ANTIMICROBIAL SUSCEPTIBILITY COAGULASE-NEGATIVE STAPHYLOCOCCI CAUSING SERIOUS BACTEREMIC EPISODES IN CHILDREN

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1 SERIOUS BACTEREMIC EPISODES IN CHILDREN Sample ES-02 (2016) was a simulated blood culture isolate from a neonate with sepsis. The sample was sent for organism identification and antimicrobial susceptibility testing using laboratories' routinely applied methods. 1-6 The sample contained Staphylococcus capitis, a coagulase-negative staphylococcus (CoNS) species, in pure culture having a generally susceptible antibiogram except for a beta-lactamase-mediated resistance to penicillins (ampicillin and penicillin). However, this strain also has a mobile cfr gene encoding for low-level resistance to numerous antimicrobial classes including phenicols (chloramphenicol), lincosamides (clindamycin), oxazolidinones (linezolid), pleuromutilins (retapamulin), and some streptogramins. The cfr-containing S. capitis was distributed as an ungraded educational challenge to determine the ability of currently marketed susceptibility testing products to detect and categorize these emerging resistances in the clinical setting of bacteremia (neonatal ICU environment). Organism Identification Responses of S. capitis (555 participants; 64.4%), CoNS not otherwise specified (197; 22.8%), or a Gram-positive organism (15; 1.7%) were considered acceptable identification performance (89.1% overall). The most common erroneous identifications were another CoNS species (75 participants; 8.7%) or a coagulase positive Staphylococcus species (8; 0.9%). The best identification performances to species level were by the MALDI-TOF (100.0%), Vitek 2 (91.9%), and BD Phoenix (80.0%) systems. None of these methods produced an error of calling the organism another CoNS. However, MicroScan only achieved the correct species identification at the rate of 43.5%, and misidentified this challenge as another CoNS in 18.2% of participant responses. The inaccurate MicroScan responses were most commonly S. epidermidis, S. auricularis, and S. hominis. S. capitis is the seventh most important human pathogen among staphylococci, with S. aureus and S. epidermidis being ranked first and second, respectively. S. capitis are Gram-positive, non-motile, nonspore-forming, catalase-positive, coagulase-negative organisms that occur as single cocci, pairs, or grape-like clusters. They are facultative anaerobes that grow on standard laboratory isolation media and produce colonies that appear raised, opaque, circular, and glossy, with some strains displaying delayed yellow pigmentation. 7,8 Based on DNA relatedness studies, S. capitis has been classified into two subspecies, S. capitis subsp. capitis and S. capitis subsp. ureolyticus. 8 Automated commercial systems are available for identification of CoNS, including Vitek 2, MicroScan, API, and BD BBL Crystal. 7 These systems have limitations, as strains from the same species can have varied phenotypic differences; misidentification rates for S. capitis have been reported as high as 18.8% for some of these methodologies Genotypic methods, including 16S, tuf and soda gene sequencing, can identify members of the CoNS group more accurately than phenotypic methods. 7,13 Biochemical identification approaches are increasingly being replaced by matrix-assisted laser desorption ionization -

2 time of flight (MALDI-TOF) technology, which has proven to produce accurate, timely and cost-effective results for CoNS, including S. capitis. 14 CoNS are normal inhabitants of the skin and mucous membranes of humans and animals, with S. capitis being found on human skin of the scalp, face, ears and neck. 7 CoNS can appear as a contamination of the sample during processing, a physiological colonization of the skin, or as a clinically significant infection; thus, assessing the clinical relevance in a culture can be challenging. 15 S. capitis has been reported as a cause of endocarditis and nosocomial late-onset sepsis (LONS) in neonatal intensive-care units. 