Margie Morgan

Risk Factors for Community-Associated Methicillin-Resistant Staphylococcus aureus Skin Infections among HIV-Positive Men Who Have Sex with Men

We investigated community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) skin infections among HIV-positive men who have sex with men. We performed a matched case-control study of 35 case patients and 76 control subjects. CA-MRSA skin infections were associated with high-risk sex and drug-using behaviors and with environmental exposures but not with immune status.

Emerging Technologies for Rapid Identification of Bloodstream Pathogens

Technologies for rapid microbial identification are poised to revolutionize clinical microbiology and enable informed decision making for patients with life-threatening bloodstream infections. Species identification of microorganisms in positive blood cultures can be performed in minutes using commercial fluorescence in situ hybridization tests or mass spectroscopy. Microorganisms in positive blood cultures can also be identified within 1-2.5 hours using automated polymerase chain reaction-based systems that can also detect selected antibiotic resistance markers, such as methicillin resistance. When combined with antibiotic stewardship programs, these approaches improve clinical outcomes and reduce healthcare expenditures. Tests for direct detection in whole blood samples are highly desirable because of their potential to identify bloodstream pathogens without waiting 1-2 days for blood cultures to become positive. However, results for pathogen detection in whole blood do not overlap with those of conventional blood culture techniques and we are still learning how best to use these approaches.

Multicenter Evaluation of the Staphylococcus QuickFISH Method for Simultaneous Identification of Staphylococcus aureus and Coagulase-Negative Staphylococci Directly from Blood Culture Bottles in Less than 30 Minutes

ABSTRACT A novel rapid peptide nucleic acid fluorescence in situ hybridization (FISH) method, Staphylococcus QuickFISH, for the direct detection of Staphylococcus species from positive blood culture bottles was evaluated in a multicenter clinical study. The method utilizes a microscope slide with predeposited positive- and negative-control organisms and a self-reporting 15-min hybridization step, which eliminates the need for a wash step. Five clinical laboratories tested 722 positive blood culture bottles containing Gram-positive cocci in clusters. The sensitivities for detection of Staphylococcus aureus and coagulase-negative staphylococci (CoNS) were 99.5% (217/218) and 98.8% (487/493), respectively, and the combined specificity of the assay was 89.5% (17/19). The combined positive and negative predictive values of the assay were 99.7% (696/698) and 70.8% (17/24), respectively. Studies were also performed on spiked cultures to establish the specificity and performance sensitivity of the method. Staphylococcus QuickFISH has a turnaround time (TAT) of <30 min and a hands-on time (HOT) of <5 min. The ease and speed of the method have the potential to improve the accuracy of therapeutic intervention by providing S. aureus/CoNS identification simultaneously with Gram stain results.

Liposomal encapsulation of vancomycin improves killing of methicillin-resistant Staphylococcus aureus in a murine infection model

OBJECTIVES Methicillin-resistant Staphylococcus aureus (MRSA) poses a major problem to public health worldwide. MRSA strains with increased resistance to vancomycin cause infections that are associated with greater morbidity and threaten the use of this once gold-standard antistaphylococcal drug. We investigated whether encapsulation of vancomycin within liposomes could improve its antistaphylococcal activity. METHODS Two liposomal formulations of vancomycin were prepared using a rehydration-dehydration method. MICs and MBCs of the liposomal vancomycin for strains of MRSA were determined. The efficacy of one of the liposomal vancomycin formulations was also investigated in a time-kill assay in vitro and in a murine systemic infection model. RESULTS Encapsulation in either liposome preparation decreased the vancomycin MICs and MBCs for MRSA strains by approximately 2-fold. Liposomal vancomycin increased killing of MRSA in vitro in a kinetic study. In a systemic murine infection model, treatment with a 50 mg/kg intraperitoneal injection of liposomal vancomycin improved kidney clearance of a USA300 strain by 1 log compared with an injection of 50 mg/kg of free vancomycin. CONCLUSIONS Our findings suggest that entrapment within liposomes could improve the antistaphylococcal efficacy of vancomycin.

Isolation and Characterization of Antimicrobial Compounds in Plant Extracts against Multidrug-Resistant Acinetobacter baumannii

The number of fully active antibiotic options that treat nosocomial infections due to multidrug-resistant Acinetobacter baumannii (A. baumannii) is extremely limited. Magnolia officinalis, Mahonia bealei, Rabdosia rubescens, Rosa rugosa, Rubus chingii, Scutellaria baicalensis, and Terminalia chebula plant extracts were previously shown to have growth inhibitory activity against a multidrug-resistant clinical strain of A. baumannii. In this study, the compounds responsible for their antimicrobial activity were identified by fractionating each plant extract using high performance liquid chromatography, and determining the antimicrobial activity of each fraction against A. baumannii. The chemical structures of the fractions inhibiting >40% of the bacterial growth were elucidated by liquid chromatography/mass spectrometry analysis and nuclear magnetic resonance spectroscopy. The six most active compounds were identified as: ellagic acid in Rosa rugosa; norwogonin in Scutellaria baicalensis; and chebulagic acid, chebulinic acid, corilagin, and terchebulin in Terminalia chebula. The most potent compound was identified as norwogonin with a minimum inhibitory concentration of 128 µg/mL, and minimum bactericidal concentration of 256 µg/mL against clinically relevant strains of A. baumannii. Combination studies of norwogonin with ten anti-Gram negative bacterial agents demonstrated that norwogonin did not enhance the antimicrobial activity of the synthetic antibiotics chosen for this study. In conclusion, of all identified antimicrobial compounds, norwogonin was the most potent against multidrug-resistant A. baumannii strains. Further studies are warranted to ascertain the prophylactic and therapeutic potential of norwogonin for infections due to multidrug-resistant A. baumannii.

