A total of 70 fecal samples were collected from camels in the Bikaner region for
E. coli isolation. The samples were cultured on MacConkey agar and colonies from MacConkey agar were further streaked on Eosin Methylene Blue (EMB) agar for
E. coli confirmation. All isolates exhibited pink colonies on MacConkey agar, with the characteristic green metallic sheen observed in the growth of cultures on EMB agar plates.
Biochemical identification of E. coli isolates by VITEK-2 system
Biochemical identification of
E. coli isolates using the VITEK-2 system was conducted of 35 samples (one from every two) with pure cultures at a concentration equal to 0.5 McFarland standards. The VITEK-2 Compact system positively identified
E. coli, showing excellent confidence levels with an overall probability range of 96-98% (Fig 1).
These findings align with reports by
Putra et al., (2020), which achieved 100%
E. coli identification using the automatic VITEK-2 Compact method. Similar confirmation rates were observed by
Voidarou et al., (2011) and
Al-Marri et al., (2021). Automation of biochemical tests has significantly reduced identification time, from 5-10 hours to 3 hours for Gram-negative rods, improving reliability and efficiency with minimal manual sample preparation compared to manual miniaturized biochemical tests
(Funke et al., 1998).
The VITEK-2 Compact system, known for its widespread use and automation in bacterial identification based on biochemical profiles, utilizes fluorescence and/or colorimetry. Compact plastic cards containing selective or differentiated media or reagents enable bacterial identification in a shorter time than conventional methods
(Barry et al., 2003). Ueda et al., (2015), Fadlelmula et al., (2016); Putra et al., (2020) and
El-Ghareeb et al., (2020) have collectively concluded that the VITEK-2 automated system is accepted, convenient and rapid for the correct identification of bacteria.
Moawad et al., (2018) applied the VITEK-2 system for phenotypical confirmation of extended-spectrum β-lactamase-producing isolates. Enterobacteriaceae were identified, with 87.5% being
E. coli, 6.9% Enterobacter cloacae, 2.8% Klebsiella pneumoniae and 2.8%
Citrobacter spp. Other Gram-negative and Gram-positive bacteria were also correctly identified by the VITEK-2 system.
Hara and Miller (2003) reported a correct identification rate of 93% for enteric strains, with 85.9% of gram-negative enteric strains identified at probability levels ranging from excellent to good.
Hemolysin property of E. coli isolates
In the present study 32 out of 70 camel
E. coli isolates (45.71%) produces partially hemolysis on sheep blood agar (Fig 2). Red blood cell of the host organism is lysed due to the presence of hemolysin gene which in turn helps in the spread of the pathogen in the host blood
(Bashar et al., 2011). The hemolytic activity of
E. coli is related to the presence of hemolysin genes.
Dadheech et al., (2016) and
Osman et al., (2018) had 100% recovery of
E. coli isolates producing β-hemolysis on blood agar.
The mechanism by which
E. coli causes diarrhea does not rely on the hemolytic nature of
E. coli isolates but is due to toxin produced by its strains.
Roy et al., (2006) was found 45.16%
E. coli isolates produced hemolysis on sheep blood agar. Similarly,
Shittu et al., (2010) E. coli isolates produces (45%) both α and β-hemolysis. Hemolysin production was determined to differentiate between the virulent hemolytic isolates and the avirulent non-hemolytic isolates. According to
Osman et al., (2018) 96.66%
E. coli isolates producing α-hemolysin; 3.33% isolate produced β-hemolysin instead of α–hemolysin.
Hemolytic strains are more virulent than non-hemolytic strains
(Vaish et al., 2016). α-Hemolysin, also known as cytotoxic necrotizing factor, is produced by invasive strains of
E. coli, which sets the pace for the pathogenesis of renal disease and enhances virulence in a number of clinical infections
(Herlax et al., 2010). In another cross-sectional study
Singh et al., (2021), Koutsianos et al., (2021); Grakh
et al. (2021) found none of the
E. coli isolates as hemolytic while as
Adam et al., (2022) found one isolate produce hemolysis on sheep blood agar.
