Efficient Inactivation of Clinically Relevant Antimicrobial Drug Concentrations by BacT/Alert or Bactec Resin-Containing Media in Simulated Adult Blood Cultures

Verification of the Vitek Reveal System for Direct Antimicrobial Susceptibility Testing in Gram-Negative Positive Blood Cultures

Background/Objectives: The International Organization for Standardization (ISO) 20776-2:2021, which replaces ISO 20776-2:2007, focuses solely on the performance of antimicrobial susceptibility testing (AST) assays, emphasizing the ISO 20776-1 broth microdilution method as the reference standard. Consequently, categorical agreement (CA) and associated errors should not be applied. We verified the Vitek Reveal AST assay according to both ISO 20776-2:2021 and ISO 20776-2:2007 criteria. Methods: Samples from 100 simulated and clinical Gram-negative (GN) positive blood cultures (PBCs) were tested at a large teaching hospital. The simulated GN-PBCs were obtained from a hospital collection of isolates selected to represent diverse antimicrobial resistance profiles. The Reveal assay results were compared with those from the reference assay, and the time to result (TTR) for the Reveal assay was calculated. Results: The essential agreement rates were 96.1% (816/849) for simulated and 98.8% (929/940) for clinical GN-PBC samples. The bias values were -3.1 for simulated and -11.0 for clinical samples. The CA rates were 97.7% (808/827) for simulated and 99.2% (924/931) for clinical samples. The mean TTR ± SD (hours) for resistant organisms was significantly lower (4.40 ± 1.15) than that for susceptible, increased exposure (5.52 ± 0.48) and susceptible (5.54 ± 0.49) organisms. Conclusions: Our findings reinforce the potential of the Reveal assay as a valuable tool and support its implementation in clinical microbiology laboratories.

Comparison and evaluation of neutralization of clinically frequently used antimicrobial agents using three different culture media in simulated blood cultures

The performance of BACT/ALERT FA/FN Plus (France) blood culture containing a novel resin, DL (China) blood culture containing common resin, and adsorbent-free REDOX (USA) blood culture relying on dilution for antimicrobial neutralization at %peak serum concentration was evaluated by measuring the recovery of organisms and time to detection (TTD) in nine simulated microorganism-antimicrobial combination blood cultures. Significant differences were observed in the recovery rates among the aerobic media: 87.5% for BACT/ALERT media, 42.9% for DL media, and 12.5% for REDOX media. In contrast, no statistical difference was found in the TTD between FA Plus media and DL aerobic media. For the anaerobic media, the recovery rates were 91.4% for BACT/ALERT media, 2.9% for DL media, and 14.3% for REDOX media, with significant differences only between BACT/ALERT FN Plus media and the others. Among the seven main antimicrobial categories, only BACT/ALERT FA/FN Plus culture media demonstrated high recovery of microorganisms, with the exception of carbapenems. The DL culture media exhibited a relatively high recovery rate of microorganisms in the presence of piperacillin/tazobactam, levofloxacin, and gentamicin, but only in aerobic conditions. Conversely, REDOX media displayed microorganism recovery solely in the presence of gentamicin. BACT/ALERT FA/FN Plus culture media with novel resin showed absolute advantages over DL and REDOX culture media and can, therefore, be selectively applied in clinical settings when antimicrobials are used prior to blood collection. DL culture media, containing common resin, outperformed adsorbent-free dilution-based REDOX culture media, making it a viable backup option. There is a need to focus on improving the neutralization of carbapenems with current inefficiency in all three medias.

IMPORTANCE

We present a study on performance comparison of three different commercial culture media for neutralization of antibiotic effects in simulated blood cultures. BACT/ALERT (FA Plus and FN Plus) culture media with novel resin showed absolute advantages over DL and REDOX culture media at %PSL concentration of antimicrobials.

Early assessment of blood culture negativity as a potential support tool for antimicrobial stewardship

Objective

To assess whether 48-h negative blood culture (BC) bottles are still negative at the classic 120-h incubation endpoint and whether 48 h might be the time to make antimicrobial therapy decisions.

