Abstract
This study evaluated the effects of growth medium, temperature, and incubation time on biofilm formation by Enterobacter cloacae strains. The ability to adhere to a surface was demonstrated using a microtiter plate adherence assay whereas the role of cell surface properties in biofilm formation was assessed using the coaggregation and autoaggregation assays. The architecture of the biofilms was examined under scanning electron microscope (SEM). All the strains adhered to the well of the microtiter plate when incubated for 48 h, irrespective of the growth medium and incubation temperature. It was also noted that 90% and 73% of strains prepared from nutrient broth and cultured in brain heart infusion (BHI) broth and tryptic soy broth (TSB), respectively, were able to form biofilms, in contrast to 73% and 60% strains from nutrient agar and cultured in BHI and TSB respectively grown under similar conditions. However, no statistically significant difference was observed when the two methods were compared. The coaggregation index ranged from 12% to 74%, with the best coaggregate activity observed when partnered with Streptococcus pyogenes (54%–74%). The study indicates the suitability of BHI and TSB medium for the cultivation of E. cloacae biofilms, however, temperature and incubation time significantly affect biofilm formation by these bacteria.
Highlights
E. cloacae, a Gram negative bacterium, belongs to the family Enterobacteriaceae
The optical density (OD) of non adherent (NA), weak adherent (WA), moderate adherent (MA) and strong adherent (SA) obtained when the bacteria were grown in brain heart infusion (BHI) ranged from 0.359–0.486, 0.552–1.159, 1.092–2.14 and
The results of this study revealed that E. cloacae isolates which weakly adhered to the microtiter plate demonstrated the strongest coaggregation with all the seven partner strain; these findings suggest the possibility of these strains to act as bridging organisms in multi-generic biofilms due to their ability to coaggregate with diverse coaggregating partners
Summary
E. cloacae, a Gram negative bacterium, belongs to the family Enterobacteriaceae. The bacterium comprises part of the normal flora of the gastrointestinal tract of 40%–80% of the human population and is widely distributed in the environment [1]. Biofilms are very diverse and unique, not just to the microorganism, but to the particular environment in which they are being formed This makes in vitro characterization of biofilms difficult and requires the establishment of laboratory conditions that mimic the natural setting being studied. The ability of these organisms to form biofilms at ambient temperature (25 °C), which is mostly room temperature in tropical countries, implies that under favorable conditions, they may be able to adhere to kitchen utensils and other environments leading to cross-contamination of food processed in these areas. BHI was chosen as one of the nutrient-rich laboratory medium, and TSB a less-rich (compared to BHI) culture medium which are frequently used in biofilm investigation
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