Transfer of a mobile Staphylococcus saprophyticus plasmid isolated from fermented seafood that confers tetracycline resistance

Mutation of the gidB gene causes intrinsic streptomycin resistance in Bacillus velezensis

Bacillus velezensis strain DMB07, isolated from the traditional fermented Korean soybean meju, exhibits resistance to streptomycin [minimum inhibitory concentration (MIC) 128 mg/L]. To shed light on the genetic background behind this phenotype, this study determined the complete genome sequence of strain DMB07 and compared it with the genomes of two B. velezensis strains that are sensitive to streptomycin. Compared with the streptomycin-sensitive strains, in strain DMB07 there was a mutation of a nucleotide (C58T) of the 16 S rRNA (guanine527-N7)-methyltransferase gene (gidB) that leads to a change in the amino acid sequence of the protein (Arg20Cys). This sequence of gidB gene was previously linked with streptomycin resistance. To test the hypothesis that this change in the gidB gene sequence of strain DMB07 confers streptomycin resistance, a temperature-sensitive plasmid, pIMAY-tgidBT58C, was constructed for site-directed mutation (from thymine to cytosine) of nucleotide 58 of gidB in strain DMB07. The resulting strain, DMB07gidBT58C, showed the decreased MIC value (32 mg/L) against streptomycin. Furthermore, introduction of the wild-type gidB gene into strain DMB07gidBT58C resulted in recovery of the MIC for streptomycin to 128 mg/L. Thus, a single mutation of the nucleotide sequence of the gidB gene can confer resistance to streptomycin.

Antibiotic Susceptibility and Technological Properties of Leuconostoc citreum for Selecting Starter Candidates

Antibiotic susceptibilities, hemolytic activities, and technological properties of 46 Leuconostoc citreum isolates from kimchi were evaluated to select starter candidates. All strains were susceptible to clindamycin and erythromycin, while some exhibited resistance to ampicillin, chloramphenicol, gentamicin, streptomycin, and tetracycline; all were resistant to kanamycin based on the EFSA breakpoint values for Leuconostoc species. PCR analysis did not detect resistance genes for these six antibiotics in any strain. None of the strains demonstrated clear α- or β-hemolytic activity. All strains thrived in a medium supplemented with 6% NaCl, displaying protease activity and acid in media containing 6% and 3% NaCl, respectively. Consequently, five strains, AK5T17, AK5T19, AK10M04, DMLC16, and YK10T20, were identified as starter candidates, with L. citreum strain DMLC16 emerging as the top choice due to its elevated protease and acid production capacities. These findings support the safe application of L. citreum strain DMLC16 as a starter candidate in fermented food production.

Foodborne Microbial Communities as Potential Reservoirs of Antimicrobial Resistance Genes for Pathogens: A Critical Review of the Recent Literature

Antimicrobial resistance (AMR) is a global and increasing threat to human health. Several genetic determinants of AMR are found in environmental reservoirs, including bacteria naturally associated with widely consumed fermented foods. Through the food chain, these bacteria can reach the gut, where horizontal gene transfer (HGT) can occur within the complex and populated microbial environment. Numerous studies on this topic have been published over the past decades, but a conclusive picture of the potential impact of the non-pathogenic foodborne microbial reservoir on the spread of AMR to human pathogens has not yet emerged. This review critically evaluates a comprehensive list of recent experimental studies reporting the isolation of AMR bacteria associated with fermented foods, focusing on those reporting HGT events, which represent the main driver of AMR spread within and between different bacterial communities. Overall, our analysis points to the methodological heterogeneity as a major weakness impairing determination or a causal relation between the presence of AMR determinants within the foodborne microbial reservoir and their transmission to human pathogens. The aim is therefore to highlight the main gaps and needs to better standardize future studies addressing the potential role of non-pathogenic bacteria in the spread of AMR.

Baicalin acts as an adjuvant to potentiate the activity of azithromycin against Staphylococcus saprophyticus biofilm: an in vitro, in vivo, and molecular study

Staphylococcus saprophyticus is frequently involved in various difficult-to-treat infections due to the formation of biofilms. To identify useful antibiofilm strategies, this study explored the efficacy and mechanism of baicalin in enhancing the ability of azithromycin against multidrug-resistant Staphylococcus saprophyticus-Liu-2016-Liyang, China-francolin (MDRSS) biofilms in vitro and in vivo. When azithromycin was used in combination with baicalin, the minimum inhibitory concentration in biofilm (MICB) for azithromycin decreased 4- to 512-fold. Compared with the azithromycin and baicalin groups, the combination of azithromycin and baicalin could not reduce the biofilm biomass, but the dispersion rates of biofilm were decreased and the bactericidal ability was increased. Furthermore, the relative transcript levels of WalK/R system-related genes were upregulated by the addition of baicalin or azithromycin plus baicalin compared with that of the azithromycin and blank control groups. The strong correlation relationship between the WalK/R system and the bactericidal index demonstrated that baicalin enhanced the bactericidal effect of azithromycin on MDRSS biofilms by modulating the WalK/R system. In the mouse cutaneous infection model, the combination of azithromycin and baicalin succeeded in eradicating MDRSS and decreasing pathological injuries. This study indicated that baicalin has the potential to be an adjuvant to enhance the antimicrobial activity of azithromycin against MDRSS in the biofilm form by modulating the WalK/R system.

