Non-susceptible Strains Research Articles

Clinical characteristics and microbiological profile of viridans group streptococci bacteremia in children with cancer and high-risk febrile neutropenia

Viridans group streptococci (VGS) has acquired relevance as a microorganism causing febrile neutropenia, associated with significant morbidity. To characterize episodes of bacteremia caused by VGS in children with cancer who developed high-risk febrile neutropenia (HRFN) during the period from April 2004 to June 2018 in six pediatric hospitals of Santiago, Chile. Database analysis of 4 successive, prospective and multicentric studies recording clinical and laboratory characteristics of patients, as well as antimicrobial susceptibility pattern of isolated strains. 95 episodes of VGS bacteremia in 91 children with HRFN were analyzed. It emphasizes acute myeloid leukemia as cancer type, deep neutropenia, prolonged hospitalization (15 days), with extended use of antimicrobials (14 days) and use of cytarabine in chemotherapy schemes (86% episodes). The most frequent clinical manifestations were respiratory and gastrointestinal, associating up to 26% viridans group shock syndrome. There was high resistance to β lactams. As expected, there were not non-susceptible strains to vancomycin. VGS is a relevant microorganism in children with cancer, fever and neutropenia, with a high percentage of sepsis. Resistance to β lactams is an issue that requires strict epidemiological surveillance in this population.

Species distribution and antifungal susceptibilities of bloodstream Candida isolates: a nine-years single center survey

This study analyzed the epidemiology of bloodstream infections due to Candida spp. in a tertiary referral hospital of Ancona, Italy, and their susceptibility to antifungals. The retrospective observational study from January 2010 to December 2018 identified 504 episodes of candidemia in 461 patients. Although Candida albicans remained the species most frequently isolated, Candida spp. other than C. albicans caused 49% of the overall episodes of candidemia. According to CLSI interpretation, most of the isolates resulted susceptible to antifungals. Azoles vs Candida tropicalis represented an exception. Echinocandin non-susceptibility was rare across the species. In conclusion, with the exception of C. tropicalis, the isolation of a non-susceptible Candida strains against azoles, echinocandins and amphotericin B was a rare event.

Novel Quinolone Nonsusceptible Streptococcus canis Strains with Point Mutations in Quinolone Resistance-Determining Regions and Their Related Factors.

This study investigated quinolone nonsusceptible Streptococcus canis with point mutations in quinolone resistance-determining regions (QRDRs). After selecting targets from 185 isolates, we tested antimicrobial susceptibility using levofloxacin, ciprofloxacin, norfloxacin, and moxifloxacin. We also determined the amino acid sequences of QRDRs in gyrA/gyrB/parC/parE genes and their point mutations. Finally, we performed S. canis-derived M-like protein (SCM) allele typing, multilocus sequence typing, and antimicrobial resistance genotyping. Correlations between nonsusceptible strains and their related factors were examined. We found 13 (7.0%) nonsusceptible isolates consisting of two classes, high-level minimum inhibitory concentrations (MICs) (n = 7, 3.8%) and low-level MICs (n = 6, 3.2%). Mutations Ser81Phe/Ser81Tyr/Glu85Lys in gyrA, Ser67Phe/Ser67Tyr/Asp71Tyr in parC, Asp438Asn in parE, and Gly408Asp in gyrB were observed in these nonsusceptible strains. Common mutations included Ser81 and Ser67/Asp71; additionally, we found one strain each with Glu85, Asp438, and Gly408 mutations. There was a significant correlation between nonsusceptible isolates and the presence of SCM allele type 2, sequence type 46, tetracyclineresistance genes, and macrolide/lincosamide-resistance genes. These results could be used in future, by veterinarians while treating companion animals with clinical symptoms of streptococcal infections.

Genomic profiling of antimicrobial resistance genes in clinical isolates of Salmonella Typhi from patients infected with Typhoid fever in India

