Neutrophils are essential for host defense against Staphylococcus aureus infections. Although significant progress has been made, our understanding of neutrophil interactions with S. aureus remains incomplete. To provide a more comprehensive view of this process, we investigated phagocytosis and killing of S. aureus by human neutrophils using varied assay conditions in vitro. A greater percentage of bacteria were internalized by adherent neutrophils compared to those in suspension, and, unexpectedly, uptake of S. aureus by adherent neutrophils occurred efficiently in the absence of opsonins. An antibody specific for S. aureus promoted uptake of unopsonized bacteria in suspension, but had little or no capacity to enhance phagocytosis of S. aureus opsonized with normal human serum or by adherent neutrophils. Collectively, these results indicate that assay conditions can have a significant influence on the phagocytosis and killing of S. aureus by neutrophils. More importantly, the results suggest a vaccine approach directed to enhance opsonophagocytosis alone is not sufficient to promote increased killing of S. aureus by human neutrophils. With the emergence and reemergence of antibiotic-resistant microorganisms, establishing parameters that are optimal for studying neutrophil-S. aureus interactions will pave the way towards developing immune-directed strategies for anti-staphylococcal therapies.

Neutrophils constitute a critical part of innate immunity and are well known for their ability to phagocytose and kill invading microorganisms. The microbicidal processes employed by neutrophils are highly effective at killing most ingested bacteria and fungi. However, an alternative non-phagocytic antimicrobial mechanism of neutrophils has been proposed whereby microorganisms are eliminated by neutrophil extracellular traps (NETs). NETs are comprised of DNA, histones, and antimicrobial proteins extruded by neutrophils during NETosis, a cell death pathway reported to be distinct from apoptosis, phagocytosis-induced cell death, and necrosis. Although multiple laboratories have reported NETs using various stimuli in vitro, the molecular mechanisms involved in this process have yet to be definitively elucidated, and many questions regarding the formation and putative role or function of NETs in innate host defense remain unanswered. It is with these questions in mind that we provide some reflection and perspective on NETs and NETosis.

Background Pathogen reduction technology and enhanced bacterial culture screening promise to significantly reduce the risk of transfusion‐associated septic reactions due to contaminated platelets. Recent reports suggest that these interventions lack efficacy for post‐collection and processing contamination with environmental organisms if the storage bag integrity is compromised. Case Report We report a fatal septic transfusion reaction in a 63‐year‐old patient with chronic kidney and liver disease who received a pathogen reduced platelet transfusion in anticipation of surgery. Methods The residual platelet concentrate was cultured, with the detected microorganisms undergoing 16S genotype sequencing. Separate pathogen reduction studies were performed on the recovered bacteria, including assessment for amotosalen photoproducts. The storage container was subjected to pressure testing and microscopic examination. Environmental culture screening was performed at the hospital. Results Gram negative rods were detected in the platelet unit and cultures of both platelet component and the patient's blood grew Acinetobacter baumannii complex, Leclercia adecarboxylata and Staphylococcus saprophyticus. These strains were effectively inactivated with >7.2, 7.7, and >7.1 log10 kill, respectively. The platelet storage container revealed a leak visible only on pressure testing. Hospital environmental cultures were negative and the contamination source is unknown. A. baumannii complex and S. saprophyticus 16S genotyping sequences were identical to those implicated in a previously reported septic reaction. Conclusion Findings are compatible with post‐processing environmental contamination of a pathogen reduced platelet concentrate via a non‐visible, acquired storage container leak. Efforts are warranted to actively prevent damage to, and detect defects in, platelet storage containers, and to store and transport components in clean environments.

