Incidence of carbapenem-resistant Escherichia coli ST2437 of clinical origin harbouring blaOXA-144 gene: a report from India.

AIMS: Carbapenem-resistant Escherichia coli has been categorized as a pathogen of critical priority by the World Health Organization as it is highly infectious with high mortality and morbidity rates and widespread transmission potential. Carbapenem resistance is primarily mediated by carbapenemase-encoding genes and, additionally, through intrinsic factors. In India, over the years, carbapenemase-encoding genes have been reported from diverse clinically significant pathogens. The present study identifies E. coli of clinical origin that harbours blaOXA-144. METHODS AND RESULTS: The study isolate was obtained from a tertiary referral hospital in northeast India. Carbapenemase production was investigated through culture on chromogenic agar and Rapidec Carba NP test as per manufacturer's instructions. Susceptibility of the isolate was performed by the Kirby-Bauer disc diffusion method and agar dilution method following CLSI guidelines. PCR targeting carbapenemase-encoding genes was performed, followed by transformation and conjugation experiments. Whole-genome sequencing of the isolate was done through the Illumina sequencing platform and the data were analysed using the Centre for Genomic Epidemiology database. BJD_EC180 is 6 919 180 bp in length and consists of six rRNA operons, 111 tRNA, and 6849 predicted protein-coding sequences. BJD_EC180 belonged to ST2437 and harboured the carbapenemase-encoding gene blaOXA-144 with ISAba1 upstream, along with multiple antibiotic resistance genes conferring clinical resistance towards beta-lactams, aminoglycosides, amphenicols, sulphonamides, tetracyclines, trimethoprim, and rifampin. CONCLUSIONS: Carbapenem-resistant E. coli harbouring blaOXA-144 associated with insertion sequence pose a serious health threat as their mobilization into carbapenem non-susceptible strains that will contribute to the resistance burden and therefore, needs urgent monitoring.

Concentration dependent exposure of vancomycin and teicoplanin induces vanG regulon in Staphylococcus aureus.

Therapeutic options for staphylococcus infections have been raised due to the emergence of VISA and VRSA. Six isolates of Staphylococcus aureus of clinical origin which were previously confirmed to carry vanG were selected for this study. Antimicrobial susceptibility was performed by disc diffusion method. Transcriptional expression of vanG and vanSG showed down regulation against vancomycin and teicoplanin but expression was increased with increasing concentration of antibiotics. vanUG, vanRG showed up regulation against glycopeptide exposure. The present study underscored that expression of vanG and its regulatory gene operons are dependent on concentration of vancomycin and teicoplanin exposure in S.aureus.

Molecular characterization of enteropathogenic Escherichia coli isolated from patients with gastroenteritis in a tertiary referral hospital of northeast India.

PURPOSE: Diarrhoeal illness accounts for a high morbidity and mortality both in paediatric as well as adult groups and diarrhoeagenic Escherichia coli occupies a top position as a causative agent of infectious diarrhoeal illness worldwide. The aim of the current investigation was to determine the virulence and pattern of antibiotic resistance of enteropathogenic, enterotoxigenic, and shiga toxigenic Escherichia coli that are linked to diarrhoea in patients of both adult and paediatric age groups. METHODS: A total of 50 consecutive, nonduplicate Escherichia coli isolates were collected from patients with gastro-enteritis who were admitted to different clinical wards Silchar Medical College and Hospital, Silchar, India. PCR was used to identify the virulence genes of EPEC (eaeA and bfpA), STEC (stx1, stx2, and eae) and ETEC (eltA, eltB, estA1 and estA2) in the isolates of E. coli. The antibiotic susceptibility pattern of virulent E. coli isolates were checked using disc diffusion method. Molecular typing of the virulent E. coli detected in the study based on enterobacterial repetitive intergenic consensus-polymerase chain reaction (ERIC-PCR) was also done. RESULT: Out of 50 E. coli isolates, 13 (26%) were found to carry atleast one virulence gene. 11 isolates harboured eae gene and were characterized as EPEC and two isolates carried stx1 gene of STEC. These virulent isolates showed different antibiotic susceptibility pattern and harboured single or multiple antibiotic resistance genes. ERIC PCR established 12 different clonal patterns of the virulent study isolates of E. coli harbouring. CONCLUSION: EPEC pathotypes were found to be the most detected pathotype in the stool samples. Majority of the virulent isolates were also resistant to multiple antibiotics which is a serious public health concern and therefore requires a proper surveillance and studies to track their reservoirs to contain their spread.