The development of multidrug resistance in Salmonella enterica serovar Typhi currently forms a major roadblock for the treatment of enteric fever. This poses a major health problem in endemic regions and extends to travellers returning from developing countries. The appearance of fluoroquinolone non-susceptible strains has resulted in use of ceftriaxone as drug of choice with azithromycin being recommended for uncomplicated cases of typhoid fever. A recent sporadic instance of decreased susceptibility to the latest drug regime has necessitated a detailed analysis of antimicrobial resistance genes and possible relationships with their phenotypes to facilitate selection of future treatment regimes. Whole genome sequencing (WGS) was conducted for 133 clinical isolates from typhoid patients. Sequence output files were processed for pan-genome analysis and prediction of antimicrobial resistance genes. The WGS analyses disclosed the existence of fluoroquinolone resistance conferring mutations in gyrA, gyrB, parC and parE genes of all strains. Acquired resistance determining mechanisms observed included catA1 genes for chloramphenicol resistance, dfrA7, dfrA15, sul1 and sul2 for trimethoprim-sulfamethoxazole and blaTEM-116/blaTEM-1B genes for amoxicillin. No resistance determinants were found for ceftriaxone and cefixime. The genotypes were further correlated with their respective phenotypes for chloramphenicol, ampicillin, co-trimoxazole, ciprofloxacin and ceftriaxone. A high correlation was observed between genotypes and phenotypes in isolates of S. Typhi. The pan-genome analysis revealed that core genes were enriched in metabolic functions and accessory genes were majorly implicated in pathogenesis and antimicrobial resistance. The pan-genome of S. Typhi appears to be closed (Bpan = 0.09) as analysed by Heap’s law. Simpson’s diversity index of 0.51 showed a lower level of genetic diversity among isolates of S. Typhi. Overall, this study augments the present knowledge that WGS can help predict resistance genotypes and eventual correlation with phenotypes, enabling the chance to spot AMR determinants for fast diagnosis and prioritize antibiotic use directly from sequence.

Antibiotic Resistance and Molecular Epidemiological Characteristics of Streptococcus agalactiae Isolated from Pregnant Women in Guangzhou, South China.

Streptococcus agalactiae colonization in pregnant women can cause postpartum intrauterine infections and life-threatening neonatal infections. To formulate strategies for the prevention and treatment of S. agalactiae infections, we performed a comprehensive analysis of antibiotic resistance and a molecular-based epidemiological investigation of S. agalactiae in this study. Seventy-two S. agalactiae strains, collected from pregnant women, were subjected to antibiotic susceptibility tests; then, the screened erythromycin and clindamycin nonsusceptible isolates were used for macrolides and clindamycin resistance genes detection, respectively. Detection of resistance genes, serotyping, and determination of virulence genes were performed by polymerase chain reaction. The clonal relationships among the colonized strains were evaluated by multilocus sequence typing. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) mass peak analysis was performed to discriminate the specific sequence types (STs). In our study, 69.4% and 47.2% of the strains were nonsusceptible to erythromycin and clindamycin, respectively; the multidrug resistance rate was 66.7%. All erythromycin nonsusceptible strains harbored resistance genes, whereas only 52.9% of the clindamycin nonsusceptible strains possessed the linB gene. Erythromycin resistance was mainly mediated by the ermB or mefA/E genes. Four serotypes were identified, and the most common serotype was serotype III (52.8%), followed by Ib (22.2%), Ia (18.0%), and II (4.2%). All the strains were divided into 18 STs that were assigned to nine clonal complexes. Most of the major STs were distributed into specific serotypes, including ST19/serotype III, ST17/serotype III, ST485/serotype Ia, ST862/serotype III, and ST651/serotype III. Analysis of virulence genes yielded seven clusters, of which bca-cfb-scpB-lmb (61.6%) was the predominant virulence gene cluster. Among all ST strains distributed in this region, only the ST17 strains had a mass peak at 7620 Da. The outcomes of this study are beneficial for the epidemiological comparison of colonized S. agalactiae in different regions and may be helpful for developing the strategies for the prevention of S. agalactiae infection in Guangzhou. Furthermore, our results show that MALDI-TOF MS can be used for the rapid identification of the ST17 strains.

Antimicrobial and Disinfectant Susceptibility of Salmonella Serotypes Isolated from Swine Slaughterhouses.

Salmonella remains one of the most common foodborne pathogens worldwide, and its resistance to antimicrobials and disinfectants has increased considerably over the years. Thus, monitoring its resistance to products commonly used in swine production is indispensable for the development of strategies to reduce the occurrence of bacterial resistance. In this context, our aim was to detect Salmonella at different points in swine slaughterhouses, identify the main serotypes, and evaluate their resistance to disinfectants and antimicrobials used in swine production. Salmonella at the processing plants was detected by conventional microbiology. Salmonella strains were tested for susceptibility to peracetic acid (0.5% and 1%), quaternary ammonium (0.5%), and seven antimicrobials. Twenty-eight percent of the samples were positive for Salmonella, with the most identified serotypes being Salmonella Derby, Salmonella Typhimurium, and monophasic Salmonella Typhimurium. All tested strains were susceptible to both concentrations of peracetic acid, but only 28% were susceptible to quaternary ammonium. Sixteen percent of the strains were susceptible to all tested antimicrobials. Only enrofloxacin was efficient in inhibiting the growth of all strains. The highest number of non-susceptible strains was to amoxicillin, followed by chloramphenicol, florfenicol, and doxycycline. Thirty-six percent of the strains were classified as multidrug-resistant. Salmonella were detected in all slaughtering processes, and important serotypes were recovered, including Salmonella Typhimurium, Salmonella Derby, monophasic Salmonella Typhimurium, and Salmonella Infantis. We observed high rates of resistance to quaternary ammonium and to important antimicrobial agents. Salmonella Typhimurium and Salmonella Infantis were the most resistant serotypes.

