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Yoon: Vancomycin Resistance of Staphylococcus aureus in Korean Primary Hospitals
Original Article

J Bacteriol Virol 2014;44(4):305-310.

Published online: 9 February 2014

DOI: https://doi.org/10.4167/jbv.2014.44.4.305

Vancomycin Resistance of Staphylococcus aureus in Korean Primary Hospitals

Jeongsook Yoon*

Hyundae Medical Clinic Research Center, Gyeonggi-do, Korea

*Corresponding author: Jeongsook Yoon. Hyundae Medical Clinic Research Center, 15, 34Beongil, Daewangpangyoro, Bundang-gu, Seongnam-si, Gyeonggi-do, 463-869, Korea. Phone: +82-31-712-8400, Fax: +82-31-719-3744, e-mail: js1345@medigate.net

Received 31 July 20146 October 2014       Accepted 10 October 2014

Copyright © 2014 Journal of Bacteriology and Virology

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

According to a United States study, 13 cases of vancomycin-resistant Staphylococcus aureus (VRSA) have been reported to date. In 2001, a survey conducted in Korea revealed that 0.5% of methicillin-resistant S. aureus (MRSA) isolates have a vancomycin minimum inhibitory concentration (MIC) of 4 μg/ml, and are thus referred to as vancomycin intermediate S. aureus (VISA). However there are no reports of VISA found in primary hospitals. We evaluated the MIC of vancomycin in MRSA samples obtained from primary hospitals to determine whether VISA was present in primary hospitals. The population analysis was performed to determine whether hetero-VISA was present in primary hospitals. As a result, twenty of the 103 isolates were S. aureus which were all MRSA and the vancomycin MIC was similar to that seen in tertiary hospitals. Population analysis confirmed that three strains were hetero-VISA, by showing that one strain grew in 8 μg/ml vancomycin and that two strains grew in 4 μg/ml vancomycin. In conclusion, hetero-VISA was detected in Korean primary hospitals, which may develop into VISA, however a larger sample size will be needed to confirm these results.

Keywords: S. aureus, Vancomycin intermediate S. aureus (VISA), Primary-hospital

REFERENCES

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Figure 1.
The count of CFU at each vancomycin concentration. After 10-fold dilution of bacterial solution (strain 0501) from 10−1 to 10−7, 100 μl inoculated to each serial dilution of vancomycin BHIA with sterile tip, applied evenly with a sterile swab and incubated at 35°C for 24 hours. We counted colony number and found the growth of 70 colonies of strain 0501 with 10−3 dilution at vancomycin 4 μg/ml.
jbv-44-305f1.tif
Figure 2.
Logarithmically charted CFU at each vancomycin concentration. After 10-fold dilution of bacterial suspension from 10−1 to 10−7, 100 μl of each serial dilution was inoculated on BHIA containing vancomycin, After incubation the colony numbers were counted and the colony number at each vancomycin concentration was charted logarithmically. (axis X, vancomycin concentration range; 0∼16 μg/ml, axis Y, colony count at each dilution from 10−1 to 10−7, range; 0∼8) mu50, mu3; control strain, 0501,1120,1537; test strain
jbv-44-305f2.tif
Table 1.
Minimal inhibitory concentraion of MRSA isolates against vancomycin
No Specimen MIC (μg/ml) MIC 24 hr
1 0501 2 4
2 1049 1 2
3 1054 1 2
4 1055 2 2
5 1056 1 1
6 1064 0.5 2
7 1120 1 4
8 1537 1 4
9 2041 1 2
10 2518 1 1

Each bacterial specimen solution was adjusted to 105 CFU/spot, and 10 μl was added to each vancomycin concentrated Mueller hinton agar from 0,03 to 32 μg/ml. MIC was estimated following incubation at 35°C for 24 hours.

Table 2.
Growth rate of hetero-VISA strains at each vancomycin concentration
Colony count at each vancomycin concentration (μg/ml)
0.25** 0.5 1 2 4 8
0501* Confluent† Confluent 2.7 × 105 8.3 × 104 7.0 × 104 1.1 × 104
1120 Confluent 2.6 × 105 8.1 × 104 1.6 × 104 3.2 × 103 0
1537 Confluent Confluent 1.6 × 105 5.5 × 104 3.0 × 103 0

* specimen number

** vancomycin concentration, μg/ml

† colony count

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