Al-Humam (2016) reported only (9.6%) camel
E. coli isolates showed β-hemolysis on blood agar plates.
Slime production test of E. coli isolates
Biofilm formation was measured to determine the ability of isolates to colonize surfaces for environmental survival and persistence and a virulence factor. The ability to form biofilm as determined by slime production (assessed by Congo red uptake and an adherence assay in glass tubes) revealed a heterogeneity among the isolates, ranging from weak and moderate to strong biofilm formation. 32 out of 70
E. coli isolates of camel (45.71%) were positive as biofilm formation (Fig 3). Bacteria within biofilms can withstand host immune responses and are less susceptible to antimicrobials and disinfectants (
Jenkins, 2018).
Ahmad et al., (2009) reported a result of 76.92% in the growth of brick-red black-colored colonies, indicative of pathogenic
E. coli. The Congo red binding ability serves as a phenotypic marker for distinguishing between
E. coli strains associated with septicaemia (invasive) and those that are not. It is also an epidemiological marker useful for discriminating pathogenic strains from commensals.
In a study by
Yadav et al., (2014), results indicated a Congo red binding ability of 92.86% in
E. coli isolates. Similarly,
Adam et al., (2022) found that all isolates, accounting for 100%, exhibited positive results in the Congo red (CR) binding test. The Congo red agar test (CRA test) is considered an essential parameter for monitoring virulence characteristics of
E. coli in both human and animal communities. In line with these findings,
Kagane et al., (2021) observed 100% positivity in the Congo red binding test among their
E. coli isolates.
Antibiogram study for E. coli isolates
In the present investigation, all 70
E. coli isolates were subjected to antibiotic sensitivity test using 20 different antibiotics. The response of organisms was interpreted as sensitive, intermediate and resistant based on the manufacturer guidelines (Himedia). The antibiotics tested belonged to various groups
i.e. β-lactam antibiotics, aminoglycosides, glycopeptides, phenicoles, quinolones, tetracyclines, sulphonamide, RNA synthesis inhibitor, polypeptides, macrolides and lincosamides. β-lactam antibiotics included penicillins, cephalosporins, monobactums and carbapenems.
In β-lactum group (cell wall sysnthesis inhibitors) all the isolates were resistant to Penicillin-G. In the present study, 94% isolates from were resistant to penicillin.
E. coli isolates were more resistant to ampicillinsulbactam, amoxycillin-sulbactam 76.15% and 85.71%.
E. coli isolates were least resistant with 51.42% and 54.14% resistivity to third and fourth generation cephalosporins respectively. 22.57%
E. coli isolates were sensitive and 62.42%isolates showed higher resistance to gentamicin (Table 2).
Nuesch-Inderbinen et al., (2020) reported resistance to tetracyclinefrom African camel was detected most frequently (11.7%), followed by ampicillin and streptomycin (both 10.5%) and sulfamethoxazole/trimethoprim (9.9%) and one isolatesshowed intermediate resistance to streptomycin, remaining were sensitive to amoxycillin/clavulanic acid, ciprofloxacin and kanamycin.
Bessalah et al., (2016) observed that all
E. coli isolates were sensitive to amikacin, chloramphenicol, ciprofloxacin, gentamicin and ceftiofur. The highest frequency of resistance was observed against tetracycline, ampicillin and streptomycin (52.8%, 37.1% and 21.4%, respectively). Resistance to sulfisoxazole and trimethoprim–sulfamethoxazole was noted in almost 20% and 18.5% of
E. coli isolates, respectively. A lower percentage of resistance was identified against amoxicillin/clavulanic acid (2.8%), ceftriaxone (1.4%) and cefoxitin (2.8%).
Momtaz et al., (2013) reported higher resistance rates to gentamicin and streptomycin (62.42% and 67.32%, respectively) in
E. coli isolates, which aligns with our findings.
Adelaide et al., (2008) detected elevated resistance levels for tetracycline (75.9%) and cotrimoxazole (72.4%).
Subedi et al., (2018) found that the maximum
E. coli strains were resistant to ampicillin (98%), followed by co-trimoxazole (90%), with intermediate resistance to colistin (50%) and the highest sensitivity observed against gentamicin (84%).