Methods

Data from the first collected bottles from bloodstream infection (BSI) episodes of single patients were retrospectively analyzed. Probabilities of bottles being negative at the classic endpoint were calculated from 0 to 120 h of incubation.

Results

Among BC-negative episodes (4018/4901 [82.0%]), most (2097/4018 (52.2%) occurred in medicine patients. At 48 h, probability was 100.0% (95% CI, 99.9-100.0) for all 4018 patients. Of these, 1244 (31.0%) patients remained on antibiotics until 120 h. Excluding 401 (32.2%) patients who received antibiotics for another (non-bloodstream) infection, 843 (67.8%) of 1244 patients could have merited early (48-h) discontinuation of antibiotics. Stopping treatment in these patients would have led to saving 5201 days of access (943 [18.1%] days), watch (3624 [69.7%] days), or reserve (634 [12.2%]) AWaRe groups' antibiotics, which correspond to 65.6% (5201/7928) of days of administered antibiotics in all 1244 patients.

Conclusion

As an early indicator of BC negativity, the 48-h endpoint could reliably support antimicrobial stewardship, but the clinical judgment remains imperative especially when BSI is highly suspected.

Efficient Recovery of Candida auris and Five Other Medically Important Candida Species from Blood Cultures Containing Clinically Relevant Concentrations of Antifungal Agents

Candida auris and other Candida species (C. albicans, C. glabrata, C. parapsilosis, C. tropicalis, and C. krusei) are important causes of bloodstream infection. Early or prolonged treatment with antifungal agents is often required. The inhibitory effect of antifungal agents in the patients' bloodstream may compromise the sensitivity of blood culture (BC) to diagnose and/or monitor patients with candidemia. Using a clinical BC simulation model, we compared antimicrobial drug-neutralizing BC media in BacT/Alert FA PLUS (FAP) or Bactec Plus Aerobic/F (PAF) bottles with non-neutralizing BC media in Bactec Mycosis IC/F (MICF) bottles to allow Candida growth in the presence of 100%, 50%, or 25% peak serum level (PSL) antifungal concentrations. In total, 117 organism/antifungal combinations were studied, and Candida growth was detected after incubating bottles into BacT/Alert VIRTUO or Bactec FX BC systems. Compared to control (without antifungal) bottles, both FAP and PAF bottles with 100% PSL antifungal concentrations allowed 100% recovery for C. auris, C. glabrata, and C. parapsilosis, whereas recovery was below 100% for C. albicans, C. krusei, and C. tropicalis. MICF bottles were less efficient at 100%, 50%, or 25% PSL antifungal concentrations, for all Candida species, except for C. auris. While azoles and amphotericin B did not hinder Candida growth in FAP or PAF bottles, echinocandins allowed C. auris, C. glabrata, and C. parapsilosis to grow in FAP, PAF, or MICF bottles. Overall, the maximum time to detection was 4.6 days. Taken together, our findings emphasize the reliability of BCs in patients undergoing antifungal treatment for candidemia. IMPORTANCE While echinocandins remain the preferred antifungal therapy for candidemia, bloodstream infections caused by C. auris, C. glabrata, or, at a lesser extent, C. parapsilosis may be difficult to treat with these antifungal agents. This is in view of the high propensity of the above-mentioned species to develop antifungal resistance or tolerance during treatment. Azoles and amphotericin B are possible alternatives. Thus, optimizing the recovery of Candida from BCs is important to exclude the likelihood of negative BCs for Candida species, owing to the inhibitory effect of antifungal agents present in the blood sample with which BCs are inoculated. Consistently, our results about the recovery of medically important Candida species (including C. auris) from simulated BCs in BacT/Alert FAP, Bactec PAF, or Bactec MICF bottles containing clinically relevant antifungal concentrations add support to this research topic, as well as to the use of BCs for monitoring the clinical and therapeutic course of candidemia.

