High prevalence rates of sulfonamide resistance genes
sul1
,
sul2
, and
sul3
have been observed in Gram-negative bacteria isolated from humans, domestic animals, and aquaculture species worldwide. We investigated the distribution characteristics, location, conjugative transferability, and genetic environments of
sul
genes from
Escherichia coli
isolates collected from
Penaeus vannamei
and pork samples from three large markets in Zhejiang, China. The prevalence rates of
sul
genes in sulfonamide-resistant
E. coli
isolates from
P. vannamei
and pork samples were 90.0 and 88.6%, respectively, and the prevalence of
sul1
and
sul2
was significantly higher than that of
sul3
(
p
< 0.05). Twenty-four representative
sul
-positive
E. coli
isolates were analyzed in detail. Southern blot hybridization confirmed that
sul
genes of
E. coli
isolates were located on plasmids and/or chromosomes. Transfer of resistance through conjugation was observed in all 18
E. coli
isolates harboring
sul
genes on plasmids. Replicon typing identified seven different incompatibility groups and IncF was the dominant replicon type among
sul
gene-containing plasmids from both sources. PCR walking analysis indicated that 87.5% (35/40) of
sul
gene-related fragments carried insertion sequences (ISs) belonging to a variety of families in diverse sites, with IS
26
occurring most frequently. In addition, the
sul1
gene was detected mainly in fragments carrying class 1 integrons. Co-location on the same fragment with resistance genes that may contribute to the persistence and dissemination of
sul1
and/or
sul2
genes. The diversity of mobile genetic elements and resistance genes adjacent to
sul3
was much lower than those adjacent to
sul1
and
sul2
, especially those located in chromosomes, which reduced the transmission potential of the
sul3
gene. In conclusion, combined with the results of clonal relatedness analysis by PFGE and MLST of 24 representative
E. coli
isolates from
P. vannamei
and pork samples, it showed that a small number of
sul
genes were vertically transmitted among
E. coli
from
P. vannamei
and that horizontal gene transfer was likely the main transmission mechanism of
sul
genes from both sources. Our results provide important information to better unde...
A multianalyte lateral-flow immunochromatographic technique using colloidal gold-labeled polyclonal antibodies was developed for the rapid simultaneous detection of clenbuterol and ractopamine. The assay procedure could be accomplished within 5 min, and the results of this qualitative one-step assay were evaluated visually according to whether test lines appeared or not. When applied to the swine urines, the detection limit and the half maximal inhibitory concentration (IC(50)) of the test strip under an optical density scanner were calculated to be 0.1 +/- 0.01 ng mL(-1) and 0.1 +/- 0.01 ng mL(-1), 0.56 +/- 0.08 ng mL(-1), and 0.71 +/- 0.06 ng mL(-1), respectively, the cut-off levels with the naked eye of 1 ng mL(-1) and 1 ng mL(-1) for clenbuterol and ractopamine were observed. Parallel analysis of swine urine samples with clenbuterol and ractopamine showed comparable results obtained from the multianalyte lateral-flow test strip and GC-MS. Therefore, the described multianalyte lateral-flow test strip can be used as a reliable, rapid, and cost-effective on-site screening technique for the simultaneous determination of clenbuterol and ractopamine residues in swine urine.
Salmonella can cause serious foodborne diseases. We have developed a lateral flow immunoassay combined with recombinase polymerase amplification (LFD-RPA) for detection of Salmonella in food. The conserved fragment (fimY) was selected as the target gene. Under an optimal condition (37 °C, 10 min), the sensitivity was 12 colony-forming units (CFU)/mL in a pure culture. Testing with 16 non-Salmonella strains as controls revealed that LFD-RPA was specific to the fimY gene of Salmonella. The established assay could detect Salmonella at concentrations as low as 1.29 × 102 CFU/mL in artificially contaminated samples. This detection was at a slightly higher level than that for a pure bacterial culture. Combined with the test strip reader, the LFD-RPA is a feasible method for quantitative detection of Salmonella based on the test line intensity, which was the ratio for the test line and control line of the reflected light. The method could be a potential point-of-care test in limited resource areas and provides a new approach and technical support for the diagnosis of food safety.
Staphylococcus aureus and its drug-resistant strains, which threaten public health and food safety, are in need of effective control by biopreservatives. A novel bacteriocin, pentocin JL-1, produced by Lactobacillus pentosus that was isolated from the intestinal tract of Chiloscyllium punctatum, was purified by a four-step chromatographic process. Mass spectrometry based on MALDI-TOF indicated that pentocin JL-1 has a molecular mass of 2987.23 Da. Only six of the twenty-five amino acids could be identified by Edman degradation. This bacteriocin is thermostable and tolerates a pH range of 5–7. Also, it is sensitive to proteinase K, trypsin, pepsin, and alkaline protease. This bacteriocin has a broad inhibitory spectrum against both Gram-positive and Gram-negative strains and in particular is effective against multidrug-resistant S. aureus. Additionally, we showed that the cell membrane is the target of pentocin JL-1 against methicillin-resistant S. aureus (MRSA), causing a loss of proton motive force. Furthermore, pentocin JL-1 has a drastic impact on the structure and integrity of MRSA cells. These results suggest that pentocin JL-1 has potential as a biopreservative in the food industry.
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