Molecular characterization of vancomycin-resistant Enterococci repopulating the gastrointestinal tract following treatment with a novel glycolipodepsipeptide, ramoplanin

Clinical characteristics and treatment outcomes of vancomycin-resistant Enterococcus faecium bacteremia

BACKGROUND

Vancomycin-resistant Enterococcus faecium (VRE-fm) bacteremia causes significant mortality in hospitalized patients. We sought to investigate clinical characteristics, treatment outcomes, and microbiological eradication associated with VRE-fm bacteremia.

METHODS

A retrospective cohort study was conducted and included 210 adult patients admitted between January 1, 2011 and December 31, 2015.

RESULTS

The mean Pitt bacteremia score was 4.7. ICU stay (48.6%) and mechanical ventilation (46.2%) were common. Diabetes mellitus was the most common concomitant disease (43.3%), followed by malignancies, including hematologic malignancies (14.3%) and solid cancers (28.1%). The 14-day and 28-day mortality rates were 37.1% and 50.5%, respectively. Linezolid or daptomycin treatment for at least 10 days and higher Pitt bacteremia scores were independently associated with 14-day and 28-day mortality. Longer treatment duration of linezolid or daptomycin predicted microbiological eradication independently. Daptomycin-treated patients tended to have higher 14-day and 28-day mortality, and lower microbial eradication rates (20.8% versus 8.7%; 40.6% versus 26.1%; 14.1% versus 26.1%; respectively) than linezolid-treated patients, and cumulative survival rates at 14 and 28 days tended to be lower in patients who received low-dose daptomycin (<10 mg/kg/day) than that in those who received linezolid and high-dose daptomycin (≥10 mg/kg/day); however, the differences were not statistically significant.

CONCLUSION

Higher disease severity and inappropriate treatment were associated with increased mortality and longer treatment duration of linezolid or daptomycin was associated with microbial eradication for the patient with VRE-fm bacteremia.

Vancomycin-resistant enterococcal infections: epidemiology, clinical manifestations, and optimal management

Since its discovery in England and France in 1986, vancomycin-resistant Enterococcus has increasingly become a major nosocomial pathogen worldwide. Enterococci are prolific colonizers, with tremendous genome plasticity and a propensity for persistence in hospital environments, allowing for increased transmission and the dissemination of resistance elements. Infections typically present in immunosuppressed patients who have received multiple courses of antibiotics in the past. Virulence is variable, and typical clinical manifestations include bacteremia, endocarditis, intra-abdominal and pelvic infections, urinary tract infections, skin and skin structure infections, and, rarely, central nervous system infections. As enterococci are common colonizers, careful consideration is needed before initiating targeted therapy, and source control is first priority. Current treatment options including linezolid, daptomycin, quinupristin/dalfopristin, and tigecycline have shown favorable activity against various vancomycin-resistant Enterococcus infections, but there is a lack of randomized controlled trials assessing their efficacy. Clearer distinctions in preferred therapies can be made based on adverse effects, drug interactions, and pharmacokinetic profiles. Although combination therapies and newer agents such as tedizolid, telavancin, dalbavancin, and oritavancin hold promise for the future treatment of vancomycin-resistant Enterococcus infections, further studies are needed to assess their possible clinical impact, especially in the treatment of serious infections.

Diagnosis and management of Enterococcus spp infections during rehabilitation of cold-stunned Kemp's ridley turtles (Lepidochelys kempii): 50 cases (2006-2012)

OBJECTIVE

To evaluate clinical data for cold-stunned Kemp's ridley turtles (Lepidochelys kempii) with Enterococcus spp infections during rehabilitation.

DESIGN

Retrospective case series.

ANIMALS

50 stranded cold-stunned Kemp's ridley turtles hospitalized between 2006 and 2012.

