Polymicrobial Cultures Research Articles

The microbiology of acute cholangitis and associated in-hospital mortality

Aim: Acute cholangitis is an infection that may become life-threatening. In this study, we investigated the most prevalent organisms identified in cultures, antibiotic resistance patterns and associated in-hospital mortality. Materials and Methods: Patients diagnosed as having acute cholangitis were included in the study retrospectively. The study patients were classified in two groups by culture results as culture-negative or culture-positive patients. The aim of the study was to identify offending organisms, antibiotic resistance and in-hospital mortality based on culture results. Results: Overall, 108 patients with acute cholangitis were evaluated in two groups. Sixty six patients (61.2%) had positive cultures and 43 (40%) of these patients had polymicrobial culture results. There was a predominance of gram-negative bacteria (63%) and particularly, Klebsiella spp. and E.coli were the most commonly isolated organisms. The patients who died had 90.9% positive cultures, whereas those who survived had 53.6% culture positivity (p=0.02) Conclusions: Biliary stent implantaiton was found to be the most common etiological factor for acute cholangitis. In terms of culture results, K. pneumoniae and E. coli were the most commonly isolated causative agents. ESBL resistance was found with a rate of 48.5% and carbapenem resistance was found with a rate of 22% for gram negative bacilli. Culture positivity was a risk factor in terms of in-hospital death

48. Association of Rapid Pathogen Identification and Pharmacist Intervention on Time to Optimal Antimicrobial Therapy for Bloodstream Infections at Two Community Hospitals

BackgroundAs many as 1 in 3 patients with bloodstream infections at community hospitals receive inappropriate empiric antimicrobial therapy. Studies have shown that the coupling of real-time intervention with rapid pathogen identification improves patient outcomes and decreases health-system costs at large, tertiary academic centers. The aim of this study was to assess if similar outcomes could be obtained with the implementation of real-time pharmacist intervention to rapid pathogen identification at two smaller, rural community hospitals.MethodsThis was a pre-post implementation study that occurred from September of 2019 to March 2020. This study included patients ≥18 years of age admitted with one positive blood culture. Patients were excluded if they were pregnant, had a polymicrobial blood culture, known culture prior to admission, hospice consulted prior to admission, expired prior to positive blood culture, or transferred to another hospital within 24 hours of a positive blood culture. Endpoints of patients prior to intervention were compared to patients post-implementation. The primary endpoint was time to optimal antimicrobial therapy. Secondary endpoints included time to effective antimicrobial therapy, in-hospital mortality, length of hospital stay, and overall cost of hospitalization.ResultsOf 212 patients screened, 88 patients were included with 44 patients in each group. Both groups were similar in terms of comorbidities, infection source, and causative microbial. No significant difference was seen in the mean time to optimal antimicrobial therapy (27.3±35.5 hr vs 19.4± 30 hr, p=0.265). Patients in the post-implementation group had a significantly higher mean hospitalization cost ($24,638.87± $11,080.91 vs $32,722.07±$13,076.73, p=0.013). There was no significant difference in time to effective antimicrobial therapy, in-hospital mortality, or length of hospital stay.ConclusionThere were no between-group differences in the primary outcome of time to optimal therapy, with a higher mean hospitalization cost after implementation. These results suggest further antimicrobial stewardship interventions are needed, along with larger studies conducted in the community hospital settings.Disclosures All Authors: No reported disclosures

1141. Composition of Placental Cultures and Correlation with Maternal and Infant Blood Cultures in Mothers with Suspected Chorioamnionitis

BackgroundPlacental culture is often used in combination with placental pathology in pregnant women with suspected chorioamnionitis. While multiple studies have looked at the correlation of placental cultures with neonatal outcomes, few have looked at the composition of placental cultures in terms of the number of organisms and their identification. Our study aims to describe such characteristics of placental cultures and to compare organisms found in placental cultures with those in maternal and infant blood cultures.MethodsWe performed retrospective chart reviews on mothers and infants for whom a placental pathology and culture was sent at Loyola University Medical Center between January 2017 and December 2019. We separated the mothers based the results of their placental cultures and pathologies and on the number of organisms found in each culture. We then analyzed the identification of organisms of the positive cultures and compared these organisms with positive infant and maternal blood cultures.ResultsA total of 208 placental cultures out of 279 sent (73.84%) were positive. 63 (30.29%) positive cultures were monomicrobial, while 145 (69.71%) cultures were polymicrobial. The most prevalent organisms found in all placental cultures were coagulase negative staphylococcus (26.44%), Streptococcus anginosus (16.83%), Corynebacterium species (14.90%), Lactobacillus species (14.90%), and Gardnerella vaginalis (13.94%). A small fraction of positive placental cultures was associated with positive infant and maternal blood cultures (4.33% and 3.85%, respectively). When comparing the organisms in placental cultures with those in maternal and infant blood cultures, 100% and 71% (respectively) of cases with both positive blood and placental cultures had shared organisms.Distribution of most common organisms found in monomicrobial and polymicrobial placental cultures. Distribution of placental cultures based on number of organisms. Correlation of placental cultures with infant and maternal blood cultures. ConclusionThe data collected from this study helps provide a biological profile of organisms found in placental culture for patients with suspected chorioamnionitis. Additionally, the data suggests that the organisms found in these cultures are often consistent with those found in maternal and infant blood cultures. The overall incidence of positive infant and maternal blood cultures is low as compared to positive placental cultures.Disclosures Amanda Harrington, PhD, Beckman Coulter (Scientific Research Study Investigator)

