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In 2022, an outbreak with severe bloodstream infections caused by Serratia marcescens occurred in an adult intensive care unit (ICU) in Hungary. Eight cases, five of whom died, were detected. Initial control measures could not stop the outbreak. We conducted a matched case-control study. In univariable analysis, the cases were more likely to be located around one sink in the ICU and had more medical procedures and medications than the controls, however, the multivariable analysis was not conclusive. Isolates from blood cultures of the cases and the ICU environment were closely related by whole genome sequencing and resistant or tolerant against the quaternary ammonium compound surface disinfectant used in the ICU. Thus, S. marcescens was able to survive in the environment despite regular cleaning and disinfection. The hospital replaced the disinfectant with another one, tightened the cleaning protocol and strengthened hand hygiene compliance among the healthcare workers. Together, these control measures have proved effective to prevent new cases. Our results highlight the importance of multidisciplinary outbreak investigations, including environmental sampling, molecular typing and testing for disinfectant resistance.

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In 2003-2023, amid 5,436 Acinetobacter baumannii isolates collected globally through the Multidrug-Resistant Organism Repository and Surveillance Network, 97 were ST19PAS, 34 of which carbapenem-resistant. Strains (n = 32) sampled after 2019 harboured either bla OXA-23, bla OXA-72, and/or bla NDM-5. Phylogenetic analysis of the 97 isolates and 11 publicly available ST19 genomes revealed three sub-lineages of carbapenemase-producing isolates from mainly Ukraine and Georgia, including an epidemic clone carrying all three carbapenemase genes. Infection control and global surveillance of carbapenem-resistant A. baumannii remain important.

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Methicillin-resistant Staphylococcus aureus (MRSA) is a common pathogen contributing to healthcare-associated infections, which can result in multiple sites infections. The epidemiological characteristics of MRSA exhibit variability among distinct regions and healthcare facilities. The aim of this study was to investigate the molecular epidemiology and nosocomial outbreak characteristics of MRSA in a county-level hospital in China. A total of 130 non-repetitive MRSA strains were collected from December 2020 to November 2021. Whole-genome sequencing (WGS) was performed to identify antimicrobial resistance and virulence factors. Phylogenetic analysis was conducted to ascertain genetic diversity and phylogenetic relationships. Independent transmission scenarios were determined by the phylogeny derived from single nucleotide polymorphisms (SNPs) within the core genome. All the MRSA isolates were collected from the intensive care unit (30.00%, 39/130), the department of otorhinolaryngology (10.00%, 13/130) and the department of burn unit (9.23%, 12/130). The clinical samples mainly included phlegm (53.85%, 70/130), purulent fluid (24.62%, 32/130), and secretions (8.46%, 11/130). The resistance rates to erythromycin, clindamycin and ciprofloxacin were 75.38, 40.00, and 39.23%, respectively. All the isolates belonged to 11 clonal complexes (CCs), with the major prevalent types were CC5, CC59, and CC398, accounting for 30.00% (39/130), 29.23% (38/130), and 16.92% (22/130), respectively. Twenty sequence types (STs) were identified, and ST59 (25.38%, 33/130) was the dominant lineage, followed by ST5 (23.84%, 31/130) and ST398 (16.92%, 22/130). Three different SCCmec types were investigated, most of isolates were type IV (33.85%, 44/130), followed by type II (27.69%, 36/130) and type III (0.77%, 1/130). The common clonal structures included CC5-ST5-t2460-SCCmec IIa, CC59-ST59-t437-SCCmec IV and CC398-ST398-t034-SCCmec (-), with rates of 16.92% (22/130), 14.62% (19/130), and 13.84% (18/130), respectively. Only 12 panton-valentine leucocidin (PVL) positive strains were identified. Two independent clonal outbreaks were detected, one consisting of 22 PVL-negative strains belongs to CC5-ST5-t2460-SCCmec IIa and the other consisting of 8 PVL-negative strains belongs to CC5-ST5-t311-SCCmec IIa. Overall, our study indicated that the CC5 lineage emerged as the predominant epidemic clone of MRSA, responsible for nosocomial outbreaks and transmission within a county-level hospital in China, highlighting the necessity to strengthen infection control measures for MRSA in such healthcare facilities.

