Bibliography / Thesis (MMed (Pathology. Medical Microbiology))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: Acinetobacter baumannii has emerged as one of the most troublesome nosocomial pathogens
globally. This organism causes infections that are often extremely difficult to treat because of the
widespread resistance to the major antibiotic groups. Colonization or infection with multidrugresistant
A. baumannii is associated with the following risk factors: prolonged hospital stay,
admission to an intensive care unit (ICU), mechanical ventilation, and exposure to broad spectrum
antibiotics, recent surgery, invasive procedures, and severe underlying disease.
A. baumannii has been isolated as part of the skin flora, mostly in moist regions such as axillae,
groin and toe webs. It has also been isolated from the oral cavity and respiratory tract of healthy
adults. Debilitated hospitalized patients have a high rate of colonization, especially during
nosocomial Acinetobacter outbreaks. This organism is an opportunistic pathogen as it contains
few virulence factors. Clinical manifestations of A. baumannii include nosocomial pneumonia,
nosocomial bloodstream infections, traumatic battlefield and other wound infections, urinary tract
infections, and post-neurological surgery meningitis. Fulminant community-acquired pneumonia
has recently been reported, indicating that this organism can be highly pathogenic.
The number of multidrug-resistant A. baumannii strains has been increasing worldwide in the past
few years. Therefore the selection of empirical antibiotic treatment is very challenging. Antibiotic
combinations are used mostly as empirical therapy in critically ill patients. One rationale for the
use of combination therapy is to achieve synergy between agents.
The checkerboard and time-kill methods are two traditional methods that have been used for
synergy testing. These methods are labor intensive, cumbersome, costly, and time consuming.
The E-test overlay method is a modification of the E-test method to determine synergy between
the different antibiotics. This method is easy to perform, flexible and time efficient.
The aim of this study was to assess the in vitro activity of different combinations of colistin,
rifampicin, imipenem, and tobramycin against selected clinical strains of A. baumannii using the
checkerboard and the E-test synergy methods. The MICs obtained with the E-test and broth
microdilution method were compared. The results of the disk diffusion for imipenem and
tobramycin as tested in the routine microbiology laboratory were presented for comparison. Overall good reproducibility was obtained with all three methods of sensitivity testing. The
agreement of MICs between the broth dilution and E-test methods was good with not more than
two dilution differences in MIC values for all isolates, except one in which the rifampicin E-test MIC
differed with three dilutions from the MIC obtained with the microdilution method. However, the
categorical agreement between the methods for rifampicin was poor. Although MICs did not differ
with more than two dilutions in most cases, many major errors occurred because the MICs
clustered around the breakpoints.
The combinations of colistin + rifampicin, colistin + imipenem, colistin + tobramycin, rifampicin +
tobramycin, and imipenem + tobramycin all showed indifferent or additive results by the E-test
method. No results indicating synergy were obtained for all the above-mentioned combinations.
There was one result indicating antagonistic effect for the combination of colistin + tobramycin.
The results of the checkerboard method showed results indicating synergy in four of the six
isolates for which the combination of colistin and rifampicin was tested. The other two isolates
showed indifferent/additive results. All the other combinations showed indifferent/additive results
for all isolates except isolate 30 (col + tob) and isolate 25 (rif + tob) which showed synergism. No
antagonistic results were observed by the checkerboard method.
When the results obtained with the E-test and checkerboard methods were compared, it was
noted that for most antibiotic combinations an indifferent/additive result was obtained. However,
for the colistin + rifampicin combination, the checkerboard method showed synergism for 4 of 6
isolates, whereas the E-test method showed indifference and an additive result in one. For the
rifampicin + tobramycin, and colistin + tobramycin combinations, synergism was also shown with
the checkerboard method in one isolate for each combination. The E-test method however
showed an indifferent and additive result respectively.
.
The E-test method was found to be a rapid, reproducible, easy-to-perform, and flexible method to
determine synergistic antibiotic activity. This study was however limited by low numbers of
isolates. This might explain why no synergistic results were obtained with the E-test method and
few synergistic results with the checkerboard method. Genotypic analysis using pulse-field gel
electrophoresis (PFGE) may be considered in future studies to determine relatedness of the isolates which will facilitate the selection of different strains for synergy testing. Furthermore,
clinical studies are needed to establish whether in vitro synergy testing is useful in the clinical
setting and whether the results of synergy testing will have any bearing on the clinical outcome of
patients infected with multidrug resistant A. baumannii. / AFRIKAANSE OPSOMMING: Acinetobacter baumannii het wêreldwyd as een van die mees problematiese nosokomiale
patogene verskyn. Hierdie organisme veroorsaak infeksies wat dikwels baie moeilik is om te
behandel weens wydverspreide weerstandigheid teen major antibiotikagroepe. Kolonisasie of
infeksie met multi-weerstandige A. baumannii word geassosieer met die volgende riskofaktore:
verlengde hospitaalverblyf, toelating tot ‘n intensiewe sorgeenheid (ICU), meganiese ventilasie,
blootstelling aan breëspektrum antibiotika, onlangse chirurgie, indringende prosedures en
ernstige onderliggende siekte.
