Mobile Colistin Resistance Genetic Determinants of Non-Typhoid Salmonella enterica Isolates from Russia

Polymyxin resistance, determined by mcr genes located on plasmid DNA, currently poses a high epidemiological threat. Non-typhoid Salmonella (NTS) are one of the key pathogens causing diarrheal diseases. Here, we report the isolation and whole genome sequencing of multidrug colistin-resistant/susceptible isolates of non-typhoid Salmonella enterica serovars carrying mcr genes. Non-typhoid strains of Salmonella enterica subsp. enterica were isolated during microbiological monitoring of the environment, food, and diarrheal disease patients between 2018 and 2020 in Russia (n = 586). mcr-1 genes were detected using a previously developed qPCR assay, and whole genome sequencing of mcr positive isolates was performed by both short-read (Illumina) and long-read (Oxford Nanopore) approaches. Three colistin-resistant isolates, including two isolates of S. Enteritidis and one isolate of S. Bovismorbificans, carried the mcr-1.1 gene located on IncX4 and IncI2 conjugative plasmids, respectively. The phenotypically colistin-susceptible isolate of S. Typhimurium carried a mcr-9 gene on plasmid IncHI2. In conclusion, we present the first three cases of mcr gene-carrying NTS isolates detected in Russia with both outbreak and sporadic epidemiological backgrounds.

Impact of ceftolozane/tazobactam concentrations in continuous infusion against extensively drug-resistant Pseudomonas aeruginosa isolates in a hollow-fiber infection model

Ceftolozane/tazobactam (C/T) has emerged as a potential agent for the treatment of extensively drug-resistant (XDR) Pseudomonas aeruginosa infections. As it is a time-dependent antimicrobial, prolonged infusion may help achieve pharmacokinetic/pharmacodynamic (PK/PD) targets. To compare alternative steady-state concentrations (Css) of C/T in continuous infusion (CI) against three XDR P. aeruginosa ST175 isolates with C/T minimum inhibitory concentration (MIC) values of 2 to 16 mg/L in a hollow-fiber infection model (HFIM). Duplicate 10-day HFIM assays were performed to evaluate Css of C/T in CI: one compared 20 and 45 mg/L against the C/T-susceptible isolate while the other compared 45 and 80 mg/L against the two C/T-non-susceptible isolates. C/T resistance emerged when C/T-susceptible isolate was treated with C/T in CI at a Css of 20 mg/L; which showed a deletion in the gene encoding AmpC β-lactamase. The higher dosing regimen (80 mg/L) showed a slight advantage in effectiveness. The higher dosing regimen has the greatest bactericidal effect, regardless of C/T MIC. Exposure to the suboptimal Css of 20 mg/L led to the emergence of C/T resistance in the susceptible isolate. Antimicrobial regimens should be optimized through C/T levels monitoring and dose adjustments to improve clinical management.

Mobile Colistin Resistance Genetic Determinants of Non-typhoid Salmonella enterica Isolates from Russia

Polymyxin resistance, determined by mcr genes located on plasmid DNA, currently pose a high epidemiological threat. Non-typhoid Salmonella (NTS) are one of the key pathogens causing diarrheal diseases. Here, we report the isolation and whole genome sequencing of multidrug colistin-resistant/susceptible isolates of non-typhoid Salmonella enterica serovars carries mcr genes. Non-typhoid strains of Salmonella enterica subsp. enterica were isolated during microbiological monitoring of the environment, food, and diarrheal disease patients between 2018 and 2020 in Russia (n=586). mcr-1 genes were detected using a previously developed qPCR assay and whole genome sequencing of mcr positive isolates was performed by both short-read (Illumina) and long-read (Oxford Nanopore) approaches. Three colistin-resistant isolates including two isolates of S. Enteritidis and one isolate of S. Bovismorbificans carried the mcr-1.1 gene located on IncX4 and IncI2 conjugative plasmids, respectively. The phenotypically colistin-susceptible isolate of S. Typhimurium carried a mcr-9 gene on plasmid IncHI2. In conclusion, we present the first three cases of mcr gene carrying NTS isolates detected in Russia with both outbreak and sporadic epidemiological background.