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Healthcare-associated infections caused by vancomycin-resistant Enterococcus faecium (VREFM) pose a significant threat to healthcare. Confirming the relatedness of the bacterial isolates from different patients is challenging. We aimed to assess the efficacy of IR-Biotyper, multilocus sequencing typing (MLST), and core-genome MLST (cgMLST) in comparison with whole-genome sequencing (WGS) for outbreak confirmation in the neonatal intensive care unit (NICU). Twenty VREFM isolates from four neonates and ten control isolates from unrelated patients were analyzed. Genomic DNA extraction, MLST, cgMLST, and WGS were performed. An IR-Biotyper was used with colonies obtained after 24 h of incubation on tryptic soy agar supplemented with 5% sheep blood. The optimal clustering cutoff for the IR-Biotyper was determined by comparing the results with WGS. Clustering concordance was assessed using the adjusted Rand and Wallace indices. MLST and cgMLST identified sequence types (ST) and complex types (CT), revealing suspected outbreak isolates with a predominance of ST17 and CT6553, were confirmed by WGS. For the IR-Biotyper, the proposed optimal clustering cut-off range was 0.106-0.111. Despite lower within-run precision, of the IR-Biotyper, the clustering concordance with WGS was favorable, meeting the criteria for real-time screening. This study confirmed a nosocomial outbreak of VREFM in the NICU using an IR-Biotyper, showing promising results compared to MLST. Although within-run precision requires improvement, the IR-Biotyper demonstrated high discriminatory power and clustering concordance with WGS. These findings suggest its potential as a real-time screening tool for the detection of VREFM-related nosocomial outbreaks. IMPORTANCE: In this study, we evaluated the performance of the IR-Biotyper in detecting nosocomial outbreaks caused by vancomycin-resistant Enterococcus faecium, comparing it with MLST, cgMLST, and WGS. We proposed a cutoff that showed the highest concordance compared to WGS and assessed the within-run precision of the IR-Biotyper by evaluating the consistency in genetically identical strain when repeated in the same run.

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Fourier-transform infrared (FTIR) spectroscopy has the potential to be used for bacterial typing and outbreak characterization. We evaluated FTIR for the characterization of an outbreak caused by Elizabethkingia miricola. During the 2020-2021 period, 26 isolates (23 clinical and 3 environmental) were collected and analyzed by FTIR (IR Biotyper) and core-genome MLST (cgMLST), in addition to antimicrobial susceptibility testing. FTIR spectroscopy and cgMLST showed that 22 of the isolates were related to the outbreak, including the environmental samples, with only one discordance between both methods. Then, FTIR is useful for E. miricola typing and can be easily implemented in the laboratory.

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BACKGROUND: New York State (NYS) mandates reporting of all hospital-associated communicable disease outbreaks. We describe trends in NYS surveillance for neonatal unit methicillin-resistant Staphylococcus aureus (MRSA) outbreaks, the evolution of national MRSA infection prevention and control (IPC) recommendations, and IPC measures taken by NYS neonatal units. METHODS: We evaluated trends of reported neonatal unit MRSA outbreaks by etiology from 2001 to 2017. We reviewed all reports and the use of IPC recommendations over time. RESULTS: From 2001 to 2017, 124 MRSA outbreaks were reported in 47 hospital neonatal units, with a total of 1,055 laboratory-confirmed infant cases, 18 infant deaths, and 52 laboratory-confirmed staff cases. The number of outbreaks increased with the level of care. During the study period, a higher proportion of hospitals reported implementing IPC measures, including reinforcing hand hygiene compliance (increased from 79.2% to 95.1%) and enhancing environmental cleaning and disinfection (increased from 4.2% to 78.0%) as well as performing active surveillance testing (AST) on exposed neonates (increased from 4.2% to 51.2%) and molecular testing on MRSA-positive isolates (increased from 5.3% to 18.9%). CONCLUSIONS: From 2001 to 2017, IPC measures in neonatal units increased in parallel with expanded national IPC recommendations. However, MRSA outbreaks in neonatal units continued to be frequent occurrences in NYS.

