2.3.4 Oxidase Test
test is used to identify the bacteria cytochrome c oxidase, an enzyme of
bacteria electron transport chain, when present the cytochrome c oxidase
oxidizes the reagent to purple colour end product, when the is absent the
reagent become reduced and colourles. All oxidase positive bacteria are aerobic
and can use oxygen as terminal electron acceptor in respiration. Bacteria that
are oxidase negative can either ba anaerobic, facultative, aerobic; which means
the organisms do not have cytochrome c which can the reagent.
strip was used for the test, a colony of the organism was picked from the plate
aseptically and was smeared on the strip, the inoculated area was observed for
a change of colour to purple within 10-30 seconds.
2.3.5Antibiotic Susceptibility Test
test is used to determine the susceptibility of an organism to different antibiotics.Antibiotics
are defined as substances produced wholly or partly by microorganisms
orsynthetically manufactured that kill or inhibit the growth of microorganisms
even in smallconcentrations.
is a quantitative assay that is done by placing paper disks infused with
antibiotics of aknown concentration on the surface of an already inoculated
Mueller Hinton agar plate.
diffuse from the paper disks into the agar creating a concentration gradient in
theagar. An absence of growth around a disk (called a zone of inhibition) is
measured todetermine if the organism is susceptible, intermediate and resistant
to the antibiotic accordingto the Clinical and Laboratory Standards Institute.
isolates were tested against the following antibiotics: Erythromycin(15ug),
Chloraphenicol(30ug),Tetracycline(30ug), Rifampin(5ug), Cefoxitin(30ug),
Clindamycin(2ug) and Ciprofloxacin(5ug).
from a pure culture of the test organism was emulsified in normal saline
solutionand standardized to 0.5 McFarland standard(1 × 108cfu/ml). A
sterile swab stick was thendipped into the tube and squeezed against the edge
to drain excess fluid in the swab.
was then used to streak a Mueller Hinton agar plate and the plate was allowed
to dry for3 minutes. Each antibiotic disc used was then placed on the surface
of the agar plate using a sterile forceps. The inoculated plates were
theninverted and incubated at 35°C for 18-24hours. The zone of inhibition
observed was measured for each antibiotic used and comparedto the CLSI (2015)
3.1 Information relating to sample
total of 25 isolates of Staphylococcus
was obtained from collection of 5 wastewater samples from fajuyi hall of
residence ObafemiAwolowo University, ile-ifeOsun state.
3.2 IDENTIFICATION TEST
the isolates were catalase positive except one which is negative and all were
also gram positive, all were also Dnase negative(100%). All the isolates were
both susceptible to cefoxitin and Ciprofloxacin(100%), 13 of them were
susceptible to tetracycline(72.2%) while 2 of them were resistant to chloramphenicol(11.1%),
2 and 1 of them were intermediate to clindamycin(11.1%) and rifampin(5.6%)
respectively while 6 of them were resistant to erythromycin(33.3%). As shown in
the table below