Characterization of the lytic phage MSP1 for the inhibition of multidrug-resistant Salmonella enterica serovars Thompson and its biofilm.

The increasing prevalence of multidrug-resistant (MDR) Salmonella is a serious public health threat. Intervention strategies available to control Salmonella mostly target Salmonella enterica serovars Typhimurium and Enteritidis, and little has been investigated to control serovars in serogroup C, such as S. enterica serovar Thompson, despite their increasing prevalence. Here, we isolated phages targeting MDR S. Thompson and characterized the antimicrobial activities of MSP1 phage, a virulent phage with a broad host range. MSP1 phage strongly infected S. Thompson and S. Mbandaka isolates from retail chicken and also other serovars, including Dublin, Enteritidis, Heidelberg, Paratyphi, and Typhimurium. MSP1 phage was able to inhibit the biofilm formation on stainless steel and glass formation by around 42.7-47.9 %. MSP1 phage was robust to withstand wide ranges of pH (4-12) and temperature (30-60 °C), and no genes associated with antibiotic resistance and virulence were found in the phage genome, suggesting that this phage is suitable for food application. When MSP1 phage was tested on foods (chicken meat and milk), MSP1 phage significantly reduced the level of MDR S. Thompson below the detection limit. Our findings suggest that MSP1 phage is a promising antimicrobial agent for the control of food contamination by MDR S. Thompson.

The rate of frequent co-existence of plasmid-mediated quinolone resistance (PMQR) and extended-spectrum ß-lactamase (ESBL) genes in Escherichia coli isolates from retail raw chicken in South Korea.

Since plasmid-encoded antibiotic resistance facilitates the emergence of antibiotic-resistant bacteria, the increasing prevalence of Escherichia coli harboring plasmid-mediated quinolone resistance (PMQR) and extended-spectrum ß-lactamase (ESBL) genes is a public health concern. The objective of this study is to investigate the co-existence of PMQR and ESBL genes in E. coli isolates from retail raw chicken in South Korea. Among 67 ESBL-producing E. coli isolates from 40 retail raw chicken, more than half of them carried PMQR genes, including qnrS, aac(6')-Ib-cr, and oqxAB. The qnrS was predominantly (91.4%) detected in E. coli isolates carrying both PMQR and ESBL. The aac(6')-Ib-cr was detected in seven ESBL-producing E. coli strains, and 85.7% of the aac(6')-Ib-cr-positive strains also carried qnrS. Moreover, the strains co-harboring qnrS and aac(6')-Ib-cr exhibited increased resistance to ciprofloxacin and kanamycin. These results demonstrate that PMQR genes are frequently detected in ESBL-producing E. coli isolates from retail raw chicken in South Korea.

Comparative Analysis of Aerotolerance, Antibiotic Resistance, and Virulence Gene Prevalence in Campylobacter jejuni Isolates from Retail Raw Chicken and Duck Meat in South Korea.

Human infections with Campylobacter are primarily associated with the consumption of contaminated poultry meat. In this study, we isolated Campylobacter jejuni from retail raw chicken and duck meat in Korea and compared their aerotolerance, antibiotic resistance, and virulence gene prevalence. Whereas C. jejuni isolates from chicken dominantly belonged to multilocus sequence typing (MLST) clonal complex (CC)-21, CC-45 is the common MLST sequence type in duck meat isolates. C. jejuni strains from both chicken and duck meat were highly tolerant to aerobic stress. The prevalence of virulence genes was higher in C. jejuni strains from chicken than those from duck meat. However, antibiotic resistance was higher in duck meat isolates than chicken isolates. Based on the prevalence of virulence genes and antibiotic resistance, fluoroquinolone-resistant C. jejuni strains harboring all tested virulence genes except virB11 were predominant on retail poultry. Fluoroquinolone-resistant C. jejuni strains carrying most virulence genes were more frequently isolated in summer than in winter. The comparative profiling analysis in this study successfully demonstrated that antibiotic-resistant and pathogenic strains of C. jejuni are highly prevalent on retail poultry and that retail duck meat is an important vehicle potentially transmitting C. jejuni to humans in Korea.

Microbiota Analysis for the Optimization of Campylobacter Isolation From Chicken Carcasses Using Selective Media.

