Correction: Castanea sativa (European Chestnut) Leaf Extracts Rich in Ursene and Oleanene Derivatives Block Staphylococcus aureus Virulence and Pathogenesis without Detectable Resistance.

[This corrects the article DOI: 10.1371/journal.pone.0136486.].

Detection and Prevalence of Penicillin-Susceptible Staphylococcus aureus in the United States in 2013.

Using blaZ PCR as the "gold standard," the sensitivities of CLSI penicillin zone edge and nitrocefin-based tests for ß-lactamase production in Staphylococcus aureus were 64.5% and 35.5%, respectively, with specificity of 99.8% for both methods. In 2013, 13.5% of 3,083 S. aureus isolates from 31 U.S. centers were penicillin susceptible.

Collaborative evaluation of an erythromycin-clindamycin combination well for detection of inducible clindamycin resistance in beta-hemolytic streptococci by use of the CLSI broth microdilution method.

Constitutive or inducible clindamycin resistance can occur in beta-hemolytic streptococci due to the presence of an erm gene. The Clinical and Laboratory Standards Institute (CLSI) has recommended a disk approximation test (D-zone test) with erythromycin and clindamycin disks and a single-well broth test combining erythromycin and clindamycin for detection of inducible clindamycin resistance in staphylococci, but only a disk approximation test for the beta-hemolytic streptococci. This collaborative study assessed two different erythromycin and clindamycin concentration combinations in single wells (1 µg/ml + 0.25 µg/ml [erythromycin plus clindamycin] and 1 µg/ml + 0.5 µg/ml) with three different brands of Mueller-Hinton broth supplemented with 3% lysed horse blood for testing of frozen panels prepared for this study. All labs performed the D-zone test as described by the CLSI. A total of 155 nonduplicate streptococcal isolates (50 group A, 48 group B, 28 group C, and 29 group G isolates) were tested; 99 isolates showed inducible resistance by the D-zone test. There were some differences noted based upon the test medium. The sensitivity of the erythromycin plus clindamycin combination of 1 µg/ml + 0.25 µg/ml was 91 to 100%, while the sensitivity of the combination of 1 µg/ml + 0.5 µg/ml was 95 to 100%. Specificity overall was 98%. The slightly higher sensitivity of the combination of 1 µg/ml + 0.5 µg/ml is recommended. This study has demonstrated that a single-well microdilution test incorporating erythromycin and clindamycin in combination is a sensitive and specific indicator of inducible clindamycin resistance and could be included in routine test panels.

Antimicrobial use in Europe and antimicrobial resistance in Streptococcus pneumoniae.

The study presented here determined the relationship between antimicrobial resistance in Streptococcus pneumoniae and the use of antimicrobial agents in 15 different European countries. Pneumococcal isolates (n = 1974) recovered from patients with community-acquired respiratory tract infections during the winter of 2004-2005 in 15 European countries were characterized. The overall percentages of isolates demonstrating intermediate or complete resistance to penicillin, erythromycin, tetracycline, trimethoprim-sulfamethoxazole (TMP-SMX) and ciprofloxacin were 24, 24.6, 19.8, 26.7 and 2%, respectively, as determined using the broth microdilution MIC method recommended by the Clinical and Laboratory Standards Institute. The overall and mean antimicrobial consumption levels (ACL)--i.e., the defined daily doses per 1,000 inhabitants per day--were obtained from the European Surveillance of Antimicrobial Consumption project for each of the 15 countries for the years 1998-2004. Using linear regression analysis, the mean annual ACL for beta-lactams, macrolides, tetracyclines, TMP-SMX and fluoroquinolones in each country was compared to the country-specific resistance rates determined in 2004-2005. The rate of overall antimicrobial use in all 15 European countries was significantly associated with antimicrobial resistance in S. pneumoniae. There was variation among the different antimicrobial classes as drivers of resistance, with beta-lactams having the strongest association.

Macrolide use identified as risk factor for macrolide-resistant Streptococcus pneumoniae in a 17-center case-control study.