1283. High Dose Minocycline for the Treatment of Acinetobacter Infections

Background Acinetobacter (ACB) infections are difficult to treat due to increasing drug resistance. The aim of this study is to evaluate the effectiveness of high-dose (HD) minocycline (MIN) 200mg q12h for the treatment of ACB infections Methods This is a retrospective study of pts with ACB from 1/1/19 to 10/31/20. Exclusions included non-susceptibility to MIN, age < 18 yrs, hospice care w/in 72 hrs of culture, or urine source. Use of HD MIN (IV or PO), was compared to alternative treatment (AT). Clinical and micro success at the end of therapy (EOT) was evaluated. Clinical success was elimination or improvement in signs and symptoms of infection. Micro success was eradication of ACB from the same site of infection at EOT. Length of stay (LOS), 30-day readmission (with or without ACB), isolation of a MIN non-susceptible ACB within 30 days of EOT, and adverse events related to MIN, were evaluated. Results A total of 320 pts were screened with the most common exclusion being MIN non-susceptible isolate. Of the 204 pts included, 38 received HD MIN and 166 received AT. The most common were cefepime (53/166) and meropenem (36/166). Median age (IQR) was 41 (30-50) yrs for HD MIN vs. 40 (27-48) yrs for AT. Both groups were mostly male (HD MIN: 63% vs. AT: 60%) and respiratory was the most common site (HD MIN: 61% vs. AT: 60%). HD MIN group had 74% of cultures that were polymicrobial vs. 86% in AT group. Lack of clinical response at the EOT occurred in 42% of pts on HD MIN and 37% on AT. Infection related mortality occurred in 24% on HD MIN vs. 15% on AT. In HD MIN group, 16 pts had a repeat culture from the same site after treatment with 25% still positive for ACB. In the AT group 61 pts had a repeat culture and 28% were positive for ACB. Duration of treatment (9 [6-11] days vs. 10 [2-18] days) and LOS (16 [18.25-26.75] vs. 29 [14-49]) were shorter in the HD MIN group. There was only one adverse event reported with the use of HD MIN Conclusion Pts in the HD MIN group had shorter treatment duration and a shorter LOS. Pts who received HD MIN had a lower rate of clinical cure and a higher mortality rate compared to pts in the AT group. Reasons for this difference will need to be investigated further. HD MIN should be reserved for pts who are unable to tolerate other treatment options or who have an ACB resistant to other treatment options. Disclosures All Authors: No reported disclosures

Risk factors for microbiologic failure in children with Enterobacter species bacteremia

Background Enterobacter species are an important cause of healthcare-associated bloodstream infections (BSI) in children. Up to 19% of adult patients with Enterobacter BSI have recurrence of infection resistant to third-generation cephalosporins (3GCs) while on therapy with a 3GC. Data are lacking regarding the incidence of and risk factors for recurrence of infection in children with Enterobacter BSI. Methods We conducted a retrospective case-control study of patients aged ≤21 years old admitted to Texas Children’s Hospital from January 2012 through December 2018 with Enterobacter BSI. The primary outcome was microbiologic failure from 72 hours to 30 days after the initial BSI (cases). The secondary outcome was isolation of a 3GC non-susceptible Enterobacter sp. from a patient with an initial 3GC-susceptible isolate. Results Twelve patients (6.7%) had microbiologic failure compared to 167 controls without microbiologic failure. Of the 138 patients (77.1%) with an Enterobacter sp. isolate that was initially susceptible to 3GCs, 3 (2.2%) developed a subsequent infection with a non-susceptible isolate. Predictors of microbiologic failure were having an alternative primary site of infection besides bacteremia without a focus or an urinary tract infection (OR, 9.64; 95% CI, 1.77–52.31; P < 0.01) and inadequate source control (OR, 22.16; 95% CI, 5.26–93.36; P < 0.001). Conclusions Source of infection and adequacy of source control are important considerations in preventing microbiologic failure. In-vitro susceptibilities can be used to select an antibiotic regimen for the treatment of Enterobacter BSI in children.

Risk factors for isolation of fluconazole and echinocandin non-susceptible Candida species in critically ill patients

Introduction. Resistance rates to azoles and echinocandins of Candida spp. increased over the last decade. Hypothesis/Gap Statement. Widespread use of antifungals could lead to development and dissemination of resistant Candida spp. Aim. To identify risk factors for isolation of Candida spp. non-susceptible to either fluconazole or echinocandins. Methodology. All patients hospitalized in the Intensive Care Unit (ICU) of the University General Hospital of Patras, Greece with Candida spp. isolated from clinical specimens during a ten-year period (2010–19) were included. Candida isolates were identified using Vitek-2 YST card. Consumption of antifungals was calculated. Results. During the study period, 253 isolates were included. C. non-albicans predominated (64.4 %) with C. parapsilosis being the most commonly isolated (42.3 %) followed by C. glabrata (nomenclatural change to Nakaseomyces glabrataa; 8.7 %) and C. tropicalis (11.9 %). Among all isolates, 45.8 and 28.5 % were non-susceptible and resistant to fluconazole, respectively. Concerning echinocandins, 8.7 % of isolates were non-susceptible to at least one echinocandin (anidulafungin or micafungin) and 3.1 % resistant. Multivariate analysis revealed that hospitalization during 2015–19, as compared to 2010–14, isolate being non-albicans or non-susceptible to at least one echinocandin was associated with isolation of fluconazole non-susceptible isolate. Administration of echinocandin, isolate being C. glabrata or C. tropicalis, or Candida spp. non-susceptible to fluconazole were independently associated with isolation of Candida spp. non-susceptible to at least one echinocandin. Fluconazole’s administration decreased during the study period, whereas liposomal-amphotericin B’s and echinoncandins’ administration remained stable. Conclusion. Fluconazole’s non-susceptibility increased during the study period, despite the decrease of its administration. Although echinocandins’ administration remained stable, non-susceptibility among Candida spp. increased.

