Hamzah, Siti Hawa
(2010)
Determining the clonality and
significance of coagulase-negative
staphylococci isolated from blood
cultures in HUSM.
Masters thesis, Universiti Sains Malaysia.
Abstract
Coagulase-Negative Staphylococci (CoNS) is a group of microorganisms that are
increasingly implicated as a cause of significant infection and has emerged as the most
frequent cause of nosocomial bloodstream infection. CoNS species are nonnal skin flora
and, it can be difficult to determine if CoNS species isolated from blood cultures reflect
infection or microbial contamination. At the moment, pulsed-field gel electrophoresis
(PFGE) is considered as a gold standard to diagnose the significance of CoNS isolated from
blood cultures. In this study, significance of repeated CoNS isolated from blood cultures
were evaluated by species identification, antibiogram and a molecular method, PFGE. A total of 101 pairs of Coagulase-Negative Staphylococci were analyzed during this period
of study. These isolates were identified to the species level by API Staph ID. Out of 101
pairs(, only 84 pairs (83.1%) of CoNs identified were similar species. These 84 pairs were
further analyzed by pulsed-field gel electrophoresis (PFGE) to detennine its clonality
(genotypic). However only 33 pairs had eligible PFGE result for interpretation
In this study, Staphylococcus epidermidis was the predominant species isolated (52.5%),
followed by S.capitis (10.4%) and S.chromogenes (1.9%). The percentage of methicillinresistant
CoNS was higher (68.68%) as compared to methicillin-sensitive CoNS. The percentage of same phenotype with same antibiogram pattern (40.7%) was lower as
compared to same phenotype and different antibiogram pattern (59.3%). There was a
significant association between same phenotype and same antibiogram pattern.
Out of 33 pairs of CoNS analyzed, 87.9% (29 pairs) had indistinguishable patterns which
denote the same bacterial strains. However the association between phenotypic and
genotypic cannot be made because due to failure to maintain reproducible PFGE results,
hence resulted in insignificant statistical findings. Overall laboratory concordance case was
defined as a case which were concordant for the triple tests conducted: phenotypic,
antibiogram pattern and genotypic. Out of 33 pairs of CoNS with PFGE results, 14 cases
(42.4%) were concordant cases which represent laboratory true bacteraemia and 19 cases
(57.6%) were regarded as contaminants.
In this study, there was significant association between same phenotype and antibiotic
treatment. The percentage of those who had antibiotic treatment and same phenotype was
higher (90.9%) as compared to those without antibiotic treatment (9.1%). There was
significant association for leukocyte count, nosocomial infection and antibiotic treatment
with antibiogram pattern. The association of laboratory concordance cases with clinical
parameters showed significant association between laboratory concordance cases with
blood pressure, leukocyte count and antibiotic treatment. All clinical parameters were not
significantly associated with concordance genotype. The outcome of this study showed that
genotype by pulsed-field gel electrophoresis (PFGE) failed to show any association with
clinical bacteraemia by statistical calculation due to small sample size
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