Investigation of phenotypic resistance pattern of Enterococcus faecalis isolated from blood and urine samples of patients admitted to Rasoul Akram Hospital, Tehran

Nosocomial infections can be a major challenge for medical staff and health care providers when it comes to antibiotic-resistant bacteria. Enterococcus faecalis is one of the bacteria that play an important role in nosocomial infection. Therefore, it is important to study the prevalence and pattern of resistance of this bacterium in medical centers, especially in hospitals. Inappropriate use of antibiotics has led to the increasing spread of resistant bacteria. Enterococci are now considered not only for their role in nosocomial infections but also for their increasing reistance. The parts of the body that are most infected with this bacterium are the urinary tract and blood. Enterococcal infections are very common in patients with vascular and urinary catheters, and in patients who have been hospitalized for a long time and have taken broad-spectrum antibiotics.  The aim of this research was study of phenotypic resistance pattern of E. faecalis isolated from blood and urine samples of patients admitted to Rasoul Akram General Teaching Hospital.

This case series study was performed from February 2019 to January 2020 at Rasoul Akram Hospital in Tehran. The origin of the isolated E. faecalis was urine and blood which were isolated from patients with urinary tract infection and bloodstream infection from the hospital. The grown bacteria were evaluated by catalase test, then gram-positive catalase negative cocci were examined by L-pyrrolidonyl-beta-naphthylamide (PYR) hydrolysis (BY), bi-scolin, salt tolerance tests of 6.5%. Then biochemical tests were performed to detect E. faecalis, which included motion test, 0.04% tellurium reduction and pigment production test. E. faecalis isolates were isolated after biochemical tests. Antibiogram test was performed using disc diffusion method and E-test to measure the resistance of these isolates. Antibiogram test by disk diffusion method using discs (gentamicin 10 mg), (erythromycin 15 mg), (ampicillin sulbactam 10 + 10 mg), (ampicillin 10 mg), (penicillin 10 mg), (ticoplanin 30 mg), (Rifampin 50 mg), (30 mg linezolide) from HiMedia India. The bacterial suspension was prepared from fresh culture of E. faecalis with half McFarland turbidity and cultured on Müller-Hinton agar medium. Antibiotic discs were then placed on Müller-Hinton agar medium. Vancomycin E-Test: Some bacterial colonies were removed from fresh culture by ounce and dissolved in sterile physiological saline and concentrated to half McFarland concentration. After the bacterial suspension was completely absorbed into the medium, a strip containing the vancomycin concentration gradient was placed on Müllerhinton agar medium using a pair of sterile forceps and the culture medium was kept in a 37 ° C oven for 24 hours. By examining the plates, the number in front of the intersection of the non-growth halo with the E-Test strip was considered as a small amount of the minimum concentration of growth inhibitor.

From 53 isolated E. faecalis, 46 samples (86.8%) were isolated from the urine and 7 samples (13.2%) were isolated from the blood. The source of isolation of E. faecalis was blood and urine samples from nephrology, surgical ICU, neurosurgery, transplantation, inpatient emergency, MICU, general surgery, ICU, orthopedics, internal medicine and neurological ICU wards.  The most sensitive antibiotics for these isolates were Linezolid (52), 98.1%, Vancomycin (47), 88.7%, respectively and the most resistant antibiotics to these isolates were Gentamicin antibiotic (43), 81.1%, and rifampin (34), 64.2%.

Annual nosocomial infections kill many patients around the world. Excessive use of antibiotics in medicine and agriculture has led to the development of multidrug-resistant bacteria, which are now recognized as one of the leading causes of nosocomial infections. In addition to high patient mortality, imposing high economic costs on patients and hospitals and medical centers is another consequence of microbial resistance. Enterococci are one of the most important causes of nosocomial infections, especially in intensive care units. These bacteria can be easily transmitted from one patient to another in a hospital through medical staff. In patients, the most common sites of enterococcal infection are the urinary tract, blood, and ulcers.In a study conducted by Ghasemi et al., on multidrug resistance of E. faecalis in two hospitals of Kashan, no resistance to linezolid antibiotic was observed in these isolates. In another study conducted by Najafi et al., on enterococcal antibiotic resistance in Hamadan teaching hospitals, no resistance to linezolid antibiotics was observed. Loza et al., in Spain showed that 100% of isolated enterococcal isolates were sensitive to linezolid, vancomycin and ampicillin. In this study, the most sensitive antibiotic against E. faecalis isolates was Linezolid, which is consistent with the studies mentioned above. In a study by Al-Harthi et al., on the pattern of antibiotic resistance of E. faecalis from 2003 to 2006, resistance to gentamicin was 89.6%. In this study, E. faecalis isolates had the highest resistance (81.1%) to the antibiotic gentamicin, which could be a warning to the physicians in prescribing this drug. in a study by Ghasemi et al., in Kashsn resistance to penicillin antibiotic was29.2%.  In another study conducted by Yousefi et al., on antibiotic resistance of enterococci in Ghaem Hospital of Mashhad, resistance to penicillin antibiotic was 54.5% . In the present study, resistance to penicillin antibiotics in enterococci was 54.7%. In another study conducted by Hosseinizadeh et al,. on the pattern of enterococcal resistance in Arak teaching hospitals, resistance to vancomycin antibiotic by MIC method was 14.66% . In another study conducted in India in 2013 by Suddhanshu et al., out of a total of 150 samples collected from different wards of the hospital, only 5 isolates were E. faecalis resistant to vancomycin. A study conducted by Arbabi et al., in 2015 in Rasool Akram and Milad hospitals in Tehran, out of 149 isolated Enterococcus specimens, 60% of the specimens were E. faecalis isolates. The highest resistance (77.1%) based on disk diffusion test against gentamicin antibiotic and the lowest resistance (28%) based on MIC test against vancomycin antibiotic was observed. In this study, the resistance of E. faecalis to the antibiotic vancomycin, which was performed by Etest method, was reported to be 11.3%, which is less than the study of Nikoei et al., Hosseinizadeh et al., and Arbabi et al.

The resistance of E. faecalis to antibiotics is increasing. Therefore, periodic monitoring of the resistance pattern of this bacterium can help effectively treatment of patients and reduce treatment costs. E. faecalis and Enterococcus faecium are inherently resistant to certain antibiotics, including cephalosporins, aminoglycosides, clindamycin, and fusidic acid.