Prevalence of Potential Virulence Genes in Klebsiella spp. Isolated from Cows with Clinical Mastitis on Large Chinese Dairy Farms

Comparative genomic analyses of Klebsiella pneumoniae K57 capsule serotypes isolated from bovine mastitis in China

Klebsiella pneumoniae can cause severe clinical mastitis in dairy cows, with K. pneumoniae type K57 (K57-KP) being the most common capsular serotype. To identify virulence factors and antimicrobial-resistance (AMR) genes of K57-KP with varying virulence, Galleria mellonella (greater wax moth) larvae were infected as a screening model to characterize virulence of 90 K57-KP strains, with 10 and 11 strains defined as virulent or attenuated, respectively, based on larval survival rates. Next, virulence of these 21 isolates was subsequently confirmed in adhesion and lactate dehydrogenase release assays, using bovine mammary epithelial cells cultured in vitro. Finally, genes associated with virulence and AMR were characterize with whole-genome sequencing. These 21 K57-KP strains were designated into 16 sequence types based on multi-locus sequence typing and allocated in phylogenetic analysis based on single nucleotide polymorphisms. We found great genetic diversity among isolates. In addition, adhesion-associated genes (e.g., fimA, sfaA, and focA) aminoglycoside-resistance genes (aph(6)-Id, strAB) were associated with virulence. This study provided new knowledge regarding virulence of K57-KP associated with bovine mastitis, which may inform development of novel diagnostic tools and prevention strategies for bovine mastitis.

Effective of phage cocktail against Klebsiella pneumoniae infection of murine mammary glands

Phage therapy has potential to combat antibiotic-resistant bacteria causing bovine mastitis. Our objective was to use 3 Klebsiella lytic phages to create a phage cocktail, and to compare bactericidal activity of this phage cocktail versus an individual phage, both in vitro and in vivo. Based on transmission electron microscopy, phage CM_Kpn_HB154724 belonged to Podoviridae and on double agar plates, it formed translucent plaques on the bacterial lawn of Klebsiella pneumoniae KPHB154724. In one-step growth curves, this phage had a latent period of 40 min, an outbreak period of 40 min, a burst size of 1.2 × 107 PFU/mL, and an optimal multiplicity of infection (MOI) of 1. Furthermore, it was inactivated under extreme conditions (pH ≤ 3.0 or ≥ 12.0 and temperatures of 60 or 70 °C). It had a host range of 90% and had 146 predicted genes (Illumine NovaSeq). Based on histopathology and expression of inflammatory factors interleukin-1β, tumor necrosis factor-α, interleukin-6, and prostaglandin, phage cocktail therapy had better efficiency than an individual phage in K. pneumoniae-infected murine mammary glands. In conclusion, we used 3 Klebsiella lytic phages to create a phage cocktail and confirmed its effectiveness against K. pneumoniae both in vitro (bacterial lawn) and in vivo (infected murine mammary glands).

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.

Multidrug resistant Klebsiella Pneumoniae reservoir and their capsular resistance genes in cow farms of district Peshawar, Pakistan

Klebsiella pneumoniae is a major zoonotic pathogen that causes a variety of severe illnesses as well as mastitis. The distribution of mastitis-causing K. Pneumoniae and its virulence factors vary by country and geographical location. The present study aimed to find out the occurrence of Multidrug-resistant (MDR) K. Pneumoniae and their capsular resistance genes which were undocumented previously in cow farms of district Peshawar, Pakistan. A total of 700 milk samples from symptomatic mastitic cows were screened for MDR K. Pneumoniae. Furthermore, the characterization of capsular resistance genes was done by molecular techniques. Among these samples, K. pneumoniae was found 180/700 (25.7%), while MDR K. pneumoniae was found 80/180 (44.4%). The antibiogram analysis revealed high resistance to Vancomycin (95%) while highly sensitive to Ceftazidime (80%). The distribution of capsular genes shows the most common serotype K2 gene 39/80 (48.7%), followed by serotype K1 gene 34/80 (42.5%), serotype K5 17/80 (21.2%), and serotype K54 13/80 (16.2), respectively. Moreover, the co-occurrence of serotypes K1+K2 was found at 11.25%, KI+K5 was 05%, K1+K54 was 3.75%, and K2+K5 was 7.5%, respectively. A statistically significant association (p ≤ 0.05) was found between predicted and discovered K. pneumoniae values. In conclusion, the presence of MDR K. pneumoniae in combination with capsular genes may be a possible threat to dairy farm animals and humans in Peshawar, Pakistan. It may give us special attention to follow up on hygienic practices in livestock management.

