Antimicrobial activity of daptomycin in comparison to glycopeptides and other antimicrobials when tested against numerous species of coagulase-negative Staphylococcus

Pathogenic Potential of Turicella otitidis and Staphylococcus auricularis: A Case Report

Objective: Turicella otitidis and Staphylococcus auricularis have been considered normal aural flora. Their significance in active infection is controversial. We examined a series of patients presenting with acute and chronic otitis media whose ear canal culture isolated T. otitidis and S. auricularis and explored possible pathogenicity, associated factors, and outcomes. Methods: This is a retrospective chart review of patients who presented to a tertiary center outpatient clinic between 2017 and 2022 with otologic microscopic examination of active infection and ear canal culture isolating T. otitidis or S. auricularis only. Clinical course was collected including history, microscopic otoscopy findings, interventions given, outcomes, and sensitivity results. Results: A total of 13 patients (10 with T. otitidis and 3 with S. auricularis) were included. Majority of the patients had a history of otologic surgery (92%) and tympanic membrane perforation (62%). All were treated with combinations of antibiotic otic drops (ie, fluoroquinolone, sulfa, or aminoglycoside based) ± oral antibiotics (ie, penicillin or trimethoprim/sulfamethoxazole). Otorrhea resolved among majority of patients. Otorrhea and mucosalization returned or continued among 4 patients. Sensitivity results demonstrated that 2 of 3 strains of T. otitidis were resistant to clindamycin. There was no resistance against S. auricularis for tested antibiotics. Conclusions: Our findings suggest the potential pathogenicity of T. otitidis and S. auricularis, especially among patients with prior ear surgery and tympanic membrane perforation. Violation of the epithelial barrier from surgery or trauma may contribute to their pathogenicity. Future study is warranted to elucidate pathogenicity of normal aural flora and its mechanisms.

Decreased susceptibility to vancomycin and other mechanisms of resistance to antibiotics in Staphylococcus epidermidis as a therapeutic problem in hospital treatment

Multidrug-resistant coagulase-negative staphylococci represent a real therapeutic challenge. The aim of the study was to emphasize the importance of heteroresistance to vancomycin presence in methicillin-resistant strains of S. epidermidis. The research comprised 65 strains of S. epidermidis. Heteroresistance to vancomycin was detected with the use of the agar screening method with Brain Heart Infusion and a population profile analysis (PAP test). In addition, types of cassettes and genes responsible for resistance to antibiotics for 22 multidrug resistant strains were determined. Our investigations showed that 56 of 65 S. epidermidis strains were phenotypically resistant to methicillin. The tested strains were mostly resistant to erythromycin, gentamicin, clindamycin, and ciprofloxacin. Six strains showed decreased susceptibility to vancomycin and their heterogeneous resistance profiles were confirmed with the PAP test. All tested multi-resistant strains exhibited the mecA gene. More than half of them possessed type IV cassettes. ant(4')-Ia and aac(6')/aph(2''), ermC and tetK genes were most commonly found. The described phenomenon of heteroresistance to vancomycin in multidrug resistant bacteria of the Staphylococcus genus effectively inhibits a therapeutic effect of treatment with this antibiotic. That is why it is so important to search for markers that will enable to identify heteroresistance to vancomycin strains under laboratory conditions.

Vancomycin heteroresistance among methicillin-resistant clinical isolates S. haemolyticus, S. hominis, S. simulans, and S. warneri

