Moraxella bovis, Moraxella ovis and Moraxella bovoculi: biofilm formation and lysozyme activity.

AIMS: This study aimed to verify the formation of biofilms by Moraxella bovis, Moraxella ovis and Moraxella bovoculi isolates from ruminants. In addition, the lysozyme activity against the isolates of M. bovis, M. ovis and M. bovoculi in free form and in biofilms was determined. METHODS AND RESULTS: In this study, 54 isolates of Moraxella sp. obtained from bovine and ovine clinical samples were evaluated in vitro for capacity of biofilm formation and lysozyme susceptibility in planktonic and sessile cells. In addition, biofilms produced by four Moraxella sp. isolates were visualized under scanning electron microscope (SEM). It was possible to demonstrate, for the first time, the ability to form biofilms by M. ovis and M. bovoculi. The isolates of Moraxella sp. have the capacity to form biofilms in different intensities, varying among weak, moderate and strong. It was verified that the lysozyme shows activity on Moraxella sp. in planktonic form. However, on biofilms there was a reduction in the production, but without impairing its formation, and on consolidated biofilms the lysozyme did not have the capacity to eradicate the preformed biofilms. CONCLUSIONS: This work shows the capacity of biofilm formation by Moraxella sp. of veterinary importance. The lysozyme susceptibility of Moraxella sp. in planktonic form shows that this enzyme has bacteriostatic activity on this micro-organism and it reduced the production of biofilms. SIGNIFICANCE AND IMPACT OF THE STUDY: Based on the results, it is possible to infer that the biofilm formation capacity by Moraxella sp. and the resistance to lysozyme concentrations equal to or greater than the physiological levels of the ruminant tear may be linked not only to the capacity to colonize the conjunctiva, but also to remain in this place even after healing of the lesions, being a reservoir of Moraxella sp. in a herd.

Evaluation of biofilm-forming capacity of Moraxella bovis, the primary causative agent of infectious bovine keratoconjunctivitis.

The difficulties in preventing and treating infectious bovine keratoconjunctivitis (IBK) and the consequent impact on the cattle industry worldwide emphasize the need to better understand this infectious process along with the biology of Moraxella bovis, its primary causative agent. Although there is increasing evidence that bacterial biofilms participate in a variety of ocular infections by direct biofilm formation on the surfaces of the eye, IBK has not been considered as a biofilm-based disease so far, and even more, no information is currently available regarding the ability of M. bovis to adopt a biofilm lifestyle. In the present research, we demonstrated the capacity of M. bovis clinical isolates and reference strains to form biofilms on different abiotic surfaces and culture conditions, and provided qualitative and quantitative information on the biofilm growth and architecture of mature biofilms. In addition, our data indicated that the type IV pili play a critical role in the biofilm formation in vitro. Most significantly, we proved that through exposure to MgCl2 type IV pili are removed from the cell surface, not only preventing M. bovis biofilm formation but also disassembling preformed biofilms. These results could constitute a new approach in the understanding of M. bovis colonization process in cattle eye and/or nasal cavity, and may aid in the development of future antimicrobial strategies for the control of IBK.

Assessment of Bdellovibrio bacteriovorus 109J killing of Moraxella bovis in an in vitro model of infectious bovine keratoconjunctivitis.

The objective of this study was to determine the potential of Bdellovibrio bacteriovorus 109J as an alternative non-chemotherapeutic treatment of infectious bovine keratoconjunctivitis (IBK). To accomplish this, various parameters of B. bacteriovorus predation of Moraxella bovis were determined in vitro. Initial passage of B. bacteriovorus using M. bovis as prey required 10 d for active cultures to develop compared with 2 d for culture on normal Escherichia coli prey; however by the 5th passage, time to active predatory morphology was reduced to 2 d. This high passage B. bacteriovorus culture [1 × 10(10) plaque forming units (PFU)/mL] killed 76% of M. bovis [1 × 10(7) colony forming units (CFU)/mL] present in suspension broth in a 4 h assay. The minimal level of M. bovis supporting B. bacteriovorus predation was 1 × 10(4) CFU/mL. To assess the ability of B. bacteriovorus to kill M. bovis on an epithelial surface mimicking IBK, an in vitro assay with Madin-Darby bovine kidney (MDBK) cells inoculated with 4 × 10(7) CFU/mL M. bovis was used. Treatment with a B. bacteriovorus suspension (1.6 × 10(11) PFU/mL) decreased adherence of M. bovis to MDBK cells by 6-fold at 12 h of treatment, as well as decreased the number of unattached M. bovis cells by 1.4-fold. This study demonstrates that B. bacteriovorus has potential as an effective biological control of M. bovis at levels likely present in IBK-infected corneal epithelia and ocular secretions.

