Robert J. Tibbetts

Evaluation of a Microarray-Based Assay for Rapid Identification of Gram-Positive Organisms and Resistance Markers in Positive Blood Cultures

ABSTRACT Rapid identification of pathogens directly from positive blood cultures can play a major role in reducing patient mortality rates. We evaluated the performance of the Verigene Gram-Positive Blood Culture (BC-GP) assay (Nanosphere Inc., Northbrook, IL) for detection of commonly isolated Gram-positive organisms as well as associated resistance markers from positive blood cultures. Positive blood cultures (VersaTREK; Trek Diagnostic Systems, Independence, OH) from 203 patients with Gram-positive organism infections were analyzed using the BC-GP assay within 12 h for the detection of 12 different organisms, including staphylococci, streptococci, and enterococci, as well as for the presence of 3 resistance markers (mecA, vanA, and vanB). Results were compared to those of routine laboratory methods for identification and susceptibility testing. For identification of organisms and detection of resistance markers in 178 monomicrobial positive blood cultures, the BC-GP assay showed 94% and 97% concordance, respectively, with routine methods. After 25 polymicrobial cultures were included, the results showed 92% and 96% agreement for identification and resistance markers, respectively, for a total of 203 positive cultures. In 6/25 polymicrobial cultures, at least 1 isolate was not detected. Concordance levels for detection of major pathogens such Staphylococcus aureus (n = 45) and enterococci (n = 19) were 98% and 95%, respectively. Agreement levels for detection of resistance markers such as mecA and vanA/B were 92% and 100%, respectively. The BC-GP assay is capable of providing rapid identification of Gram-positive cocci as well as detection of resistance markers directly from positive blood cultures at least 24 to 48 h earlier than conventional methods.

Staphylococcus aureus meningitis: case series and literature review.

Staphylococcus aureus meningitis is a challenging disease and little is known about its epidemiology. There are no established management guidelines. We retrospectively reviewed the clinical information, bacteriologic data, and outcomes of all 33 patients with cerebrospinal fluid (CSF) cultures positive for S aureus seen at a single urban teaching hospital from 1999 to 2008. Pulsed-field gel electrophoresis (PFGE) and polymerase chain reaction for staphylococcal cassette chromosome mec (SCCmec), accessory gene regulator (agr) typing, and Panton-Valentine leukocidin (PVL) loci were done on methicillin-resistant S aureus (MRSA) CSF isolates starting in 2005. S aureus caused 12 (36%) cases of postoperative and 21 (64%) cases of hematogenous meningitis. MRSA isolates were found in 6 (50%) cases of postoperative and 10 (48%) cases of hematogenous meningitis. Twelve (75%) of the 16 MRSA infections occurred in the last 5 years of the study. Hematogenous meningitis was associated with older age (p = 0.04), injection drug use (p < 0.01), community-acquired infection (p < 0.01), underlying disease (p = 0.01), staphylococcal infection outside the central nervous system (p = 0.01), altered mental status (p = 0.02), fever (p = 0.01), septic shock (p = 0.03), and bacteremia (p < 0.01). The analysis of the 9 MRSA isolates showed 3 PFGE types: 3 USA100 (33%), 5 USA300 (56%), and 1 USAnot100-1100 (11%). For SCCmec typing, there were 2 (22%) type II and 7 (78%) type IV. All USA300 strains were SCCmec IVa. For agr typing, there were 5 (56%) type I and 4 (44%) type II. Three isolates (33%) were positive for the PVL gene and were USA300 strains. Most patients received nafcillin or vancomycin with or without rifampin or trimethoprim/sulfamethoxazole for a mean period of 17 days (range, 1-42 d). Overall mortality was 36%, and it was associated with community-acquired infection (p = 0.02). Postoperative and hematogenous S aureus meningitis are distinct clinical syndromes. S aureus hematogenous meningitis has devastating clinical consequences and elevated mortality rates, especially if it is acquired in the community. The incidence of MRSA meningitis increased over the last 5 years of the study. Treatment of choice is nafcillin for methicillin-sensitive strains and vancomycin for MRSA strains. The addition of trimethoprim/sulfamethoxazole or rifampin to vancomycin is recommended in severe cases and community-acquired MRSA infections. Linezolid is also a good option due to its good CSF penetration and favorable case reports. The mortality rate is higher in infections acquired in the community. Abbreviations: agr = accessory gene regulator, CA-MRSA = community-associated MRSA, CNS = central nervous system, CSF = cerebrospinal fluid, MIC = minimum inhibitory concentration, MRSA = methicillin-resistant Staphylococcus aureus, MSSA = methicillin-susceptible Staphylococcus aureus, PCR = polymerase chain reaction, PFGE = pulsed-field gel electrophoresis, PVL = Panton-Valentine leukocidin, SCCmec = staphylococcal cassette chromosome mec, VP = ventriculoperitoneal.

