STANDARDIZATION STUDY FOR AGAR WELL DIFFUSION METHOD

Year 2019, Volume: 2 Issue: 2, 138 - 145, 31.12.2019

Mehmet Aytar Erman Oryaşın , Gamze Başbülbül Bülent Bozdoğan

Abstract

Antibiotic sensitivity tests are important to
determine antibiotics that can be used against disease-causing microorganisms.
Although different standardization studies for disk diffusion and MIC tests were
established by several organizations, no standardization study was done for agar well diffusion method.
Standardization for disk diffusion method, antibiogram, was done first by World
Health Organization (WHO). Today many organizations including, The European
Committee on Antimicrobial Susceptibility Testing (EUCAST) in Europe, Clinical and Laboratory Standards Institute
(CLSI) in USA, and Standardization of Antibiotic Sensitivity Tests (ADTS) group
of Turkish Microbiology Society (TMC) in Turkey developed their own
standardization methods. TMC advises the use of EUCAST protocols for studies in
Turkey.

The aim of the present study was standardization of agar well diffusion method. Disk
diffusion method from EUCAST was used as a reference method to compare results
of agar well diffusion test. For both
disk diffusion method as well as agar
well diffusion test 0.5 McFarland bacterial suspension and Mueller Hinton
Agar (MHA) media were used. For agar well
diffusion test 3 different thicknesses, 4 mm, 6 mm and 8 mm, of MH agar was
used. Also three different well diameter, 4 mm, 6 mm and 8 mm were tested. All
tests were performed as three repetitions. Two antibiotics were used for disk
diffusion tests and agar well
diffusion tests. The concentration of erythromycin and chloramphenicol were 15 µg
and 10 µg, respectively. A Gram positive and a Gram negative strain were used
for susceptibility tests, S. aureus ATCC
25923 and E. coli DH10B strains,
respectively. All of plates were incubated at 37°C for 16-18 hours. At the end
of incubation, the inhibition zones around wells were measured.

The inhibition zones of S.
aureus ATCC 25923
with erythromycin disk were 29, 30 and 31 mm on 4, 6 and 8 mm agar,
respectively. Agar well diffusion
with 4, 6 and 8 mm MHA media, erythromycin inhibition zones were 21, 25 and 29
mm, 22, 26 and 30 mm, and 23, 27 and 31 mm, respectively. The inhibition zones of E. coli
DH10B with chloramphenicol disk were 25, 26 and 27 mm on 4, 6 and 8 mm agar,
respectively. Agar well diffusion
with 4, 6 and 8 mm MHA media, chloramphenicol inhibition zones were 5, 6 and 7
mm, 15, 16 and 17 mm, and 25, 26 and 27 mm, respectively. It was observed that
the disk diffusion inhibition zones were in accordance with the results of 8 mm
agar well zone, in every MH agar
thicknesses. As the standard for disk diffusion test the MHA thickness is 4 mm,
the agar well diameter for this
thickness is 8 mm. So for standardization of agar well diffusion tests, the MHA thickness should be 4 mm and the
diameter should be 8 mm.  

A standardization method for agar well diffusion test is necessary to compare results obtained
elsewhere. Our study is the first study for standardization of agar well diffusion test.
Standardization assays should be done by other laboratories to determine a
worldwide usable and comparable agar well
diffusion method. 

Keywords

Agarwell, Standardization, Media thickness, Well diameter

AGAR WELL DİFÜZYON YÖNTEMİNDE STANDARDİZASYON ÇALIŞMASI

Abstract

Antibiyotik
duyarlılık testleri hastalık etkeni mikroorganizmalara karşı kullanılabilecek
antibiyotiklerin belirlenmesinde önemlidir. Antibiyogram testlerinde farklı
kuruluşlar tarafından standardizasyon çalışması yapılmasına karşın agar well testleri için standardizasyon
çalışmasının yapılmadığı görülmüş ve bu çalışmada disk difüzyon testiyle
karşılaştırmalı standardizasyon çalışması yapılması amaçlanmıştır. Testler 0,5 McFarland
bulanıklıkta bakteri süspansiyonu ile 3 farklı kalınlıkta (4, 6, 8 mm) Mueller Hinton
agar besiyeri ve 3 farklı çapta kuyucuk (4, 6, 8 mm) kullanılarak üç tekrarlı
olacak şekilde yürütülmüştür. S. aureus ATCC
25923 ve E. coli DH10B bakterileri
için sırasıyla eritromisin (15µg) ve kloramfenikol (10µg) antibiyotikleri
kullanılmıştır. Tüm petriler 16-18 saat, 37°C’de inkübe edilmiştir. İnkübasyon
sonunda disklerin ve kuyucukların etraflarında oluşan inhibisyon zonları
ölçülmüştür. Antibiyotik duyarlılık testinde kullanılan agar well yöntemi için yaptığımız standardizasyon çalışmasında en
uygun Mueller Hinton Agar besiyeri kalınlığı ve kuyucuk çapı saptanmıştır. Agar
kalınlığı ne olursa olsun, disk difüzyon zon çapıyla agar well kuyucuk zon çapının 8 mm kuyucukla eşleştiği görülmüştür.
Agar kalınlığı arttıkça inhibisyon zonu artmaktadır. Disk difüzyon testinde
standart 4 mm kalınlığındaki besiyeri olduğu için bu kalınlıktaki besiyerinde
disk difüzyon sonucuna uyan inhibisyon zonu oluşturan kuyucuk çapı 8 mm olarak
saptanmıştır. Standart ölçüm için 4 mm agar kalınlığı ve 8 mm kuyucuk çapı
olmalıdır.

Çalışmamız
agar well difüzyon konusundaki ilk
standardizasyon çalışmasıdır. Diğer laboratuvarların benzer standardizasyon
çalışmaları yapmaları halinde agar well
difüzyon yöntemini tüm dünyada geçerli olabilecek bir standarda
kavuşturabiliriz.

Keywords

Agarwell, Standardizasyon, Besiyeri kalınlığı, Kuyucuk çapı

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