Efficacy of antimicrobial therapy for bovine acute <i>Klebsiella pneumoniae </i>mastitis

The purpose of this retrospective study was to assess the efficacy of antimicrobial therapy for bovine acute Klebsiella pneumoniae mastitis. We evaluated data from cattle in Ehime, Japan, with naturally occurring acute mastitis due to K. pneumoniae (n=208) or Escherichia coli (n=201). Survival was significantly shorter in cattle with acute K. pneumoniae mastitis (median, 76 days) compared with the disease caused by E. coli (median 464 days). In 2004–2008, because both species were highly susceptible to cefazolin, cases of K. pneumoniae and E. coli mastitis were treated solely with cefazolin, yielding clinical cure rates of 52.8% for K. pneumoniae and 86.0% for E. coli. However, since 2009, the efficacy of treatment of K. pneumoniae mastitis with cefazolin alone has decreased. When cefazolin administered on the first disease day led to clinical improvement, treatment with cefazolin was continued. However, when cefazolin administered on the first disease day failed to yield clinical improvement, the antibiotic was switched to a fluoroquinolone on the second day, resulting in cure rates of 76.7% for K. pneumoniae and 80.0% for E. coli. These findings suggest that, when the first-line drug (e.g., cefazolin) is ineffective, promptly changing to a second-line drug (e.g., a fluoroquinolone) increases the cure rate for bovine K. pneumoniae mastitis.

An overview on mastitis-associated Escherichia coli: Pathogenicity, host immunity and the use of alternative therapies

Escherichia coli is one of the leading causes of bovine mastitis; it can cause sub-clinical, and clinical mastitis characterized by systemic changes, abnormal appearance of milk, and udder inflammation. E. coli pathogenicity in the bovine udder is due to the interaction between its virulence factors and the host factors; it was also linked to the presence of a new pathotype termed mammary pathogenic E. coli (MPEC). However, the presence of this pathotype is commonly debated. Its main virulence factor is the lipopolysaccharide (LPS) that is responsible for causing an endotoxic shock, and inducing a strong immune response by binding to the toll-like receptor 4 (TLR4), and stimulating the expression of chemokines (such as IL-8, and RANTES) and pro-inflammatory cytokines (such as IL-6, and IL-1β). This strong immune response could be used to develop alternative and safe approaches to control E. coli causing bovine mastitis by targeting pro-inflammatory cytokines that can damage the host tissue. The need for alternative treatments against E. coli is due to its ability to resist many conventional antibiotics, which is a huge challenge for curing ill animals. Therefore, the aim of this review was to highlight the pathogenicity of E. coli in the mammary gland, discuss the presence of the new putative pathotype, the mammary pathogenic E. coli (MPEC) pathotype, study the host's immune response, and the alternative treatments that are used against mastitis-associated E. coli.

Shielding Effect of Escherichia coli O-Antigen Polysaccharide on J5-Induced Cross-Reactive Antibodies

Despite intensive research, mastitis remains an important disease in dairy cattle with a significant impact on animal welfare, use of antibiotics, and, in the end, the economy of dairy farms. Although vaccines available so far have shown limited efficacy against coliform mastitis, vaccination is considered one of the measures that could limit the consequences of mastitis.

Escherichia coli is the leading cause of severe mastitis in dairy farms. As E. coli mastitis is refractory to the hygienic control measures adapted to contagious mastitis, efficient vaccines are in demand. Existing mastitis vaccines, based on the use of killed rough E. coli J5 as the antigen, aim at inducing phagocytosis by neutrophils. We assessed the binding of J5-induced antibodies to isogenic rough and smooth strains along with a panel of mastitis-associated E. coli. Analysis by enzyme-linked immunosorbent assay revealed that antibodies to OmpA or killed J5 bind readily to rough E. coli but poorly to smooth strains. Flow cytometry analysis indicated that immunization with J5 induced antibodies that cross-reacted with rough E. coli strains but with only a small subpopulation of smooth strains. We identified type 1 fimbriae as the target of most antibodies cross-reacting with the smooth strains. These results suggest that the O-polysaccharide of lipopolysaccharide shields the outer membrane antigens and that only fiber antigens protruding at the bacterial surface can elicit antibodies reacting with mastitis-associated E. coli. We evaluated J5-induced antibodies in an opsonophagocytic killing assay with bovine neutrophils. J5 immune serum was not more efficient than preimmune serum, showing that immunization did not improve on the already high efficiency of naturally acquired antibodies to E. coli. In conclusion, it is unlikely that the efficiency of J5 vaccines is related to the induction of opsonic antibodies. Consequently, other research directions, such as cell-mediated immunity, should be explored to improve E. coli mastitis vaccines.

