Oxacillin Resistance Research Articles

Antimicrobial activity of dalbavancin and comparators against Staphylococcus aureus causing pneumonia in patients with and without cystic fibrosis

The activities of dalbavancin and comparator agents were evaluated against Staphylococcus aureus isolated from the lower respiratory tract of cystic fibrosis (CF) and non-CF patients with pneumonia. Bacterial isolates (n = 357) were collected from CF patients in 36 medical centers worldwide (2018–2019) and susceptibility tested using reference broth microdilution. Susceptibility results from these isolates were compared with those for 725 S. aureus isolates consecutively collected from non-CF patients with pneumonia from the same medical centers over the same period. Only isolates determined to be the probable cause of pneumonia were included in the study. Susceptibility profiles were very similar among isolates from CF and non-CF patients. Dalbavancin exhibited potent activity (MIC50/90, 0.03/0.03 mg/L) and complete coverage (100.0% susceptibility) against isolates from CF and non-CF patients. Ceftaroline (MIC50/90, 0.25/1 mg/L) was active against 97.8% and 98.1% of isolates from CF and non-CF patients, respectively. Oxacillin resistance (MRSA) rates were 27.7% among CF and 28.7% among non-CF patients. Among MRSA isolates from CF/non-CF patients (n = 99/208), susceptibility to ceftaroline, clindamycin, levofloxacin, and tetracycline were 91.9%/93.3%, 58.6%/64.4%, 40.4%/29.3%, and 83.8%/89.4%, respectively. Dalbavancin demonstrated high potency against S. aureus from CF and non-CF patients and may represent a valuable treatment option for CF patients with MRSA pulmonary infection.

Improved diagnostic prediction of the pathogenicity of bloodstream isolates of Staphylococcus epidermidis.

With an estimated 440,000 active cases occurring each year, medical device associated infections pose a significant burden on the US healthcare system, costing about $9.8 billion in 2013. Staphylococcus epidermidis is the most common cause of these device-associated infections, which typically involve isolates that are multi-drug resistant and possess multiple virulence factors. S. epidermidis is also frequently a benign contaminant of otherwise sterile blood cultures. Therefore, tests that distinguish pathogenic from non-pathogenic isolates would improve the accuracy of diagnosis and prevent overuse/misuse of antibiotics. Attempts to use multi-locus sequence typing (MLST) with machine learning for this purpose had poor accuracy (~73%). In this study we sought to improve the diagnostic accuracy of predicting pathogenicity by focusing on phenotypic markers (i.e., antibiotic resistance, growth fitness in human plasma, and biofilm forming capacity) and the presence of specific virulence genes (i.e., mecA, ses1, and sdrF). Commensal isolates from healthy individuals (n = 23), blood culture contaminants (n = 21), and pathogenic isolates considered true bacteremia (n = 54) were used. Multiple machine learning approaches were applied to characterize strains as pathogenic vs non-pathogenic. The combination of phenotypic markers and virulence genes improved the diagnostic accuracy to 82.4% (sensitivity: 84.9% and specificity: 80.9%). Oxacillin resistance was the most important variable followed by growth rate in plasma. This work shows promise for the addition of phenotypic testing in clinical diagnostic applications.

Genomics accurately predicts antimicrobial resistance in Staphylococcus pseudintermedius collected as part of Vet-LIRN resistance monitoring

Whole-genome sequencing (WGS) has changed our understanding of bacterial pathogens, aiding outbreak investigations and advancing our knowledge of their genetic features. However, there has been limited use of genomics to understand antimicrobial resistance of veterinary pathogens, which would help identify emerging resistance mechanisms and track their spread. The objectives of this study were to evaluate the correlation between resistance genotypes and phenotypes for Staphylococcus pseudintermedius, a major pathogen of companion animals, by comparing broth microdilution antimicrobial susceptibility testing and WGS. From 2017–2019, we conducted antimicrobial susceptibility testing and WGS on S. pseudintermedius isolates collected from dogs in the United States as a part of the Veterinary Laboratory Investigation and Response Network (Vet-LIRN) antimicrobial resistance monitoring program. Across thirteen antimicrobials in nine classes, resistance genotypes correlated with clinical resistance phenotypes 98.4 % of the time among a collection of 592 isolates. Our findings represent isolates from diverse lineages based on phylogenetic analyses, and these strong correlations are comparable to those from studies of several human pathogens such as Staphylococcus aureus and Salmonella enterica. We uncovered some important findings, including that 32.3 % of isolates had the mecA gene, which correlated with oxacillin resistance 97.0 % of the time. We also identified a novel rpoB mutation likely encoding rifampin resistance. These results show the value in using WGS to assess antimicrobial resistance in veterinary pathogens and to reveal putative new mechanisms of resistance.