16,17 Antimicrobial Susceptibility Testing (ungraded) Participants were asked to perform antimicrobial susceptibility testing on this S. capitis isolate. This strain was selected to challenge proper staphylococcal identification and to determine antimicrobial coverage across numerous classes of antimicrobial agents active against Gram- positive cocci. The initial reference laboratory antimicrobial susceptibility testing was conducted using the standardized reference broth microdilution method, 1 and susceptibility categories were determined by applying CLSI, EUCAST, and USCAST document breakpoints, 3-5 where available. The reference laboratory testing reported results for a total of 23 agents (Table 1) that demonstrated varied antimicrobial activity against this CoNS strain. However, the S. capitis carried a cfr gene with documented elevated MIC values for three more commonly tested agents (chloramphenicol, clindamycin, and linezolid). Consensus MIC categorical accuracy ranged from only 10.7% (linezolid) to 100% (five drugs); see Table 2. Among the 20 antimicrobials having susceptible reference results, the participant-reported accuracy was 97.2 (ceftriaxone) to 100.0%. The cfr resistance mechanism encodes resistances to phenicols (chloramphenicol), lincosamides (clindamycin), oxazolidinones (linezolid), pleuromutilins (retapamulin, tiamulin), and streptogramin A (component of quinupristin-dalfopristin combination). This level of resistance can be modest (reference linezolid MIC at 8 µg/ml) and the clindamycin resistance is not routinely associated with resistance to the macrolides such as erythromycin, azithromycin, or clarithromycin. This pattern of resistances has the acronym of phlopsa (see Emerging Resistance Mechanisms, below). The strain was also resistant to ampicillin and penicillin secondary to the production of a potent penicillinase.

3 Table 1. Listing of expected reference susceptibility testing categorical results for this S. capitis (culture of blood) sent as ungraded sample ES-02 (2016). Clinical setting was a bacteremia sample from a neonate. Antimicrobials listed by susceptibility category (Reference MIC in µg/ml): a Susceptible Intermediate Resistant Azithromycin (0.12) None Chloramphenicol (>128) Ceftaroline ( 0.06) Clindamycin (>2) Ceftriaxone (1) Linezolid (8) Daptomycin (1) Penicillin (1) Dalbavancin (0.008) Doxycycline ( 0.06) Erythromycin ( 0.06) Gentamicin ( 1) Levofloxacin (0.25) Minocycline ( 0.06) Oritavancin (0.03) Oxacillin ( 0.25) Quinupristin-Dalfopristin (1) Telavancin (0.06) Teicoplanin ( 0.5) Tetracycline ( 0.5) Tigecycline (0.12) TMP-SMX b ( 0.5) Vancomycin (0.5) a. Susceptibility categories determined by CLSI M100-S26 (2016) and EUCAST (2016) [3-5]. b. TMP-SMX = trimethoprim-sulfamethoxazole

4 Table 2. Participant performance for selected agents ( 50 response by one or both tests) listed by disk agar diffusion (DD) and quantitative MIC methods for ES-02 (2016), a S.capitis with a cfr gene. DD MIC Antimicrobial Agent Acceptable Category a No. % correct No. % correct Amoxicillin-Clavulanate Susceptible Ampicillin Resistant Ampicillin-Sulbactam Susceptible Azithromycin Susceptible Cefazolin Susceptible Ceftriaxone Susceptible Chloramphenicol Resistant Ciprofloxacin Susceptible Clindamycin Resistant Daptomycin Susceptible Doxycycline Susceptible Erythromycin Susceptible-Intermediate Gentamicin Susceptible Imipenem Susceptible Levofloxacin Susceptible Linezolid Resistant Moxifloxacin Susceptible Oxacillin Susceptible Penicillin Resistant Quinupristin-Dalfopristin Susceptible Rifampin Susceptible TMP-SMX b Susceptible Tetracycline Susceptible Tigecycline Susceptible Vancomycin Susceptible a. Correct categorical interpretation was determined by the reference MIC using the M07-A10 method [1], and CLSI M100-S26, EUCAST and USCAST breakpoint criteria [3-5], where available (exception tigecycline) [6]. b. TMP-SMX = trimethoprim-sulfamethoxazole The ability of contemporary systems to detect this low-level resistance across the five drug classes was generally poor, with greatest accuracy observed for chloramphenicol (76.5%) and clindamycin (72.4%). Detection was particularly suboptimal for the oxazolidinones (linezolid at 10.7%). Erythromycin remained active with 98.6% susceptible or intermediate results reported. The discord of clindamycin- resistant and active macrolide results should promote a high suspicion for this emerging type of acquired transmissible resistance gene. The two other drug classes compromised by this mechanism were either not

