Enterococci as a One Health indicator of antimicrobial resistance

The rapid increase of antimicrobial-resistant bacteria in humans and livestock is concerning. Antimicrobials are essential for the treatment of disease in modern day medicine, and their misuse in humans and food animals has contributed to an increase in the prevalence of antimicrobial-resistant bacteria. Globally, antimicrobial resistance is recognized as a One Health problem affecting humans, animals, and environment. Enterococcal species are Gram-positive bacteria that are widely distributed in nature. Their occurrence, prevalence, and persistence across the One Health continuum make them an ideal candidate to study antimicrobial resistance from a One Health perspective. The objective of this review was to summarize the role of enterococci as an indicator of antimicrobial resistance across One Health sectors. We also briefly address the prevalence of enterococci in human, animal, and environmental settings. In addition, a 16S RNA gene-based phylogenetic tree was constructed to visualize the evolutionary relationship among enterococcal species and whether they segregate based on host environment. We also review the genomic basis of antimicrobial resistance in enterococcal species across the One Health continuum.

Large diversity of linezolid-resistant isolates discovered in food-producing animals through linezolid selective monitoring in Belgium in 2019

Background

Linezolid is a critically important antibiotic used to treat human infections caused by MRSA and VRE. While linezolid is not licensed for food-producing animals, linezolid-resistant (LR) isolates have been reported in European countries, including Belgium.

Objectives

To: (i) assess LR occurrence in staphylococci and enterococci isolated from different Belgian food-producing animals in 2019 through selective monitoring; and (ii) investigate the genomes and relatedness of these isolates.

Methods

Faecal samples (n = 1325) and nasal swab samples (n = 148) were analysed with a protocol designed to select LR bacteria, including a 44–48 h incubation period. The presence of LR chromosomal mutations, transferable LR genes and their genetic organizations and other resistance genes, as well as LR isolate relatedness (from this study and the NCBI database) were assessed through WGS.

Results

The LR rate differed widely between animal host species, with the highest rates occurring in nasal samples from pigs and sows (25.7% and 20.5%, respectively) and faecal samples from veal calves (16.4%). WGS results showed that LR determinants are present in a large diversity of isolates circulating in the agricultural sector, with some isolates closely related to human isolates, posing a human health risk.

Conclusions

LR dedicated monitoring with WGS analysis could help to better understand the spread of LR. Cross-selection of LR transferable genes through other antibiotic use should be considered in future action plans aimed at combatting antimicrobial resistance and in future objectives for the rational use of antibiotics in a One Health perspective.

Spread of Linezolid-Resistant Enterococcus spp. in Human Clinical Isolates in the Czech Republic

The aim of this study was to map and investigate linezolid resistance mechanisms in linezolid-resistant enterococci in the Czech Republic from 2009 to 2019. Altogether, 1442 isolates of Enterococcus faecium and Enterococcus faecalis were examined in the National Reference Laboratory for Antibiotics. Among them, 8% of isolates (n = 115) were resistant to linezolid (E. faecium/n = 106, E. faecalis/n = 9). Only three strains of E. faecium were resistant to tigecycline, 72.6% of isolates were resistant to vancomycin. One isolate of E. faecium harbored the cfr gene. The majority (87%, n = 11) of E. faecium strains were resistant to linezolid because of the mutation G2576T in the domain V of the 23S rRNA. This mutation was detected also in two strains of E. faecalis. The presence of the optrA gene was the dominant mechanism of linezolid resistance in E. faecalis isolates. None of enterococci contained cfrB, poxtA genes, or any amino acid mutation in genes encoding ribosomal proteins. No mechanism of resistance was identified in 4 out of 106 E. faecium linezolid resistant isolates in this study. Seventeen sequence types (STs) including four novel STs were identified in this work. Clonal complex CC17 was found in all E. faecium isolates.