IMPORTANCE Despite intensive research, mastitis remains an important disease in dairy cattle with a significant impact on animal welfare, use of antibiotics, and, in the end, the economy of dairy farms. Although vaccines available so far have shown limited efficacy against coliform mastitis, vaccination is considered one of the measures that could limit the consequences of mastitis. One reason for the lack of efficiency of current vaccines likely stems from the current evaluation of vaccines that relies mostly on measuring antibody production against vaccine antigens. This report clearly shows that vaccine-induced antibodies fail to bind to most mastitis-associated E. coli strains because of the presence of an O-antigen and, thus, do not allow for improved phagocytosis of pathogens. As a consequence, this report calls for revised criteria for the evaluation of vaccines and suggests that cell-mediated immunity should be targeted by new vaccinal strategies. More generally, these results could be extended to other vaccine development strategies targeting coliform bacteria.

Enterobactin Deficiency in a Coliform Mastitis Isolate Decreases Its Fitness in a Murine Model: A Preliminary Host-Pathogen Interaction Study

Iron is an essential nutrient for bacterial growth. Therefore, bacteria have evolved chelation mechanisms to acquire iron for their survival. Enterobactin, a chelator with high affinity for ferric iron, is secreted by Escherichia coli and contributes to its improved bacterial fitness. In this preliminary study, we evaluated enterobactin deficiency both in vitro and in vivo in the context of E. coli mastitis. Firstly, we showed that expression of lipocalin 2, a protein produced by the host that is able to both bind and deplete enterobactin, is increased upon E. coli infection in the cow's mastitic mammary gland. Secondly, we demonstrated in vitro that enterobactin deficiency does not alter interleukin (IL)-8 expression in bovine mammary epithelial cells and its associated neutrophil recruitment. However, a significantly increased reactive oxygen species production of these neutrophils was observed. Thirdly, we showed there was no significant difference in bacterial in vitro growth between the enterobactin-deficient mutant and its wild-type counterpart. However, when further explored in a murine model for bovine mastitis, the enterobactin-deficient mutant vs. the wild-type strain revealed a significant reduction of the bacterial load and, consequently, a decrease in pro-inflammatory cytokines (IL-1α,-1β,-4,-6, and-8). A reduced neutrophilic influx was also observed immunohistochemically. These findings therefore identify interference of the enterobactin iron-scavenging mechanism as a potential measure to decrease the fitness of E. coli in the mastitic mammary gland.

A comparative study of the complete lipopolysaccharide structures and biosynthesis loci of Bordetella avium, B. hinzii, and B. trematum

A dozen species of human and animal pathogens have been described to date in the Bordetella genus, with the majority being respiratory tract pathogens. Bordetella avium lipopolysaccharides have been shown to be important virulence factors for this bird pathogen. B. hinzii is closely related to the B. avium species, but has also been isolated from humans. B. trematum is associated to ear and blood infections in humans. Its lipid A structure, the biological active moiety of LPS, was found to be closely related to those of B. avium and B. hinzii. It is important to unveil the subtle structural modifications orchestrated during the LPS biosynthetic pathway to better understand host adaptation. The present data are also important in the context of deciphering the virulence pathways of this important genus containing the major pathogens B. pertussis and B. parapertussis, responsible for whooping cough. We recently reported the isolated lipid A structures of the three presented species, following the previously identified O-chain structures. In the present study, we provide details on the free and O-chain-linked core oligosaccharides which were required to characterize the complete LPS structures. Data are presented here in relation to relevant biosynthesis genes. The present characterization of the three species is well illustrated by Matrix Assisted Laser Desorption Mass Spectrometry experiments, and data were obtained mainly on native LPS molecules for the first time.