Background Strategies to reduce platelet (PLT) bacterial contamination include donor screening, skin disinfection, sample diversion, bacterial culture, pathogen reduction (PR), and day‐of‐transfusion tests. We report bacterial sepsis following a pathogen‐reduced PLT transfusion. Case Report An adult male with relapsed acute lymphoblastic leukemia was successfully treated for central catheter–associated Staphylococcus aureus bacteremia. A peripherally inserted central catheter (PICC) was placed. Chills, rigors, and flushing developed immediately after PICC‐infused pathogen‐reduced PLTs, progressing to septic shock requiring intensive care management. Methods PICC and peripheral blood (PB), transfused bag saline flushes (TBFs), environmental samples, and the pathogen‐reduced untransfused co‐component (CC) were cultured. Plasma metagenomic and bacterial isolate whole‐genome sequencing; PLT mitochondrial DNA (mtDNA) testing of untransfused CC and TBF; CC testing for amotosalen (S‐59)/S‐59 photoproducts; isolate PR studies (INTERCEPT); and TBF polymerase chain reaction for recipient Y‐chromosome DNA were performed. Results PB and PICC cultures grew Acinetobacter calcoaceticus/baumannii complex (ACBC). TBF was gram‐positive; mass spectrometry identified ACBC and Staphylococcus saprophyticus (SS). CC Gram stain and cultures were negative. Environmental cultures, some done after decontamination, were ACBC/SS negative. Posttransfusion patient plasma and TBF ACBC sequences were genetically identical. No Y‐chromosome signal was detected in TBF. S‐59 photoproducts and evidence of mtDNA amplification inhibition were found in the CC. Spiking PR studies showed >5.9‐log inactivation for both isolates. Donor skin cultures for Acinetobacter were negative. Conclusion CC sterility, PR studies, residual S‐59 photoproducts, and mtDNA amplification inhibition suggest successful PR. Unidentified environmental sources and inherent or acquired bag defects may have contributed to postmanufacturing pathogen‐reduced PLT contamination.

Background and objectives Red blood cell concentrates (RBCC) are susceptible to bacterial contamination despite cold storage. A reliable evaluation of strategies to minimize the risk of RBCC-associated bacterial transmission requires the use of suitable reference bacteria. Already existing Transfusion-Relevant Bacteria Reference Strains (TRBRS) for platelet concentrates fail to grow in RBCC. Consequently, the ISBT TTID, Working Party, Bacterial Subgroup, conducted an international study on TRBRS for RBCC.Materials and methods Six bacterial strains (Listeria monocytogenes PEI-A-199, Serratia liquefaciens PEI-A-184, Serratia marcescens PEI-B-P-56, Pseudomonas fluorescens PEI-B-P-77, Yersinia enterocolitica PEI-A-105, Yersinia enterocolitica PEI-A-176) were distributed to 15 laboratories worldwide for enumeration, identification, and determination of growth kinetics in RBCC at days 7, 14, 21, 28, 35 and 42 of storage after low-count spiking (10-25 CFU/RBCC).Results Bacterial proliferation in RBCC was obtained for most strains, except for S. marcescens, which grew only at 4 of 15 laboratories. S. liquefaciens, S. marcescens, P. fluorescens and the two Y. enterocolitica strains reached the stationary phase between days 14 and 21 of RBCC storage with a bacterial 692This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.concentration of approximately 10 9 CFU/ml. L. monocytogenes displayed slower growth kinetics reaching 10 6 -10 7 CFU/ml after 42 days. ConclusionThe results illustrate the importance of conducting comprehensive studies to establish well-characterized reference strains, which can be a tool to assess strategies and methods used to ameliorate blood safety. The WHO Expert Committee on Biological Standardization adopted the five successful strains as official RBCC reference strains. Our study also highlights the relevance of visual inspection to interdict contaminated RBC units.

BackgroundFatty acid modifying enzyme (FAME) has been shown to modify free fatty acids to alleviate their bactericidal effect by esterifying fatty acids to cholesterol or alcohols. Although it has been shown in previous studies that FAME is required for Staphylococcus aureus survival in skin abscesses, FAME is poorly studied compared to other virulence factors. FAME activity had also been detected in coagulase-negative staphylococci (CNS). However, FAME activity was only surveyed after a bacterial culture was grown for 24 h. Therefore if FAME activity was earlier in the growth phase, it would not have been detected by the assay and those strains would have been labeled as FAME negative.ResultsFifty CNS bovine mastitis isolates and several S. aureus, Escherichia coli, and Streptococcus uberis strains were assayed for FAME activity over 24 h. FAME activity was detected in 54% of CNS and 80% S. aureus strains surveyed but none in E. coli or S. uberis. While some CNS strains produced FAME activity comparable to the lab strain of S. aureus, the pattern of FAME activity varied among strains and across species of staphylococci. All CNS that produced FAME activity also exhibited lipase activity. Lipase activity relative to colony forming units of these CNS decreased over the 24 h growth period. No relationship was observed between somatic cell count in the milk and FAME activity in CNS.ConclusionsSome staphylococcal species surveyed produced FAME activity, but E. coli and S. uberis strains did not. All FAME producing CNS exhibited lipase activity which may indicate that both these enzymes work in concert to alter fatty acids in the bacterial environment.

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