Characteristics of linezolid-resistant Enterococcus faecalis isolates from broiler breeder farms

Linezolid is an oxazolidinone class antibiotic used for treatment infections caused by various multidrug-resistant gram-positive pathogens including enterococci. However, recently, linezolid-resistant isolates in animals are considered as a human health hazard. In a broiler operation system, antimicrobial resistance can be transferred to the environment and commercial broiler via the fecal-oral route. Therefore, this study was conducted to investigate the prevalence and characteristics of linezolid-resistant Enterococcus faecalis (E. faecalis) from broiler parent stock in a broiler operation system. Among 297 E. faecalis isolates from 85 flocks in 8 broiler breeder farms, the prevalence of chloramphenicol- and linezolid-resistant isolates was 0 to 12.1% and 0 to 8.0%, respectively; however, there were no significant differences between farms. Therefore, a total of 14 (4.7%) chloramphenicol- and/or linezolid-resistant E. faecalis showed resistance to 7 or more antimicrobial classes. The drug-resistance gene optrA, which can confer resistance to linezolid, tedizolid, and phenicols, was found in 8 (2.69%) isolates, and 7 (2.36%) of the 8 optrA-positive isolates co-carried the phenicol exporter gene fexA. However, E. faecalis isolates from 3 of 8 broiler breeder farms only carried the optrA and/or fexA genes. As linezolid is one of the last antimicrobial treatments of choice for multidrug-resistant gram-positive pathogens including E. faecalis, the presence of antibiotic-resistant E. faecalis in broiler breeder farms should be monitored to prevent the introduction of linezolid-resistant strains to the food chain.

Hospital outbreak caused by linezolid resistant Enterococcus faecium in Upper Austria

Background

Enterococcus faecium is part of the human gastrointestinal flora but may act as opportunistic pathogen. Environmental persistence, high colonization capability and diverse intrinsic and acquired resistance mechanisms make it especially successful in nosocomial high-risk settings. In March 2014, an outbreak of Linezolid resistant Enterococcus faecium (LREfm) was observed at the hematooncology department of a tertiary care center in Upper Austria.

Methods

We report on the outbreak investigation together with the whole genome sequencing (WGS)-based typing results including also non-outbreak LREfm and susceptible isolates.

Results

The 54 investigated isolates could be divided in six clusters based on cgMLST. Cluster one comprised LREfm isolates of genotype ST117 and CT24, which was identified as the causative clone of the outbreak. In addition, the detection of four other clusters comprising isolates originating from hematooncology patients but also at other hospitals, pointed to LREfm transmission between local healthcare facilities. LREfm patients (n = 36) were typically at risk for acquisition of nosocomial pathogens because of immunosuppression, frequent hospitalization and antibiotic therapies. Seven of these 36 patients developed LREfm infection but were successfully treated. After termination of the initial outbreak, sporadic cases occurred despite a bundle of applied outbreak control interventions.

Conclusions

WGS proved to be an effective tool to differentiate several LREfm clusters in an outbreak. Active screening for LREfm is important in a high-risk setting such as hematooncology, where multiple introductions are possible and occur despite intensified infection control measures.

Electronic supplementary material

The online version of this article (10.1186/s13756-019-0598-z) contains supplementary material, which is available to authorized users.

Effect of tedizolid on clinical Enterococcus isolates: in vitro activity, distribution of virulence factor, resistance genes and multilocus sequence typing

