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557. Impact of Heavy Metal Exposure in the Transcriptional Response of Methicillin--Resistant Staphylococcus aureus (MRSA)-USA300 Latin-American Variant (USA300-LV)

Abstract Background USA 300-LV is the predominant MRSA clone in Colombia and contains a genomic island designated “COMER” with genes for copper (Cu) and mercury (Hg) resistance. HM environmental contamination is a serious threat to public health in Colombia and could also influence the selection and evolution of HM resistance genes in MRSA. Here, we investigate the global transcriptomic responses of USA300-LV after exposure to HM under the hypothesis that USA300-LV strains are highly capable of sustaining higher HM concentrations Methods We performed comparative RNAseq experiments in USA300-LV clinical strain (CA-MRSA12). Total RNA was isolated in exponential phase in the absence and presence of sub-inhibitory concentrations of Cu and Hg (3 replicates). cDNA libraries were prepared and sequenced on an Illumina platform. Differentially expressed genes (DEG) were calculated by DeSeq2 (p-adjusted value ˂ 0.01) and results on 19 selected genes were confirmed by qRT-PCR. Results US300-LV exhibited a larger number of differentially expressed genes when exposed to Hg (n = 114) compared with Cu treatment (n = 16). The most common functional groups of genes upregulated after Hg exposure included those involved in amino acid metabolism (n = 18). In contrast, 45 genes were downregulated after Hg exposure, mostly associated to host immune system defense (n = 11). qRT-PCR confirmed that the most upregulated genes were those involved in murein hydrolase activity, Hg resistance and the transcriptional regulator Cro/CI. Of 9 genes that were downregulated, functional groups included ype VII secretion system, immune modulators and leucocidins. Copper treatment resulted in only 12 genes that were upregulated including those in the COMER element (n = 6), aminoacid metabolism (n = 3), ROS response (n = 1), host immune system defense (n = 1) and unknown function (n = 1). Downregulated genes were those associated to host immune system defense (n = 2), energy generation (n = 1) and unknown function (n = 1). Conclusion Differential adaptive responses after exposure to HM in USA300-LV suggest a role in the evolution of antimicrobial resistance and successful spread in the region. Metabolic adaptations involving amino acid metabolism seem to play a role in the evolution of HM resistance in MRSA. Disclosures All authors: No reported disclosures.

Background. USA 300-LV is the predominant MRSA clone in Colombia and contains a genomic island designated "COMER" with genes for copper (Cu) and mercury (Hg) resistance. HM environmental contamination is a serious threat to public health in Colombia and could also influence the selection and evolution of HM resistance genes in MRSA. Here, we investigate the global transcriptomic responses of USA300-LV after exposure to HM under the hypothesis that USA300-LV strains are highly capable of sustaining higher HM concentrations

Methods.
We performed comparative RNAseq experiments in USA300-LV clinical strain (CA-MRSA12). Total RNA was isolated in exponential phase in the absence and presence of sub-inhibitory concentrations of Cu and Hg (3 replicates). cDNA libraries were prepared and sequenced on an Illumina platform. Differentially expressed genes (DEG) were calculated by DeSeq2 (p-adjusted value ˂ 0.01) and results on 19 selected genes were confirmed by qRT-PCR.
Results. US300-LV exhibited a larger number of differentially expressed genes when exposed to Hg (n = 114) compared with Cu treatment (n = 16). The most common functional groups of genes upregulated after Hg exposure included those involved in amino acid metabolism (n = 18). In contrast, 45 genes were downregulated after Hg exposure, mostly associated to host immune system defense (n = 11). qRT-PCR confirmed that the most upregulated genes were those involved in murein hydrolase activity, Hg resistance and the transcriptional regulator Cro/CI. Of 9 genes that were downregulated, functional groups included ype VII secretion system, immune modulators and leucocidins. Copper treatment resulted in only 12 genes that were upregulated including those in the COMER element (n = 6), aminoacid metabolism (n = 3), ROS response (n = 1), host immune system defense (n = 1) and unknown function (n = 1). Downregulated genes were those associated to host immune system defense (n = 2), energy generation (n = 1) and unknown function (n = 1).
Conclusion. Differential adaptive responses after exposure to HM in USA300-LV suggest a role in the evolution of antimicrobial resistance and successful spread in the region. Metabolic adaptations involving amino acid metabolism seem to play a role in the evolution of HM resistance in MRSA.
Disclosures. All authors: No reported disclosures. Background. Evidence suggests that interventions such as MRSA decolonization are useful in the prevention of MRSA bloodstream infections (BSI) both during hospitalization and post-discharge. However, decolonization may be costly and have diminishing effectiveness when used on all inpatients. Hospital length of stay (LOS) is a known risk factor for MRSA BSI. To determine whether LOS could be useful in prioritizing patients for intervention, we aimed to evaluate (i) distribution of time from admission to hospital-onset (HO) MRSA BSI, and (ii) frequency and LOS of hospitalizations that preceded community-onset (CO) MRSA BSI.