The frequency of sensitivity of most susceptible antimicrobial agents observed chloramphenicol (71.14%), followed by enrofloxacin (60%), sulphadiazine (48.575%) and co-trimoxazole (48.28%) in camel
E. coli isolates. Less susceptibleor intermediate antibiotics areoxytetracycline (37.49%), ciprofloxacin (31.42%) and gentamicin (22.57%). This finding is similar to Bessalah
et al. (2016) who also reported chloramphenicol as most sensitive antimicrobial agent. This finding is also similar with those of previous reports on isolates associated with genital and mastitis infections of camels
(Mshelia et al., 2014). Azad et al., (2017) reported 36% sensitivity to gentamicin and 100% to erythromycin.
Bhave et al., (2019) revealed high degree of resistance to commonly used antimicrobials, namely tetracycline (95.89%), trimethoprim (89.04%), colistin (82.88%) and ciprofloxacin (54.11%). However, further studies would be required in order to correlate the use of antimicrobials with the fecal carriage of AMR in camels.
Profiling of antibiotic resistance associated genes in E. coli isolates
The present study was conducted to investigate detection of some genes responsible for imparting antibiotic resistance to the
E. coli isolates obtained from the camel fecal samples. The outcome of this study resulted as presence of
blaTEM,
sul2,
sul3,
strA,
aadA,
tetA,
tetB in
E. coli isolates. The
blaTEM gene imparts resistance against various β-lactam antibiotic like penicillin and ampicillin,
Sul2 gene imparts resistance against sulfamethoxazole antibiotics,
strA against streptomycin,
tetA and
tetB for tetracycline,
aadA gene encodes for aminoglycosides adenyl transferase enzyme which imparts resistance to amino glycosides antibiotics such as streptomycin.
In the present study the
blaTEM gene was detected in fifty six out of seventy (80%) camel isolates (Fig 4), for
sul2 gene eighteen out of seventy (25.71%)
E. coli isolates (Fig 5)
, Sul3 gene was obtained as twenty two out of seventy (31.42%) isolates, twenty nine out of seventy (42.85%) camel isolates for
strA gene (Fig 6), twenty eight of seventy (40%) isolates carried the
aadA gene (Fig 7) and twenty two out of seventy (31.42%) were found positive for
tetB gene (Fig 8).
tetA
, tetC
, tetD
, tetE
, gene was not found in any isolate (Table 3).
Bhave
et al. (2019) observed
blaTEM (20%),
blaCTX-M (40%) and
blaOXA (6.66%) in
E. coli isolates respectively. Abd El Tawab
et al. (2016) detected
blaTEM gene in the genomic DNA (100%) in all isolates and 56.25% in plasmid DNA. While
blaSHV gene was detected in the genomic DNA of (37.50%) and in plasmid DNA (28.12%) isolates.
Carvalho et al., (2020) and
Nuesch-Inderbinen et al., (2020) isolated
blaCTX-M-1 producing
E. coli from camel.
Saidani et al., (2019) reported
blaTEM gene in 18% isolates and the occurrence of CTX-M-15- and CTX-M-1-producing Enterobacteriaceae in camel.
Resistance to sulfonamides was due to the horizontal spread of resistance genes, expressing drug-insensitive variants of the target enzymes dihydropteroate synthase and dihydrofolate reductase, for sulfonamide and trimethoprim, respectively.In present study, a low resistance was observed in camel isolates for
sul2 and
sul3 gene. Ngbede
et al. (2021) detected
Sul2 and
Sul3 in 71.42% in camel
E. coli isolates from Nigeria. Ben Sallem
et al. (2012) isolated
Escherichia coli with 100% prevalence of
sul2 gene from healthy food-producing animals in Tunisia. Rawat
et al. (2022) observed sulfonamide resistance gene
sul3 (44%),
sul2 (28%) among the poultry isolates from North India. 36.9%;
sul1 (1 isolate),
sul2 (4 isolates).
Lanz
et al. (2003) highest tetracycline resistance phenotypes observed in the
E. coli isolates were linked to the presence of the
tetA gene (63.2%) and considered to be the gene commonly identified followed by
tetB (34.5%) in the
E. coli isolates. They are among the widest spread
tet genes found in Enterobacteriaceae and their occurrence was within the range reported by other investigators.