Keeping alert to the hypervirulent K1, K2, K3, K5, K54 and K57 strains of Klebsiella pneumoniae within dairy production process

Klebsiella pneumoniae (Kp) is now recognized as an urgent threat to public health since the emergence of multidrug-resistant and hypervirulent isolates. We identified a hypervirulent K2 isolate from the milk samples possibly associated with an infection incident in children, which raised the alarm to the zoonotic potential of bovine mastitis Kp as a foodborne pathogen. Subsequently, numerous K1, K2, K3, K5, K54 and K57 strains were identified from mastitis milk samples, and showed high pathogenicity in infected mouse. Further analysis based on complete genomes found that these isolates showed closely evolutionary relationships with the human hypervirulent strains in diverse phylogenetic lineages, suggesting their potential risk to public health.

Correlation between Polymerase Chain Reaction Identification of Iron Acquisition Genes and an Iron-Deficient Incubation Test for Klebsiella pneumoniae Isolates from Bovine Mastitis

We investigated the correlation between the polymerase chain reaction (PCR) identification of six virulence genes associated with siderophore activation and the iron-uptake system (iron-acquisition genes; iucA, entB, fepA, ybtS, psn, and kfu) in mastitis-associated Klebsiella pneumoniae (K. pneumoniae). The growth of 37 K. pneumoniae isolates from the milk of cows with mild mastitis reared on Japanese dairy farms between October 2012 and December 2014 was examined by incubation in an iron-deficient medium. entB-, fepA-, or ybtS-positive isolates grew significantly better than entB-, fepA-, or ybtS-negative isolates after incubating in an iron-deficient medium for three days. Interestingly, the growth of isolates with 0 and ≥4 PCR-positive iron-acquisition genes in the iron-deficient medium were significantly different by day 2, while isolates with 2, 3, and ≥4 PCR-positive iron-acquisition genes grew significantly better than those with no PCR-positive iron-acquisition genes by day 3. Based on the correlation between the results of PCR and iron-deficient incubation tests, iron-deficient incubation for three days can be used to estimate the presence or absence of iron-acquisition genes in mastitis-associated K. pneumoniae.

Combating Bovine Mastitis in the Dairy Sector in an Era of Antimicrobial Resistance: Ethno-veterinary Medicinal Option as a Viable Alternative Approach

Bovine mastitis (BM) is the traditional infectious condition in reared cattle which may result in serious repercussions ranging from animal welfare to economic issues. Owing to the high costs associated with preventative practices and therapeutic measures, lower milk output, and early culling, bovine mastitis is accountable for most of the financial losses suffered in cattle farming. Streptococcus agalactiae, Staphylococcus aureus, Streptococcus dysgalactiae and coliform bacteria are the predominant pathogens for bovine mastitis. In addition, the occurrence of BM has been linked to lactation stage and poor management, in the latter case, the poor stabling conditions around udder hygiene. BM occurs throughout the world, with varying rates of Streptococcus agalactiae infection in different regions. Despite the modern techniques, such as the appropriate milking practices that are applied, lower levels of pathogen vulnerability may help to prevent the development of the disease, BM treatment is primarily reliant on antibiotics for both prophylactic and therapeutic purposes. Nevertheless, as a result of the proliferation of bacterial agents to withstand the antibiotic effects, these therapies have frequently proven ineffectual, resulting in persistent BM. Consequently, alternative medicines for the management of udder inflammation have been researched, notably natural compounds derived from plants. This review focuses on BM in terms of its risk factors, pathogenesis, management, the molecular identification of causative agents, as well as the application of ethno-veterinary medicine as an alternative therapy.

Virulence Determinants and Plasmid-Mediated Colistin Resistance mcr Genes in Gram-Negative Bacteria Isolated From Bovine Milk