Enterococcal infections have become one of the most challenging nosocomial problems. Tedizolid, the second oxazolidinone, is 4-fold to 8-fold more potent in vivo and in vitro than linezolid against enterococci. However, the characteristics of tedizolid related to enterococci isolates in China remain elusive. The aim of this study was to evaluate in vitro activity of tedizolid against enterococcal isolates from patients with infections at a teaching hospital in China and to investigate the correlations between in vitro tedizolid activity against enterococci and the distribution of multilocus sequence types (MLST), resistance genes and virulence factors. A total of 289 non-duplicate Enterococcus faecalis strains and 68 E. faecium strains were isolated. Tedizolid inhibited 95.24% of all enterococcal isolates with an MIC ≤ 0.5μg/ml. Seventeen E. faecalis strains had an MIC > 0.5 μg/ml, and all E. faecium were inhibited at MIC ≤ 0.5 μg/ml. The proportion of tedizolid non-susceptible E. faecalis strains with optrA genes was higher than that among tedizolid-susceptible strains. Tedizolid exhibited good in vitro activity against all E. faecium strains, including multidrug-resistant E. faecium carrying tet(M), tet(L), tet(U),erm(A), erm(B) and erm(C) genes. In summary, tedizolid has an advantage (higher sensitivity rate) compared to linezolid among enterococci, except for isolates expressing the plasmid-encoded optrA gene.

Concentration-dependent enrichment of resistant Enterococcus faecium exposed to linezolid in an in vitro dynamic model

To explore the relationship between pharmacokinetic variables and enterococcal resistance to linezolid, a vancomycin-resistant strain whose mutant prevention concentration (MPC) exceeded the MIC by two fold was selected among six clinical isolates of Enterococcus faecium. The selected strain was exposed to simulated pharmacokinetics of twice-daily linezolid for five days. Mutants resistant to 2 × MIC of the antibiotic were enriched at ratios of the 24-h area under the concentration-time curve (AUC₂₄) to the MIC of 15 and 30 h but not at 60 and 120 h. These observations could be explained by the different times when antibiotic concentrations exceed the MPC (T_>MPC): 0 to 14, 63 and 100% of the dosing interval. Using the area under the bacterial mutant concentration-time curve (AUBC_M) determined in this study and in previous work with other E. faecium strains (MPC/MIC 4), a strain-independent T_>MPC relationship with mutant enrichment was established.

Molecular Epidemiology of Vancomycin-Resistant Enterococcus faecalis and Enterococcus faecium Isolated from Clinical Specimens in the Northwest of Iran

This study was conducted to investigate the phenotypic and genotypic characteristics of vancomycin-resistant Enterococcus faecalis and Enterococcus faecium. Antibiotic resistance and virulence genes in the aforementioned resistant isolates were studied using the epsilometer (E)-test and polymerase chain reaction (PCR). These isolates were subjected to typing by pulsed-field gel electrophoresis (PFGE). Thirty vancomycin-resistant enterococci (VRE; 18.75%) were isolated from a total of 160 various clinical specimens cultured for any bacterial growth. Of these, 11 (36.7%) isolates were identified as E. faecalis and 19 (63.3%) as E. faecium. Minimum inhibitory concentrations (MICs) of vancomycin, teicoplanin, and three alternative therapeutic options (linezolid, daptomycin, and quinupristin/dalfopristin) were determined using the E-test. Multiplex PCR was done for confirming species, identification of the resistant genotypes, and the detection of the virulence genes. Finally, the clonal relationship of all VRE strains was studied by PFGE. All VRE strains showed vancomycin MIC ≥256 μg/mL, and 27 (90%) isolates carried the vanA gene, whereas none of the isolates carried vanB. The most common resistance antibiotic pattern observed was toward rifampicin (n = 30 [100%]). Among all virulence genes studied, gelE (n = 28 [93.33%]) was found as the most prevalent virulent gene. VRE isolates exhibited 90%, 46.67%, 100%, and 66.67% resistance to teicoplanin, linezolid, quinupristin/dalfopristin, and daptomycin, respectively. Molecular typing demonstrated 16 PFGE types of VRE isolates (A-P). Although vanA was carried by most of the isolates, PFGE displayed small clonal dissemination among VR E. faecium and VR E. faecalis species.