High Heterogeneity of Multidrug-Resistant Enterobacteriaceae Fecal Levels in Hospitalized Patients Is Partially Driven by Intravenous β-Lactams.

Multidrug-resistant Enterobacteriaceae (MRE) colonize the intestine asymptomatically from where they can breach into the bloodstream and cause life-threatening infections, especially in heavily colonized patients. Despite the clinical relevance of MRE colonization levels, we know little about how they vary in hospitalized patients and the clinical factors that determine those levels. Here, we conducted one of the largest studies of MRE fecal levels by tracking longitudinally 133 acute leukemia patients and monitoring their MRE levels over time through extensive culturing. MRE were defined as Enterobacteriaceae species that acquired nonsusceptibility to ≥1 agent in ≥3 antimicrobial categories. In addition, due to the selective media used, the MRE had to be resistant to third-generation cephalosporins. MRE were detected in 60% of the patients, but their fecal levels varied considerably among patients and within the same patient (>6 and 4 orders of magnitude, respectively). Multivariate analysis of clinical metadata revealed an impact of intravenous beta-lactams (i.e., meropenem and piperacillin-tazobactam), which significantly diminished the fecal MRE levels in hospitalized patients. Consistent with a direct action of beta-lactams, we found an effect only when the patient was colonized with strains sensitive to the administered beta-lactam (P < 0.001) but not with nonsusceptible strains. We report previously unobserved inter- and intraindividual heterogeneity in MRE fecal levels, suggesting that quantitative surveillance is more informative than qualitative surveillance of hospitalized patients. In addition, our study highlights the relevance of incorporating antibiotic treatment and susceptibility data of gut-colonizing pathogens for future clinical studies and in clinical decision-making.

Molecular epidemiology, antimicrobial susceptibility, and characterization of fluoroquinolone non-susceptible Streptococcus pyogenes in Japan

Streptococcus pyogenes (Group A streptococci: GAS) are known to cause a wide variety of human illnesses, some of which can be life-threatening. Usually, penicillin is the first-choice agent for the treatment of GAS infections. For patients with penicillin or beta-lactam antibiotics allergies, macrolide drugs are recommended as an alternative therapy. However, an increased prevalence of macrolide-resistant GAS (MRGAS) has been reported in many countries. Furthermore, fluoroquinolone non-susceptible GAS has been reported. The present study was focused on determining the features of fluoroquinolone non-susceptible strains collected from children with pharyngotonsillitis in the southwestern areas of Japan. To reveal the characteristics of fluoroquinolone non-susceptible GAS, we investigated the MIC, T-serotype, emm typing, and PFGE of 298 GAS strains isolated in the Fukuoka southwest area of Japan between 2011 and 2013. We determined that fluoroquinolone non-susceptibility shows a MIC to tosufloxacin of ≧1 μg/ml.We identified 33 (11.1%) fluoroquinolone non-susceptible GAS strains. In these strains, 6 T-serotypes and 9 emm/MLST patterns were detected. The predominant combinations were emm6/ST382 (14 strains, 42.4%) and emm89/ST101 (5 strains, 15.2%). PFGE classified 10 pulsotypes, and each was quite different.These results showed that fluoroquinolone non-susceptible GAS strains have a variety of origins. The usage of fluoroquinolone drugs could have a negative effect on the antimicrobial drug sensitivity of GAS in Japan. Considering such a situation, continuous monitoring of quinolone non-susceptible GAS is necessary.

