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 Table of Contents  
ORIGINAL ARTICLE
Year : 2017  |  Volume : 2  |  Issue : 1  |  Page : 22-28

Prevalence of efflux genes and ribosomal protection genes among tetracycline-resistant Aeromonas hydrophila isolated from diarrheic patients in Iraq


1 Department of Microbiology, College of Medicine, Babylon University, Hilla, Iraq
2 Center of Environmental Research, Babylon University, Hilla, Iraq

Date of Submission09-Dec-2016
Date of Acceptance03-Mar-2017
Date of Web Publication1-Jun-2017

Correspondence Address:
Alaa Hani Al-Charrakh
Department of Microbiology, College of Medicine, Babylon University, Hilla, Babylon Governorate
Iraq
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/bjhs.bjhs_53_16

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  Abstract 

Objective: The aim of this study was to investigate the prevalence of tetracycline-resistant Aeromonas hydrophila isolated from clinical sources in Iraq, using polymerase chain reaction (PCR) technique.
Materials and Methods: A total of 822 samples were collected from patients suffering from diarrhea. Isolates were identified using biochemical tests, Vitek 2 system, and 16S rRNA specific primer. PCR was used to detect tetracycline-resistant isolates.
Results: Out of the 822 clinical samples collected, 13 Aeromonas spp. isolates (1.58%) were recovered, out of which eight isolates (61.53%) were identified as A. hydrophila. Results found that all tetracycline-resistant isolates carried at least one of the tet genes examined. Among efflux genes, tet (A) was most commonly observed in isolates, followed by efflux tet gene (tet B and C) and ribosomal protection protein (tet O). However, efflux genes tet (D and G) were not detected in any of the isolates.
Conclusions: The prevalence of tet O chromosomal protection protein among A. hydrophila isolates was first recorded in Iraq and in many other neighboring countries.

Keywords: Aeromonas hydrophila, clinical sources, efflux genes, ribosomal protection gene, tetracycline resistance


How to cite this article:
Al-Charrakh AH, Al-Shalah LA. Prevalence of efflux genes and ribosomal protection genes among tetracycline-resistant Aeromonas hydrophila isolated from diarrheic patients in Iraq. BLDE Univ J Health Sci 2017;2:22-8

How to cite this URL:
Al-Charrakh AH, Al-Shalah LA. Prevalence of efflux genes and ribosomal protection genes among tetracycline-resistant Aeromonas hydrophila isolated from diarrheic patients in Iraq. BLDE Univ J Health Sci [serial online] 2017 [cited 2019 Sep 22];2:22-8. Available from: http://www.bldeujournalhs.in/text.asp?2017/2/1/22/207428

Members of the genus Aeromonas are facultatively anaerobic, rod-shaped oxidase positive, Gram-negative bacteria, and mesophilic and facultative anaerobic bacteria. Some species are pathogenic for animals and humans. Aeromonas species are widely distributed in the aquatic environment, including raw and processed drinking water and have been frequently isolated from various food products such as fish and shellfish, raw meat, vegetables, and raw milk. In addition, in recent years, aeromonades have been implicated as the causative agents of human disease, ranging from gastroenteritis to wound infections.[1],[2]

The genus Aeromonas comprises important human pathogens causing primary and secondary septicemia in immunocompromised persons, serious wound infections in healthy individuals and in patients undergoing medical leech therapy, and a number of less well-described illnesses such as peritonitis, meningitis, and infections of the eye, joints, and bones. Gastroenteritis, the most common clinical manifestation, remains controversial.[3]

Aeromonas species are known to cause severe diarrheal disease of short duration or chronic loose stools in children, the elderly, or the immunocompromised individuals and they have been implicated in travelers' diarrhea. They are commonly isolated from fecal sample of children <5 years old, whereas their isolation from other body sites usually occurred in adult populations.[4],[5]

Tetracyclines belong to a family of broad-spectrum antibiotics that inhibit protein synthesis in Gram-positive and Gram-negative bacteria by preventing the binding of aminoacyl-tRNA molecules to the 30S ribosomal subunit and inhibiting protein synthesis,[6] contributing to higher levels of microbial resistance, especially among the genus Aeromonas.[5] The aim of this study was to evaluate the incidence and spreading of Aeromonas hydrophila isolated from diarrheic patients in Hilla city, Iraq, and study the tetracycline resistance at molecular level by detecting efflux pump genes and ribosomal protection protein genes responsible for tetracycline resistance among these isolates.