1330. Development of a Pediatric Emergency Department (ED) Uropathogen Antibiogram and Empiric Urinary Tract Infection (UTI) Treatment Algorithm

BackgroundAntimicrobial Stewardship efforts in adult ED settings lead to improved patient outcomes and fewer adverse events. However, there are limited data on incorporation of multiple interventions to assist with empiric and definitive antibiotic therapy selection, particularly in the pediatric ED setting. The purpose of this project was to create an antibiogram and empiric UTI treatment algorithm for use in a pediatric ED.MethodsThis is a multi-phase program implementation in a pediatric ED. Patients aged 2 months -18 years presenting to the ED between January to December 2018 with an ICD10 code for cystitis or pyelonephritis and collection of urine culture were included. Patients were excluded if they were admitted to an inpatient unit or they had a polymicrobial urine culture result. The antibiogram was prepared by including the first isolate of a species from each patient in the given time frame using Clinical and Laboratory Standards Institute recommendations.ResultsA total of 145 unique patients with 160 ED encounters were included in phase I of the project. Median patient age was 5 years (IQR 1.4-8). Discharge diagnosis for 75% of the 160 ED encounters was pyelonephritis. Urogenital flora was cultured from 19.4% of cultures and 21.2% of cultures were without any growth. The most common pathogen isolated was E. coli (39.4%). For ages 2 months – 18 years, susceptibility of urinary E. coli isolates was 95.5% for nitrofurantoin, 92.5% each for ceftriaxone and ciprofloxacin, and 85.1% for cefazolin. Cefdinir and cephalexin were the empiric antibiotics prescribed on discharge 76.3% of the time. After consideration of factors such as antimicrobial stewardship and spectrum of activity, cephalexin was chosen as the treatment of choice for the 2 months – 11 years age group. For children ≥ 12 years, nitrofurantoin was selected as preferred treatment for uncomplicated cystitis while cephalexin was selected as preferred treatment for pyelonephritis.M Health Fairview University of Minnesota Masonic Childrens ED 2018 E coli isolate antibiogram ConclusionAn empiric UTI treatment algorithm incorporating local antimicrobial susceptibility pattern alongside recommendations from national organizations was created. Phase II of the project will evaluate the implementation of the algorithm to determine its impact on readmission rates and antibiotic/pathogen mismatch.Disclosures Elizabeth B. Hirsch, PharmD, Merck (Grant/Research Support)Nabriva Therapeutics (Advisor or Review Panel member)

318 Bovine liver abscess complex: Likely causes and tested solutions

Abstract The liver abscess (LA) complex is commonly associated with high energy, limited roughage rations. Aggressive grain processing increases starch availability, leading to increased lactic acid production and lower rumen pH, potentially causing lactic acidosis. Rumen lesions may result from repeated bouts of lactic acidosis, likely allowing penetration of bacteria into the bloodstream, and have been associated with incidence of LA. Additionally, consumption of sharp objects can cause penetration of rumen epithelium and likely promote bacterial entry into the bloodstream. Research has successfully induced LA in both cattle and sheep from intraportal infusion of Fusobacterium necrophorum. F. necrophorum is a gram-negative, non-sporeforming anaerobe commensal to the rumen that likely enters the liver via the portal vein due to a damaged rumen wall. F. necrophorum has a plethora of virulence factors that support LA formation; however, recent research has indicated that LA contain polymicrobial cultures, and some have questioned if bacteria other than F. necrophorum can cause LA. Liver abscesses are not solely limited to animals on a high-energy diet; they have also been documented in cull beef-type and dairy-type cows. Production losses from LA are associated with reduction in dry-matter intake, average daily gain, gain:feed, live weight, hot carcass weight, dressed carcass yield, and subcutaneous fat depth, concomitant with increased carcass trim. To reduce the incidence of LA, cattle feeders typically include tylosin in the diet; multiple studies have reported a 20 to 38 percentage point reduction in the incidence of LA present at slaughter. Four additional antibiotics (bacitracin, chlortetracycline, oxytetracycline, virginiamycin) are approved for the prevention of LA. Feeding antibiotics to food animals is a contemporary social issue with limited societal support. Tested alternatives to antimicrobial control for LA include vaccination with F. necrophorum leukotoxoid or bacterin, feeding essential oils, enzymatic feed treatment, and feeding yeast fermentation products.