Evaluation of a novel chromogenic screening method for detection of carbapenem-resistant Escherichia coli.

Introduction. Early detection of carbapenem-resistant Escherichia coli (CREco), categorized as a critical priority pathogen by the World Health Organization (WHO), is crucial in optimizing therapeutic options and to thwart outbreaks in clinical settings.Gap statement. The need of the hour is a diagnostic method that can detect carbapenem resistance conferred by intrinsic or acquired carbapenem resistance mechanisms or both.Aim. The study investigates the performance of a novel screening chromogenic method for detection of CREco.Methodology. Carbapenem-susceptible (n=23) and non-susceptible (n=90) E. coli were used to investigate the efficiency of the blue chromogenic test. All of the isolates were received from a tertiary referral hospital in Silchar, India and subjected to the blue chromogenic test and observed for colour change. A colour change from colourless to blue is interpreted as a positive result. The test results were further compared with available methods for detection of carbapenem resistance conferred by carbapenemase production or other carbapenem resistance mechanisms.Results. The blue chromogenic test generated 100 % (CI: 95.98-100 %) sensitive and 100 % (CI: 85.75-100 %) specific results for the detection of CREco with no false-positive or false-negative results. Within 3 h after incubation, the test detects all CREco with carbapenemase activity. Additionally, the blue chromogenic test also positively detected E. coli harbouring carbapenemase variants and with efflux and porin activity, compared to other phenotypic-based approaches.Conclusion. The study highlights a novel method that is highly sensitive and specific, inexpensive, rapid and user-friendly for the detection of CREco. With the surge and expansion of CREco, this sensitive, specific, user-friendly and inexpensive method can be used in laboratories with limited facilities for early detection of CREco, thereby improving infection control along with averting future outbreaks.

Emergence of carbapenem-resistant enterobacterales co-harboring blaOXA-78 and blaOXA-58 from India.

BACKGROUND: Carbapenem-Resistant Enterobacterales (CRE) has been categorized as pathogens of critical priority by World Health organization (WHO) as they pose significant threat to global public health. Carbapenemase production considered as the principal resistance mechanism against carbapenems and with the recent surge and expansion of carbapenemases and its variants among clinically significant bacteria in India, the present study reports expansion blaOXA-78 and blaOXA-58 of in CRE of clinical origin. METHODS: Bacterial isolates were collected from a tertiary referral hospital and identified through VITEK® 2 Compact automated System (Biomerieux, France). Rapidec® Carba NP (Biomerieux, France) was used to investigate carbapenemase production followed by antibiotic susceptibility testing through Kirby-Bauer Disc Diffusion method and agar dilution method. Class D carbapenemase genes were targeted through PCR assay followed by investigation of horizontal transmission of blaOXA-58 and blaOXA-78. Whole genome sequencing was carried out using Illumina platform to investigate the genetic context of blaOXA-58 and blaOXA-78 genes and further characterization of the CRE isolates. RESULTS: The carbapenem-resistant Escherichia coli (BJD_EC456) and Serratia marcescens (BJD_SM81) received during the study from the tertiary referral hospital were isolated from sputum and blood samples respectively. PCR assay followed by whole genome sequencing revealed that the isolates co-harbor blaOXA-58 and blaOXA-78, a variant of blaOXA-51. Horizontal transfer of blaOXA-58 and blaOXA-78 genes were unsuccessful as these genes were located on the chromosome of the study isolates. Transposon Tn6080 was linked to blaOXA-78 in the upstream region while the insertion sequences ISAba26 and ISCfr1 were identified in the upstream and downstream region of blaOXA-58 gene respectively. In addition, both the isolates were co-harboring multiple antibiotic resistance genes conferring clinical resistance towards beta-lactams, aminoglycosides, fluroquinolones, sulphonamides, tetracyclines. BJD_EC180 belonged to ST2437 while BJD_SM81 was of an unknown sequence type. The nucleotide sequences of blaOXA-78 (OQ533021) and blaOXA-58 (OQ533022) have been deposited in GenBank. CONCLUSIONS: The study provides a local epidemiological information regarding carbapenem resistance aided by transposon and insertion sequences associated blaOXA-78 and blaOXA-58 genes associated and warrants continuous monitoring to prevent their further dissemination into carbapenem non-susceptible strains thereby contributing to carbapenem resistance burden which is currently a global concern.

