The Path of More Resistance: A Comparison of NHSN and CLSI Criteria in Developing Cumulative Antimicrobial Susceptibility Test Reports and Institutional Antibiograms

Background In the absence of antimicrobial susceptibility data, the institutional antibiogram is a valuable tool to guide clinicians in the empiric treatment of infections. However, there is a misunderstanding on how best to prepare cumulative antimicrobial susceptibility testing reports (CASTRs) to guide empiric therapy (e.g., routine antibiogram) versus monitoring antimicrobial resistance, with the former following guidance from the Clinical Laboratory Standards Institute (CLSI), and the latter from Center for Disease Control and Preventions National Healthcare Safety Network (NHSN). These criteria vary markedly in their exclusion or inclusion of isolates cultured repeatedly from the same patient. Methods We compared rates of non-susceptibility (NS)using annual data from a large teaching healthcare system subset to isolates eligible by either NHSN criteria or CLSI criteria. Results For a panel of the three most prevalent gram-negative pathogens in combination with clinically relevant antimicrobial agents (or priority pathogen-agent combinations, PPACs), we found that the inclusion of duplicate isolates by NHSN criteria yielded higher NS rates than when CLSI criteria (for which duplicate isolates are not included) were applied. Conclusions Patients with duplicate isolates may not be representative of antimicrobial resistance within a population. For this reason, users of CASTR data should carefully consider that the criteria used to generate these reports can impact resulting NS rates, and therefore maintain the distinction between CASTRs created for different purposes.

Detection of OqxAB Efflux Pumps, a Multidrug-Resistant Agent in Bacterial Infection in Patients Referring to Teaching Hospitals in Ahvaz, Southwest of Iran

Antibiotic resistance mechanisms in Enterobacteriaceae are causative agents of global health problems. Bacterial infections due to multidrug resistance (MDR) may be mediated by the overexpression of efflux pumps. In this study, we investigated the prevalence of oqxA and oqxB genes as two encoding agents of efflux pumps and the determination of antibiotic resistance rate in clinical isolates of Enterobacteriaceae. In this study, 100 Enterobacteriaceae isolates collected from different clinical specimens of infectious patients, such as wounds, urine, blood, discharge, and abscesses except stool, were examined. Identification of the isolates was performed using standard biochemical tests such as TSI, citrate, urea, lysine, SIM, MR-VP, and gas production. The antimicrobial susceptibility test was carried out by the Kirby–Bauer disk diffusion method according to CLSI guidelines, and finally, the oqxA and oqxB genes were detected by the PCR method. Among 100 Enterobacteriaceae isolates, Escherichia coli and Enterobacter gergoviae were the most common isolates with 71% and 20%, respectively. Also, the lowest isolates belonged to Enterobacter cloacae (3%) and Klebsiella pneumoniae (1%). Out of 100 Enterobacteriaceae isolates, 37 isolates (37%) were positive for at least one of oqxA or oqxB genes, while both of these genes were detected among 12% of them. oqxAB genes were detected in 8 cases of 20 (40%) Enterobacter gergoviae and 4 cases of 71 (5.7%) E. coli isolates. The antimicrobial susceptibility test showed that all isolates (100%) were susceptible to imipenem, while the maximum resistance to piperacillin, ceftriaxone, and cefotaxime were 69%, 55%, and 55%, respectively. Also, the results of this study showed that antibiotic resistance in Enterobacteriaceae isolates caused by oqxAB genes is increasing among patients in Iran. Therefore, identification of resistant isolates and antibiotic monitoring programs are essential to prevent the spread of MDR isolates.