The emerging problem of linezolid-resistant enterococci

Enterococcus is a significant pathogen in numerous infections, particularly in nosocomial infections, and is thus a great challenge to clinicians. Linezolid (LNZ), an oxazolidinone antibiotic, is an important therapeutic option for infections caused by Gram-positive bacterial pathogens, especially vancomycin-resistant enterococci. A systematic review was performed of the available literature on LNZ-resistant enterococci (LRE) to characterise these infections with respect to epidemiological, microbiological and clinical features. The results validated the potency of LNZ against enterococcal infections, with a sustained susceptibility rate of 99.8% in ZAAPS and 99.2% in LEADER surveillance programmes. Patients with LRE had been predominantly exposed to LNZ prior to isolation of LRE, with a mean treatment duration of 29.8±48.8days for Enterococcus faecalis and 23.1±21.4days for Enterococcus faecium. Paradoxically, LRE could also develop in patients without prior LNZ exposure. LNZ resistance was attributed to 23S rRNA (G2576T) mutations (51.2% of E. faecalis and 80.5% of E. faecium) as well as presence of the cfr gene (4.7% and 4.8%, respectively), which could transfer horizontally among the strains. In addition to the cfr gene, 32 cases of optrA-positive LRE were identified. Further study is required to determine the prevalence of novel resistance genes. The emergence of LRE thus hampers the treatment of such infections, which warrants worldwide surveillance.

First outbreak of colonization by linezolid- and glycopeptide-resistant Enterococcus faecium harbouring the cfr gene in a UK nephrology unit

AIM

To describe an outbreak of colonization by linezolid- and glycopeptide-resistant Enterococcus faecium harbouring the cfr gene in a UK nephrology unit.

METHODS

Isolates of linezolid-resistant E. faecium were typed by pulsed-field gel electrophoresis (PFGE), and examined by polymerase chain reaction (PCR) and sequencing for the transmissible cfr gene that confers resistance to linezolid. Enhanced environmental cleaning, initial and weekly screening of all patients, and monitoring of adherence to standard infection control precautions were implemented.

FINDINGS

Five patients with pre-existing renal disease were found to have rectal colonization with linezolid-resistant E. faecium over a two-week period. The index case was a 57-year-old male from India who had travelled to the UK. One patient also had a linezolid-resistant E. faecium of a different PFGE profile isolated from a heel wound. All isolates were confirmed to harbour the cfr gene by PCR and Sanger sequencing, and all were resistant to glycopeptides (VanA phenotype).

CONCLUSIONS

This article describes the first UK outbreak with a single strain of linezolid- and glycopeptide-resistant E. faecium harbouring the cfr gene, affecting five patients in a nephrology unit. Following the implementation of aggressive infection control measures, no further cases were detected beyond a two-week period.

Linezolid: a promising option in the treatment of Gram-positives

Linezolid, an oxazolidinone antimicrobial agent that acts by inhibiting protein synthesis in a unique fashion, is used in the treatment of community-acquired pneumonia, skin and soft-tissue infections and other infections caused by Gram-positive bacteria including VRE and methicillin-resistant staphylococci. Currently, linezolid resistance among these pathogens remains low, commonly <1.0%, although the prevalence of antibiotic resistance is increasing in many countries. Therefore, the development of resistance by clinical isolates should prompt increased attention of clinical laboratories to routinely perform linezolid susceptibility testing for this important agent and should be taken into account when considering its therapeutic use. Considering the importance of linezolid in the treatment of infections caused by Gram-positive bacteria, this review was undertaken to optimize the clinical use of this antibiotic.

Nationwide Surveillance of Novel Oxazolidinone Resistance Gene optrA in Enterococcus Isolates in China from 2004 to 2014

A total of 2,201 nonduplicate enterococcal isolates collected from 29 hospitals in 23 cities in China between 2004 and 2014 were screened for the oxazolidinone resistance gene optrA; 45 isolates (2.0%) were optrA positive with 11 OptrA variants identified. The positive rate of optrA increased from 0.4% to 3.9% during the 10-year surveillance period. Pulsed-field gel electrophoresis (PFGE) and multilocus sequence type (MLST) analysis revealed that 37 optrA-positive Enterococcus faecalis isolates clustered into 25 PFGE patterns and 21 sequence types, while 6 Enterococcus faecium isolates represented 6 PFGE patterns and 6 sequence types. The present study underscores the importance of routine and persistent monitoring of oxazolidinone resistance and optrA gene.

