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Vancomycin Resistance among Enterococci: Further Limiting Our Therapeutic Options

Introduction: Enterococci are indigenous flora of the intestinal tract, oral cavity & genitourinary tract of human. Over recent years, there is increased interest in Enterococci not only because of their serious infections but because of their increasing resistance to many antimicrobials. Vancomycin being the only alternative available. But over the time, there has been increase in Vancomycin Resistance which has spread globally. The aim of this study was to determine the prevalence of Vancomycin Resistant Enterococci (VRE) isolated from various clinical specimens in a tertiary care hospital in North India. Material and methods: A cross-sectional study was conducted in the Department of Microbiology, Government Medical College, Amritsar from July 1st, 2018 to June 30th, 2019. All the samples received were processed and identification of Enterococci was made by using standard microbiological techniques. Antimicrobial susceptibility was performed by Kirby Bauer disc diffusion method as per CLSI guidelines. Results: Out of total clinical samples (11,098), 3,551 (31.9%) were found to be culture positive. Among the culture positive, 91 (2.56%) isolates were identified as Enterococcus species comprising of 37 E.faecalis (41%) and 54 E.faecium (59%). Maximum number of Enterococci were isolated from urine samples (54.92%) followed by pus & body fluids (38.02%) and blood (7.04%). 9.52% of E.faecium isolates were found to be resistant to vancomycin. All the strains were 100% susceptible to Linezolid, Teicoplanin & Quinupristin-dalfopristin. Conclusion: Enterococci have become the major pathogenic bacteria that cause hospital-acquired infections due to multiple-antimicrobial resistance. VRE has emerged as important nosocomial pathogen and pose serious threat to patients. Vancomycin should be cautiously used else we would be left with very few therapeutic options.


INTRODUCTION
Enterococci are indigenous flora of the intestinal tract, oral cavity & genitourinary tract of human. 1 The genus Enterococcus consists of Gram positive cocci, catalase negative, non spore forming, facultative anaerobes that often occur in pairs or short chains. This genus comprises of Enterococcus faecalis, E.faecium, E.durans, E.gallinarum, E.avium, E.italicus, etc. E.faecalis is the most common species found in clinical specimens whereas E.faecium is notorious for being drug resistant. 2 Over recent years, there is increased interest in Enterococci not only because of their serious infections but because of their increasing resistance to many antimicrobials.
Enterococci are multidrug resistant bacteria, which are resistant to penicillins, low level aminoglycosides, sulfonamides, cephalosporins and cotrimoxazole. Combination of penicillin and gentamycin had been the mainstay of treatment till now but with emergence of high level aminoglycosides resistance (HLAR), Vancomycin is the only alternative available. Vancomycin is a glycopeptide which inhibits cell wall synthesis, but over the time, there has been increase in Vancomycin Resistance which has spread globally. Resistance to Vancomycin is because of alteration at the target site i.e. D-alanyl D-alanine side chain of peptidoglycan layer is replaced by D-alanyl D-serine or D-alanyl D-lactate. Most common risk factors associated with Vancomycin Resistant Enterococci (VRE) are patients suffering from chronic renal failure, cancer, organ transplant recipients, longer stay in hospital more so in ICU. 3 Study aimed to determine the prevalence of VRE isolated from various clinical specimens in a tertiary care hospital in North India.

MATERIAL AND METHODS
A cross-sectional study was conducted in the Department of Microbiology, Government Medical College, Amritsar for a period of one year (July 1 st , 2018 to June 30 th , 2019). All the samples (pus, urine, blood, body fluids, sputum, etc.) received from the indoor patients of all age groups admitted in Government Medical College & Hospital, Amritsar were included in the study. The samples were processed and cultured on Blood Agar and MacConkey's Agar and incubated for 24 hours aerobically at 37°C. Identification of Enterococci were made based on the colony characters, motility, gram staining and by using standard microbiological techniques. 4 Antimicrobial susceptibility was performed by Kirby Bauer disc diffusion method as per CLSI guidelines. 5 Various antibiotics included were:-penicillin (10µg), ampicillin (10µg), ciprofloxacin (5µg), tetracycline (30µg), erythromycin (15µg), vancomycin (30µg), high level gentamycin (120µg), high level streptomycin (300µg). Enterococcus isolates with vancomycin zone size ≤14mm were further tested with linezolid (30µg), teicoplanin (30µg) and quinupristin-dalfopristin (15µg). Minimum Inhibitory Concentration (MIC) to vancomycin of these isolates was also assessed as per CLSI guidelines. 5

DISCUSSION
In the past two decades, Enterococcus was introduced as the third leading cause of hospital-acquired infections after Escherichia coli and Staphylococcus. 6 Recently, Enterococcus is the second leading cause of urinary tract infections and the third leading cause of bacteremia worldwide. 7 The prevalence of Enterococcal isolates in the present study was 2.56%, in comparison to 3.53% from a study conducted in Rajasthan, 2016 8  The increasing resistance of Enterococci to many antimicrobial agents like β lactam antibiotics, aminoglycosides and most importantly glycopeptides like vancomycin have made it a important nosocomial pathogen. 17 Vancomycin has long been considered for treatment of Enterococcus infections but now, its resistance has been increasingly reported from all parts of the world. Thus, for vancomycin-resistant E. faecium, we are left behind with few therapeutic options like Linezolid, an oxazolidinone antimicrobial and Quinupristin-dalfopristin. 18 The high prevalence of multidrug resistant Enterococcal infection in a tertiary care set up is due to excessive and indiscriminate use of broad spectrum antibiotics and high rate of patient transfer from peripheral centres. The emergence of VRE has been attributed to the inprudent use of vancomycin, colonization pressure and noncompliance with the infection control measures. 8 For long time, Enterococci were frequently considered as normal flora. Recently, due to its role in causing variety of infections in hospitalized patients and increasing resistance to different antibiotics has generated interest among researchers to understand the pathogenicity of Enterococcus. 8

CONCLUSION
Increased prevalence of MDR Enterococci in hospitalized patients has become a major cause of concern leaving few therapeutic options. To curb the menace of emerging VRE, antimicrobial stewardships, active screening of high risk patients is highly required. In conclusion, early detection of patients infected with VRE is essential component to prevent its nosocomial transmission.