Evaluation of the biofilm formation capacity of Pasteurella multocida strains isolated from cases of fowl cholera and swine lungs and its relationship with pathogenicity

Role of biofilms in antimicrobial resistance of the bacterial bovine respiratory disease complex

An increase in chronic, non-responsive bovine respiratory disease (BRD) infections in North American feedlot cattle is observed each fall, a time when cattle are administered multiple antimicrobial treatments for BRD. A number of factors are responsible for BRD antimicrobial treatment failure, with formation of biofilms possibly being one. It is widely accepted that biofilms play a role in chronic infections in humans and it has been hypothesized that they are the default lifestyle of most bacteria. However, research on bacterial biofilms associated with livestock is scarce and significant knowledge gaps exist in our understanding of their role in AMR of the bacterial BRD complex. The four main bacterial species of the BRD complex, Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, and Mycoplasma bovis are able to form biofilms in vitro and there is evidence that at least H. somni retains this ability in vivo. However, there is a need to elucidate whether their biofilm-forming ability contributes to pathogenicity and antimicrobial treatment failure of BRD. Overall, a better understanding of the possible role of BRD bacterial biofilms in clinical disease and AMR could assist in the prevention and management of respiratory infections in feedlot cattle. We review and discuss the current knowledge of BRD bacteria biofilm biology, study methodologies, and their possible relationship to AMR.

First study on capsular serotypes and virulence factors of Pasteurella multocida isolates from Phan Rang sheep in Vietnam

Background and Aim: Pasteurella multocida is considered as a main factor mediating pneumonic pasteurellosis in ruminants, including sheep. It is also a current threat to Phan Rang sheep in Vietnam. This study aimed to characterize P. multocida isolated from Phan Rang sheep, their antibiotic resistance profile, and the prevalence of some virulence-associated genes of these strains. Materials and Methods: Bacteria were isolated on brain heart infusion, 10% sheep blood agar plates, and screened by biochemical tests. The polymerase chain reaction technique was used with specific primers to identify P. multocida, the presence of virulence-associated genes, and serotypes of isolates. Antimicrobial susceptibility and biofilm formation of isolates were examined using the disk diffusion method and crystal violet-based method, respectively. Results: A total of 41 P. multocida strains were isolated from 485 samples from clinically sick and healthy sheep. Of the isolates, 58.53% were serotype A, 9.75% were serotype B, and 31.71% were serotype D. Healthy animals were infected with serotype D only. All 15 virulence genes were identified in all strains isolated from clinically sick sheep, while strains isolated from healthy sheep carried 11/15 virulence genes tested. Among virulence-associated genes exbB, exbD, tonB, ompA, oma87, fimA, hgbA, and nanB were detected in over 90% of isolates, whereas hgbB, nanH, tbpA and pfhA were less frequent. Interestingly, pmHAS and tadD were highly prevalent in capsular type A strains, whereas the toxA gene was detected in capsular type D strains only. All of the isolated strains were fully susceptible to enrofloxacin, ciprofloxacin, neomycin, and ofloxacin. About 92.68% were susceptible to chloramphenicol and 90.24% to amikacin, but there was high resistance to erythromycin, tetracycline, and amoxicillin. Our results reveal that 53.65% of 41 isolates could produce biofilm, whereas 46.34% could not. Conclusion: Pasteurella multocida from Phan Rang sheep possess many virulence genes and resistance to several common antibiotics such as erythromycin, tetracycline, and amoxicillin. The results are an important warning regarding antibiotic resistance of P. multocida.

