Molecular Epidemiology and Antimicrobial Resistance of Outbreaks of Klebsiella pneumoniae Clinical Mastitis in Chinese Dairy Farms

Invited review: Antimicrobial resistance genes in milk-A 10-year systematic review and critical comment

The occurrence of antibiotic resistance genes (ARG) in milk is eagerly discussed as a public health risk, and frequently investigated. Here, we perform a systematic review on the abundance of antimicrobial resistance genes in milk from primary production over a 10-year period. We aim to provide a comprehensive dataset on known and emerging antimicrobial resistance genes in major mastitis pathogens, occurring worldwide in milk at primary production, and to critically discuss the relevance and constraints of these findings. We searched PubMed for peer-reviewed studies published between 2012 and 2022 that fit fixed combinations of key words and did not meet exclusion criteria such as "mixed with other sources." For synthesis, data on occurrence was extracted from studies and supplements. To address plausibility issues, we performed an National Center of Biotechnology Information Basic Local Alignment Search Tool (BLAST) search. Our search revealed 2,222 publications in total. Of them, 500 studies were eligible for full-text reads and 306 publications were included in data compilation. An overwhelming majority of studies dealt with mecA in Staphylococcus aureus, followed by extended-spectrum β-lactamase-encoding genes such as blaCTXM in Escherichia coli, while other mastitis pathogens, such as Streptococcus spp., were scarcely investigated. In most cases, <5% of milk samples were positive for major pathogens bearing the antimicrobial resistance gene of interest. However, huge study-to-study differences were found between regions, but also on a national level. For instance, the estimate prevalence of Escherichia coli-borne blaCTXM in mastitis milk samples ranged from 0.0% to 55%, with a median value of 7.3%, but in healthy individuals and bulk milk, the prevalence ranged from 0.0% to 20.0%, with a median value of 0.8%. Several studies reported antimicrobial resistance genes for the very first time in a species, but did not stand up to scrutiny. As an example, frequent detection of blaTEM-genes in streptococci is most likely attributed to contamination of molecular reagents, as reported elsewhere. Despite the large amount of data, there is a need for more quality control, more representative sampling of milk, more quantitative research, and deeper insights into bacterial genomics, to identify relevant or emerging antimicrobial resistance genes in milk. Considering a low percentage of contaminated milk samples, unknown ARG concentrations, and an unproven role in human disease, the risk attributed to ARG in milk seems to be exaggerated by far. However, the risk of ARG selection on farm, resulting in low treatment success in cattle, is a real one and should be met by prudent use of antibiotics.

Antimicrobial potential of a novel K5-specific phage and its recombinant strains against Klebsiella pneumoniae in milk

The nutrient-rich composition of milk creates an optimal environment for bacterial proliferation, making the inhibition of microbial growth essential for maintaining dairy product quality and ensuring consumer safety. Klebsiella pneumoniae is an important contaminant of milk and a leading cause of bovine mastitis. Although the increasingly serious antibiotic resistance has led to a renewed interest in phage therapy, research on antimicrobial potential of Klebsiella phages in milk remains scarce. The K5 serotype of K. pneumoniae is a major concern due to its high virulence and prevalence in dairy farming operations. Despite its clinical and economic importance, the availability of phages specifically targeting this serotype remains substantially limited. Here, we successfully isolated and sequenced 2 K1-specific Klebsiella phages, P284 and P287, and one K5-specific Klebsiella phage P252. We identified the receptor-binding proteins with depolymerization activity in these phages. The phage library against K5 K. pneumoniae was enriched by phage genome modification. Specifically, we replaced the receptor-binding protein of K1-specific phage P284 with that of K5-specific phage P252, resulting in the generation of recombinant phages T and F, which exhibit specific lytic activity against K5 K. pneumoniae. Compared with phage P252, recombinant phages T and F exhibited better and more prolonged antibacterial potential in planktonic assay. In addition, all these K5-specific phages could significantly inhibit bacterial growth and reduce bacterial populations in milk at 4°C and 38°C. In summary, this study provided K5-specific phages with potential application in managing K. pneumoniae contamination and infection in the dairy industry.

