Bacteria in the genus Acinetobacter have been known to colonize a wide array of ecological systems of which water, soil, sludge, wastewater, plants' root, and animals have been prominent. In this study, water samples were collected from three selected rivers in the Eastern Cape Province, South Africa for the assessment of the incidence of Acinetobacter species, and quite a good number of bacteria in the genus Acinetobacter were presumptively recovered from the water samples. In recent times, freshwater resources have been noted to be a hotspot of Acinetobacter species. Maravić et al.  carried out an assessment of the microbial community in the urban riverine environment in Croatia, where 57 of the isolates belong to the genus Acinetobacter. Krizova et al.  also noted the widespread of Acinetobacter bohemicus sp. nov. in the water environment in the Czech Republic. In India, Arsenic-resistant Acinetobacter soli, Acinetobacter venetianus, Acinetobacter junii, Acinetobacter baumannii and Acinetobacter calcoaceticus were reported .
Besides, the composition of the bacterial community in a freshwater aquaculture environment was investigated in China by . The study reported that the relative abundance of Acinetobacter species was 0.5% of the total bacterial community. In 2014, Zhao and others  isolated a set of bacteria from the zinc and arsenic polluted river in Northeastern China, where bacteria belonging to the genus Acinetobacter were found to be prominent. The occurrence and distribution of Acinetobacter spp. in freshwater resources in the study further validated the findings in other reports [29, 31].
All isolates that were positive for the recA (425 bp) (Figure 1) were taken as belonging to the Acinetobacter genus. Chen et al  developed a multiplex PCR amplification assay for the initial molecular identification of Acinetobacter species using a recA gene-specific primer before delineating them into species namely, Acinetobacter baumannii, Acinetobacter nosocomialis and Acinetobacter pittii by using species-specific primers. Comparably, Chiang et al.  demonstrated a PCR assay targeting recA gene for the detection of Acinetobacter baumannii in patients suffering from endotracheal aspirates in the intensive care unit (ICU) of Taipei Veterans General Hospital.
Eight hundred and fourty-four isolates positive for the Acinetobacter genus were further delineated into its species. Figure 2 and 3 represents gel images of the amplicons of the expected band size of 208 bp for Acinetobacter baumannii and 294 bp for Acinetobacter nosocomialis with respect to the gyrB gene. Acinetobacter baumannii, Acinetobacter nosocomialis, and Acinetobacter pittii are known nosocomial pathogens, which could cause multiple antibiotic resistant infections [2, 32, 34] in immune-compromised patients . Park and others  investigated the presence of Acinetobacter species in the bloodstream of patients with a blood infection in a tertiary-care hospital in Korea between August 2003 and February 2010. Their findings showed that Acinetobacter baumannii and Acinetobacter nosocomialis were prevalent in the samples collected. Similarly, Anh et al. , recovered 160 A. baumannii isolates from sputum, blood, pus and fluid aspirates of patients in three Hospitals in Vietnam within a period of two years (between 2012 and 2014). These findings showed that the nosocomial pathogens could colonize any part of the human body to cause infections. Sileem et al. , in addition to others, carried out a study on the occurrence of Acinetobacter baumannii in the ICU and its impact on the mortality rate.
In the present study, Acinetobacter baumannii and Acinetobacter nosocomialis were recovered from freshwater resources. Several Acinetobacter species have been recovered from soil, water, and wastewater environments; however, the occurrence of A. baumannii and Acinetobacter nosocomialis in a natural environment, besides hospital settings, has been uncommon in the past few years. But in recent times, it is now very clear that such nosocomial pathogens could be isolated from other ecosystems [3, 4, 38]. Fernando et al.  showed evidence of the occurrence of Acinetobacter baumannii in the surface water resources collected from the South Nation River (SNR) drainage basin in Eastern Ontario, Canada, in 2013. Goswami et al.  also isolated A. baumannii from the river in West Bengal, India. The isolation of the pathogen from water sources might be due to contamination coming from hospital wastewater and materials.
The virulence traits of the clinically important Acinetobacter species such as A. baumannii and A. nosocomialis have been a major research focus in recent times [17, 39]. This is due to the nature of A. baumannii infections as well as the role virulence genes play in the pathogenicity of the emerging waterborne pathogen. Virulence genes are the mechanisms through which A. baumannii initiates pathogenesis [39, 40, 41], most especially in the clinical settings. In this study, the occurrence of these pathogens in the freshwater resources was evaluated, and the virulence factors harboured by them were also considered. Although, A. baumannii had been confirmed to harbour several virulence factors (genes), seven of these (afa/draBC, epsA, fimH, OmpA, PAI, sfa/focDE, and traT) are reported in this study. Most of the reports on the virulence genes harbored by A. baumannii are usually associated with isolates from clinical environment, whereas there are rare reports on A. baumannii from a natural environment harboring virulence genes. Findings of this study showed that OmpA gene was predominantly exhibited by the A. baumannii in all the rivers sampled, fimH and epsA genes were also detected in many of the isolates, whereas afa/draBC, PAI, Sfa/focDE, and traT were detected in a few Acinetobacter isolates. As such, the exhibition of virulence genes varies from one isolate to the other, which was also reported among clinical isolates known for nosocomial infections . The OmpA gene is the main outer membrane protein (OMP) located on the A. baumannii membrane [43, 44], which readily influence the virulence of an A. baumannii isolate . These observations corroborate the findings of this current study which report that the virulence profiles of individual isolate varied greatly and OmpA was mostly detected .
Generally, the outer membranes of Gram-negative bacteria are made up of the OMPs, lipopolysaccharides and phospholipids layer . The presence of outer membrane protein A gene (OmpA) in the A. baumanni isolated from the natural environment is of a major concern based with respect to pathogenesis [39, 40, 41]. Besides, studies have shown that A. baumannii uses OmpA for adhesion to the lung epithelial cell by interacting with a cell cytoskeleton such as fibronectin on the cell surface and thereby inducing pneumonia [45, 46, 47, 48, 49]. It also causes cell death through caspase-3 activation [50, 51]. Similarly, A. baumannii could be responsible for apoptosis through the translocation of its OmpA into the mitochondria and the nucleus of host cells [47, 52, 53]. The combination of the roles played by OmpA makes it an important virulence factor in the pathogenesis of A. baumannii infection. Moreover, antibiotic resistance in A. baumannii is also associated with OmpA [54, 55]. It was suggested that OmpA was involved in the removal of antibiotics from the periplasmic space membrane efflux systems . The survival and persistence of A. baumannii in the cell are enhanced by OmpA due to the formation of biofilms and surface motility.