Imipenem and meropenem influence the Las/Rhl quorum-sensing systems in clinical isolates of Pseudomonas aeruginosa.

The present study was conducted to study the influence of imipenem and meropenem at subinhibitory concentration on the transcriptional response of Las/Rhl quorum-sensing systems in isolates of Pseudomonas aeruginosa. In the present study, six representative carbapenem nonsusceptible clinical isolates of P. aeruginosa were obtained. The agar dilution method was used to determine the minimum inhibitory concentration against imipenem and meropenem. The bacterial isolates were then cultured up to the early log phase in fresh Luria Bertani (LB) broths at 37°C with and without 2 µg mL-1 imipenem and meropenem, respectively. mRNA was then isolated from the bacterial isolates and was immediately reverse-transcribed to cDNA. The relative quantity of the expression of the lasI, lasR, rhlI, and rhlR genes was assessed by quantitative real-time Polymerase Chain Reaction (PCR) using the ΔΔCt method. The transcriptional response of the lasI and lasR genes was upregulated at subinhibitory concentration of meropenem. In contrast, the transcriptional response of the lasI, lasR, and rhlR genes was downregulated at subinhibitory concentration of imipenem as compared to the expression in untreated isolates. The data obtained in the current study showcased the ability of imipenem and meropenem to influence the response of the quorum-sensing genes at subinhibitory concentration.

Transcriptional Response of vanB Operon in Staphylococcus aureus Against Vancomycin and Teicoplanin Stress.

Staphylococcus aureus is a global pathogen and is responsible for causing severe life-threatening infections. The current study was designed to investigate transcriptional expression of different core, regulatory, and accessory genes within vanB operon under differential exposure of vancomycin and teicoplanin. Four isolates selected for the study, were confirmed to harbour vanB gene in which three isolates showed MIC breakpoint above 16 µg/ml and one isolate above 8 µg/ml against vancomycin while teicoplanin showed higher MIC breakpoint as compared to vancomycin. Antibiotic susceptibility results showed that these isolates were susceptible towards imipenem and linezolid. Transcriptional expressional analysis of the core gene of vanB operon showed that expression of vanB is increased under vancomycin stress but is inversely proportional to increase in the concentration of the vancomycin while under teicoplanin stress the expression of vanB showed no significant pattern. Similar expressional pattern was found for vanH gene for both the glycopeptides. In case of vanX, expression was significantly increased at 1 µg/ml exposure of vancomycin, however, no pattern could be observed in case of teicoplanin stress. In case of regulatory gene, vanR, significant increase in expression was observed under vancomycin and teicoplanin stress of 1 µg/ml, however vanS, showed significant increase in the expression under 1 µg/ml of vancomycin. The accessory gene, vanY showed marginal increase in expression under both the antibiotic, while in case of vanW, the expressional pattern was found to be inversely proportional to the increasing antibiotic concentration.

Two non-active site residues W165 and L166 prominently influence the beta-lactam hydrolytic ability of OXA-23 beta-lactamase.

Dissemination of class D OXA-type carbapenemases is one of the significant causes of beta-lactam resistance in Gram-negative bacteria. The amino acid residues present near the active site are involved in hydrolytic mechanism of class D carbapenemases, though it is not identified in OXA-23. Here, with the help of site-directed mutagenesis, we aimed to explicate the importance of the residues W165, L166 and V167 of the possible omega loop and residue D222 in the short ß5-ß6 loop on the activity of OXA-23. All the residues were substituted with alanine. The resultant proteins were assayed for the changes in activity in E. coli cells and purified for in vitro activity, and stability assessment. E. coli cells harboring OXA-23_W165A and OXA-23_L166A, individually, exhibited a significant decrease in resistance towards beta-lactam antibiotics as compared to OXA-23. Further, purified OXA-23_W165A and OXA-23_L166A imparted about >4-fold decrease in catalytic efficiency and displayed reduced thermal stability as compared to OXA-23. Bocillin-FL binding assay revealed that W165A substitution results in improper N-carboxylation of K82, leading to deacylation deficient OXA-23. Therefore, we infer that the residue W165 maintains the integrity of N-carboxylated lysine (K82) of OXA-23 and the residue L166 might be responsible for properly orientating the antibiotic molecules.