508. Gentamicin Non-susceptibility is Associated with Persistence of Carbapenem-Resistant Klebsiella pneumoniae in the Urinary Tract

BackgroundUrinary tract infection (UTI) is the most common clinical manifestation of carbapenem-resistant Klebsiella pneumoniae (CRKp). Persistent CRKp bacteriuria is associated with the spread of CRKp and antibiotic overuse. Risk factors for persistent CRKp bacteriuria are uncertain.MethodsCRACKLE-1 was a multicenter, prospective study that included 960 patients with at least one carbapenem-resistant Enterobacteriaceae (CRE)-positive culture from December 2011 to June 2016 collected from 18 hospitals encompassing 8 healthcare systems in the Midwestern US and North Carolina. Patients with CRKp bacteriuria who were discharged alive from index hospitalization were included in the current study, and sporadic (single positive CRKp urine culture) and persistent (≥2 CRKp urine cultures during independent hospital admissions occurring at least 2 days apart) cases were compared. Antibiotic susceptibility testing was performed by local laboratories. Amikacin, gentamicin (GENT), and trimethoprim/sulfamethoxazole were included in the analysis based on variance and frequency of testing. The CDC/National Healthcare Safety Network criteria for UTI were used.ResultsCRKp was the most common CRE isolate (n = 869, prevalence 91%). In patients with CRKp, 527 had CRKp isolated from the urine (prevalence 61%, 95% CI 0.57, 0.64). Of these, 486 patients, of whom 129 (27%) were diagnosed with a UTI, were discharged alive. Notably, 135/486 (28%) patients with CRKp bacteriuria were readmitted and yielded a second urine culture of CRKp. Most patients with persistent bacteriuria, 99/135 (73%), were asymptomatic at initial admission. Of these patients, 20/99 (20%) were diagnosed with a UTI at second admission. In multivariable analysis, only GENT non-susceptibility was associated with an increased risk (adjusted OR 1.66, 95% CI 1.10–2.49) of persistent bacteriuria. Persistent bacteriuria was independent of GENT treatment during index hospitalization (GENT was used in 15% of patients).ConclusionBacteriuria with GENT non-susceptible CRKp strains was associated with persistent bacteriuria. As this was independent of GENT treatment, GENT resistance determinants may be co-transmitted along with traits that promote bacterial persistence in CRKp. Disclosures All authors: No reported disclosures.

627. Molecular Epidemiology of Daptomycin-resistant Staphylococcus aureus Causing Bloodstream Infections

BackgroundDaptomycin (Dap) has become increasingly important to combat infections caused by Staphylococcus aureus (SA). However, reports of daptomycin nonsusceptible (DNS) SA strains have emerged over the recent years, specifically with alteration of the MprF gene. Mutations in this gene lead to an increase in lysyl-phosphatidyl glycerol production resulting in a lower susceptibility to Dap and cationic antimicrobial peptides. Point mutations in the cls2 gene have also been associated with DNS SA through similar mechanisms of action. This study describes the gene mutations involved in our patients with SA bloodstream infections (BSIs) that developed Dap resistance.MethodsThis is a retrospective study in a tertiary healthcare system in southeast Michigan. SA blood isolates were sequenced through a gene-by-gene approach using Ridom SeqSphere. Charts were reviewed for clinical and laboratory data. Dap minimum inhibitory concentrations (MICs) were determined by E-test. DNS was defined as an MIC > 1.0 µg/mL.ResultsFrom December 3, 2015 to May 8, 2017, 7 patients were identified with DNS SA BSI. Mean age of the patients was 59 (SD = 13.7) and 86% were male. Mean bacteremia duration was 7 days (SD = 6.3), mean hospital length of stay was 13 days (SD = 9.8), 5 isolates were methicillin-resistant SA, and 2 were methicillin-sensitive SA. When comparing molecular sequencing of all seven patients with their Dap-sensitive strains vs. resistant strains, all patients, except for patient 3, had a point mutation at different allele loci in the MprF gene (Table 1). Additionally, two patients had point mutations in the cls2 gene. When comparing all 27 strains from the seven patients, each cluster was attributed to an individual patient with the exception of cluster one that included patients 5 and 6 suggesting transmission (Figure 1).ConclusionDNS SA is infrequent; however, the present study shows that it can emerge both from methicillin-resistant and -susceptible SA most commonly when developing MprF and cls2 gene mutations as seen in our patients. Patient 3 was the exception in our analysis and likely developed DNS SA through another gene mutation. Further studies are necessary to know the frequency of each mutation with all genes associated with DNS SA, and epidemiological risk factors of transmission. Disclosures All authors: No reported disclosures

1588. Delafloxacin Activity Against Staphylococcus aureus with Reduced Susceptibility or Resistance to Methicillin, Vancomycin, Daptomycin, or Linezolid