5 tested/reported (pleuromutilins) or were tested in combination (quinupristin-dalfopristin), where the other component remains active thus producing a susceptible category result (1µg/ml; Table 1). The ability of various commercial systems to recognize the elevated MIC values for linezolid ranged from 0.0% (BD Phoenix, Sensititre) to 7.3% (MicroScan) to only 20.0% (Vitek 2). The clindamycin resistance was best determined by Vitek 2 (76.9%) > MicroScan (68.4%) > disk diffusion method (62.5%). MicroScan was the only method reported for chloramphenicol MIC testing with 76.5% correct resistant MICs among 51 results. Vitek 2 (357 responses) and MicroScan (354 responses) dominated the MIC values at a 98.2% combined use level, based on reported vancomycin results. Therapeutic Considerations for Serious CoNS Infections in Children Neonatal sepsis is an infection that occurs in the first 28 days of life, or up to 4 weeks after the expected due date for preterm infants. 18 Two types of infections are defined: early-onset neonatal sepsis (EONS), which occurs up to 7 days in postnatal life, and late-onset neonatal sepsis (LONS). 18 In the pre-antibiotic era, the case fatality rate of neonatal sepsis was high, exceeding 80%. 19 The fatality rate fell to less than 20% overall by the 1960s due to the introduction of antimicrobials and the development of modern perinatal care. 19 CoNS are ubiquitous in the environment, readily colonize newborns, and remain part of normal microflora throughout life. 21 They have the ability to colonize and grow on indwelling medical device surfaces and form biofilms. 21 Because of these characteristics, CoNS are the most common cause of bacteremia related to indwelling devices, and most of these infections have been hospital-acquired. CoNS cause a variety of serious infections that include central nervous system shunt infections, native or prosthetic valve endocarditis, urinary tract infections, bone and joint infections, and endophthalmitis. 22 CoNS have been reported as the most common cause of bloodstream infections in neonatal intensive care units. 23,24 In the 2015 USA SENTRY Antimicrobial Surveillance Program, CoNS was the 5th most common organism isolated (5.8%) from all significant bloodstream infections, and S. capitis represented 5.8% of the CoNS isolates identified using MALDI-TOF-MS. The clinical significance of a positive blood culture for CoNS may be difficult to assess. Various clinical and laboratory definitions have been proposed to differentiate true infection from contamination, and the most commonly used criteria requires at least two positive blood cultures collected from two different venous sampling sites. 25 In the pediatric population, however, it is uncommon to collect multiple blood culture bottles, especially for neonates. 26 Guidelines for obtaining adequate blood culture specimens for adults are well described, but they are less clear in pediatric populations. 27 The single most important

6 factor in recovering pathogens from blood is the volume of the sample. Due to the potentially very small size of neonates, this may present a difficulty. 27 Current IDSA and ASM guidelines recommend collecting 3-4% of total patient blood volume when patients weigh <12.7 kg, and % when >12.8 kg. 28 Lowlevel bacteremia may be more common than previously believed, and <1 ml of blood collected may be inadequate to detect <4 CFU/ml. 29 CoNS exhibit a high rate of methicillin (oxacillin) resistance (63.4% in the global SENTRY Program, ), and resistance to multiple other antimicrobial agents further complicates the treatment of systemic infections. Although CoNS are usually susceptible to glycopeptides, increased MIC values for teicoplanin (32.3% at 4 μg/ml) and/or vancomycin (28.2% at 2 μg/ml [SENTRY ]) are being more frequently reported and may be associated with poor clinical outcome. 30,31 Oxazolidinone resistance is uncommon with only 0.4% of isolates from the global SENTRY Program ( ) exhibiting linezolid MIC values 8 µg/ml. In the SENTRY Program ( ), all CoNS were susceptible to vancomycin and >99.9% susceptible to daptomycin. Pathogens associated with EONS are typically Enterobacteriaceae, Group B streptococci, Enterococcus spp. and Listeria monocytogenes [32, 33]. The most common bacterial species associated with LONS catheter-associated infections are CoNS and S. aureus. 32,33 Initial therapies may include penicillinase-resistant penicillins (oxacillin, nafcillin) and gentamicin. 