Besides being an essential part of the skin microbiome, coagulase-negative staphylococci are the etiological factors of serious infections. The aim of the study was to evaluate the heteroresistance to vancomycin and the potential antimicrobial efficacy of teicoplanin and daptomycin against the multiresistant strains of S. haemolyticus, S. hominis, S. warneri, and S. simulans. The study covered 80 clinical coagulase-negative staphylococci. Teicoplanin, vancomycin, and daptomycin MICs for the tested strains were determined according to EUCAST recommendation. The vanA and vanB genes were searched. The brain heart infusion screen agar method detected vancomycin heteroresistance. The population analysis profile method and analysis of autolytic activity were applied for the strains growing on BHI containing 4 mg/L vancomycin. Seven S. haemolyticus, two S. hominis, and two S. warneri strains presented a heterogeneous resistance to vancomycin. Their subpopulations were able to grow on a medium containing 4-12 mg/L of vancomycin. Monitoring heteroresistance to peptide antibiotics, which are often the last resort in staphylococcal infections, is essential due to the severe crisis in antibiotic therapy and the lack of alternatives to treat infections with multiresistant strains. Our work highlights the selection of resistant strains and the need for more careful use of peptide antibiotics.

Prevalence of Antimicrobial Resistance in Select Bacteria From Retail Seafood-United States, 2019

In 2019, the United States National Antimicrobial Resistance Monitoring System (NARMS) surveyed raw salmon, shrimp, and tilapia from retail grocery outlets in eight states to assess the prevalence of bacterial contamination and antimicrobial resistance (AMR) in the isolates. Prevalence of the targeted bacterial genera ranged among the commodities: Salmonella (0%-0.4%), Aeromonas (19%-26%), Vibrio (7%-43%), Pseudomonas aeruginosa (0.8%-2.3%), Staphylococcus (23%-30%), and Enterococcus (39%-66%). Shrimp had the highest odds (OR: 2.8, CI: 2.0-3.9) of being contaminated with at least one species of these bacteria, as were seafood sourced from Asia vs. North America (OR: 2.7; CI: 1.8-4.7) and Latin America and the Caribbean vs. North America (OR: 1.6; CI: 1.1-2.3) and seafood sold at the counter vs. sold frozen (OR: 2.1; CI: 1.6-2.9). Isolates exhibited pan-susceptibility (Salmonella and P. aeruginosa) or low prevalence of resistance (<10%) to most antimicrobials tested, with few exceptions. Seafood marketed as farm-raised had lower odds of contamination with antimicrobial resistant bacteria compared to wild-caught seafood (OR: 0.4, CI: 0.2-0.7). Antimicrobial resistance genes (ARGs) were detected for various classes of medically important antimicrobials. Clinically relevant ARGs included carbapenemases (bla IMI-2, bla NDM-1) and extended spectrum β-lactamases (ESBLs; bla CTX-M-55). This population-scale study of AMR in seafood sold in the United States provided the basis for NARMS seafood monitoring, which began in 2020.

Clinical Infections, Antibiotic Resistance, and Pathogenesis of Staphylococcus haemolyticus

Staphylococcus haemolyticus (S. haemolyticus) constitutes the main part of the human skin microbiota. It is widespread in hospitals and among medical staff, resulting in being an emerging microbe causing nosocomial infections. S. haemolyticus, especially strains that cause nosocomial infections, are more resistant to antibiotics than other coagulase-negative Staphylococci. There is clear evidence that the resistance genes can be acquired by other Staphylococcus species through S. haemolyticus. Severe infections are recorded with S. haemolyticus such as meningitis, endocarditis, prosthetic joint infections, bacteremia, septicemia, peritonitis, and otitis, especially in immunocompromised patients. In addition, S. haemolyticus species were detected in dogs, breed kennels, and food animals. The main feature of pathogenic S. haemolyticus isolates is the formation of a biofilm which is involved in catheter-associated infections and other nosocomial infections. Besides the biofilm formation, S. haemolyticus secretes other factors for bacterial adherence and invasion such as enterotoxins, hemolysins, and fibronectin-binding proteins. In this review, we give updates on the clinical infections associated with S. haemolyticus, highlighting the antibiotic resistance patterns of these isolates, and the virulence factors associated with the disease development.