Tn5406, a staphylococcal transposon associated with macrolide-lincosamide-streptograminb resistance in clinical isolates of Staphylococcus aureus.

PURPOSE: In this study, we aimed to investigate the occurrence of MLSb resistance in clinical isolates of Staphylococcus aureus with respect to their association with transposons. METHODS: The present study was performed with clinical isolates of S. aureus. The MLSb resistant phenotypes in the obtained isolates were determined by D zone test or double disc diffusion test as per CLSI 2020 guidelines. MLSb resistance encoding genes were detected by PCR. The genes tested were ermA, ermB, ermC, msrA, mphC, vga, vgb and lnuB. The MLSb resistant Staphylococcal isolates were selected to analyze the association of the genes with mobile genetic elements Tn554, Tn5406, Tn917, Tn6133, Tn551 by PCR based method. Primer pairs were designed using sequences from transposons and the resistance genes, respectively. RESULTS: During this study, 268 isolates of S. aureus were obtained of which 233 (86.94%) isolates exhibited different MLSb resistant phenotypes. The predominant gene among the MLSb resistant isolates was msrA followed by vgaA and mphC genes. PCR assay was employed to determine whether the genes msrA, mphC and vgaA were carried by Tn554, Tn5406, Tn917, Tn6133, Tn551 transposons. PCR amplification with the designed primer pairs revealed vgaA gene being part of Tn5406. CONCLUSION: The presence of Tn5406 in all the vgaA harboring isolates highlights its potential of spread across isolates. Moreover, the co-existence of different MLSb resistance encoding genes observed in the study shows that the combination of genes involved in different mechanism mediated the nature of MLSb resistance.

Small Molecule IITR00693 (2-Aminoperimidine) Synergizes Polymyxin B Activity against Staphylococcus aureus and Pseudomonas aeruginosa.

The rise of antibiotic resistance among skin-infecting pathogens poses an urgent threat to public health and has fueled the search for new therapies. Enhancing the potency of currently used antibiotics is an alternative for the treatment of infections caused by drug-resistant pathogens. In this study, we aimed to identify a small molecule that can potentiate currently used antibiotics. IITR00693 (2-aminoperimidine), a novel antibacterial small molecule, potentiates the antibacterial activity of polymyxin B against Staphylococcus aureus and Pseudomonas aeruginosa. Herein, we investigated in detail the mode of action of this interaction and the molecule's capability to combat soft-tissue infections caused by S. aureus and P. aeruginosa. A microdilution checkerboard assay was performed to determine the synergistic interaction between polymyxin B and IITR00693 in clinical isolates of S. aureus and P. aeruginosa. Time-kill kinetics, post-antibiotic effect, and resistance generation studies were performed to assess the pharmacodynamics of the combination. Assays based on different fluorescent probes were performed to decipher the mechanism of action of this combination. The in vivo efficacy of the IITR00693-polymyxin B combination was determined in a murine acute wound infection model. IITR00693 exhibited broad-spectrum antibacterial activity. IITR00693 potentiated polymyxin B and colistin against polymyxin-resistant S. aureus. IITR00693 prevented the generation of resistant mutants against multiple antibiotics. The IITR00693-polymyxin B combination decreased the S. aureus count by >3 log10 CFU in a murine acute wound infection model. IITR00693 is a potential and promising candidate for the treatment of soft-tissue infections along with polymyxins.

Escherichia coli harbouring strAB with reduced susceptibility towards gentamicin and amikacin: a single centre study from India.

In this study we report the presence of streptomycin resistance gene strAB within clinical isolates of Escherichia coli where streptomycin is not used to treat Gram-negative infections. In total, 135 E. coli isolates were obtained for the study. PCR based detection of strAB was performed in the study isolates followed by assessment of horizontal transferability. Cloning of strAB was done in laboratory strain E. coli DH5α. Pre-cloning and post-cloning susceptibility of the strain was done for assessment of acquired resistance. Among tested isolates, 89 were found to harbour strAB and it was encoded within a IncI1 type plasmid. Cloning experiments revealed the strAB gene showed unusual non-susceptibility towards amikacin and gentamicin. The study highlighted that strAB, which has a role in streptomycin resistance, may also have a role in reduced susceptibility towards gentamicin and amikacin within a clinical setting.

Elevated expression of rsmI can act as a reporter of aminoglycoside resistance in Escherichia coli using kanamycin as signal molecule.