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IMPORTANCE: Elizabethkingia meningoseptica is an emerging infectious agent associated with life-threatening infections in immunocompromised individuals. However, there are limited data available on the genomic features of E. meningoseptica. This study aims to characterize the geographical distribution, phylogenetic evolution, pathogenesis, and transmission of this bacterium. A systematic analysis of the E. meningoseptica genome revealed that a common ancestor of this bacterium existed 90 years ago. The evolutionary history showed no significant relationship with the sample source, origin, or region, despite the presence of genetic diversity. Whole genome sequencing data also demonstrated that E. meningoseptica bacteria possess inherent resistance and pathogenicity, enabling them to spread within the same hospital and even across borders. This study highlights the potential for E. meningoseptica to cause severe nosocomial outbreaks and horizontal transmission between countries worldwide. The available evidence is crucial for the development of evidence-based public health policies to prevent global outbreaks caused by emerging pathogens.

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Abstract Carbapenemase-producing-Serratia marcescens isolates, although infrequent, are considered important nosocomial pathogens due to their intrinsic resistance to polymyxins, which limits therapeutic options. We describe a nosocomial outbreak of SME-4-producing S. marcescens in Buenos Aires city which, in our knowledge, represents the first one in South America.

Resumen Los aislamientos de origen nosocomial de Serratia marcescens productores de car-bapenemasa, si bien son infrecuentes, son considerados importantes patógenos debido a su resistencia intrínseca a las polimixinas, lo cual limita aún más las opciones terapéuticas. En este trabajo se describe un brote nosocomial causado por S. marcescens portadora de car-bapenemasa de tipo SME-4 en la Ciudad de Buenos Aires, el cual representaría el primero en Sudamérica.

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Fusarium, a common fungus, emerges as a pathogen in severely immunocompromised patients. We present a series of patients who developed invasive fusariosis (IF) during admission to an acute leukaemia ward: an outbreak of 12 cases in June and July 2018, followed by four sporadic cases until 2021. No case was reported earlier. All patients were clustered in the same location with indoor air and water installations found to be contaminated with Fusarium spp. thus a nosocomial outbreak was assumed. Following the water installation replacement, the number of Fusarium cases dramatically dropped to one or two isolated instances per year in the same location. All 16 patients had acute leukaemia and developed IF during severe neutropenia following induction therapy. IF diagnosis was based on positive blood cultures (14 patients) and/or on tissue biopsies (3 patients). The median time from admission to the IF onset was 20 days, and from the first day of severe neutropenia (≤500/mm3) was 11.5 days. All patients were febrile, eight had moderate-to-severe myalgias, eight had respiratory involvements: lung lesions and/or sinusitis and seven had characteristic skin lesions. Follow-up: 12 out of 16 (75%) were alive on Day 90; nine out of 15 (60%) were alive on Month 6. All with intractable neutropenia died. In severely neutropenic febrile patients, the triad of respiratory involvement/skin lesions/severe myalgia may suggest Fusarium aetiology. The ability to recover from neutropenia is critical to surmount IF. The indoor environment in immunocompromised dedicated settings must be constantly controlled.