Presence of Polyketide Synthase (PKS) Gene and Counterpart Virulence Determinants in Klebsiella pneumoniae Strains Enhances Colorectal Cancer Progression In-Vitro

Klebsiella pneumoniae (K. pneumoniae) colonizes the human gut and is a causative factor of pyogenic liver abscess (PLA). Retrospective studies conducted on K. pneumoniae PLA patients revealed subsequent CRC development in later years of their life with increasing prevalence of these strains harbouring polyketide synthase (PKS) genes. To our knowledge there are no known studies directly implicating K. pneumoniae with CRC to date. Our aims are to characterize K. pneumoniae isolates from CRC patients and investigate its effects on cell proliferation in vitro. K. pneumoniae isolates were characterized by screening virulence genes including polyketide synthase (PKS), biofilm assay, antibiotic susceptibility, and string test to determine hypervirulent (hvKp) strains. Solubilised antigens of selected K. pneumoniae isolates were co-cultured with primary colon cell lines and CRC cell lines (Stage I-IV) for 48 h. The enhancement of proliferation was measured through MTT and ECIS assay. Twenty-five percent of K. pneumoniae isolates were PKS-positive out of which 50% were hvKp strains. The majority of the isolates were from the more virulent serotype of K1 (30%) and K2 (50%). PKS-positive K. pneumoniae isolates did not possess genes to confer carbapenem resistance but instead were more highly associated with siderophore genes (aerobactin, enterobactin, and yersiniabactin) and allantoin metabolism genes (allS, allS2). Cell proliferation in primary colon, SW1116 (Stage I), and SW480 (Stage II) CRC cell lines were enhanced when co-cultured with PKS-positive K. pneumoniae antigens. ECIS revealed enhanced cell proliferation upon recurrent antigen exposure. This demonstrates the possible role that PKS-positive K. pneumoniae has in exacerbating CRC progression.

First report from Bangladesh on genetic diversity of multidrug-resistant Pasteurella multocida type B:2 in fowl cholera

Background and Aim:

Fowl cholera (FC) caused by Pasteurella multocida is a highly contagious bacterial disease of global importance for poultry production. The severity and incidence of FC caused by P. multocida may vary considerably depending on several factors associated with the host (including species and age of infected birds), the environment, and the bacterial strain. This study aimed to investigate the genetic diversity of multidrug-resistant P. multocida strains isolated from FC outbreaks in laying hens from commercial farms of Bangladesh.

Materials and Methods:

We collected 57 samples of suspected FC, including 36 live and 21 dead laying hens. P. multocida isolates were characterized by biochemical and molecular-biological methods.

Results:

Twenty-two strains of P. multocida were isolated from these samples through phenotypic and genotypic characterization. The strains were grouped into two distinct random amplification of polymorphic DNA (RAPD) biotypes harboring a range of pathogenic genes; exbB, ompH, ptfA, nanB, sodC, and hgbA. In this study, 90.90% and 81.82% P. multocida strains were multidrug-resistant and biofilm formers, respectively. Whole-genome sequencing of the two representative RAPD phylotypes confirmed as P. multocida type B: L2:ST122, harboring a number of virulence factors-associated genes (VFGs), and antimicrobial resistance (AMR) genes (ARGs). In addition, pan-genome analysis revealed 90 unique genes in the genomes of P. multocida predicted to be associated with versatile metabolic functions, pathogenicity, virulence, and AMR.

Conclusion:

This is first-ever report on the association of P. multocida genotype B: L2:ST122 and related VFGs and ARGs in the pathogenesis of FC in laying hens. This study also provides a genetic context for future researches on the evolutionary diversity of P. multocida strains and their host adaptation.

Variability in in vitro biofilm production and antimicrobial sensitivity pattern among Pasteurella multocida strains

Biofilm production, hitherto an uncharacterized feature among circulating Pasteurella multocida strains, was studied along with the antibiotic susceptibility pattern. On the basis of biofilm formation ability, all the strains were categorized into four groups under six different culture conditions: strong biofilm-forming (22%), moderate (19%), weak (51%), and non-adherent (7%). Strains from serogroups A and B formed significant biofilms in at least one culture condition whereas strains from serogroup D were unable to form biofilms. All strains were found to be susceptible to tetracycline. In addition, the correlation between diverse factors (host, capsule type, clinical condition and the tadD gene) as well as antimicrobial susceptibility in biofilm production were analyzed by Joint distribution models, and showed that enrofloxacin and azithromycin resistant strains were positively correlated with strong biofilm production.

