Abstract
Background
With more people being exposed to antibiotics, intestinal microflora faces constant pressure of antibiotic selection, which has resulted in the emergence of multidrug resistant strains. This may pose a severe problem as intestinal Enterobacteriaceae members are commonly implicated in human infections.
Aims
This surveillance study was undertaken to investigate the carriage of carbapenem-resistant Enterobacteriaceae (CRE) in the gastrointestinal tract among patients attending the outpatient clinic in a tertiary care center of East Delhi, India.
Method
We performed a prospective surveillance study to screen 242 Enterobacteriaceae isolates for carbapenemase production from the stool samples of 123 outpatients attending a tertiary care hospital in East Delhi over a four-month period.
Results
Twenty-four (9.9 per cent) isolates demonstrated carbapenemase activity among 242 screened Enterobacteriaceae isolates. Four stool samples had two isolates of different species, both eliciting this feature and therefore indicating presence of multiple carbapenem-resistant Enterobacteriaceae (CRE) isolates in a single sample.
Conclusion
Screening for carriage of CRE in stools of patients undergoing elective or emergency gastrointestinal surgical procedures, with haematological malignancies taking chemotherapy, or those planned for bone marrow transplantation can guide clinicians about gut colonisation of multidrug-resistant Enterobacteriaceae as these groups of patients are at risk of possible endogenous infection.
Keywords: Carbapenem resistant Enterobacteriaceae, gut colonisation, prophylactic antibiotic
What this study adds:
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What is known about this subject?
To our knowledge, this is the first Indian study investigating the prevalence of CRE in stool samples from an urban area.
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What is the key finding of this report?
This type of surveillance study can guide clinicians and clinical microbiologists about colonisation of such multidrug-resistant strains in the human gastrointestinal tract, a major reservoir of Enterobacteriaceae isolates that can act as source of infection, particularly in immune-compromised patients.
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What are the implications for policy, research, and practice?
Active surveillance is a key part in preventing the spread of drug-resistant strains as gastrointestinal carriers may serve as the reservoir for cross-transmission in the healthcare setting as well as the community.
Background
The human gastrointestinal tract is a reservoir of pathogens causing infections such as urinary tract infections (UTI), skin soft tissue infections (SSI), and nosocomial infections.1 Bacterial translocation is the invasion of indigenous intestinal bacteria through the gut mucosa to normally sterile tissues and the internal organs. Bacterial translocation occurs more frequently in patients with intestinal obstruction and in immunocompromised patients and is the cause of subsequent sepsis. Factors that can trigger bacterial translocation from the gut are host immune deficiencies and immunosuppression, disturbances in the normal ecological balance of gut, mucosal barrier permeability, obstructive jaundice, or stress.2 With an increase in the number of people being exposed to antibiotics, the intestinal microflora faces constant pressure of antibiotic selection, which has resulted in the emergence of multidrug-resistant strains including carbapenem-resistant strains. This may pose a severe problem as intestinal Enterobacteriaceae are most commonly implicated in human infections and antibiotic options in infections caused by carbapenem-resistant Enterobacteriaceae (CRE) may be limited to colistin, tigecycline, and polymyxin B. Routine laboratory culturing of stool samples for diagnosing common clinical pathogens may often overlook commensal Enterobacteriaceae that can harbour resistant phenotypes. Antibiotic overuse and improper sanitation and hygiene in urban slum areas can lead to the rapid spread and large scale carriage of multi- or pan-drug-resistant isolates in the intestinal microbiota that can be a potential cause of endogenous and exogenous infections.3 The US Centers for Disease Control and Prevention (CDC) has issued guidelines for hospital surveillance of CRE;4 however, there are no surveillance studies on screening of CRE in stool isolates in an Indian cohort of patients. With this in mind we performed a prospective surveillance study for four months to evaluate the carriage of CRE from Enterobacteriaceae isolates from stool samples of patients attending the outpatient clinics in a tertiary care centre of East Delhi. This was undertaken to look for carriage of CRE isolates over one time period, irrespective of the patient symptoms or any history of present/previous antibiotic treatment.