Direct Identification of Microorganisms from Positive Blood Cultures by MALDI-TOF MS Using an in-House Tween® 80 Method: Experimental and Clinical Study

It has been reported that direct identification from blood culture bottles with positive signals and reporting the results to the clinics earlier has positive effects on mortality and morbidity. Extraction methods especially using detergents are used for the direct identification from the bottles which give positive signal. For this purpose, in-house methods developed based on the usage of saponin are widely available in the literature. In this study, it was aimed to develop a simple, easy-to-apply and reliable protocol for identifying the agent directly from the blood culture bottle that gives positive signal with the use of detergent Tween® 80, and to study the obtained protocol in clinical samples in a routine microbiology laboratory and to evaluate the results. The study was carried out in two stages, the experimental stage where the method was developed and the clinical stage where the method was applied. In the experimental stage, blood culture bottles were created with standard strains and isolates previously diagnosed with the 16S rRNA method. 10% solution of Tween® 80 was prepared with distilled water. 1 ml sample was transferred from the bottle that gave positive signal to the microcentrifuge tube, 100 µl of 10% solution of Tween® 80 was added, vortexed for 10 seconds and then incubated for 5 minutes at room temperature. The tubes were centrifuged for 5 min at 14.000 rpm, the supernatant was discarded and the pellet was washed with 1 ml of distilled water and centrifuged at 14.000 rpm for 5 minutes in three times. Samples taken from the pellets were rubbed on the slide and dried on air. Firstly, 1 µl of 70% formic acid, then 1 µl, of matrix solution was added and it was used after drying. In the second stage of the study, the method was applied to the 502 vials giving positive signal in the Microbiology Laboratory of Ankara University Faculty of Medicine Ibni Sina Hospital between 17 April 2018-31 August 2018 and the results were compared with the subculture results. The results obtained at the end of extraction in the experimental stage were compared with the subculture results and no statistical difference was found. In 383 (82.9%) bottles among 462 (92.1%) bottles with monomicrobial positive cultures, compatible results with the subculture results were obtained. Of the microorganisms correctly identified, 350 (91.3%) were bacteria and 33 (8.7%) were fungi. On the other hand, 216 (56.4%) of the bacteria were gram positive and 134 (34.9%) of them were gram negative bacteria. At least one microorganism was correctly identified in 19 (47.5%) of 40 (7.9%) bottles with polymicrobial blood cultures. Their distribution was gram negative (n= 10) and gram positive (n= 8) and yeast (n= 1). No microorganisms were identified in six bottles with polymicrobial cultures. According to the results, we believe that this in-house method developed using Tween® 80 will be a routinely applicable method for blood culture bottles that give positive signal in microbiology laboratories and it will contribute to the early diagnosis.

Clinical and Genomic Epidemiology of Carbapenem-Nonsusceptible Citrobacter spp. at a Tertiary Health Care Center over 2 Decades.

Carbapenem-nonsusceptible Citrobacter spp. (CNSC) are increasingly recognized as health care-associated pathogens. Information regarding their clinical epidemiology, genetic diversity, and mechanisms of carbapenem resistance is lacking. We examined microbiology records of adult patients at the University of Pittsburgh Medical Center (UMPC) Presbyterian Hospital (PUH) from 2000 to 2018 for CNSC, as defined by ertapenem nonsusceptibility. Over this time frame, the proportion of CNSC increased from 4% to 10% (P = 0.03), as did daily defined carbapenem doses/1,000 patient days (6.52 to 34.5; R2 = 0.831; P < 0.001), which correlated with the observed increase in CNSC (lag = 0 years; R2 = 0.660). Twenty CNSC isolates from 19 patients at PUH and other UPMC hospitals were available for further analysis, including whole-genome short-read sequencing and additional antimicrobial susceptibility testing. Of the 19 patients, nearly all acquired CNSC in the health care setting and over half had polymicrobial cultures containing at least one other organism. Among the 20 CNSC isolates, Citrobacter freundii was the predominant species identified (60%). CNSC genomes were compared with genomes of carbapenem-susceptible Citrobacter spp. from UPMC and with other publicly available CNSC genomes. Isolates carrying genes encoding carbapenemases (blaKPC-2,blaKPC-3, and blaNDM-1) were also long-read sequenced, and their carbapenemase-encoding plasmid sequences were compared with one another and with publicly available sequences. Phylogenetic analysis of 102 UPMC Citrobacter genomes showed that CNSC from our setting did not cluster together. Similarly, a global phylogeny of 64 CNSC genomes showed a diverse population structure. Our findings suggest that both local and global CNSC populations are genetically diverse and that CNSC harbor carbapenemase-encoding plasmids found in other Enterobacterales.