Anti-Inflammatory Effects of Weissella cibaria SDS2.1 Against Klebsiella pneumoniae-Induced Mammary Gland Inflammation

Dairy cows are highly susceptible to mastitis caused by Klebsiella pneumoniae, and treating these infections poses a challenge due to the resistance of the bacterium to common antibiotics. This study aimed to evaluate the safety of W. cibaria SDS2.1 and investigate its protective effects against K. pneumoniae-induced mastitis. The safety of W. cibaria SDS2.1 was assessed through comprehensive analyses, including antibiotic resistance profiling, hemolysis assays, cell cytotoxicity tests, and whole-genome sequencing. Furthermore, its ability to protect against cellular and tissue damage caused by K. pneumoniae-induced mastitis was evaluated using both in vitro and in vivo models. Our results revealed that W. cibaria SDS2.1 was non-hemolytic, non-cytotoxic, and significantly inhibited the growth of K. pneumoniae (p < 0.05). Additionally, W. cibaria SDS2.1 effectively reduced the adhesion and invasion of K. pneumoniae. In the K. pneumoniae-induced mouse mastitis model, W. cibaria SDS2.1 significantly reduced myeloperoxidase (MPO) activity, mammary tissue damage, and the expression of inflammatory cytokines (IL-6, IL-1β, and TNF-α) (p < 0.05). In K. pneumoniae-infected bovine mammary epithelial cells (bMECs), W. cibaria SDS2.1 significantly decreased lactate dehydrogenase (LDH) release, indicating reduced cellular damage. These findings demonstrate that W. cibaria SDS2.1 exhibits anti-inflammatory properties in experimental models, suggesting its potential role in mitigating K. pneumoniae-induced mastitis.

Detection of CRISPR‒Cas and type I R-M systems in Klebsiella pneumoniae of human and animal origins and their relationship to antibiotic resistance and virulence

The clustered regularly interspaced short palindromic repeats (CRISPR)‒CRISPR-associated protein (Cas) and restriction‒modification (R-M) systems are important immune systems in bacteria. Information about the distributions of these two systems in Klebsiella pneumoniae from different hosts and their mutual effect on antibiotic resistance and virulence is still limited. In this study, the whole genomes of 520 strains of K. pneumoniae from GenBank, including 325 from humans and 195 from animals, were collected for CRISPR‒Cas systems and type I R-M systems, virulence genes, antibiotic resistance genes, and multilocus sequence typing detection. The results showed that host origin had no obvious influence on the distributions of the two systems (CRISPR‒Cas systems in 29.8% and 24.1%, type I R-M systems in 9.8% and 11.8% of human-origin and animal-origin strains, respectively) in K. pneumoniae. Identical spacer sequences from different hosts demonstrated there was a risk of human-animal transmission. All virulence genes (yersiniabactin, colibactin, aerobactin, salmochelin, rmpADC, and rmpA2) detection rates were higher when only the CRISPR‒Cas systems were present but were all reduced when coexisting with type I R-M systems. However, a lower prevalence of most antibiotic-resistance genes was found when the CRISPR‒Cas systems were alone, and when type I R-M systems were coexisting, some of the antibiotic resistance gene incidence rates were even lower (quinolones, macrolides, tetracyclines and carbapenems), and some of them were higher instead (aminoglycosides, clindamycins, rifampicin-associated, sulfonamides, methotrexates, beta-lactamases and ultrabroad-spectrum beta-lactamases). The synergistic and opposed effects of the two systems on virulence and antibiotic-resistance genes need further study.IMPORTANCEK. pneumoniae is an important opportunistic pathogen responsible for both human and animal infections, and the emergence of hypervirulent and multidrug-resistant K. pneumoniae has made it difficult to control this pathogen worldwide. Here, we find that CRISPR‒Cas and restriction-modification systems, which function as adaptive and innate immune systems in bacteria, have synergistic and opposed effects on virulence and antibiotic resistance genes in K. pneumoniae. Moreover, this study provides insights into the distributions of the two systems in K. pneumoniae from different hosts, and there is no significant difference in the prevalence of the two systems among K. pneumoniae spp. In addition, this study also characterizes the CRISPR arrays of K. pneumoniae from different hosts, suggesting that the strains sharing the same spacer sequences have the potential to spread between humans and animals.

