Staphylococcus aureus and Acinetobacter baumannii Inhibit Osseointegration of Orthopedic Implants.

Bacterial infections routinely cause inflammation and thereby impair osseointegration of orthopedic implants. Acinetobacter spp., which cause osteomyelitis following trauma, on or off the battlefield, were, however, reported to cause neither osteomyelitis nor osteolysis in rodents. We therefore compared the effects of Acinetobacter strain M2 to those of Staphylococcus aureus in a murine implant infection model. Sterile implants and implants with adherent bacteria were inserted in the femur of mice. Bacterial burden, levels of proinflammatory cytokines, and osseointegration were measured. All infections were localized to the implant site. Infection with either S. aureus or Acinetobacter strain M2 increased the levels of proinflammatory cytokines and the chemokine CCL2 in the surrounding femurs, inhibited bone formation around the implant, and caused loss of the surrounding cortical bone, leading to decreases in both histomorphometric and biomechanical measures of osseointegration. Genetic deletion of TLR2 and TLR4 from the mice partially reduced the effects of Acinetobacter strain M2 on osseointegration but did not alter the effects of S. aureus. This is the first report that Acinetobacter spp. impair osseointegration of orthopedic implants in mice, and the murine model developed for this study will be useful for future efforts to clarify the mechanism of implant failure due to Acinetobacter spp. and to assess novel diagnostic tools or therapeutic agents.

Clinical outcomes and bacterial characteristics of carbapenem-resistant Klebsiella pneumoniae complex among patients from different global regions (CRACKLE-2): a prospective, multicentre, cohort study.

BACKGROUND: Carbapenem-resistant Klebsiella pneumoniae (CRKP) is a global threat. We therefore analysed the bacterial characteristics of CRKP infections and the clinical outcomes of patients with CRKP infections across different countries. METHODS: In this prospective, multicentre, cohort study (CRACKLE-2), hospitalised patients with cultures positive for CRKP were recruited from 71 hospitals in Argentina, Australia, Chile, China, Colombia, Lebanon, Singapore, and the USA. The first culture positive for CRKP was included for each unique patient. Clinical data on post-hospitalisation death and readmission were collected from health records, and whole genome sequencing was done on all isolates. The primary outcome was a desirability of outcome ranking at 30 days after the index culture, and, along with bacterial characteristics and 30-day all-cause mortality (a key secondary outcome), was compared between patients from China, South America, and the USA. The desirability of outcome ranking was adjusted for location before admission, Charlson comorbidity index, age at culture, Pitt bacteremia score, and anatomical culture source through inverse probability weighting; mortality was adjusted for the same confounders, plus region where relevant, through multivariable logistic regression. This study is registered at ClinicalTrials.gov, NCT03646227, and is complete. FINDINGS: Between June 13, 2017, and Nov 30, 2018, 991 patients were enrolled, of whom 502 (51%) met the criteria for CRKP infection and 489 (49%) had positive cultures that were considered colonisation. We observed little intra-country genetic variation in CRKP. Infected patients from the USA were more acutely ill than were patients from China or South America (median Pitt bacteremia score 3 [IQR 2-6] vs 2 [0-4] vs 2 [0-4]) and had more comorbidities (median Charlson comorbidity index 3 [IQR 2-5] vs 1 [0-3] vs 1 [0-2]). Adjusted desirability of outcome ranking outcomes were similar in infected patients from China (n=246), South America (n=109), and the USA (n=130); the estimates were 53% (95% CI 42-65) for China versus South America, 50% (41-61) for the USA versus China, and 53% (41-66) for the USA versus South America. In patients with CRKP infections, unadjusted 30-day mortality was lower in China (12%, 95% CI 8-16; 29 of 246) than in the USA (23%, 16-30; 30 of 130) and South America (28%, 20-37; 31 of 109). Adjusted 30-day all-cause mortality was higher in South America than in China (adjusted odds ratio [aOR] 4·82, 95% CI 2·22-10·50) and the USA (aOR 3·34, 1·50-7·47), with the mortality difference between the USA and China no longer being significant (aOR 1·44, 0·70-2·96). INTERPRETATION: Global CRKP epidemics have important regional differences in patients' baseline characteristics and clinical outcomes, and in bacterial characteristics. Research findings from one region might not be generalisable to other regions. FUNDING: The National Institutes of Health.