A major increase of bacterial resistance to colistin, a last-resort treatment for severe infections, was observed globally. Using colistin in livestock rearing is believed to be the ground of mobilized colistin resistance (mcr) gene circulation and is of crucial concern to public health. This study aimed to determine the frequency and virulence characteristics of colistin-resistant Gram-negative bacteria from the milk of mastitic cows and raw unpasteurized milk in Egypt. One hundred and seventeen strains belonging to Enterobacteriaceae (n = 90), Pseudomonas aeruginosa (n = 10), and Aeromonas hydrophila (n = 17) were screened for colistin resistance by antimicrobial susceptibility testing. The genetic characteristics of colistin-resistant strains were investigated for mcr-1-9 genes, phylogenetic groups, and virulence genes. Moreover, we evaluated four commonly used biocides in dairy farms for teat disinfection toward colistin-resistant strains. Multidrug-resistant (MDR) and extensive drug-resistant (XDR) phenotypes were detected in 82.91% (97/117) and 3.42% (4/117) of the isolates, respectively. Of the 117 tested isolates, 61 (52.14%) were colistin resistant (MIC >2 mg/L), distributed as 24/70 (34.29%) from clinical mastitis, 10/11 (90.91%) from subclinical mastitis, and 27/36 (75%) from raw milk. Of these 61 colistin-resistant isolates, 47 (19 from clinical mastitis, 8 from subclinical mastitis, and 20 from raw milk) harbored plasmid-borne mcr genes. The mcr-1 gene was identified in 31.91%, mcr-2 in 29.79%, mcr-3 in 34.04%, and each of mcr-4 and mcr-7 in 2.13% of the colistin-resistant isolates. Among these isolates, 42.55% (20/47) were E. coli, 21.28% (10/47) A. hydrophila, 19.12% (9/47) K. pneumoniae, and 17.02% (8/47) P. aeruginosa. This is the first report of mcr-3 and mcr-7 in P. aeruginosa. Conjugation experiments using the broth-mating technique showed successful transfer of colistin resistance to E. coli J53-recipient strain. Different combinations of virulence genes were observed among colistin-resistant isolates with almost all isolates harboring genes. Hydrogen peroxide has the best efficiency against all bacterial isolates even at a low concentration (10%). In conclusion, the dissemination of mobile colistin resistance mcr gene and its variants between MDR- and XDR-virulent Gram-negative isolates from dairy cattle confirms the spread of mcr genes at all levels; animals, humans, and environmental, and heralds the penetration of the last-resort antimicrobial against MDR bacteria. Consequently, a decision to ban colistin in food animals is urgently required to fight XDR and MDR bacteria.

Virulence profiles of Klebsiella pneumoniae isolated from 2 large dairy farms in China

We recently reported on the diversity of Klebsiella pneumoniae isolated from dairy herds in China. In our previous work, isolates from subclinical mastitis (SCM) had lower indices of diversity when compared with bacteria from other sources, possibly due to a contagious-like spread of udder adapted strains. Here we explored the virulence profile and capsular types of K. pneumoniae isolated from different sources on 2 dairy farms in China. Our overarching goal was to gain insights on the role of virulence genes toward the severity of mastitis caused by K. pneumoniae. A total of 1,484 samples were collected from clinical mastitis (CM; n = 355), SCM (n = 561), bulk tank milk (BTM; n = 130), and environmental and extramammary (EE) sites (n = 438). From those, 431 K. pneumoniae isolates were obtained, including 129, 77, 66, and 159 isolates from CM, SCM, BTM, and EE samples, respectively. Polymerase chain reactions were used to determine the capsular types and to detect potential virulence genes in all isolates. No significant farm effects were observed when comparing the distribution of most virulence genes in K. pneumoniae isolated from each source. K57 was the most prevalent capsular type in K. pneumoniae from all sources, but with increased detection rate in isolates from CM. entB, kfu, fimH1, mrkD, and β-d-lacZ were frequently detected in K. pneumoniae from all sources. β-d-lacZ, entB, and ituA were more prevalent in isolates from CM, whereas kfu, allS, and nif were more frequently detected in isolates from SCM. ybtS, aerobactin, and rpmA had increased prevalence in K. pneumoniae from BTM when compared with bacteria from other sources. No association was detected between virulence genes and the severity of CM. K57 and the nif gene had the highest discriminatory power to classify isolates from CM and SCM, respectively. Based on our findings, it is likely that K57 is the dominant capsular type in K. pneumoniae causing CM in large Chinese dairy herds. Likewise, we demonstrated that β-d-lacZ is disseminated in K. pneumoniae isolated from large Chinese dairy farms, irrespectively of the source of bacteria. Our results also suggest a low contribution of the virulence profile of K. pneumoniae toward CM severity. Finally, the role of nif in increasing the adaptability to the udder and promoting a contagious-like spread of K. pneumoniae warrants further investigation.