  Materials and Methods Top


Sample collection and isolation of bacterial isolates

This cross-sectional study was designed to assess the occurrence of tetracycline-resistant A. hydrophila in patients with diarrhea. A total of 822 fecal samples were collected from rectal swab (routine work) and from patients suffering from diarrhea who were attending public health laboratory, Hilla city, Iraq. The period of specimen collection and analysis was extended from October 2015 to February 2016.

For isolation and identification of bacterial isolates, all specimens were cultured on alkaline peptone water, and then transferred to TCBS and MacConkey agar by swabbing and incubated at 37°C for 24 h. Each primary positive culture was identified depending on the morphological properties such as shape, swarming, odor, and lactose or nonlactose fermentation on MacConkey agar.[7] Different biochemical tests were used for the identification of bacterial isolates according to standard methods.[7],[8] Vitek 2 system (BioMerieux, France) was used to confirm the identification according to the manufacturer's instructions. Finally, identification was confirmed using 16S rRNA-specific primer using molecular technique (polymerase chain reaction [PCR]).

In light of antibiotic susceptibility results of our previous study,[9] eight tetracycline-resistant hydrophila isolates were detected using phenotypic methods. Out of the 822 clinical samples collected, 13 isolates (1.58%) were belonged to Aeromonas spp., out of which eight A. hydrophila isolates (61.53%) were obtained. These bacterial isolates were identified as A. hydrophila based on their morphology, biochemical tests [8] in addition to Vitek 2 system, and as suggested previously.[9]

Extraction and quantification of DNA

For genomic DNA extraction, a single colony of cultivated bacteria, which had been incubated overnight, was transferred to 2 ml of sterile Luria broth and incubated at 37°C for 18–20 h. The DNA was extracted and purified using Genomic DNA kit (EURx/Korea). All the clinical isolates were screened for chromosomal DNA according to manufacturer's instructions. The total DNA was used to detect 16S rRNA, efflux pump, and ribosomal protection protein genes. For plasmid DNA extraction, a single colony of cultivated bacteria, which had been incubated overnight, was transferred to 2 ml of sterile Luria broth and incubated at 37°C for 18–20 h. The DNA was extracted and purified using high-speed mini DNA plasmid extraction kit (Geneaid Biotech, Taiwan) according to manufacturer's instructions. Plasmid DNA was used to detect efflux genes.

Chromosomal and plasmid DNAs obtained were used as templates for all PCR experiments. The PCR reactions were carried out in a thermal cycler (Clever, UK). Before PCR assay, and to quantify the DNA concentration (ng/μL), the quantification of DNA samples was carried out by means of a spectrophotometric reading using 1 μL aliquots of genomic DNA with a NanoDrop™ spectrometer (NanoDrop Technologies, Inc., USA), adopting the manufacturer's recommendations. The concentration of DNA was estimated from absorbance at 260 nm. DNA profiles were performed using bacterial DNA and loading buffer according to the manufacturer's instructions (Bioneer, Korea).

Polymerase chain reaction protocols

The DNA extracts of A. hydrophila isolates were subjected to different genes by PCR. The protocols used were according to manufacturer's instructions. Different resistance primers of efflux protein genes (tet A, tet B, tet C, tet D, tet E), (tet G and tet L), and ribosomal protection protein genes tet (M) and tet (O) were used. In addition, specific primer (16S rRNA) was used for bacterial identification of A. hydrophila. Stock solution of these primers was prepared according to the information of manufactured company listed with primers. Primer types and sequences are shown in [Table 1].
Table 1: Sequence and concentration of primers used in the study

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Five microliters of DNA was added to Master Mix, and then 10 μl of primer (3 μl for up- and down-stream, 4 μl free distal water) was added to the mix information labeled with Master Mix. The compassions were mixed carefully and then placed in a thermocycler (after incubation at 94°C for 5 min) and running according to conditions of each primer mentioned above. The following temperature profiles for PCR amplification of tetracycline-resistant gene fragments were applied over 40 cycles [Table 2].
Table 2: Polymerase chain reaction conditions for efflux protein genes and ribosomal protection genes

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After PCR, the profiles of amplification products were detected by gel electrophoresis according to the procedure of Sambrook and Russel.[12] Five microliters of the total reaction mixture was loaded on a 1.2% agarose gel and electrophoresed at 100 V at 70 mA for 60 min. The amplified DNA fragments were visualized by ultraviolet illumination after agarose gel electrophoresis and Ecodye (and ethidium bromide) staining by standard procedures.