Antimicrobial resistance, virulence genes and biofilm formation in Enterococcus species isolated from milk of sheep and goat with subclinical mastitis

This study is designed to discuss the antimicrobial resistance, virulence determinants and biofilm formation capacity of Enterococcus spp. isolated from milk of sheep and goat with subclinical mastitis in Qena, Egypt. The obtained isolates were identified by the VITEK2 system and 16S rDNA sequencing as E. faecalis, E. faecium, E. casseliflavus and E. hirae. Overall, E. faecalis and E. faecium were the dominant species recovered from mastitic milk samples. The antimicrobial susceptibility test evidenced multidrug resistance of the isolates against the following antimicrobials: oxacillin (89.2.%), followed by vancomycin (75.7%) and linezolid (70.3%). Also, most of these isolates (73%) could form biofilms. For example, 18.9% of Enterococcus strains formed strong biofilm, whereas 32.4% of isolates formed moderate biofilm and 21.6% of isolates formed weak biofilm. The most prevalent resistance genes found in our isolates were blaZ (54%), vanA (40%), ermB (51.4%), tetM (13.5%) and optrA (10.8%). Moreover, asa1 (37.8%), cylA (42.3%), gelE (78.4%), esp (32.4%), EF3314(48.6%) and ace (75.5%) were the most common virulence genes. A significant correlation was found between biofilm formation, multidrug resistance and virulence genes of the isolates. This study highlights several aspects of virulence and harmfulness of Enterococcus strains isolated from subclinical mastitic milk, which necessitates continuous inspection and monitoring of dairy animals.

1079. Development of Tebipenem MIC Antimicrobial Susceptibility Test for Gram-negative Bacteria on MicroScan Dried Gram-negative MIC Panels

Background Development of a tebipenem antimicrobial susceptibility test was completed for the MicroScan Dried Gram-negative MIC (MSDGN) Panel when compared to CLSI broth microdilution reference panels. Methods Development was conducted by comparing MICs obtained using the MSDGN panel to MICs using a CLSI broth microdilution reference panel. A total of 669 Enterobacterales isolates were tested at 16, 18, and 20 hour incubation times using the turbidity and Prompt®* methods of inoculation. MSDGN panels were incubated at 35 ± 2ºC and read on the WalkAway System, the autoSCAN-4 instrument, and read visually. Frozen reference panels, prepared according to ISO/CLSI methodology, were inoculated using the turbidity inoculation method. All frozen reference panels were incubated at 35 ± 2ºC and read visually. Dilution sequence evaluated is 0.03-32 µg/mL. Results When compared to frozen reference panel results, essential agreement for all isolates tested during development are as follows: Conclusion The development data showed that tebipenem MIC results for Enterobacterales obtained with the MSDGN panel correlate well with MICs obtained using frozen reference panels. Essential agreement is > 90% for all inoculation and read methods. For Investigational Use Only. The performance characteristics of this product have not been established. * Prompt® is a registered trademark of 3M Company, St. Paul, MN USA. © 2021 Beckman Coulter. All rights reserved. Beckman Coulter, the stylized logo, and the Beckman Coulter product and service marks mentioned herein are trademarks or registered trademarks of Beckman Coulter, Inc. in the United States and other countries. Disclosures Jose Enrique Fernandez, n/a, Beckman Coulter (Employee) Vasna Carr, n/a, Beckman Coulter (Employee) Renae Miller, n/a, Beckman Coulter (Employee)

Phenotypic and Genotypic Determination of Resistance to Common Disinfectants Among Strains of Pseudomonas Aeruginosa Producing and Non-Producing Biofilm Isolated From Iran

Background: One of the most important reasons for human mortality worldwide is Hospital-acquired infections, which can be controlled by efficient use of proper disinfectants for the Hospital settings. The main aim of the present survey was to assess the susceptibility of Pseudomonas aeruginosa producing and non-producing biofilm isolated to the five commonly used Hospital disinfectants, and evaluation of the synergistic effect of selective disinfectants and Ethylene-diamine-tetra acetic acid (EDTA), and the effect of exposure to sub-inhibitory concentrations of Sodium hypochlorite on antimicrobial susceptibility test.Results: The results showed that Sodium hypochlorite 5%, and Ethanol 70% is the most and less potent disinfectants against Pseudomonas aeruginosa, respectively. Clearly, the addition of EDTA increased the efficacy of selected disinfectants significantly. The changes in the antibiotic-resistance profiles after exposure to sub-inhibitory concentrations of disinfectants were observed for different classes of antibiotics. As well as near the all isolates harbored efflux pump genes and produced biofilm. Conclusion: For disinfection of Hospital surfaces and instruments, the mixture of disinfectant and EDTA were the most suitable selection in this study. In our study, it was clear that exposure to sub-inhibitory concentrations of disinfectants results in resistance to antibiotics. Also, strong and intermediate biofilm formers belonged to MDR/XDR strains.