Evaluation of a Real-Time PCR Assay for the Detection of the Klebsiella pneumoniae Carbapenemase Genes in Microbiological Samples in Comparison With the Modified Hodge Test

Transfer of the bla(KPC) genes encoding the Klebsiella pneumoniae carbapenemase (KPC) are increasingly responsible for emerging carbapenem resistance. The modified Hodge test (MHT) is recommended for the detection of KPC. We compared MHT with a real-time polymerase chain reaction (PCR) assay targeting common subtypes of bla(KPC), using previously described forward and reverse primer sequences. The PCR product was detected using SYBR Green (Applied Biosystems, Foster City, CA) and confirmed by melt curve analysis. PCR was positive in 96% (52/54) of isolates that were MHT+, 90% (28/31) of MHT- isolates were PCR-, and the results were strongly correlated (P = .0001; Fisher exact test). The PCR assay is a sensitive, specific, and rapid test for detecting bla(KPC) genes. It could help optimize patient care by reducing the time taken to institute appropriate antimicrobial therapy and so help improve patient outcomes.

Comparison of time to positivity of the VersaTREK® REDOX 80-mL and the REDOX EZ draw 40-mL blood culture bottles for common bacterial bloodstream pathogens

The VersaTREK(®) microbial detection system offers 2 media formulations, an aerobic and an anaerobic bottle available in a 40-mL direct draw format and an 80-mL format. The 40-mL EZ Draw(®) bottle can be inoculated with a maximum volume of 5 mL, while the REDOX 80-mL bottle accommodates a 10-mL volume. The effect of volume of blood inoculum on time to positivity (TTP) has not been clearly established with these bottle types. This study utilized simulated blood cultures seeded with clinically relevant microorganisms in human blood to evaluate the impact of inoculum volume and organism load on TTP for the 2 bottle types. For 13/15 organisms, the EZ Draw bottle flagged positive earlier than the REDOX 80-mL bottles. The lower volume of blood inoculum did not negatively impact TTP using the EZ Draw blood culture bottles as compared to REDOX 80-mL bottles.

Characterization of Salmonella Isangi possessing a CTX-M15 ESBL associated with an outbreak in a US Hospital

Over an approximately 50-day period in 2015, an outbreak of CTX-M-15 extended spectrum β-lactamase-(ESBL)-possessing Salmonella Isangi occurred among 19 adult surgical patients and one healthcare worker (HCW) at a large urban tertiary care hospital in the United States. A total of 45 S. Isangi isolates were isolated from stool (35), blood (4), urine (3), respiratory (2), and wound (1) cultures. Phenotypically, all but three isolates demonstrated resistance to ampicillin, ampicillin/sulbactam, ceftriaxone, and cefepime, and one isolate was resistant to ertapenem. Genotypically, a single CTX-M-15 ESBL was identified in all but three isolates by real-time PCR. Interestingly, two of the CTX-M-15 negative, susceptible isolates were isolated from a single patient who initially had a CTX-M positive, resistant strain. Isolates were clonally related, including both resistant and susceptible strains, as confirmed by pulse field gel electrophoresis (PFGE). This is the first case of a novel Salmonella outbreak at this hospital, and we believe it to be the first case of an S. Isangi serotype outbreak in the United States.

Stewardship opportunities in viral pneumonia: Why not the immunocompromised?