Clonal Diversity, Low-Level and Heterogeneous Oxacillin Resistance of Oxacillin Sensitive MRSA.

PurposeThis study investigates the phenotypic and genotypic resistance features of OS-MRSA clinical isolates and their distinctive sensitivities to oxacillin.Methods1200 clinical isolates of Staphylococcus aureus were enrolled in this study. Automated antibiotics susceptibility tests on VITEK-2 and BD Phoenix-100TM, cefoxitin disc diffusion method, oxacillin broth microdilution method, mecA, and mecC gene detection were performed to identify OS-MRSA. MLST, PFGE, SCCmec, and spa typing methods were employed to determine genotypes of OS-MRSA isolates. Heterogeneous resistance of OS-MRSA isolates was detected using the population analysis profiling method, and PBP2a latex agglutination assay was used to detect the expression of PBP2a protein for 14 OS-MRSA isolates and their highly resistant subpopulations.ResultsA total of 14 OS-MRSA isolates (1.17%, 14/1200) were identified, and all of the isolates were confirmed to be positive with the mecA gene and negative with the mecC gene. All of the 14 OS-MRSA isolates were identified as MSSA by VITEK-2, BD Phonenix-100, and oxacillin broth microdilution methods, while 21.43% (3/14) isolates were determined to be MRSA by the cefoxitin disk diffusion method. Genotypes of the 14 OS-MRSA isolates were diverse, and no dominant clones were identified. The prevalence of pvl gene among 14 OS-MRSA isolates was high up to 64.29% (9/14). All of the isolates showed heterogeneous resistance to oxacillin, while frequencies of the oxacillin-resistant subpopulations ranged from 10−9 to 10−5 and differed significantly among different isolates.ConclusionThe overall prevalence of OS-MRSA was relatively lower, but lower oxacillin MICs, low testing sensitivity of routine antibiotics susceptibility testing methods and weak PBP2a protein expression were observed in this study. 14 OS-MRSA showed diverse genotypes and universal heterogeneous resistance, and inaccurate laboratory identification and improper antimicrobial usage may promote the induction of highly resistant subpopulations and lead to treatment failure.

Staphylococcal bacterial contamination of portable electronic devices in a large veterinary hospital

Portable electronic devices are used regularly within the veterinary and medical environments. Use of these in clinical areas may predispose them to bacterial contamination and they could act as fomites, transmitting infection between clinicians and patients. To determine the prevalence, origin and nature of Staphylococcal bacterial contamination on the surface of portable electronic devices used in a large small animal hospital. Staff were surveyed on the frequency of portable electronic device use and device-cleaning routines. Portable electronic devices were swabbed for staphylococcus species. Cultured cocci were tested for antimicrobial resistance and identified at the species level to help determine the likely source (human or animal). Forty one of 48 (85%) of staff used a portable electronic device every day within the hospital. Useable swabs were obtained from 47 portable electronic devices. Staphylococci were found on 68% of portable electronic devices. Vancomycin and Oxacillin resistance were seen in 17 of 46 (37%) and 1 of 46 (2%) isolated colonies respectively, including four vancomycin resistant, coagulase-positive staphylococci. 44% of staff never cleaned their device. Portable electronic devices are commonly used in veterinary hospitals, but few staff routinely disinfect them. The use of disinfectant to reduce colony counts should be implemented when forming protocols for these devices in the hospital. The majority of staphylococci found were of likely human origin. It is suggested that contamination is therefore more likely to be originating from staff rather than patients.

Comprehensive Genomic Investigation of Adaptive Mutations Driving the Low-Level Oxacillin Resistance Phenotype in Staphylococcus aureus.