Emergence of linezolid- and vancomycin-resistant Enterococcus faecium in a department for hematologic stem cell transplantation

Background

Prevalence of vancomycin-resistant enterococci has increased in Germany. Here, we report the cluster of linezolid- and vancomycin-resistant Enterococcus faecium (LVRE) in a German department for hematologic stem cell transplantation (HSCT).

Methods

In this retrospective analysis we included all patients with LVRE in a university-based department for HSCT in 2014 and 2015. Patients chart reviews were used to investigate the epidemiology and clinical outcome. Available LVRE isolates underwent detailed microbiological characterization and genotyping by pulsed-field gel electrophoresis (PFGE).

Results

In total, 20 patients with LVRE were identified within the observed time period. All except two patients underwent allogeneic HSCT. Surveillance culture results from incoming patients and chart review revealed that 10 of 20 patients were colonized at hospital admission. Eight of 10 patients with in-hospital acquired LVRE had previous linezolid treatment. Analysis of spatio-temporal patterns showed no evidence for LVRE patient-to-patient or environment-to-patient transmission within the HSCT department. In five cases (25 %) LVRE bloodstream infection occurred. Nine LVRE isolates could be saved for characterization. Eight isolates carried vanA, one isolate vanB. PFGE analysis showed that four different LVRE clones were responsible for the cluster. One single genotype was present in six LVRE isolates whereupon the corresponding patients were all referred from the same hospital to the HSCT department.

Conclusions

This is the first report demonstrating the emergence of LVRE in a German HSCT department. (L)VRE screening at patients’ admission and appropriate infection control strategies were sufficient to prevent any transmission. Further studies in this predisposed patient collective are warranted.

Emergence of linezolid resistance in hepatobiliary infections caused by Enterococcus faecium

Enterococcal infections are common in liver transplantation and hepatopancreaticobiliary (HPB) surgery. Linezolid is frequently used to treat not only vancomycin-resistant Enterococcus (VRE), but also vancomycin-sensitive Enterococcus (VSE) infections, and resistance can develop. This study evaluated all the Liver Unit patients who developed infections with linezolid-resistant Enterococcus (LRE) in order to elicit the association with prior linezolid usage, to explore possible risk factors for infection, and to better understand the epidemiology of these isolates in this patient group. Between 2010 and 2015, infections with LRE developed in 10 patients (8 following liver transplantation and 2 following HPB surgery) after 22-108 days of treatment. Selected pulsed-field gel electrophoresis demonstrated that 2 out of 10 patients were cocolonized with different strains and indicated that cross-transmission may have occurred. In conclusion, in this group of patients with complex hepatobiliary infections, the optimal antibiotic strategies for the treatment of Enterococcus faecium infections are not clearly defined, and there is a significant risk of emergence of resistance to linezolid in E. faecium after exposure to this agent in patients, especially in the presence of a deep source of infection on a background of hepatic artery insufficiency. Caution is needed when using prolonged courses of linezolid in this setting, and further studies are necessary to determine the optimum treatment.

Emergence of linezolid-resistant coagulase-negative staphylococci in an intensive care unit

BACKGROUND

The aim of this study was to report the emergence of linezolid-resistant coagulase-negative staphylococci (CoNS) in an intensive care unit.

METHODS

An observational study was conducted in critically ill patients with colonization or infection by linezolid-resistant CoNS between January 2010 and December 2014. We analyzed the epidemiological and clinical features, and the mechanism of resistance to linezolid. We also evaluated the association between the incidence of linezolid-resistant CoNS strains and the consumption of linezolid in the study period.

