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1. ISSN 2231-6027
International Journal of
Oral Health Sciences
Official Publication of Bapuji Dental College Alumni Association.
Volume 9 • Issue 1 • January-June 2019
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2. 20 © 2019 International Journal of Oral Health Sciences | Published by Wolters Kluwer - Medknow
Evaluation of biological effects of X‑radiography and
computed tomography scan on oral microflora
Ali Abdul Hussein S Al‑Janabi, Mohammid Hamid H AI-Baghdadi1
Departments of Microbiology and 1
Physiology, College of Medicine, University of Karbala, Karbala, Iraq
Original Article
INTRODUCTION
Radiation techniques have become an indispensable part in
the diagnosis of many diseases of the human body. X‑rays,
which are an electromagnetic radiation of extremely short
wavelength and high frequency, are commonly utilized
as a diagnostic tool in modern medicine.[1]
Their high
energy allows X‑rays to pass through the biological matter
of the body, producing images of internal structures.[2]
X‑radiography and computed tomography (CT) scan are
the most common types of X‑ray techniques that are
widely used at present. A patient may be recommended
to attend for either of these applications for diagnosis
or treatment.[1,3]
X‑ray has several disadvantageous roles
against living things, mainly the production of mutations
in DNA sequences or causing cell death.[1,4‑6]
These harmful
effects depend on many factors such as radiation dose,
type of radiation, organism’s age, and part of the body
exposed to radiation.[4]
The human body has numerous microorganisms (MOs) of
various types living in and on its parts as a normal flora.[7,8]
Introduction: X‑ray is the most valuable tool for diagnosis of various diseases. Its radiation energy has a
serious effect on living cells. The effects of X‑radiography and computed tomography (CT) scans on the
viability of oral microflora in the human were investigated.
Methods: A total of 432 patients in two groups exposed to X‑radiation were included in a cohort study.
Group I (215) was exposed to X‑radiography and Group II (217) to CT scan. Swab samples from the oral
cavity were collected. Viability of normal oral flora in those patients was measured by microbial counting
before and after exposure.
Results: Radiation of X‑ray techniques, especially for CT scan, showed an effect on most of bacterial
multiplication by increasing their count after exposure. Meanwhile, fungal isolates and one of the
bacteria (Staphylococcus aureus) were decreased in number after exposure. Some isolates were not affected
by radiation from X‑radiography.
Conclusion: Radiation of routinely diagnostic X‑ray found to play an important role in disturbance of microbial
counting balance among oral flora through increasing the density of most kinds of them. Limitation of
X‑ray exposure is a safety precaution that should be taken to prevent adverse effects on normal flora of
the human body.
Keywords: Computed tomography‑scan, microflora, oral, X‑radiography
Abstract
Address for correspondence: Prof. Ali Abdul Hussein S Al‑Janabi, Department of Microbiology, College of Medicine, University of Karbala, Karbala, Iraq.
E‑mail: aljanabi_bio@yahoo.com
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DOI:
10.4103/ijohs.ijohs_53_18
How to cite this article: Al-Janabi AA, AI-Baghdadi MH. Evaluation of
biological effects of X-radiography and computed tomography scan on oral
microflora. Int J Oral Health Sci 2019;9:20-4.
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3. Al‑Janabi and Ai‑Baghdadi: X‑radiography and CT scan on oral microflora
International Journal of Oral Health Sciences | Volume 9 | Issue 1| January-June 2019 21
The oral cavity is considered an enriched environment
with >500 species of normal flora.[8]
Thus, exposure of
the human body to X‑radiation will absolutely not only be
restricted to the human cells but also affect its normal flora.
Such types of exposure could have potentially harmful
effects. Variable results have been obtained for the desirable
effects of X‑rays on normal flora ranging from effective[9,10]
to ineffective.[11]
Depending on dose, X‑ray radiation with
low‑to‑medium energy has shown no effect on some types
of bacteria,[5]
while the exposure of other bacteria to the
same dose of X‑rays revealed a significant decrease in cell
number.[10]
Viability of oral MOs in patients exposed to different
techniques producing of X‑radiation was investigated.