32,33 Where methicillin resistance in staphylococci is high, therapies should include vancomycin and an aminoglycoside (gentamicin). If new symptoms occur, then amikacin or a third-generation cephalosporin may be added. 32,33 Emerging Resistance Mechanisms Among CoNS Bacterial resistance to the oxazolidinone agents (linezolid) was described during drug development as occurring at a frequency of <1 resistant mutant per CFU of S. aureus ATCC 29213, and was even more remote among enterococci. 34 Some isolates developed resistance during Phase 3 trials for linezolid, followed by sporadic reports of resistance occurrence after regulatory agency approval. These cases were well investigated and proven to be dominantly associated with mutations in the bacterial 23S ribosomal RNA. 35 These early studies were followed by several reports documenting the development of linezolid resistance among Gram-positive isolates and most cases were associated with prolonged therapeutic exposure to linezolid (>21 days) Over 15 years of successful clinical use, low rates of resistance have been documented during global surveillance studies. 40,41 However, despite this favorable scenario, the dynamics of linezolid resistance have changed drastically, especially among coagulase-negative staphylococci (CoNS) and Enterococcus faecalis. 35,41 Although alterations in the 23S rrna gene were the main resistance

7 mechanism reported earlier and still remain commonly detected in Enterococcus faecium, other mechanisms have been recently documented, including plasmid-mediated resistance determinants. Among the latter, the cfr gene has been observed among staphylococci, 42,43 but several reports have described the detection of cfr among other bacterial species of human and animal origin. 44,45 Despite its propensity for genetic mobilization, the prevalence of isolates carrying cfr has not increased over time, although sporadic hospital-based outbreaks have been documented. 40,41,46-49 optra was another more recently described plasmid-located resistance gene, which encodes for an ATP-binding cassette transporter (efflux-pump) that results in resistance or elevated MIC values for oxazolidinones (linezolid and tedizolid) and phenicols (chloramphenicol and florfenicol). 50 This gene was initially detected in E. faecalis and E. faecium isolates of human and animal origin in the Asia-Western Pacific region. 50,51 However, more recent studies reported the presence of optra-positive E. faecalis isolates causing infections in patients hospitalized in the USA and Europe. 40,41 In fact, optra has become as prevalent as mutations in the 23S rrna gene in surveillance E. faecalis isolates during the most recent years, 52 and reports have documented the concomitant presence of cfr and optra. 53,54 The scenario of oxazolidinone resistance has also changed significantly among S. epidermidis and other species of CoNS, where resistance was initially less prevalent, and when detected, typically presented the usual alterations in 23S rrna. 35 Currently, these isolates exhibit more diverse and complex mechanisms of resistance. Among these, alterations in the ribosomal proteins L3 and L4 have become commonplace for the linezolid-nonsusceptible CoNS, and are often observed in conjunction with modifications in the 23S rrna and/or the presence of cfr. 35,40,41 The presence of linezolid resistance mechanisms in CoNS may become a serious concern, since these organisms have gained clinical relevance (LONS) and certain lineages can adapt and become established in the nosocomial environment thus causing opportunistic infections. 55 Moreover, these CoNS can serve as a reservoir for cfr transfer to the other Gram-positive species. The strain associated with ES-02 was sent to illustrate the emerging linezolid resistance mechanisms (alterations in L3 and L4 with concomitant presence of cfr and/or 23S rrna gene mutations) currently observed among CoNS clinical isolates. References 1. CLSI. M07-A10. Methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically; approved standard- tenth edition. Wayne, PA: Clinical and Laboratory Standards Institute; CLSI. M02-A12. Performance standards for antimicrobial disk susceptibility tests; Twelfth Edition. Wayne, PA: Clinical and Laboratory Standards Institute; 2015.