Bacteriophage has beneficial effects in a murine model of Klebsiella pneumoniae mastitis

Bovine mastitis caused by Klebsiella pneumoniae is usually treated with antibiotics, thereby potentially increasing antimicrobial resistance. The objective of this study was to evaluate efficacy of a bacteriophage, isolated from dairy farm wastewater, as a treatment for a murine model of K. pneumoniae mastitis. A lytic bacteriophage CM8-1 was isolated, morphological and biological characteristics were assessed with transmission electron microscopy and double-layer plate, and its genome was sequenced and analyzed. Furthermore, effectiveness of this bacteriophage for treatment of a murine model of K. pneumoniae mastitis was evaluated based on the following mammary gland characteristics: morphological changes; number of K. pneumoniae; and mRNA and protein expression of pro-inflammatory factors TNF-α, IL-1β, IL-6, and IL-8. Bacteriophage CM8-1 had an incubation period of 30 min and a burst time of 20 min. Its viability and adsorption were stable at 30 to 50°C, but decreased significantly at >60°C, with no significant change in viability or infectivity at pH 6 to 10. In a murine model of K. pneumoniae mastitis, injecting bacteriophage CM8-1 into the mammary gland 2 h after inoculation with K. pneumoniae resulted in reductions in bacterial counts in the murine mammary gland, improvements in mammary gland tissue morphology, and reductions in mRNA and protein expression of pro-inflammatory factors. Bacteriophage CM8-1 had stable biological characteristics and suppressed K. pneumoniae mastitis when injected into the mammary gland 2 h latera in mice bacterial inoculation.

Klebsiella pneumoniae infection causes mitochondrial damage and dysfunction in bovine mammary epithelial cells

Klebsiella pneumoniae, an important cause of bovine mastitis worldwide, is strongly pathogenic to bovine mammary epithelial cells (bMECs). Our objective was to determine the role of mitochondrial damage in the pathogenicity of K. pneumoniae on bMECs, by assessing several classical indicators of mitochondrial dysfunction, as well as differentially expressed genes (DEGs). Two K. pneumoniae strains (HLJ-D2 and HB-AF5), isolated from cows with clinical mastitis (CM), were used to infect bMECs (MAC-T line) cultured in vitro. In whole-transcriptome analysis of bMECs at 6 h post-infection (hpi), there were 3453 up-regulated and 3470 down-regulated genes for HLJ-D2, whereas for HB-AF5, there were 2891 up-regulated and 3278 down-regulated genes (P < 0.05). Based on GO term enrichment of differentially expressed genes (DEGs), relative to the controls, the primary categories altered in K. pneumoniae-infected bMECs included cellular macromolecule metabolism, metabolic process, binding, molecular function, etc. Infections increased (P < 0.05) malondialdehyde concentrations and formation of reactive oxygen species in bMECs. Additionally, both bacterial strains decreased (P < 0.05) total antioxidant capacity in bMECs at 6 and 12 hpi. Furthermore, infections decreased (P < 0.05) mitochondrial membrane potential and increased (P < 0.01) mitochondrial calcium concentrations. Finally, severe mitochondrial swelling and vacuolation, as well as mitochondrial rupture and cristae degeneration, were detected in infected bMECs. In conclusion, K. pneumoniae infections induced profound mitochondrial damage and dysfunction in bMECs; we inferred that this caused cellular damage and contributes to the pathogenesis of K. pneumoniae-induced CM in dairy cows.

Bacteriophages isolated from dairy farm mitigated Klebsiella pneumoniae-induced inflammation in bovine mammary epithelial cells cultured in vitro

Background

Klebsiella pneumoniae, an environmental pathogen causing mastitis in dairy cattle, is often resistant to antibiotics. K. pneumoniae was used as the host bacteria to support bacteriophage replication; 2 bacteriophages, CM8-1 and SJT-2 were isolated and considered to have therapeutic potential. In the present study, we determined the ability of these 2 bacteriophages to mitigate cytotoxicity, pathomorphological changes, inflammatory responses and apoptosis induced by K. pneumoniae (bacteriophage to K. pneumoniae MOI 1:10) in bovine mammary epithelial cells (bMECs) cultured in vitro.

Results

Bacteriophages reduced bacterial adhesion and invasion and cytotoxicity (lactate dehydrogenase release). Morphological changes in bMECs, including swelling, shrinkage, necrosis and hematoxylin and eosin staining of cytoplasm, were apparent 4 to 8 h after infection with K. pneumoniae, but each bacteriophage significantly suppressed damage and decreased TNF-α and IL-1β concentrations. K. pneumoniae enhanced mRNA expression of TLR4, NF-κB, TNF-α, IL-1β, IL-6, IL-8, caspase-3, caspase-9 and cyt-c in bMECs and increased apoptosis of bMECs, although these effects were mitigated by treatment with either bacteriophage for 8 h.