PROCEDURES

Medical records for turtles from which Enterococcus spp were isolated were reviewed retrospectively, and clinical data, including morphometric data, body temperature at admission, physical examination findings, antimicrobial medication history, history of medications administered IV, environmental data, day of diagnosis, clinical signs at diagnosis, microbiological testing results, sources of positive culture results, hematologic and plasma biochemical data, cytologic and histopathologic results, radiographic findings, antimicrobial treatments, time to first negative culture result, treatment duration, results of subsequent cultures, and case outcome, were collated and analyzed.

RESULTS

Enterococcus spp were isolated from bacteriologic cultures of blood, bone, joint, and respiratory tract samples and a skin lesion, with supporting evidence of infection provided by histopathologic, cytologic, and radiographic data. Positive culture results were associated with clinical problems such as lethargy, anorexia, and lameness. Most (34/43 [79%]) turtles for which an antemortem diagnosis was made survived with treatment and were released into the wild.

CONCLUSIONS AND CLINICAL RELEVANCE

Cold-stunned Kemp's ridley turtles may be affected by serious Enterococcus spp infections during rehabilitation. Recognition and treatment of these infections are important for successful rehabilitation.

Increased Susceptibility to Vancomycin-Resistant Enterococcus Intestinal Colonization Persists After Completion of Anti-Anaerobic Antibiotic Treatment in Mice

Background:

Antibiotic-associated disruption of the indigenous intestinal microflora may persist beyond the treatment period. Although piperacillin/tazobactam inhibits the establishment of vancomycin-resistant Enterococcus (VRE) stool colonization in mice during treatment, we hypothesized that this agent and other anti-anaerobic antibiotics would increase susceptibility to colonization during the period of recovery of the intestinal microflora.

Design:

Mice received 104 colony-forming units of vancomycin-resistant E. faecium by orogastric inoculation 2, 5, or 10 days after completing 5 days of subcutaneous antibiotic treatment, or both during and 2 days after the completion of treatment. Denaturing gradient gel electrophoresis (DGGE) was performed to assess changes in the intestinal microflora.

Results:

Anti-anaerobic antibiotics (ie, piperacillin/tazobactam, cefoxitin, and clindamycin) caused significant disruption of the indigenous microflora (mean DGGE similarity indices ≤ 27% in comparison with saline controls) and promoted the establishment of high-density colonization when VRE was inoculated 2 or 5, but not 10, days following treatment (P < .001). Piperacillin/tazobactam exhibited a biphasic effect on the establishment of colonization (ie, inhibition when exposed to VRE during treatment and promotion when exposed to VRE after discontinuation of treatment), resulting in greater overall promotion of colonization than did agents with minimal anti-anaerobic activity (ie, levofloxacin, cefepime, and aztreonam) when VRE was inoculated both during and 2 days after treatment (P< .001).

Conclusion:

Patients receiving anti-anaerobic antibiotics, including piperacillin/tazobactam, may be susceptible to the establishment of high-density VRE colonization during the period of recovery of the anaerobic microflora.

In vitro activity of ramoplanin and comparator drugs against anaerobic intestinal bacteria from the perspective of potential utility in pathology involving bowel flora

Susceptibility of intestinal bacteria to various antimicrobial agents in vitro, together with levels of those agents achieved in the gut, provides information on the likely impact of the agents on the intestinal flora. Orally administered drugs that are poorly absorbed may be useful for treatment of intestinal infections and for certain other situations in which intestinal bacteria may play a role. The antimicrobial activity of ramoplanin (MDL 62,198) against 928 strains of intestinal anaerobic bacteria was determined using the NCCLS-approved Wadsworth brucella laked-blood agar dilution method. The activity of ramoplanin was compared with that of ampicillin, bacitracin, metronidazole, trimethoprim/sulfamethoxazole (TMP/SMX), and vancomycin. The organisms tested included Bacteroides fragilis group (n=89), other Bacteroides species (n=16), other anaerobic Gram-negative rods (n=56) anaerobic cocci (n=114), Clostridium species (n=426), and non-sporeforming anaerobic Gram-positive rods (n=227). The overall MIC(90)s of ramoplanin, ampicillin, bacitracin, metronidazole, and vancomycin were 256, 32, 128, 16, and 128 mcg/ml, respectively. Ramoplanin was almost always highly active vs. Gram-positive organisms and relatively poor in activity against Gram-negative organisms, particularly Bacteroides, Bilophila, Prevotella, and Veillonella. Vancomycin was quite similar to ramoplanin in its activity. Ampicillin was relatively poor in activity vs. organisms that often produce beta-lactamase, including most of the Gram-negative rods as well as Clostridium bolteae and C. clostridioforme. Bacitracin was relatively poor in activity against most anaerobic Gram-negative rods, but better vs. most Gram-positive organisms. Metronidazole was very active against all groups other than bifidobacteria and some strains of other types of non-sporeforming Gram-positive bacilli. TMP/SMX was very poorly active, with an MIC(90) of >2048 mcg/ml.