A case of acute focal bacterial nephritis caused by methicillin-resistant Staphylococcus saprophyticus in a 13-year-old adolescent girl treated with daptomycin

Staphylococcus saprophyticus is a gram-positive, coagulase-negative member of the Staphylococcus genus and is second only to Escherichia coli as a cause of urinary tract infections in the young female population. S. saprophyticus usually has good susceptibility to drugs commonly used to treat urinary tract infections, but it is often methicillin-resistant. Here we report a case of acute focal bacterial nephritis in a 13-year-old female patient caused by methicillin-resistant S. saprophyticus and treated with daptomycin (DAP). The patient had a history of unilateral hearing loss and presented to her previous physician with a 3-day history of fever, right-sided abdominal pain, and diarrhea. Cefotaxime antimicrobial chemotherapy was initiated as an empiric therapy targeting E. coli, the most frequent cause of community-onset pyelonephritis. Vancomycin (VCM) was started for acute focal bacterial nephritis caused by methicillin-resistant S. saprophyticus but was stopped due to allergy and replaced with DAP. After 13 days of treatment with DAP, the patient received 17 days of treatment with sulfamethoxazole-trimethoprim combination therapy. The patient experienced no adverse events and did not relapse. DAP is a relatively new anti-methicillin-resistant Staphylococcus aureus drug used to treat gram-positive cocci infections. It is primarily excreted by the kidneys, which may be desirable in treating urinary tract infections. For children who cannot receive VCM for any reason, DAP may be a viable alternative.

•

S. saprophyticus is a common cause of urinary tract infections in young women.

•

The use of daptomycin for urinary tract infections in children is rare.

•

Vancomycin (VCM) is usually used to treat methicillin-resistant S. saprophyticus.

•

If VCM is unavailable, daptomycin can used to treat urinary tract infections in such cases.

Tailoring Antimicrobial Susceptibility Testing to Individual Species of Coagulase-Negative Staphylococci: Next Up, Staphylococcus epidermidis

Accurate detection of methicillin resistance among staphylococci is vital for patient care. Methicillin resistance is most commonly mediated by acquisition of the mecA gene, which encodes an altered penicillin binding protein, PBP2a. Application of phenotypic methods to detect mecA-mediated beta-lactam resistance in staphylococci is becoming more complex as species-specific differences are identified among coagulase-negative staphylococci (CoNS). Previously, interpretative criteria and antimicrobial susceptibility testing (AST) methods specific to the CoNS group were used to evaluate Staphylococcus epidermidis A manuscript by S. N. Naccache, K. Callan, C.-A. D. Burnham, M. A. Wallace, et al. (J Clin Microbiol 57:e00961-19, 2019, https://doi.org/10.1128/JCM.00961-19) details experiments revealing that S. epidermidis, the most common clinically isolated CoNS, requires tailored use of previously described methods and interpretive criteria to reliably identify the presence of mecA-mediated methicillin resistance.

Prevalence of mupirocin and chlorhexidine resistance among methicillin-resistant coagulase-negative staphylococci isolated during methicillin-resistant Staphylococcus aureus decolonization strategies

BACKGROUND

The widespread of methicillin-resistant Staphylococcus aureus (MRSA) antimicrobial decolonization in the clinical setting may lead to an increase in the prevalence of multiresistance to coagulase-negative staphylococci (CoNS) owing to their selection. This study aimed to investigate the impact of MRSA decolonization strategies, using mupirocin and chlorhexidine, on their CoNS susceptibility.

METHODS

A total of 312 CoNS isolates were collected before starting the decolonization protocols "baseline strains" (BLS) group, 330 isolates were collected after application of the targeted decolonization protocol "targeted decolonization strains" group, and 355 isolates were collected after application of the universal decolonization protocol "universal decolonization strains" group. Methicillin-resistant CoNS (MR-CoNS) were identified and tested for mupirocin and chlorhexidine susceptibilities. Heptaplex polymerase chain reaction assay was applied for simultaneous screening for chlorhexidine (CHX-R) and mupirocin resistance (Mu-R) genes.