Impact of fenbendazole resistance in Ascaridia dissimilis on the economics of production in turkeys

Feed conversion efficiency is among the most important factors affecting profitable production of poultry. Infections with parasitic nematodes can decrease efficiency of production, making parasite control through the use of anthelmintics an important component of health management. In ruminants and horses, anthelmintic resistance is highly prevalent in many of the most important nematode species, which greatly impacts their control. Recently, we identified resistance to fenbendazole in an isolate of Ascaridia dissimilis, the most common intestinal helminth of turkeys. Using this drug-resistant isolate, we investigated the impact that failure to control infections has on weight gain and feed conversion in growing turkeys. Birds were infected on Day 0 with either a fenbendazole-susceptible or -resistant isolate, and then half were treated with fenbendazole (SafeGuard® Aquasol) at 4- and 8-weeks post infection. Feed intake and bird weight were measured for each pen weekly throughout the study, and feed conversion rate was calculated. Necropsy was performed on birds from each treatment group to assess worm burdens at weeks 7 and 9 post infection. In the birds infected with the susceptible isolate, fenbendazole-treated groups had significantly better feed conversion as compared to untreated groups. In contrast, there were no significant differences in feed conversion between the fenbendazole-treated and untreated groups in the birds infected with the resistant isolate. At both weeks 7 and 9, worm burdens were significantly different between the treated and untreated birds infected with the drug-susceptible isolate, but not in the birds infected with the drug-resistant isolate. These significant effects on feed conversion were seen despite having a rather low worm establishment in the birds. Overall, these data indicate that A. dissimilis can produce significant reductions in feed conversion, and that failure of treatment due to the presence of fenbendazole-resistant worms can have a significant economic impact on turkey production. Furthermore, given the low worm burdens and an abbreviated grow out period of this study, the levels of production loss we measured may be an underestimate of the true impact that fenbendazole-resistant worms may have on a commercial operation.

The Occurrence of Antimicrobial-Resistant Salmonella enterica in Hatcheries and Dissemination in an Integrated Broiler Chicken Operation in Korea

Positive identification rates of Salmonella enterica in hatcheries and upstream breeder farms were 16.4% (36/220) and 3.0% (6/200), respectively. Among the Salmonella serovars identified in the hatcheries, S. enterica ser. Albany (17/36, 47.2%) was the most prevalent, followed by the serovars S. enterica ser. Montevideo (11/36, 30.6%) and S. enterica ser. Senftenberg (5/36, 13.9%), which were also predominant. Thirty-six isolates showed resistance to at least one antimicrobial tested, of which 52.8% (n = 19) were multidrug resistant (MDR). Thirty-three isolates (enrofloxacin, MIC ≥ 0.25) showed point mutations in the gyrA and parC genes. One isolate, S. enterica ser. Virchow, carrying the blaCTX-M-15 gene from the breeder farm was ceftiofur resistant. Pulsed-field gel electrophoresis (PFGE) showed that 52.0% S. enterica ser. Montevideo and 29.6% S. enterica ser. Albany isolates sourced from the downstream of hatcheries along the broiler chicken supply chain carried the same PFGE types as those of the hatcheries. Thus, the hatcheries showed a high prevalence of Salmonella isolates with high antimicrobial resistance and no susceptible isolate. The AMR isolates from hatcheries originating from breeder farms could disseminate to the final retail market along the broiler chicken supply chain. The emergence of AMR Salmonella in hatcheries may be due to the horizontal spread of resistant isolates. Therefore, Salmonella control in hatcheries, particularly its horizontal transmission, is important.