Antistaphylococcal penicillins such as oxacillin are the key antibiotics in the treatment of invasive methicillin-susceptible Staphylococcus aureus (MSSA) infections; however, mec gene-independent resistance adaptation can cause treatment failure. Despite its clinical relevance, the basis of this phenomenon remains poorly understood. Here, we investigated the genomic adaptation to oxacillin at an unprecedented scale using a large collection of 503 clinical mec-negative isolates and 30 in vitro-adapted isolates from independent oxacillin exposures. By combining comparative genomics, evolutionary convergence, and genome-wide association analysis, we found 21 genetic loci associated with low-level oxacillin resistance, underscoring the polygenic nature of this phenotype. Evidence of adaptation was particularly strong for the c-di-AMP signal transduction pathways (gdpP and dacA) and in the clpXP chaperone-protease complex. The role of mutations in gdpP in conferring low-level oxacillin resistance was confirmed by allele-swapping experiments. We found that resistance to oxacillin emerges at high frequency in vitro (median, 2.9 × 10-6; interquartile range [IQR], 1.9 × 10-6 to 3.9 × 10-6), which is consistent with a recurrent minimum inhibitory concentration (MIC) increase across the global phylogeny of clinical isolates. Nevertheless, adaptation in clinical isolates appears sporadically, with no stably adapted lineages, suggesting a high fitness cost of resistance, confirmed by growth assessment of mutants in rich media. Our data provide a broader understanding of the emergence and dynamics of oxacillin resistance adaptation in S. aureus and a framework for future surveillance of this clinically important phenomenon.IMPORTANCE The majority of Staphylococcus aureus strains causing human disease are methicillin-susceptible (MSSA) and can be treated with antistaphylococcal penicillins (such as oxacillin). While acquisition of the mec gene represents the main resistance mechanism to oxacillin, S. aureus can acquire low-level resistance through adaptive mutations in other genes. In this study, we used genomic approaches to understand the basis of S. aureus adaption to oxacillin and its dynamic at the population level. By combining a genome analysis of clinical isolates from persistent MSSA infections, in vitro selection of oxacillin resistance, and genome-wide association analysis on a large collection of isolates, we identified 21 genes linked to secondary oxacillin resistance. Adaptive mutations in these genes were easy to select when S. aureus was exposed to oxacillin, but they also came at a substantial cost in terms of bacterial fitness, suggesting that this phenotype emerges preferentially in the setting of sustained antibiotic exposure.

Detection of the agr System and Resistance to Antimicrobials in Biofilm-Producing S. epidermidis.

The ability of Staphylococcus epidermidis to produce virulence factors, such as biofilm, added to its increased resistance to antimicrobials can cause infections that are difficult to treat. Many staphylococcal virulence factors are under the control of the accessory gene regulator (agr). The objective of this study was to establish the agr locus and susceptibility of biofilm-producing S. epidermidis specimens to antimicrobial agents, through PCR reactions, reverse transcription polymerase chain reaction (RT-PCR), and the determination of minimum inhibitory concentration (MIC), and to analyze the clonal profile of 300 strains isolated from blood culture specimens from inpatients at a University Hospital in Brazil, over a 20-year period by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) techniques. The ica operon expression was shown in 83.6% strains, bhp gene in 11.5%, and aap gene in 32.8%. Oxacillin resistance was detected in 90.1%, while 4.9% showed tigecycline resistance, and intermediate resistance to quinupristin/dalfopristin was identified in 0.4%. Clonal profile determination showed 11 clusters, with the ST2 type determined as the major cluster. The S. epidermidis biofilm producer demonstrated a predominance of agr I locus, oxacillin resistance, and SCCmec III as well as the potential dissemination of pathogenic clones in hospital settings over long periods.

Code-Sharing in Cost-of-Illness Calculations: An Application to Antibiotic-Resistant Bloodstream Infections.

Background: More data-driven evidence is needed on the cost of antibiotic resistance. Both Japan and England have large surveillance and administrative datasets. Code sharing of costing models enables reduced duplication of effort in research.Objective: To estimate the burden of antibiotic-resistant Staphylococcus aureus bloodstream infections (BSIs) in Japan, utilizing code that was written to estimate the hospital burden of antibiotic-resistant Escherichia coli BSIs in England. Additionally, the process in which the code-sharing and application was performed is detailed, to aid future such use of code-sharing in health economics.Methods: National administrative data sources were linked with voluntary surveillance data within the Japan case study. R software code, which created multistate models to estimate the excess length of stay associated with different exposures of interest, was adapted from previous use and run on this dataset. Unit costs were applied to estimate healthcare system burden in 2017 international dollars (I$).Results: Clear supporting documentation alongside open-access code, licensing, and formal communication channels, helped the re-application of costing code from the English setting within the Japanese setting. From the Japanese healthcare system perspective, it was estimated that there was an excess cost of I$6,392 per S. aureus BSI, whilst oxacillin resistance was associated with an additional I$8,155.Conclusions: S. aureus resistance profiles other than methicillin may substantially impact hospital costs. The sharing of costing models within the field of antibiotic resistance is a feasible way to increase burden evidence efficiently, allowing for decision makers (with appropriate data available) to gain rapid cost-of-illness estimates.