RESULTS

During the study period 49 patients had a linezolid-resistant CoNS strain isolated from clinical samples (blood in 42 cases, urine in 6, peritoneal fluid in 1). Molecular study showed a combination of mechanisms of resistance. Most patients were critically ill (APACHE II score = 21.9 ± 8.3) and nearly all had undergone surgery and invasive procedures, and had prior exposure to antibiotics. Linezolid-resistant CoNS were considered to be contaminants in 42 patients and associated with infection in 7 patients, comprising bacteremia and septic shock in most of them. They were successfully treated with glycopeptides or daptomycin. A modest significant correlation was observed between the decrease in linezolid consumption and the lower incidence of resistant isolates.

CONCLUSIONS

Linezolid-resistant CoNS had emerged in critically ill patients with severe underlying diseases and prior antibiotic exposure. Most isolates represented colonization; however, linezolid-resistant CoNS can produce serious infections in critically ill patients. Glycopeptides and daptomycin seem to provide useful alternatives for therapy of these infections. A relationship was found between linezolid consumption and the incidence of linezolid-resistant CoNS strains.

Assessment of the in vitro synergy of daptomycin plus linezolid against multidrug-resistant enterococci

The widespread incidence of enterococci resistant to ampicillin, vancomycin and aminoglycosides, the first-line anti-enterococcal antibiotics, has made the treatment of severe enterococcal infections difficult and alternatives should be explored. We investigated the activity of daptomycin combined with linezolid against three Enterococcus faecalis and four Enterococcus faecium strains resistant to standard drugs used for therapy. Minimum inhibitory concentrations (MICs) were determined by the broth dilution method. Drug interactions were assessed by the checkerboard and time-kill methods. Synergy was defined by a fractional inhibitory concentration index (FICI) of ≤0.5 or a ≥2log₁₀CFU/mL killing at 24h with the combination in comparison with killing by the most active single agent. Indifference was defined by a FICI>0.5-4.0 or a 1-2log₁₀CFU/mL killing compared with the most active single agent. MICs of daptomycin were 2-4μg/mL for E. faecalis and 2-8μg/mL for E. faecium. MICs of linezolid were 1-2μg/mL for all bacteria. In the checkerboard assay, five isolates showed synergism (FICI<0.5) and two showed indifference (FICIs of 0.53 and 2). Killing studies revealed synergy of daptomycin plus linezolid against four isolates (2.2-3.7log₁₀CFU/mL kill) and indifference (1.1-1.6log₁₀CFU/mL kill) for the other three strains. Antagonism was not observed. In conclusion, the combination of daptomycin and linezolid had a synergistic or indifferent effect against multidrug-resistant enterococci. Additional studies are needed to explore the potential of this combination for severe enterococcal infections when first-line antibiotic combinations cannot be used.

Recurrent linezolid-resistant Enterococcus faecalis infection in a patient with pneumonia

OBJECTIVE

It has been reported that LZD-resistant Enterococcus in the gastrointestinal tract of mice colonizes persistently and shows variable minimum inhibitor concentration (MIC) values. However, the colonization characteristics of Enterococcus with LZD resistance in patients remain elusive. Here, we report the case of a patient with recurrent pneumonia due to infection with LZD-resistant Enterococcus faecalis strains. The colonization characteristics of the strains isolated from this patient were analyzed.

METHODS

Ten E. faecalis strains were isolated from tracheal secretions obtained from the patient during five recurrences of pneumonia over the course of 10 months. Clonal relationships were determined by pulsed-field gel electrophoresis (PFGE) with SmaI-macrorestricted genomic DNA. The susceptibility of the isolates to LZD was determined by Etest in Mueller-Hinton agar.