RESULTS

Mu-R prevalence of MR-CoNS among the BLS group was considered moderate (9.1%); however, CHX-R in the BLS group was 5.8%, the rate of which significantly increased among the universal decolonization strains group.

DISCUSSION

Both MRSA decolonization strategies have an additional benefit in reducing the prevalence of MR-CoNS. The prevalence Mu-R rate didn't change significantly during either of the MRSA decolonization practices that may be due to the local nature of mupirocin application on the nasal mucosa only. In contrast CHX-R that was found to be significantly higher among the UDS group.

CONCLUSIONS

Our findings indicate that both MRSA decolonization strategies have an additional benefit in reducing the prevalence of MR-CoNS. Although the universal MRSA decolonization has superior efficacy in decolonization of CoNS, it may increase the risk of selecting CHX-R and Mu-R. In addition, other potential resistance genes should be studied.

Evolution of Daptomycin Resistance in Coagulase-Negative Staphylococci Involves Mutations of the Essential Two-Component Regulator WalKR

Coagulase-negative staphylococci (CoNS) represent one of the major causes of health care- and medical device-associated infections. Emerging antimicrobial resistance has complicated the treatment of systemic infections caused by CoNS. Here, we describe the prevalence of antimicrobial resistance in clinical CoNS strains from a tertiary care hospital over a 4-year period, and we observed a significant increase in resistance to daptomycin. Notably, Staphylococcus capitis accounted for the majority of these daptomycin-resistant (DAP-R) CoNS. To further investigate the mechanisms of daptomycin resistance in CoNS, daptomycin-susceptible clinical strains of S. capitis and Staphylococcus epidermidis underwent in vitro daptomycin exposure to generate DAP-R CoNS mutants. Unlike that seen with Staphylococcus aureus, alteration of cell surface charge was not observed in the DAP-R CoNS strains, but biofilm formation was compromised. Whole-genome sequencing analysis of the DAP-R CoNS strains identified single nucleotide polymorphisms (SNPs) in walKR, the essential two-component regulatory system controlling cell wall biogenesis. PCR and sequencing of walK and walR from 17 DAP-R CoNS clinical isolates identified seven nonsynonymous mutations. The results were confirmed by the recreation of the walK SNP in S. epidermidis, which resulted in reduced susceptibility to daptomycin and vancomycin. This study highlights the significance of CoNS in evolving daptomycin resistance and showed that walKR is shared among the staphylococcal species and is involved in antibiotic resistance development. Notably, we did not observe mutations in genes responsible for phospholipid biosynthesis or an altered cell surface charge, suggesting that reduced daptomycin susceptibility in CoNS may emerge in a fashion distinct from that in S. aureus.

Emergence of daptomycin non-susceptible coagulase-negative Staphylococci in patients with cardiovascular device infections: Two cases report investigated by whole genome analysis

RATIONALE

Daptomycin (DAP) is a key drug for treating severe Staphylococcus infections. The emergence of DAP non-susceptible Staphylococcus aureus has been widely recognized in clinical situations, although the clinical status of DAP non-susceptible coagulase-negative Staphylococcus (CoNS) infections is unclear. We encountered 2 cases of cardiovascular device infections that were associated with DAP non-susceptible CoNS.

PATIENT CONCERNS

The first case involved a 60-year-old woman with a pump pocket infection in a left ventricular assist device. DAP non-susceptible Staphylococcus capitis subsp. ureolyticus was isolated from a blood culture after treatment using vancomycin (10 days) and DAP (6 days). The second case involved a 71-year-old man with an aortic graft infection. DAP non-susceptible S capitis subsp. ureolyticus was detected in pus after treatment using vancomycin (2 weeks) and DAP (1 week) without complete removal and debridement.

DIAGNOSIS

Cardiovascular device infections caused by DAP non-susceptible CoNS.