  Results Top


Results of the present study revealed that the following tet genes were detected: efflux (tet A, B, C, D, E, G, and L) genes and ribosomal protection protein (tet M and O) genes. Results found that all tetracycline-resistant isolates carried at least one of the tet genes examined [Table 3].
Table 3: Genetic profile of efflux pump tet gene and ribosomal protection protein genes in Aeromonas hydrophila isolates

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Regarding efflux genes, tet A was most commonly observed in A. hydrophila isolates (8), found in 6 (75%) [Figure 1] and [Figure 2], followed by tet B and tet C [Figure 1], [Figure 3], and [Figure 4]. Tet E efflux gene was found in two isolates [Figure 6] and tet L [Figure 8] in one isolate. However, efflux pump genes, tet D and G, were not detected in any of the A. hydrophila isolates tested [Figure 5] and [Figure 7].
Figure 1: Percentages of efflux pump genes and ribosomal protection genes of Aeromonas hydrophila

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Figure 2: Ecodye-stained agarose gel electrophoresis (1.2%) of polymerase chain reaction-amplified products from extracted DNA of Aeromonas hydrophila isolates and amplified with primer of tet A gene (211 bp)

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Figure 3: Ecodye-stained agarose gel electrophoresis (1.2%) of polymerase chain reaction-amplified products from extracted DNA of Aeromonas hydrophila isolates and amplified with primer of tet B gene (391 bp)

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Figure 4: Ecodye-stained agarose gel electrophoresis (1.2%) of polymerase chain reaction-amplified products from extracted DNA of Aeromonas hydrophila isolates and amplified with primer of tet C gene (897 bp)

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Figure 5: Ethidium bromide-stained agarose gel electrophoresis (1.2%) of polymerase chain reaction-amplified products from extracted DNA of Aeromonas hydrophila isolates and amplified with primer of tet D gene (844 bp)

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Figure 6: Ethidium bromide-stained agarose gel electrophoresis (1.2%) of polymerase chain reaction-amplified products from extracted DNA of Aeromonas hydrophila isolates and amplified with primer of tet E gene (744 bp)

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Figure 7: Ecodye-stained agarose gel electrophoresis (1.2%) of polymerase chain reaction-amplified products from extracted DNA of Aeromonas hydrophila isolates and amplified with primer of tet G gene (241 bp)

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Figure 8: Ethidium bromide-stained agarose gel electrophoresis (1.2%) of polymerase chain reaction-amplified products from extracted DNA of Aeromonas hydrophila isolates and amplified with primer of tet L gene (311 bp)

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Regarding ribosomal protection protein, tet O was detected in five isolates (62.5%) [Figure 9] and tet M [Figure 10] was detected in only one isolate (12.5%).
Figure 9: Ethidium bromide-stained agarose gel electrophoresis (1.2%) of polymerase chain reaction-amplified products from extracted DNA of Aeromonas hydrophila isolates and amplified with primer of tet O gene (354 bp)

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Figure 10: Ethidium bromide-stained agarose gel electrophoresis (1.2%) of polymerase chain reaction-amplified products from extracted DNA of Aeromonas hydrophila isolates and amplified with primer of tet M gene (305 bp)

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Results revealed that tet O ribosomal protection protein gene was detected in 5 isolates (62.5%) of A. hydrophila [Figure 1]. To to our knowledge, this result is the first record in Iraq and in many other neighboring countries.

Although few studies are available concerning tetracycline-resistant A. hydrophila isolated from human samples, results of this study revealed the prevalence of tetracycline-resistant A. hydrophila recovered from the clinical sources. The result of this study is the first record in Iraq.


  Discussion Top


Using phenotypic methods, all A. hydrophila isolates (8) were determined previously as tetracycline resistant.[9] Regarding prevalence of tetracycline-resistant A. hydrophila recovered from the clinical sources, few studies are available concerning tetracycline-resistant A. hydrophila isolated from human samples. Results found that all tetracycline-resistant A. hydrophila isolates carried at least one of the tet genes examined. The result of this study is the first record in Iraq.

