A free elution immunoassay for chloramphenicol in chicken and egg after magnetic ZIF-8 adsorption separation

The excellent adsorption and rapid separation capabilities of magnetic MOFs make them desirable pretreatment materials for solid substrates.In this study,magnetic ZIF-8(mZIF-8)was synthesized in situ by a one-step method in the aqueous solution of magnetic beads.Isothermal adsorption verified that the maximum adsorption capacity of(011)crystal-exposed rhombic dodecahedral ZIF-8 for chloramphenicol was up to 128.31 mg/g(mZIF-8=67.18 mg/g).Kinetic adsorption revealed that the type of ZIF-8/mZIF-8 adsorption on chloramphenicol belongs to the pseudo-secondary adsorption kinetics of chemical monomolecular layers.Characterization by FTIR,XPS,and XRD revealed that mZIF-8 interacts with chloramphenicol mainly byπ-πelectron stacking,electrostatic attraction,and hydrogen bonding interaction.ELISA confirmed that chloramphenicol remained antigenically active after adsorption by mZIF-8.The adsorption and separation of chloramphenicol residues in chicken and egg were completed by mZIF-8 within 20 min.mZIF-8 can be used directly for elution-free ELISA after the adsorption of chloramphenicol.The limits of detection(IC10)of the mZIF-8+ELISA in chicken and eggs were 1.18 ng/mL and 0.64 ng/mL,respectively.mZIF-8 is expected to be used as a magnetic solid-phase extraction material for the rapid pretreatment of antibiotic residues in other complex solid matrices.

Epidemiology and genetic characterization of tet(X4)-positive Klebsiella pneumoniae and Klebsiella quasipneumoniae isolated from raw meat in Chengdu City, China

The rapid spread of mobile tigecycline resistance presents a significant public health threat,particularly with the increasing prevalence of tet(X4)-positive Enterobacterales across various species.This study aimed to inves-tigate the epidemic features and transmission dynamics of tet(X4)-positive Klebsiella pneumoniae(K.pneumo-niae)through the analysis of 206 raw meats,including pork(n=182),beef(n=16),duck(n=5),and chicken(n=3).These samples were collected from schools,markets,and restaurants in Chengdu City,China.A total of 25 isolates were obtained from 13 administrative regions.All isolates exhibited resistance to tetracycline,tigecycline,ampicillin,chloramphenicol,and florfenicol.Over half of the isolates also demon-strated resistance to streptomycin(80%),sulfamethoxazole/trimethoprim(72%),ciprofloxacin(64%),and ampicillin/sulbactam(56%).Among these strains,14 distinct sequence types(STs)were identified,revealing evidence of inter-regional clonal spread,notably among 9 K.pneumoniae ST3393.Phylogenetic analysis revealed the presence of two K.pneumoniae ST5 closely resembling hypervirulent K.pneumoniae from Jiangsu.Importantly,12 isolates were capable of transferring tigecycline resistance to Escherichia coli J53.Further plasmid analysis showed that the tet(X4)-harboring plasmids in K.pneumoniae could be classified into four types,primarily belonging to the IncFIA(HI1)/HI1A/HI1B hybrid plasmid(n=16)and IncFII plasmid(n=7),which significantly contributed to the cross-species dissemination of tet(X4).In summary,this study highlights the prevalence of MDR tet(X4)-positive K.pneumoniae in Chengdu,driven predominantly by clonal expansion and plasmid-mediated horizontal gene transfer.These findings emphasize the importance of contin-uous surveillance of tet(X4)-positive K.pneumoniae in raw meat and the implementation of effective measures to control their spread.