INTERVENTIONS AND OUTCOMES

Whole genome sequencing of these strains revealed multiple mutations in genes that are related to DAP-non-susceptibility in S aureus, which created amino acid substitutions in mprF, dltAB, dltD, rpoC, yycG, cls2, pgsA, and vraSR. To the very best of our knowledge, the substitution patterns were not identical to those previously reported in DAP non-susceptibile S aureus.

LESSONS

Clinicians should be cautious regarding the emergence of DAP non-susceptible CoNS, especially in cases with implanted prosthetic devices, inadequate debridement, and prior usage of vancomycin and DAP. Further studies are needed to understand the relevance of these genetic changes and DAP-non-susceptibility in CoNS strains.

Are coagulase-negative staphylococci virulent?

BACKGROUND

Progress in contemporary medicine is associated with an increasing number of immunocompromised individuals. In this vulnerable group, the underlying disease together with long-term hospitalization and the use of medical devices facilitate infections by opportunistic pathogens, of which coagulase-negative staphylococci (CoNS) represent a prime example.

OBJECTIVES

The diversity of CoNS with species- and strain-specific differences concerning virulence and clinical impact is highlighted. A focus is on the ability of CoNS to generate biofilms on biotic and abiotic surfaces, which enables skin and mucosa colonization as well as establishment of CoNS on indwelling foreign bodies.

SOURCES

Literature about the virulence of CoNS listed in PubMed was reviewed.

CONTENT

Most catheter-related and prosthetic joint infections as well as most other device-related infections are caused by CoNS, specifically by Staphylococcus epidermidis and Staphylococcus haemolyticus. A common theme of CoNS infections is a high antibiotic resistance rate, which often limits treatment options and contributes to the significant health and economic burden imposed by CoNS.

IMPLICATIONS

Breaching the skin barrier along with the insertion of medical devices offers CoNS opportunities to gain access to host tissues and to sustain there by forming biofilms on foreign body surfaces. Biofilms represent the perfect niche to protect CoNS from both the host immune response and the action of antibiotics. Their particular lifestyle, combined with conditions that facilitate host colonization and infection, has led to the growing impact of CoNS as pathogens. Moreover, CoNS may serve as hidden reservoirs for antibiotic resistance and virulence traits.

Comparative activity of ceftobiprole against coagulase-negative staphylococci from the BSAC Bacteraemia Surveillance Programme, 2013-2015

Coagulase-negative staphylococci (CoNS) are a significant cause of bacteraemia, the treatment of which is becoming increasingly complex due to the emergence of multidrug-resistant strains. This study aimed to evaluate the in vitro activity of ceftobiprole, an advanced-generation cephalosporin, as compared with other antimicrobial agents against CoNS from patients with bacteraemia. As part of the British Society for Antimicrobial Chemotherapy (BSAC) Bacteraemia Surveillance Programme, 650 blood isolates of CoNS were obtained from patients with bacteraemia at 74 centres throughout the UK and Ireland for the years 2013–2015. Minimum inhibitory concentrations (MICs) of ceftobiprole and other antimicrobial agents were determined using the BSAC agar dilution method. Susceptibility was assessed by European Committee on Antimicrobial Susceptibility Testing (EUCAST) criteria. The majority of the isolates (63.2%) were Staphylococcus epidermidis. Overall, methicillin resistance, as determined by oxacillin susceptibility testing, was observed in 64.2% of isolates. The MIC_50/90 of ceftobiprole was 1/2 mg/L, and 100% of CoNS isolates were inhibited at the EUCAST ceftobiprole non-species-specific pharmacokinetic/pharmacodynamic breakpoint of 4 mg/L. Only one isolate was resistant to vancomycin. Overall rates of resistance to ciprofloxacin, clindamycin, erythromycin and teicoplanin were 50.5, 25.1, 68.2 and 20.9%, respectively. In S. epidermidis, resistance to oxacillin was associated with increased resistance to other antimicrobials. Ceftobiprole demonstrated in vitro activity against all CoNS species isolated from patients with bacteraemia and was active against species resistant to other antistaphylococcal antimicrobials. The collection of clinical data regarding the efficacy of ceftobiprole in treating CoNS bacteraemia is warranted.