Risk Factors for and Mechanisms of COlistin Resistance Among Enterobacterales: Getting at the CORE of the Issue.

BACKGROUND: Despite the recent emergence of plasmid-mediated colistin resistance, the epidemiology and mechanisms of colistin-resistant Enterobacterales (CORE) infections remain poorly understood. METHODS: A case-case-control study was conducted utilizing routine clinical isolates obtained at a single tertiary health system in Ann Arbor, Michigan. Patients with CORE isolates from January 1, 2016, to March 31, 2017, were matched 1:1 with patients with colistin-susceptible Enterobacterales (COSE) and uninfected controls. Multivariable logistic regression was used to compare clinical and microbiologic features of patients with CORE and COSE to controls. A subset of available CORE isolates underwent whole-genome sequencing to identify putative colistin resistance genes. RESULTS: Of 16 373 tested clinical isolates, 166 (0.99%) were colistin-resistant, representing 103 unique patients. Among 103 CORE isolates, 103 COSE isolates, and 102 uninfected controls, antibiotic exposure in the antecedent 90 days and age >55 years were predictors of both CORE and COSE. Of 33 isolates that underwent whole-genome sequencing, a large variety of mutations associated with colistin resistance were identified, including 4 mcr-1/mcr-1.1 genes and 4 pmrA/B mutations among 9 Escherichia coli isolates and 5 mgrB and 3 PmrA mutations among 8 Klebsiella pneumoniae isolates. Genetic mutations found in Enterobacter species were not associated with known phenotypic colistin resistance. CONCLUSIONS: Increased age and prior antibiotic receipt were associated with increased risk for patients with CORE and for patients with COSE. Mcr-1, pmrA/B, and mgrB were the predominant colistin resistance-associated mutations identified among E. coli and K. pneumoniae, respectively. Mechanisms of colistin resistance among Enterobacter species could not be determined.

Targeting Multidrug-Resistant Acinetobacter spp.: Sulbactam and the Diazabicyclooctenone ß-Lactamase Inhibitor ETX2514 as a Novel Therapeutic Agent.

Multidrug-resistant (MDR) Acinetobacter spp. poses a significant therapeutic challenge in part due to the presence of chromosomally encoded ß-lactamases, including class C Acinetobacter-derived cephalosporinases (ADC) and class D oxacillinases (OXA), as well as plasmid-mediated class A ß-lactamases. Importantly, OXA-like ß-lactamases represent a gap in the spectrum of inhibition by recently approved ß-lactamase inhibitors such as avibactam and vaborbactam. ETX2514 is a novel, rationally designed, diazabicyclooctenone inhibitor that effectively targets class A, C, and D ß-lactamases. We show that addition of ETX2514 significantly increased the susceptibility of clinical Acinetobacterbaumannii isolates to sulbactam. AdeB and AdeJ were identified to be key efflux constituents for ETX2514 in A. baumannii The combination of sulbactam and ETX2514 was efficacious against A. baumannii carrying blaTEM-1, blaADC-82, blaOXA-23, and blaOXA-66 in a neutropenic murine thigh infection model. We also show that, in vitro, ETX2514 inhibited ADC-7 (k2/Ki 1.0 ± 0.1 × 106 M-1 s-1) and OXA-58 (k2/Ki 2.5 ± 0.3 × 105 M-1 s-1). Cocrystallization of ETX2514 with OXA-24/40 revealed hydrogen bonding interactions between ETX2514 and residues R261, S219, and S128 of OXA-24/40 in addition to a chloride ion occupied in the active site. Further, the C3 methyl group of ETX2514 shifts the position of M223. In conclusion, the sulbactam-ETX2514 combination possesses a broadened inhibitory range to include class D ß-lactamases as well as class A and C ß-lactamases and is a promising therapeutic candidate for infections caused by MDR Acinetobacter spp.IMPORTANCE The number and diversity of ß-lactamases are steadily increasing. The emergence of ß-lactamases that hydrolyze carbapenems poses a significant threat to our antibiotic armamentarium. The explosion of OXA enzymes that are carbapenem hydrolyzers is a major challenge (carbapenem-hydrolyzing class D [CHD]). An urgent need exists to discover ß-lactamase inhibitors with class D activity. The sulbactam-ETX2514 combination demonstrates the potential to become a treatment regimen of choice for Acinetobacter spp. producing class D ß-lactamases.