Background. Antibiotic resistance is often spread through bacterial populations via conjugative plasmids. However, plasmid transfer is not well recognized in clinical settings because of technical limitations, and health care-associated infections are usually caused by clonal transmission of a single pathogen. In 2015, multiple species of carbapenem-resistant Enterobacteriaceae (CRE), all producing a rare carbapenemase, were identified among patients in an intensive care unit. 'this observation suggested a large, previously unrecognized plasmid transmission chain and prompted our investigation. Methods. Electronic medical record reviews, infection control observations, and environmental sampling completed the epidemiologic outbreak investigation. A laboratory analysis, conducted on patient and environmental isolates, included long-read whole-genome sequencing to fully elucidate plasmid DNA structures. Bioinformatics analyses were applied to infer plasmid transmission chains and results were subsequently confirmed using plasmid conjugation experiments. Results. We identified 14 Verona integron-encoded metallo-beta-lactamase (VIM)-producing CRE in 12 patients, and 1 additional isolate was obtained from a patient room sink drain. Whole-genome sequencing identified the horizontal transfer of bla(VIM-1), a rare carbapenem resistance mechanism in the United States, via a promiscuous incompatibility group A/C2 plasmid that spread among 5 bacterial species isolated from patients and the environment. Conclusions. This investigation represents the largest known outbreak of VIM-producing CRE in the United States to date, which comprises numerous bacterial species and strains. We present evidence of in-hospital plasmid transmission, as well as environmental contamination. Our findings demonstrate the potential for 2 types of hospital-acquired infection outbreaks: those due to clonal expansion and those due to the spread of conjugative plasmids encoding antibiotic resistance across species.

Aztreonam-avibactam is a drug combination pending phase 3 clinical trials and is suggested for treatment of severe infections caused by metallo-beta-lactamase (MBL)-producing Enterobacterales by combining ceftazidime-avibactam and aztreonam. Beginning in 2019, four Antibiotic Resistance Laboratory Network regional laboratories offered aztreonam-avibactam susceptibility testing by broth microdilution.

Background: Aztreonam/avibactam is a combination agent that shows promise in treating infections caused by highLy antibiotic-resistant MBL-producing EnterobacteraLes. This combination can be achieved by combining two FDA-approved drugs: ceftazidime/avibactam and aztreonam. It is unknown whether ceftazidime in the combination ceftazidime/aztreonam/avibactam has a synergistic or antagonistic effect on the in vitro activity of aztreonam/avibactam by significantly increasing or decreasing the MIC. Objectives: To determine whether increasing ceftazidime concentrations affect the MICs of aztreonam/avibactam done. Methods: A custom 8 x 8 chequerboard broth microdiLution (BMD) panel was made using a digital dispenser (Hewlett-Packard, Corvallis, OR, USA). The panel included orthogonal 2-fold dilution series of aztreonam and ceftazidime ranging from 0.5 to 64 mg/L. Avibactam concentration was kept constant at 4 mg/L throughout the chequerboard. Thirty-seven EnterobacteraLes isoLates from the CDC & FDA Antibiotic Resistance Isolate Bank or CDC's internal collection with intermediate or resistant interpretations to aztreonam and ceftazidime/avibactam were included for testing. All isolates harboured at least one of the following MBL genes: bIa(IMP), bla(NDM) or bla(VIM). Results: Regardless of the concentration of ceftazidime, aztreonam/avibactam with ceftazidime MICs for all 37 isolates were within one 2-fold doubling dilution of the aztreonam/avibactam MIC. Conclusions: Ceftazidime, in the combination ceftazidime/avibactam/aztreonam, did not affect the in vitro activity of aztreonam/avibactam in this sample of isolates. These findings can help assure clinical and public health Laboratories that testing of aztreonam/avibactam by BMD can act as a reliable surrogate test when the combination of ceftazidime/avibactam and aztreonam is being considered for treatment of highly antibiotic-resistant MBL-producing Enterobacterales.

