Impaired biofilm formation in Salmonella enterica serovar Abortusovis

ABOU ASSALI L, ; SARNACKI SH,; BETANCOURT DM,; MANUELIAN CJ; RUBINO S,; NOTO LLANA M; GIACOMODONATO MN

Jornada; X JORNADAS DE JÓVENES INVESTIGADORES; 2021

Facultad de Ciencias Veterinarias, Universidad de Buenos Aires.

Salmonella Abortusovis infection is one of the most important causes of infectious late-term abortion as well as birth of weak lambs in sheep in many countries throughout the world. Even though S. Abortusovis, an ovine-restricted serotype, is reportable to the World Organization for Animal Health, outbreaks are underdiagnosed in several regions. Salmonella strains that cause gastroenteritis in multiple host species have retained an ability to form the rdar (red, dry and rough colonies) morphotype, a biofilm physiology hypothesized to be important for Salmonella transmission. In contrast, Salmonella serovars that are host-adapted or even host-restricted like S. Typhi have lost this capability. There is no information about biofilm formation by S. Abortusovis strains. In this regard, this study was aimed to investigate the ability of S. Abortusovis SS44 clinical isolate to generate biofilm. We observed that SS44 strain is unable to develop pellicles at the air-liquid interface (score=0) compared to the clinical isolate of S. Enteritidis ArJEG and ATCC S. Typhimurium strains 14028 and SL1344 (score=4). Then, morphotyping, visualized under a stereomicroscope, was used to investigate whether the impaired biofilm formation found in S. Abortusovis is related to a diminished production of cellulose and/or curli. SS44 strain showed saw (smooth and white) colony morphology after 3 days of growth at 28˚C on Congo red agar, indicating the absence of curli and cellulose production. On the contrary, S. Enteritidis and S. Typhimurium wild type strains display rdar morphotype, which reflects the coexpression of curli fimbriae and cellulose. We compared SS44, Whole Genome Sequence Project: AUYQ02, with typical biofilm producer strains (S. Typhimurium: 14028, SL1344 and D23580 and S. Enteritidis 4931) and non-biofilm producers isolates (S. Enteritidis D7795, S. Typhi TY2 and CT18) for bioinformatics analysis. Strain sequences were obtained from the National Centre for Biotechnology Information. Sequencing alignments were performed using MEGA07 program. We analyzed CsgD conservation, a master biofilm regulator, which controls the expression of genes involved in rdar morphology formation pathway. It was found that CsgD sequence was highly conserved between S. Abortusovis, S. Typhimurium and S. Enteritidis strains and those were different from S. Typhi due to truncation of 8 amino acids from the C-terminus of CsgD, as was shown previously. Also, it was observed that S. Abortusovis possessed premature stop codons in four genes which play a role in the curli fimbriae synthesis (csgC and csgF), cellulose production (adrA) and stress regulator (cpxR), generating truncated proteins that could have altered functions. Altogether, our results demonstrate, for the first time, that S. Abortusovis SS44 lost the capability to express rdar morphotype that may represent an additional signature of host adaptation. Improved knowledge about the natural lifecycle of S. Abortusovis would allow us to reduce the bacterial load on sheep and their environment and prevent abortions.