Isolation of Harveyi clade Vibrio spp. collected in aquaculture farms: How can the identification issue be addressed?

Aquaculture is a fast growing industry with its development hampered by bacterial diseases. Vibriosis caused by Harveyi clade strains is known for causing heavy loss especially in shrimp aquaculture farms. For farm treatment and pathogen spread management, veterinarians and researchers need reliable bacterial identification tools. A range of identification methods have been presented for Vibrio spp. in recent literature but little feedback on their performance have been made available to this day. This study aims at comparing Vibrio spp. identification methods and providing guidance on their use. Fifty farms were sampled and bacterial colonies were isolated using specific culture media before microscopic analysis and genomic profiling using ERIC-PCR. A preliminary identification step was carried out using MALDI-ToF mass spectrometry. Four methods were compared for strain identification on 14 newly isolated Harveyi clade Vibrio spp. strains: whole genome sequencing (digital DNA DNA Hybridization (dDDH)), 5 MLSA schemes, ferric uptake regulation (fur) and lecithin-dependent haemolysin (ldh) single gene based identification methods. Apart from dDDH which is a reference method, no technique could identify all the isolates to the species level. The other tested techniques allowed a faster, cheaper but sub genus clade identification which can be interesting when absolute precision is not required. In this regard, MALDI-ToF and fur based identification seemed especially promising.

In vitro activity of novel anti-MRSA cephalosporins and comparator antimicrobial agents against staphylococci involved in prosthetic joint infections.

OBJECTIVES: Ceftaroline and ceftobiprole are new parenteral cephalosporins with potent activity against methicillin-resistant (MR) staphylococci, which are the leading cause of prosthetic joint infections (PJIs). The aim of this study was to determine and compare the in vitro activities of both molecules against staphylococcal isolates recovered from clinically documented PJIs. METHODS: A collection of 200 non-duplicate clinical isolates [100 Staphylococcus aureus and 100 coagulase-negative staphylococci (CoNS), including 19 and 27 MR isolates, respectively] was studied. Minimum inhibitory concentrations (MICs) of oxacillin, ceftaroline, ceftobiprole, vancomycin, teicoplanin, clindamycin, levofloxacin, linezolid and daptomycin were determined by the broth microdilution method. Bactericidal activity (at 4× MIC) of ceftaroline, ceftobiprole, vancomycin, teicoplanin, linezolid and daptomycin was assessed by time-kill assay. RESULTS: Among the S. aureus isolates, 100% were susceptible to ceftaroline (MIC50/90, 0.25/0.5µg/mL) and 98% were susceptible to ceftobiprole (MIC50/90, 0.5/1µg/mL), regardless of their methicillin resistance. The two ceftobiprole-non-susceptible strains (including one MRSA) showed MICs at 4mg/L. Against CoNS isolates, ceftaroline and ceftobiprole exhibited in vitro potency with MIC50/90 values at 0.06/0.25µg/mL and 0.25/1µg/mL, respectively. At 4× MIC, ceftaroline and ceftobiprole showed rapid and marked bactericidal activity against both S. aureus and CoNS (after 24/12h and 12/6h of incubation, respectively), whilst none of the other molecules tested had a bactericidal effect by 24h. CONCLUSIONS: This study showed that ceftaroline and ceftobiprole have excellent in vitro activity against clinical isolates of staphylococci involved in PJIs. These molecules may therefore represent promising alternatives for the treatment of such infections.