METHODS
Patients
A cohort study was designed to study the effects of
X‑radiation producing by two techniques on normal oral
flora in patients with various types of head diseases (brain,
mouth disease, sinusitis, and jaws) at Al Ammam Al‑Hussein
General Teaching Hospital of Karbala Province (Iraq)
from January to April 2017. A total of 432 volunteer
patients with informed consent (parent agreement was
obtained for children) were divided into two groups. The
first group (Group I) involved 215 patients (80 males,
age = 8–72 years and 135 females, age = 11–80 years)
exposed to 0.03 mSv radiation of X‑radiography on
the skull part (67–79 keV, 250 mAs, and 0.014 s) of
Shimadzu, Japan. The second group (Group II) involved
217 patients (101 males; age = 6–70 years and 116 females;
age = 5–65 years) exposed to 2 mSv radiation of CT scan
on the head (keV 100, 280 mA, CTDIvol [CT dose index]
= 24.41 mGy, dose length product = 474.8 mGy, 7.25 s)
of Philips, France. Patients with infectious diseases such
as pharyngitis, tonsillitis, and candidiasis were excluded
from the study.
Microbial isolation
A sterile moisturized swab was used for the isolation of
oral MO by rotation the swab on the surface of hard
palate of the oral cavity of all of patients before and after
radiation exposure. The specimens were collected from
the patients at the same visiting time to the hospital, and
the periods between the collection of specimens before
and after exposure were separated only by radiation
exposure time. Collected swabs were immediately cultured
on blood agar and MacConkey agar (HiMedia, India)
and incubated at 37°C for 48 h. Grown isolates were
diagnosed based on culture features and biochemical
characters by API 20E for bacteria and API 20C for
yeasts (BioMérieux, France). Total number of growing
MOs (cfu) was calculated by counting the grown colonies
on the surface of culture media.
Statistical analysis
Data were analyzed statistically using the analysis of
variance test. Differences between microbial counting
before and after exposure, X‑radiation techniques, and sex
were determined at the minimum level of P < 0.01 which
is considered a statistically significant level.
RESULTS
Radiation effect of X‑rays generated by two techniques
against oral microflora was investigated through counting
the microbial number before and after exposure.
Seven bacteria (Viridans Streptococci, Streptococcus
pneumonia, Streptococcus pyogenes, Staphylococcus epidermidis,
Staphylococcus aureus, Haemophilus influenzae, and Neisseria
meningitidis) and two fungal species (Candida spp. and
Cryptococcus neoformans) were diagnosed. Microbial counting
after exposure revealed a greater number for most of the
isolates [Table 1]. Meanwhile, isolate count from females
was significantly higher (P < 0.01) than for males. The
radiation of X‑radiography showed effective role on the
multiplication of oral MOs through increase their cell
number with a significant difference (P < 0.01) from CT
scan [Table 1].
Based on the species level, all of the isolated bacteria
except S. aureus increased their cell number after exposure
to both types of X‑radiation [Figures 1‑4]. Meanwhile,
cells of two fungi decreased their count after exposure to
X‑rays [Figures 1‑4].
Bacterial isolates from some patients, especially from males,
showed no difference in their number either before or
Table 1: Total number of patients with microbial count before and after exposure to X‑radiation
Sex Total number of patients with microbial count Total
numberX‑radiography CT‑scan
High counts before High counts after Equal counts High counts before High counts after Equal counts
Male 38±1.3 46a
±0.8 10a
±2 51c
±2.1 59±0.7 11a
±1 215
Female 50±3 92b
±3 9b
±1 24b,c
±2 33±0.9 9b
±0.3 217
Total number 88 138 19 75 92 20 432
Similar letters indicate a statistically significant difference at P<0.01. CT: Computed tomography

4. Al‑Janabi and Ai‑Baghdadi: X‑radiography and CT scan on oral microflora
22 International Journal of Oral Health Sciences | Volume 9 | Issue 1| January-June 2019
after exposure to X‑radiography which was considered an
indicator for the absence of radiation effect on their cell
viability [Figures 1 and 2]. This result was not observed with
exposure to CT scan radiation [Figures 3 and 4].