Variability in Characterizing Escherichia coli from Cattle Feces: A Cautionary Tale

Shiga toxin-producing Escherichia coli (STEC) are diverse bacteria, with seven serogroups (O26, O45, O103, O111, O121, O145, O157; "Top 7") of interest due to their predominance in human disease. Confirmation of STEC relies on a combination of culturing, immunological and molecular assays, but no single gold standard for identification exists. In this study, we compared analysis of STEC between three independent laboratories (LAB) using different methodologies. In LAB A, colonies of Top 7 were picked after serogroup-specific immunomagnetic separation of feces from western-Canadian slaughter cattle. A fraction of each colony was tested by PCR (stx1, stx2, eae, O group), and Top 7 isolates were saved as glycerol stocks (n = 689). In LAB B, a subsample of isolates (n = 171) were evaluated for stx1 and stx2 using different primer sets. For this, approximately half of the PCR were performed using original DNA template provided by LAB A and half using DNA extracted from sub-cultured isolates. All Top 7 isolates were sub-cultured by LAB A and shipped to LAB C for traditional serotyping (TS) to determine O and H groups, with PCR-confirmation of virulence genes using a third set of primers. By TS, 76% of O groups (525/689) matched PCR-determined O groups. Lowest proportions (p < 0.05) of O group matches between PCR and TS (62.6% and 69.8%) occurred for O26 and O45 serogroups, respectively. PCR-detection of stx differed most between LAB A and LAB C. Excluding isolates where O groups by PCR and TS did not match, detection of stx1 was most consistent (p < 0.01) for O111 and O157:H7/NM. In contrast, for O45 and O103, stx1 was detected in >65% of isolates by LAB A and <5% by LAB C. Stx2 was only detected by LAB C in isolates of serogroups O121, O145, and O157:H7/NM. LAB B also detected stx2 in O26 and O157:H12/H29, while LAB A detected stx2 in all serogroups. Excluding O111 and O157:H7/NM, marked changes in stx detection were observed between initial isolation and sub-cultures of the same isolate. While multiple explanations exist for discordant O-typing between PCR and TS and for differences in stx detection across labs, these data suggest that assays for STEC classification may require re-evaluation and/or standardization.

Early transcriptional events in the udder and teat after intra-mammary Escherichia coli and Staphylococcus aureus challenge

Intra-mammary bacterial infections can result in harmful clinical mastitis or subclinical mastitis with persistent infections. Research during the last decades closely examined the pathophysiology of inflamed udders. Initial events after pathogen perception but before the onset of mastitis have not been examined in vivo. The objective of this study was to develop a mastitis model in cows by monitoring initial transcriptional pathogen-specific host response before clinical signs occur. We applied a short-term infection model to analyse transcripts encoding chemokines, cytokines and antimicrobial molecules in the teat cistern (TC) and lobulo-alveolar parenchyma (LP) up to 3 h after challenge with E. and Staphylococcus aureus. Both pathogens elicited an immune reaction by 1 h after challenge. Escherichia coli induced all analysed factors ( CCL20, CXCL8, TNF, IL6, IL12B, IL10, LAP, S100A9); however, S. aureus failed to induce IL12B, IL10, LAP and S100A9 expression. The E. coli-induced up-regulation was 25–105 times greater than that after S. aureus challenge. Almost all the responses were restricted to the TC. The short-term mastitis model demonstrates that a divergent pathogen-specific response is generated during the first h. It confirms that the first transcripts are generated in the TC prior to a response in the LP.

Serotype O:8 isolates in the Yersinia pseudotuberculosis complex have different O-antigen gene clusters and produce various forms of rough LPS

In Yersinia pseudotuberculosis complex, the O-antigen of LPS is used for the serological characterization of strains, and 21 serotypes have been identified to date. The O-antigen biosynthesis gene cluster and corresponding O-antigen structure have been described for 18, leaving O:8, O:13 and O:14 unresolved. In this study, two O:8 isolates were examined. The O-antigen gene cluster sequence of strain 151 was near identical to serotype O:4a, though a frame-shift mutation was found in ddhD, while No. 6 was different to 151 and carried the O:1b gene cluster. Structural analysis revealed that No. 6 produced a deeply truncated LPS, suggesting a mutation within the waaF gene. Both ddhD and waaF were cloned and expressed in 151 and No. 6 strains, respectively, and it appeared that expression of ddhD gene in strain 151 restored the O-antigen on LPS, while waaF in No. 6 resulted in an LPS truncated less severely but still without the O-antigen, suggesting that other mutations occurred in this strain. Thus, both O:8 isolates were found to be spontaneous O-antigen-negative mutants derived from other validated serotypes, and we propose to remove this serotype from the O-serotyping scheme, as the O:8 serological specificity is not based on the O-antigen.