A. baumannii kan deel vorm van die normale velflora, veral in die axillae, inguinale area en tussen
die tone. Dit is ook al vanuit die mondholte en die respiratoriese traktus van gesonde volwassenes
geïsoleer. Verswakte gehospitaliseerde pasiënte word veral gekoloniseer gedurende nosokomiale
Acinetobacter uitbrake. Hierdie organisme is ‘n opportunistiese patogeen en bevat min virulensie
faktore. Kliniese manifestasies van A. baumannii sluit nosokomiale pneumonie, nosokomiale
bloedstroom infeksies, troumatiese slagveld- en ander wondinfeksies, urienweginfeksies en
meningitis wat volg op neurologiese chirurgie in. Fulminerende gemeenskapsverworwe
pneumonie is onlangs beskryf en dui aan dat hierdie organisme hoogs patogenies kan wees.
Die aantal multi-weerstandige A. baumannii stamme het wêreldwyd toegeneem oor die laaste
paar jare. Daarom is die seleksie van empiriese antibiotiese behandeling ‘n uitdaging. Antibiotika
kombinasies word meestal as empiriese behandeling in ernstige siek pasiënte gebruik. Die
beginsel hiervan is om sinergistiese werking tussen agente te verkry.
Die “checkerboard” en “time-kill” metodes is twee tradisionele metodes van sinergisme toetsing.
Hierdie metodes is werksintensief, duur en tydrowend. Die E-toets sinergisme metode is gebaseer
op die E-toets metode. Hierdie metode is maklik, buigbaar en tydseffektief.
Die doel van hierdie studie was om die in vitro aktiwiteit tussen verskillende antibiotika
kombinasies van colistin, rifampisien, imipenem, en tobramisien teen geselekteerde kliniese A.
baumannii isolate te toets met die “checkerboard” en E-toets sinergisme toetsing metodes. Die
minimum inhibitoriese konsentrasies (MIKs) verkry met die E-toets en “broth microdilution” metode
is ook vergelyk. Die resultate van die skyfie diffusie metode (die metode wat in die roetiene mikrobiologie laboratorium gebruik word) vir imipenem en tobramisien word ook verskaf vir
vergelyking van die resultate van verskillende sensitiwiteitsmetodes.
In oorsig is goeie herhaalbaarheid van resultate verkry met al drie metodes van
sensitiwiteitstoetsing. Die ooreenstemming van MIKs tussen die “broth dilution” en E-toets
metodes was goed en resultate het met nie meer as twee verdunnings in MIK waardes verskil nie.
Daar is een uitsondering waar die rifampisien E-toets MIK waarde met drie verdunnings van die
MIK waarde verkry met die “microdilution” metode verskil. Die ooreenstemming tussen die
sensitiwiteitskategorie resultate tussen die twee metodes was egter swak vir rifampisien. Alhoewel
die MIKs in die meeste gevalle met nie meer as twee verdunnings in waarde verskil het nie, was
daar baie major foute aangetoon omdat die MIKs rondom die breekpunte geval het.
Die kombinasies van colistin + rifampisien, colistin + imipenem, colistin + tobramisien, rifampisien
+ tobramisien, en imipenem + tobramisien het oorwegend slegs matige interaksie met die E-toets
metode getoon. Geen sinergisme is verkry met enige van die antibiotika kombinasies met hierdie
metode nie. Daar was egter een resultaat wat antagonisme getoon het vir die kombinasie van
colistin + tobramycin.
Die resultate van die “checkerboard” metode het sinergisme getoon in vier van die ses isolate wat
vir die kombinasie van colistin en rifampisien getoets was. Die ander twee isolate het slegs matige
interaksie getoon. Al die ander kombinasies het ook slegs matige interaksie getoon, behalwe in
isolaat 30 (col + tob) en isolaat 25 (rif + tob) waar die spesifieke kombinasies sinergisme getoon
het. Geen antagonisme is waargeneem met die “checkerboard” metode nie.
Met vergelyking van die E-toets en “checkerboard” metodes, is dit opmerklik dat vir die meeste
van die antibiotika kombinasies slegs matige interaksie verkry is. Vir die colistin + rifampisien
kombinasie toon die “checkerboard” metode egter sinergisme vir 4 uit 6 isolate, terwyl die E-toets
metode slegs matige interaksie toon. Vir rifampisien + tobramisien, en colistin + tobramisien
kombinasies is sinergisme getoon met die “checkerboard” metode in een isolaat vir elke
kombinasie. Die E-toets metode het slegs matige interaksie getoon. Die E-toets sinergisme metode was vinnig, herhaalbaar en maklik om uit te voer. Hierdie studie
word egter beperk deur lae getalle van isolate. Dit mag verklaar waarom geen sinergistiese
resultate met die E-toets metode verkry is nie en die min sinergistiese resultate met die
“checkerboard” metode. Genotipiese analiese met “pulse-field gel electrophoresis” mag in
aanmerking geneem word in toekomstige studies om die verwantskap tussen isolate te bepaal wat
die seleksie van verskillende stamme vir sinergisme toetsing sal vergemaklik. Verder, kliniese
studies is nodig om te bepaal of in vitro sinergisme toetsing van waarde is en of die resultate van
sinergisme toetsing ‘n rol speel in die kliniese uitkoms van pasënte geïnfekteer met multiweerstandige
A. baumannii. / The National Health Laboratory Serivice
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/5228 |
| Date | 12 1900 |
| Creators | Martin, Siseko |
| Contributors | Orth, Heidi, University of Stellenbosch. Faculty of Health Sciences. Dept. of Pathology. Medical Microbiology. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | xvi, 76 p. |
| Rights | University of Stellenbosch |
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