Citation
Woldegiorgis, Erkihun Aklilu
(2010)
Molecular heterogeneity of methicillin-resistant staphylocococcus aureus isolated from humans, animals and environmental surfaces.
Masters thesis, Universiti Putra Malaysia.
Abstract
Methicillin-resistant Staphylococcus aureus (MRSA) has long been known to cause
nosocomial infections worldwide since its emergence in the early 1960s. Nowadays,
this organism is found to prevail in the wider community and is becoming an emerging
problem in veterinary medicine. This study aimed to determine the molecular
heterogeneity of the MRSA isolates obtained from human, pets (cats and dogs), and the
environment. Swab samples were collected from 103 veterinary medicine students, 28
University Veterinary Hospital (UVH) staff, 100 pets (50 cats and 50 dogs), and 200
environmental surfaces. Conventional biochemical tests, Staphytect Plus® identification
kit, growth on selective media, antibiotic sensitivity test (AST), and minimum inhibitory
concentration (MIC) determination were used for phenotypic identification while mecA
gene detection was used for genotypic detection of MRSA. A total of 43 MRSA were
successfully isolated from the different sources. Prevalence rates were 23.3% (24/103),
7.14 (2/28), 8.0% [(8/100), 6.0% (5/50) cats and 10.0% (5/50) dogs], 4.5% (9/200) in students, UVH staff, pets and environment respectively. All MRSA isolates were found
to be resistant to three or more antimicrobial agents. The oxacillin MICs ranged from 1.5
μg/mL to ≥256 μg/mL with the majority (86.0%), having MICs of ≥ 4 μg/mL. The
mecA gene was found to be present in 83.7% (36/43) of the isolates. Although mecA
gene amplification has been accepted as the gold standard for MRSA detection, several
other factors are known to confer S. aureus resistance against methicillin. Molecular
fingerprinting by pulsed-field gel electrophoresis (PFGE) classified the isolates into
three clusters with 26 pulsotypes and three subtypes. Few isolates from the same source
category shared similar or close relationship with each other. However, the finger print
patterns for the isolates among the different source categories appeared to be too
heterogeneous and sporadic. The multi locus sequencing typing (MLST) analyses
grouped the selected 10 isolates (5 from human, 3 from pets, and 2 from environmental)
into 5 clonal complexes (CCs) and two singletons comprising nine sequence types (STs).
Two STs, ST59 and ST5 were previously reported from neighboring countries such as
Singapore and Thailand indicating a regional spread of the clones with the potential
contribution of human movement. Staphylococcal protein A gene (spa) sequence typing
revealed nine distinct spa types including one new spa type (t5697). Combinations of
MLST and spa typing methods have revealed the molecular heterogeneity within and in
between most of the tested MRSA isolates. The molecular fingerprints of the isolates
revealed similarities between human and pets and human and the environment and these
are suggestive of the inter-transmission and spread of the MRSA clones from one of the
sources to the other. Since there is no database on the molecular fingerprints of MRSA
isolates in the country, the findings from this study serve as a baseline data for future
studies and to design comprehensive and contextual control strategies to contain further
spread of MRSA.
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