Teicoplanin resistance in Staphylococcus haemolyticus is associated with mutations in histidine kinases VraS and WalK

We investigated the genetic basis of glycopeptide resistance in laboratory-derived strains of S. haemolyticus with emphasis on differences between vancomycin and teicoplanin. The genomes of two stable teicoplanin-resistant laboratory mutants selected on vancomycin or teicoplanin were sequenced and compared to parental S. haemolyticus strain W2/124. Only the two non-synonymous mutations, VraS Q289K and WalK V550L were identified. No other mutations or genome rearrangements were detected. Increased cell wall thickness, resistance to lysostaphin-induced lysis and adaptation of cell growth rates specifically to teicoplanin were phenotypes observed in a sequenced strain with the VraS Q289K mutation. Neither of the VraS Q289K and WalK V550L mutations was present in the genomes of 121S. haemolyticus clinical isolates. However, all but two of the teicoplanin resistant strains carried non-synonymous SNPs in vraSRTU and walKR-YycHIJ operons pointing to their importance for the glycopeptide resistance.

Clinical Characteristics of Methicillin-resistant Coagulase-negative Staphylococcal Bacteremia in a Tertiary Hospital

Objective Coagulase-negative staphylococci are among the most frequently isolated microorganisms in blood cultures. The aim of this study was to assess [1] the clinical characteristics of methicillin-resistant, coagulase-negative staphylococci bacteremia and [2] the susceptibility of the isolated bacteria to glycopeptides. Methods We retrospectively reviewed the medical records of 70 patients from whom methicillin-resistant coagulase-negative staphylococci had been isolated at Osaka City University Hospital between January 2010 and December 2013. We evaluated the patients' background, severity and prognosis of the disease, and the susceptibility of the isolated methicillin-resistant coagulase-negative staphylococci to glycopeptides. Results Out of the 70 patients tested, 28 (40.0%) had leukemia, and 36 (51.4%) had been treated for febrile neutropenia. Infection with Staphylococcus epidermidis accounted for 78.6% of patients. Thirty-nine cases (55.7%) were related to intravascular catheters, and 39 (55.7%) were treated using teicoplanin as a first-line therapy. The 30-day mortality rate was 4.3%. Regarding susceptibility, 20% of all isolates were non-susceptible to teicoplanin. According to multivariate analyses, it was observed that premedication using glycopeptides was independently associated with teicoplanin non-susceptibility (p=0.03; hazard ratio = 5.64; 95% confidence interval, 1.16-26.76). Conclusion Our results suggest that clinicians must use glycopeptides appropriately to prevent the development of further antibiotic resistance in methicillin-resistant coagulase-negative staphylococci.

Clinical significance of coagulase-negative staphylococci isolates from nosocomial bloodstream infections

BACKGROUND

Identification of coagulase-negative staphylococci (CoNS) as nosocomial pathogens or contaminants is significant for microbiologists and clinicians. This study aimed to determine the frequency of isolation and antimicrobial resistance patterns of CoNS isolates from nosocomial bloodstream infections (BSIs) and to identify risk factors associated with true bacteremia caused by these emerging pathogens in a Saudi tertiary care hospital.

METHODS

All CoNS-positive cultures from inpatients were identified using the standard methods during a 10-month period. Antimicrobial susceptibility testing was done using the reference broth microdilution method.