BackgroundDelafloxacin is a recently approved anionic fluoroquinolone antibiotic with broad-spectrum activity against Gram-positive and Gram-negative organisms. The drug has been approved for patients with acute bacterial skin and skin structure infections including those caused by methicillin-resistant S. aureus. There is limited data available against methicillin-resistant S. aureus blood isolates (MRSABI), vancomycin intermediate strains (VISA), vancomycin-resistant strains (VRSA), daptomycin non-susceptible strains (DNSSA) and linezolid-resistant S. aureus (LRSA).MethodsAntimicrobial activity of delafloxacin, levofloxacin, vancomycin, daptomycin, ceftaroline, and linezolid was determined against recent (2016–2018) MRSABI (110), VRSA (15), VISA (35), DNSSA (40), and LRSA (6). Broth microdilution testing using Mueller–Hinton broth was used to determine minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) according to CLSI guidelines. FDA breakpoints were used to determine delafloxacin susceptibility, and CLSI breakpoints were used for all other antibiotics.ResultsAntimicrobial MIC90 expressed in mg/L and (% susceptible) MRSABI VISA VRSA DNSSA Delafloxacin1 (68)1 (40)4 (7)1 (38)Levofloxacin>16 (38)>16 (9)> 16 (0)>16 (15)Vancomycin1 (99)8 (0)>64 (0)8 (35)Daptomycin1 (96)4 (26)1 (100)4 (0)Ceftaroline1 (99)1 (100)1 (100)1 (100)Linezolid2 (100)2 (100)2 (100)2 (100)None of the LRSA were susceptible to delafloxacin or levofloxacin. All strains that were susceptible to the antimicrobial agents above had an MBC that was the same as the MIC or one dilution greater except for linezolid which demonstrated an MBC that was more than eight-fold greater than the MIC. For MRSABI isolates with a levofloxacin MIC ≥ 8 mg/L (55/110) suggesting multiple mutations in the quinolone-resistant determining region, the delafloxacin MIC90 was 1 mg/L with a 36.4% susceptibility rate.ConclusionDelafloxacin demonstrates superior activity to levofloxacin against recent MRSA blood isolates, VISA, VRSA, and DNSSA.Disclosures All authors: No reported disclosures.

1539. Dalbavancin, Vancomycin, and Daptomycin Alone and in Combination with Cefazolin Against Vancomycin Intermediate-Resistant (VISA) and Daptomycin Non-Susceptible (DNS) Staphylococcus aureus

BackgroundGlycopeptides and lipopeptides, more specifically vancomycin (VAN) and daptomycin (DAP) have been principally utilized in treating MRSA infections. Due to continued use, MRSA strains have developed resistance to these antibiotics including vancomycin intermediate susceptible Staphylococcus aureus (VISA) and daptomycin non-susceptible strains (DNS). Lipoglycopeptides; notably dalbavancin (DAL), have been employed due to their ease of administration and enhanced activity against highly resistant S. aureus. As previously demonstrated, the use of β-lactams, specifically cefazolin (CFZ) in combination with anti-MRSA drug therapy has been effective in eradicating S. aureus complicated by increased resistance. The objective of this study was to evaluate the activity of DAL, VAN, and DAP, alone and in combination with CFZ in a pharmacokinetic/pharmacodynamic (PK/PD) model.MethodsThe well-characterized DNS-VISA strain, D712, was evaluated in eight different regimens in duplicate via a one-compartment 7-day PK/PD model. The experimental regimens were as follows: D712 growth control, DAL 1500 mg given on day 1, VAN 2 g given every 12 hours, DAP 10 mg/kg once-daily, CFZ 2 g given every 8 hours and DAL, DAP, and VAN in combination with CFZ.ResultsThe combinations of DAL+CFZ, VAN+CFZ, and DAP+CFZ demonstrated a significant log10 CFU/mL reduction (more than 5 log 10 CFU/mL and up to detection limit), compared with each drug used as monotherapy (P < 0.001). Neither DAP nor VAN demonstrated sustained bactericidal activity, (represented by a >3-log10 CFU/mL reduction from baseline) and resulted in significant regrowth, when administered alone. However, the DAP +CFZ, and VAN+CFZ combination models demonstrated bactericidal activity at 4 hours and 24 hours, respectively. While DAL alone did demonstrate bactericidal activity, the DAL+CFZ combination was more rapidly bactericidal, achieving a > 3-log reduction from baseline in 8 hours vs. 48 hours (P < 0.05).ConclusionThe combination of DAL, VAN, or DAP with CFZ demonstrated significantly improved activity against this multiple drug-resistant S. aureus strain. Further research is warranted, both in vivo and in vitro, to explore the synergistic capabilities of anti-MRSA drug therapy in combination with β-lactams.Disclosures All authors: No reported disclosures.

Azithromycin non-susceptible Shigella circulating in Israel, 2014-2016.

