BackgroundRecent studies have favored the use of cefazolin over nafcillin for the treatment of methicillin-susceptible Staphylococcus aureus (MSSA) bacteremia. The clinical influence of the cefazolin inoculum effect (CzIE) in the effectiveness of cephalosporins for severe MSSA infections has not been evaluated.MethodsWe prospectively included patients from 3 Argentinian hospitals with S. aureus bacteremia. Cefazolin minimum inhibitory concentrations (MICs) were determined at standard (105 colony-forming units [CFU]/mL) and high (107 CFU/mL) inoculum. The CzIE was defined as an increase of MIC to ≥16 µg/mL when tested at high inoculum. Whole-genome sequencing was performed in all isolates.ResultsA total of 77 patients, contributing 89 MSSA isolates, were included in the study; 42 patients (54.5%) had isolates with the CzIE. In univariate analysis, patients with MSSA exhibiting the CzIE had increased 30-day mortality (P = .034) and were more likely to have catheter-associated or unknown source of bacteremia (P = .033) compared with patients infected with MSSA isolates without the CzIE. No statistically significant difference between the groups was observed in age, clinical illness severity, place of acquisition (community vs hospital), or presence of endocarditis. The CzIE remained associated with increased 30-day mortality in multivariate analysis (risk ratio, 2.65; 95% confidence interval, 1.10–6.42; P = .03). MSSA genomes displayed a high degree of heterogeneity, and the CzIE was not associated with a specific lineage.ConclusionsIn patients with MSSA bacteremia where cephalosporins are used as firstline therapy, the CzIE was associated with increased 30-day mortality. Clinicians should be cautious when using cefazolin as firstline therapy for these infections.

Polymyxins are last-resort antimicrobial agents used to treat infections caused by carbapenem-resistant Due to the worldwide dissemination of polymyxin resistance in animal and human isolates, we aimed to characterize polymyxin resistance associated with the presence of in and nonfermenter Gram-negative bacilli, using isolates collected retrospectively in Colombia from 2002 to 2016. A total of 5,887 Gram-negative clinical isolates were studied, and 513 were found to be resistant to the polymyxins. Susceptibility to colistin was confirmed by broth microdilution for all-positive isolates, and these were further subjected to whole-genome sequencing (WGS). The localization of was confirmed by S1 pulsed-field gel electrophoresis (S1-PFGE) and CeuI-PFGE hybridization. Transferability was evaluated by mating assays. A total of 12 colistin-resistant isolates recovered after 2013 harbored, including 8 , 3 serovar Typhimurium, and 1 isolate isolates were unrelated by PFGE and belonged to 7 different sequence types (STs) and phylogroups. Typhimurium and isolates belonged to ST34 and ST307, respectively. The gene was plasmid borne in all isolates but two isolates which harbored it on the chromosome. Conjugation of was successful in 8 of 10 isolates (8.2 × 10 to 2.07 × 10 cell per recipient). Plasmid sequences showed that the plasmids belonged to four different Inc groups (a new IncP-1 variant and the IncFII, IncHI1, and IncH families). Our results indicate that is circulating in clinical isolates of colistin-resistant in Colombia and is mainly harbored in transferable plasmids.

The increase in antibiotic resistant bacteria has raised global concern regarding the future effectiveness of antibiotics. Human activities that influence microbial communities and environmental resistomes can generate additional risks to human health. In this work, we characterized aquatic microbial communities and their resistomes in samples collected at three sites along the Bogotá River and from wastewaters at three city hospitals, and investigated community profiles and antibiotic resistance genes (ARGs) as a function of anthropogenic contamination. The presence of antibiotics and other commonly used drugs increased in locations highly impacted by human activities, while the diverse microbial communities varied among sites and sampling times, separating upstream river samples from more contaminated hospital and river samples. Clinically relevant antibiotic resistant pathogens and ARGs were more abundant in contaminated water samples. Tracking of resistant determinants to upstream river waters and city sources suggested that human activities foster the spread of ARGs, some of which were co-localized with mobile genetic elements in assembled metagenomic contigs. Human contamination of this water ecosystem changed both community structure and environmental resistomes that can pose a risk to human health.