Antimicrobial resistance profiles and molecular epidemiology of Klebsiella pneumoniae isolates from Scottish bovine mastitis cases

Klebsiella pneumoniae are opportunistic pathogens which can cause mastitis in dairy cattle. K. pneumoniae mastitis often has a poor cure rate and can lead to the development of chronic infection, which has an impact on both health and production. However, there are few studies which aim to fully characterize K. pneumoniae by whole-genome sequencing from bovine mastitis cases. Here, K. pneumoniae isolates associated with mastitis in dairy cattle were identified using matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) and whole-genome sequencing. Furthermore, whole-genome sequence data were used for phylogenetic analyses and both virulence and antimicrobial resistance (AMR) prediction, in parallel with phenotypic AMR testing. Forty-two isolates identified as K. pneumoniae were subject to whole-genome sequencing, with 31 multi-locus sequence types being observed, suggesting the source of these isolates was likely environmental. Isolates were examined for key virulence determinants encoding acquired siderophores, colibactin, and hypermucoidy. The majority of these were absent, except for ybST (encoding yersiniabactin) which was present in six isolates. Across the dataset, there were notable levels of phenotypic AMR against streptomycin (26.2%) and tetracycline (19%), and intermediate susceptibility to cephalexin (26.2%) and neomycin (21.4%). Of importance was the detection of two ESBL-producing isolates, which demonstrated multi-drug resistance to amoxicillin-clavulanic acid, streptomycin, tetracycline, cefotaxime, cephalexin, and cefquinome.

Molecular characterization of Klebsiella pneumoniae in clinical bovine mastitis in 14 provinces in China

The mastitis caused by Klebsiella pneumoniae (K. pneumoniae) is increasing in the dairy cows. To investigate the epidemic of K. pneumoniae of China, 131 strains were isolated from 495 clinical mastitis milk samples (26.5%) from 14 provinces in China. Among the isolates, K57 was the dominant serotype (45.0%) and 19 (14.5%) isolates were identified as hypervirulent K. pneumoniae (hvKP). The mrkA, entB, wabG and fimH genes were prevalent virulence genes while rmpA, magA, and ycf were not found in K. pneumoniae. Furthermore, K. pneumoniae had serious antibiotic resistance and multiple β-lactamase genes, including blaTEM, blaSHV, blaNDM, blaCTX-M, blaDHA, and blaKPC. Biofilm was an important factor in bacterial resistance and persistent infection, and 77.1% isolates could form biofilm. Although acylated homoserine lactone (AHL, a Gram-negative bacterial quorum sensing signal molecule) was not confirmed among the K. pneumoniae isolates, exogenous AHLs could reduce the biofilm formation ability of the K. pneumoniae strains. Three new ST types (ST6781, ST6782, and ST6783) were first identified in this study. The MLST phylogenetic tree showed the distribution of mastitis associated K. pneumoniae strains had no regular pattern, which confirmed high genomic diversity of mastitis associated K. pneumoniae. In conclusion, the high rate of isolation and serious antibiotic resistance of K. pneumonia were found in this study and indicated a potential threat to public health from the food chain.

Effect of baicalin on eradicating biofilms of bovine milk derived Acinetobacter lwoffii

BACKGROUND

Acinetobacter lwoffii (A.lwoffii) is a serious zoonotic pathogen that has been identified as a cause of infections such as meningitis, bacteremia and pneumonia. In recent years, the infection rate and detection rate of A.lwoffii is increasing, especially in the breeding industry. Due to the presence of biofilms, it is difficult to eradicate and has become a potential super drug-resistant bacteria. Therefore, eradication of preformed biofilm is an alternative therapeutic action to control A.lwoffii infection. The present study aimed to clarify that baicalin could eradicate A.lwoffii biofilm in dairy cows, and to explore the mechanism of baicalin eradicating A.lwoffii.