Shigella species remains a major diarrhoeagenic agent, affecting mostly children, with global high incidence and high mortality rate specially in developing areas. Although azithromycin is recommended for treatment of shigellosis, there are currently no CLSI susceptibility breakpoints, accordingly no routine antimicrobial susceptibility test is performed in the clinical laboratory. The purpose of this study was to estimate the prevalence, resistance profile and molecular epidemiology of azithromycin non-susceptible Shigella strains in Israel during a three year period. Shigella isolates (n = 1,170) referred to the National Reference Center during 2014–2016, were included in this study. Serotyping was performed by slide agglutination. Resistance genes, mph(A) and erm(B), were identified by PCR and the phenotype profile was determined by broth microdilution (BMD). Genetic relatedness was assessed by wgMLST. Decreased susceptibility to azithromycin (DSA) phenotype and genotype were detected in various Shigella species and serotypes related to diverse genetic backgrounds and antimicrobial profiles: 6% (26/423) of Shigella flexneri and 2% (16/747) of Shigella sonnei displayed DSA (MIC16 mg/L). Correlation of this phenotype with the presence of mph(A) and erm(B) genes was confirmed. All DSA-strains displayed resistance to ≥3 different antimicrobial classes. Among DSA-strains, 14% were resistant to quinolones and 5% displayed resistance to ceftriaxone. Most of these strains (32/42) were isolated from children in the southern and central regions of Israel. Clonality and significant relatedness was confirmed by PFGE and wgMLST. The presence of macrolide resistance genes among the different species and lineages reflects the transmissible nature of these genes. The emergence of DSA-Shigella reinforces the necessity to establish clinical breakpoints that would warrant routine testing, reporting and surveillance for this drug of choice.

Impact of Cefotaxime Non-susceptibility on the Clinical Outcomes of Bacteremic Pneumococcal Pneumonia.

Background: We aimed to analyze the impact of cefotaxime non-susceptibility on the 30-day mortality rate in patients receiving a third-generation cephalosporin for pneumococcal bacteremic pneumonia. Methods: We conducted a retrospective observational study of prospectively collected data from the Hospital Clinic of Barcelona. All adult patients with monomicrobial bacteremic pneumonia due to Streptococcus pneumoniae and treated with a third-generation cephalosporin from January 1991 to December 2016 were included. Risk factors associated with 30-day mortality were evaluated by univariate and multivariate analyses. Results: During the study period, 721 eligible episodes were identified, and data on the susceptibility to cefotaxime was obtainable for 690 episodes. Sixty six (10%) cases were due to a cefotaxime non-susceptible strain with a 30-day mortality rate of 8%. Variables associated with 30-day mortality were age, chronic liver disease, septic shock, and the McCabe score. Infection by a cefotaxime non-susceptible S. pneumoniae did not increase the mortality rate. Conclusion: Despite the prevalence of cefotaxime, non-susceptible S. pneumoniae has increased in recent years. We found no evidence to suggest that patients hospitalized with bacteremic pneumonia due to these strains had worse clinical outcomes than patients with susceptible strains.

In vitro activity of newer antimicrobials against penicillin non-susceptible strains of Streptococcus pneumoniae.

Background: Since the first isolation of Streptococcus pneumoniae with low penicillin susceptibility in the 1960s, resistant strains have spread over the globe, causing substantial problems in the treatment of pneumococcal infections. However, in Germany, rates of non-susceptibility are still below 5%.Methods: Since 2009 clinical pneumococcal strains have been collected at the Center for Infectious Diseases, Heidelberg University Hospital, Germany. In this study, 56 of these strains were chosen due to their decreased penicillin susceptibility (minimal inhibitory concentration (MIC)≥0.12 µg/mL). Sixteen of these strains even showed an MIC of ≥2 µg/mL. We examined the in vitro activity of newer antimicrobials known to be active against Gram-positive bacteria. For this purpose MICs of ceftaroline, ceftobiprole, dalbavancin, delafloxacin, eravacycline, tedizolid, and telavancin were determined and evaluated.Results: All of the 7 antimicrobial agents inhibited pneumococcal growth at concentrations of 0.5 µg/mL or lower. Currently, clinical breakpoints are only available for two substances, ceftaroline and ceftobiprole. According to these breakpoints, all MICs were below the susceptibility breakpoint; however, there was a correlation between high penicillin MICs (≥2 µg/mL) and MICs near the ceftaroline and ceftobiprole susceptibility breakpoint. The other agents showed very promising effects against all tested strains with the lowest MIC90 of 0.002 µg/mL for telavancin.Conclusion: Consequently, this study demonstrates the promising in vitro activity of newer antimicrobials against penicillin non-susceptible strains of S. pneumoniae.