Ceftaroline activity against Staphylococcus aureus isolated from patients with infective endocarditis, worldwide (2010–2019)

ObjectiveTo evaluate the antimicrobial activity of ceftaroline against Staphylococcus aureus isolated from patients with infective endocarditis (IE). Methods23,833 S. aureus isolates were collected consecutively from patients with bloodstream infections (BSI) from 2010 to 2019, via the SENTRY Antimicrobial Surveillance Program, including 396 isolates from patients with a diagnosis of IE. Isolates were collected from 340 medical centers worldwide and susceptibility tested by reference broth microdilution in a monitoring laboratory. ResultsThe oxacillin resistance (MRSA) rate was 29.0% among IE isolates, and was higher in North America (40.3%) than in Europe (25.4%) or the Latin America/Asia-Pacific region (LATAM-APAC; 18.6%). Ceftaroline was active against 95.2% of IE isolates (MIC50/90, 0.25/1 mg/L), with ceftaroline susceptibility higher in North America (99.2%) and LATAM-APAC (98.3%) than in Europe (92.0%). Among MRSA isolates from IE (n = 115; MIC50/90, 1/2 mg/L), ceftaroline susceptibility was 98.0% in North America, 90.9% in LATAM-APAC, and 68.5% in Europe. Among BSI isolates, MRSA rates were 43.6% in North America and 25.6% in Europe, while ceftaroline susceptibility rates were 98.1% in North America and 95.4% in Europe. ConclusionsCeftaroline demonstrated potent in vitro activity against a large collection of S. aureus isolates recovered from patients with BSI, including IE.

Frequency and Antimicrobial Susceptibility of Bacterial Agents Causing Peritoneal Dialysis-Related Peritonitis: A Two-Center Experience

Background: Peritonitis remains a significant complication of peritoneal dialysis (PD) in children. Objectives: The current study aimed to evaluate the causative agents of PD-related peritonitis in pediatric patients treated by continuous ambulatory peritoneal dialysis (CAPD) in order to provide evidence for improving the empirical treatment of PD-related peritonitis and avoid antimicrobial resistance. Methods: The medical records of children diagnosed with PD-related peritonitis hospitalized at Mofid and Ali-Asghar Children’s Hospitals from January 2018 to December 2019 were retrospectively reviewed. Cases of relapsing peritonitis and fungal peritonitis were excluded. Data on demographics, clinical manifestations, para-clinical evaluations, peritoneal fluid culture and antibiogram, and antibiotic regimen were analyzed. Results: A total of 23 CAPD children aged 1 - 17 years were hospitalized with a confirmed diagnosis of PD-related peritonitis, accounting for a total of 27 peritonitis cases. The most frequent manifestation of peritonitis was cloudy dialysate (85.2%), followed by abdominal pain (59.3%). Gram-negative organisms were isolated in 48.1% of cases, and 4 cases had negative cultures. The frequency of antibiotic prescription within 14 days of admission was significantly higher in culture-negative cases (P = 0.002), and abdominal pain was more prevalent in Gram-negative peritonitis (P = 0.004). All Gram-negative organisms were sensitive to ceftazidime and imipenem; while 61.6% of them were sensitive to gentamycin. All Gram-positive organisms were sensitive to cefazolin, and vancomycin was effective against all Staphylococcus strains. Oxacillin resistance was reported in 50% of Staphylococcus strains. Conclusions: PD-related peritonitis should be suspected even in cases with clear dialysis effluent who present with other manifestations of peritonitis such as fever or abdominal pain. Moreover, intraperitoneal administration of a first-generation cephalosporin (cefazolin) combined with ceftazidime was an appropriate therapeutic option for empiric therapy.

In vitro antibiotic resistance of Staphylococci isolated from different animal species

The purpose of this study is to investigate resistance to antibiotics of Staphylococcus species isolated from various samples belonging to different animal species. Among 48 Staphylococcus spp. strains, Staphylococcus intermedius was the most common species, followed by S. aureus, S. epidermidis, S. hyicus, S. saprophyticus. In a total of 48 Staphylococcus strains, the highest antibiotic resistance was observed to oxacillin (79.17%), tetracycline (39.58%), and ampicillin and cefoxitin (31.25%). Of 48 Staphylococcus strains, 42 showed resistance to at least one antimicrobial agent, while 23 of the strains had multidrug resistance. Antimicrobial resistance to tetracycline and ampicillin, erythromycin, streptomycin was detected frequently in S. aureus,S. intermedius, and S. epidermidis, respectively. Resistance rates for ampicillin, cefoxitin, and enrofloxacin were determined as 66.67% in S. hyicus strains. S. saprophyticus was determined to show resistance to 13 antibiotics other than meropenem. The highest antibiotic resistance was determined in S. aureus, S. intermedius, S. epidermidis, and in 48 Staphylococcus strains to oxacillin. Consequently, this study revealed resistance to various antibiotics in Staphylococcus species. Additionally, the presence of high oxacillin resistance and multidrug resistance in the Staphylococcus strains revealed the importance of determination of antimicrobial susceptibility before treatment and for rational use of antibiotics.

