Susceptibility testing of the polymyxins (colistin and polymyxin B) is challenging for clinical laboratories. The Clinical and Laboratory Standards Institute (CLSI) Antimicrobial Susceptibility Testing Subcommittee evaluated two methods to enable accurate testing of these agents. These methods were a colistin broth disk elution (CBDE) and a colistin agar test (CAT), the latter of which was evaluated using two inoculum volumes, 1 μl (CAT-1) and 10 μl (CAT-10). The methods were evaluated using a collection of 270 isolates of Enterobacterales, 122 Pseudomonas aeruginosa isolates, and 106 Acinetobacter spp. isolates. Overall, 94.4% of CBDE results were in essential agreement and 97.9% in categorical agreement (CA) with reference broth microdilution MICs. Nine very major errors (VME; 3.2%) and 3 major errors (ME; 0.9%) were observed. With the CBDE, 98.6% CA was observed for Enterobacterales (2.5% VME, 0% ME), 99.3% CA was observed for P. aeruginosa (0% VME, 0.7% ME), and 93.1% CA was observed for Acinetobacter spp. (5.6% VME, 3.3% ME). Overall, CA was 94.9% with 6.8% VME using CAT-1 and improved to 98.3% with 3.9% VME using CAT-10. No ME were observed using either CAT-1 or CAT-10. Using the CAT-1/CAT-10, the CA observed was 99.4%/99.7% for Enterobacterales (1%/0.5% VME), 98.7%/100% for P. aeruginosa (8.3%/0% VME), and 88.5%/92.3% for Acinetobacter spp. (21.4%/14.3% VME). Based on these data, the CLSI antimicrobial susceptibility testing (AST) subcommittee endorsed the CBDE and CAT-10 methods for colistin testing of Enterobacterales and P. aeruginosa.
Background Rapid blood culture diagnostics are costly and of unclearbenefit for patients with Gram-negative bacilli (GNB) bloodstream infections (BSIs). We conducted a multicenter, prospective, randomized controlled trial comparing outcomes of patients with GNB BSI who had blood culture testing with standard of care (SOC) culture and antimicrobial susceptibility testing (AST) versus rapid organism identification (ID) and phenotypic AST using the Accelerate Pheno™ System (RAPID). Methods Patients with positive blood cultures with Gram stains showing GNB were randomized to SOC testing with antimicrobial stewardship review (AS) or RAPID with AS, at two medical centers between 10/2017-10/2018. The primary outcome was time to first antibiotic modification within 72 hours of randomization. Results Of 500 randomized subjects, 448 were included (226 SOC, 222 RAPID). Mean (S.D.) hours to results was faster for RAPID than SOC for organism ID [2.7 (1.2) vs 11.7 (10.5), p < 0.001] and AST [13.5 (56) vs. 44.9 (12.1), p<0.001]. Median (IQR) hours to first antibiotic modification was faster in the RAPID vs. SOC arm for overall antibiotics [8.6 (2.6, 27.6) vs. 14.9 (3.3, 41.1), difference 6.3, p=0.02] and Gram-negative antibiotics [17.3 (4.9, 72) vs. 42.1 (10.1, 72), difference 24.8, p<0.001]. Median (IQR) hours to antibiotic escalation was faster in the RAPID vs. SOC arm for antimicrobial-resistant BSIs [18.4 (5.8, 72) vs. 61.7 (30.4, 72), difference 43.3, p=0.01]. There were no statistically significant differences between the arms in patient outcomes including mortality and length of stay. Conclusion Rapid organism ID and phenotypic AST led to faster changes in antibiotic therapy for Gram-negative BSIs. (Funded by the U.S. NIH UM1AI104681; ClinicalTrials.gov number, NCT03218397.)