Comparison of the efficacy of ramoplanin and vancomycin in both in vitro and in vivo models of clindamycin-induced Clostridium difficile infection

OBJECTIVES

Treatment of Clostridium difficile infection (CDI) is limited primarily to either metronidazole or vancomycin. We compared vancomycin and a novel glycolipodepsipeptide, ramoplanin, in both hamster and in vitro gut models of clindamycin-induced CDI.

METHODS

We used an in vitro triple-stage chemostat model that simulates the human gut, and an in vivo hamster model, both primed with clindamycin.

RESULTS

Clindamycin exposure elicited symptomatic disease in the hamster model, and promoted C. difficile germination and toxin production in the gut model. C. difficile germination and toxin production were not associated with depletion of gut microflora in the gut model, but were temporarily associated with subinhibitory concentrations of clindamycin. Both ramoplanin and vancomycin were associated with rapid symptom resolution in the hamster model, and rapid toxin titre decrease in the in vitro gut model. In both models of CDI, vancomycin was associated with greater persistence of C. difficile spores. C. difficile spores were recovered significantly more often from the caecal contents of vancomycin-treated (n = 19/23) compared with ramoplanin-treated (n = 6/23) hamsters (P < 0.05).

CONCLUSIONS

Results from the in vitro gut and hamster models were concordant. Ramoplanin and vancomycin were similarly effective at reducing cytotoxin production in the gut CDI model and in resolving symptoms in the hamster model. Ramoplanin may be more effective than vancomycin at killing spores and preventing spore recrudescence. These findings suggest a potential therapeutic role for ramoplanin in CDI that requires further clinical investigation.

Approaches to vancomycin-resistant enterococci

PURPOSE OF REVIEW

This article reviews recent publications regarding new antimicrobial drugs for the treatment of vancomycin-resistant enterococci.

RECENT FINDINGS

Newer drugs against vancomycin-resistant enterococci are now available or will soon be available. Quinupristin-dalfopristin, a streptogramin, and linezolid, an oxazolidinone, are effective and safe but only bacteriostatic against enterococi. Bacterial isolates resistant to either antibiotic have been described. Daptomycin, a lipopeptide antimicrobial, has good in-vitro bactericidal activity against enterococci, but very limited clinical data exist regarding the treatment of serious enterococcal infection with this compound. Ramoplanin, the first glycolipodepsipeptide antimicrobial in clinical trials, is not systemically absorbed after oral administration, and is being evaluated for the prevention of bloodstream infection in patients colonized with vancomycin-resistant enterococci. Oritavancin and dalbavancin (both glycopeptides) and tigecycline (a monocycline derivative) are being evaluated in phase II and III trials and are not yet commercially available.

SUMMARY

Treatment of vancomycin-resistant enterococci continues to be problematical although these new drugs offer some hope. The rational use of antibiotics, strict guidelines for the use of new compounds, and adherence to infection control practices continue to be essential components of the management of vancomycin-resistant enterococci colonization and infection.