Background Ceftolozane-tazobactam (CT) is a newly approved cephalosporin/β-lactamase inhibitor combination with excellent in vitro activity against multidrug-resistant (MDR) P. aeruginosa. Unfortunately, CT-resistance (CT-R) has already been reported. In this work, we evaluate mutational pathways associated with high level of CT-R and assess the role of AmpC in a clinical strain-pair of MDR P. aeruginosa.Methods A CT susceptible isolate of P. aeruginosa (2365) and its CT-R derivatives (2366 and 2367) were recovered from the infected device of a patient before and after treatment with CT. Minimum inhibitory concentrations (MICs) to CT were determined by Etest. Resistance mediated by AmpC hyperproduction was evaluated using ceftazidime (CAZ) and meropenem (MER) with and without cloxacillin (CLOX) at concentration of 1 mg/ml. In addition, the β-lactamase hydrolysis activity was determined for crude cell lysate of the isolates using a spectrophotometric assay for nitrocefin degradation. Furthermore, whole genome sequencing of the three strains was performed and compared (2365 vs. 2366 and 2367). Reads from each isolate were mapped against the genome of the reference strain PAO1. Variants identified by GATK, SamTools and CLC Genomics Workbench 8.5 were selected and annotated with SnpEff.ResultsStrain 2365 had a CT MIC of 0.75 mg/ml while 2366 and 2367 have MICs > 256 mg/ml. AmpC hyperproduction test was positive only for the susceptible isolate (2365). In concordance, the hydrolysis assay showed a lack of nitrocefin degradation by CT-R 2366 compared with its CT-susceptible isolate 2365. Notably, the three strains (S and R) exhibited a truncated AmpD. Comparison of the resistant derivatives vs. 2365 and 2367 showed a 7 amino acid deletion in the Ω-loop of the β-lactamase AmpC in both resistant derivatives and mutations in genes predicted to encode a hypothetical protein, an ABC transporter ATP-binding protein and a multidrug resistance operon repressor MexR.Conclusion Our results suggest that the deletion in the Ω-loop of AmpC in 2366 and 2367 does not contribute to CT-R in these P. aeruginosa strains. Further characterization of AmpC and other predicted proteins identified by WGS are needed to determine the mechanism of CT-R.Disclosures All authors: No reported disclosures.

BackgroundCarbapenemase-producing Enterobacteriaceae (CPE) currently pose a significant global public health threat. KPC carbapenemases are highly endemic in Colombia mostly among Enterobacteriaceae. In Klebsiella pneumoniae (Kpn), horizontal transfer of genes encoding KPC and expansion of isolates belonging to clonal group (CG) 258 resulted in epidemic levels of carbapenemase-producing Kpn. We aimed to understand the dynamics of transmission of KPC-genes among CPE infecting and colonizing patients in an endemic area of Colombia.MethodsWe conducted a surveillance study in 3 hospitals around Medellin, Antioquia (November 2013 to October 2015) that included patients colonized and infected (by physician criteria) with CPE. The isolates were collected, identified and typed initially using rep-PCR. A subset of isolates were chosen for Whole Genome Sequencing on the Illumina platform based on initial molecular characterization. De-novo assembly and maximum likelihood phylogenetic analyses were performed in all sequenced isolates.ResultsA total of 131 KPC-producing Enterobacteriaceae isolates were recovered from 77 colonized and 29 infected patients. A total of 76 selected isolates were sequenced. In Kpn, compartmentalization of KPC-3 within CG258 was observed, whereas KPC-2 was identified in different genetic backgrounds but not in CG258. In E. coli, blaKPC-2 was found in two clusters belonging to ST131 and ST349. In one hospital both Kpn (ST36,15,101,140, 502) and E. coli shared a 56 Kb plasmid harboring blaKPC-2 with high degree of identity to the conjugative IncN plasmid N3. The blaKPC-2 gene was found within a variation of Tn4401b harboring ISKpn6 and carrying both a Tn3-transposase and a resolvase. E. cloacae, C. freundii and S. marcescens only harbored KPC-2 (and not KPC-3) within the same Tn4401b structure.ConclusionThe KPC epidemic in an area of high endemicity in Colombia is driven by horizontal transfer of plasmids harboring blaKPC-2 among members of the Enterobacteriaceae family. These findings are consistent with a KPC-plasmid epidemic rather than clonal expansion of a successful genetic lineage. Controlling the KPC epidemic in Colombia would be challenging and is likely influenced by antibiotic consumption rather than patient to patient transmission.Disclosures A. M. Rada, COLCIENCIAS: Student, Research grant and Research support; N. Orozco, COLCIENCIAS: Research Contractor, Salary; C. Hernández-Gómez, Merck Sharp and Dohme, Pfizer: Consultant, Consulting fee; C. Pallares, Merck Sharp & Dohme, Pfizer: Consultant, Consulting fee; M. V. Villegas, Merck Sharp & Dohme, Pfizer: Consultant, Consulting fee and Research support; E. Restrepo, COLCIENCIAS: Investigator, Research support