Emergence Of Enterococci Research Articles

Fecal Emergence of Vancomycin-Resistant Enterococci after Prophylactic Intravenous Vancomycin

Purpose: To determine the emergence of vancomycin-resistant enterococci (VRE) in stool after prophylactic intravenous treatment with vancomycin in patients undergoing surgery for congenital heart disease. Design: Prospective comparative study. Setting: Multidisciplinary and post-cardiac surgery pediatric intensive care units. Patients: Forty-one consecutive children aged 3 days to 18 years who underwent cardiac surgery and had not been treated with any antibiotics for 14 days prior to operation. All had positive stool cultures for enterococci. Eighteen children received only intravenous cefuroxime, 75 mg/kg/day for 2 days (control group), and 23 also received intravenous vancomycin, 30 mg/kg/day divided into 2 doses (study group). Intervention: Stool cultures for enterococci. Measurements and Results: Stool samples for bacterial culture were obtained before the antibiotic treatment, every day during the treatment, and 2 days after the drugs were discontinued. In cases of growth disappearance, cultures were taken until growth reappearance or discharge. In one of the 18 cefuroxime-treated children, fecal enterococcal growth disappeared one day after prophylactic treatment, and vancomycin-sensitive enterococci reappeared on the third day. In 5 of 23 vancomycin-prophylactic treated children, enterococcal growth disappeared after the second dose of vancomycin. The stool cultures then became positive for vancomycin-sensitive enterococci in 3 of the children and positive for vancomycin-resistant enterococci in one. In the fifth child, findings remained negative. Conclusions: Perioperative prophylactic treatment with intravenous vancomycin in children undergoing surgical treatment for congenital heart disease does not seem to significantly increase fecal VRE when given over a short period.

In vitro activity of LY333328 (oritavancin) against Gram-positive aerobic cocci and synergy with ciprofloxacin against enterococci.

Gram-positive cocci are a major cause of nosocomial bacteraemias and are often resistant to most antibiotics. The emergence of enterococci with reduced susceptibility to vancomycin has created an urgent need for novel antibiotics to combat infections associated with these bacteria. In this study the in vitro activity of LY333328 (oritavancin), a semi-synthetic glycopeptide, was evaluated. LY333328 was effective against all strains of staphylococci, streptococci and enterococci tested. A combination of LY333328 and ciprofloxacin was additive for 50% of Enterococcus faecium strains resistant to both vancomycin and ciprofloxacin, and for 100% of vancomycin-susceptible and either ciprofloxacin-susceptible or -resistant strains.

Positive Urine Nitrite Test

The aim of this study was to determine the potential ability of the urine nitrite test (NT) to predict the class of organism causing urinary tract infection. We retrospectively reviewed the records of all adult patients with a positive urine culture over a 6-month period. The infecting microorganisms and the urine NT results were recorded. A total of 729 positive cultures met inclusion criteria. Twenty-one (11%) of the 190 gram-positive organisms and 199 (46%) of the 429 gram-negative organisms yielded a positive NT. Only 5.3% of samples with pure growth of enterococcus yielded a positive NT. The predictive value that a sample yielding a positive NT would show pure growth of enterococcus was low at 2.3%. A positive NT is highly predictive of the absence of pure enterococcal bacteriuria.

Vancomycin-resistant enterococcal infections.

Enterococci are best known as antibiotic-resistant opportunistic pathogens that are commonly recovered from patients who have received multiple courses of antibiotics and have been hospitalized for prolonged periods.1–6 These organisms were well established as a cause of endocarditis and urinary tract infections by the early 1900s,3 and members of the species Enterococcus faecalis were known to be a common cause of nosocomial infections by the early 1980s.3,7–9 The emergence of enterococci with resistance to vancomycin, seen predominantly in the species E. faecium, has been followed by an increase in the frequency with which this species is recovered. . . .

Vancomycin-resistant enterococci

Enterococci have been recognized as an important cause of nosocomial infections for almost 20 years and as a cause of endocarditis for almost a century. While long known for their capacity of displaying multiple antibiotic resistant traits, the extent to which this could occur was not fully appreciated until the emergence of enterococci with acquired resistance to vancomycin; this resistance has been particularly problematic because it often occurs in the uncommon subset of enterococci that are also highly resistant to ampicillin-a combination with devastating therapeutic consequences. The observation that vancomycin resistance can be transferred to and expressed in other gram-positive organisms, for which vancomycin is often considered the primary therapeutic alternative, is a chilling reminder of just how close we may be to a wide array of potentially untreatable "killer" microbes.

Factors influencing the vitek gram-positive susceptibility system's detection of vanB-encoded vancomycin resistance among enterococci.