Quaternary variations in the structural assembly of N-acetylglucosamine-6-phosphate deacetylase from Pasteurella multocida

N-acetylglucosamine 6-phosphate deacetylase (NagA) catalyzes the conversion of N-acetylglucosamine-6-phosphate to glucosamine-6-phosphate in amino sugar catabolism. This conversion is an essential step in the catabolism of sialic acid in several pathogenic bacteria, including Pasteurella multocida, and thus NagA is identified as a potential drug target. Here, we report the unique structural features of NagA from P. multocida (PmNagA) resolved to 1.95 Å. PmNagA displays an altered quaternary architecture with unique interface interactions compared to its close homolog, the Escherichia coli NagA (EcNagA). We confirmed that the altered quaternary structure is not a crystallographic artifact using single particle electron cryo-microscopy. Analysis of the determined crystal structure reveals a set of hot-spot residues involved in novel interactions at the dimer-dimer interface. PmNagA binds to one Zn2+ ion in the active site and demonstrates kinetic parameters comparable to other bacterial homologs. Kinetic studies reveal that at high substrate concentrations (~10-fold the KM ), the tetrameric PmNagA displays hysteresis similar to its distant neighbor, the dimeric Staphylococcus aureus NagA (SaNagA). Our findings provide key information on structural and functional properties of NagA in P. multocida that could be utilized to design novel antibacterials.

Biofilm Formation by Avian Pathogenic Escherichia coli is Not Related to In Vivo Pathogenicity

Avian pathogenic Escherichia coli (APEC) is one of the pathogens that most concerns the poultry industry worldwide due to the economic losses it can cause. APEC persistence and survival, both in the environment and in the host, may be a consequence of biofilm-producing capabilities. The aim of this study was to evaluate APEC strains' biofilm production and its relationship to in vivo pathogenicity. Two hundred thirty-eight APEC isolates from three different origins (broiler bedding material, cellulite lesions, and respiratory diseases) were selected. The in vivo pathogenicity index (PI) was determined. Biofilm formation was evaluated using a microplate assay with analysis of colony morphology in Congo Red agar in order to detect the phenotypic expression of curli fimbriae and cellulose. Regarding biofilm production, it was observed that 55.8% of the strains produced biofilms. In the morphological test, 88.2% of the isolates expressed one or both components at one of the temperatures at least, and 11.8% of the isolates did not express curli or cellulose. Cellulose production was significantly higher at 25 °C. On the other hand, curli production was significantly higher at 37 °C. The study data indicate that there is no association between biofilm production and in vivo pathogenicity.

Biofilm formation by Salmonella Enteritidis and Salmonella Typhimurium isolated from avian sources is partially related with their in vivo pathogenicity

Salmonella Enteritidis and Salmonella Typhimurium are among the most prevalent serotypes isolated from salmonellosis outbreaks and poultry. Salmonella spp. have the capacity to form biofilms on several surfaces, which can favour survival in hostile environments, such as slaughterhouses. Salmonella strains present differences in pathogenicity. However, there is little information regarding the pathogenicity of S. Enteritidis and S. Typhimurium isolated from avian sources and their relationship to biofilm production. The aim of this study was to use a novel pathogenicity index and a biofilm production assay to evaluate their relationships within these serotypes. In addition, we detected the presence of the spiA and agfA genes in these strains. Biofilm formation was investigated at two temperatures (37 °C and 28 °C) using microtiter plate assay, and the results were compared with the individual pathogenicity index of each strain. PCR was used to detect spiA and agfA, virulence genes associated with biofilm production. S. Enteritidis and S. Typhimurium strains were capable of producing biofilm at 37 °C and 28 °C. Sixty-two percent and 59.5% of S. Enteritidis and 73.8% and 46.2% of S. Typhimurium produced biofilm at 37 °C and 28 °C, respectively. Biofilm production at 37 °C was significantly higher in both serotypes. Only S. Enteritidis was capable of adhering strongly at both temperatures. Biofilm production was related to pathogenicity index only at 28 °C for S. Enteritidis. spiA and agfA were found in almost all strains and were not statistically associated with biofilm production.