Blood Cultures for the Diagnosis of Infective Endocarditis: What Is the Benefit of Prolonged Incubation?

To assess the need for prolonged incubation of blood culture bottles beyond five days for the diagnosis of infectious endocarditis (IE), we conducted a retrospective cohort study of 6109 sets of two blood culture bottles involving 1211 patients admitted to the Henri Mondor University Hospital for suspicion of IE between 1 January 2016 and 31 December 2019. Among the 322 patients with IE, 194 had positive blood cultures in our centre. Only one patient with a time-to-positivity blood culture of more than 120 h (5 days) was found. The main cause for the 22 patients with positive blood cultures after five days was contamination with Cutibacterium acnes. Our results do not support extending the duration of incubation of blood culture bottles beyond five days for the diagnosis of infectious endocarditis, with the exception of patients with risk factors for C. acnes infection.

Simulated Pediatric Blood Cultures to Assess the Inactivation of Clinically Relevant Antimicrobial Drug Concentrations in Resin-Containing Bottles

The bacteremia level as well as the administration of antibiotics before blood collection may significantly affect the recovery of bacterial pathogens from pediatric blood cultures in BacT/Alert Virtuo or Bactec FX BC systems, which remain the common techniques to diagnose bacteremia in pediatric patients. We simulated pediatric blood cultures with low or intermediate bacteremia level to evaluate BacT/Alert PF Plus and Bactec Peds Plus blood culture bottles for resin-based inactivation of 16 antibiotic-bacterium combinations. Overall, 105/192 (54.7%) of BacT/Alert PF Plus bottles and 69/192 (36.0%) of Bactec Peds Plus bottles allowed organisms to grow when exposed to antibiotics. In particular, both BacT/Alert PF Plus and Bactec Peds Plus bottles proved to be effective with piperacillin/tazobactam and Pseudomonas aeruginosa or with oxacillin and methicillin-susceptible Staphylococcus aureus (100% growth), whereas no effectiveness was apparent with ceftriaxone and Escherichia coli, Streptococcus agalactiae, or Streptococcus pneumoniae or with cefepime and E. coli (0% growth). In some relevant instances (e.g., with vancomycin and methicillin-resistant S. aureus or Streptococcus pneumoniae), BacT/Alert PF Plus bottles were superior to Bactec Peds Plus bottles. Together, these findings underscore the potentiality of resin-containing bottles to enhance diagnosis of bacteremia in pediatric patients on antimicrobial therapy. This is particularly true with one of the evaluated BC systems and with simulated intermediate bacteremia level only.

Inactivation of Clinically Frequently Used Antimicrobial Agents By BacT/ALERT FAN Plus and BACTEC Aerobic and Anaerobic Culture Media in Simulated Blood Cultures: First Comparative Evaluation in China Mainland

Purpose

To evaluate the antimicrobial inactivation capabilities of BacT/ALERT (FA Plus and FN Plus) and BACTEC (Plus Aerobic/F and Lytic/10 Anaerobic/F) media.

Patients and Methods

The inactivation capabilities of the commercial blood culture media were compared using 21 microorganism-antimicrobial combinations in simulated adult blood cultures.

Results

BacT/ALERT culture media demonstrated higher detection rates than the BACTEC culture media. The recovery rates of the aerobic bottles were 74/115 (64.3%) for FA Plus bottles and 64/115 (55.7%) for BACTEC Aerobic Plus bottles. The BacT/ALERT FAN Plus culture media exhibited a shorter time to detection (TTD). The TTD of FA Plus media was 14.7 h, 4.85 h shorter than the BACTEC Aerobic media (19.55 h), while the TTDs of FN Plus media and BACTEC Anaerobic media were 16.8 h and 18.4 h, respectively.

Conclusion

BacT/ALERT (FA Plus and FN Plus) media showed relative, but not absolute, advantages, as it had higher detection rates and shorter TTD and thus can be selectively applied to patients with prior use of antimicrobial agents before blood culture samples are taken.