Isolation, Identification, and Antimicrobial Susceptibility Profiles of Staphylococcus aureus from Clinical Mastitis in Sebeta Town Dairy Farms

A cross-sectional study was carried out in and around Sebeta town dairy farms, Finfinne special zone, Ethiopia, from December 2019 to May 2020 to isolate, identify, and test antimicrobial susceptibility profile of Staphylococcus aureus from clinical mastitis. A total of 116 milk samples were purposively collected from 57 lactating cows with clinical mastitis. Isolation and identification of Staphylococcus aureus were carried out by using primary and secondary biochemical tests. Besides, Biolog was used for microbial identification systems. To know if the isolates develop resistance to antibiotics, the antimicrobial susceptibility test (ATS) was performed on Mueller-Hinton agar by the disk diffusion method. From a total of 57 lactating cows and 116 teat quarters examined, 21.05% (12/57) and 15.52% (18/116) were positive for S. aureus from clinical mastitis, respectively. From a total of 116 milk samples collected, 15.52% (18/116) Staphylococcus aureus were isolated, and from 11 farms surveyed, about 72.72% (8/11) overall farm prevalence of clinical mastitis due to S. aureus was recorded. All the 18 Staphylococcus aureus isolates were found susceptible to sulphamethoxazole/trimethoprim, erythromycin, gentamicin, ciprofloxacin, and chloramphenicol. However, high level of resistance was observed to common drugs such as penicillin (88.89%, 16/18) and tetracycline (61.11%, 11/18). The observed high level of resistance to penicillin and tetracycline also indicates the need to visit our treatment guidelines for mastitis caused by Staphylococcus aureus. Therefore, improved management and early treatment of the cases with drug of choice after the antimicrobial susceptibility test for each specific case can reduce chance of further development of resistance and are imperative to tackle clinical mastitis occurring at Sebeta and other similar farms in Ethiopia.

Salmonella enterica subsp. diarizonae Harboring ST233, ST1263, and ST1845 in Children

ObjectiveThis study aims to analyze the molecular epidemiology, resistance, and pathogenicity of Salmonella enterica subsp. diarizonae isolated from children.MethodsWhole genome sequencing was carried out, and molecular serotypes, sequence types, resistance genes, and virulence genes of S. enterica subsp. diarizonae isolates were analyzed. Antimicrobial susceptibility test was determined by commercialized microdilution method.ResultsA total of three isolates of S. enterica subsp. diarizonae were isolated during 2015 to 2020. The molecular serotypes of the three strains were 61:c:z35, 61:l,v:1,5,7:[z57], and 65:k:z, respectively, and the sequence types were ST1845, ST233, and ST1263. All the three isolates were susceptible to ceftriaxone, ceftazidime, cefepime, amoxycillin/clavulanic acid, piperacillin/tazobactam, ertapenem, imipenem, levofloxacin, and trimethoprim/sulfamethoxazole. No other resistant gene was detected except aac(6’)-Iaa. There were no resistant plasmids detected in all the three isolates. A total of 76 genes were present in all isolates, containing 49 genes of Type III Secretion System (T3SS) mediated by SPI-1and SPI-2, 13 genes of adherence (type 1 fimbriae, Agf, and MisL-related genes), 11 genes of iron uptake (Yersiniabactin), two genes of magnesium uptake, and one gene of typhoid toxin(cdtB).ConclusionThe serotypes and sequence types of S. enterica subsp. diarizonae isolates were rarely reported in children; all the S. enterica subsp. diarizonae isolates were susceptible to detected antibiotics; T3SS, adherence, iron uptake, magnesium uptake, and typhoid toxin were responsible for pathogenicity of the S. enterica subsp. diarizonae isolates in children.