The distribution of bacterial genes according to the site of infection
A total of 26 Enterobacteriaceae isolates were isolated from different clinical cases and were diagnosed by using vitek -2 system , the number each isolates were (5) E.coli, (5) K.pneumoniae, (5) Salmonella typhi, (5) Shigella dysentery, (2) Serratia marcescens and (4) Proteus vulgaris. The prevalence of traT and iss genes was 100% in both of respiratory and intestinal isolates while the percent of traT and iss genes in blood isolates were 100% and 50%, respectively whereas the prevalence of virulence genes in blood culture isolates which have (68.7%) and the occurrence of traT and iss genes observed in UTI isolates was 80 % and 60%, respectively (Table 1). The virulence-associated phenotypes including complement resistance, adhesion and invasion, and maintenance within macrophages in S. typhimurium have been caused by different members of OMPs group (Pulkkinen and Miller ,1991 and Heffernan et al., 1994). The contribution of OMPs has been showed in bacterial serum-resistance by their inactivation of complement at the C3, C9, and C5b-9 steps (Wooley et al., 1993 and Biedzka-sarek et al., 2005). The iss gene was first recognized in a human septicemic E. coli strain (Nolan et al.,1992). The iss and traT genes were present among 95.5% and 86.4% of E.coli strains of blood infections and only among 68.8 % and 43.8% of the intestinal infections , respectively (Fernandez-Beros et al., 1990), this result is comparable with the current study. The occurrence of the iss gene was higher in tissue isolates that clarify the role of this protein in pathogenesis of a vain pathogenic E.coli APEC strains (Nolan et al., 1992 and Johnson et al., 2008a). The traT genes were existent in most of the ETEC E.coli strains, this is may be due to ColV plasmids that are capable to transmission fully among varied  E. coli strains, giving these strains some virulence-related characteristics (Fernandez-Beros et al., 1990).

Table (1):
The size and sequences of primers used in current study.

Molecular detection of virulence factors genes among Enterobacteriaceae isolates
The traT and iss genes which encoded important virulence factors that are linked with human serum resistance were genetically scanned by using PCR technique for recognition of the existence of these genes in 26 isolates of Enterobacteriaceae family, it was found that 21(80.7%) of Enterobacterial isolates were contained traT gene at 288bp while only 17(65.38%) of isolates were contained iss gene at 258bp. A group of outer membrane protein (OMP) genes has been documented in the Enterobacteriaceae species including Escherichia coli, Shigella flexneri, Salmonella typhimurium, Klebsiella pneumoniae, Serratia marcescens, Proteus vulgaris, Proteus mirabilis, and Providencia stuartii. One or two peptidoglycan-associated main outer membrane proteins were found in all studied strains (Hofstra et al.,1980). The current data approved with other study which detect the commonness of traT in Gram negative bacteria, particularly E. coli, Salmonella, Shigella and Klebsiella, It was showed in a higher percentage among the E. coli strains isolated from the blood stream of patients with bacteremia /septicemia or from feces of patients with gastrointestinal  infections (50-70%) while the incidence of traT in strains isolated from cases of urinary tract infections was variable (Montenegro et al.,1985).

Table (2):
The dissemination of genes among bacterial isolates according to the site of infection.

The PCR result observed in Figure 1 shows that 100 % of Salmonella typhi and Serratia marcescens isolates gave positive result for traT gene. OMPs has significant role in pathogenesis of S. typhimurium and Y enterocolitica (Heffernan et al.,1994).

Table (3):
The occurrence of virulence factors genes among bacterial species.

In the current study traT gene was identified in 80% K. pneumoniae and Shigella dysentery isolates, this result compatible with other study which found that traT gene was detected in (78.5%). of K. pneumoniae (Wasfi et al., 2016) while Kuo et al., 2017 (Kus et al., 2017) detected  traT gene in 11.3% of K.pneumonia isolates. 75% and 60% of E. coli and Proteus isolates were positive for traT gene, respectively (Fig. 1), this result parallel with other study by Wooly et al., 1993 who showed that 57.1% of E.coli isolates were contained traT gene and  Wu et al., 2007 showed presence of traT genes in most of the E.coli O149 isolates. Fernandez-Beros et al.,1990 showed that the iss and traT genes were existent among 95.5 % and 86.4 % of the E.coli blood isolates and only among 68.8 % and 43.8 % of the intestinal isolates, correspondingly. Previously it was described a ColV plasmid, among E.coli isolates from blood and intestinal sources, ColV plasmids confer Escherichia coli with some virulence genes including iss and traT (Aguero et al., 1984 and Skyberg et al.,2008). ColV plasmids are capable to transmission completely among diverse E. coli strains, providing those strains with several virulence-linked features (Fernandez-Beros et al., 1990).

The occurrence of iss gene product at 258 bp in E. coli and Shigella dysentery isolates was 80% while it was 60% among K. pneumonia ,Salmonella typhi isolates and 50% of Proteus vulgaris and Serratia marcescens isolates as showed in Fig. 2. This result comparable with a study of Badouei et al., 2015 who found that the occurrence of the iss gene in  a vain E.coli strains was 90.3% in the septicemic isolates and 64.3% among cecal isolates and also approved with a study of Vaz et al., 2017 who observed the occurrence of iss gene was ranged from 75 to 91% among the ExPEC strains and was ranged from 49 to 57% among the fecal strains ,while other study showed that 30% of uropathogenic E.coli isolates were positive for iss gene and only 8% of K.pneumoniae isolates were contained iss gene (Hassan, 2015).

The iss gene was represented one of the most prevalent virulence genes in extra-intestinal pathogenic strains and three alleles of iss were recognized among E. coli isolates (Johnson et al., 2008b). Human serum resistance among ExPEC permits persistence in the host’s blood stream and can possibly distribute to cause human infections through the food chain is indistinct, it can colonize the intestinal area and prompt virulence gene transmission to human strains. For example, APEC strains and urogenital pathogenic E. coli (UPEC) causing human infections were revealed to share large genomic sequences (Johnson et al.,2008a and Kariyawasam et al.,2007).

The present study concluded that high distribution  of genes encoded for outer membrane proteins responsible for human complement resistance among Enterobacteriaceae species isolated from different clinical infections and also these genes were detected among extraintestinal infections isolates .