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 Table of Contents  
Year : 2019  |  Volume : 9  |  Issue : 1  |  Page : 20-24

Evaluation of biological effects of X-radiography and computed tomography scan on oral microflora

1 Department of Microbiology, College of Medicine, University of Karbala, Karbala, Iraq
2 Department of Physiology, College of Medicine, University of Karbala, Karbala, Iraq

Date of Web Publication17-May-2019

Correspondence Address:
Prof. Ali Abdul Hussein S Al-Janabi
Department of Microbiology, College of Medicine, University of Karbala, Karbala
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ijohs.ijohs_53_18

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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

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

How to cite this URL:
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 [serial online] 2019 [cited 2022 Aug 18];9:20-4. Available from: https://www.ijohsjournal.org/text.asp?2019/9/1/20/258574

  Introduction Top

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],[5],[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] 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 Top


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 Top

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 More Details 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].
Table 1: Total number of patients with microbial count before and after exposure to X-radiation

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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 [Figure 1], [Figure 2], [Figure 3], [Figure 4]. Meanwhile, cells of two fungi decreased their count after exposure to X-rays [Figure 1], [Figure 2], [Figure 3], [Figure 4].
Figure 1: Total number of microbial isolates from males before and after exposure to radiation of X-radiography

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Figure 2: Total number of microbial isolates from females before and after exposure to radiation of X-radiography

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Figure 3: Total number of microbial isolates from males before and after exposure to radiation of computed tomography scan

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Figure 4: Total number of microbial isolates from females before and after exposure to radiation of computed tomography scan

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Bacterial isolates from some patients, especially from males, showed no difference in their number either before or after exposure to X-radiography which was considered an indicator for the absence of radiation effect on their cell viability [Figure 1] and [Figure 2]. This result was not observed with exposure to CT scan radiation [Figure 3] and [Figure 4].

  Discussion Top

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]

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 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 Top

Exposure to routine diagnostic X-rays induces increased density of most of the normal oral flora. X-radiography 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.

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Conflicts of interest

There are no conflicts of interest.

  References Top

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4]

  [Table 1]


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