Enterococcus faecalis inhibits Klebsiella pneumoniae growth in polymicrobial biofilms in a glucose-enriched medium

Catheter-related urinary tract infections are one of the most common biofilm-associated diseases. Within biofilms, bacteria cooperate, compete, or have neutral interactions. This study aimed to investigate the interactions in polymicrobial biofilms of Klebsiella pneumoniae and Enterococcus faecalis, two of the most common uropathogens. Although K. pneumoniae was the most adherent strain, it could not maintain dominance in the polymicrobial biofilm due to the lactic acid produced by E. faecalis in a glucose-enriched medium. This result was supported by the use of E. faecalis V583 ldh-1/ldh-2 double mutant (non-producer of lactic acid), which did not inhibit the growth of K. pneumoniae. Lyophilized cell-free supernatants obtained from E. faecalis biofilms also showed antimicrobial/anti-biofilm activity against K. pneumoniae. Conversely, there were no significant differences in planktonic polymicrobial cultures. In summary, E. faecalis modifies the pH by lactic acid production in polymicrobial biofilms, which impairs the growth of K. pneumoniae.

Treatment of chronic Osteomyelitis with vascularized bone flaps in one-stage-procedure.

Chronic osteomyelitis is a long-standing infection of the bone. Treatment is often combined, using antibiotics and surgery (with radical debridement and secondary or concomitant reconstruction). One-stage management is an alternative approach, with few reported cases in literature. We carried out an observational retrospective multicenter study to evaluate the results of one-stage reconstructions with vascularized bone flaps. We assessed bone and infection healing in 14 cases, with a mean follow-up of 63.6 months. Bone union was obtained in 10 cases (71.4 %) in a mean period of 7.9 months. Nonunion occurred in 4 cases (28.6 %), 2 of them with infection persistence. Bone nonunion risk increases in polymicrobial infections (p = 0.0269) and in compromised hosts (p = 0.0110). Infection healing was achieved in 11 cases (78.6 %). Fistula recurred in 3 cases of forearm osteomyelitis (21.4 %) in 10 months on average. Infection recurrence is associated with polymicrobial infections (p = 0.0378) and is higher in internal fixation and compromised hosts with no statistically significant relation. One-stage surgical treatment seems to be an effective approach in selected patients, in particular when an important impairment of local soft tissue and bone exposure are present, and immediate bone coverage with vascularized soft tissue is needed. Most complications occurred in compromised hosts and in patients with polymicrobial cultures. Further research, with comparison between one and two-stage procedures, is needed in order to strengthen the level of evidence.

Method for obtaining blood culture while diagnosing bloodstream infection.

Diagnosing of bloodstream infection (BSI) in outpatients is essential. A large blood volume is required to obtain blood culture (CLSI): 2 sets, 40ml of blood for diagnosing in 95% cases of bacteremia. Molecular-genetic methods can not replace blood culture method, but they accelerate the identification of any pathogen. Culturomics gives a combination of different conditions for isolating microorganisms from a sample and along with their genetic identification. We used the patent method for direct inoculation of buffy-coat from 4,5ml of a venous blood sample and MALDI-ToF identification method. In 382 outpatients examined there were received 183 blood cultures (48,0%), more often among women (65,6%) and young people (74,9%). The causative agents of community-acquired bloodstream infection were aerobes (73,4%), anaerobes (24,2%), fungi (2,4%). The gram-positive cocci were prevailing (51,4%) and the gram-negative rods were isolated rather seldom (9,6%). BSI was monomicrobial (66,5%) and polymicrobial (33,5%). Polymicrobial blood cultures had 2, 3, 4 agents in one blood sample (75,4%, 18,8%, 5,8%, respectively). There were also found combinations of different species of aerobes (47,8%), aerobes with anaerobes (42%). BSI caused complications of the primary disease of the respiratory system, urogenital system and in 100% of cases after plastic surgery. A small blood volume is required for buffy-coat inoculation, the direct agar culture reduces the response time to 2 days, so it makes genetic identification possible on the 2nd day from the moment of blood collection.

Evolutionary trends in bacteria isolated from moderate and severe diabetic foot infections in a Portuguese tertiary center

IntroductionDiabetic Foot infections (DFI) are a major cause of hospitalization in patients with diabetes. The microbiological study of diabetic ulcers is essential to adequate antibiotic therapy and to minimize the selection of resistant microorganisms. The aim of this study was to characterize and to compare the evolution of isolated microorganisms between the biennium 2010–2011 and 2016–2017, in hospitalized patients with DFI. Material and methodsRetrospective evaluation of the clinical and analytical data of patients who were admitted due to DFI in 2010–2011 (group 2010/11) and 2016–2017 (group 2016/17). Only the first hospitalization for each patient was included. An adequate descriptive and comparative statistical analysis was performed. ResultsThere were 274 admissions due to DFI, 151 in 2010/11 and 123 in 2016/17. There was an increase in admissions due to neuroischemic DFI (51.0% in 2010/11 to 61.8% in 2016/17, p = 0.048). Staphylococcus aureus (SA) was the most common isolate in 2010/11 (26.7%). In 2016/17 most cultures were mixed polymicrobial and isolation of Enterobacteriaceae and Pseudomonas aeruginosa increased from 2010/11 to 2016/17 (15.9% to 30.6%, p = 0.001, and 9.1% to 13.7%, p = 0.048, respectively). ConclusionThere was an increase in the prevalence of neuroischemic DFU. The Enterobacteriaceae family replaced SA as the most prevalent pathogen in DFI, with an increase in the isolation of gram-negative microorganisms and mixed polymicrobial cultures. Chronic neuroischemic infected ulcers usually present distinct bacterial isolates; knowledge about the most common agents is warranted in order to better select empiric antibiotic therapy.