8 3. CLSI. M100-S26. Performance standards for antimicrobial susceptibility testing: 26th informational supplement. Wayne, PA: Clinical and Laboratory Standards Institute; EUCAST. Breakpoint tables for interpretation of MICs and zone diameters. Version 6.0, January 2016.: European Committee on Antimicrobial Susceptibility Testing; USCAST. Breakpoint tables for interpretations of MICs and Zone Diameters, Version 2.0, June 2016; Tygacil. Tygacil Package Insert. Philadelphia, PA: Wyeth Pharmeceuticals; Jorgensen JH, Pfaller MA, Carroll KC, Funke G, Landry ML, Richter SS, et al. Manual of Clinical Microbiology, 11th ed. Washington, D.C.: ASM Press; Bannerman TL, Kloos WE. Staphylococcus capitis subsp. ureolyticus subsp. nov. from human skin. Int J Syst Bacteriol Jan;41(1): Dubois D, Leyssene D, Chacornac JP, Kostrzewa M, Schmit PO, Talon R, et al. Identification of a variety of Staphylococcus species by matrix-assisted laser desorption ionization-time of flight mass spectrometry. J Clin Microbiol Mar;48(3): Kim M, Heo SR, Choi SH, Kwon H, Park JS, Seong MW, et al. Comparison of the MicroScan, VITEK 2, and Crystal GP with 16S rrna sequencing and MicroSeq 500 v2.0 analysis for coagulase-negative Staphylococci. BMC Microbiol. 2008;8: Patteet L, Goossens H, Ieven M. Validation of the MicroScan-96 for the species identification and methicillin susceptibility testing of clinical significant coagulase-negative staphylococci. Eur J Clin Microbiol Infect Dis May;31(5): Alexopoulou K, Foka A, Petinaki E, Jelastopulu E, Dimitracopoulos G, Spiliopoulou I. Comparison of two commercial methods with PCR restriction fragment length polymorphism of the tuf gene in the identification of coagulase-negative staphylococci. Lett Appl Microbiol Oct;43(4): Heikens E, Fleer A, Paauw A, Florijn A, Fluit AC. Comparison of genotypic and phenotypic methods for species-level identification of clinical isolates of coagulase-negative staphylococci. J Clin Microbiol May;43(5): Delport JA, Peters G, Diagre D, Lannigan R, John M. Identification of coagulase-negative Staphylococci by the Bruker MALDI-TOF Biotyper Compared to the Vitek 2 and MIS Gas liquid chromatography. J Bacteriol Mycol Open Access. 2015;1(1): Becker K, Heilmann C, Peters G. Coagulase-negative staphylococci. Clin Microbiol Rev Oct;27(4):

9 16. Cone LA, Sontz EM, Wilson JW, Mitruka SN. Staphylococcus capitis endocarditis due to a transvenous endocardial pacemaker infection: case report and review of Staphylococcus capitis endocarditis. Int J Infect Dis Nov;9(6): Butin M, Rasigade JP, Martins-Simoes P, Meugnier H, Lemriss H, Goering RV, et al. Wide geographical dissemination of the multiresistant Staphylococcus capitis NRCS-A clone in neonatal intensive-care units. Clin Microbiol Infect Sep 25:in press. 18. Qazi SA, Stoll BJ. Neonatal sepsis: a major global public health challenge. The Pediatric infectious disease journal Jan;28(1 Suppl):S Bizzarro MJ, Raskind C, Baltimore RS, Gallagher PG. Seventy-five years of neonatal sepsis at Yale: Pediatrics Sep;116(3): Kloos WE, Musselwhite MS. Distribution and persistence of Staphylococcus and Micrococcus species and other aerobic bacteria on human skin. Appl Microbiol Biotechnol Sep;30(3): Uckay I, Pittet D, Vaudaux P, Sax H, Lew D, Waldvogel F. Foreign body infections due to Staphylococcus epidermidis. Ann Med. 2009;41(2): Casey AL, Lambert PA, Elliott TS. Staphylococci. Int J Antimicrob Agents May;29 Suppl 3:S Gaynes RP, Edwards JR, Jarvis WR, Culver DH, Tolson JS, Martone