Since contaminated poultry meat is the major source of transmitting Campylobacter jejuni to humans, the isolation of Campylobacter from poultry carcasses is frequently performed in many countries as a baseline survey to ensure food safety. However, existing isolation methods have technical limitations in isolating this fastidious bacterium, such as a growth competition with indigenous bacteria in food samples. In this study, we compared the differences in microbiota compositions between Bolton and Preston selective media, two most common selective media to isolate Campylobacter, and investigated how different microbiota compositions resulting from different enrichment methods may affect isolation frequencies. A next-generation sequencing (NGS) analysis of 16S rRNA demonstrated that Bolton and Preston-selective enrichments generated different microbiota structures that shared only 31.57% of Operating Taxonomic Unit (OTU) types. Particularly, Escherichia was highly prevalent in Bolton selective media, and the enrichment cultures that increase Escherichia negatively affected the efficacy of Campylobacter isolation. Furthermore, the combination of the selective media made a significant difference in the isolation frequency. The Bolton broth and Preston agar combination exhibited the highest (60.0%) frequencies of Campylobacter isolation, whereas the Bolton broth and Bolton agar combination showed the lowest (2.5%). These results show that each selective medium generates a unique microbiota structure and that the sequence of combining the selective media also critically affects the isolation frequency by altering microbiota compositions. In this study, we demonstrated how a microbiota analysis using NGS can be utilized to optimize a protocol for bacterial isolation from food samples.

Predominance of blaCTX-M-65 and blaCTX-M-55 in extended-spectrum ß-lactamase-producing Escherichia coli from raw retail chicken in South Korea.

OBJECTIVES: Extended-spectrum ß-lactamase-producing Escherichia coli (ESBL-EC) are a serious public health concern worldwide. The aim of this study was to characterise ESBL-EC isolated from raw retail chicken in South Korea. METHODS: The antimicrobial resistance, phylogenetic group and virulence gene prevalence of 67 ESBL-EC isolated from retail chicken in South Korea were investigated. RESULTS: All of the isolates possessed blaCTX-M genes, predominantly blaCTX-M-65 (52.2%) and blaCTX-M-55 (25.4%), and three isolates harboured both blaCTX-M-65 and blaCTX-M-55. More than one-half of the ESBL-EC strains also carried blaTEM. Antimicrobial susceptibility testing revealed that 98.5% of the strains were multidrug-resistant (MDR). Phylogenetic analysis showed that group A was predominant (56.7%), followed by B1 (19.4%), E (8.9%), B2 (6.0%) and D (6.0%). Virulence genes associated with extraintestinal pathogenic E. coli (ExPEC) were frequently detected in isolates of phylogenetic groups B1, B2, D and E. CONCLUSION: The results in this study demonstrate that retail chicken in South Korea is highly contaminated with MDR ESBL-EC and may serve as a reservoir for transmitting ExPEC to humans.

Linezolid for treatment of chronic extensively drug-resistant tuberculosis.

BACKGROUND: Linezolid has antimycobacterial activity in vitro and is increasingly used for patients with highly drug-resistant tuberculosis. METHODS: We enrolled 41 patients who had sputum-culture-positive extensively drug-resistant (XDR) tuberculosis and who had not had a response to any available chemotherapeutic option during the previous 6 months. Patients were randomly assigned to linezolid therapy that started immediately or after 2 months, at a dose of 600 mg per day, without a change in their background regimen. The primary end point was the time to sputum-culture conversion on solid medium, with data censored 4 months after study entry. After confirmed sputum-smear conversion or 4 months (whichever came first), patients underwent a second randomization to continued linezolid therapy at a dose of 600 mg per day or 300 mg per day for at least an additional 18 months, with careful toxicity monitoring. RESULTS: By 4 months, 15 of the 19 patients (79%) in the immediate-start group and 7 of the 20 (35%) in the delayed-start group had culture conversion (P=0.001). Most patients (34 of 39 [87%]) had a negative sputum culture within 6 months after linezolid had been added to their drug regimen. Of the 38 patients with exposure to linezolid, 31 (82%) had clinically significant adverse events that were possibly or probably related to linezolid, including 3 patients who discontinued therapy. Patients who received 300 mg per day after the second randomization had fewer adverse events than those who continued taking 600 mg per day. Thirteen patients completed therapy and have not had a relapse. Four cases of acquired resistance to linezolid have been observed. CONCLUSIONS: Linezolid is effective at achieving culture conversion among patients with treatment-refractory XDR pulmonary tuberculosis, but patients must be monitored carefully for adverse events. (Funded by the National Institute of Allergy and Infectious Diseases and the Ministry of Health and Welfare, South Korea; ClinicalTrials.gov number, NCT00727844.).