Applicability of an in-house saponin-based extraction method in Bruker Biotyper matrix-assisted laser desorption/ionization time-of-flight mass spectrometry system for identifying bacterial and fungal species in positively flagged pediatric VersaTREK blood cultures

Early identification of pathogens causing bloodstream infection (BSI) is critical for prompt administration of appropriate antimicrobial therapy. We used an in-house saponin-based extraction method to evaluate the performance of Bruker Biotyper MALDI-TOF MS system (MALDI Biotyper) for bacterial and fungal identification in 2013 positively-flagged VersaTREK blood culture bottles. A total of 180 monomicrobial and 23 polymicrobial positive blood cultures were investigated. Among monomicrobial positive blood cultures, the MALDI Biotyper recognized 90.6% and 81.7% of organisms directly from the flagged blood culture bottles to the genus and species levels, respectively. The MALDI Biotyper also correctly characterized one of the polymicrobial organisms to the species level in 20 (87%) bottles and to the genus level in 21 (91.3%) bottles. The overall identification rate using our protocol was 90.6% (184/203) and 82.3% (167/203) for genus and species levels, respectively. Identification accuracy was higher for Gram-positive than Gram-negative organisms and was the lowest for yeasts. Score values of identification were ≥1.500 for 200 (98.5%) bottles, ≥1.700 for 195 (96.1%) bottles and ≥2.000 for 182 (89.7%) bottles. Moreover, 83.5% and 92% of the isolates were identified precisely to species and genus level with the lower cutoff score of 1.500. Using our protocol also helped identifying BSI pathogens 18-24h earlier compared to the sub-cultured colonies. Using Bruker MALDI Biotyper for identification of isolates directly from positive VersaTREK blood culture bottles, our in-house saponin-based protocol provided a more rapid turn-around time for correct identification of BSI pathogens than the conventional methods.

Trends in the Proportion of Time Spent Outpatient While Receiving Antibiotics for Treatment of Gram-Negative Rod Bacteremia Among Allogeneic Hematopoietic Cell Transplant Recipients

Background Gram-negative rod bacteremia (GNRB) is a leading cause of morbidity and mortality among allogeneic hematopoietic cell transplant (HCT) recipients. Historically, GNRB has been treated with inpatient intravenous antibiotic therapies. However, outpatient antibiotic delivery has been shown to lower costs, decrease complications and may reduce rates of hospital-acquired multidrug-resistant organism (MDRO) infections. Despite such advantages, there are no data assessing trends in outpatient management of GNRB among allogeneic HCT recipients nor on the impact changing resistance profiles have on such trends. We estimated the linear time-trend, shape of trend, and average proportion of treatment time spent outpatient for allogeneic HCT recipients with GNRB. Methods First 100 day post-HCT data were retrospectively examined for adult patients transplanted at a single institution between 2007 and 2017. We defined GNRB as blood culture confirmed GNR, limited our analysis to first infections, and presumed antibiotic duration lasted 14 days. We estimated the direction and magnitude of the time trend and tested for an association between calendar year and proportion of time spent outpatient using linear analysis with a continuous year variable. We accounted for a priori selected confounders (graft vs. host disease (GVHD), neutropenia, conditioning regimen, location of GNRB diagnosis, polymicrobial culture, MDRO (Stenotrophomonas maltophilia isolates or resistance to ³1 agents in ³3 categories: cephalosporins, beta-lactamase inhibitors, carbapenems, aminoglycosides, and fluoroquinolones), and age at diagnosis) using adjusted linear analysis and estimated the shape of the time-trend using a linear model with a natural spline for time. We tested if MDRO modified the outpatient temporal trend using a likelihood ratio test. Results Of the 2,165 allogeneic HCT recipients included, 252 (11.6%) experienced 1 or more GNRB with available resistance data. Twenty-four (9.5%) analyzed infections were polymicrobial and 75 (29.8%) were MDR. On average, patients received 59.2% of their antibiotic treatment in an outpatient setting. We observed a crude and adjusted per year decline in the proportion of treatment time spent outpatient (crude: -2.6% [95% CI: -1.0, -4.2%]; adjusted: -1.1% [-2.5, 0.2%]); the decline was non-linear (Figure 1). MDR, GVHD, neutropenia, and being inpatient at diagnosis were associated with a smaller proportion of treatment time spent outpatient and MDR status was found to modify the association between calendar year and proportion of time spent outpatient (p-value: 0.04; Figure 2). Conclusion The proportion of GNRB antibiotic treatment time allogeneic HCT recipients spent in the outpatient setting declined between 2007 and 2017. However, this decline was explained by severity of illness and infection complexity factors, such as MDR and GVHD.

