Controlled Multicenter Evaluation of a Bacteriophage Based Method for the Rapid Detection of Staphylococcusaureus in Positive Blood Cultures.

Feb 2013

Bhowmick T, Mirrett S, Reller LB, Price C, Qi C, Weinstein MP, Kirn TJ.

Source

UMDNJ-Robert Wood Johnson Medical School, 1 Robert Wood Johnson Place, New Brunswick, NJ 08901.

Abstract

Staphylococci are a frequent cause of bloodstream infections (BSIs). Appropriate antibiotic treatment for BSIs may be delayed because conventional laboratory testing methods take 48-72 hours to identify and characterize isolates from positive blood cultures. We evaluated a novel assay based on bacteriophage amplification that identifies S. aureus and differentiates between methicillin-susceptible and methicillin-resistant S. aureus (MSSA and MRSA, respectively) in samples taken directly from signal positive BACTEC™ blood culture bottles within 24 hours of positive signal, with results available within 5 hours. The performance of the MicroPhage KeyPath™ MRSA/MSSA Blood Culture Test was compared to conventional identification and susceptibility testing methods. At four sites, we collectively tested a total of 1165 specimens of which 1116 were included in our analysis. Compared to standard methods, the KeyPath™ MRSA/MSSA Blood Culture Test demonstrated a sensitivity, specificity, positive predictive value and negative predictive value of 91.8%, 98.3%, 96.3% and 96.1%, respectively for correctly identifying S. aureus. Of those correctly identified as S. aureus (n=334), 99.1% were correctly categorized as either MSSA or MRSA. Analysis of a subset of the data revealed that the KeyPath™ MRSA/MSSA Blood Culture Test delivered results a median of 30 hours sooner than conventional methods (a median of 46.9 hours vs a median of 16.9 hours). Although the sensitivity of the test in detecting S. aureus-positive samples is not high, its accuracy in determining methicillin resistance and susceptibility among positives is very high. These characteristics may enable earlier implementation of appropriate antibiotic treatment for many S. aureus BSI patients. (Subsets of these results were presented at the 2010 ICAAC meeting in Boston, MA and the 2011 ASM meeting in New Orleans).

PubMed

Short communication: methicillin-resistant Staphylococcus aureus detection in US bulk tank milk.

Short communication: methicillin-resistant Staphylococcus aureus detection in US bulk tank milk.
J Dairy Sci. 2009 Oct

Virgin JE, Van Slyke TM, Lombard JE, Zadoks RN.
USDA, APHIS, VS, Centers for Epidemiology and Animal Health, Fort Collins, CO 80526-8117, USA.

* USDA:APHIS:VS, Centers for Epidemiology and Animal Health, 2150 Centre Ave., Bldg B, Fort Collins, CO 80526-8117 Quality Milk Production Services, College of Veterinary Medicine, Cornell University, Ithaca, NY14850-1263
1 Corresponding author: jason.e.lombard@aphis.usda.gov

Staphylococcus aureus is a major cause of mastitis in dairy cattle. This study estimated the herd prevalence of methicillin-resistant Staph. aureus (MRSA) among US dairy herds by testing bulk tank milk (BTM) samples using genotypic and phenotypic methods. A nationally representative sample of 542 operations had BTM cultured for Staph. aureus, and 218 BTM samples were positive upon initial culture. After 4 wk to 4 mo of frozen storage, 87% of 218 samples (n = 190) were still culture positive for Staph. aureus on blood agar, but none were positive for MRSA on the selective indicator medium CHROMagar MRSA. A duplex PCR was used to detect the Staph. aureus-specific nuc gene and the methicillin resistance gene, mecA, in mixed staphylococcal isolates from the 190 BTM samples that were positive for Staph. aureus after storage. Seven samples tested positive for nuc and mecA, and 2 samples tested positive for mecA only. MecA-positive Staphylococcus spp., but not MRSA, were subsequently isolated from 5 samples, whereas neither mecA-positive Staphylococcus spp. nor MRSA was isolated from the remaining 4 samples. Presence of methicillin-resistant, coagulase-negative Staphylococcus spp. may complicate the detection of MRSA by means of PCR on BTM. Bulk tank milk in the United States is not a common source of MRSA.

Journal of Dairy Science