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Multidrug-resistant Pseudomonas aeruginosa is an increasing clinical problem worldwide. The aim of this study was to describe the first outbreak of a Verona integron-borne metallo-ß-lactamase (VIM)-2-producing P. aeruginosa strain in Sweden and its expansion in the region. A cluster of multidrug-resistant P. aeruginosa appeared at two neighbouring hospitals in 2006. The isolates were characterized by PCR, pulsed-field gel electrophoresis (PFGE), and whole-genome sequencing. Patient charts, laboratory records, and hygiene routines were reviewed, and patients, staff, and the environment were screened. The investigation revealed a clonal outbreak of a VIM-2-producing P. aeruginosa strain belonging to the high-risk clonal complex 111, susceptible only to gentamicin and colistin. No direct contact between patients could be established, but most of them had stayed in certain rooms/wards weeks to months apart. Cultures from two sinks yielded growth of the same strain. The outbreak ended when control measures against the sinks were taken, but new cases occurred in a tertiary care hospital in the region. In conclusion, when facing prolonged outbreaks with this bacterium, sinks and other water sources in the hospital environment should be considered. By implementing proactive control measures to limit the bacterial load in sinks, the waterborne transmission of P. aeruginosa may be reduced.

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Carbapenemase-producing-Serratia marcescens isolates, although infrequent, are considered important nosocomial pathogens due to their intrinsic resistance to polymyxins, which limits therapeutic options. We describe a nosocomial outbreak of SME-4-producing S. marcescens in Buenos Aires city which, in our knowledge, represents the first one in South America.

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Background: The Omicron variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is 2 to 3 times more contagious than the Delta variant and poses a new challenge in containing transmission in community and health care settings. Transmission in hospitals can cause nosocomial outbreak infections and affect patients and health care workers. This study describes a coronavirus disease 2019 (COVID-19) outbreak in a medical ward. The purpose of the investigation was to determine the transmission source of the outbreak, as well as the measures implemented to prevent and control it. Methods: A cluster of SARS-CoV-2 infections that affected health care workers, inpatients, and caregivers was thoroughly researched in a medical ward. There were several strict outbreak measures implemented in our hospital, and these measures controlled the nosocomial COVID-19 outbreak in this study. Results: Seven cases of SARS-CoV-2 infection were diagnosed within 2 days in the medical ward. The infection control team declared a nosocomial outbreak of the COVID-19 Omicron variant. Several strict outbreak measures were implemented as follows: 1. The medical ward was closed and cleaning and disinfection were performed. 2. All patients and caregivers with negative test results were transferred to a spare COVID-19 isolation ward. 3. Relatives' visits were not allowed, and no new patient was admitted during the outbreak period. 4. Health care workers were retrained on wearing personal protective equipment and enhanced techniques and practices of hand hygiene, social distancing, and self-monitoring of fever and respiratory symptoms. Conclusion: This outbreak occurred in a non-COVID-19 ward during the COVID-19 Omicron variant phase of the pandemic. Our strict outbreak measures halted and contained the nosocomial COVID-19 outbreak in 10 days. Future studies are needed to establish a standard policy of COVID-19 outbreak measure implementation.

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In 2019, an outbreak of pharyngoconjunctival fever (PCF) occurred at a swimming center in Zhejiang Province, China. A total of 97 (13.55%) of the 716 amateur swimmers had illnesses, with 24 patients (24.74%) hospitalized in the pediatric ward. Human adenovirus serotype 7 (HAdV-7) was isolated from one concentrated water from the swimming pool, and 20 of 97 positive cases without liver damage. This outbreak led to a nosocomial outbreak in the pediatric ward, in which 1 nurse had a fever and was confirmed to be adenovirus positive. The hexon, fiber, and penton genes from 20 outbreak cases, 1 water sample, and 1 nurse had 100% homology. Furthermore, 2 cases admitted to the pediatric ward, 2 parents, and 1 doctor were confirmed to be human coronaviruses (HCoV-229E) positive. Finally, all outbreak cases had fully recovered, regardless of a single infection (adenovirus or HCoV-229E) or coinfection of these two viruses simultaneously. Thus, PCF and acute respiratory disease outbreaks in Zhejiang were caused by the completely homologous type 7 adenovirus and HCoV-229E, respectively. The swimming pool water contaminated with HAdV-7 was most likely the source of the PCF outbreak, whereas nosocomial transmission might be the source of HCoV-229E outbreak.