We aimed to design and analyse expressional response of endogenous and exogenous 16S rRNA methyl transferase genes under sub inhibitory concentration stress of different clinically relevant aminoglycoside antibiotics in Escherichia coli to identify an endogenous marker. One hundred twenty nine aminoglycoside resistant E. coli of clinical origin were collected for detection of 16S rRNA methyl transferase genes by PCR assay and each gene type was cloned within E. coli JM107. Parent isolates were subjected to plasmid elimination by SDS treatment. Expression analysis of both acquired and endogenous 16S rRNA methyl transferase genes were performed by quantitative real-time PCR in clones and parent isolates under aminoglycoside stress (4 mg/L). Majority of the isolates were harbouring rmtC (35/129), followed by rmtB (32/129), rmtA (21/129), rmtE (13/129), armA (11/129) rmtF (9/129) and rmtH (8/129). Plasmid was successfully eliminated for all the isolates with 6% of SDS. Expression analysis indicates that kanamycin, tobramycin and netilmicin stress could increase the expression of 16S rRNA methyltransferese genes. In the presence of kanamycin stress the expression of rsmI was consistently elevated for all the wild type isolates and clones tested. Except for isolates harbouring rmtB and rmtC expression of rsmE and rsmF was increased in the presence of all aminoglycosides. For all the cured mutants it was apparently observed that expression of endogenous methyl transferases were marginally increased. Elevated expression of constitutive rsmI can be used as a potential biomarker for detection of acquired 16S rRNA methyl transferase mediated aminoglycoside resistance by using sub inhibitory concentration of kanamycin as signal molecule.

Colistin exposure enhances expression of eptB in colistin-resistant Escherichia coli co-harboring mcr-1.

Colistin resistance has increased due to the increasing and inappropriate use of this antibiotic. The mechanism involves modification of lipid A with phosphoethanolamine (PEtN) and/or 4-amino-4deoxy-L-arabinose (L-Ara4N). EptA and eptB catalyze the transfer of phosphoethanolamine to lipid A. In this study, gene network was constructed to find the associated genes related to colistin resistance, and further in vitro validation by transcriptional analysis was performed. In silico studies showed that eptB gene is a highly interconnected node in colistin resistance gene network. To ascertain these findings twelve colistin-resistant clinical isolates of Escherichia coli were selected in which five were harboring the plasmid-mediated mcr-1. Screening for colistin resistance was performed by broth microdilution (BMD) method and Rapid polymyxin NP test. PCR confirmed the presence of the eptA and eptB genes in all isolates and five isolates were harboring mcr-1. Transcriptional expression in five isolates harboring mcr-1, showed an enhanced expression of eptB when exposed under sub-inhibitory colistin stress. The present study for the first time highlighted genetic interplay between mcr-1 and eptA and eptB under colistin exposure.

Transcriptional analysis of prsA and vraTS regulatory system in methicillin resistant Staphylococcus aureus against oxacillin stress.

PURPOSE: The prsA and vraTSR regulatory systems play a unique role in methicillin resistance by modifying the peptidoglycan cell wall PBP2 and involving cell wall stress response in Staphylococcus aureus. This study was designed to observe the transcriptional response of prsA and vraTSR system under oxacillin stress in S.aureus. METHODS: In this study, three clinical isolates of Staphylococcus aureus and a laboratory strain were examined. All the isolates were tested for mecA gene by PCR assay and were also tested for prsA, vraT, vraS and vraR gene. The transcriptional responses of the prsA gene along with the vraTSR regulatory system in these isolates was observed under normal conditions and exposed to 2 â€‹µg/ml and 4 â€‹µg/ml of oxacillin stress by quantitative real-time PCR assay. RESULTS: The result of transcriptional analysis confirmed that under oxacillin stress, the expressions of vraS and vraT are increased with the increase in the concentration of oxacillin. However, prsA has shown no significant expression under oxacillin stress. CONCLUSION: Although prsA did not show any specific expressional pattern, the study highlights the role of vraS and vraT regulatory system in conferring a methicillin-resistant phenotype when exposed to subinhibitory concentrations of oxacillin, which could act as a potential target for the next-generation antimicrobials.

Molecular characterization of extended spectrum beta lactamases in clinical isolates of Escherichia coli and Klebsiella spp from a tertiary care hospital of South Eastern Assam.