WJ. Nosocomial infections among neonates in high-risk nurseries in the United States. National Nosocomial Infections Surveillance System. Pediatrics Sep;98(3 Pt 1): Stoll BJ, Hansen N, Fanaroff AA, Wright LL, Carlo WA, Ehrenkranz RA, et al. Late-onset sepsis in very low birth weight neonates: the experience of the NICHD Neonatal Research Network. Pediatrics Aug;110(2 Pt 1): Elzi L, Babouee B, Vogeli N, Laffer R, Dangel M, Frei R, et al. How to discriminate contamination from bloodstream infection due to coagulase-negative staphylococci: A prospective study with 654 patients. Clin Microbiol Infect Jun 12;18:E355-E Connell TG, Rele M, Cowley D, Buttery JP, Curtis N. How reliable is a negative blood culture result? Volume of blood submitted for culture in routine practice in a children's hospital. Pediatrics May;119(5): Dien Bard J, McElvania TeKippe E. Diagnosis of Bloodstream Infections in Children. J Clin Microbiol Jun;54(6): Baron EJ, Miller JM, Weinstein MP, Richter SS, Gilligan PH, Thomson RB, Jr., et al. A guide to utilization of the microbiology laboratory for diagnosis of infectious diseases: 2013

10 recommendations by the Infectious Diseases Society of America (IDSA) and the American Society for Microbiology (ASM)(a). Clin Infect Dis Aug;57(4):e22-e Schelonka RL, Chai MK, Yoder BA, Hensley D, Brockett RM, Ascher DP. Volume of blood required to detect common neonatal pathogens. J Pediatr Aug;129(2): Tacconelli E, Tumbarello M, Donati KG, Bettio M, Spanu T, Leone F, et al. Glycopeptide resistance among coagulase-negative staphylococci that cause bacteremia: epidemiological and clinical findings from a case-control study. Clin Infect Dis Nov 15;33(10): Cremniter J, Slassi A, Quincampoix JC, Sivadon-Tardy V, Bauer T, Porcher R, et al. Decreased susceptibility to teicoplanin and vancomycin in coagulase-negative Staphylococci isolated from orthopedic-device-associated infections. J Clin Microbiol Apr;48(4): Schlossberg D. Clinical Infectious Disease. Cambridge, United Kingdom: Cambridge University Press; Marchant EA, Boyce GK, Sadarangani M, Lavoie PM. Neonatal sepsis due to coagulase-negative staphylococci. Clin Dev Immunol. 2013;2013: Zurenko GE, Yagi BH, Schaadt RD, Allison JW, Kilburn JO, Glickman SE, et al. In vitro activities of U and U , novel oxazolidinone antibacterial agents. Antimicrob Agents Chemother Apr;40(4): Mendes RE, Deshpande LM, Jones RN. Linezolid update: stable in vitro activity following more than a decade of clinical use and summary of associated resistance mechanisms. Drug Resist Updat Apr;17(1-2): Tsiodras S, Gold HS, Sakoulas G, Eliopoulos GM, Wennersten C, Venkataraman L, et al. Linezolid resistance in a clinical isolate of Staphylococcus aureus. Lancet Jul 21;358(9277): Tsakris A, Pillai SK, Gold HS, Thauvin-Eliopoulos C, Venkataraman L, Wennersten C, et al. Persistence of rrna operon mutated copies and rapid re-emergence of linezolid resistance in Staphylococcus aureus. J Antimicrob Chemother Sep;60(3): Meka VG, Gold HS. Antimicrobial resistance to linezolid. Clin Infect Dis Oct 1;39(7): ZYVOX. ZYVOX Package Insert Mendes RE, Hogan PA, Jones RN, Sader HS, Flamm RK. Surveillance for linezolid resistance via the Zyvox(R) Annual Appraisal of Potency and Spectrum (ZAAPS) programme (2014): evolving resistance mechanisms with stable susceptibility rates. J Antimicrob Chemother Mar 23;71(7):