Background: New antimicrobials are being developed as a response to the global threat of multidrug-resistant and panresistant bacterial pathogens. Cefiderocol (FDC; Shionogi & Co) is a novel parenteral siderophore cephalosporin with activity against gram-negative rods. Here, we report on the in vitro activity of FDC against multidrug-resistant gram-negative isolates collected by the CDC, including isolates available through the CDC and FDA Antibiotic Resistance Isolate Bank (AR Isolate Bank). Methods: The challenge set of gram-negative isolates (n = 339), most of which were obtained from the AR isolate bank (n = 258), comprised 188 Enterobacteriaceae (ENT), 72 Pseudomonas aeruginosa (PSA), and 79 Acinetobacter baumannii (ACB). Minimum inhibitory concentrations (MICs) for FDC in iron-depleted cation-adjusted Mueller-Hinton broth were determined using frozen reference broth microdilution panels (IHMA, Schaumburg, IL) according to CLSI guidelines. Isolates displaying nonsusceptibility to FDC (MIC >4 µg/mL) underwent additional testing with β-lactamase inhibitors (FDC with 4 µg/mL avibactam, FDC with 100 µg/ml dipicolinic acid (DPA), and FDC with both 100 µg/mL dipicolinic acid (DPA) and 4 µg/mL avibactam). Results: Cefiderocol MICs ranged from ≤0.03 to >64 µg/mL, and 313 (92.3%) isolates displayed susceptibility to FDC (MIC ≤4 μg/mL). The proportions of susceptible ENT, PSA, and ACB were 93.1%, 94.4%, and 88.6%, respectively. Among isolates harboring Ambler class A, class B, or class D carbapenemases, the proportions of susceptible isolates were 96.5%, 79.5%, and 94.0%, respectively. Overall, 26 (7.7%) isolates were categorized as FDC nonsusceptible (MIC ≥ 8 µg/mL); 65% of these were NDM producers. We selected 23 isolates for testing with β-lactamase inhibitors. The combination FDC-avibactam reduced the MIC to susceptible for all isolates harboring an Ambler class A or D carbapenemase, except for 1 OXA-71–producing ACB and 1 KPC-producing Citrobacter farmeri. The combination FDC-DPA reduced the MIC to susceptible for 9 of 13 (69.2%) NDM-producing and 4 of 4 (100%) OXA-23–producing ACB. By combining FDC with both DPA and avibactam, the MIC was reduced to susceptible (91%) for all but 1 KPC-producing and 1 NDM-producing Enterobacteriaceae isolate. Conclusions: Cefiderocol (FDC) demonstrated potent activity against a diverse collection of multidrug-resistant, gram-negative isolates, including producers of Ambler class A, B, and D carbapenemases. Among the 26 FDC nonsusceptible isolates, 65% were NDM positive. Our data indicate that FDC combined with β-lactamase inhibitors may restore susceptibility in FDC nonsusceptible isolates. Additional studies are needed to understand the underlying mechanism(s) of FDC resistance and to further explore the use of β-lactamase inhibitors in combination with FDC.Funding: NoneDisclosures: None

Aztreonam-avibactam is a combination antimicrobial agent with activity against carbapenemase-producing Enterobacteriaceae (CPE) with metallo-β-lactamases (MβLs). Although aztreonam-avibactam is not yet approved by the U.S. Food and Drug Administration (FDA), clinicians can administer this combination by using two FDA-approved drugs: aztreonam and ceftazidime-avibactam. This combination of drugs is recommended by multiple experts for treatment of serious infections caused by MβL-producing CPE. At present, in vitro antimicrobial susceptibility testing (AST) of aztreonam-avibactam is not commercially available; thus, most clinicians receive no laboratory-based guidance that can support consideration of aztreonam-avibactam for serious CPE infections. Here, we report our internal validation for aztreonam-avibactam AST by reference broth microdilution (BMD) according to Clinical and Laboratory Standards Institute (CLSI) guidelines. The validation was performed using custom frozen reference BMD panels prepared in-house at the Centers for Disease Control and Prevention (CDC). In addition, we took this opportunity to evaluate a new panel-making method using a digital dispenser, the Hewlett Packard (HP) D300e. Our studies demonstrate that the performance characteristics of digitally dispensed panels were equivalent to those of conventionally prepared frozen reference BMD panels for a number of drugs, including aztreonam-avibactam. We found the HP D300e digital dispenser to be easy to use and to provide the capacity to prepare complex drug panels. Our findings will help other clinical and public health laboratories implement susceptibility testing for aztreonam-avibactam.

The treatment of infections caused by carbapenem-resistant Enterobacterales , especially New Delhi metallo-β-lactamase (NDM)-producing bacteria, is challenging. Although less common in the United States than some other carbapenemase producers, NDM-producing bacteria are a public health threat due to the limited treatment options available. Here, we report on the antibiotic susceptibility of 275 contemporary NDM-producing Enterobacterales collected from 30 U.