Molecular characterization of ESBLs in clinical isolates of Escherichia coli and Klebsiella spp from a tertiary care hospital of South Eastern Assam was done by detection of blaTEM, blaSHV, blaCTX-M, blaOXA-2, blaOXA-10, blaPER, blaVEB and blaGES by Multiplex PCR. One hundred isolates yielded 44 bands of ESBL genes. CTX-M was most frequently isolated gene (36/44). Two isolates carried a combination of 2 genes CTX-M and OXA-2. Apart from CTX-M, the study isolates were also found to harbour TEM(n â€‹= â€‹3), OXA-2 (n â€‹= â€‹6) OXA-10 (n â€‹= â€‹1),GES(n â€‹= â€‹2) genes.

Antimicrobial resistance in patients with suspected urinary tract infections in primary care in Assam, India.

OBJECTIVES: We investigated the prevalence and diversity of antimicrobial resistance in bacteria isolated from urine samples of community-onset urinary tract infection (UTI) patients in southern Assam, India. METHODS: Freshly voided midstream urine samples were collected from patients attending primary healthcare centres, with the patients' epidemiological data also recorded. Species identification was confirmed using a VITEK 2 compact automated system. Phenotypic confirmation of ESBLs was performed using the combined disc diffusion method (CLSI 2017) and carbapenemase production was phenotypically characterized using a modified Hodge test. Common ESBLs and carbapenem-resistance mechanisms were determined in Escherichia coli isolates using PCR assays. Incompatibility typing of the conjugable plasmids was determined by PCR-based replicon typing; the phylotypes and MLSTs were also analysed. RESULTS: A total of 301 (59.7%) samples showed significant bacteriuria along with symptoms of UTI and among them 103 isolates were identified as E. coli of multiple STs (ST3268, ST3430, ST4671 and others). Among them, 26.2% (27/103) were phenotypically ESBL producers whereas 12.6% (13/103) were carbapenemase producers. This study describes the occurrence of diverse ESBL genes-bla CTX-M-15, bla SHV-148, bla PER-1 and bla TEM-and two E. coli isolates carrying the bla NDM-1 carbapenemase gene. ESBL genes were located within transconjugable plasmids of IncP and IncF type whereas bla NDM-1 was carried in an IncFrepB type plasmid. CONCLUSIONS: This study illustrates the high rate of MDR in E. coli causing UTI in primary care in rural Assam. UTIs caused by ESBL- or MBL-producing bacteria are very difficult to treat and can often lead to treatment failure. Thus, future research should focus on rapid diagnostics to enable targeted treatment options and reduce the treatment failure likely to occur with commonly prescribed antibiotics, which will help to combat antimicrobial resistance and the burden of UTIs.

Subinhibitory concentration stress of colistin enhanced PhoPQ expression in Escherichia coli harboring mcr-1.

The increased and inappropriate use of colistin led to the emergence of its resistance among Gram-negative bacterial isolates and the most common mechanism of colistin resistance in Gram-negative bacteria is the modification of the lipopolysaccharide mediated by two-component regulatory systems, PhoPQ and PmrAB. The aim of the present study was to investigate the transcriptional expression of the PhoPQ system against colistin stress in clinical isolates of Escherichia coli with colistin-resistant phenotype. Six colistin-resistant E. coli isolates were obtained from Silchar Medical College and Hospital, Silchar that were of clinical origin and received for routine culture and sensitivity testing. Screening for colistin resistance was done by broth microdilution method and further screened for the presence of the different types of plasmid-mediated colistin resistance mcr genes namely, mcr-1 to mcr-10 by polymerase chain reaction (PCR). The screened positive isolates were subjected to PCR assay targeting phoP and phoQ genes and their expression was measured by quantitative real-time PCR. The results of this study revealed that two E. coli isolates (TS2 and TS4) were found to carry the mcr-1 gene. PhoP and PhoQ gene amplification was observed in all the isolates. Transcriptional analysis showed that the isolates harboring the mcr-1 gene showed an enhanced level of expression in the PhoP, PhoQ genes in the presence of a subinhibitory concentration of colistin whereas no significant expression was observed for the isolates which were devoid of the mcr gene. This study demonstrates the involvement of mcr-1 in the PhoPQ system in clinical isolates of colistin-resistant E. coli which will help in designing a molecular marker for detecting colistin-resistant E. coli and contribute to the assessment of resistance burden and infection control strategy.