RESULTS

The homology of these strains was demonstrated by PFGE, suggesting that occult bacterial colonization by LZD-resistant E. faecalis is possible as late as a year after exposure to LZD. These strains showed variable MICs as determined by the Etest. LZD-resistant isolates contained single or double nucleotide mutations in domain V of 23S rRNA as confirmed by PCR and sequencing. The sensitivity of the strains to vancomycin was demonstrated by broth macrodilution, and vancomycin was an effective clinical treatment on each occasion.

CONCLUSIONS

Our results indicate that LZD-resistant E. faecalis strains may colonize persistently in vivo, leading to recurrent infection.

To swab or not to swab? A prospective analysis of 341 SICU VRE screens

BACKGROUND

Vancomycin-resistant Enterococcus (VRE) screening is routine practice in many intensive care units despite the question of its clinical significance. The value of VRE screening at predicting subsequent VRE or other hospital-acquired infection (HAI) is unknown. The purpose of this investigation was to examine the rate of subsequent VRE HAI in patients undergoing VRE screening.

METHODS

This study was conducted in a 24-bed surgical intensive care unit (SICU) at a Level I trauma center. Patients admitted to the SICU between February and August 2011 who had rectal swab for VRE screening within 72 hours were followed prospectively for the development of VRE and other HAIs. Demographics, clinical characteristics, and infection rates were compared between VRE-positive and VRE-negative patients. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of VRE screening for predicting subsequent VRE HAI were calculated.

RESULTS

A total of 341 patients had VRE screening within 72 hours of SICU admission, with 32 VRE-positive (9%) and 309 VRE-negative (91%) patients. VRE-positive patients had a higher incidence of any HAI (78% vs. 35%, p < 0.001). Eight VRE-positive patients (25%) developed VRE HAI compared with only 3 VRE-negative patients (1%) (p < 0.001). VRE screening had a 73% sensitivity, 93% specificity, 25% PPV, and 99% NPV for determining subsequent VRE HAI.

CONCLUSION

VRE colonization was present in 9% of SICU patients at admission. Negative VRE screen result had a high specificity and NPV for the development of subsequent VRE HAI. Empiric treatment of VRE infection may be unnecessary in VRE-negative patients.

LEVEL OF EVIDENCE

Prognostic/epidemiologic study, level III. Therapeutic study, level IV.

The emergence of linezolid resistance among Enterococci in intestinal microbiota of treated patients is unrelated to individual pharmacokinetic characteristics

Linezolid is an antimicrobial agent for the treatment of multiresistant Gram-positive infections. We assessed the impact of linezolid on the microbiota and the emergence of resistance and investigated its relationship with plasma pharmacokinetics of the antibiotic. Twenty-eight patients were treated for the first time with linezolid administered orally (n = 17) or parenterally (n = 11) at 600 mg twice a day. Linezolid plasma pharmacokinetic analysis was performed on day 7. Colonization by fecal enterococci, pharyngeal streptococci, and nasal staphylococci were assessed using selective media with or without supplemental linezolid. The resistance to linezolid was characterized. The treatment led to a decrease of enterococci, staphylococci, and streptococci in the fecal (P = 0.03), nasal, and pharyngeal (P < 0.01) microbiotas. The appearance of resistant strains was observed only in enterococci from the fecal microbiota between the 7th and 21st days of treatment in four patients (14.3%). The resistance was mainly due for the first time to the mutation G2447T in the 23S rRNA gene. No pharmacokinetic parameters were significantly different between the patients, regardless of the appearance of resistance. The emergence of linezolid resistance during treatment was observed only in the intestinal microbiota and unrelated to pharmacokinetic parameters. However, colonization by Gram-positive bacteria was reduced as a result of treatment in all microbiotas.

