Source or Sink: Examining the Role of Biofilms in Transmission of Mycobacterium spp. in Laboratory Zebrafish

Abstract

Zebrafish health is a primary research concern because diseases can have unintended impacts on experimental endpoints. Ideally, research would be conducted using disease-free fish or fish with known disease status. Mycobacteriosis is a common bacterial disease in wild and captive fishes, including zebrafish. Despite its prevalence, the dynamics of transmission and potential sources of mycobacterial infections in zebrafish are only partially understood. One suspected natural infection source is surface biofilms on tanks and other system components. This study investigates the role that tank biofilms play in mycobacteriosis in laboratory zebrafish by evaluating the establishment of biofilms from bacteria shed from fish, and conversely, the acquisition of infections in fish from surface biofilms. We found that zebrafish infected with Mycobacterium chelonae shed bacteria through feces, and bacteria are transmitted to tank biofilms from one to 16 weeks postinfection. We also found that zebrafish acquire M. chelonae infections as soon as 2 weeks when introduced to tanks with established M. chelonae biofilms. The results from this study highlight the role that tank biofilms play as both a reservoir and source of mycobacterial infections in zebrafish. Results support the inclusion of biofilm surveillance and prevention as part of a disease control program in zebrafish research facilities.

Keywords: spp.; biofilm; husbandry; zebrafish.

FIG. 1.

Prevalence of M. chelonae infections for the two modes of infection [oral Gelly Belly (GB) infection vs. IP injection infection]. Different diagnostic methods include histology (white bars), in vivo GFP screening (gray bars, and liver/spleen culture (black bars). Statistically significant differences between diagnostic methods used are indicated (+), as well as those between sexes are also indicated (*). GFP, green fluorescence protein.

FIG. 2.

Examples of the different diagnostic methods used in this study. Comparative brightfield and FITC screening was used to identify areas of GFP expression (compare A, D, G to B, E, H). For the transmission from fish to biofilms, study histology was also used to identify acid fast bacteria in granulomas (encircled in C, F, I). SB, swim bladder.

FIG. 3.

Prevalence of M. chelonae infections following incubation in M. chelonae biofilm tanks based on four diagnostic methods: in vivo GFP screening with and without subset dissection, subset liver/spleen culture, and subset liver/spleen PCR. Statistically significant differences between diagnostic methods used are indicated (+).