Polymicrobial Interactions Induce Multidrug Tolerance in Staphylococcus aureus Through Energy Depletion.

Staphylococcus aureus is responsible for a high number of relapsing infections, which are often mediated by the protective nature of biofilms. Polymicrobial biofilms appear to be more tolerant to antibiotic treatment, however, the underlying mechanisms for this remain unclear. Polymicrobial biofilm and planktonic cultures formed by S. aureus and Candida albicans are 10- to 100-fold more tolerant to oxacillin, vancomycin, ciprofloxacin, delafloxacin, and rifampicin compared to monocultures of S. aureus. The possibility of C. albicans matrix components physically blocking antibiotic molecules from reaching S. aureus was ruled out as oxacillin, ciprofloxacin, delafloxacin, and rifampicin were able to diffuse through polymicrobial biofilms. Based on previous findings that S. aureus forms drug tolerant persister cells through ATP depletion, we examined nutrient deprivation by determining glucose availability, which indirectly correlates to ATP production via the tricarboxylic acid (TCA) cycle. Using an extracellular glucose assay, we confirmed that S. aureus and C. albicans polymicrobial cultures depleted available glucose faster than the respective monocultures. Supporting this finding, S. aureus exhibited decreased TCA cycle activity, specifically fumarase expression, when grown in the presence of C. albicans. In addition, S. aureus grown in polymicrobial cultures displayed 2.2-fold more cells with low membrane potential and a 13% reduction in intracellular ATP concentrations than in monocultures. Collectively, these data demonstrate that decreased metabolic activity through nutrient deprivation is a mechanism for increased antibiotic tolerance within polymicrobial cultures.

A new culture-based method for rapid identification of microorganisms in polymicrobial blood cultures by MALDI-TOF MS

BackgroundThe application of matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry (MS) to microbial identification has allowed the development of rapid methods for identification of microorganisms directly in positive, blood cultures (BCs). These methods can yield accurate results for monomicrobial BCs, but often fail to identify multiple microorganisms in polymicrobial BCs. The present study was aimed at establishing a rapid and simple method for identification of bacteria and yeast in polymicrobial BCs from patients with bloodstream infection.ResultsThe rapid method herein proposed is based on short-term culture in liquid media allowing selective growth of microorganisms recovered from polymicrobial BCs, followed by rapid identification by MALDI-TOF MS. To evaluate the accuracy of this method, 56 polymicrobial BCs were comparatively analyzed with the rapid and routine methods. The results showed concordant identification for both microbial species in 43/50 (86%) BCs containing two different microorganisms, and for two microbial species in six BCs containing more than two different species. Overall, 102/119 (85.7%) microorganisms were concordantly identified by the rapid and routine methods using a cut-off value of 1.700 for valid identification. The mean time to identification after BC positivity was about 4.2 h for streptococci/enterococci, 8.7 h for staphylococci, 11.1 h for Gram-negative bacteria, and 14.4 h for yeast, allowing a significant time saving compared to the routine method.ConclusionsThe proposed method allowed rapid and reliable microbial identification in polymicrobial BCs, and could provide clinicians with timely, useful information to streamline empirical antimicrobial therapy in critically ill patients.

2281. Ceftolozane–tazobactam (C/T) Treatment Outcomes in Immunocompromised (IC) Patients with Multidrug-Resistant (MDR) Pseudomonas aeruginosa (PA) Infections

BackgroundEvaluations of clinical use and real-world outcomes following C/T treatment exist; however, data assessing outcomes in IC patients are limited. This study evaluated treatment patterns and clinical outcomes of IC patients treated with C/T for MDR PA across 15 US hospitals.MethodsAdult IC inpatients treated for ≥ 24 hours with C/T admitted between 12/14–5/18 for MDR PA infections were included in this retrospective multicenter cohort study. IC was defined as patients with previous solid-organ transplant (SOT), diseases that suppress resistance to infection (HIV/AIDS, leukemia, lymphoma), or receipt of immunosuppressants, chemotherapy, radiation, long-term low-dose (≥ 1 month) or recent high-dose steroids (> 5 days). Clinical and microbiologic data were extracted from electronic records. The primary outcomes were all-cause 30-day mortality and clinical cure, defined as no escalation/additional therapy and improved signs and symptoms from baseline to end of therapy. PA isolates were characterized as MDR if non-susceptible to ≥ 3 classes of antipseudomonal agents. Classification and regression tree (CART) analysis was used to identify the 30-day mortality split in APACHE II scores.ResultsSeventy patients were included; 58 (83%) had received immunosuppressive agents, 47 (67%) had history of SOT, and 19 (27%) had diseases suppressing resistance to infection. Mean patient age was 57 ± 14 years, median (interquartile range) patient APACHE II and Charlson Comorbidity Index scores were 18 (12.5) and 5 (3.75), respectively, with 33 (47%) receiving ICU care at C/T initiation. The most frequent infection sources were respiratory (56%), wound (11%), intraabdominal (10%), and blood and urine (9% each), with 36% having a polymicrobial culture. All-cause 30-day mortality was 19% (n = 13) with clinical cure achieved in 48 (69%) patients. CART analysis identified the 30-day mortality split at APACHE II score > 25 (76% vs. 24%; P = 0.002).ConclusionOf 70 IC patients treated with C/T for MDR PA, clinical cure was achieved in 69% and mortality was 19%, consistent with other evaluations reporting on a cross section of patient populations. C/T represents a promising agent for treatment of PA resistant to many traditional antipseudomonal agents in this high-risk population.DisclosuresElizabeth B. Hirsch, PharmD, Merck: Grant/Research Support, Research Grant; Nabriva Therapeutics: Advisory Board; Paratek Pharmaceuticals: Advisory Board