Background: The capacity to monitor the emergence of carbapenemase-producing organisms (CPO) is critical in limiting transmission. CPO-colonized patients can be identified by screening rectal specimens for carbapenemase genes and the Cepheid GeneXpert Carba-R (XCR), the only FDA-approved test, is limited to 5 carbapenemase genes and cannot identify the bacterial species. Objective: We describe the development and validation of culture-based methods for the detection of CPO in rectal cultures (RCs) and nonrectal cultures (NRCs) of tracheal aspirate and axilla-groin swabs. Methods: Colonization screening was performed at 3 US healthcare facilities; specimens of RC swabs and NRC ESwabs were collected. Each specimen was inoculated to a MacConkey broth enrichment tube for overnight incubation then were subcultured to MacConkey agar with meropenem and ertapenem 10 µg disks (BEMA) and CHROMagar KPC (KCHR) or CHROMagar Acinetobacter (ACHR). All media were evaluated for the presence of carbapenem-resistant organisms; suspect colonies were screened by real-time PCR for the most common carbapenemase genes. MALDI-TOF was performed for species identification. BEMA, a previously validated method, was the comparator for 52 RCs; clinical culture (CC) served as the comparator method for 66 NRCs. Select CPO-positive and -negative specimens underwent reproducibility testing. Results: Among 56 patients undergoing colonization screening, 12 (21%) carried a CPO. Only 1 patient had CPO solely from RC. Also, 6 patients had both CPO-positive RC and NRC, and 5 patients only had a CPO-positive NRC. Of the latter, 4 had a CPO-positive tracheal specimen, and 1 had a positive culture from both tracheal and axilla-groin specimens. Sensitivity of BEMA (70%) for NRC was lower than for KCHR (96%) and ACHR (88 %) for all specimens. All methods showed a specificity of 100% and reproducibility of 92%. The detected CPO included OXA-23–positive Acinetobacter baumannii, NDM-positive Escherichia coli, KPC-positive Pseudomonas aeruginosa and 4 genera of KPC-positive Enterobacteriaceae. Conclusions:The addition of nonrectal specimens and use of selective media contributed to increased sensitivity and enhanced identification of CPO-colonized patients. Positive cultures were equally distributed among the 3 specimen types. The addition of the nonrectal specimens resulted in the identification of more colonized patients. The culture-based method was successful in detecting an array of different CPOs and target genes, including genes not detected by the Carba-R assay (eg, blaOXA-23-like). Enhanced isolation and characterization of CPOs will be key in aiding epidemiologic investigations and strengthening targeted guidance for containment strategies.Funding: NoneDisclosures: We discuss the drug combination aztreonam-avibactam and acknowledge that this drug combination is not currently FDA approved.

We describe an outbreak of imipenemase metallo-beta-lactamase-producing organisms in a long-term-care facility (LTCF) amid a larger community outbreak of extended-spectrum beta-lactamase-producing organisms. Transmission was propagated by inadequate infection prevention practices. We provided infection prevention recommendations and education, facilitated colonization screening, and increased interfacility communication. This outbreak demonstrates the unmet need for infection prevention education in long-term-care facilities and the importance of prompt public health response to ensure appropriate identification, containment, and prevention of emerging resistance. Published by Elsevier Inc. on behalf of Association for Professionals in Infection Control and Epidemiology, Inc.

We report 2 cases of melioidosis in women with diabetes admitted to an emergency department in the US Virgin Islands during October 2017. These cases emerged after Hurricanes Irma and Maria and did not have a definitively identified source. Poor outcomes were observed when septicemia and pulmonary involvement were present.

Increased use of colistin in both human and veterinary medicine has led to the emergence of plasmid-mediated colistin resistance (mcr genes). In this study, we report the development of a real-time PCR assay using TaqMan probe-based chemistry for detection of mcr genes from bacterial isolates. Positive control isolates harboring mcr-1 and mcr-2 yielded exponential amplification curves with the assay, and the amplification efficiency was 98% and 96% for mcr-1 and mcr-2, respectively. Each target gene could be reproducibly detected from a sample containing 10(3) cfu/mL of mcr-harboring bacteria, and there was no cross-reactivity with DNA extracted from several multidrug-resistant bacteria harboring other resistance genes, but lacking mcr genes. Both sensitivity and specificity of the mcr real-time PCR assay were 100% in a method validation performed with a set of 25 previously well-characterized bacterial isolates containing mcr-positive and -negative bacteria. This newly developed assay is a rapid and sensitive tool for detecting emerging mcr genes in cultured bacterial isolates. The assay was successfully validated according to quality standards of the Clinical Laboratory Improvement Amendments (CLIA).