A retrospective analysis of Pseudomonas aeruginosa bloodstream infections: prevalence, risk factors, and outcome in carbapenem-susceptible and -non-susceptible infections

BackgroundPseudomonas aeruginosa (PA) is a leading cause of nosocomial infections, and carbapenem non-susceptible strains are a major threat to patient safety.MethodsA single center, retrospective comparative analysis of carbapenem-non-susceptible PA (CnSPA) and carbapenem-susceptible PA (CSPA) bloodstream infections (BSIs) was conducted between January 1, 2007, and December 31, 2016. Prevalence and risk factors associated with CnSPA BSIs were examined.ResultsThe study enrolled 340 patients with PA BSIs; 30.0% (N = 101) of patients had CnSPA. High APACHE II scores (≥15), central venous catheterization, and delayed application of appropriate definitive therapy were independently associated with higher risk of mortality in PA BSIs. Multivariate analysis revealed that respiratory disease and exposure to carbapenems within the previous 90 days to onset of BSI were independent risk factors for acquisition of CnSPA BSIs. Overall all-cause 30-day mortality associated with PA BSIs was 26.8% (91/340). In addition, mortality was higher in patients with CnSPA than in those with CSPA (37.6% vs. 22.2%, respectively; P = 0.003). Corticosteroid therapy and delayed receipt of effective definitive therapy were independent risk factors for death from CnSPA BSIs.ConclusionIncreased incidence of CnSPA BSIs was observed during the study period, with higher mortality seen in patients with these infections. Respiratory disease and exposure to carbapenems were independent risk factors for development of CnSPA BSIs. Appropriate definitive therapy reduced mortality rates. BLBLIs were as effective as carbapenems as a treatment for PA BSIs.

Detection of vancomycin nonsusceptible strains in clinical isolates of Staphylococcus aureus in northern Iran.

Glycopeptides, particularly the cell wall-acting antibiotic vancomycin, are the safest cure for methicillin-resistant Staphylococcus aureus. The aim of this study was to evaluate nonsusceptibility of clinical isolates of S. aureus to vancomycin and investigate mutations in vraSR, a cell wall synthesis regulator gene, in vancomycin-resistant strains. Susceptibility of 110 clinical strains of S. aureus to methicillin and vancomycin were determined using disc diffusion method and determination of minimum inhibitory concentration, respectively. Presence of mecA and vanA genes was determined by PCR. Determination of spa types and mutations of the vraSR gene in vancomycin nonsusceptible isolates were assessed by PCR-sequencing analyses. In total, 47 isolates (42.73%) were recognized as MRSA, three (2.73%) strains were resistant to vancomycin, and eight (7.27%) strains were vancomycin intermediates. The MIC of vancomycin was 4-64μg/ml in these isolates. All vancomycin nonsusceptible S. aureus strains were mecA positive and one isolate was positive for the vanA gene. Spa type t030 was found as the most common type. In vraSR sequence analysis, all 11 vancomycin nonsusceptible isolates had the D59E mutation in the vraR and E45G in vraS genes. R117H, R121S, and R121I are the other identified missense mutations in the vraR gene. The identification of a high percentage of MRSA and presence of VRSA and VISA isolates is a serious warning about the treatment of future MRSA infections and reveals the need for new and effective therapeutic agents.

Impact on Antifungal Susceptibility Patterns of Previous vs. Revised Clinical and Laboratory Standards Institute Breakpoints for Candida Species Isolated from Candidemia: Experience of Two Tertiary Care Institutions in Japan

Candidemia has a high mortality rate. Identifying prognostic factors of candidemia, based on each regional data, is essential for better management. The Clinical and Laboratory Standards Institute (CLSI) recently revised Candida species-specific breakpoints (R-BP) for antifungal agents. Few studies have investigated the detection performance of resistance in Candida species by comparing the R-BP and previous species non-specific CLSI breakpoint (P-BP) among patients with candidemia. The primary objective was to investigate the impact of the R-BP on the antifungal susceptibility patterns of Candida species, while the secondary objective was to identify the prognostic factors of candidemia. A total of 193 Candida species isolated from 187 patients with candidemia between January 2007 and December 2016 were examined. Susceptibility based on CLSI M27-A3 was defined as the P-BP and based on species-specific CLSI M59 or M60 breakpoint was defined as the R-BP. Multivariate Cox's hazard analysis was performed to identify prognostic factors within 30 days of the diagnosis of candidemia. A significant difference was observed in the susceptibility rate to fluconazole (FLCZ) (P-BP; 93.0% vs. R-BP; 79.4%) and to voriconazole (VRCZ) (P-BP; 97.2% vs. R-BP; 91.0%). The susceptibilities of C. parapsilosis, C. glabrata, and C. tropicalis to azole antifungal agents were markedly lower with the R-BP. Based on the R-BP, anti-fungal therapy was regarded as inappropriate for approximately 10% of the patients. The 30-day mortality rate was 29.4%. In a multivariate Cox's hazard analysis, age, lung disease, C. albicans, and the absence of antifungal therapy were associated with a high mortality rate, whereas serum albumin, C. parapsilosis, surgical wards, the removal of central venous catheter (CVC), and follow-up blood culture tests to confirm the clearance of Candida species were associated with a lower mortality rate. Early initiation of antifungal therapy, removal of CVC, and follow-up blood culture tests are essential for improving the outcome. The R-BP efficiently detected non-susceptible strains to FLCZ and VRCZ, particularly in non-albicans Candida species. The present results support the importance of antifungal susceptibility tests and interpretations based on the R-BP among patients with candidemia.

