Effects of sub-inhibitory biocides exposure on the antibiotic susceptibility patterns and resistance genes of Enterococcus sp.
Biocides are chemical substances that are used for many centuries for destroying and inhibiting the growth of microorganisms and have been applied extensively for controlling nosocomial infections. However, extensive used of biocides in healthcare system poses risk for emergence and spread of...
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| Format: | Thesis |
| Language: | English |
| Published: |
2018
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/85481/1/FPSK%28m%29%202019%2070%20ir.pdf |
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| Summary: | Biocides are chemical substances that are used for many centuries for destroying
and inhibiting the growth of microorganisms and have been applied extensively
for controlling nosocomial infections. However, extensive used of biocides in
healthcare system poses risk for emergence and spread of antibiotic resistance
genes among clinical isolates. There is still limited studies on the effect and
bacterial response to exposure of biocides especially at sub-inhibitory
concentrations. Enterococcus is one of the most significant cause of nosocomial
infection and bacteremia with Enterococcus faecalis and Enterococcus faecium
emerged as the two most common species in this genus that contribute to the
infections. For this reason, this study is focused on deciphering the effects of
sub-inhibitory concentration of biocides exposure on antimicrobial susceptibility
patterns of these two important clinical species.
Four clinical isolates; 2 E. faecalis and 2 E. faecium were collected between May
2009 and March 2010 from Hospital Kuala Lumpur, Malaysia. These isolates
were tested with 4 common biocides in healthcare settings for determination of
minimum inhibitory concentration (MIC) using broth microdilution method. The
MICs of both E. faecalis and E. faecium isolates obtained for sodium
hypochlorite was between 0.78 to 0.87 mg/ml; hydrogen peroxide (0.01 to 0.05
%), ethanol (0.6 to 1.8 %) and chlorhexidine digluconate (1.7 to 2.9 mg/ml).
These isolates were then exposed to the sub-inhibitory concentration of biocides
calculated as MIC/2 and tested against 6 antibiotics using disk-diffusion and
broth microdilution techniques following CLSI (2016) guidelines. Overall,
15.6% of the cultures show reduced susceptibility (from susceptible to
intermediate, intermediate to resistant or susceptible to resistant) to teicoplanin,
vancomycin, ampicillin and linezolid. One of the E. faecalis isolate which is EF2
isolate showed an increased in MIC and became resistance to ampicillin after the
biocides exposure. The growth profile of the biocides exposed isolates was then determined by
measuring OD600 for 16 hours. The EF2 isolate which was exposed to subinhibitory
concentration of biocides showed slight delay in the log phase as
compared to the non-exposed EF2 isolate. However, exposure to sub-inhibitory
concentration of hydrogen peroxide does not give any effects to the ultrastructure
and morphology of E. faecalis. Molecular study of the E. faecalis (EF2) and
ampicillin resistance EF2 isolate (EF2r) showed that both of them contain pbp4
gene. Sequence analysis revealed that there was no mutation detected within the
pbp4 gene thus implies that exposure to sub-inhibitory concentration of biocides
does not cause any mutation within the resistance gene that subsequently lead to
ampicillin resistant-E. faecalis EF2r. In conclusion, this study showed that
exposure to sub-inhibitory concentration of biocides is able to change the
antibiotic susceptibility patterns of Enterococcus and lead to changes in the
growth profile but does not has any detectable effects to the ultrastructure and
morphology of the bacteria. Therefore, continual monitoring and appropriate
regulatory measures of biocides usage is necessary to control the emergence of
antimicrobial resistance among clinical isolates. |
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