Major discrepancy between factual antibiotic resistance and consumption in South of France: analysis of 539,037 bacterial strains

The burden of antibiotic resistance is currently estimated by mathematical modeling, without real count of resistance to key antibiotics. Here we report the real rate of resistance to key antibiotics in bacteria isolated from humans during a 5 years period in a large area in southeast in France. We conducted a retrospective study on antibiotic susceptibility of 539,107 clinical strains isolated from hospital and private laboratories in south of France area from January 2014 to January 2019. The resistance rate to key antibiotics as well as the proportion of bacteria classified as Difficult-to-Treat (DTR) were determined and compared with the Mann–Whitney U test, the χ2 test or the Fisher’s exact test. Among 539,037 isolates, we did not observe any significant increase or decrease in resistance to key antibiotics for 5 years, (oxacillin resistance in Staphylococcus aureus, carbapenem resistance in enterobacteria and Pseudomonas aeruginosa and 3rd generation cephalosporin resistance in Escherichia coli and Klebsiella pneumoniae). However, we observed a significant decrease in imipenem resistance for Acinetobacter baumannii from 2014 to 2018 (24.19–12.27%; p = 0.005) and a significant increase of ceftriaxone resistance in Klebsiella pneumoniae (9.9–24.03%; p = 0.001) and Enterobacter cloacae (24.05–42.05%; p = 0.004). Of these 539,037 isolates, 1604 (0.3%) had a DTR phenotype. Over a 5-year period, we did not observe a burden of AR in our region despite a high rate of antibiotic consumption in our country. These results highlight the need for implementation of real-time AR surveillance systems which use factual data.

Implications of Oxacillin-Resistant, mecA-Negative Staphylococcus aureus Detected in NICU MRSA Surveillance Cultures

Background: Weekly surveillance to identify neonatal intensive care unit (NICU) infants with methicillin-resistant S. aureus (MRSA) nasal colonization was performed using Remel Spectra MRSA chromogenic media. An increased MRSA colonization rate from baseline was detected in 2019, prompting additional review of all positive MRSA NICU screening cultures from 2019. Methods: A subset of 23 positive cultures were interrogated in detail. Species-level identification was confirmed using matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) with a Bruker Biotyper. Penicillin-binding protein 2a (PBP2a) testing was performed using the Alere culture colony test, and cefoxitin and oxacillin susceptibility were assessed via Kirby-Bauer disk-diffusion methods (for the purpose of this analysis, oxacillin zone sizes 18 mm were considered susceptible). Molecular detection of mecA and mecC genes using PCR was performed. Results: All 23 isolates in the subset group were confirmed as S. aureus based on MALDI-TOF testing. Moreover, 8 isolates (35%) were confirmed as MRSA based on cefoxitin susceptibility, positive rapid PBP2a testing, and mecA PCR results. Overall, 15 isolates (65%) tested cefoxitin-susceptible and PBP2a negative with negative mecA and mecC gene testing. Of these, 1 (7%) tested oxacillin-susceptible based on disk-diffusion testing, consistent with methicillin-susceptible S. aureus (MSSA). The remaining 14 isolates (93%) tested oxacillin resistant based on oxacillin zone size. Conclusions: Our findings indicate the detection of mecA/mecC negative S. aureus isolates demonstrating oxacillin resistance and growth on Remel Spectra MRSA chromogenic media. These results have important implications for infection prevention surveillance efforts to detect MRSA and raise questions regarding optimal antibiotic therapy in patients with isolates displaying this phenotype.Funding: NoneDisclosures: None

Phenotypic and Genotypic Characterization of Methicillin-Resistant Coagulase-Negative Staphylococci as an Etiological Agent of Bovine Mastitis in Egypt