Impact of rapid diagnostic tests on the management of patients presenting with Enterobacteriaceae bacteremia

ObjectivePathogens are usually identified from blood cultures using a two-step procedure: Gram staining on the day of bacterial growth (D0), followed by identification and susceptibility testing the following day (D1). We aimed to evaluate the use of rapid tests performed on D0 in patients presenting with Enterobacteriaceae bacteremia. Patients and methodsPatients with≥1 positive monomicrobial blood culture with Gram staining suggestive of an Enterobacteriaceae were prospectively included. Two successive strategies were evaluated: i) conventional strategy (CS), ii) combination of a rapid identification test and third-generation cephalosporin susceptibility testing (rapid strategy, e.g. RS). ResultsEighty-three patients were included (CS=42; RS=41). Compared with CS, the median delay of identification was significantly shorter with RS (22 hours [20–27] vs. 47 hours [42–53]; P<0.001). Patients in the RS group more frequently received an effective (82.9% vs. 73.8%, P=0.43) and appropriate (70.7% vs. 54.7%, P=0.17) antibiotic therapy on D1. Moreover, all five RS patients infected with a non-susceptible strain received an effective therapy on D1 versus only three of eight CS patients. ConclusionsUse of rapid testing was associated with a reduced time to result availability. This strategy should be useful to initiate an early effective and appropriate therapy and to improve the care of patients.

711. Molecular Epidemiology of Daptomycin Nonsusceptibility in Methicillin-Resistant Staphylococcus aureus (MRSA) Bacteremia

BackgroundWhile methicillin resistance in S. aureus strains is prevalent, non-susceptibility to vancomycin and daptomycin, first-line treatments for bacteremia, has emerged as well. Little is known about the molecular epidemiology of daptomycin resistance in S. aureus strains.MethodsA retrospective study was conducted at an 800-bed hospital in Detroit, Michigan. Blood isolates of S. aureus were obtained over time in patients with persistent bacteremia. Isolates were initially classified as MRSA/MSSA and MIC testing was done by the clinical microbiology laboratory; MICs were reconfirmed by a separate laboratory using Etest strips and microdilution broth testing. Non-susceptibility to daptomycin was defined as an MIC > 1 mg/mL. Isolates from each patient were also assessed for genomic similarity using pulse field gel electrophoresis (PFGE) and placed in the same PFGE group if they were 3 80% similar by Dice coefficient. Whole genome sequencing (WGS) on isolates and template strain ATCC29213 was done by the Applied Genomics Technology Center.ResultsThere were 27 isolates from seven patients in the following distribution: six isolates each from Patients 1 and 2; three isolates each from Patients 3, 4, and 5; five isolates from Patient 6; and one isolate from Patient 7. All isolates from Patients 1 and 3 (n = 9) were classified as MSSA strains and the remainder were MRSA strains. Daptomycin nonsusceptible strains were found in the initial isolate on therapy in two patients and the MIC increased from first to last isolates in the other five patients. A PFGE dendrogram comparing isolates within each patient and with established CDC lineages determined that (1) each patient’s first and last isolate remained within the same strain type and (2) the PFGE groups were USA100 (n = 8), USA300 (n = 7), USA900 (n = 6), and USA1000 (n = 3). WGS revealed the presence of vraSR, mprF, dltA, cls2, and gdpD, genes implicated in resistance to both vancomycin and daptomycin. However, gdpD was not detected in isolates classified as MSSA.ConclusionNo genetic modification of strains from each patient was seen between the first isolate obtained and the last. The presence of cell wall regulation genes in both daptomycin susceptible and nonsusceptible strains suggests gene upregulation.Disclosures M. J. Zervos, Merck: Consultant and Grant Investigator, Grant recipient.