GCS and GGS range from pharyngitis, skin infections to septicemia (4-6). The purpose of
this study was to describe the emm-types of GCS and GGS from different sites of isolation and if possible
correlate certain types to clinical presentation and severity of disease.
Methodology
Isolates from throat swabs and wounds were collected during two one-month periods in 2008 and 2011 and
isolates from blood from 1st of January 2008 to 31st of December 2011. Species determination was made by
MALDI-TOF MS. All isolates were subjected to emm-typing. The medical records were studied for data on
mortality. Statistical analyses were made with the Prism 6 software, using the Chi2-test.
Results
262 isolates, 183 GGS and 79 GCS were identified and 252 were speciated to SD by MALDI-TOF MS. The
predominant emm-type among GCS isolates was StG62647, constituting 54%. Among GGS isolates the
distribution of emm-types was more scattered and the four most prevalent were StG6 (20%), StG643 (20%),
StG485 (14%) and StG480 (8%). There was a statistically significant difference in emm-type distribution
between throat and blood isolates for the GCS of our study, the deviation in emm-type distribution between
throat and blood isolates of GGS was not. Study of patient medical records revealed no fatalities among the cases
with GCS bacteremia, whereas 12% of the patients with GGS bacteremia succumbed.
Conclusions
GCS and GGS expresses different emm-types. The emm-types of GCS and GGS from different sites of isolation
were similar, suggesting that emm-types cannot be associated to certain disease presentations. Furthermore, there
was no association between certain emm-types and mortality.
Paper III:
Clinical and microbiological features of bacteremia with Streptococcus equi
Kristina Trell, Bo Nilson, Ann-Cathrine Petersson and Magnus Rasmussen
Background
SE is a zoonotic pathogen causing human infections and has been related to consumption of unpasteurized milk
products and to contact with horses (13-17). The purpose of this retrospective study was to investigate how
frequent bacteremia with SE occurs and to describe the clinical presentation.
Methodology
Blood isolates of GCS from 1st of January 2003 to 31st of December 2014 were analyzed with MALDI-TOF
MS and isolates identified as Streptococcus equi were subjected to sequencing of the 16rRNA and rpoB genes.
Subtyping based on sequencing of the M-like protein SzP was made. Patient records were reviewed.
Results
167 blood isolates of GCS were subjected to MALDI-TOF MS and 149 SD and 18 SE were identified.
Sequencing of the 16SrRNA and rpoB gene of the SE isolates confirmed species determination. The SE isolates
were typable by sequencing of the gene encoding SzP. Review of the medical records revealed contact with
domestic animals in ten cases. Thirteen patients fulfilled the SIRS-criteria and seven developed severe sepsis.
The most common clinical syndrome was bacteremia of unknown origin in five cases. Septic arthritis was
diagnosed in four patients. Furthermore two cases of pneumonia, two cases of suspected catheter-related
infection, one case of meningitis and mycotic aortic aneurysm respectively were seen. There were no fatalities.
Conclusions
Eighteen cases of SE were found during a thirteen-year period, which confirms that SE is a rare cause of
infection in humans. No temporal or geographical clustering was found in our material. Furthermore there were
reports of domestic animals in ten of the patient records. This suggests sporadic transmission possibly from
domestic animals. Our study indicates that sporadic cases of SE bacteremia has a favorable prognosis.
Determination of species with MALDI- TOF MS was possible and were shown to have a high specificity. We
argue that species determination of GCS can offer important clues to the understanding of the mode of
acquisition of GCS.
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