Vaccine against infectious bovine keratoconjunctivitis: a new approach to optimize the production of highly piliated Moraxella bovis cells.

Pili are the principal antigens and virulence factors of Moraxella bovis, the etiological agent of infectious bovine keratoconjunctivitis (IBK). Although it has been reported that the low efficacy of whole cell vaccines against IBK is mainly due to the difficulties in keeping the cellular piliation level of M. bovis during the growth of bacteria in stirred bioreactors, the problem has not yet been overcome because the mechanisms involved in the loss of piliation are still not fully clarified. In this work we found that during the culture of M. bovis in liquid media, around 15% of the cells changed from piliated to non-piliated phenotypes at the end of the growth. Nevertheless, we demonstrated that the main cause of cellular piliation loss in M. bovis growing in stirred and/or sparged bioreactors is due to shear forces, which are a function of the volumetric gassed power drawn (P(g)V(-1)). Therefore, we tested here the use of bubble column bioreactors to protect M. bovis cell-bound pili from mechanical agitation damage effects. These bioreactors operated at a superficial air velocity of 0.0065 m s(-1) yielded a cellular piliation level of 25%, in contrast to 1% obtained for stirred bioreactors. The addition of carboxymethylcellulose (CMC) at 0.10% (w v(-1)) to culture medium proved to be suitable to improve the final piliation level (65%). We demonstrated by FT-IR spectroscopy and ELISA technique, that this chemical additive has a pili protective role interacting with the cells but without affecting pili antigenic properties.

Q pili enhance the attachment of Moraxella bovis to bovine corneas in vitro.

Moraxella bovis, the causative agent of infectious bovine keratoconjunctivitis, exhibits several virulence factors, including pili, haemolysin, leukotoxin, and proteases. The pili are filamentous appendages which mediate bacterial adherence. Prior studies have shown that Q-piliated M. bovis Epp63 are more infectious and more pathogenic than I-piliated and non-piliated isogenic variants, suggesting that Q pili per se, or traits associated with Q-pilin expression, promote the early association of Q-piliated bacteria with bovine corneal tissue. In order to better evaluate the role of Q pili in M. bovis attachment, several M. bovis strains and a recombinant P. aeruginosa strain which elaborates M. bovis Q pili but not P. aeruginosa PAK pili, were evaluated using an in vitro corneal attachment assay. For each strain tested, piliated organisms attached better than non-piliated bacteria. M. bovis Epp63 Q-piliated bacteria adhered better than either the I-piliated or non-piliated isogenic variants. Finally, recombinant P. aeruginosa organisms elaborating M. bovis Q pili adhered better than the parent P. aeruginosa strain which did not produce M. bovis pili. These results indicate that the presence of pili, especially Q pili, enhances the attachment of bacteria to bovine cornea in vitro.

Bacterial differentiation within Moraxella bovis colonies growing at the interface of the agar medium with the Petri dish.

Moraxella bovis was found to colonize the interface between agar and the polystyrene Petri dish, producing circular colonies when the inoculum was stabbed at a single point. The bacteria occurred in a thin layer of nearly uniform thickness, and colonial expansion occurred in at least two temporal phases. In the first phase, the radial colonial expansion was slow and non-linear. In the second phase, the radial expansion was linear. The interfacial colonies possessed three characteristic concentric growth zones. At the periphery was a narrow ring zone that enclosed another wider ring zone, which, in turn, surrounded a central circular zone. Different bacterial phase variants were recovered from these zones. The two outer ring zones yielded bacteria that formed agar surface colonies of spreading-corroding morphology, while cells from the innermost zone always yielded colonies with a different morphology. The uniform thickness of the colonies implied that replication was restricted to the outermost ring, and that the bacteria within the inner ring and inner circle had entered a quiescent state. The inner ring appeared to represent the lag in time needed for the replicative form to differentiate into the quiescent form. A different kind of variant was associated with wedge-shaped sectors within the colonies. The greatest number of these clonal variants appeared shortly after inoculation and their frequency decreased after the onset of linear growth. The period of slowest colonization coincided with highest frequency of clonal variant expression. It is proposed that the proliferative rate of the parental bacterial population exerted selective pressure on the expression of new clonal variants.