Among 177 carbapenemase-producing Gram-negative bacilli (108 KPC, 32 NDM, 11 IMP, 8 OXA-48, 4 OXA-181, 2 OXA-232, 5 IMI, 4 VIM, and 3 SME producers), aztreonam-avibactam was active against all isolates except two NDM producers with elevated MICs of 8/4 and 16/4 mg/liter; ceftazidime-avibactam was active against all KPC-, IMI-, SME-, and most OXA-48 group-producing isolates (93%) but not metallo--lactamase producers. Among older and contemporary antimicrobials, the most active were colistin, tigecycline, and fosfomycin, with overall susceptibilities of 88%, 79%, and 78%, respectively. The recent emergence and global dissemination of carbapenemase-producing Gram-negative bacilli (CP-GNB) pose a significant therapeutic challenge. Avibactam is a diazabicyclooctane non--lactam -lactamase inhibitor with broad activity against Ambler class A and C -lactamases and certain class D -lactamases by covalent acylation of the -lactamase active site serine residue. It restores susceptibility of Enterobacteriaceae harboring extended-spectrum -lactamases (ESBLs), AmpC cephalosporinases, and class A carbapenemases to ceftazidime or ceftaroline (1). In vitro studies of avibactam in combination with aztreonam have also demonstrated activity against Enterobacteriaceae harboring NDM (a class B metallo--lactamase); however, there are scant data for the other less commonly encountered carbapenemases (2-4).The aim of this study was to examine the activities of ceftazidime and aztreonam with and without avibactam against a large, contemporary, international collection of CP-GNB with diverse resistance mechanisms, with MICs determined using agar dilution as recommended by the Clinical and Laboratory Standards Institute (CLSI) (5, 6). A secondary aim was to evaluate the activity of antimicrobials commonly used to treat CP-GNB infections, including the "legacy antibiotics" colistin, amdinocillin (mecillinam), and fosfomycin. A total of 177 CP-GNB were studied (Table 1), comprising 122 and 53 clinical isolates from the United States and Singapore, respectively, and 2 NCTC (National Collection of Type Cultures, United Kingdom) reference isolates. These consisted of 172 Enterobacteriaceae isolates (107 KPC, 32 NDM, 8 OXA-48, 4 OXA-181, 2 OXA-232, 5 IMI, 3 SME, and 11 IMP producers) and 5 Pseudomonas aeruginosa isolates (4 VIM producers and 1 KPC producer). Genotypic characterization was performed using PCR/sequencing as previously described (7-15). All CP-GNB isolates tested positive by the CarbaNP test (16), except for one isolate each of OXA-181 and OXA-232, which were CarbaNP negative, and one OXA-48-producing isolate, which was CarbaNP indeterminate. In addition, as a control/comparator group, we studied 29 Enterobacteriaceae (11 Klebsiella pneumoniae and 18 Escherichia coli isolates), including 18 ESBL producers (10 with porin loss), 6 plasmid-mediated AmpC producers (1 with porin loss and another coproducing an ESBL), and 5 derepressed AmpC mutants (2 with porin loss).(This work was presented in part at the 54th Interscience Conf...
Failure to eradicate Helicobacter pylori infection is often a result of antimicrobial resistance, which for clarithromycin is typically mediated by specific point mutations in the 23S rRNA gene. The purpose of this study was to define current patterns of antimicrobial susceptibility in H. pylori isolates derived primarily from the United States and to survey them for the presence of point mutations in the 23S rRNA gene and assess the ability of these mutations to predict phenotypic clarithromycin susceptibility. Antimicrobial susceptibility testing was performed using agar dilution on 413 H. pylori isolates submitted to Mayo Medical Laboratories for susceptibility testing. For a subset of these isolates, a 150-bp segment of the 23S rRNA gene was sequenced. A total of 1,970 MICs were reported over the 4-year study period. The rate of clarithromycin resistance was high (70.4%), and elevated MICs were frequently observed for metronidazole (82.4% of isolates had an MIC of Ͼ8 g/ml) and ciprofloxacin (53.5% of isolates had an MIC of Ͼ1 g/ml). A total of 111 archived H. pylori isolates underwent 23S rRNA gene sequencing; we found 95% concordance between genotypes and phenotypes (P ϭ 0.9802). Resistance to clarithromycin was most commonly due to an A2143G mutation (82%), followed by A2142G (14%) and A2142C (4%) mutations. Clinical H. pylori isolates derived primarily from the United States demonstrated a high rate of clarithromycin resistance and elevated metronidazole and ciprofloxacin MICs. The relative distribution of point mutations at positions 2143 and 2142 in the 23S rRNA gene in clarithromycin-resistant H. pylori was similar to that reported from other parts of the world; these mutations predict phenotypic resistance to clarithromycin.
ObjectiveTo evaluate whole-genome sequencing (WGS) as a molecular typing tool for MRSA outbreak investigation.DesignInvestigation of MRSA colonization/infection in a neonatal intensive care unit (NICU) over 3 years (2014–2017).SettingSingle-center level IV NICU.PatientsNICU infants and healthcare workers (HCWs).MethodsInfants were screened for MRSA using a swab of the anterior nares, axilla, and groin, initially by targeted (ring) screening, and later by universal weekly screening. Clinical cultures were collected as indicated. HCWs were screened once using swabs of the anterior nares. MRSA isolates were typed using WGS with core-genome multilocus sequence typing (cgMLST) analysis and by pulsed-field gel electrophoresis (PFGE). Colonized and infected infants and HCWs were decolonized. Control strategies included reinforcement of hand hygiene, use of contact precautions, cohorting, enhanced environmental cleaning, and remodeling of the NICU.ResultsWe identified 64 MRSA-positive infants: 53 (83%) by screening and 11 (17%) by clinical cultures. Of 85 screened HCWs, 5 (6%) were MRSA positive. WGS of MRSA isolates identified 2 large clusters (WGS groups 1 and 2), 1 small cluster (WGS group 3), and 8 unrelated isolates. PFGE failed to distinguish WGS group 2 and 3 isolates. WGS groups 1 and 2 were codistributed over time. HCW MRSA isolates were primarily in WGS group 1. New infant MRSA cases declined after implementation of the control interventions.ConclusionWe identified 2 contemporaneous MRSA outbreaks alongside sporadic cases in a NICU. WGS was used to determine strain relatedness at a higher resolution than PFGE and was useful in guiding efforts to control MRSA transmission.
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