Comparison of O-Antigen Gene Clusters of All O-Serogroups of Escherichia coli and Proposal for Adopting a New Nomenclature for O-Typing

Escherichia coli strains are classified based on O-antigens that are components of the lipopolysaccharide (LPS) in the cell envelope. O-antigens are important virulence factors, targets of both the innate and adaptive immune system, and play a role in host-pathogen interactions. Because they are highly immunogenic and display antigenic specificity unique for each strain, O-antigens are the biomarkers for designating O-types. Immunologically, 185 O-serogroups and 11 OX-groups exist for classification. Conventional serotyping for O-typing entails agglutination reactions between the O-antigen and antisera generated against each O-group. The procedure is labor intensive, not always accurate, and exhibits equivocal results. In this report, we present the sequences of 71 O-antigen gene clusters (O-AGC) and a comparison of all 196 O- and OX-groups. Many of the designated O-types, applied for classification over several decades, exhibited similar nucleotide sequences of the O-AGCs and cross-reacted serologically. Some O-AGCs carried insertion sequences and others had only a few nucleotide differences between them. Thus, based on these findings, it is proposed that several of the E. coli O-groups may be merged. Knowledge of the O-AGC sequences facilitates the development of molecular diagnostic platforms that are rapid, accurate, and reliable that can replace conventional serotyping. Additionally, with the scientific knowledge presented, new frontiers in the discovery of biomarkers, understanding the roles of O-antigens in the innate and adaptive immune system and pathogenesis, the development of glycoconjugate vaccines, and other investigations, can be explored.

Location-specific expression of chemokines, TNF-α and S100 proteins in a teat explant model

The distal compartments of the udder are the first to interact with invading pathogens. The regulatory and effector functions of two major teat regions [Fürstenberg's rosette (FR); teat cistern (TC)] are largely unknown. The objective of this study was to establish an in vitro model with explants of the FR and the TC to analyse their response towards Escherichia coli LPS and Staphylococcus aureus lipoteichoic acid (LTA). Quantitative stereological analysis confirmed differences in the cellular composition of FR and TC explants. Chemokine (CXCL8, CCL5, CCL20) and TNF-α mRNA were expressed at low levels in both locations. Explant stimulation with LPS increased the mRNA abundance of all tested chemokines and TNF-α. Stimulation with LTA only induced CCL20 and CXCL8. LPS- and LTA-stimulated explant supernatants contained CXCL8 and CXCL3. Supernatants significantly attracted neutrophils in vitro. Compared with TC, the FR showed high constitutive mRNA expression of S100 proteins (A8, A9, A12). In the TC, both LPS and LTA significantly induced S100A8, whereas S100A9 and S100A12 expression was only induced by LPS. The novel model system underpins the role of the teat for recognising pathogens and shaping a pathogen- and location-specific immune response.

Diagnostic potential of monoclonal antibodies specific to the unique O-antigen of multidrug-resistant epidemic Escherichia coli clone ST131-O25b:H4

The Escherichia coli lineage sequence type 131 (ST131)-O25b:H4 is a globally spread multidrug-resistant clone responsible for a great proportion of extraintestinal infections. Driven by the significant medical needs associated with this successful pathogenic lineage, we generated murine monoclonal antibodies (MAbs) against its lipopolysaccharide (LPS) O25b antigen in order to develop quick diagnostic tests. Murine monoclonal antibodies were generated by immunizing mice with whole killed nonencapsulated ST131-O25b E. coli cells and screening hybridoma supernatants for binding to purified LPS molecules obtained from an E. coli ST131-O25b clinical isolate. The MAbs selected for further study bound to the surface of live E. coli O25b strains irrespective of the capsular type expressed, while they did not bind to bacteria or purified LPS from other serotypes, including the related classical O25 antigen (O25a). Using these specific MAbs, we developed a latex bead-based agglutination assay that has greater specificity and is quicker and simpler than the currently available typing methods. The high specificities of these MAbs can be explained by the novel structure of the O25b repeating unit elucidated in this article. Based on comparative analysis by nuclear magnetic resonance (NMR) and mass spectrometry, the N-acetyl-fucose in the O25a O-antigen had been replaced by O-acetyl-rhamnose in the O25b repeating unit. The genetic determinants responsible for this structural variation were identified by aligning the corresponding genetic loci and were confirmed by trans-complementation of a rough mutant by the subserotype-specific fragments of the rfb operons.