To study molecular genetic characteristics and antibiotic resistance patterns of methicillin-resistance coagulase-negative staphylococci (CoNS) from mastitic cows in Egypt. Methods: The study material consisted of 205 milk samples. Milk was bacteriologically tested. Hemolytic activity and adhesive properties of CoNS isolates were also evaluated. Fifty CoNS isolates were submitted to in vitro susceptibility testing by the disk diffusion method. From the pool of 50 CoNS isolates, 15 Methicillin resistance isolates. were screened for genes encoding staphylococcal enterotoxin B (seb), toxic shock syndrome toxin1 (tss), intracellular adhesin D (icaD), and Methicillin resistance (mecA) by PCR. Results: CoNS were serotyped into three species S. haemolyticus, S. saprophyticus, and S. epidermidis. S. saprophyticus was the predominant CoNS species isolated from cows with clinical mastitis whereas S. epidermidis was the most prevalent one in subclinical mastitis cases. Susceptibility screening against 10 antibiotics determined 68% CoNS isolates as multidrug-resistant. High resistance was observed against penicillin (84%) and oxacillin (50%). The methicillin resistance gene, mecA was found in 73.33% isolates and interestingly, 26.67% of mecA negative isolates were oxacillin resistance. Of all the genes examined, 33.3% of examined isolates were positive for the staphylococcal enterotoxin B (seb) gene. Biofilm production was confirmed in 12% of CoNS. Conclusions: CoNS as an emerging cause for 60% of clinical mastitis and 67.27% of subclinical mastitis in cows in Egypt, and harboring the virulence genes rendering them as a potential threat for veterinary and public health and are also harboring resistance against penicillin and oxacillin the core for numerous novel intramammary combinations.

ANTIMICROBIAL ACTIVITY OF CEFTAROLINE AGAINST STAPHYLOCOCCUS AUREUS ISOLATED FROM PATIENTS WITH INFECTIVE ENDOCARDITIS WORLDWIDE (2010-2019)

SESSION TITLE: Chest Infections Posters SESSION TYPE: Original Investigation Posters PRESENTED ON: October 18-21, 2020 PURPOSE: Ceftaroline is approved by the United States (US) Food and Drug Administration for community-acquired bacterial pneumonia and skin and skin-structure infections, including cases with concurrent bacteremia, and has demonstrated efficacy in cases of infective endocarditis (IE). We evaluated the antimicrobial activity of ceftaroline against S. aureus isolated from patients with IE. METHODS: 23,834 S. aureus isolates were collected consecutively from patients with bloodstream infections (BSI) from 2010 to 2019 via the SENTRY Antimicrobial Surveillance Program, including 396 isolates patients with a diagnosis of IE. IE isolates were collected from 19 medical centers in the US (n=124), 34 in Europe (EUR; n=213), and 22 in other geographic regions (n=59) and were tested for susceptibility against ceftaroline and comparators by reference broth microdilution method in a monitoring laboratory (JMI Laboratories). RESULTS: Among IE isolates, the overall oxacillin resistance (MRSA) rate was 29.0%, but this rate was higher in the US (40.3%) than EUR (25.4%) and other regions (18.6%). Ceftaroline was active against 95.2% of IE isolates (MIC50/90, 0.25/1 mg/L) and ceftaroline susceptibility was higher in the US (99.2%) and other regions (98.3%) than EUR (92.0%). Among oxacillin-susceptible (MSSA) isolates, the highest ceftaroline MIC value was 0.5 mg/L (94.7% inhibited at ≤0.25 mg/L). Among MRSA isolates from IE (n=115; MIC50/90, 1/2 mg/L), ceftaroline susceptibility was 98.0% in the US and 68.5% in EUR (90.9% in other regions; n=11). The highest ceftaroline MIC was only 2 mg/L and all ceftaroline-nonsusceptible isolates were categorized as susceptible dose dependent or intermediate (0.0% resistant). Dalbavancin (MIC50/90, ≤0.03/0.06 mg/L), daptomycin (MIC50/90, 0.25/0.5 mg/L), linezolid (MIC50/90, 1/2 mg/L), teicoplanin (MIC50/90, ≤2/≤2 mg/L), tigecycline (MIC50/90, 0.06/0.12 mg/L), and vancomycin (MIC50/90, 1/1 mg/L) exhibited complete activity (100.0% susceptible) against S. aureus from IE. Among all BSI S. aureus isolates (n=23,834), MRSA rates were 43.6% in the US and 25.6% in EUR, and ceftaroline susceptibility rates were 98.1% in the US and 95.4% in EUR. CONCLUSIONS: Ceftaroline exhibited potent in vitro activity against a large collection of S. aureus isolates recovered from patients with IE. Ceftaroline was particularly active against MRSA-causing BSI and IE in US medical centers. These results support further investigations to determine the role of ceftaroline in the treatment of IE. CLINICAL IMPLICATIONS: These results support further investigations to determine the role of ceftaroline in the treatment of IE. DISCLOSURES: No relevant relationships by Cecilia Carvalhaes, source=Web Response no disclosure on file for Rodrigo Mendes; Research Contractor relationship with Allergan Please note: $1001 - $5000 Added 03/11/2020 by Helio Sader, source=Web Response, value=Grant/Research Support no disclosure on file for Streit Streit

