Biofilms are means of protection to bacteria against antibiotics and antibodies. Catheters and others tube devices used by patients are prone to accumulation of thick layers of biofilms as hiding place for etiologic agents, resulting in substantial morbidity and mortality. Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of hospital-acquired infections. Vancomycin remains the only treatment of choice for MRSA infections. In the present study a vancomycin resistant S. aureus (VRSA) (Labeled as CP2) was isolated from the blood of a post-operative cardiac patient. It harbors a plasmid which carry vanA gene and exhibited low-level vancomycin resistance (MIC 16 μg/ml), high level of oxacillin/methicillin resistance (MIC 500 μg/ml) and was sensitive to teicoplanin. CP2 also found to carry icaA gene on its chromosome. This strain exhibited resistance to triton-X100 induced autolysis under sub-inhibitory concentration of vancomycin and produced some extracellular matrix material that surrounding the cells. These characteristic features have warranted us to study the biofilm formation by CP2 on biomedical indwellings in presence of vancomycin and oxacillin. Our findings suggest that sub-lethal dose of vancomycin induced the biofilm formation by CP2 on nylon and silicon indwellings whereas oxacillin facilitated the biofilm formation on glass surfaces exclusively. This implicates that not only the antibiotics but also the indwelling material influences biofilm formation. Therefore, these implants serve as potential surfaces for bacterial adhesion that lead to biofilm formation, thus provide hiding places for pathogens from the actions of antimicrobials.

A total of 180 food borne isolates of methicillin resistant Staphylococcus aureus (MRSA) (oxacillin MICs 864 μg/ml) were used in the present study to investigate the effect of oxacillin on biofilm formation and its detachment process. Majority (98.3%) of these isolates were found to carry icaA gene. Out of 180 isolates 35.5% were identified as MRSA and 64.4% were methicillin sensitive S. aureus (MSSA). Biofilm studies by con-red agar and tube methods revealed that 57% of the MRSA isolates were biofilm producers. Polymerase chain reaction studies suggested that all of the biofilm positive MRSA isolates belong to SCCmec type IV and carry agr type II. This showed the strong association of SCCmec IV agr type II and biofilm formation in food borne MRSA. Conversely, only 13.7% of the MSSA isolates were biofilm positive and majority was found to carry agr type II. It has been noticed that oxacillin has regulatory effect on icaA expression and induce the icaA dependent polysaccharide intracellular adhesin (PIA) production and biofilm formation. This was confirmed by Real Time PCR studies of MRSA and MSSA isolates. Quantitative analysis showed that most of the MRSA isolates started biofilm formation after 24 h of incubation in the presence of sub-inhibitory concentration of oxacillin and achieved highest adhesion on glass slide after 48 h. The control in the absence of oxacillin showed slow conversion from planktonic to biofilm mode of growth (Table 1). Another novel feature of most of these biofilm producing isolates is the reduction in (Optical Density) OD, which is noticed after 48 h of incubation. Possibly, after 48 h oxacillin loses its toxicity or consumed the cells re-adapt to the planktonic state, possibly, by the activation of accessory gene regulator A (agrA) which has an important role in biofilm dispersal.

The present study was conducted to investigate the significance of small colony variants (SCVs) in biofilm life cycle of methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA). All of these MRSA and MSSA isolates were recovered from different food commodities. Molecular typing showed that 21 MRSA isolates carry SCCmecA type IV and belong to agr type II. Out of 15 MSSA isolates, 7 were found to carry agr type II, 5 agr type I and 2 agr type III. All of the MRSA isolates studied adopted biofilm mode of growth after exposure to sublethal doses of oxacillin. MSSA isolates, on the other hand, were biofilm producers by nature, that is, without exposure to any stress. The biomass of the biofilm reaches its maximum thickness after 48 h of incubation at 35 °C. It was noticed that biofilm population consists of wild type and SCVs. Moreover, the number of SCVs increases with the age of biofilm. The SCVs of MRSA were unable to readopt biofilm mode of growth independently, irrespective of the presence or absence of oxacillin. The SCVs of MSSA, on the other hand, quickly revert to normal life just after a single subculture and show biofilm formation without any stress. Molecular studies showed a parallel reduction in the expression of the genes icaA, sigβ and sarA, and also in the extracellular matrix production in SCVs of MRSA. This might be due to oxacillin as it seems to be a stress factor responsible for induction of biofilm formation in MRSA isolates. Contrary to the wild type, SCVs are metabolically inactive and do not respond to oxacillin, which is only active against the growing cells. Therefore, stress-responsive genes, that is, sigβ and sarA, are not induced. Conversely, MSSA isolates are natural biofilm producers without induction through any known factors.

Among the trace elements, selenium (Se) has great demand as a health supplement. Compared to its other forms, selenium nanoparticles have minor toxicity, superior reactivity, and excellent bioavailability. The present study was conducted to produce selenium nanoparticles (SeNPs) via a biosynthetic approach using probiotic Bacillus subtilis BSN313 in an economical and easy manner. The BSN313 exhibited a gradual increase in Se reduction and production of SeNPs up to 5–200 µg/mL of its environmental Se. However, the capability was decreased beyond that concentration. The capacity for extracellular SeNP production was evidenced by the emergence of red color, then confirmed by a microscopic approach. Produced SeNPs were purified, freeze-dried, and subsequently characterized systematically using UV–Vis spectroscopy, FTIR, Zetasizer, SEM–EDS, and TEM techniques. SEM–EDS analysis proved the presence of selenium as the foremost constituent of SeNPs. With an average particle size of 530 nm, SeNPs were shown to have a −26.9 (mV) zeta potential and −2.11 µm cm/Vs electrophoretic mobility in water. SeNPs produced during both the 24 and 48 h incubation periods showed good antioxidant activity in terms of DPPH and ABST scavenging action at a concentration of 150 µg/mL with no significant differences (p > 0.05). Moreover, 200 µg/mL of SeNPs showed antibacterial reactivity against Escherichia coli ATCC 8739, Staphylococcus aureus ATCC 9027, and Pseudomonas aeruginosa ATCC 25923. In the future, this work will be helpful to produce biogenic SeNPs using probiotic Bacillus subtilis BSN313 as biofactories, with the potential for safe use in biomedical and nutritional applications.

The main aim of this work was to screen, isolate, and identify a probiotic selenium (Se)‐resistant strain of Bacillus subtilis, using the 16S rDNA sequencing approach and subsequently optimize conditions. Initially, conditions were enhanced in two univariate optimization environments: shakings flask and a bioreactor. After solving optimization for selected variables, conditions were further optimized using orthogonal array testing. The results were further evaluated by the analysis of variance, in support of Se enrichment. In a bioreactor, based on R and F values, the order of effect of selected conditions on Se enrichment was stirring speed > initial pH > temperature > Se addition time. The stirring speed of the bioreactor was most significant, due to the suspension of reduced Se, as it formed. After absolute optimization, strain BSN313 was able to enrich Se up to 2,123 µg/g of dry weight, which is 7.58 times greater than the baseline Se‐resistance. Practical applications Systematic studies of selenium enrichment conditions will facilitate the successful development of an organic selenium source and the safe use of Bacillus subtilis strain (BSN313) as a food supplement. Selenium‐enriched probiotic bacteria are reported to provide many health benefits to the host, due to antipathogenic, antioxidative, anticarcinogenic, antimutagenic, and anti‐inflammatory activities.