Antimicrobials in shrimp aquaculture in the United States: regulatory status and safety concerns

Draft Genome Sequences of 14 Fluoroquinolone-Resistant Escherichia coli Isolates from Imported Shrimp

We report the draft genome sequences of 14 fluoroquinolone-resistant Escherichia coli strains that were isolated from imported shrimp. All isolates contained multiple point mutations in the quinolone resistance-determining regions (QRDRs) and non-QRDRs of gyrA, parC, and parE genes. The data improve the understanding of fluoroquinolone resistance and indicate resistance mechanisms.

Bioengineered Probiotics: Synthetic Biology Can Provide Live Cell Therapeutics for the Treatment of Foodborne Diseases

The rising prevalence of antibiotic resistant microbial pathogens presents an ominous health and economic challenge to modern society. The discovery and large-scale development of antibiotic drugs in previous decades was transformational, providing cheap, effective treatment for what would previously have been a lethal infection. As microbial strains resistant to many or even all antibiotic drug treatments have evolved, there is an urgent need for new drugs or antimicrobial treatments to control these pathogens. The ability to sequence and mine the genomes of an increasing number of microbial strains from previously unexplored environments has the potential to identify new natural product antibiotic biosynthesis pathways. This coupled with the power of synthetic biology to generate new production chassis, biosensors and “weaponized” live cell therapeutics may provide new means to combat the rapidly evolving threat of drug resistant microbial pathogens. This review focuses on the application of synthetic biology to construct probiotic strains that have been endowed with functionalities allowing them to identify, compete with and in some cases kill microbial pathogens as well as stimulate host immunity. Weaponized probiotics may have the greatest potential for use against pathogens that infect the gastrointestinal tract: Vibrio cholerae, Staphylococcus aureus, Clostridium perfringens and Clostridioides difficile. The potential benefits of engineered probiotics are highlighted along with the challenges that must still be met before these intriguing and exciting new therapeutic tools can be widely deployed.

Molecular characterization of fluoroquinolone-resistant Aeromonas spp. isolated from imported shrimp

Sixty-three nalidixic acid-resistant Aeromonas sp. isolates were obtained from imported shrimp. Phylogenetic analysis of gyrB sequences indicated that 18 were A. enteropelogenes, 26 were A. caviae, and 19 were A. sobria. Double missense mutations in the quinolone resistance-determining region (QRDR) of gyrA at codon 83 (Ser→Val/Ile) and codon 92 (Leu→Met) coupled with a point mutation of parC at codon 80 (Ser→Ile/Phe) conferred high levels of quinolone resistance in the isolates. A majority of A. enteropelogenes and A. caviae strains harbored toxin genes, whereas only a few A. sobria strains harbored these genes. The fluoroquinolone-resistant Aeromonas spp. exhibited higher cytotoxicity than fluoroquinolone-sensitive, virulent Aeromonas spp. to rat epithelial cells.

Isolation and characterization of multidrug-resistant Klebsiella spp. isolated from shrimp imported from Thailand

A study was undertaken to isolate and characterize tetracycline and nalidixic acid-resistant Klebsiella spp. in farm-raised, imported shrimp sold in the United States. Sixty-seven multiple antibiotic-resistant Klebsiella spp. strains were isolated from imported shrimp samples. Using morphological and biochemical methods, fifty-three strains were tentatively identified as Klebsiella pneumoniae and fourteen as K. oxytoca. Although all isolates were resistant to tetracycline, only 8 were resistant to nalidixic acid. These 8 isolates were further screened by PCR for quinolone resistance genes (qnrA, B, S, gyrA, B and parC). PCR protocols failed to amplify any qnr genes. The purified PCR amplicons of gyrA, gyrB and parC were sequenced and analyzed for point mutations that confer resistance to fluoroquinolone antibiotics. Analysis of the sequences of the gyrA amplicons from nalidixic acid-resistant Klebsiella spp. indicated two point mutations in gyrA at positions 83 (Ser→Phe) and 87 (Asp→Ala). Sequence analysis of the parC amplicons indicated an amino acid change at position 80 (Ser→Ile). No mutations were detected in gyrB. Template DNA from all isolates was screened for tetracycline resistance genes (tetA-E). Oligonucleotide primers specifically targeting a 305-bp region of tetB and a 477-bp region of tetD successfully amplified sequences from 91.0 and 44.0% of the isolates, respectively. None of the isolates contained tetA, tetC or tetE genes. Plasmids (2.0-16.0kb) were found in 23 of the 67 isolates. XbaI-PFGE identified 32 distinct macro restriction patterns (mrps) among the 61 multiple drug-resistant Klebsiella spp. that were typable. Our results indicate that imported shrimp is a reservoir for multidrug resistant Klebsiella spp. and potential health risks posed by such strains should not be underestimated.