Effect of Clinically Meaningful Antibiotic Concentrations on Recovery of Escherichia coli and Klebsiella pneumoniae Isolates from Anaerobic Blood Culture Bottles with and without Antibiotic Binding Resins

Blood cultures are routinely collected in pairs of aerobic and anaerobic bottles. Artificial sterilization of Gram-negative bacteria in aerobic bottles containing clinically meaningful antibiotic concentrations has previously been observed. This study assessed recovery from anaerobic bottles with and without antibiotic binding resins. We studied the recovery of Escherichia coli and Klebsiella pneumoniae when exposed to meropenem, imipenem, cefepime, cefazolin, levofloxacin, and piperacillin-tazobactam in resin-containing BacT/Alert FN Plus and BD Bactec Plus anaerobic/F bottles as well as resin-free BacT/Alert SN and BD Bactec standard anaerobic bottles. Bottles were inoculated with bacteria and whole blood containing peak, midpoint, or trough concentrations and incubated for up to 120 hours in their respective detection systems. In E. coli resin-containing bottles, recovery was observed in 10/24 (42%), 17/24 (71%), and 18/24 (75%) (P = 0.034) of those exposed to peak, midpoint, and trough concentrations, respectively. In K. pneumoniae resin-containing bottles, recovery was observed in 8/16 (50%), 10/16 (63%), and 10/16 (63%) (P = 0.710), respectively. No growth was detected in bottles containing cefepime regardless of concentration, while recovery was observed in the presence of all concentrations of cefazolin and piperacillin-tazobactam. Recovery in bottles with meropenem and imipenem was more frequently observed in BacT/Alert FN Plus bottles compared with Bactec Plus bottles. Resin-free bottles demonstrated significantly lower recovery than bottles containing binding resin. Clinical concentrations of certain antibiotics can adversely affect detection of E. coli and K. pneumoniae in anaerobic blood culture bottles. Obtaining blood cultures immediately before a dose and utilizing resin-containing anaerobic bottles will maximize the likelihood of recovery.

Recovery of Gram-Negative Bacteria from Aerobic Blood Culture Bottles Containing Antibiotic Binding Resins after Exposure to β-Lactam and Fluoroquinolone Concentrations

Blood culture bottles containing antibiotic binding resins are routinely used to minimize artificial sterilization in the presence of antibiotics. However, the resin binding kinetics can differ between antibiotics and concentrations. This study assessed the impact of clinically meaningful peak, midpoint, and trough concentrations of meropenem, imipenem, cefepime, cefazolin, levofloxacin, and piperacillin-tazobactam on the recovery of Pseudomonas aeruginosa, Escherichia coli, and Klebsiella pneumoniae from resin-containing BacT/Alert FA Plus and Bactec Aerobic/F blood culture bottles. P. aeruginosa-inoculated bottles alarmed positive in 4/20 (20%), 16/20 (80%), and 20/20 (100%) of those with peak, midpoint, and trough concentrations of antipseudomonal agents, respectively (P ≤ 0.001). E. coli was recovered from 8/24 (33%), 11/24 (46%), and 14/24 (58%) of bottles with peak, midpoint, and trough concentrations, respectively (P = 0.221). K. pneumoniae was recovered from 8/16 (50%) at all concentrations of the studied antibiotics (P = 1.0). BacT/Alert and Bactec bottles inoculated with antibiotics and P. aeruginosa had similar times to detection (TTD) (P = 0.352); however, antibiotic-containing BacT/Alert bottles had a shorter TTD compared with antibiotic-containing Bactec bottles for E. coli (P = 0.026) and K. pneumoniae (P ≤ 0.001). Pathogen recovery in BacT/Alert FA Plus and Bactec Aerobic/F blood culture bottles containing antibiotic binding resins was greatly reduced in the presence of antibiotics, especially at higher concentrations. These data support the practice of drawing blood cultures immediately before an antibiotic dose to maximize the chances of pathogen recovery.