RESULTS

The results showed that compared to the control group, the 4 MIC of baicalin significantly eradicated the preformed biofilm, and the effect was stable at this concentration, the number of viable bacteria in the biofilm was decreased by 0.67 Log10CFU/mL. The total fluorescence intensity of biofilm bacteria decreased significantly, with a reduction rate of 67.0%. There were 833 differentially expressed genes (367 up-regulated and 466 down-regulated), whose functions mainly focused on oxidative phosphorylation, biofilm regulation system and trehalose synthesis. Molecular docking analysis predicted 11 groups of target proteins that were well combined with baicalin, and the content of trehalose decreased significantly after the biofilm of A.lwoffii was treated with baicalin.

CONCLUSIONS

The present study evaluated the antibiofilm potential of baicalin against A.lwoffii. Baicalin revealed strong antibiofilm potential against A.lwoffii. Baicalin induced biofilm eradication may be related to oxidative phosphorylation and TCSs. Moreover, the decrease of trehalose content may be related to biofilm eradication.

Epidemiological, Virulence, and Antibiotic Resistance Analysis of Klebsiella pneumoniae, a Major Source of Threat to Livestock and Poultry in Some Regions of Xinjiang, China

Klebsiella pneumoniae (K. pneumoniae) is recognized as a zoonotic pathogen with an increasing threat to livestock and poultry. However, research on K. pneumoniae of animal origin remains limited. To address the gap, a comprehensive investigation was carried out by collecting a total of 311 samples from the farms of four animal species (dairy cow, chicken, sheep, and pig) in selected areas of Xinjiang, China. Isolates were identified by khe gene amplification and 16S rRNA gene sequencing. Genotyping of K. pneumonia isolates was performed using wzi typing and multilocus sequence typing (MLST). PCR was employed to identify virulence and resistance genes. An antibiotic susceptibility test was conducted using the Kirby-Bauer method. The findings revealed an isolation of 62 K. pneumoniae strains, with an average isolation rate of 19.94%, with the highest proportion originating from cattle sources (33.33%). Over 85.00% of these isolates harbored six virulence genes (wabG, uge, fimH, markD, entB, and ureA); while more than 75.00% of isolates possessed four resistance genes (blaTEM, blaSHV, oqxA, and gyrA). All isolates exhibited complete resistance to ampicillin and demonstrated substantial resistance to sulfisoxazole, amoxicillin/clavulanic acid, and enrofloxacin, with an antibiotic resistance rate of more than 50%. Furthermore, 48.39% (30/62) of isolates were classified as multidrug-resistant (MDR) strains, with a significantly higher isolation rate observed in the swine farms (66.67%) compared to other farms. Genetic characterization revealed the classification of the 62 isolates into 30 distinct wzi allele types or 35 different sequence types (STs). Notably, we identified K. pneumoniae strains of dairy and swine origin belonging to the same ST42 and wzi33-KL64 types, as well as strains of dairy and chicken origin belonging to the same wzi31-KL31-K31 type. These findings emphasize the widespread occurrence of drug-resistant K. pneumoniae across diverse animal sources in Xinjiang, underscoring the high prevalence of multidrug resistance. Additionally, our results suggest the potential for animal-to-animal transmission of K. pneumoniae and there was a correlation between virulence genes and antibiotic resistance genes. Moreover, the current study provides valuable data on the prevalence, antibiotic resistance, and genetic diversity of K. pneumoniae originating from diverse animal sources in Xinjiang, China.