Prospective, multicenter evaluation of the BD GeneOhm VanR assay for direct, rapid detection of vancomycin-resistant Enterococcus species in perianal and rectal specimens.

The BD GeneOhm VanR assay (BD Diagnostics, San Diego, CA), a qualitative test for the rapid detection of vancomycin-resistant enterococci (VRE) from rectal and/or perianal swabs, combines integrated nucleic acid extraction and automated polymerase chain reaction for the detection of vanA and/or vanB gene sequences. We studied 1,027 perianal and rectal swab specimens from 3 geographically distinct US sites (prevalence rates, 13.1%-25.8%). Direct swab specimens were tested by the assay and compared with direct culture. The sensitivity, specificity, and positive and negative predictive values of the assay were 93.2%, 81.9%, 54.4%, and 98.1%, respectively. The specificity was limited largely due to false-positives in the vanB portion of the assay. Specificity with perianal swabs was significantly greater than with rectal swabs, 87.1% vs 74.7%, respectively (P < .0001). When used only to detect resistance conferred by vanA, the assay was 88.3% (158/179) sensitive and 95.8% (802/837) specific, with positive and negative predictive values of 81.9% and 97.4%, respectively. The assay is a simple, rapid, and acceptable method for screening for VRE in a variety of populations in which vanA is the predominant genotype. Samples positive for the vanB genotype should be confirmed by culture owing to the apparent high number of false-positive results.

Screening of herbal extracts against multi-drug resistant Acinetobacter baumannii.

Antibiotic resistance is increasing resulting in a decreasing number of fully active antimicrobial agents available to treat infections with multi‐drug resistant (MDR) bacteria. Herbal medicines may offer alternative treatment options. A direct inoculation method simulating the standard disc diffusion assay was developed to determine in vitro antimicrobial activity of sixty herbal extracts against MDR‐Acinetobacter baumannii (A. baumannii). Eighteen herbal extracts inhibited MDR‐A. baumannii on agar plates, although the magnitude and quality of bacterial inhibition differed considerably among the antibacterial herbal extracts. Next, minimal inhibitory concentration (MIC) of these antibacterial herbal extracts was calculated using a broth microdilution assay. For most herbal extracts, the larger the zone of inhibition on agar plates, the lower the MIC. In general, hetero‐resistance on agar plates correlated with higher MIC. The skip well phenomenon was seen with two herbal extracts. In conclusion, 30% of the screened herbal extracts demonstrated in vitro antibacterial activity against MDR‐A. baumannii using similar rigorous testing methods as those commonly employed for assessing antimicrobial activity of synthetic antibacterial agents. Characterization of a specific compound conferring this antibacterial activity of the herbal extracts may help to identify novel antimicrobial agents active against highly resistant bacteria. Copyright

Multicenter Evaluation of a New Shortened Peptide Nucleic Acid Fluorescence In Situ Hybridization Procedure for Species Identification of Select Gram-Negative Bacilli from Blood Cultures

ABSTRACT A shortened protocol for two peptide nucleic acid fluorescence in situ hybridization (PNA FISH) assays for the detection of Gram-negative bacilli from positive blood cultures was evaluated in a multicenter trial. There was 100% concordance between the two protocols for each assay (368 of 368 and 370 of 370 results) and 99.7% (367 of 368 and 369 of 370 results) agreement with routine laboratory techniques.

A 1.5 hour procedure for identification of Enterococcus Species directly from blood cultures.

Enterococci are a common cause of bacteremia with E. faecalis being the predominant species followed by E. faecium. Because resistance to ampicillin and vancomycin in E. faecalis is still uncommon compared to resistance in E. faecium, the development of rapid tests allowing differentiation between enterococcal species is important for appropriate therapy and resistance surveillance. The E. faecalis OE PNA FISH assay (AdvanDx, Woburn, MA) uses species-specific peptide nucleic acid (PNA) probes in a fluorescence in situ hybridization format and offers a time to results of 1.5 hours and the potential of providing important information for species-specific treatment. Multicenter studies were performed to assess the performance of the 1.5 hour E. faecalis/OE PNA FISH procedure compared to the original 2.5 hour assay procedure and to standard bacteriology methods for the identification of enterococci directly from a positive blood culture bottle.

In vitro activity of antibiotic combinations against multidrug‐resistant strains of Acinetobacter baumannii and the effects of their antibiotic resistance determinants

Various combinations of antibiotics are reported to show synergy in treating nosocomial infections with multidrug-resistant (MDR) Acinetobacter baumannii (A. baumannii). Here, we studied hospital-acquired outbreak strains of MDR A. baumannii to evaluate optimal combinations of antibiotics. One hundred and twenty-one strains were grouped into one major and one minor clonal group based on repetitive PCR amplification. Twenty representative strains were tested for antibiotic synergy using Etest(®). Five strains were further analyzed by analytical isoelectric focusing and PCR to identify β-lactamase genes or other antibiotic resistance determinants. Our investigation showed that the outbreak strains of MDR A. baumannii belonged to two dominant clones. A combination of colistin and doxycycline showed the best result, being additive or synergistic against 70% of tested strains. Antibiotic additivity was observed more frequently than synergy. Strains possessing the same clonality did not necessarily demonstrate the same response to antibiotic combinations in vitro. We conclude that the effect of antibiotic combinations on our outbreak strains of MDR A. baumannii seemed strain-specific. The bacterial response to antibiotic combinations is probably a result of complex interactions between multiple concomitant antibiotic resistance determinants in each strain.