Most of the studies focused on tet genes of A. hydrophila in fish because the widespread nature of aeromonades is a result of their adaptation toward a different aqua medium including lakes, rivers, and drinking water.[13],[14]

Furushita et al.[15] suggested that tet genes from fish farm bacteria have the same origins as those from clinical strains. They also found that sequence analysis indicated the identity in tet genes between the fish farm bacteria and clinical bacteria: 99.3%–99.9% for tet B, 98.2%–100% for tet C, 99.7%–100% for tet D, 92.0%–96.2% for tet G, and 97.1%–100% for tet Y.

Igbinosa and Okoh [16] assessed the prevalence of antibiotic-resistant Aeromonas species isolated from Alice and Fort Beaufort wastewater treatment plant in the Eastern Cape Province of South Africa and they found that tet C was not detected in any of the Aeromonas isolates. Balassiano et al.[17] analyzed the involvement of tet A and tet E genes in the tetracycline resistance of 16 strains of genus Aeromonas, isolated from clinical and food sources. PCR revealed that 37.5% of the samples were positive for tet A and also 37.5% were tet E positive. One isolate was positive for both genes.

The prevalence of efflux gene (tet A) (75%) of A. hydrophila was also reported by several authors. Jacobs and Chenia [18] isolated Aeromonas spp. from South African aquaculture systems and they reported the prevalence of tet A and tet E genes. They reported that single and multiple class A family tet determinants were observed in 27% and 48.7% of isolates, respectively, with tet A being the most prevalent tet determinant type. Hedayatianfard et al.[19] showed that the most widely distributed resistance gene was gene tet A and at the least known resistance gene was tet M among the studied bacteria of the genus Aeromonas. On the other hand, Andersen and Sandaa [20] reported that tet A determinant was detected in only 5% of the isolates and tet D was detected in 4% of the isolates. While they found that tet E was found in 63% of isolates and it was the most widespread determinant in bacterial isolates obtained from polluted and unpolluted marine sediments in Norway and Denmark.

Results of this study found that efflux pump genes (tet D and tet G) were not detected in any of the A. hydrophila isolates. In contrast, several authors reported the prevalence of efflux tet gene (tet D) in A. hydrophila isolated from fish pathogens.[21] In conclusion, the data from other studies showed that bacterial isolates from aquaculture sources in Australia harbor a variety of tetracycline-resistant genes; tet A, tet D, tet E, and tet M genes were found in Aeromonas spp., while no tet B, tet C, or tet Y determinants were detected.[22]

Interestingly, one of our isolates also contained both tet A and tet E genes. Therefore, it is evident that tetracycline-resistant determinants such as tet E, tet A, and tet D (in that order) are also present in aquaculture in Australia, just as in other geographical regions. However, the widespread occurrence of tet M in this isolates is not surprising because this class of tetracycline-resistant determinant has been recently described in aquaculture.[23]

Furushita et al.[15] in a study of 66 tet-resistant strains isolated from fishes collected at three different fish farms located in the southern part of Japan reported a prevalence of tet B in 31 of tet-resistant bacteria, and then tet Y in six, and tet C and tet D in four strains.

Jacobs and Chenia [18] reported the occurrence of more than one tet-resistant genes with the majority of isolates possessing two tet determinants with the tet A and tet E as well as tet B and tet D/tet H combination being observed. Three tet genes (tet D, tet E, and tet M) were found in two strains of Aeromonas spp.


  Conclusions Top


The prevalence of tetracycline-resistant A. hydrophila recovered from the clinical sources in this study is the first record in Iraq. Very few studies are available concerning tetracycline resistance in A. hydrophila isolated from human samples. Furthermore, it can be concluded that the prevalence of tet O chromosomal protection protein among A. hydrophila isolates in the present study was first recorded in Iraq and in many other neighboring countries.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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Balassiano IT, Bastos Mdo C, Madureira DJ, Silva IG, Freitas-Almeida AC, Oliveira SS. The involvement of tetA and tetE tetracycline resistance genes in plasmid and chromosomal resistance of Aeromonas in Brazilian strains. Mem Inst Oswaldo Cruz 2007;102:861-6.  Back to cited text no. 17
    
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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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