Clinical Significance of Isolates Known to Be Blood Culture Contaminants in Pediatric Patients

Background and objectives: The objective of this study was to investigate the clinical significance of isolates from blood stream infection known to be blood culture contaminants in pediatric patients. Materials and Methods: Microbiological reports and medical records of all blood culture tests issued from 2002 to 2012 (n = 76,331) were retrospectively reviewed. Evaluation for potential contaminants were done by reviewing medical records of patients with the following isolates: coagulase-negative Staphylococcus, viridans group Streptococcus, Bacillus, Corynebacterium, Micrococcus, Aerococcus, and Proprionibacterium species. Repeated cultures with same isolates were considered as a single case. Cases were evaluated for their status as a pathogen. Results: Coagulase-negative Staphylococcus had clinical significance in 23.8% of all cases. Its rate of being a true pathogen was particularly high in patients with malignancy (43.7%). Viridans group Streptococcus showed clinical significance in 46.2% of all cases. Its rate of being a true pathogen was similar regardless of the underlying morbidity of the patient. The rate of being a true pathogens for remaining isolates was 27.7% for Bacillus and 19.0% for Corynebacterium species. Conclusions: Coagulase-negative Staphylococcus and viridans group Streptococcus isolates showed high probability of being true pathogens in the pediatric population, especially in patients with underlying malignancy.

EarlyIn VitroandIn VivoDevelopment of High-Level Daptomycin Resistance Is Common in Mitis Group Streptococci after Exposure to Daptomycin

ABSTRACTThe development of high-level daptomycin resistance (HLDR; MIC of ≥256 mg/liter) after exposure to daptomycin has recently been reported in viridans group streptococcus (VGS) isolates. Our study objectives were as follows: to know whetherin vitrodevelopment of HLDR after exposure to daptomycin was common among clinical isolates of VGS andStreptococcus bovis; to determine whether HLDR also developed during the administration of daptomycin to treat experimental endocarditis caused by the daptomycin-susceptible, penicillin-resistantStreptococcus mitisstrainS. mitis351; and to establish whether combination with gentamicin prevented the development of HLDRin vitroandin vivo. In vitrostudies were performed with 114 VGS strains (mitis group, 92; anginosus group, 10; mutans group, 8; and salivarius group, 4) and 54Streptococcus bovisstrains isolated from 168 consecutive patients with infective endocarditis diagnosed between 1995 and 2010. HLDR was only observed after 24 h of exposure to daptomycin in 27% of the mitis group, including 27% ofS. mitisisolates, 47% ofS. oralisisolates, and 13% ofS. sanguisisolates. In our experimental model, HLDR was detected in 7/11 (63%) and 8/12 (67%) isolates recovered from vegetations after 48 h of daptomycin administered at 6 mg/kg of body weight/24 h and 10 mg/kg/24 h, respectively.In vitro, time-kill experiments showed that daptomycin plus gentamicin was bactericidal againstS. mitis351 at tested concentrations of 0.5 and 1 times the MIC and prevented the development of HLDR.In vivo, the addition of gentamicin at 1 mg/kg/8 h to both daptomycin arms prevented HLDR in 21 out of 23 (91%) rabbits. Daptomycin plus gentamicin was at least as effective as vancomycin plus gentamicin. In conclusion, HLDR develops rapidly and frequentlyin vitroandin vivoamong mitis group streptococci. Combining daptomycin with gentamicin enhanced its activity and prevented the development of HLDR in most cases.

Worldwide Appraisal and Update (2010) of Telavancin Activity Tested against a Collection of Gram-Positive Clinical Pathogens from Five Continents

ABSTRACTA total of 15,480 Gram-positive pathogens were collected from 89 sites in the United States, Europe, the Asia-Pacific region, and Latin America in 2010. Telavancin was active against indicatedStaphylococcus aureus(MIC50/90, 0.12/0.25 μg/ml), vancomycin-susceptibleEnterococcus faecalis(MIC50/90, 0.5/0.5 μg/ml), and beta-hemolytic (MIC50/90, 0.06/0.12 μg/ml) and viridans group streptococcus (MIC50/90, 0.03/0.06 μg/ml) isolates. These MIC results showed potency for telavancin equal to or greater than that of comparators. Thesein vitrodata confirm a continued potent activity of telavancin when tested against contemporary Gram-positive clinical isolates.

Raman Spectroscopy of Xylitol Uptake and Metabolism in Gram-Positive and Gram-Negative Bacteria

ABSTRACTVisible-wavelength Raman spectroscopy was used to investigate the uptake and metabolism of the five-carbon sugar alcohol xylitol by Gram-positive viridans group streptococcus and the two extensively used strains of Gram-negativeEscherichia coli,E. coliC andE. coliK-12.E. coliC, but notE. coliK-12, contains a complete xylitol operon, and the viridans group streptococcus contains an incomplete xylitol operon used to metabolize the xylitol. Raman spectra from xylitol-exposed viridans group streptococcus exhibited significant changes that persisted even in progeny grown from the xylitol-exposed mother cells in a xylitol-free medium for 24 h. This behavior was not observed in theE. coliK-12. In both viridans group streptococcus and theE. coliC derivative HF4714, the metabolic intermediates are stably formed to create an anomaly in bacterial normal survival. The uptake of xylitol by Gram-positive and Gram-negative pathogens occurs even in the presence of other high-calorie sugars, and its stable integration within the bacterial cell wall may discontinue bacterial multiplication. This could be a contributing factor for the known efficacy of xylitol when taken as a prophylactic measure to prevent or reduce occurrences of persistent infection. Specifically, these bacteria are causative agents for several important diseases of children such as pneumonia, otitis media, meningitis, and dental caries. If properly explored, such an inexpensive and harmless sugar-alcohol, alone or used in conjunction with fluoride, would pave the way to an alternative preventive therapy for these childhood diseases when the causative pathogens have become resistant to modern medicines such as antibiotics and vaccine immunotherapy.

Activity of Linezolid against 3,251 Strains of Uncommonly Isolated Gram-Positive Organisms: Report from the SENTRY Antimicrobial Surveillance Program

ABSTRACT Linezolid was tested against 32 species of uncommonly isolated gram-positive organisms (3,251 strains) by reference MIC methods and found to be highly active (MIC50 range, 0.25 to 2 μg/ml; MIC90 range, 0.25 to 2 μg/ml). Only one isolate (viridans group streptococcus; 0.03% of tested strains) was resistant to linezolid.

Isolated Native Tricuspid Valve Endocarditis Caused by Viridans Streptococcus

The present report describes a case of native tricuspid valve endocarditis caused by viridans group streptococcus in a 43-year-old man who had recently undergone dental extraction. The patient had no history of intravenous drug use, heart disease or right heart catheterization. Although there have been scattered reports of unusual organisms, to the authors' knowledge, this is the first case of viridans group streptococcal endocarditis involving only the tricuspid valve after dental manipulation.