The objective of this study was to understand the conjugative transmissibility of resistance plasmids present in 205 Salmonella enterica isolates from bovine sources. Polymerase chain reaction (PCR)–based replicon typing was used to type plasmid replicons. Conjugation experiments were preformed in triplicate at 30°C and 37°C on solid medium. PCR mapping of the A/C transfer gene operon was done on 17 Salmonella Newport isolates that were only positive for A/C. Eighty-six percent (n = 177) of the Salmonella isolates were multidrug resistant (MDR) with resistance to 3–12 antimicrobial agents. Of these, 82% (n = 146) were resistant to extended-spectrum cephalosporins and possessed a bla_CMY gene. A/C was the predominant replicon detected, present in 90% (n = 160) of the MDR isolates. Twenty-three percent (n = 37) of the A/C-positive strains were positive for a second replicon. Replicons coresident with A/C included I1, N, B/O, HI1, and HI2. Only 31% (n = 54) of the MDR isolates produced transconjugants, and most of these donors carried multiple replicons. A/C cotransferred with B/O, N, and I1 at both 30°C and 37°C and with HI2 at 30°C. Seven Salmonella Newport isolates that produced transconjugants possessed only the single A/C replicon and lacked bla_CMY. PCR mapping of the A/C transfer gene operon in ten Salmonella Newport isolates that carried bla_CMY revealed a bla_CMY inverted repeat element integrated between the traA and traC genes. These results suggest that A/C may have been a conjugative plasmid before the integration of bla_CMY into the transfer gene operon. Additionally, transfer deficient A/C replicons may be mobilized in the presence of certain compatible conjugative plasmids.

The objective of this study was to determine if conjugative transfer of antimicrobial resistance plasmids could occur between donor and recipient bac

Staphylococcus aureus (S. aureus) causes gastrointestinal illness worldwide. Disinfectants are used throughout the food chain for pathogenic bacteria control. We investigated S. aureus bioavailability in swine Mandibular lymph node tissue (MLT) and pork sausage meat (PSM), established susceptibility values for S. aureus to disinfectants, and determined the multilocus sequence type of MRSA strains. Antimicrobial and disinfectant susceptibility profiles were determined for 164 S. aureus strains isolated from swine feces (n = 63), MLT (n = 49) and PSM (n = 52). No antimicrobial resistance (AMR) was detected to daptomycin, nitrofurantoin, linezolid, and tigecycline, while high AMR prevalence was determined to erythromycin (50.6%), tylosin tartrate (42.7%), penicillin (72%), and tetracycline (68.9%). Methicillin-resistant S. aureus (MRSA) strains, ST398 (n = 6) and ST5 (n = 1), were found in the MLT and PSM, 4 MRSA in MLT and 3 MRSA strains in the PSM. About 17.5% of feces strains and 41.6% of MLT and PSM strains were resistant to chlorhexidine. All strains were susceptible to triclosan and benzalkonium chloride, with no cross-resistance between antimicrobials and disinfectants. Six MRSA strains had elevated susceptibilities to 18 disinfectants. The use of formaldehyde and tris(hydroxylmethyl)nitromethane in DC&R was not effective, which can add chemicals to the environment. Didecyldimethylammonium chloride and benzyldimethylhexadecylammonium chloride were equally effective disinfectants. ST398 and ST5 MRSA strains had elevated susceptibilities to 75% of the disinfectants tested. This study establishes susceptibility values for S. aureus strains from swine feces, mandibular lymph node tissue, and commercial pork sausage against 24 disinfectants. Since it was demonstrated that S. aureus and MRSA strains can be found deep within swine lymph node tissue, it may be beneficial for the consumer if raw swine lymph node tissue is not used in uncooked food products and pork sausage.

Aims To evaluate antibacterial properties of methylsulfonylmethane (MSM) on Escherichia coli (MDRE21) and Salmonella enterica serovar Kinshasa (SK132). Methods and Results Bacterial proliferation analysis was measured spectrophotometrically during log phase growth with 0, 3, 5, 7, 10, 12 and 16% MSM. To assess the mechanism of inhibition, cultures were grown overnight with 0–16% MSM and enumerated on unmedicated brain–heart infusion agar (BHIA) or BHIA with 0–16% MSM. The long‐term viability studies were done to evaluate the impact of 10% MSM. Absorbance data indicated a dose‐dependent inhibition from 0 to 16% MSM. There was no growth of MDRE21 or SK132 on BHIA in 10–16% MSM. Both strains enumerated on unmedicated BHIA from overnight cultures with 10–16% MSM were able to partially recover. Conclusions Recovery after MSM removal may be indicative of a bacteriostatic mechanism of inhibition. The long‐term viability studies illustrated that neither MDRE21 nor SK132 could be rescued from 10% MSM after 5 or 6 days respectively. Significance and Impact of the Study Methylsulfonylmethane antibacterial activity may prove useful during pre or postharvest food safety as a disinfectant. The primary benefit being, its clinical safety to humans. Comparisons to other disinfectants would also need to be done to determine if MSM was superior to those already on the market and would be cost effective.