Phylogenetic characterization and multidrug resistance of bacteria isolated from seafood cocktails

The continual increase in resistance to antibacterial drugs has become a major public health problem, and their indiscriminate use in agriculture, aquaculture, and the treatment of human and animal diseases has severely contributed to the occurrence and spread of multidrug resistance genes. This study phylogenetically characterized multidrug-resistant bacteria isolated from seafood cocktails. Seafood cocktail dishes from 20 establishments on public roads were sampled. Samples were grown on TCBS agar and blood agar. Forty colonies with different macro- and microscopic characteristics were isolated. The 16S rRNA gene V4 and V6 hypervariable regions were amplified, sequenced and phylogenetically analyzed. Antibacterial drug resistance was determined by disk diffusion assay. Isolated bacteria were identical to species of the genera Enterococcus, Proteus, Vibrio, Staphylococcus, Lactococcus, Vagococcus, Micrococcus, Acinetobacter, Enterobacter, and Brevibacterium, with 75-100% presenting resistance or intermediate resistance to dicloxacillin, ampicillin, and penicillin; 50-70% to cephalosporins; 30-67.5% to amikacin, netilmicin and gentamicin; 40% to nitrofurantoin and other antibacterial drugs; 25% to chloramphenicol; and 2.5% to trimethoprim with sulfamethoxazole. In general, 80% of the bacteria showed resistance to multiple antibiotics. The high degree of bacterial resistance to antibacterial drugs indicates that their use in producing raw material for marine foods requires established guidelines and the implementation of good practices.

Comparative Genomics Analysis Demonstrated a Link Between Staphylococci Isolated From Different Sources: A Possible Public Health Risk

Coagulase-negative staphylococci (CoNS) have been recovered from different ecological niches, however, little is known about the genetic relatedness of these isolates. In this study, we used whole genome sequencing to compare mecA positive (mecA ⁺) Staphylococcus epidermidis, Staphylococcus haemolyticus and Staphylococcus hominis isolates recovered from hand-touched surfaces from general public settings in East and West London with data of isolates deposited to European Nucleotide Archive (ENA) by other research groups. These included isolates associated with hospital settings (including those recovered from patients), healthy humans, livestock, pets, plants and natural, and other public environments. Using core and accessory phylogenetic analyses we were able to identify that the mecA⁺ S. epidermidis and S. haemolyticus isolates recovered from general public settings were genetically related to isolates recovered from the bloodstream, urinary tract and eye infections. S. epidermidis isolates recovered in our study were also shown to be genetically related to isolates previously recovered from livestock/livestock housing, whereas S. haemolyticus isolates were genetically related to isolates recovered from a dog and kefir (fermented cow milk drink). MecA ⁺ S. hominis isolates were not genetically related to any isolates recovered from clinical samples but were genetically related to isolates recovered from mosquitoes, air samples (residential areas) and kefir. All three species showed to have genetic relatedness to isolates recovered from healthy humans. These results show that CoNS isolates in this study share genetic similarities with those of different lineages and that mecA⁺ S. epidermidis and S. haemolyticus isolates found in general public settings in this study may pose a risk to public health.

Species Distribution, Antimicrobial Resistance, and Enterotoxigenicity of Non-aureus Staphylococci in Retail Chicken Meat

Non-aureus staphylococci (NAS), including coagulase-negative staphylococci, have emerged as important causes of opportunistic infections in humans and animals and a potential cause of staphylococcal food poisoning. In this study, we investigated (i) the staphylococcal species profiles of NAS in in retail chicken meat, (ii) the phenotypic and genotypic factors associated with antimicrobial resistance in the NAS isolates, and (iii) the prevalence of classical and newer staphylococcal enterotoxin (SE) genes. A total of 58 NAS of nine different species were isolated from retail raw chicken meat samples. The occurrence of multidrug resistance in the NAS, particularly S. agnetis and S. chromogenes, with high resistance rates against tetracycline or fluoroquinolones were confirmed. The tetracycline resistance was associated with the presence of tet(L) in S. chromogenes and S. hyicus or tet(K) in S. saprophyticus. The occurrence of fluoroquinolone resistance in S. agnetis and S. chromogenes was usually associated with mutations in the quinolone resistance determining regions (QRDR) of gyrA and parC. In addition, the frequent presence of SE genes, especially seh, sej, and sep, was detected in S. agnetis and S. chromogenes. Our findings suggest that NAS in raw chicken meat can have potential roles as reservoirs for antimicrobial resistance and enterotoxin genes.

Staphylococcus saprophyticus Proteomic Analyses Elucidate Differences in the Protein Repertories among Clinical Strains Related to Virulence and Persistence

Staphylococcus saprophyticus is a Gram-positive and coagulase negative cocci that composes the skin microbiota and can act as an opportunistic agent causing urinary tract infections, being more frequent in sexually active young women. The ability of a pathogen to cause infection in the host is associated to its ability to adhere to host cells and to survive host immune defenses. In this work, we presented the comparative proteomic profile of three S. saprophyticus strains. It was possible to characterize differences in the proteome content, specially related to expression of virulence factors. We compiled this data and previous data and we detected one strain (9325) possessing higher production and secretion of proteins related to virulence. Our results show that phenotypic, genotypic, and proteomic differences reflect in the ability to survive during interaction with host cells, since the 9325 strain presented a higher survival rate after macrophage interaction. In counterpart, the 7108 strain that possesses lower content of proteins related to virulence presented higher ability to form biofilm suggesting that this strain can be better adapted to persist in the host and in the environment. Our work describes, for the first time, proteomic flexibility among S. saprophyticus strains, reflecting in virulence and persistence.