The objective of the case-control study presented here was to examine the risk factors for macrolide-resistant Streptococcus pneumoniae. As part of a 44-center U.S. surveillance study, 1,817 unique isolates of S. pneumoniae were collected from November 2002 through April 2003. Seventy-five randomly selected macrolide-resistant isolates (cases) were each matched with one susceptible control. Macrolide use in the 6 weeks prior to sample collection was reported for seven cases and one control. The final conditional logistic regression model identified two statistically significant variables: a history of alcohol abuse was protective, while macrolide use in the 6 weeks prior to sample collection was a significant risk factor for macrolide-resistant S. pneumoniae. Macrolide resistance was associated with use of any antibiotic during the prior 6 weeks, and was most strongly associated with previous macrolide use.

The molecular epidemiology of Streptococcus pneumoniae with quinolone resistance mutations.

BACKGROUND: The purpose of this study was to determine the prevalence of fluoroquinolone resistance and quinolone resistance-determining region (QRDR) mutations among Streptococcus pneumoniae isolates in the United States during the period of 2001-2002. A second objective was to examine the genetic relatedness of pneumococcal isolates with parC and/or gyrA mutations during the period of 1994-2002. METHODS: Susceptibility testing was performed for 1902 S. pneumoniae isolates collected in the United States during the period of 2001-2002. On the basis of the minimum inhibitory concentration (MIC) of ciprofloxacin, 146 isolates were selected from the 2001-2002 study for QRDR analysis of parC, parE, gyrA, and gyrB genes. The genetic relatedness of isolates with parC and/or gyrA mutations from 2001-2002 (n=55) and from 3 US surveillance studies conducted during 1994-2000 (n=56) was determined by pulsed-field gel electrophoresis (PFGE). RESULTS: Between 1999-2000 and 2001-2002, there was a 2-fold increase in the rate of ciprofloxacin resistance (MIC, >or=4 micro g/mL), from 1.2% to 2.7%, and in the rate of levofloxacin nonsusceptibility (MIC, >or=4 micro g/mL), from 0.6% to 1.3%. The 111 isolates with parC and/or gyrA mutations were assigned to 48 different PFGE types. Forty-four isolates (40%) belonged to 8 PFGE types that were closely related to widespread clones. Fifteen of the 43 levofloxacin-nonsusceptible pneumococci (LNSP) belonged to 4 PFGE types that were closely related to major clones (Spain(23F)-1 [n=6]; Spain(6B)-2 [n=5], Taiwan(19F)-14 [n=2], and Tennessee(23F)-4 [n=2]). CONCLUSION: The population of fluoroquinolone-resistant S. pneumoniae in the United States has increased but remains genetically diverse. However, 35% of LNSP were related to widespread pneumococcal clones, increasing the potential for the rapid spread of quinolone resistance in this species.

The in vitro activity of daptomycin against Staphylococcus aureus and Enterococcus species.

OBJECTIVE: The purpose of this study was to examine the in vitro activity of daptomycin using an optimal calcium (Ca2+) concentration (50 mg/L) against a diverse collection of enterococcal and Staphylococcus aureus clinical isolates, including glycopeptide-resistant enterococci (GRE) and methicillin-resistant S. aureus (MRSA). METHODS: The activity of daptomycin was compared with the activities of seven other agents against 1483 enterococcal and S. aureus clinical isolates, including 303 GRE and 193 methicillin-resistant S. aureus (MRSA) strains. Susceptibility testing was performed by the NCCLS broth microdilution method, with one exception: Mueller-Hinton (MH) broth was supplemented to a physiological level of 50 mg/L Ca2+ when testing daptomycin. Daptomycin zone diameters were determined by disc diffusion with MH agar plates containing Ca2+ 50 mg/L. RESULTS: All staphylococcal isolates tested, and the majority of enterococcal isolates (96.5%), would be considered susceptible to daptomycin if the breakpoint previously proposed of or = 20 mm, and all of the enterococcal isolates had daptomycin zone diameters > or = 17 mm. CONCLUSIONS: Overall, daptomycin showed potent activity against S. aureus and enterococcal isolates, comparable to quinupristin-dalfopristin and linezolid.