Genetic Profiling of Methicillin-resistant Staphylococcus aureus in An African Hospital by Multiplex-PCR

Objectives: Methicillin resistant Staphylococcus aureus (MRSA) nasal carriage often precedes infection. This work aims to genetically profile the MRSA carriage of resistant genes (mecA, blaZ and tetM) and certain virulence genes (nuc, pvl, spa and scn) obtained from human nasal cavity. Methods: Phenotypically confirmed Staphylococcus aureus were Screened for oxacillin resistance and assessed for β-lactamase production. Further confirmation of identity obtained by multiplex PCR of the 16SrRNA, mecA, tetM, pvl, nuc, spa and scn genes. DNA gel fingerprint analysis was carried out and the bands were clustered in a dendrogram. Results: The study analysed 81 Staphylococcus aureus isolates for Methicillin resistance out of which 38 (46.9%) were MRSA. The DNA extraction method was effective for all MRSA isolates evaluated. All phenotypic MRSA isolates (100%) were positive for the S. aureus specific 16SrRNA gene confirming that these isolates were S. aureus strains. The nuc gene was detected in 19/38 (50%) of the MRSA isolates, blaZ gene in 14/38 (36.8%) and tetM in 18/38 (47.4%). Conclusions: The need for improved vigilance to recognize MRSA strains cannot be overemphasized. If MRSA control is not tracked, these strains will increase exponentially. J Microbiol Infect Dis 2020; 10(3):144-153.

Microbiological Profile and Drug Sensitivity Pattern in Persistently Discharging Ears: A Tertiary Level Hospital Based Retrospective Study

Introduction Antimicrobial resistance is an emerging issue resulting from the misuse of antibiotics in today’s world. As an effect of it, cases with persistent ear discharge not responding to the conventional oral antibiotics prescribed in ear pathologies are seen increasing in our day to-day practice. This study aims to review the microbiological growth and the pattern of their antibiotic sensitivity in this group of population.
 MethodsThis was a retrospective study which was conducted at the Department of ENT-HNS of Tribhuvan University Teaching Hospital. Record files of all cases who presented with persistently discharging ear for more than 2 weeks and not responding to oral antibiotics, between January 2017 to March 2020 were assessed. Cases of chronic otitis media (COM) squamous with persistent discharge were excluded as most of the times it is the disease process rather than type of organism which causes the persistence of ear discharge despite the use of antibiotics.
 ResultsCOM mucosal and cavity infection following modified radical mastoidectomy (MRM) were the commonest pathologies. Pseudomonas aeruginosa (PA) and Coagulase negative Staphylococcus (CoNS) were the commonest bacterial isolates. Pseudomonas aeruginosa showed a good sensitivity to antibiotics like Tazobactam and Piperacillin and resistance to conventionally used antibiotics like Ciprofloxacin and Levofloxacin. Similarly, CoNS had good sensitivity to antibiotics like Oxacillin and Levofloxacin and resistance to conventionally used antibiotics like Amoxicillin.
 ConclusionCOM mucosal and post MRM cavity infection are the commonest pathologies presenting with persistent ear discharge with PA and CoNS as the predominant isolates. Pseudomonas aeruginosa holds a good sensitivity to drugs like Tazobactam and Piperacillin; and CoNS to drugs like Oxacillin and Levofloxacin.

Microbiological Profile and Drug Sensitivity Pattern in Persistently Discharging Ears: A Tertiary Level Hospital Based Retrospective Study

