Sodium chloride-esculin hydrolysis test for rapid identification of enterococci

Study of vancomycin and high-level aminoglycoside-resistant Enterococcus species and evaluation of a rapid spot test for enterococci from Central Referral Hospital, Sikkim, India

BACKGROUND:

Enterococcus is an important pathogen, and with its emergence of resistance to multiple antimicrobials, the management of infection is becoming increasingly difficult.

AIM:

The aim of the study is to determine the prevalence, antibiotic resistance, and risk factors associated with enterococcal infection or colonization.

MATERIALS AND METHODS:

In this prospective study, samples from inpatients were screened for resistant enterococci. Antibiotic susceptibility testing was performed using the disc diffusion method and minimum inhibitory concentration by the agar dilution method. A modification of a test tube method of sodium chloride-esculin hydrolysis to a spot test was evaluated for its rapidity and reliability in the presumptive diagnosis of enterococci.

STATISTICAL ANALYSIS USED:

Fisher's exact test was used for continuous (Student's t-test) and categorical variables. Multivariate analysis was performed with logistic regression using IBM SPSS 20.0 software (Armonk, NY, USA).

RESULTS:

Enterococcus species were isolated from 182 samples: Enterococcus faecalis (68.7%), Enterococcus faecium (20.9%), Enterococcus gallinarum (6%), and Enterococcus durans (4.4%). Maximum resistance was to ciprofloxacin (59.3%) and least to linezolid (0.5%). The isolation rate of vancomycin-resistant enterococci (VRE) was 13.7%; 30.2% and 20.9% were of high-level gentamicin and streptomycin, respectively. All 182 Enterococcus species gave positive results within 30–60 min by the rapid spot test.

CONCLUSIONS:

Overall, high-level aminoglycoside resistance (HLAR) was observed more than glycopeptide resistance. Surveillance strategies need to be upgraded and implemented in order to prevent the emergence and further spread of not only VRE but also HLAR enterococci in the hospital. The spot test gave reliable and rapid results in presumptive identification of enterococci.

Role of house flies in the ecology of Enterococcus faecalis from wastewater treatment facilities

Enterococci are important nosocomial pathogens, with Enterococcus faecalis most commonly responsible for human infections. In this study, we used several measures to test the hypothesis that house flies, Musca domestica (L.), acquire and disseminate antibiotic-resistant and potentially virulent E. faecalis from wastewater treatment facilities (WWTF) to the surrounding urban environment. House flies and sludge from four WWTF (1-4) as well as house flies from three urban sites close to WWTF-1 were collected and cultured for enterococci. Enterococci were identified, quantified, screened for antibiotic resistance and virulence traits, and assessed for clonality. Of the 11 antibiotics tested, E. faecalis was most commonly resistant to tetracycline, doxycycline, streptomycin, gentamicin, and erythromycin, and these traits were intra-species horizontally transferrable by in vitro conjugation. Profiles of E. faecalis (prevalence, antibiotic resistance, and virulence traits) from each of WWTF sludge and associated house flies were similar, indicating that flies successfully acquired these bacteria from this substrate. The greatest number of E. faecalis with antibiotic resistance and virulence factors (i.e., gelatinase, cytolysin, enterococcus surface protein, and aggregation substance) originated from WWTF-1 that processed meat waste from a nearby commercial meat-processing plant, suggesting an agricultural rather than human clinical source of these isolates. E. faecalis from house flies collected from three sites 0.7-1.5 km away from WWTF-1 were also similar in their antibiotic resistance profiles; however, antibiotic resistance was significantly less frequent. Clonal diversity assessment using pulsed-field gel electrophoresis revealed the same clones of E. faecalis from sludge and house flies from WWTF-1 but not from the three urban sites close to WWTF-1. This study demonstrates that house flies acquire antibiotic-resistant enterococci from WWTF and potentially disseminate them to the surrounding environment.

Liquid medium for rapid presumptive identification of group B streptococci

A suitable test was developed for distinguishing group B streptococci from other beta-hemolytic streptococci during growth in liquid medium. One hundred and sixty of 161 human group B strains tested yielded positive reactions within a 5 h incubation. The dye medium tested is a reliable substitute for more expensive serological procedures.

The life and times of the Enterococcus

Enterococci are important human pathogens that are increasingly resistant to antimicrobial agents. These organisms were previously considered part of the genus Streptococcus but have recently been reclassified into their own genus, called Enterococcus. To date, 12 species pathogenic for humans have been described, including the most common human isolates, Enterococcus faecalis and E. faecium. Enterococci cause between 5 and 15% of cases of endocarditis, which is best treated by the combination of a cell wall-active agent (such as penicillin or vancomycin, neither of which alone is usually bactericidal) and an aminoglycoside to which the organism is not highly resistant; this characteristically results in a synergistic bactericidal effect. High-level resistance (MIC, greater than or equal to 2,000 micrograms/ml) to the aminoglycoside eliminates the expected bactericidal effect, and such resistance has now been described for all aminoglycosides. Enterococci can also cause urinary tract infections; intraabdominal, pelvic, and wound infections; superinfections (particularly in patients receiving expanded-spectrum cephalosporins); and bacteremias (often together with other organisms). They are now the third most common organism seen in nosocomial infections. For most of these infections, single-drug therapy, most often with penicillin, ampicillin, or vancomycin, is adequate. Enterococci have a large number of both inherent and acquired resistance traits, including resistance to cephalosporins, clindamycin, tetracycline, and penicillinase-resistant penicillins such as oxacillin, among others. The most recent resistance traits reported are penicillinase resistance (apparently acquired from staphylococci) and vancomycin resistance, both of which can be transferred to other enterococci. It appears likely that we will soon be faced with increasing numbers of enterococci for which there is no adequate therapy.