11 41. Flamm RK, Mendes RE, Hogan PA, Streit JM, Ross JE, Jones RN. Linezolid surveillance results for the United States (LEADER Surveillance Program 2014). Antimicrob Agents Chemother Feb 1;60(4): Mendes RE, Deshpande LM, Castanheira M, DiPersio J, Saubolle MA, Jones RN. First report of cfr-mediated resistance to linezolid in human staphylococcal clinical isolates recovered in the United States. Antimicrob Agents Chemother Jun;52(6): Long KS, Poehlsgaard J, Kehrenberg C, Schwarz S, Vester B. The cfr rrna methyltransferase confers resistance to phenicols, lincosamides, oxazolidinones, pleuromutilins, and streptogramin A antibiotics. Antimicrob Agents Chemother Jul;50(7): Shen J, Wang Y, Schwarz S. Presence and dissemination of the multiresistance gene cfr in Grampositive and Gram-negative bacteria. J Antimicrob Chemother Aug;68(8): Deshpande LM, Ashcraft DS, Kahn HP, Pankey G, Jones RN, Farrell DJ, et al. Detection of a New cfr-like Gene, cfr(b), in Enterococcus faecium Isolates Recovered from Human Specimens in the United States as Part of the SENTRY Antimicrobial Surveillance Program. Antimicrob Agents Chemother Oct;59(10): Mendes RE, Deshpande LM, Bonilla HF, Schwarz S, Huband MD, Jones RN, et al. Dissemination of a pscfs3-like cfr-carrying plasmid in Staphylococcus aureus and Staphylococcus epidermidis clinical isolates recovered from hospitals in Ohio. Antimicrob Agents Chemother Jul;57(7): Morales G, Picazo JJ, Baos E, Candel FJ, Arribi A, Pelaez B, et al. Resistance to linezolid is mediated by the cfr gene in the first report of an outbreak of linezolid-resistant Staphylococcus aureus. Clin Infect Dis. 2010;50(6): O'Connor C, Powell J, Finnegan C, O'Gorman A, Barrett S, Hopkins KL, et al. Incidence, management and outcomes of the first cfr-mediated linezolid-resistant Staphylococcus epidermidis outbreak in a tertiary referral centre in the Republic of Ireland. J Hosp Infect Aug;90(4): Baos E, Candel FJ, Merino P, Pena I, Picazo JJ. Characterization and monitoring of linezolidresistant clinical isolates of Staphylococcus epidermidis in an intensive care unit 4 years after an outbreak of infection by cfr-mediated linezolid-resistant Staphylococcus aureus. Diagn Microbiol Infect Dis Jul;76(3): Wang Y, Lv Y, Cai J, Schwarz S, Cui L, Hu Z, et al. A novel gene, optra, that confers transferable resistance to oxazolidinones and phenicols and its presence in Enterococcus faecalis and Enterococcus faecium of human and animal origin. J Antimicrob Chemother Aug;70(8):

12 51. Cai J, Wang Y, Schwarz S, Lv H, Li Y, Liao K, et al. Enterococcal isolates carrying the novel oxazolidinone resistance gene optra from hospitals in Zhejiang, Guangdong, and Henan, China, Clin Microbiol Infect Dec;21(12):1095 e RE Mendes LD, M Castanheira, RK Flamm. Evolving linezolid resistance mechanisms in a worldwide collection of Enterococcal clinical isolates: results from the SENTRY antimicrobial surveillance program. ASM Microbe; 2016; Boston, MA, USA; Li D, Wang Y, Schwarz S, Cai J, Fan R, Li J, et al. Co-location of the oxazolidinone resistance genes optra and cfr on a multiresistance plasmid from Staphylococcus sciuri. J Antimicrob Chemother Jun;71(6): Brenciani A, Morroni G, Vincenzi C, Manso E, Mingoia M, Giovanetti E, et al. Detection in Italy of two clinical Enterococcus faecium isolates carrying both the oxazolidinone and phenicol resistance gene optra and a silent multiresistance gene cfr. J Antimicrob Chemother Apr;71(4): Mendes RE, Deshpande LM, Costello A, Farrell DJ. Molecular epidemiology of Staphylococcus epidermidis clinical isolates from USA hospitals. Antimicrob Agents Chemother Jun 11;56(9):