2007. Impact of Combining Rapid Diagnostics with an Interpretation Guide on Vancomycin Usage for Contaminant Blood Cultures Growing Coagulase-Negative Staphylococci (CoNS)

BackgroundContaminant blood cultures can lead to unnecessary antibiotic use, longer admissions and increased costs. Rapid diagnostics, like the BioFire® FilmArray® Blood Culture Identification (BCID) Panel, can potentially lessen these harms. BioFire BCID was implemented at VA Greater Los Angeles in 7/2017. When providers review BCID results, they are also directed to an interpretation guide developed by our antimicrobial stewardship program. This study aimed to determine the impact of BioFire BCID with this interpretation guide on unnecessary vancomycin use for contaminant blood cultures growing CoNS.MethodsThis was a retrospective cohort study on adult inpatients with contaminant blood cultures positive for CoNS. We evaluated cases before BCID (April 2016–July 2017) and after BCID (July 7/2017–December 2018) implementation. Cases with patients who died or were discharged prior to preliminary results, polymicrobial cultures, no empiric vancomycin use, or where vancomycin was indicated were excluded. We defined a “case” as anytime a provider concurrently ordered blood cultures and empiric antibiotics. Our primary outcome was the duration of unnecessary vancomycin. Secondary outcomes were time to discontinuation/modification of any empiric antibiotic, length of stay (LOS), LOS in ICU and 30-day mortality.ResultsA total of 99 cases were included (N = 45 pre-BCID; N = 54 post-BCID). Demographics between the 2 groups were largely similar except the post-BCID group had more patients with end-stage renal disease (ESRD) (14 vs. 4, P = 0.037) and more frequent infectious disease (ID) consultation (21 vs. 8, P = 0.027). The post-BCID group had shorter mean duration of unnecessary vancomycin (53.0 hours vs. 38.1 hours, P = 0.0029). After controlling for ESRD and ID involvement, the mean duration of unnecessary vancomycin was not significantly different between the 2 groups (P = 0.30 and P = 0.49, respectively). There was no difference in time to modification/discontinuation of any empiric antibiotic (44.6 hr vs. 35.0 hr, P = 0.36). There was no difference in mean LOS, mean LOS in ICU, or 30-day mortality.ConclusionShorter duration of unnecessary vancomycin for CoNS bacteremia after BCID implementation and provision of an interpretation guide may have been driven in part by more frequent ID consultation.Disclosures All authors: No reported disclosures.

206. Variations in the frequency and impact of polymicrobial cultures in adults with invasive Group B Streptococcal (GBS) infection at the US Veterans Health Administration

BackgroundGBS, a colonizer of human skin, genitourinary and gastrointestinal tracts, is responsible for increasing rates of invasive infection among non-pregnant adults in the United States. GBS is often isolated with other bacteria; however, the clinical significance of polymicrobial cultures in patients with invasive GBS infection is unknown. Our aim was to characterize polymicrobial cultures in patients with invasive GBS infection and explore their impact on mortality at 30 days.MethodsWithin the VHA Corporate Data Warehouse, we identified veterans active in VHA between 2008–2017 with invasive GBS infection according to CDC’s surveillance definitions. Reports of cultures from blood, bone and sterile fluid with GBS were assessed for the presence of other bacteria.We used International Classification of Disease (ICD) codes to define the type of invasive GBS infection. We compared 30-day all-cause mortality between patients with cultures that identified only GBS (monomicrobial cases) and patients with cultures that identified GBS and other bacteria (polymicrobial cases).ResultsOf 4780 incident cases of invasive GBS infection identified between 2008–2017, 1204 (25%) were polymicrobial. The proportion of polymicrobial cases varied by type of invasive GBS infection, ranging from 58% in osteomyelitis to 10–15%in meningitis, endocarditis, skin and soft-tissue infections, and septic arthritis (table). Staphylococcus aureuswas found in 516 (43%) of polymicrobial cases;there were variations in the bacteria isolated by type of infection (figure). Overall, there was no difference in 30-day mortality between polymicrobial and monomicrobial cases of invasive GBS infection (both 8%). However, when compared with monomicrobial cases, 30-day mortality was doubled in polymicrobial cases of pneumonia and bacteremia (15% vs. 31% and 11% vs. 22%, respectively).ConclusionThe frequency, composition and mortality of polymicrobial cases vary according to the type of invasive GBS infection. Polymicrobial infection could be an important determinant of outcome in certain invasive GBS infections. The effect of polymicrobial infection involving GBS, relative to age, severity of illness and underlying comorbidities, needs further exploration. Disclosures All authors: No reported disclosures.