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BACKGROUND: The microbial community composition of urban environments is primarily determined by human activity. The use of metagenomics to explore how microbial communities are shaped in a city provides a novel input that can improve decisions on public health measures, architectural design, and urban resilience. Of note, the sewage system in a city acts as a complex reservoir of bacteria, pharmaceuticals, and antimicrobial resistant (AMR) genes that can be an important source of epidemiological information. Hospital effluents are rich in patient-derived bacteria and can thus readily become a birthplace and hotspot reservoir for antibiotic resistant pathogens which are eventually incorporated into the environment. Yet, the scope to which nosocomial outbreaks impact the urban environment is still poorly understood. RESULTS: In this work, we extensively show that different urban waters from creeks, beaches, sewage spillways and collector pipes enclose discrete microbial communities that are characterized by a differential degree of contamination and admixture with human-derived bacteria. The abundance of human bacteria correlates with the abundance of AMR genes in the environment, with beta-lactamases being the top-contributing class to distinguish low vs. highly-impacted urban environments. Indeed, the abundance of beta-lactamase resistance and carbapenem resistance determinants in the urban environment significantly increased in a 1-year period. This was in line with a pronounced increase of nosocomial carbapenem-resistant infections reported during the same period that was mainly driven by an outbreak-causing, carbapenemase-producing Klebsiella pneumoniae (KPC) ST-11 strain. Genome-resolved metagenomics of urban waters before and after this outbreak, coupled with high-resolution whole-genome sequencing, confirmed the dissemination of the ST-11 strain and a novel KPC megaplasmid from the hospital to the urban environment. City-wide analysis showed that geospatial dissemination of the KPC megaplasmid in the urban environment inversely depended on the sewage system infrastructure. CONCLUSIONS: We show how urban metagenomics and outbreak genomic surveillance can be coupled to generate relevant information for infection control, antibiotic stewardship, and pathogen epidemiology. Our results highlight the need to better characterize and understand how human-derived bacteria and antimicrobial resistance disseminate in the urban environment to incorporate this information in the development of effluent treatment infrastructure and public health policies. Video Abstract.

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Background: We experienced a nosocomial outbreak of coronavirus disease 2019 (COVID-19) from November 2020 to February 2021, during the third wave of the pandemic in Japan. Methods: We retrospectively assessed the characteristics and data of 20 inpatients undergoing hemodialysis who were hospitalized for treatment of diseases other than COVID-19 during the COVID-19 nosocomial outbreak ("inpatient," IP), and of 10 outpatients undergoing hemodialysis who were hospitalized for the care of COVID-19 under outpatient visits ("outpatient," OP). Results: Eleven patients in the IP group (55%) and one in the OP group (10%) died. Kaplan-Meier analysis showed that the IP group died more rapidly than the OP group (p = 0.02). Multivariate analysis among all hemodialysis patients showed that the IP group was not at risk of mortality independently; however, the activity of daily life (ADL) dependency was found to be an independent factor in increasing the risk of mortality (hazard ratio: 7.618). Conclusion: Our findings show that the nosocomial infected group has a worse prognosis, although it is not an independent predictor for the risk of mortality. ADL dependency could predict the risk of mortality in all hemodialysis patients with COVID-19 during the third wave pandemic in Japan.

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BACKGROUND: The COVID-19 pandemic has resulted in the disruption of healthcare systems. Vienna General Hospital (VGH), a tertiary hospital located in Austria, ran at almost full capacity despite high levels of community SARS-CoV-2 transmission and limited isolation room capacity. To ensure safe patient care, a bundle of infection prevention and control (IPC) measures including universal pre-admission screening and serial SARS-CoV-2 testing during hospitalization was implemented. We evaluated whether testing as part of our IPC approach was effective in preventing hospital outbreaks during different stages of the pandemic. METHODS: In this retrospective single center study, we analyzed the SARS-CoV-2 PCR test results of cases admitted to VGH between a low (15/05/2020-01/08/2020) and a high incidence period (15/09/2020-18/05/2021). Outcomes were the diagnostic yield of (a) admission screening, (b) the yield of serial testing during hospitalization and (c) the occurrence of healthcare-associated COVID-19 (HA-COVID-19) and SARS-CoV-2 related hospital outbreaks. RESULTS: The admission test positivity rate was 0.2% during the low and 2.3% during the high incidence phase. Regarding test conversions, 0.04% (low incidence phase) and 0.5% (high incidence phase) of initially negative cases converted to a positive test result within 7 days after admission The HA-COVID-19 incidence rate per 100,000 patient days was 1.0 (low incidence phase) and 10.7 (high incidence phase). One COVID-19 outbreak affecting eight patients in total could be potentially ascribed to the non-compliance with our IPC protocol. CONCLUSION: Testing in conjunction with other IPC measures enabled the safe provision of patient care at a hospital with predominantly shared patient rooms despite high case numbers in the community.