Antimicrobial management of viral pneumonia has proven to be a challenge in hospitalized immunocompromised patients. A host of factors contribute to the dilemma, such as diagnostic uncertainty, lack of organism identification, and clinical status of the patient. Respiratory virus panel (RVP) use was compared between 131 immunocompromised patients who received send‐out (n = 56) vs in‐house (n = 75) testing. Antimicrobial optimization interventions consisted of antiviral addition/discontinuation, antibiotic discontinuation/de‐escalation, or modification of immunosuppressive regimen. After implementation of an in‐house test with audit and feedback, turnaround time of the RVP was reduced from 46.7 to 5.5 hours (P < .001) and time to intervention was reduced from 52.1 to 13.9 hours (P < .001), yet the frequency of antimicrobial optimization interventions was unchanged (30.7% vs 35.7%). Differences were not observed in duration of empiric antibiotic therapy or length of stay. The overall discontinuation rate for patients tested with a RVP was low (4.6%), and those with positive RVP (n = 43) had antibiotics stopped in 14% of cases. Bacterial pneumonia coinfection was confirmed in 2 patients. Further systematic efforts should be taken to reduce antibiotic use in viral pneumonia and identify the major barriers in the immunocompromised population.

Microbiology Comment Nudge Improves Pneumonia Prescribing

Abstract Background Systematic and behavioral interventions are needed to improve antibiotic use for common conditions like pneumonia. Methods Single pretest, post-test quasi-experiment in a 4-hospital health system in metropolitan Detroit, Michigan. Hospitalized patients treated with anti-methicillin-resistant Staphylococcus aureus and antipseudomonal antibiotics for respiratory infections from August 1, 2015, through January 31, 2016, and August 1, 2016, through January 31, 2017, were eligible for inclusion. Beginning in May 2016, respiratory cultures with no dominant organism growth and no Pseudomonas sp. or Staphylococcus aureus were reported by the clinical microbiology laboratory as “commensal respiratory flora only: No S. aureus/MRSA [methicillin-resistant Staphylococcus aureus] or P. [Pseudomonas] aeruginosa.” Before intervention, these were reported as “commensal respiratory flora.” The primary end point was de-escalation or discontinuation of anti-methicillin-resistant Staphylococcus aureus or antipseudomonal therapy. Secondary clinical and safety outcomes included nephrotoxicity and in-hospital, all-cause mortality. Results Two hundred ten patients were included in the study. De-escalation/discontinuation was more commonly performed in the intervention group (39% vs 73%, P < .001). After adjusting for APACHE II and Charlson Comorbidity Index, the intervention comment was associated with a 5.5-fold increased odds of de-escalation (adjusted odds ratio, 5.5; 95% confidence interval, 2.8–10.7). Acute kidney injury was reduced in the intervention phase (31% vs 14%, P = .003). No difference in all-cause mortality was detected between the groups (30% vs 18%, P = .052). Conclusion A simple, behavioral nudge in microbiology reporting increased de-escalation and discontinuation of unnecessary broad-spectrum antibiotics. This highlights the importance of clear, persuasive communication of diagnostic testing in improving antibiotic prescribing behaviors.

Crossover Study of Silver-Embedded White Coats in Clinical Practice

BackgroundSilver has antimicrobial properties and application in infection prevention. This study compared silver-embedded coats to polyester white coats during clinical practice. MethodsThis study was a prospective randomized crossover with deception. Consenting medical residents were assigned to wear silver-embedded or control coats for 1 week and then crossed over. Bacterial cultures were obtained from 3 sites on the coat at baseline and 7 days. Bacterial growth (CFU/mL) was log transformed, and means were compared. ResultsSeventeen participants were enrolled. Sixty-one percent of control and 45% of silver coats had bacterial growth at baseline (P = 0.113). After 7 days of wear, 98% versus 90% had growth (P = 0.205). At 7 days, a log reduction of −0.40 (0.09 to −0.71) (P = 0.011) for aggregate of all 3 sites was seen favoring silver coats. Two hundred seventy-seven bacterial isolates (124 silver, 153 control) were analyzed. Species distribution was similar between the coats. ConclusionsDuring routine clinical use, silver coats were associated with a modest reduction in bacterial contamination compared to control coats. Clinical correlation to transmission of nosocomial organisms warrants further study.