DISCUSSION
X‑rays are a type of ionizing radiation which is produced by
a special machine through an acceleration or deceleration
of charged particles that have a wave or particle‑like
properties,[1]
first discovered over 100 years ago.[12]
Nowadays, X‑radiography and CT scan are considered the
two main applications of X‑rays that are commonly used in
different medical fields. The X‑radiography machine usually
produces a single beam of X‑rays which are directed at the
chosen part of the human body to get a picture on specific
film,[1,12]
whereas CT‑scan or computed axial tomography
scan differs from X‑radiography by its ability to generate
cross‑sections with two‑dimensional images of the body
through the rotation of X‑rays around the patient.[3,13]
Figure 1: Total number of microbial isolates from males before and
after exposure to radiation of X‑radiography
Figure 3: Total number of microbial isolates from males before and
after exposure to radiation of computed tomography scan
For penetration ability of X‑rays through opaque materials,
short wavelength and high energy of individual X‑ray
photons are adopted to obtain useful images for the
diagnosis of various diseases such as dental cavities, bone
fracture, and cancer.[1,12]
On the other hand, high‑energy
power of X‑ray has harmful effects on living cells. It causes
damage in the DNA backbone resulting in a mutation or
cell death through the ionization of materials. Impact
of X‑ray photons into tissue matter will release free
electrons and unstable ions that affect DNA structure
causing mutation.[5,14]
In addition, X‑radiation of biological
materials results in forming hydroxyl radicals causing cell
death.[1,5]
Several types of MO are living in the oral cavity as a normal
flora which distributed on the surface of the hard and
soft oral tissues.[7,8]
The relationship between such type of
MO with each other or with the host immunity is almost
complex, but it is constantly under normal conditions.[15]
A pathogenic nature of most of oral microflora is usually
under the control of other members at the same place
Figure 2: Total number of microbial isolates from females before and
after exposure to radiation of X‑radiography
Figure 4: Total number of microbial isolates from females before and
after exposure to radiation of computed tomography scan

5. Al‑Janabi and Ai‑Baghdadi: X‑radiography and CT scan on oral microflora
International Journal of Oral Health Sciences | Volume 9 | Issue 1| January-June 2019 23
or by the innate immune system, and any disturbance
of such control will lead to a locality or systematically
disease.[15,16]
None of our involved patients found to suffer
from any of oral infectious disease to make the study
more clear about the effects of X‑radiation on only oral
microflora. Sensitivity of MOs toward X‑rays is variable
depending on many factors such as type of microbes,
density of cells, nature of the environment, dose rate,
and type of radiation.[4,5,11,17]
Previously, several studies
demonstrated that the viability of bacteria was not affected
by low‑to‑medium energy of X‑rays and also there was
no mutation effect on these exposed bacteria.[5,6,11]
On
the other hand, X‑rays were found to act as sterilizing
agents upon a culture of Balantidium coli and Erythrobacillus
prodigiosus[9]
or even on soil MOs.[10]
In the present study,
most bacteria were induced to increase their cell number
after exposure to X‑rays, which means that ionization
energy of X‑rays is an effective stimulating factor to
increase the multiplication rate of bacteria after a single
exposure with unknown mechanism. Density of bacteria
in the oral cavity could have a role in this phenomenon,
especially with Streptococcus species that are already found in
a mouth with a high density. Elevation of bacteria density
usually provides a protective role against the harmful
effects of X‑rays.[17]
In comparison with S. epidermidis,
S. aureus showed more sensitivity to the harmful effects of
X‑rays. This may be related to low count of S. aureus that
is normally found in the oral cavity.[18]
However, genetic
damage by X‑rays may not be immediately observed until
several generations later.[4]
