Prevalence, resistance phenotypes, and fluoroquinolone resistance genes of Salmonella isolates from raw milk of healthy dairy cows in Henan province, China.

OBJECTIVE: Salmonella isolates have been discovered in many regions of the world. We investigated the prevalence and resistance of Salmonella isolates in raw milk of healthy dairy cows on farms in different regions of Henan Province, China. MATERIALS AND METHODS: From July 2020 to November 2021, 422 raw milk samples were collected. The minimum inhibitory concentrations (MICs) of 16 antimicrobial agents against 89 Salmonella strains detected from the raw milk samples were determined using the broth microdilution method, and the resistance genes for fluoroquinolones were identified using polymerase chain reaction. RESULTS: Eighty-nine (21.09%) Salmonella isolates were recovered from 422 raw milk samples. The Salmonella strains exhibited high resistance to amoxicillin (100.00%), tylosin (95.50%), and lincomycin (95.50%). Additionally, tigecycline showed good activity against Salmonella, with an MIC50 of 0.25 µg/mL. All Salmonella isolates showed multidrug resistance (MDR), and >50% of the strains showed resistance to more than six antimicrobials. The strains from Jiaozuo exhibited 100% resistance to amoxicillin, terramycin, tylosin, and lincomycin. Two efflux pump genes, oqxA and oqxB, had the highest carrying rates of 66.29% and 64.04%, respectively. Additionally, the carrying rates of oqxA and oqxB were high in Shangqiu, Zhengzhou, and Jiaozuo. The carrying rates of aac(6')-Ib-cr in Shangqiu and Zhengzhou were 33.33% and 38.46%, respectively. CONCLUSIONS: This study revealed a high prevalence of Salmonella isolates obtained from raw milk of healthy dairy cows in different regions of Henan Province, China. The Salmonella strains exhibited various degrees of MDR. Salmonella can be transmitted to humans via consumption of contaminated raw milk; thus, the presence of resistance genes poses a potential threat to public health, highlighting the need for vigilant monitoring of Salmonella isolates.

Antimicrobial mechanisms of traditional Chinese medicine and reversal of drug resistance: a narrative review.

OBJECTIVE: In recent years, the extensive use of antibiotics worldwide has led to an increase in the number of drug-resistant bacterial strains, thus resulting in an increasingly severe degree of bacterial resistance. For thousands of years, traditional Chinese medicine (TCM) has provided natural and unique advantages in the treatment of infectious diseases. Therefore, it is important to develop further and use TCM to treat clinical infections caused by drug-resistant bacteria. MATERIALS AND METHODS: A literature search was performed using PubMed, Web of Science, Google Scholar, and the China National Knowledge Infrastructure databases. The articles were analyzed to extract information on the antimicrobial effects of Chinese herbal medicines, compounded Chinese medicines, monomeric compounds of herbal origin, and the combined use of Chinese medicine and antimicrobial drugs and to determine the synergistic effect of the combination of Chinese medicine and antibiotics, as well as investigate the possibility of restoring the antibiotic sensitivity of drug-resistant strains. RESULTS: The mechanisms underlying the antibacterial properties of TCM involve altering membrane permeability, inhibiting protein and nucleic acid synthesis, inhibiting enzyme activity in vivo, and controlling the ability of pathogenic bacteria. In addition, the mechanism underlying TCM-induced reversal of bacterial drug resistance is discussed, particularly in terms of the elimination of resistant (R) plasmids and the inhibition of extended-spectrum ß-lactamases, bacterial biofilm formation, and bacterial efflux pump activity. CONCLUSIONS: This paper reviewed the recent relevant literature on antimicrobial action and its mechanisms, as well as the mechanisms of drug resistance reversal by TCM to provide a reference for clinical drug use, prevention and control of bacterial infection, and research and development of new drugs.

Research progress on the oxazolidinone drug linezolid resistance.

OBJECTIVE: The oxazolidinone drug linezolid is mainly used for severe infections caused by multidrug-resistant Gram-positive bacteria. However, emerging linezolid resistance is aggravating difficulties in the treatment of certain infectious diseases. The objective of this review was to provide a reference for researchers and clinicians to be able to better face together the serious challenge of antimicrobial resistance. MATERIALS AND METHODS: A systematic literature search was performed using PubMed, Web of Science, Google Scholar, and the China National Knowledge Infrastructure (CNKI) database. The articles were scrutinized to extract information on oxazolidinone drug linezolid resistance, and the prevalence of the resistance gene optrA. We reviewed the latest advances in epidemic properties, resistance mechanism, and transfer mechanism of linezolid resistance genes in different isolates isolated from various samples worldwide. RESULTS: Initially, it was thought that linezolid resistance was related to the change in drug target mediated by mutations in the 23S rRNA gene, rplC, rplD, and cfr. optrA was discovered in 2015, and is a gene encoding oxazolidinone resistance, which exists in both plasmids and chromosomes, but mostly plasmids. The emergence of the novel plasmid-borne ABC transporter gene optrA expanded the understanding of the mechanism of linezolid resistance. CONCLUSIONS: At present, the prevalence of linezolid resistance has become increasingly serious. The resistance gene optrA has been reported in Enterococcus, Staphylococcus squirrel and Streptococcus, which indicates that this gene has a strong ability to spread across bacteria, so the prevalence and spread of optrA gene should be monitored carefully.