Selenomethionine Inhibits NF-κB-mediated Inflammatory Responses of Bovine Mammary Epithelial Cells Caused by Klebsiella pneumoniae by Increasing Autophagic Flux

Klebsiella pneumoniae (K. pneumoniae) is one of the major pathogens causing bovine clinical mastitis. Autophagy maintains cellular homeostasis and resists excessive inflammation in eukaryotic organisms. Selenomethionine (Se-Met) is commonly used as a source of selenium supplementation for dairy cows. This study aimed to investigate the effects of Se-Met on inflammatory responses mediated by nuclear factor-kappa B (NF-κB) through autophagy. We infected bovine mammary epithelial cell line (MAC-T) with K. pneumoniae and examined the expression of autophagy-related proteins and changes in autophagic vesicles, LC3 puncta, and autophagic flux at various intervals. The results showed that K. pneumoniae activated the early-stage autophagy of MAC-T cells. The levels of LC3-II, Beclin1, and ATG5, as well as the number of LC3 puncta and autophagic vesicles, increased after 2 h post-treatment. However, the late-stage autophagic flux was blocked. Furthermore, the effect of autophagy on NF-κB-mediated inflammation was investigated with different autophagy levels. The findings showed that enhanced autophagy inhibited the K. pneumoniae-induced inflammatory responses of MAC-T cells. The opposite results were found with the inhibition of autophagy. Finally, we examined the effect of Se-Met on NF-κB-mediated inflammation based on autophagy. The results indicated that Se-Met alleviated K. pneumoniae-induced autophagic flux blockage, inhibited NF-κB-mediated inflammation, and decreased the adhesion of K. pneumoniae to MAC-T cells. The inhibitory effect of Se-Met on NF-κB-mediated inflammation could be partially blocked by the autophagy inhibitor chloroquine (CQ). Overall, Se-Met attenuated K. pneumoniae-induced NF-κB-mediated inflammatory responses by enhancing autophagic flux.

Understanding mastitis: Microbiome, control strategies, and prevalence - A comprehensive review

Mastitis significantly affects the udder tissue in dairy cattle, leading to inflammation, discomfort, and a decline in both milk yield and quality. The condition can be attributed to an array of microbial agents that access the mammary gland through multiple pathways. The ramifications of this ailment are not merely confined to animal welfare but extend to the financial viability of the livestock industry. This review offers a historical lens on mastitis, tracing its documentation back to 1851, and examines its global distribution with a focus on regional differences in prevalence and antimicrobial resistance (AMR) patterns. Specific microbial genes and communities implicated in both mastitis and AMR are explored, including Staphylococcus aureus, Streptococcus agalactiae,Streptococcus dysagalactiae, Streptococcus uberis Escherichia coli, Klebsiella pneumoniae, Mycoplasma bovis, Corynebacterium bovis, among others. These microorganisms have evolved diverse strategies to elude host immune responses and neutralize commonly administered antibiotics, complicating management efforts. The review aims a comprehensive overview of the current knowledge and research gaps on mastitis and AMR, and to highlight the need for a One Health approach to address this global health issue. Such an approach entails multi-disciplinary cooperation to foster judicious antibiotic use, enhance preventive measures against mastitis, and bolster surveillance and monitoring of AMR in pathogens responsible for mastitis.

Bovine mastitis, a worldwide impact disease: Prevalence, antimicrobial resistance, and viable alternative approaches

Bovine mastitis is globally considered one of the most important diseases within dairy herds, mainly due to the associated economic losses. The most prevalent etiology are bacteria, classified into contagious and environmental, with Staphylococcus aureus, Streptococcus agalactiae, Streptococcus uberis, Escherichia coli and Klebsiella pneumoniae being the most common pathogens associated with mastitis cases. To date these pathogens are resistant to the most common active ingredients used for mastitis treatment. According to recent studies resistance to new antimicrobials has increased, which is why developing of alternative treatments is imperative. Therefore the present review aims to summarize the reports about bovine mastitis along 10 years, emphasizing bacterial etiology, its epidemiology, and the current situation of antimicrobial resistance, as well as the development of alternative treatments for this pathology. Analyzed data showed that the prevalence of major pathogens associated with bovine mastitis varied according to geographical region. Moreover, these pathogens are classified as multidrug-resistant, since the effectiveness of antimicrobials on them has decreased. To date, several studies have focused on the research of alternative treatments, among them vegetal extracts, essential oils, or peptides. Some other works have reported the application of nanotechnology and polymers against bacteria associated with bovine mastitis. Results demonstrated that these alternatives may be effective on bacteria associated with bovine mastitis.