Conclusions

Bacteriophages CM8-1 and SJT-2 mitigated K. pneumoniae-induced inflammation in bMECs cultured in vitro. Therefore, the potential of these bacteriophages for treating mastitis in cows should be determined in clinical trials.

Genetic diversity and molecular epidemiology of outbreaks of Klebsiella pneumoniae mastitis on two large Chinese dairy farms

Klebsiella pneumoniae is an opportunistic and environmental mastitis-causing pathogen, with potential for contagious transmission. Repetitive element sequence-based PCR was used to determine genetic diversity and explore potential transmission and reservoirs for mastitis caused by K. pneumoniae on 2 large Chinese dairy farms. A total of 1,354 samples was collected from the 2 dairy farms, including milk samples from cows with subclinical and clinical mastitis, bedding, feces, feed, teat skin, and milking liners. Environmental samples were collected from all barns and milking parlors and extramammary samples from randomly selected dairy cows on both farms. In total, 272 and 93 K. pneumoniae isolates were obtained from Farms A and B, respectively (with ~8K and 2K lactating cows, respectively). Isolation rates from clinical mastitis (CM), subclinical mastitis (SCM), and environmental or extramammary samples were 34, 23 and 37%, respectively for Farm A and 42, 3, and 34% for Farm B. The K. pneumoniae isolated from CM milk and extramammary or environmental sources had high genetic diversity (index of diversity >90%) on the 2 farms and from SCM on Farm A. However, on Farm B, 9 SCM isolates were classified as 2 genotypes, resulting in a relatively low index of diversity (Simpson's index of diversity = 0.39; 95% CI = 0.08-0.70). Genotypes of K. pneumoniae causing mastitis were commonly detected in feces, bedding, and milking liners (Farm A), or from teat skin, sawdust bedding, and feed (Farm B). Based on its high level of genetic diversity, we inferred K. pneumoniae was an opportunistic and environmental pathogen causing outbreaks of CM on these 2 large Chinese dairy farms. Nevertheless, that only a few genotypes caused SCM implied some strains had increased udder adaptability and a contagious nature or a common extramammary source. Finally, control of intramammary infections caused by K. pneumoniae on large Chinese dairy farms must consider farm-level predictors, as the 2 outbreaks had distinct potential environmental sources of infection.

Klebsiella pneumoniae isolated from bovine mastitis is cytopathogenic for bovine mammary epithelial cells

Klebsiella pneumoniae, a common cause of clinical mastitis (CM) in dairy cows, can cause severe clinical symptoms. However, its pathogenicity in the bovine mammary gland is not well understood. Our objectives were to establish an in vitro infection model of K. pneumoniae on bovine mammary epithelial cells (bMEC) to assess (1) cytopathogenicity (adhesive and invasive ability, damage and apoptosis, pro-inflammatory effects) of K. pneumoniae on bMEC and (2) the role of hypermucoviscous (HMV) phenotype on cytopathogenicity. Two K. pneumoniae isolates from CM cows, 1 HMV and 1 non-HMV, were used to infect bMEC. Adhesion and invasion ability, release of lactate dehydrogenase (LDH), ultrastructural morphology, apoptosis, transcriptional expression of pro-inflammatory genes and production of pro-inflammatory cytokines were characterized at various intervals. Both K. pneumoniae isolates rapidly adhered to and invaded bMEC within 1 h post infection (pi), causing ultrastructural damage (swelling of mitochondria and vesicle formation on cell surface) after 3 h pi and apoptotic death after 9 h pi. In addition, K. pneumoniae promoted transcriptional expression of pro-inflammatory genes IL-6, IL-8, IL-1β, and tumor necrosis factor (TNF)-α and production of IL-8, IL-1β, and TNF-α cytokines. Compared with non-HMV K. pneumoniae, the HMV isolate had lower adhesive and invasive abilities but caused more serious cellular damage. In conclusion, K. pneumoniae was cytopathogenic on bMEC and induced a pro-inflammatory response; however, the HMV phenotype did not have a key role in pathogenicity. Therefore, more attention should be paid to milk loss, and targeted prevention and treatment strategies should be implemented in Klebsiella mastitis episodes.