Prevalence and characterization of beta-lactamase-producing Escherichia coli isolates from a tertiary care hospital in India

Introduction

Escherichia coli is one of the most common pathogens among the family Enterobacteriaceae causing various infections worldwide. The increasing spread of resistance to extended generation cephalosporin group of drugs is on the rise in both community and hospital settings. Resistance to cephalosporins is due to the production of extended-spectrum beta-lactamases (ESBLs). However, Amp-C-β lactamase (Amp C) cephalosporinases may also be attributed by the acquisition of a plasmid-mediated Amp C enzyme or due to overexpression of the chromosomally encoded Amp C enzyme in E. coli.[1] Plasmid-mediated Amp C genes are derived from the chromosomal Amp C genes of several members of the family Enterobacteriaceae, including Enterobacter cloacae, Citrobacter freundii, Morganella morganii, and Hafnia alvei. The Amp C is a major clinical concern because these organisms overexpressing it are usually resistant to all the β-lactam drugs, except for cefpirome, cefepime, and the carbapenems.[2] There is also an increasing occurrence of carbapenem resistance in E. coli due to the production of a diverse group of carbapenemases. These enzymes are capable of hydrolyzing almost all β-lactams, including carbapenems. The genes encoding carbapenemases are usually encoded on mobile genetic elements like the plasmids.[3]

The β-lactamase-producing Enterobacteriaceae are mostly cross-resistant to other commonly used class of antibiotics such as aminoglycosides, trimethoprim-sulfamethoxazole, and fluoroquinolones, thus resulting in very few therapeutic options in a clinical setting. These multidrug-resistant organisms have higher mortality rates and medical costs than those due to non-β-lactamase-producing Enterobacteriaceae. Thus, the surveillance of these β-lactamase-producing Enterobacteriaceae is important for clinical care.[4] In the present study, an attempt was made to estimate the prevalence of ESBL, Amp C, and carbapenemases produced by E. coli.

Materials and Methods

Results

In our study, the clinical isolates were obtained from the following samples which included blood 26/196 (13.2%), sterile body fluids 40/196 (20.4%), endotracheal aspirate 19/193 (9.6%), pus 66/196 (33.6%), and urine 45/196 (22.9%). The distribution of E. coli strains according to the type of specimen is shown in Figure 1. The E. coli strains included in our study revealed high resistance rates against other antibiotics such as cefepime (89%), CTX (95.4%), CZD (85.4%), ceftriaxone (91.8%), cefpodoxime (92.7%), aztreonam (56.3%), piperacillin /tazobactam (89.2%), ticarcillin/clavulanic acid (76.3%), meropenem (63.2%), and doripenem (61.1%) as depicted in Figure 2.

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Figure 1

Distribution of Escherichia coli isolates according to the type of specimen

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Figure 2

Antibiotic resistance pattern of Escherichia coli isolates

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Discussion

Emergence of ESBLs, Amp C, and carbapenemase -producing Enterobacteriaceae presents a significant diagnostic and therapeutic challenge in the management of infections. The risk factors leading to infections with such multidrug-resistant organisms include increased length of hospital stay, prolonged stay in the intensive care units, arterial or urinary catheterization, and exposure to various broad-spectrum antibiotics. The detection of these resistant isolates on a daily basis in a clinical laboratory is quite challenging.[13]

The prevalence of ESBL in our study was estimated to be 88.3%. The prevalence of ESBLs reported from various other studies from India ranges from 60% to 80%.[1415] Combined disk diffusion test was more sensitive than the E-test combination test used for the detection of ESBL. The above finding was consistent with other studies.[1314] According to CLSI for Enterobacteriaceae, MIC ≥2 μg/ml against cefpodoxime, CZD, aztreonam, CTX, and ceftriaxone is regarded as a possible ESBL producer. In our study, the MIC of isolates resistant to third-generation cephalosporin was in the range of 2–64 μg/ml against the CZD. About 68.3% of the isolates had an MIC of 64 μg/ml, and these were clinical isolates from pyogenic infections.

Although there are no CLSI guidelines for the detection of Amp C production, reduced cefoxitin susceptibility was taken as an indicator of Amp C production.[16] In our study, the Amp C production among E. coli was 42.2% which was concordant with other studies from India.[1718] We observed coexistence of ESBL and Amp C in 19.6% of the E. coli isolates which was consistent with previous reports.[19] In our study, the ESBL and Amp-C producers were highly resistant to other antibiotics such as aztreonam (56.3%), piperacillin/tazobactam (89.2%), ticarcillin/clavulanic acid (76.3%), meropenem (63.2%), and doripenem (61.1%).

Among the various tests performed for the detection of MBLs, CDT performed with meropenem and EDTA showed the highest sensitivity 58.8% (95% confidence interval [CI] - 48.2%–68.6%) but low specificity rate 66.6% (95% CI - 35.4%–87.9%), whereas CDT performed with imipenem and EDTA exhibited a better specificity 77.7% (45.2%–93.6%), and among the DDST, CZD with 2MPA showed the highest sensitivity 87.2% (95% CI - 79%–92.5%) but low specificity of 33.3% (95% CI - 12%–64.5%). Previously published studies had found that the above methods to be a better predictor of MBL production with high sensitivity and specificity rates;[2021] however, in our study, we have found that the above methods were not a true predictor of MBL production because of lower sensitivity and specificity rates. In case of boronic acid disk test for the detection of KPCs, meropenem was found to be the most sensitive substrate, which was similar to previously published studies.[1122]

The prevalence of carbapenemase-producing E. coli in our hospital setting was found to be as high as 65%. This was similar to the prevalence rates obtained in similar studies from other parts of India.[2324] Phenotypic tests showing reduced carbapenem susceptibility are used for the identification of carbapenemase-producing organisms. The carbapenems have varied MICs for different carbapenemase producers. In our study, ertapenem was found to be an ideal candidate for screening the carbapenemase producers. This is consistent with other previously published studies.[925] Ertapenem has also been proposed to be the most suitable carbapenem for the identification of KPC producers which harbors low-level resistance to carbapenems.[26] Most of the carbapenem-resistant E. coli isolates were also resistant to other antimicrobial agents that were routinely used in the laboratory as observed in other studies.[2728] Our study also revealed high resistance rates against other antibiotics such as cefepime (89%), CTX (95.4%), CZD (85.4%), ceftriaxone (91.8%), cefpodoxime (92.7%), aztreonam (56.3%), piperacillin/tazobactam (89.2%), and ticarcillin/clavulanic acid (76.3%). The occurrence of coresistance to other antibiotic class of drugs may be due to plasmids or insertion sequences which transmits these resistance determinants seen in CRE isolates.[27] In our study, the most common genes encoding ESBL, Amp C, and carbapenemase genes in E. coli was bla_TEM, 67.3% bla_FOX (21.9%) and bla_NDM-1 (61.7%). The above finding was coherent to other studies from India.[29]

Conclusion

The present study highlights the high burden of ESBL, Amp C, and carbapenemase-producing multidrug-resistant E. coli isolates from a tertiary care center in India. This situation is alarming as these multidrug-resistant organisms are refractory to the commonly used antibiotics in clinical setting. A strong antimicrobial stewardship program is the need of the hour along with emphasis on strict hospital infection control practices to prevent the dissemination of these multidrug-resistant organisms.