RESULTS

A total of 208 isolates were identified; of these 75 (32.2%) were considered infection associated, and 133 (67.8%) were considered contamination. S. epidermidis accounted for 34.7% of bacteremia cases, followed by S. hominis (21.3%), S. haemolyticus (16%), and S. saprophyticus (12%). Central venous catheters (p ≤ 0.0001), prior antibiotic therapy (p ≤ 0.0001), the occurrence of more than one positive blood culture (p ≤ 0.0001), and intensive care unit (ICU) admission (p = 0.007) were all independently associated with CoNS bacteremia. Overall, all isolates were highly resistant to penicillin (94.7%), oxacillin (90.7%), and erythromycin (85.3%). The rates of susceptibility to vancomycin, daptomycin, and teicoplanin were 98.7%, 98.7%, and 93.3%, respectively.

CONCLUSIONS

Our results further highlight that accurate identification and susceptibility testing of CoNS isolates from nosocomial BSIs are crucial to minimize excessive antibiotic use and unnecessary catheter removal. In addition, daptomycin may be an efficient alternative therapeutic option for CoNS resistant to oxacillin and other commonly used antibiotics.

Coagulase-negative staphylococci

The definition of the heterogeneous group of coagulase-negative staphylococci (CoNS) is still based on diagnostic procedures that fulfill the clinical need to differentiate between Staphylococcus aureus and those staphylococci classified historically as being less or nonpathogenic. Due to patient- and procedure-related changes, CoNS now represent one of the major nosocomial pathogens, with S. epidermidis and S. haemolyticus being the most significant species. They account substantially for foreign body-related infections and infections in preterm newborns. While S. saprophyticus has been associated with acute urethritis, S. lugdunensis has a unique status, in some aspects resembling S. aureus in causing infectious endocarditis. In addition to CoNS found as food-associated saprophytes, many other CoNS species colonize the skin and mucous membranes of humans and animals and are less frequently involved in clinically manifested infections. This blurred gradation in terms of pathogenicity is reflected by species- and strain-specific virulence factors and the development of different host-defending strategies. Clearly, CoNS possess fewer virulence properties than S. aureus, with a respectively different disease spectrum. In this regard, host susceptibility is much more important. Therapeutically, CoNS are challenging due to the large proportion of methicillin-resistant strains and increasing numbers of isolates with less susceptibility to glycopeptides.

A current perspective on daptomycin for the clinical microbiologist

Daptomycin is a lipopeptide antimicrobial with in vitro bactericidal activity against Gram-positive bacteria that was first approved for clinical use in 2004 in the United States. Since this time, significant data have emerged regarding the use of daptomycin for the treatment of serious infections, such as bacteremia and endocarditis, caused by Gram-positive pathogens. However, there are also increasing reports of daptomycin nonsusceptibility, in Staphylococcus aureus and, in particular, Enterococcus faecium and Enterococcus faecalis. Such nonsusceptibility is largely in the context of prolonged treatment courses and infections with high bacterial burdens, but it may occur in the absence of prior daptomycin exposure. Nonsusceptibility in both S. aureus and Enterococcus is mediated by adaptations to cell wall homeostasis and membrane phospholipid metabolism. This review summarizes the data on daptomycin, including daptomycin's unique mode of action and spectrum of activity and mechanisms for nonsusceptibility in key pathogens, including S. aureus, E. faecium, and E. faecalis. The challenges faced by the clinical laboratory in obtaining accurate susceptibility results and reporting daptomycin MICs are also discussed.

Ceftaroline activity tested against uncommonly isolated Gram-positive pathogens: report from the SENTRY Antimicrobial Surveillance Program (2008-2011)

Ceftaroline was tested against 1859 clinically significant Gram-positive organisms from uncommonly isolated species. The organisms (31 species/groups) were collected from 133 medical centres worldwide over a 4-year period (2008-2011). Coagulase-negative staphylococci were generally susceptible to ceftaroline, with MIC50 values (minimum inhibitory concentration required to inhibit 50% of the isolates) of 0.06-0.5mg/L. Ceftaroline was active against Micrococcus spp. [minimum inhibitory concentration required to inhibit 90% of the isolates (MIC90)=0.06 mg/L], but showed more limited potency versus some Corynebacterium spp. and Listeria monocytogenes isolates. Ceftaroline was active against all β-haemolytic streptococci and viridans group streptococcal species/groups listed, with MIC50 and MIC90 values ranging from ≤ 0.015 mg/L to 0.03 mg/L and from ≤ 0.015 mg/L to 0.5mg/L, respectively. Based on these in vitro findings, ceftaroline may have a potential role in the treatment of infections caused by these rarer species as guided by reference MIC test results.