1022. Is it Time to Re-Evaluate Oral Β-Lactam Antibiotics for Step-Down Therapy of Uncomplicated Gram-Negative Bacteremia?

BackgroundBloodstream infections (BSI) due to Enterobacteriaceae often require empiric intravenous (IV) antibiotics. Oral antibiotics for the definitive treatment of these infections have been reserved to antibiotics with “high” oral bioavailability, mainly fluoroquinolones (FQ). Safety concerns and increasing resistance associated with FQ has modified clinical practice to identify alternative oral therapies. Select β-lactam (BL) antibiotics are well-tolerated, have moderately high bioavailability, and possess in-vitro activity against Escherichia coli (E. coli), Klebsiella pneumoniae (K. pneumoniae), and Proteus mirabilis (P. mirabilis). Limited evidence exists for oral BL step-down therapy for definitive treatment of BSI due to these organisms.MethodsThis retrospective cohort study compares clinical outcomes of patients treated with oral BL antibiotics to those who received oral FQ or trimethoprim/sulfamethoxazole (TS) for the treatment of BSI due to E. coli, K. pneumoniae, and P. mirabilis. The primary outcome is a composite of 30-day all-cause mortality, 30-day readmission due to recurrence, and/or change in oral antibiotic therapy. Secondary endpoints include 90-day development of Clostridium difficile infection, 90-day all-cause readmission, hospital length of stay (LOS), and 90-day recovery of a multi-drug-resistant organism.ResultsNine hundred eighty-one patients were screened and 397 adult patients were included. Excluded patients: IV only (n = 291), polymicrobial blood culture (n = 112), immunocompromised (n = 61), other (n = 120). Two-hundred patients received oral step-down therapy with a BL, and 197 with either an FQ or TS. E. coli was the causative organism for most patients in both groups, and urinary tract was the most common source of BSI. The median total duration of therapy was 14 days in both groups. There was no significant difference in the primary composite endpoint (7% vs. 5.6%, P = 0.561). There was no mortality or differences in secondary outcomes, except LOS (6 vs. 5 days, P = 0.043).ConclusionUtilization of oral BL for the step-down therapy of uncomplicated BSI due to E. coli, K. pneumoniae, and P. mirabilis did not result in worse outcomes compared with those receiving oral FQ or TS.Disclosures All authors: No reported disclosures.

1419. A Rare Case of Clostridium beijerinckii Traumatic Osteomyelitis

BackgroundWe present a case of Clostridium beijerinckii osteomyelitis in the presence of retained foreign bodies not seen on MRI.MethodsA 45-year-old female with type 2 diabetes sustained multiple open right leg injuries, grossly contaminated with gravel, after a motor vehicle collision. She underwent external fixation (ex-fix) and 5 irrigations and debridements (I&D) initially. Polymicrobial intraoperative cultures (Cx) were treated with vancomycin and ertapenem for 6 weeks. One month post-antibiotic completion, pain, and swelling developed in ankle; contrast MRI revealed avascular necrosis and osteomyelitis (OM) of talus. Cx from repeat I&D grew same organisms; meropenem was recommended for 6 weeks. During meropenem week 6, pain was minimal and wound was closed. During attempt to implant hardware, pus was seen around peroneal tendon. Cx grew Clostridium species and Bacteroides from tibia, calcaneus, talus, and peroneal tendon sheath; meropenem was continued. Pain worsened 3 weeks later; I&D revealed pus in lateral ankle. To better access the medial ankle, a longitudinal incision was made along posterior tibial tendon, perpendicular to prior surgical incision. Immediate purulence, grass blades, and rocks were seen. Brucella agar had a rare gray colony at 48 hours and was subbed to blood and Brucella agar; it grew on Brucella agar with aero tolerance test. Gram stain showed Gram-positive rods with subterminal spores. Rapid ANA panel identified isolate as Clostridium beijerinckii (Cb) with > 99.9% probability and bioscore 1/24.ResultsCb is a strict anaerobic gram-positive rod with oval subterminal spores. Found in soil and water, its main use is industrial solvent production. Infection by Cb is rare; only 2 cases of OM, 1 traumatic endophthalmitis, and 1 mitral valve endocarditis have been reported. While uncommon, Clostridial osteomyelitis is associated with contaminated open traumatic injuries. It can be difficult to eradicate, despite aggressive surgical intervention and appropriate antibiotics.ConclusionThis is the third case of Cb OM described. Anaerobic cultures should be collected during I&D of open traumatic wounds. If infection persists, careful intraoperative evaluation of wound for residual foreign bodies, even if not seen radiologically, should be performed. Disclosures All authors: No reported disclosures.