Bugs, hosts and ICU environment: countering pan-resistance in nosocomial microbiota and treating bacterial infections in the critical care setting

ICUs are areas where resistance problems are the largest, and these constitute a major problem for the intensivist's clinical practice. Main resistance phenotypes among nosocomial microbiota are (i) vancomycin-resistance/heteroresistance and tolerance in grampositives (MRSA, enterococci) and (ii) efflux pumps/enzymatic resistance mechanisms (ESBLs, AmpC, metallo-betalactamases) in gramnegatives. These phenotypes are found at different rates in pathogens causing respiratory (nosocomial pneumonia/ventilator-associated pneumonia), bloodstream (primary bacteremia/catheter-associated bacteremia), urinary, intraabdominal and surgical wound infections and endocarditis in the ICU. New antibiotics are available to overcome non-susceptibility in grampositives; however, accumulation of resistance traits in gramnegatives has led to multidrug resistance, a worrisome problem nowadays. This article reviews microorganism/infection risk factors for multidrug resistance, suggesting adequate empirical treatments. Drugs, patient and environmental factors all play a role in the decision to prescribe/recommend antibiotic regimens in the specific ICU patient, implying that intensivists should be familiar with available drugs, environmental epidemiology and patient factors.

Evaluating the impact of a pharmacist's absence from an antimicrobial stewardship team

PURPOSE

Results of a study to determine the impact of a clinical pharmacist's temporary absence from a hospital's antimicrobial stewardship team are presented.

METHODS

A retrospective chart review was conducted to compare the appropriateness of the use of selected antimicrobial medications with and without regular pharmacist involvement on the hospital's antimicrobial stewardship team. The charts of two samples of patients were evaluated: (1) 119 patients who had received prolonged (≥72 hours) imipenem-cilastatin, linezolid, or micafungin therapy over a three-month period during which a clinical pharmacist routinely provided interventions to help ensure the drugs were used according to institutional guidelines and (2) 111 patients treated with one of the three drugs during a three-month period when the clinical pharmacist did not serve on the stewardship team.

RESULTS

Relative to the period of active pharmacist involvement in antimicrobial stewardship, rates of inappropriate use of imipenem-cilastatin, linezolid, and micafungin during the pharmacist's absence were deemed to have increased by 27, 39, and 35 percentage points, respectively, with corresponding increases in the average duration of therapy of 0.7, 4.0, and 3.2 days; in addition, the number of cases of Clostridium difficile infection increased more than threefold (from 8 to 25) during the pharmacist's absence.

CONCLUSION

The temporary absence of a pharmacist from the antimicrobial stewardship team was associated with increased rates of inappropriate use of restricted antimicrobial agents and consequent increases in average durations of therapy.

Genetic modifications to temperate Enterococcus faecalis phage Ef11 that abolish the establishment of lysogeny and sensitivity to repressor, and increase host range and productivity of lytic infection

Ef11 is a temperate bacteriophage originally isolated by induction from a lysogenic Enterococcus faecalis strain recovered from an infected root canal, and the Ef11 prophage is widely disseminated among strains of E. faecalis. Because E. faecalis has emerged as a significant opportunistic human pathogen, we were interested in examining the genes and regulatory sequences predicted to be critical in the establishment/maintenance of lysogeny by Ef11 as a first step in the construction of the genome of a virulent, highly lytic phage that could be used in treating serious E. faecalis infections. Passage of Ef11 in E. faecalis JH2-2 yielded a variant that produced large, extensively spreading plaques in lawns of indicator cells, and elevated phage titres in broth cultures. Genetic analysis of the cloned virus producing the large plaques revealed that the variant was a recombinant between Ef11 and a defective FL1C-like prophage located in the E. faecalis JH2-2 chromosome. The recombinant possessed five ORFs of the defective FL1C-like prophage in place of six ORFs of the Ef11 genome. Deletion of the putative lysogeny gene module (ORFs 31-36) and replacement of the putative cro promoter from the recombinant phage genome with a nisin-inducible promoter resulted in no loss of virus infectivity. The genetic construct incorporating all the aforementioned Ef11 genomic modifications resulted in the generation of a variant that was incapable of lysogeny and insensitive to repressor, rendering it virulent and highly lytic, with a notably extended host range.