Daptomycin activity against uncommonly isolated streptococcal and other gram-positive species groups

A total of 1,356 clinical isolates were tested against daptomycin by broth microdilution methods. Daptomycin was active against seven groups of viridans group streptococci (MIC50 and MIC90 values ranging from ≤0.06 and ≤0.06 μg/ml [Streptococcus bovis and Streptococcus dysgalactiae] to 0.5 and 1 μg/ml [Streptococcus mitis, Streptococcus oralis, and Streptococcus parasanguinis], respectively), beta-hemolytic streptococci serogroups C, F, and G (MIC50 and MIC90, ≤0.06 to 0.25 and 0.12 to 0.25 μg/ml, respectively), Corynebacterium spp. (MIC50 and MIC90, ≤0.06 and 0.12 μg/ml, respectively), and Micrococcus spp. (MIC50 and MIC90, ≤0.06 and 0.25 μg/ml, respectively). Listeria monocytogenes exhibited higher daptomycin MICs (MIC50 and MIC90, 2 and 4 μg/ml, respectively) than other tested organisms.

Antimicrobial activity of daptomycin tested against Gram-positive pathogens collected in Europe, Latin America, and selected countries in the Asia-Pacific Region (2011)

We report the results of the international daptomycin surveillance programs for Europe, Latin America, and selected Asia-Pacific nations. A total of 7948 consecutive Gram-positive organisms of clinical significance were collected in 2011 and susceptibility tested against daptomycin and various comparator agents by Clinical and Laboratory Standards Institute (Clinical and Laboratory Standards Institute. M07-A9. Methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically; approved standard: ninth edition Wayne, PA: CLSI. 2012.; Cubicin Package Insert 2012. Cubist Pharmaceuticals, Inc, Lexington, MA. Available at http://www.cubicin.com/pdf/PrescribingInformation.pdf. Accessed January 1, 2012.) broth microdilution methods. The test medium was adjusted to contain physiological levels of calcium (50 mg/L) when testing daptomycin. Daptomycin exhibited potent activity against methicillin-susceptible and -resistant Staphylococcus aureus overall and for each region (MIC(50/90), 0.25-0.5/0.5 μg/mL), with susceptibility rates at 100.0% in Latin America, Australia/New Zealand, and India, and at 99.9% in Europe. The daptomycin MIC(50/90) for coagulase-negative staphylococci was also at 0.25-0.5/0.5 μg/mL, and only 1 isolate was considered nonsusceptible with a MIC value at 2 μg/mL. Daptomycin was also highly active against Enterococcus faecalis (MIC(50/90), 1/1-2 μg/mL) and E. faecium (MIC(50/90), 2/2 μg/mL for both vancomycin-susceptible and -resistant isolates). All enterococcal isolates were susceptible to daptomycin (MIC, ≤4 μg/mL) and tigecycline. Susceptibility to linezolid for E. faecalis was at 100.0%, while for E. faecium regional susceptibility rates were at 100.0% except in Europe (99.0%). Viridans group streptococci (MIC(50/90), 0.25/1 μg/mL) and β-haemolytic streptococci (MIC(50/90), ≤0.06/0.25 μg/mL) continue to be very susceptible to daptomycin. In summary, the results of this investigation document the high potency and wide spectrum of daptomycin when tested against a large resistance-surveillance collection of Gram-positive pathogens and indicate that daptomycin nonsusceptibility remains rare among indicated species after many years of clinical use worldwide.