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A large clonal outbreak caused by vancomycin-resistant Enterococcus faecium (VRE) affected the Bern University Hospital group from the end of December 2017 until July 2020. We describe the characteristics of the outbreak and the bundle of infection prevention and control (IPC) measures implemented. The outbreak was first recognised when two concomitant cases of VRE bloodstream infection were identified on the oncology ward. During 32 months, 518 patients in the 1,300-bed hospital group were identified as vanB VRE carriers. Eighteen (3.5%) patients developed an invasive infection, of whom seven had bacteraemia. In 2018, a subset of 328 isolates were analysed by whole genome sequencing, 312 of which were identified as sequence type (ST) 796. The initial IPC measures were implemented with a focus on the affected wards. However, in June 2018, ST796 caused another increase in cases, and the management strategy was intensified and escalated to a hospital-wide level. The clinical impact of this large nosocomial VRE outbreak with the emergent clone ST796 was modest. A hospital-wide approach with a multimodal IPC bundle was successful against this highly transmissible strain.

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BACKGROUND: Nosocomial outbreaks of COVID-19 have been reported sporadically since the beginning of the COVID-19 pandemic. We sought to study the transmission dynamics in a nosocomial COVID-19 outbreak in our centre. METHODS: This was a retrospective cohort study in a 500 bedded tertiary care hospital in South India. Inpatients who were suspected to have likely or definite hospital-acquired COVID-19 and hospital staff members who were found to be COVID-19 positive during the same time frame were studied and the likely transmission dynamics described. RESULTS: During the study period, 173 patients were diagnosed to have COVID-19, out of which, 15 (8.6%) patients who fulfilled the criteria for likely or definitely hospital-acquired COVID-19 infection were identified from six different wards. During the same period, 121 hospital staff members were diagnosed with COVID-19. Out of these, 18 (14.9%) hospital staff members were identified who could have been the potential source of infection for these 15 patients based on the overlap of location of the staff and the patients, and their infectivity windows. Direct contact and fomite transmission were likely the predominant driver of transmission in our study as there was use of universal face masks and face shields. CONCLUSION: Despite the admission of a large number of COVID-19 patients and a relatively large proportion of hospital staff members who tested positive for the disease, the proportion of nosocomial COVID-19 in our centre remained low. A policy of universal gloving, coupled with the already existing practice of universal N95 masking and face shield use, could potentially bring down the rate of nosocomial COVID-19 even further.

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A protracted outbreak of New Delhi metallo-ß-lactamase (NDM)-producing carbapenem-resistant Klebsiella pneumoniae started in Tuscany, Italy, in November 2018 and continued in 2020 and through 2021. To understand the regional emergence and transmission dynamics over time, we collected and sequenced the genomes of 117 extensively drug-resistant, NDM-producing K. pneumoniae isolates cultured over a 20-mo period from 76 patients at several healthcare facilities in southeast Tuscany. All isolates belonged to high-risk clone ST-147 and were typically nonsusceptible to all first-line antibiotics. Albeit sporadic, resistances to colistin, tigecycline, and fosfomycin were also observed as a result of repeated, independent mutations. Genomic analysis revealed that ST-147 isolates circulating in Tuscany were monophyletic and highly genetically related (including a network of 42 patients from the same hospital and sharing nearly identical isolates), and shared a recent ancestor with clinical isolates from the Middle East. While the blaNDM-1 gene was carried by an IncFIB-type plasmid, our investigations revealed that the ST-147 lineage from Italy also acquired a hybrid IncFIB/IncHIB-type plasmid carrying the 16S methyltransferase armA gene as well as key virulence biomarkers often found in hypervirulent isolates. This plasmid shared extensive homologies with mosaic plasmids circulating globally including from ST-11 and ST-307 convergent lineages. Phenotypically, the carriage of this hybrid plasmid resulted in increased siderophore production but did not confer virulence to the level of an archetypical, hypervirulent K. pneumoniae in a subcutaneous model of infection with immunocompetent CD1 mice. Our findings highlight the importance of performing genomic surveillance to identify emerging threats.