Studies were conducted to identify factors contributing to the inability of the Vitek Gram-Positive Susceptibility system (GPS; bioMerieux, Vitek, Inc., Hazelwood, Mo.) to reliably detect vanB-mediated vancomycin resistance among enterococci. To some extent the accuracy of the GPS depended on a particular strain's level of resistance, as all isolates for which vancomycin MICs were > or = 128 mu g/ml were readily detected but detection of resistance expressed by several strains for which MICs were < or = 64 mu g/ml was sporadic. Factors besides the level of resistance were studied in two vanB strains. For one strain (Enterococcus faecium U8304), the ability of GPS to detect resistance was accurate and consistent, while for the other (Enterococcus faecalis V583), GPS results were inconsistent and unreliable. Using these isolates, we established that growth medium had the most notable effect on the detection of resistance. In the absence of vancomycin, Vitek GPS broth supported growth comparable to that obtained with brain heart infusion broth for both E. faecium U8304 and E. faecalis V583. However, in the presence of vancomycin the growth patterns changed dramatically so that neither VanB strain grew well in Vitek broth, and growth of V583 was barely detectable after 8 h of incubation. In contrast, good growth of both strains was observed in brain heart infusion broth supplemented with vancomycin. Additionally, the same medium effect was observed with other inducibly resistant VanB strains. In conclusion, although Vitek broth can support good enterococcal growth, this medium does not sufficiently support expression of vancomycin resistance by certain strains to allow them to be detected by the Vitek automated system. Furthermore, this observation establishes that the type of growth medium used can substantially influence the expression of vancomycin resistance and indicates that medium-based strategies should be explored for the enhancement of resistance detection among commercial systems.

Future Prospects and Therapeutic Potential of Streptogramins

Dramatic changes in the epidemiology and susceptibility patterns of Gram-positive cocci during the last decade have mandated new approaches to the management of many bacterial infections. For example, there has been a sharp increase in the incidence of infections caused by Staphylococcus aureus, particularly those resistant to methicillin (MRSA), and methicillin-resistant coagulase-negative staphylococci, particularly those associated with foreign bodies and indwelling medical devices. Additionally, the worldwide spread of Streptococcus pneumoniae strains resistant to penicillin and macrolides, and the emergence of enterococci (particularly Enterococcus faecium) resistant to vancomycin, teicoplanin and other antibiotics, present further therapeutic problems. New antibacterial agents are urgently required to meet the challenges posed by these epidemiological trends. The semisynthetic streptogramins, a unique class of antibacterials currently under development, offer promise in the treatment of such multiresistant infections. Possible future applications include treatment of infections caused by the following organisms: MRSA, enterococci resistant to vancomycin, macrolides or lincosamides; and beta-lactam-resistant streptococci. They may also prove useful as therapy for children with staphylococcal infection and patients with multiresistant infections who are unable to tolerate vancomycin, including patients with skin and soft tissue infections caused by Gram-positive pathogens, patients with osteomyelitis, foreign body associated infections, endocarditis and sepsis due to Gram-positive bacteria. Clinical trials are required to evaluate the efficacy and tolerability of streptogramins in these settings.

Growth of Enterococcus, Lactococcus and Streptococcus strains and environmental isolates in liquid media and their reactions on BEEA

Growth of known species of Enterococcus, Lactococcus and Streptococcus and Aerococcus viridans in selective and nonselective liquid media routinely used to enumerate faecal streptococci was measured optically at different temperatures. Growth of environmental isolates was measured in some of these media. Growth of the reference strains on Bile esculin azide agar at elevated incubation temperatures was tested. The results revealed only minor differences between media but strong influence of incubation temperature. Some media tended to yield higher cell densities than others. For many species the inoculum size affected maximum turbidity. To combine selective media with selective incubation temperatures seems to be necessary to achieve satisfactory reliability in traditional liquid enumeration methods for faecal streptococci. Because of the diversity of this group, optimal selectivity and recovery can hardly be achieved simultaneously.

An Introduction to Molecular Hospital Epidemiology

One of the primary goals of the hospital epidemiologist is the identification and characterization of nosocomial outbreaks. Outbreaks usually are identified by the recovery of a unique strain from a cluster of patients infected with a nosocomially acquired pathogen. Until recently, the microbiologic tools available to any hospital epidemiologist permitted identification of novel strains by speciation and antibiogram. Thus, most outbreak descriptions consisted of the identification of an unusual species or the appearance of a new antibiotic resistance phenotype in a recognized nosocomial pathogen. The emergence of enterococci in this decade or the emergence of methicillin-resistant Staphylococcus aureus (MRSA) in the 1970s am notable examples. Where resources have existed, additional methods have been used for further discrimination. Outbreak and endemic strains have been compared by phage typing, serologic typing, and capsular typing. For example, beta-hemolytic streptococci may be grouped by Lancefield antisera, and Staphylococcus aureus may be grouped by phage typing. However, certain Lancefield groups and certain phage groups are common among epidemic and endemic isolates, which may prevent identification of a specific epidemic strain.