Dose of radiation is another important factor to induce
harmful effects on living cells. CT scan is usually used in
high dose (5–50 mSv to each organ imaged) compared
with X‑radiography.[19,20]
In general, a dose of more than 5
mSv that is usually generated by CT scan for the diagnosis
of different organs of the human body is equivalent to
over 250 chest X‑radiographies.[13]
Thus, a single CT scan
of the chest produced a higher radiation dose than a
chest radiograph by a factor which is estimated to about
100–1000 times more.[19]
This high dose of CT radiation
is often needed to examine the entire chest within a
single‑breath hold.[19]
Therefore, the density of bacteria
exposed to CT scan is often expected to decrease compared
with that exposed to X‑radiography. This was clearly noted
when isolated bacteria decreased their count after exposure
to X‑radiography with a significant difference from CT
scan. In addition to cell viability, genetic materials are the
parts of MOs most sensitive to the effects of radiation.[21]
Effect of X‑radiation dose on MO is usually given variable
results based on variable factors that could be related to the
radiation dose, type or location of affected MOs, and time
of exposure. Zappala et al. concluded that soil MO did not
affect by the low dose of X‑ray or CT scan radiation.[6]
High
doses of radiation (10 kGy) are also not effected on most
of MO.[22]
Several studies demonstrate that X‑radiation has
a harmful effect on MOs even at low doses. The applied of
2 kGy of X‑radiation on a population of aerobic bacteria
and fungi revealed a significantly decreased with increasing
of irradiation doses.[23]
About 98% of bacteria found on
10‑nm thick bismuth film were killed after exposure to
2.5 Gy of X‑ray.[24]
However, doses between 30 and 120 Gy
of X‑ray decreased bacterial cell density more than twice.[25]
The resistance of bacteria to antibiotic is also affected by
the dose of X‑ray exposure as noted with S. aureus when
its resistance toward five antibiotics was decreased after
exposure to low dose of X‑ray.[26]
Time of exposure is an additional factor that can affect
the viability of MOs. Exposure of an organism to X‑rays
for 50 min was found to decrease its cell density through
the effects of radiation energy on cell viability and their
proliferative activity.[27]
The X‑radiography usually takes
less than a second, while CT scan takes 15–20 s. Therefore,
MOs will remain under the effect of CT scan radiation for
a longer time. Thus, bacterial count in the present study
showed a significantly lower number after exposure to CT
radiation than to X‑radiography.
Fungi were revealed more sensitive to the harmful effects
of X‑rays. Candida sp. and C. neoformans were the most
frequently isolated fungi from involved patients. Total
count of these yeasts was decreased after exposure to
both types of X‑radiation. This result can indicate that
stimulation of bacteria in the oral cavity to increase their
cell count after exposure to X‑ray will be associated
with a decrease of fungal cells through the elevation of
competition level between bacteria and fungi.[7]
Induction of bacteria to fast multiplying by X‑rays gives
a serious indicator for the harmful effect of X‑rays on
the human body. Most of the normal oral flora have a
potential ability to cause diseases.[8]
Thus, an increase in
their numbers may produce more diseases. Therefore,
it is important to limit the exposure rate of X‑radiation,
especially with CT scan. Magnetic resonance imaging and
ultrasound are the best alternative choice for reducing the
risk of X‑rays.[13,19]
CONCLUSION
Exposure to routine diagnostic X‑rays induces increased
density of most of the normal oral flora. X‑radiography

6. Al‑Janabi and Ai‑Baghdadi: X‑radiography and CT scan on oral microflora
24 International Journal of Oral Health Sciences | Volume 9 | Issue 1| January-June 2019
had a major role to encourage oral MOs for elevating their
count compared with CT scan. Reducing exposure to X‑ray
is safety precaution that should be taken to minimize any
effects on normal flora of the human body.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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