1440. The Genetic Basis for a Neisseria gonorrhoeae Clinical Isolate That Contains mtrR-79 Mutation But Is Highly Susceptible to Antibiotics Effluxed by the Mtr Pump System

Background Neisseria gonorrhoeae (NG) possesses multiple drug efflux systems that play an important role in evading antibiotics in the treatment for gonorrhea and in helping this pathogen to evade innate antimicrobial defenses during infection. The mtrR-79 and mtr120 mutations in the promoter region between mtrR and mtrCDE are common mutations contributing to overexpression of the MtrCDE efflux pump resulting in increased efflux to multiple antibiotics including macrolides, β-lactams and tetracycline. However, we found a NG clinical isolate that contains the mtrR-79 mutation but is highly susceptible to antibiotics effluxed by the MtrCDE pump system. Methods PCR amplification, DNA sequencing and natural transformation were used to investigate the genetic basis responsible for the increased susceptibility by this isolate. Results We amplified by PCR the individual genes of mtrCDE, respectively, from this susceptible isolate as well as a NG isolate that contains the mtrR-79 mutation with increased efflux; there was no difference in the size of PCR products between the susceptible isolate and the isolate with increased efflux, indicating there was no large deletion/insertion in these genes. DNA sequence analysis of mtrCDE revealed the susceptible isolate also contained a loss-of-function mutation ΔGC from a 6 GC repeat GCGCGCGCGCGC in mtrC resulting in MtrC A117 frameshift predicted to produce a truncated MtrC protein that results in a low efflux phenotype. Natural transformation of the susceptible isolate with a wild type mtrC and selection with ciprofloxacin generated transformants that corrected the ΔGC mutation and restored the increased efflux phenotype. Conclusion Our results indicate that genotyping of mtrR and the promoter region between mtrR and mtrCDE is insufficient to predict increased efflux phenotype and provide direct evidence that NG isolates with elevated efflux is able to genetically revert to low efflux via loss-of-function mutations in the coding region of the efflux pump genes. Disclosures Jianzhong Huang, PhD, GlaxoSmithKline (Employee, Shareholder) Karen Ingraham, MS, GlaxoSmithKline (Employee, Shareholder)

1626. Synergistic Effect of Cefiderocol with Other Antibiotics Against PER-Producing Acinetobacter baumannii Isolates from the Multinational SIDERO-WT Studies

Background Cefiderocol (CFDC), a novel siderophore cephalosporin, showed potent activity at minimum inhibitory concentrations (MICs) of ≤4 μg/mL against ≥99% of Gram-negative isolates in the multinational SIDERO-WT studies. PER-producing Acinetobacter baumannii, mainly from Russia, showed high CFDC MICs of 8– &gt;64 μg/mL. This study evaluated the synergistic effects of CFDC combined with other antibiotics against PER-producing A. baumannii isolates with high CFDC MICs. Methods Two isolates of PER-producing A. baumannii with resistance to CFDC (MIC 16 μg/mL), meropenem (MEM; MIC 64 μg/mL), ceftazidime-avibactam (CZA; MIC 64/4 μg/mL), amikacin (AMK; MIC 32 or 64 μg/mL), and ciprofloxacin (CIP; MIC ≥64 μg/mL) were tested. Against ampicillin-sulbactam (SAM), one isolate was resistant (MIC 32/64 μg/mL) and another was susceptible (MIC 8/16 μg/mL). Effects of CFDC combined with other antibiotics were evaluated by checkerboard assay and chemostat model reproducing humanized antibiotic exposure. The checkerboard assay used a single agent (e.g. ceftazidime [CAZ], avibactam [AVI], ampicillin [AMP] or sulbactam [SUL]). Iron-depleted cation-adjusted Mueller‒Hinton broth was used as the standard medium for CFDC, as recommended by the Clinical Laboratory and Standards Institute. Results Against both isolates, synergy with CFDC was seen for two β-lactamase inhibitors, AVI and SUL, with a fractional inhibitory concentration (FIC) index of 0.026–0.033 and 0.26–0.27, respectively. A synergistic to additive effect was seen for MEM and AMK, with an FIC index of 0.53–0.75 and 0.25–0.52, respectively. In the chemostat model, regrowth during 24-h treatment was observed with single agents (CFDC 2 g, q8h, 3-h infusion; MEM 2 g, q8h, 1-h infusion; CZA 2 g, q8h, 2-h infusion; SAM 3 g, q8h, 3-h infusion; AMK 15 mg/kg, q8h, 3-h infusion) for both isolates, including the SAM-susceptible isolate. However, no regrowth was seen when CFDC was combined with CZA, MEM, SAM or AMK. Conclusion The most potent synergy was seen between CFDC and AVI against PER-producing A. baumannii with a decreased MIC to ≤1 µg/mL for all isolates, followed by SUL and MEM. Under humanized pharmacokinetic exposure, combination of CFDC and CZA, MEM, SAM or AMK is expected to be effective against PER-producing A. baumannii in spite of high CFDC MICs. Disclosures Yoshinori Yamano, PhD, Shionogi & Co., Ltd. (Employee) Miki Takemura, MSc, Shionogi & Co., Ltd. (Employee) Naomi Anan, MSc, Shionogi & Co., Ltd. (Employee) Rio Nakamura, BSc, Shionogi & Co., Ltd. (Employee) Roger Echols, MD, Shionogi Inc. (Consultant)