Efficacy of oral ramoplanin for inhibition of intestinal colonization by vancomycin-resistant enterococci in mice

Ramoplanin is a glycolipodepsipeptide antibiotic with activity against gram-positive bacteria that is in clinical trials for prevention of vancomycin-resistant Enterococcus (VRE) bloodstream infections and treatment of Clostridium difficile diarrhea. Orally administered ramoplanin suppresses VRE intestinal colonization, but recurrences after discontinuation of treatment have frequently been observed. We used a mouse model to examine the efficacy of ramoplanin for inhibition of VRE colonization and evaluated the etiology of recurrences of colonization. Eight days of treatment with ramoplanin (100 microg/ml) in drinking water suppressed VRE to undetectable levels, but 100% of mice developed recurrent colonization; a higher dose of 500 microg/ml in water was associated with recurrent colonization in 50% of mice. Two of eight (25%) mice treated with the 100-microg/ml dose of ramoplanin had low levels of VRE in their cecal tissues on day 8 despite undetectable levels in stool and cecal contents. Mice that received prior ramoplanin treatment did not develop VRE overgrowth when challenged with 10(7) CFU of oral VRE 1, 2, or 4 days later. In communal cages, rapid cross-transmission and overgrowth of VRE was observed among clindamycin-treated mice; ramoplanin treatment effectively suppressed VRE overgrowth in such communal cages. Ramoplanin treatment promoted increased density of indigenous Enterobacteriaceae and overgrowth of an exogenously administered Klebsiella pneumoniae isolate. These results demonstrate the efficacy of ramoplanin for inhibition of VRE colonization and suggest that some recurrences occur due to reexpansion of organisms that persist within the lining of the colon. Ramoplanin treatment may be associated with overgrowth of gram-negative bacilli.

Coexistence of vancomycin-resistant enterococci and Staphylococcus aureus in the intestinal tracts of hospitalized patients

The potential for transfer of vancomycin-resistance genes from enterococci to Staphylococcus aureus exists when these organisms share an ecologic niche. We performed an 8-month prospective study to determine the frequency at which S. aureus and vancomycin-resistant enterococci (VRE) coexist in the intestinal tracts of VRE-colonized patients and evaluated whether antianaerobic antibiotic therapy promoted increased density of S. aureus colonization. Of 37 patients colonized with vancomycin-resistant Enterococcus faecium, 23 (62%) had S. aureus recovered from stool specimens and 20 (87%) had methicillin-resistant strains. There was no significant difference in the mean density (+/- standard deviation) of S. aureus during versus > or =1 month after discontinuation of antianaerobic antibiotic therapy (5.1+/-1.5 vs. 4.7+/-1.6 log10 colony-forming units per gram of stool; P=.34). No S. aureus isolates were resistant to vancomycin. S. aureus and VRE often coexist in the intestinal tract, providing a potential reservoir for the emergence of vancomycin-resistant S. aureus isolates.

Chemistry and biology of the ramoplanin family of peptide antibiotics

The peptide antibiotic ramoplanin factor A2 is a promising clinical candidate for treatment of Gram-positive bacterial infections that are resistant to antibiotics such as glycopeptides, macrolides, and penicillins. Since its discovery in 1984, no clinical or laboratory-generated resistance to this antibiotic has been reported. The mechanism of action of ramoplanin involves sequestration of peptidoglycan biosynthesis Lipid intermediates, thus physically occluding these substrates from proper utilization by the late-stage peptidoglycan biosynthesis enzymes MurG and the transglycosylases (TGases). Ramoplanin is structurally related to two cell wall active lipodepsipeptide antibiotics, janiemycin, and enduracidin, and is functionally related to members of the lantibiotic class of antimicrobial peptides (mersacidin, actagardine, nisin, and epidermin) and glycopeptide antibiotics (vancomycin and teicoplanin). Peptidomimetic chemotherapeutics derived from the ramoplanin sequence may find future use as antibiotics against vancomycin-resistant Enterococcus faecium (VRE), methicillin-resistant Staphylococcus aureus (MRSA), and related pathogens. Here we review the chemistry and biology of the ramoplanins including its discovery, structure elucidation, biosynthesis, antimicrobial activity, mechanism of action, and total synthesis.