Evaluating Length of Stay Data for Use in Targeting Prevention of Methicillin-Resistant
Methods. MRSA-positive blood cultures among adults admitted to New York hospitals from 2013 to 20s16 were identified in the Centers for Disease Control and Prevention's (CDC's) National Healthcare Safety Network (NHSN). We linked these data to admissions in New York's hospital discharge dataset, the Statewide Planning and Research Cooperative System (SPARCS), where the NHSN blood culture collection date was between a patient's SPARCS admission and discharge dates and there was an exact match for birth date, gender and facility. Time to MRSA BSI was defined as the number of days from admission (day 1) to collection of a blood culture positive for MRSA. We defined positive blood cultures collected on days 1-3 as CO, and those collected ≥day 4 as HO.
Results. We linked 10,425 (79%) MRSA BSIs from NHSN to SPARCS. 78% (8,147) of MRSA BSIs were CO and 22% (2,278) were HO. The median time to HO MRSA BSI was 10 days (IQR 6-21) (Figure 1), in contrast to the median LOS for all hospitalizations of 4 days (IQR 3-7). By definition, 35% of all hospitalizations were never at risk of HO MRSA BSI because their LOS was < 4 days. Among CO MRSA BSI, 48% were discharged from a hospital in the 90 days preceding their BSI (Figure 2). The median LOS of these prior hospitalizations was 8 days (IQR 5-14), and 87% were at least 4 days in length.
Conclusion. Over half of HO MRSA BSI occur on or after day 10 of hospitalization and a large fraction of CO MRSA BSI had a lengthy hospitalization shortly before their BSI diagnosis. Our results suggest that patients likely to have a long LOS could be evaluated as potential targets for prevention strategies (e.g., decolonization) to reduce both HO and CO MRSA BSI.

Disclosures. All authors:
No reported disclosures. Background. Methicillin-resistant staphylococcus aureus (MRSA) bloodstream infection (BSI) is associated with significant morbidity and mortality. Healthcareassociated (HCA) MRSA infection (occurring >48 hours after hospitalization or in those with prior healthcare exposure) has traditionally been associated with severe invasive disease, while community-associated (CA) MRSA infection (occurring within 48 hours of hospitalization and without prior healthcare exposure) has been observed in otherwise healthy individuals. We characterized the epidemiology, resistance patterns, and clinical outcomes associated with MRSA BSI over a 5 year period comparing patients with community-onset bacteremia to those with hospital onset bacteremia.

Two Different Beasts: Comparing Epidemiology of Healthcare-Associated vs. Community-Acquired Methicillin-Resistant Staphylococcus aureus Bacteremia
Methods. We performed a retrospective chart review of 151 MRSA bloodstream infections from 2013-2018 at the University of Alberta Hospital (Edmonton, Canada). We assessed each BSI by: classification (CA vs. HCA), presence of MRSA risk factors, source of infection, MRSA resistance, rate of ICU admission, and 30-day mortality.
Conclusion. Invasive MRSA infection continues to be associated with significant morbidity and mortality. We found that healthcare-associated MRSA BSI was associated with a high rate of prior MRSA colonization as well as a higher rate of ICU admission and 30-day mortality. There are significant differences in the demographics of patients with CA BSI compared with HCA BSI. Interventions to prevent these infections need to be targeted to the geographic location of acquisition.
Disclosures. All authors: No reported disclosures. Background. Methicillin-resistant staphylococcus aureus (MRSA) colonization of hospitalized patients is associated with higher readmission rates and increased morbidity. Depending on the mechanisms of transmission, numerous potential control interventions exist to reduce the burden of disease. However, given the preponderance of asymptomatic