Carbapenemase-producing carbapenem-resistant Enterobacteriaceae (CP-CRE) express plasmid-encoded carbapenemases, enzymes that inactivate carbapenem antibiotics. They have the potential for epidemic spread through personto-person transmission and horizontal transfer of resistance mechanisms (1,2). Typically, CP-CRE are associated with health care exposure. Clinical CRE infections can have mortality rates as high as 50% (3); however, the majority of CRE patients are asymptomatic. These asymptomatic colonized patients can serve as a source for transmission to other patients (4). On August 11, 2016, two Klebsiella pneumoniae carbapenemase (KPC)–producing CP-CRE isolates from clinical cultures were reported from patients hospitalized at a rural, community hospital in Kentucky; CRE had not been identified previously at this facility. During the next 4 months, an additional 21 CRE isolates were identified from facility patients, resulting in a total of 23 isolates, including 17 K. pneumoniae, five Escherichia coli, and one Enterobacter cloacae isolate. Seventeen (74%) of these isolates were identified through patient screening cultures; the rest were from clinical cultures. Two carbapenemase types were identified through testing of 14 available isolates; 13 produced KPC and one produced New Delhi metallo-ß-lactamase. All CP-CRE were K. pneumoniae with the exception of two KPC-producing E. coli. Pulsed-field gel electrophoresis of these isolates identified three indistinguishable pairs, one of which was the KPC-producing E. coli isolates. Medical chart review and patient interviews indicated that the patients from whom each pair had been isolated had exposure to the emergency department or to the same medical-surgical ward, suggesting transmission on these units. Common health care exposures outside the hospital were not identified among the three pairs. Five of 13 interviewed patients reported receipt of health care outside the local area; three might have introduced CP-CRE into the facility, including one patient who was not screened at admission and two who had CRE identified from admission screening. Targeted environmental cultures identified CP-CRE on an emergency department environmental services cart and from the floor sink drain of the involved medicalsurgical ward’s environmental services closet. This investigation suggested CP-CRE in this Kentucky facility was likely attributable to both importation into and transmission within the facility and highlights two points relevant to CP-CRE control. First, demonstration of environmental services cart contamination is notable and suggests a possible role for cleaning equipment in CP-CRE spread. This equipment can move between patient rooms and might not be cleaned regularly. Further investigation is needed to better understand the role of this equipment in transmission of resistant organisms in health care facilities. Second, although CP-CRE has been primarily identified from urban areas, these multidrug-resistant organisms can be introduced into rural areas by patients with exposure to health care in higher CP-CRE–prevalence areas, resulting in local transmission. Facilities in lower CP-CRE–prevalence areas that treat patients who also access care in higher prevalence areas should be aware of this risk. Recommendations to this facility included initiation of CRE surveillance for patients at high risk (e.g., patients with health care exposures during the past year in areas with known higher CP-CRE prevalence); reinforcement of daily and terminal cleaning practices by the environmental services team, including daily cleaning of environmental services carts; and working with facilities in its patient-sharing network to implement a regional CP-CRE prevention strategy (5,6).

On November 1, 2016, a point prevalence survey was conducted at a Chicago skilled nursing facility with ventilated residents to understand the prevalence of carbapenemase-producing organisms in health care facilities in the Chicago region. The survey identified 20 patients with Verona integron-encoded metallo-beta-lactamase–producing carbapenem-resistant Pseudomonas aeruginosa.

In 2016, the mcr-1 gene was identified from whole genome sequencing (WGS) of bacterial isolates cultured from 2 Connecticut residents with diarrhea. Mcr-1 is located on a plasmid, which can be shared among bacteria and confers resistance to colistin, a last-line antibiotic used to treat multidrug-resistant infections. The Connecticut Department of Public Health and the Centers for Disease Control and Prevention collaborated to assess possible routes of exposure to mcr-1 and potential spread. Patients and close contacts (household and travel companions) were interviewed about symptoms, travel, foods, animal contact, and health care exposures. Rectal swabs from the patients and their close contacts, and surface samples from the kitchen and bathroom of 1 patient’s home were tested for mcr-1 by polymerase chain reaction. The PulseNet database was searched for isolates with pulsed-field gel electrophoresis (PFGE) patterns identical to those of the mcr-1-positive isolates; WGS data for matching isolates were screened for mcr-1. The plasmids from both isolates were compared by DNA sequencing. Mcr-1 was identified in an Escherichia coli isolate from a child and in a Salmonella Enteritidis (SE) isolate from an adult with no known connection to the child. Both patients reported recent travel to the Dominican Republic (DR); stool specimens containing mcr-1 were collected 2 and 10 days, respectively, after return. Their trips occurred a month apart; no specific common exposures were reported. All rectal swabs and environmental samples collected during the ensuing investigations were mcr-1 negative. The E. coli isolate had a unique PFGE pattern. Mcr-1 was not found among 170 PFGE-matching SE isolates. Plasmids from the two isolates containing mcr-1 were identical by DNA sequencing. WGS resulted in detection of the mcr-1 resistance gene in different bacterial species from 2 Connecticut residents. Both reported diarrhea after DR trips, and had identical plasmids containing mcr-1. Follow-up cultures and screening PFGE-matching isolates did not identify additional mcr-1. These investigations highlight the need for an improved understanding of the role of international travel in importation of this resistance gene. All authors: No reported disclosures.

