The present study investigates the effect of surface hydrophobicity and media on in vitro biofilm formation potential of S. aureus isolates from two dairies. There was lack of correlation between biofilm formation potential of S. aureus and sampling points but not with the source of isolation. Biofilm formation was more pronounced on hydrophobic polypropylene (PP) than hydrophilic stainless steel (SSC). A better correlation was established between the biofilms on SSC and PP when analyzed by crystal violet staining than conventional plating method. On comparative evaluation of nutrient rich and diluted growth media, enhanced biofilm formation was observed in latter (1/20 tryptic soya broth). Highest survival in the preformed biofilms was observed at incubation temperature of 25 °C in sterilized skim milk rather than TSB. The present study signify preferable adherence of S. aureus on hydrophobic surfaces and potential survival within preformed biofilm at temperatures prevalent in dairy industries.

The present study investigates the effect of adaptive resistance to ciprofloxacin (Cip) and benzalkonium chloride (BC) on biofilm formation potential (BFP), efflux pump activity (EPA) and haemolysin activity of Escherichia coli isolates of dairy origin. All the isolates, irrespective of antimicrobial susceptibility, developed significant adaptive resistance (P < 0·05). All the resistant phenotypes (antibiotic resistant: AR; & biocide resistant: BR) were stronger biofilm former and post-adaptation, an insignificant change was observed in their BFP. Whereas, post-adaptation, non-resistant isolates (antibiotic non-resistant: ANR; biocide non-resistant: BNR) transformed from poor or moderate to strong biofilm formers. Post-adaptive percentage increase in EPA was highly significant in non-resistant categories (P < 0·01) and significant at P < 0·05 in BR category. Interestingly, post-adaptive increase in EPA in BR isolates was more than that in AR yet, the latter exhibited greater adaptive resistance than the former. These findings indicated prevalence of some other specific resistance mechanism/s responsible for adaptive resistance against Cip. Strain specific variations were observed for stability of adaptive resistance and haemolysin activity for all the categories. Our findings especially in reference to post-adaptation upgradation of BFP status of non-resistant isolates seems to be providing an insight into the process of conversion of non-resistant isolate into resistant ones with enhanced BFP. These observations emphasize the serious implications of sub-lethal residual levels of antimicrobials in food environments and suggest a role of food chain in emergence of antimicrobial resistances.

The present study was undertaken to investigate the role of efflux pump activity (EPA) in conferring adaptive and cross resistances against ciprofloxacin (CF) and benzalkonium chloride (BC) in dairy isolates of Pseudomonas aeruginosa. Biofilm formation potential was correlated with development of adaptive resistance in originally resistant strains. Irrespective of parent strains's susceptibility, isolates developed substantial adaptive resistance against CF and BC. Significant difference was observed in ability of non resistant isolates to develop adaptive resistance against CF and BC (P < 0.02) and subsequent cross resistance. EPA was quantified using EtBr (Ethidium Bromide) model and its role was more prominent [confirmed by its inhibition using efflux pump inhibitor (EPI) 2,4-dinitrophenol (DNP)], in conferring adaptive resistance (P = 0.147) than cross resistance (P = 0.343). Reduction in adaptive resistances due to EPI was more evident in originally non resistant strains, which reaffirms EPA as probable mechanism of adaptive resistance. The present study perhaps first of its kind, suggests an active role of EPA in conferring adaptive and cross resistances in food related P. aeruginosa isolates and supports reverse hypothesis that antibiotic-resistant organisms eventually become tolerant to other antibacterial agents as well.

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The present study was undertaken with objectives of; a) to investigate and compare Pseudomonas aeruginosa isolates from two dairies for biofilm formation potential and, b) to compares three common biocides for biofilm eradication efficiencies. Amongst the isolates from commercial dairy, 70 % were strong and/or moderate biofilm former in comparison to 40 % isolates from small scale dairy. All isolates, irrespective of source, exhibited higher susceptibility to biocides in planktonic stage than in biofilm. Antibiofilm efficiencies of three biocides i.e. benzalkonium chloride, sodium hypochlorite and iodophore were determined in terms of their microbial biofilms eradicating concentration (MBEC). Our findings show that the three biocides were ineffective against preformed biofilms at recommended in-use concentrations. Biofilms were the most resistant to benzalkonium chloride and least against iodophore. A trend of decreasing MBECs was observed with extended contact time. The findings of present study warrant for a systematic approach for selecting types and concentrations of biocide for application as antibiofilm agent in food industry.