O-antigen polymerase adopts a distributive mechanism for lipopolysaccharide biosynthesis

Bacterial lipopolysaccharide (LPS) is an essential cell envelope component for gram-negative bacteria. As the most variable region of LPS, O antigens serve as important virulence determinants for many bacteria and represent a promising carbohydrate source for glycoconjugate vaccines. In the Wzy-dependent O-antigen biosynthetic pathway, the integral membrane protein Wzy was shown to be the sole enzyme responsible for polymerization of O-repeat unit. Its catalytic mechanism, however, remains elusive. Herein, Wzy was successfully overexpressed in Escherichia coli with an N-terminal His10-tag. Blue native polyacrylamide gel electrophoresis (BN-PAGE) revealed that the Wzy protein exists in its native confirmation as a dimer. Subsequently, we chemo-enzymatically synthesized the substrates of Wzy, the lipid-PP-linked repeat units. Together with an optimized O-antigen visualization method, we monitored the production of reaction intermediates at varying times. We present here our result as the first biochemical evidence that Wzy functions in a distributive manner.

Structural studies of the O-antigenic polysaccharide of the bovine mastitis isolate Escherichia coli serotype O174

Escherichia coli is one of the major causative agents of bovine mastitis, a disease affecting dairy herds. The lipopolysaccharide (LPS) of E. coli was plays a prominent role during infection. Here, we report on the O-antigen chemical structure of the LPS from Escherichia coli strain 2188 (serotype O174:H28) isolated from a mastitis-diseased cow. The structure of the OPS was analyzed by 1 and 2D NMR spectroscopy, and methylation analysis, which identified the branched repeating tetrasaccharide biological unit. [structure: see text].

The rapidly emerging ESBL-producing Escherichia coli O25-ST131 clone carries LPS core synthesis genes of the K-12 type

The clone Escherichia coli O25 ST131, typically producing extended-spectrum beta-lactamases (ESBLs), has spread globally and became the dominant type among extraintestinal isolates at many parts of the world. However, the reasons behind the emergence and success of this clone are only partially understood. We compared the core type genes by PCR of ESBL-producing and ESBL-nonproducing strains isolated from urinary tract infections in the United Arab Emirates and found a surprisingly high frequency of the K-12 core type (44.6%) among members of the former group, while in the latter one, it was as low (3.7%), as reported earlier. The high figure was almost entirely attributable to the presence of members of the clone O25 ST131 among ESBL producers. Strains from the same clone isolated in Europe also carried the K-12 core type genes. Sequencing the entire core operon of an O25 ST131 isolate revealed a high level of similarity to known K-12 core gene sequences and an almost complete identity with a recently sequenced non-O25 ST131 fecal isolate. The exact chemical structure and whether and how this unusual core type contributed to the sudden emergence of ST131 require further investigations.

Detection of O antigens in Escherichia coli

Lipopolysaccharide on the surface of Escherichia coli constitutes the O antigens which are important virulence factors that are targets of both the innate and adaptive immune systems and play a major role in host-pathogen interactions. O antigens are responsible for antigenic specificity of the strain and determine the O serogroup. The designation of O serogroups is important for classifying E. coli strains, for epidemiological studies, in tracing the source of outbreaks of gastrointestinal or other illness, and for linking the source to the infection. For conventional serogroup identification, serotyping by agglutination reactions against antisera developed for each of the O serogroups has been used. In the last decade, many O-antigen gene clusters that encode for the enzymes responsible for the synthesis of the variable oligosaccharide region on the surface of the bacteria have been sequenced and characterized. Unique gene sequences within the O-antigen gene clusters have been targeted for identification and detection of many O groups using the polymerase chain reaction and microarrays. This review summarizes current knowledge on the DNA sequences of the O-antigen gene clusters, genetic-based methods for O-group determination and detection of pathogenic E. coli based on O-antigen and virulence gene detection, and provides perspectives on future developments in the field.