Method
This surveillance study was conducted on stool samples from 123 patients attending the outpatient departments of a tertiary care hospital of East Delhi that caters for populations belonging to the urban slum areas and resettlement colonies of East Delhi and Western Uttar Pradesh. The samples were received in the Hospital Laboratory Services (HLS) for four months in 2011 for routine examination. These samples were cultured on MacConkey’s medium (HiMedia, India). Multiple isolates of family Enterobacteriaceae were purified from a single sample and subsequently one to three different Enterobacteriaceae isolates per sample were tested for carbapenemase activity by the conventional Modified Hodge Test (MHT) as per CLSI guidelines.6 A Re-modification of the MHT (RMHT) was performed to increase its sensitivity and demonstrate zinc dependency.7
Results
Among the 123 stool samples cultured, 242 Enterobacteriaceae isolates were identified using conventional methods,8 purified, and screened by the MHT and the RMHT. MHT and RMHT were read as negative, slight indentation, definite indentation, and strong indentation of the ATCC 25922 E. coli control strain in the background. Interpretation of this reading was classified as negative, indeterminate, and positive as per CLSI guidelines.6 Among the 242 isolates, 208 were negative by either of the tests. To rule out the subjective nature of the test, 10 isolates with slight indentation (Table 1) were interpreted as indeterminate. The remaining 24 isolates interpreted as positive were further identified and subjected to antimicrobial susceptibility testing by the Microscan WalkAwayR Plus (Siemens, Mumbai, India) automated system. All the 24 isolates showed MIC ≥ 4μg/ml for imipenem and meropenem. Four samples had at least two isolates, both being different species, which were positive for both MHT and the RMHT indicating presence of multiple CRE isolates in a single sample. Among the 24 isolates, 16 demonstrated zinc dependency on the RMHT indicating presence of metallo beta-lactamases. The Microscan WalkAwayR Plus indicated presence of ESBL (Extended Spectrum Beta-Lactamase) in all 24 CRE isolates on the basis of difference in the MIC’s of Cefotaxime/Cefotaxime + Clavulanate and Ceftazidime/Ceftazidime + Clavulanate.
Table 1. Isolates with slight indentation.
| Serial No | Reading of | No of isolates | Organism | Interpretation | |
|---|---|---|---|---|---|
| MHT | RMHT | ||||
| 1 | Negative | Negative | 208 | 102 EC, 80 KP, 24 CF, 1 CK, 1EA | Negative |
| 2 | Negative | Slight indentation(+) | 4 | 1EC,3KP | Indeterminate |
| 3 | Slight indentation(+) | Slight indentation(+) | 6 | 3EC,3KP | Indeterminate |
| 4 | Negative | Definite indentation(++) | 3 | 3EC | Positive |
| 5 | Slight indentation(+) | Definite indentation(++) | 11 | 6EC, 2KP, 2CF, 1EA | Positive |
| 6 | Definite indentation(++) | Definite indentation(++) | 8 | 3EC, 2KP, 3CF | Positive |
| 7 | Definite indentation(++) | Strong indentation(+++) | 2 | 2EC | Positive |
| Total positive | 24 | ||||
EC: Escherichia coli, KP:Klebsiella pneumoniae, CF: Citobacter freundii, CK: Citrobacter koseri , EA: Enterobacter aerogenes
Discussion
The emergence and spread of carbapenem-resistant Enterobacteriaceae (CRE) producing acquired carbapenemases have created a global public health crisis.9
Knowledge about the prevalence of CRE and other drug-resistant organisms in the intestine can help in formulating antibiotic policy in management of sepsis as a complication of extensive gut surgery or patients with haematological malignancy under chemotherapy or bone marrow transplantation. Das et al. mention that neonates with Gram negative bacilli in the gut had a higher incidence of clinical sepsis than those without.10 In 50 per cent of cases, the genotypes of the organisms found in the blood were indistinguishable from their gut counterpart.
Our study had a number of limitations, including short duration and, due to lack of funding, source molecular typing of the isolates could not be performed. However, phenotypic methods were employed for the detection of CRE and, by a phenotypic confirmation method, it was found that 9.9 per cent Enterobacteriaceae isolates were CRE.
The drug-resistant organisms we have identified may remain for months in the gut of the carrier without causing any symptoms or translocate through the gut epithelium, induce healthcare-associated infections, undergo cross-transmission to other individuals, and cause limited outbreaks.11 Active surveillance of drug-resistant strains, including extended-spectrum beta-lactamase-producing Enterobacteriaceae and carbapenem-resistant Enterobacteriaceae is an important component of any infection control program, and more surveillance studies need to be performed in India to provide a better understanding of the prevalence of drug-resistant strains as gut colonisers. Screening of drug-resistant Enterobacteriaceae can help in formulating antibiotic policy for a hospital, particularly for oncology and critically ill patients in ICUs, as these organisms can act as sources of endogenous infections.
Conclusion
Screening for carriage of CREs in stool in patients undergoing elective or emergency gastrointestinal surgical procedures, in patients with haematological malignancies taking chemotherapy, or patients with planned bone marrow transplantation can guide treating clinicians about gut colonisation of multi-drug resistant Enterobacteriaceae as these groups of patients are at risk of possible endogenous infection. This can also help in starting appropriate prophylactic antibiotics if required. Treating clinicians as well as microbiologists must be aware of the prevalence of CRE isolates in the human intestinal tract as these types of drug-resistant strains are potential sources of endogenous infections.
ACKNOWLEDGEMENTS
We would like to thank Hospital Laboratory Services of our hospital for providing us with the stool samples received for routine examination.
Footnotes
PEER REVIEW
Not commissioned. Externally peer reviewed.
CONFLICTS OF INTEREST
The authors declare that they have no competing interests.
Please cite this paper as: Rai S, Das D, Niranjan DK, Singh NP, Kaur IR. Carriage prevalence of carbapenem-resistant Enterobacteriaceae in stool samples: A surveillance study. AMJ 2014, 7, 2, 64-67.http//dx.doi.org/10.4066/AMJ.2014.1926
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