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BACKGROUND: Corynebacterium striatum was confirmed to be an important opportunistic pathogen, which could lead to multiple-site infections and presented high prevalence of multidrug resistance, particularly to quinolone antibiotics. This study aimed to investigate the mechanism underlying resistance to quinolones and the epidemiological features of 410 quinolone-resistant C. striatum clinical strains isolated from three tertiary hospitals in China. METHODS: A total of 410 C. striatum clinical strains were isolated from different clinical samples of patients admitted to three tertiary teaching hospitals in China. Antibiotic susceptibility testing was performed using the microdilution broth method and pulsed-field gel electrophoresis (PFGE) was used for genotyping. Gene sequencing was used to identify possible mutations in the quinolone resistance-determining regions (QRDRs) of gyrA. RESULTS: In total, 410 C. striatum isolates were sensitive to vancomycin, linezolid, and daptomycin but resistant to ciprofloxacin. Depending on the antibiotic susceptibility testing results of 12 antimicrobial agents, the 410 C. striatum strains were classified into 12 resistant biotypes; of these, the three biotypes R1, R2, and R3 were dominant and accounted for 47.3% (194/410), 21.0% (86/410), and 23.2% (95/410) of the resistant biotypes, respectively. Mutations in the QRDRs ofgyrA were detected in all quinolone-resistant C. striatum isolates, and 97.3% of the isolates (399/410) showed double mutations in codons 87 and 91 of the QRDRs of gyrA. Ser-87 to Phe-87 and Asp-91 to Ala-91 double mutation in C. striatum was the most prevalent and accounted for 72.2% (296/410) of all mutations. Four new mutations in gyrA were identified in this study; these included Ser-87 to Tyr-87 and Asp-91 to Ala-91 (double mutation, 101 isolates); Ser-87 to Val-87 and Asp-91 toGly-91 (double mutation, one isolate); Ser-87 to Val-87 and Asp-91 to Ala-91 (double mutation, one isolate); and Ser-87 to Ile-87 (single mutation, one isolate). The minimum inhibitory concentration of ciprofloxacin for isolates with double (96.5%; 385/399) and single (72.7%; 8/11) mutations was high (≥ 32 µg/mL). Based on the PFGE typing results, 101 randomly selected C. striatum strains were classified into 50 genotypes (T01-T50), including the three multidrug-resistant epidemic clones T02, T06, and T28; these accounted for 14.9% (15/101), 5.9% (6/101), and 11.9% (12/101) of all genotypes, respectively. The multidrug-resistant T02 clone was identified in hospitals A and C and persisted from 2016 to 2018. Three outbreaks resulting from the T02, T06, and T28 clones were observed among intensive care unit (ICU) patients in hospital C between April and May 2019. CONCLUSIONS: Quinolone-resistant C. striatum isolates showed a high prevalence of multidrug resistance. Point mutations in the QRDRs of gyrA conferred quinolone resistance to C. striatum, and several mutations in gyrA were newly found in this study. The great clonal diversity, high-level quinolone resistance and increased prevalence among patients susceptible to C. striatum isolates deserve more attention in the future. Moreover, more thorough investigation of the relationship between quinolone exposure and resistance evolution in C. striatum is necessary.

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