Abstract Background Few options remain for treatment of infections caused by multi-drug resistant (MDR), carbapenemase-producing gram-negative pathogens. Cefiderocol (CFDC; Shionogi & Co. Ltd), is a novel parenteral siderophore cephalosporin that enters the bacterial cell through the iron–siderophore uptake system. Here we report on the in vitro activity of CFDC against a set of well-characterized MDR gram-negative isolates collected by the Centers for Disease Control and Prevention. Methods Minimum inhibitory concentrations (MIC) values for CFDC in iron-depleted cation-adjusted Mueller Hinton broth were determined using reference broth microdilution. Study isolates (n = 315) included Enterobacteriaceae (59%), Pseudomonas aeruginosa (19%), Acinetobacter baumannii (17%), Stenotrophomonas maltophilia (4%), and Burkholderia cepacia complex (1%). Of these, 229 (73%) were carbapenemase-producers including Ambler Class A- (37%), Class B- (29%) and Class D- type (29%) enzymes. The remaining isolates included 51 β-lactam-resistant isolates that were non-carbapenemase-producers, and 35 β-lactam-susceptible isolates. Results were interpreted using suggested CFDC breakpoints of Sensitive ≤4 μg/mL and Resistant ≥16 μg/mL. Results The majority of the isolates (90.8%) were categorized as CFDC susceptible; the percentage of isolates with a CFDC MIC ≤4 μg/mL among Enterobacteriaceae, P. aeruginosa, and A. baumannii was 87.5%, 100%, and 89%, respectively. Percentage of isolates with a CFDC MIC ≤4 μg/mL that harbored a carbapenemase of the Class A-, Class B-, and Class D-type was 91.8%, 74.8%, 98.0%, respectively. By applying suggested breakpoints, 12 isolates were categorized as intermediate and 17 as resistant. The resistant isolates included 11 NDM-, 2 OXA-23- and 4 KPC-positive organisms. Conclusion Cefiderocol showed potent activity against MDR gram-negative pathogens including Class A, B, and D carbapenemase-producing isolates. Of note, all P. aeruginosa, including Class B metallo-β-lactamase producers, were susceptible to CFDC. Disclosures All authors: No reported disclosures.

Colistin is considered a critically important antimicrobial for its role in the treatment of severe multidrug-resistant infections. Colistin resistance conferred by the plasmid-mediated gene mcr-1 has been reported in enteric pathogens globally since 2015, but remains rare in the United States. We describe the search for mcr-1 among nontyphoidal Salmonella (NTS) and the identification of the first human cases in the United States. Whole genome sequencing (WGS) was performed on NTS isolates from humans by state health departments, from retail meat by the US Food and Drug Administration, and from food animals by the US Department of Agriculture. Sequences were uploaded to the National Center for Biotechnology Information and screened through their pathogen detection pipeline for the presence of resistance determinants (including mcr-1) beginning in late 2015; screening included some retrospective sequences. Isolates with the suspected mcr-1 gene were submitted to CDC for confirmatory PCR. Epidemiological information on human cases was collected from state health departments. Over 70,000 Salmonella isolates from humans, retail meat, and food animals were screened for mcr-1. No NTS with mcr-1 were identified in retail meat or food animals. Four human cases of NTS with mcr-1 were identified by WGS and three were confirmed by PCR (1 pending testing): Salmonella Corvallis in an 18-year-old man from Tennessee (isolation July 2014), Salmonella Enteritidis in a 55 year-old woman from Connecticut (isolation May 2016), Salmonella Typhimurium in a 57-year-old woman from Virginia (isolation November 2016), and Salmonella Enteritidis in a 47-year-old man from Minnesota (isolation April 2017). All patients traveled internationally in the 10 days prior to illness onset. NTS rarely contain mcr-1 in the United States. To date, all human cases have been linked to international travel, reflecting the higher prevalence of mcr-1 reported from other parts of the world. The absence of mcr-1 in NTS from US food animals and retail meat is likely because colistin has not been used in food animal agriculture in the United States, underscoring the importance of a One Health approach to combat antimicrobial resistance. All authors: No reported disclosures.