Emergence of Enterococcus as a significant pathogen.

Enterococci are components of the normal bowel flora of humans and other animals. They are often found as part of a mixed flora in intraabdominal and pelvic infections, but their role in these settings has been difficult to assess; early studies suggested that they were not important pathogens under these circumstances. Indeed, it was thought that treatments eliminating most of the other organisms from these sites of mixed infection would often lead to spontaneous eradication of the enterococcal component as well. As a result, the enterococci were generally considered harmless commensals. Recent studies, however, have documented the pathogenic potential of these organisms and in fact have shown convincingly that they are significant nosocomial pathogens. Enterococci are also capable of causing a variety of community-acquired infections.

A selective and diagnostic medium for use in the enumeration of Listeria spp. in foods

A new medium, called RAPAMY agar, has been elaborated for the isolation from and the enumeration of Listeria spp. in foods. It is based on Ralovich's nalidixic acid-trypaflavin-agar with the following modifications: (i) the slight inhibitory properties of that medium were overcome by the use of Columbia Blood agar base instead of tryptose agar and the addition of 0.05% ferric ammonium citrate and 2.5% egg yolk emulsion; (ii) selectivity was improved by the addition of 0.25% 2-phenyl ethanol and incubation under microaerobic conditions; (iii) the medium was provided with two diagnostic traits by the addition of (a) aesculin + ferric ammonium citrate; and (b) d-mannitol and phenol red. The growth of Enterococcus spp., the only organisms other than Listeria spp. which grow on RAPAMY agar, was not inhibited by the addition of 20 μg·ml −1 Cefoxitin (Moxolactam). Higher levels inhibited some Listeria spp., but not the enterococci. The medium recovered Listeria spp. quantitatively and allowed recovery from foods colonized by Enterococcus spp. at levels upto 10 2 per g.

Moxalactam in nosocomial infections with Serratia marcescens.

Ten critically ill patients presenting with nosocomial infection caused by Serratia marcescens (SM) not responding to prior chemotherapy were treated in an open study with Moxalactam (MOX) alone [6] or in combination with an aminoglycoside [4]. In initial disc diffusion tests, all isolates of SM were highly susceptible to MOX. Clinically, three patients were cured and four improved. Three patients died: one from SM pneumonia, one from gangrenous cholecystitis and another from ARDS. Bacteriologically, SM were eliminated from blood cultures in all seven patients with septicemia but were recovered post mortem from the lung of one patient. In three cases with localized infection, SM were eliminated once and persisted twice. Selection of resistant SM was observed in three patients but became clinically relevant in one case only. Resistant SM strains also showed reduced susceptibility to other cephalosporins and aminoglycosides. Emergence of enterococci occurred four times, in two cases with clinical consequences. MOX is a useful drug for the treatment of SM infections, but a definite risk of selecting multiresistant SM strains and of enterococcal overgrowth must be kept in mind.

Emergence of Streptococcus faecalis isolates with high-level resistance to multiple aminocyclitol aminoglycosides

Isolates of Streptococcus faecalis were occcasionally found to be resistant to gentamicin concentrations of 500 μg/ml in a microdilution tray. Additional tests were performed with 28 such isolates. They all demonstrated high-level resistance (minimum inhibitory concentration > 2000 μg/ml) to gentamicin, kanamycin, sisomicin, streptomycin, and tobramycin. This high-level aminoglycoside resistance was associated with total resistance to in vitro synergism when each aminoglycoside was combined with ampicillin. In addition to ampicillin-aminoglycoside combinations, ampicillin-vancomycin, ampicillin-rifampin, rifampin-vancomycin, and vancomycin-gentamicin combinations were also tested; all failed to exhibit an in vitro synergistic-bactericidal effect against these enterococci. The emergence of enterococci with high-level resistance to multiple aminoglycosides in this clinical population is a source of grave concern with obvious therapeutic implications in situations such as endocarditis, where an in vitro bactericidal effect is thought to be necessary for a cure. No drug or combination of drugs was found to be bactericidal for these isolates. It is suspected that similar isolates of group D streptococci with high-level resistance to gentamicin may emerge in other institutions but go unrecognized. Surveillance by others for identifying this newly emerging pathogen carrying multiple resistance and a continued search for a satisfactory chemotherapeutic agent(s) are encouraged.

Antibiotic-induced lysis of enterococci.