Introduction: Antimicrobial resistance is an emerging issue resulting from the misuse of antibiotics in today’s world. As an effect of it, cases with persistent ear discharge not responding to the conventional oral antibiotics prescribed in ear pathologies are seen increasing in our day to-day practice. This study aims to review the microbiological growth and the pattern of their antibiotic sensitivity in this group of population. Methods: This was a retrospective study which was conducted at the Department of ENT-HNS of Tribhuvan University Teaching Hospital. Record files of all cases who presented with persistently discharging ear for more than 2 weeks and not responding to oral antibiotics, between January 2017 to March 2020 were assessed. Cases of chronic otitis media (COM) squamous with persistent discharge were excluded as most of the times it is the disease process rather than type of organism which causes the persistence of ear discharge despite the use of antibiotics. Results: COM mucosal and cavity infection following modified radical mastoidectomy (MRM) were the commonest pathologies. Pseudomonas aeruginosa (PA) and Coagulase negative Staphylococcus (CoNS) were the commonest bacterial isolates. Pseudomonas aeruginosa showed a good sensitivity to antibiotics like Tazobactam and Piperacillin and resistance to conventionally used antibiotics like Ciprofloxacin and Levofloxacin. Similarly, CoNS had good sensitivity to antibiotics like Oxacillin and Levofloxacin and resistance to conventionally used antibiotics like Amoxicillin. Conclusion: COM mucosal and post MRM cavity infection are the commonest pathologies presenting with persistent ear discharge with PA and CoNS as the predominant isolates. Pseudomonas aeruginosa holds a good sensitivity to drugs like Tazobactam and Piperacillin; and CoNS to drugs like Oxacillin and Levofloxacin.

Prenylated phenolics as promising candidates for combination antibacterial therapy: Morusin and kuwanon G

Combination of antibiotics with natural products is a promising strategy for potentiating antibiotic activity and overcoming antibiotic resistance. The purpose of the present study was to investigate whether morusin and kuwanon G, prenylated phenolics in Morus species, have the ability to enhance antibiotic activity and reverse antibiotic resistance in Staphylococcus aureus and Staphylococcus epidermidis. Commonly used antibiotics (oxacillin, erythromycin, gentamicin, ciprofloxacin, tetracycline, clindamycin) were selected for the combination studies. Checkerboard and time-kill assays were used to investigate potential bacteriostatic and bactericidal synergistic interactions, respectively between morusin or kuwanon G and antibiotics. According to both fractional inhibitory concentration index and response surface models, twenty combinations (14 morusin-antibiotic combinations, six kuwanon G-antibiotic combinations) displaying bacteriostatic synergy were identified, with 4–512-fold reduction in the minimum inhibitory concentration values of antibiotics in combination. Both morusin and kuwanon G reversed oxacillin resistance of methicillin-resistant Staphylococcus aureus. In addition, morusin reversed tetracycline resistance of Staphylococcus epidermidis. At half of the minimum inhibitory concentrations, combinations of morusin with oxacillin or gentamicin showed bactericidal synergy against methicillin-resistant Staphylococcus aureus. Fluorescence and differential interference contrast microscopy and scanning electron microscopy showed an increase in the membrane permeability and massive leakage of cellular content in methicillin-resistant Staphylococcus aureus exposed to morusin or kuwanon G. Overall, our findings strongly indicate that both prenylated compounds are good candidates for the development of novel antibacterial combination therapies.

Current status of oxacillin-susceptible mecA-positive Staphylococcus aureus infection in Shanghai, China: A multicenter study

Oxacillin-susceptible mecA-positive Staphylococcus aureus (OS-MRSA) represents an important issue, as its oxacillin susceptibility has contributed to misidentification by conventional susceptibility tests and consequently potential therapeutic failure, but limited data on the current status of OS-MRSA infection in Chinese hospitals are available. This multicenter study performed a battery of susceptibility tests and diagnostic tests for 956 S. aureus isolates from 10 hospitals, including automated susceptibility testing on VITEK 2, broth microdilution, disk diffusion, and detection of PBB2a, mecA gene and mecC gene. For all identified OS-MRSA, multi-locus sequence typing (MLST), together with spa typing, SCCmec typing and PVL detecting, was carried out. OS-MRSA, most of which were from pediatric inpatients, represented 1.8% (17/956) of total isolates. Of these 17 OS-MRSA, 10 were ST59, followed by ST965 (3/17), and 11 carried SCCmec type IV, while 5 carried SCCmec type V, but only one was Panton-Valentine leucocidin (PVL)-positive, also, 16 had one or two point mutations within mecA promoter. OS-MRSA had inducible oxacillin resistance and significantly lower MDR (Multi-Drug Resistant) rate. We observed that the VITEK 2 system exhibited some deficiency in OS-MRSA detection, whereas cefoxitin disk diffusion was shown to be a reliable and cost-saving alternative and should be supplemented in detecting S. aureus with borderline oxacillin susceptible MICs. This study has characterized phenotypically and molecularly OS-MRSA in China, and provided insights into more effective management of OS-MRSA.