The molecular epidemiology of penicillin-resistant Streptococcus pneumoniae in the United States, 1994-2000.

The genetic relatedness of 672 penicillin-resistant isolates of Streptococcus pneumoniae (PRSP) recovered during national surveillance studies conducted in the United States during the periods of 1994-1995, 1997-1998, and 1999-2000 was determined by use of pulsed-field gel electrophoresis (PFGE). Overall, 104 different PFGE types were elucidated. For all study periods combined, the 12 most prevalent PFGE types included >75% of all isolates, and 5 types were closely related to widespread clones (Spain(23F)-1, France(9V)-3, Spain(6B)-2, Tennessee(23F)-4, and Taiwan(19F)-14). From 1994-1995 to 1999-2000, 3 major PFGE types (not closely related to 16 recognized clones) increased in prevalence. Multidrug resistance was identified among 96%-100% of the isolates in 9 of 12 predominant PFGE types. The prevalence of erythromycin resistance increased within 4 major PFGE types. These observations support the hypothesis that the dominant factor in the emergence of PRSP in the United States during the 1990s has been human-to-human spread of relatively few clonal groups that harbor resistance determinants to multiple classes of antibiotics.

Antimicrobial resistance among clinical isolates of Streptococcus pneumoniae in the United States during 1999--2000, including a comparison of resistance rates since 1994--1995.

A total of 1,531 recent clinical isolates of Streptococcus pneumoniae were collected from 33 medical centers nationwide during the winter of 1999--2000 and characterized at a central laboratory. Of these isolates, 34.2% were penicillin nonsusceptible (MIC > or = 0.12 microg/ml) and 21.5% were high-level resistant (MIC > or = 2 microg/ml). MICs to all beta-lactam antimicrobials increased as penicillin MICs increased. Resistance rates among non-beta-lactam agents were the following: macrolides, 25.2 to 25.7%; clindamycin, 8.9%; tetracycline, 16.3%; chloramphenicol, 8.3%; and trimethoprim-sulfamethoxazole (TMP-SMX), 30.3%. Resistance to non-beta-lactam agents was higher among penicillin-resistant strains than penicillin-susceptible strains; 22.4% of S. pneumoniae were multiresistant. Resistance to vancomycin and quinupristin-dalfopristin was not detected. Resistance to rifampin was 0.1%. Testing of seven fluoroquinolones resulted in the following rank order of in vitro activity: gemifloxacin > sitafloxacin > moxifloxacin > gatifloxacin > levofloxacin = ciprofloxacin > ofloxacin. For 1.4% of strains, ciprofloxacin MICs were > or = 4 microg/ml. The MIC(90)s (MICs at which 90% of isolates were inhibited) of two ketolides were 0.06 microg/ml (ABT773) and 0.12 microg/ml (telithromycin). The MIC(90) of linezolid was 2 microg/ml. Overall, antimicrobial resistance was highest among middle ear fluid and sinus isolates of S. pneumoniae; lowest resistance rates were noted with isolates from cerebrospinal fluid and blood. Resistant isolates were most often recovered from children 0 to 5 years of age and from patients in the southeastern United States. This study represents a continuation of two previous national studies, one in 1994--1995 and the other in 1997--1998. Resistance rates with S. pneumoniae have increased markedly in the United States during the past 5 years. Increases in resistance from 1994--1995 to 1999--2000 for selected antimicrobial agents were as follows: penicillin, 10.6%; erythromycin, 16.1%; tetracycline, 9.0%; TMP-SMX, 9.1%; and chloramphenicol, 4.0%, the increase in multiresistance was 13.3%. Despite awareness and prevention efforts, antimicrobial resistance with S. pneumoniae continues to increase in the United States.