Enterococci are resistant to penicillin killing in vivo and in vitro. Because some bacteria resistant to penicillin killing have reduced autolytic activity, we examined the lysis of clinical enterococcal isolates suspended in buffer (spontaneous lysis), and compared it with their susceptibility to antibiotic-induced lysis and killing. We found significant correlations between spontaneous and antibiotic-induced lysis, using five antibiotics that inhibit cell wall synthesis (penicillin, cephalothin, bacitracin, cycloserine, and vancomycin). Among isolates, strains more rapidly lysed by one antibiotic were more rapidly lysed by the other antibiotics, and more susceptible to spontaneous lysis. In studies involving a single strain grown in different media, spontaneous lysis also correlated closely with antibiotic-induced lysis. These results are consistent with a common mechanism for spontaneous and antibiotic-induced lysis, such as the autolytic enzyme system. Human serum was one of the least permissive media tested for enterococcal growth and antibiotic-induced lysis and killing. We suggest that the inhibitory effect of human serum on growth and the activation of the enterococcal autolytic enzyme system may be a critical factor in the resistance of enterococcal endocarditis to treatment with penicillin alone.

Development of a selective enterococcus medium based on manganese ion deficiency, sodium azide, and alkaline pH.

Rogosa broth, without its salt supplement and dissolved in deionized water, was adapted for the selective isolation and enumeration of enterococci. This medium supported good growth of enterococci, but it suppressed growth of other lactic acid bacteria. The sensitivity and specificity of the medium were tested after addition of various increasing concentrations of NaN(3) against known strains of enterococci and other bacteria. Many strains of Streptococcus faecium showed low azide tolerance; optimal growth was obtained at a concentration of 0.01% NaN(3), which totally or partially inhibited unrelated species of lactic acid bacteria. The selectivity of the medium was further increased by pH adjustment to 9.6. Carbonate and Tween 80 were added to overcome partial inhibition of enterococcal growth by the new combination of selective conditions. The final medium was evaluated in agar form in isolations from human and animal feces, polluted water, meat, and dairy products. Counts were obtained after 16 to 17 h of incubation at 37 C. The isolates satisfactorily conformed to the group characteristics of enterococci.

Development of a Selective Enterococcus Medium Based on Manganese Ion Deficiency, Sodium Azide, and Alkaline pH

Rogosa broth, without its salt supplement and dissolved in deionized water, was adapted for the selective isolation and enumeration of enterococci. This medium supported good growth of enterococci, but it suppressed growth of other lactic acid bacteria. The sensitivity and specificity of the medium were tested after addition of various increasing concentrations of NaN(3) against known strains of enterococci and other bacteria. Many strains of Streptococcus faecium showed low azide tolerance; optimal growth was obtained at a concentration of 0.01% NaN(3), which totally or partially inhibited unrelated species of lactic acid bacteria. The selectivity of the medium was further increased by pH adjustment to 9.6. Carbonate and Tween 80 were added to overcome partial inhibition of enterococcal growth by the new combination of selective conditions. The final medium was evaluated in agar form in isolations from human and animal feces, polluted water, meat, and dairy products. Counts were obtained after 16 to 17 h of incubation at 37 C. The isolates satisfactorily conformed to the group characteristics of enterococci.

Über die Veränderungen der normalen Darmflora des Menschen durch Bactrim&lt;sup&gt;®&lt;/sup&gt;

On investigating the effect of Bactrim on the normal intestinal flora we found that administration for ten days caused no decrease in the absolute number of organisms in the stools of the trial subjects. Cultures showed, however, a slightly lower growth rate. The proportion of bacteroids remained unchanged but there was a slight diminution of anaerobic lactobaciUi and enterococci. Increased growth of enterococci observed in one trial subject could not be attributed with certainty to Bactrim. In all the subjects investigated Bactrim caused complete eradication of enterobacteria; in none was there emergence of pathogenic organisms. Compared with broad spectrum antibiotics given orally, Bactrim exerts a protective influence on normal intestinal flora.

Studies on the Relationship Between Composition of Diet and Intestinal Bacteria

A decrease in the intake of vitamin B1 in the rat's intestine leads to an increase in the growth of Enterococci and Esch. coli bacteria and a concurrent decrease in the amount of Lactobacilli and it's gradually decomposing in the intestinal tract.An increase in the intake of vitamin B1 decreases the amount of Enterococci and partially decrease the amount of Esch. coli bacteria in the rat's intestine and increases the amount of Lact. bacilli.The isolated faeces of decrease in the amount of vitamin B1 in the rat's intestinal bacteria is organized by the increase of the following intestinal bacteria: Esch. coli var. acidilactici, Esch. coli, and Esch. coli var. communior.