Objective(s): This study was designed to determine the relationship of Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli isolates in multispecies biofilms and their individual phenotypic characters in biofilm consortia. Materials and Methods: The subject isolates were recovered from different food samples and identified on the basis of growth on differential and selective media. Tube methods, Congo-red agar method, and scanning electron microscopy (SEM) were used to study biofilms phenotypes. The hydrophobicity of the strains was evaluated by the adhesion to apolar solvent. Results: The results showed that E. coli dominated the pre-biofilm stage. It has been observed that E. coli adopted biofilm life much before S. aureus and P. aeruginosa. However, after adopting biofilm lifestyle, slowly and gradually, P. aeruginosa dominated the consortia and dispersed other stakeholders. The subject isolates of P. aeruginosa produce cis-2-decanoic acid to disperse or inhibit S. aureus and E. coli biofilms. Gas-chromatography and mass spectrometry results showed that cis-2-decanoic was higher in the co-culture condition and increased at late log-phase or at stationary phase. Although majority of S. aureus were unable to compete with P. aeruginosa, however, a minor population competed, survived, and persisted in biofilm consortia as small colony variants. The survivors showed higher expression of sigB and sarA genes. P. aeruginosa showed comparatively higher hydrophobic surface properties. Conclusion: Comparative analysis showed that cell surface hydrophobicity, growth rate, and small colony variants (SCVs) are correlated in biofilm consortia of the P. aeruginosa, S. aureus, and E. coli.

The present study discusses a biofilm-positive P. aeruginosa isolate that survives at pH levels ranging from 4.0 to 9.0. The biofilm consortia were colonized with different phenotypes i.e., planktonic, slow-growing and metabolically inactive small colony variants (SCVs). The lower base of the consortia was occupied by SCVs. These cells were strongly attached to solid surfaces and interconnected through a network of nanotubes. Nanotubes were observed at the stationary phase of biofilm indwellers and were more prominent after applying weight to the consortia. The scanning electron micrographs indicated that the nanotubes are polar appendages with intraspecies connectivity. The micrographs indicated variations in physical dimensions (length, width, and height) and a considerable reduction in volume due to weight pressure. A total of 35 cells were randomly selected. The mean volume of cells before the application of weight was 0.288 µm³, which was reduced to 0.144 µm³ after the application of weight. It was observed that a single cell may produce as many as six nanotubes, connected simultaneously to six neighbouring cells in different directions. The in-depth analysis confirmed that these structures were the intra-species connecting tools as no free nanotubes were found. Furthermore, after the application of weight, cells incapable of producing nanotubes were wiped out and the surface was covered by nanotube producers. This suggests that the nanotubes give a selective advantage to the cells to resist harsh environmental conditions and weight pressure. After the removal of weight and proper supply of nutrients, these phenotypes reverted to normal planktonic lifestyles. It is concluded that the nanotubes are not merely the phenomenon of dying cells; rather they are a connectivity tool which helps connected cells to tolerate and resist environmental stress.

Objectives: Objective: This study was designed to explore the role of different phenotypes of P. aeruginosa in the development, stability and persistence of biofilm. Methods: A total of seventeen (17) waterborne biofilm producing strains of P. aeruginosa were studied. These isolates were identified on the basis of typical phenotypic characters and the tube method was used for the study of biofilms. Population and phenotypic variance were studied by the drop plate method. The hydrophobicity of strains was evaluated by the bacterial adhesion to apolar solvent test. Results: Study showed that the subject isolates of P. aeruginosa adopted a biofilm life style after 36 h of incubation at 35 °C. After 24 h the adhesion started, but it was reversible and easily dispersed by simple washing. However, after 36 h the irreversible adhesion was noticed. The biofilm consortia harbor three different phenotypes: i. wild types, showed typical P. aeruginosa characters on Cetrimide agar; ii. Slow growers, showed poor pigmentation and take >36 h for colony development, and iii. Small colony variants (SCVs) are metabolically inactive and producing pinpointed non pigmented colonies. Comparative analysis showed that these phenotypes i.e. SCVs were highly hydrophobic and persistent in biofilm consortia due to the production of excessive amounts of exopolysaccharides. Conclusions: This study showed that phenotypic heterogeneity is a characteristic feature of P. aeruginosa biofilms and all of these phenotypes have a major role in stability and persistence of biofilm consortia. J Microbiol Infect Dis 2020; 10(1):10-17.

Objective(s): The current study aimed to investigate the control and treatment of biofilm-producing isolates of Pseudomonas aeruginosa using silicon nanoparticles (SiNPs).Materials and Methods: Biofilm-producing isolates of P. aeruginosa were recovered from various food samples and identified through fluorescent green colony formation on selective and differential media, as well as the amplification of oprI and oprL genes. Tube methods, Congo-red agar method, and scanning electron microscopy (SEM) were used to study biofilm phenotypes. The effect of SiNPs was evaluated by broth dilution assay.Results: The biofilm assay revealed that these isolates formed biofilms on glass surfaces within 72 hr of incubation. Scanning electron micrographs showed that the biofilm communities were composed of multicellular clusters of P. aeruginosa encased in matrix material. However, these isolates were unable to form biofilms on SiNPs-coated surfaces. The results showed that the planktonic isolates of P. aeruginosa were comparatively sensitive to the antibacterial properties of SiNPs, with minimum inhibitory concentration (MIC) ranging from 100 to 200 mu g/ml. Contrarily, the biofilms were found to be 500 times more tolerant to the highest concentration of SiNPs (MIC of 500 mu g/ml) and were more resistant. Under static conditions, the sedimentation of SiNPs resulted in their ineffectiveness. However, under shaking conditions, the biofilms were effectively dispersed and the cells were lysed. The results showed that SiNPs were effective against both the planktonic and the metabolically inactive forms of P. aeruginosa. Conclusion: This study suggests that SiNPs could be a useful tool for preventing the formation of biofilms and removing pre-existing biofilms.

Spices are used in almost all types of food preparation, and their microbial contamination can lead to spoilage and pose a risk to public health

In the modern household, refrigerators play a central role in preserving food freshness. However, the microbial landscape within these appliances, particularly the formation of biofilms, remains a significant concern for food safety and hygiene. This study investigated biofilm formation in household refrigerator environments to understand the potential risks associated with microorganisms and their implications for food safety. The study was conducted by examining a total of 80 refrigerators of residents of Karachi, over a 15-day period. employing rigorous methodologies to assess optical density (OD), Colony Forming Units (CFU/cm²), and Scanning Electron Microscopy (SEM) to uncover bacterial species' abilities to develop biofilms. Results revealed that 12 out of the 80 slides displayed positive biofilm formation based on both OD and CFU criteria. Strong biofilm producers encompassed Acinetobacter, Listeria, P. aeruginosa, E. coli, Bacillus, Salmonella, and others. Notably, P. aeruginosa was a common component across different biofilm categories. In vitro studies on individual isolates further confirmed biofilm-forming capabilities. P. aeruginosa isolates exhibited strong biofilm formation, while E. coli isolates displayed weak capabilities. Enterococci isolates generally formed weak to moderate biofilms. In summary, our study reveals the prevalence of biofilm formation in household refrigerators, with significant microbial risks posed by species like P. aeruginosa. These findings underscore the importance of stringent hygiene practices for ensuring food safety at home.