Virulence of an emerging pathogenic lineage of Vibrio nigripulchritudo is dependent on two plasmids

Vibrioses are the predominant bacterial infections in marine shrimp farms. Vibrio nigripulchritudo is an emerging pathogen of the cultured shrimp Litopenaeus stylirostris in New Caledonia and other regions in the Indo-Pacific. The molecular determinants of V. nigripulchritudo pathogenicity are unknown; however, molecular epidemiological studies have revealed that recent pathogenic V. nigripulchritudo isolates from New Caledonia all cluster into a monophyletic clade and contain a small plasmid, pB1067. Here, we report that a large plasmid, pA1066 (247 kb), can also serve as a marker for virulent V. nigripulchritudo, and that an ancestral version of this plasmid was likely acquired prior to other virulence-linked markers. Additionally, we demonstrate that pA1066 is critical for the full virulence of V. nigripulchritudo in several newly developed experimental models of infection. Plasmid pB1067 also contributes to virulence; only strains containing both plasmids induced the highest level of shrimp mortality. Thus, it appears that these plasmids, which are absent from non-pathogenic isolates, may be driving forces, as well as markers, for the emergence of a pathogenic lineage of V. nigripulchritudo.

Antimicrobial resistance in bacteria isolated from aquaculture sources in Australia

AIMS

To carry out a preliminary assessment of the occurrence of resistance to antimicrobials in bacteria that has been isolated from a variety of aquaculture species and environments in Australia.

METHOD AND RESULTS

A total of 100 Gram-negative (Vibrio spp. and Aeromonas spp. predominantly) and four Gram-positive bacteria isolated from farmed fish, crustaceans and water from crab larval rearing tanks were obtained from diagnostic laboratories from different parts of Australia. All the isolates were tested for sensitivity to 19 antibiotics and Minimal Inhibitory Concentrations were determined by the agar dilution method. Plasmid DNA was isolated by the alkali lysis method. Resistance to ampicillin, amoxycillin, cephalexin and erythromycin was widespread; resistance to oxytetracycline, tetracycline, nalidixic acid and sulfonamides was common but resistance to chloramphenicol, florfenicol, ceftiofur, cephalothin, cefoperazone, oxolinic acid, gentamicin, kanamycin and trimethoprim was less common. All strains were susceptible to ciprofloxacin. Multiple resistance was also observed and 74.4% of resistant isolates had between one and ten plasmids with sizes ranging 2-51 kbp.

CONCLUSIONS

No antibiotics are registered for use in aquaculture in Australia but these results suggest that there has been significant off-label use.

SIGNIFICANCE AND IMPACT OF STUDY

Transfer of antibiotic resistant bacteria to humans via the food chain is a significant health concern. In comparison with studies on terrestrial food producing animals, there are fewer studies on antibiotic resistance in bacteria from aquaculture enterprises and this study provides further support to the view that there is the risk of transfer of resistant bacteria to humans from consumption of aquaculture products. From the Australian perspective, although there are no products registered for use in aquaculture, antimicrobial resistance is present in isolates from aquaculture and aquaculture environments.

Veterinary pharmacovigilance. Part 4. Adverse reactions in humans to veterinary medicinal products

Although seemingly rare, adverse reactions to veterinary products do occur. These may arise from inadvertent exposure during use or as a result of occupational accidents. They are often mild in nature and include adverse effects such as minor skin reactions. However, more serious reactions may occur, and they are not restricted to the effects of the veterinary medicines themselves. For example, high-pressure injection injuries may occur as a result of accidents occurring during animal vaccination operations. This paper reviews some of these events, mentions where appropriate the regulatory actions taken, and describes some of the measures used to minimise such effects in the future, and serves to bring the issues discussed here to the attention of pharmacologists, pharmacoepidemiologists and others who train those who use veterinary medicinal products.

Confirmation of multiple tetracycline residues in milk and oxytetracycline in shrimp by liquid chromatography-particle beam mass spectrometry

A confirmation procedure is described for detection of residues of six tetracyclines in bovine milk, and oxytetracycline in shrimp. Residues are extracted from milk or shrimp tissue using metal chelate affinity chromatography. The extracts are desalted, further concentrated using polymeric solid-phase extraction, and chromatographed on a polymeric reversed-phase column. Analysis is by methane negative ion chemical ionization on a quadrupole mass spectrometer using a particle beam interface. Data are acquired in partial scan mode, monitoring from m/z 378 to m/z 480. The procedure was validated with control milk and shrimp, fortified milk (30 ng/ml) and shrimp (100 ng/g), and milk and tissue from animals treated with the drugs.