Genotypic and Phylogenetic Profiling of Biofilm-Forming Staphylococcus Isolates Recovered from Device-Associated Chronic Infections: A Case–Control Study from Northern India

Background: Biofilm-forming Staphylococcus spp. are a major cause of persistent, device-associated infections and frequently harbour multidrug resistance, notably methicillin resistance. Robust local data linking biofilm intensity, species distribution and antimicrobial profiles remain scarce.In a prospective case–control study at a tertiary-care centre in Mandi. 200 non-duplicate Staphylococcus isolates from patients with indwelling medical devices ≥48 h (cases) and 50 isolates from community-onset uncomplicated infections (controls) were analysed. Species identification employed standard biochemical tests; methicillin resistance was screened with cefoxitin discs. Biofilm formation was quantified by tissue-culture plate (TCP) assay and compared with tube method (TM) and Congo-red agar (CRA). Antibiotic susceptibility testing followed CLSI disk-diffusion guidelines.Staphylococcus aureus predominated (179/250, 71.6 %). Biofilm positivity was significantly higher in cases than controls (78.5 % vs 16.0 %; χ² = 69.63, p < 0.001). TCP detected biofilm in 78.0 % of case isolates, outperforming TM (70.5 %) and CRA (39.0 %) (χ² = 113.96, p < 0.001). Methicillin-resistant staphylococci (MRSA/MRCoNS) constituted 67.0 % of case isolates and were biofilm-positive in 80.6 %. Among biofilm producers, highest resistance was noted to penicillin G (61.2 %), cefoxitin (46.4 %) and erythromycin (45.2 %), whereas linezolid (64.4 % susceptible) and tetracycline (42.4 % susceptible) retained useful activity. Presence of a chronic comorbidity markedly increased the likelihood of isolating a biofilm producer (adjusted OR 5.3; 95 % CI 2.8–10.1; p < 0.001). Device-associated infections in our setting are dominated by biofilm-forming, methicillin-resistant Staphylococcus spp. TCP assay offers the best laboratory yield. High resistance rates underscore the need for biofilm-targeted stewardship and reinforce linezolid as a reliable therapeutic option. Molecular typing of clonal complexes is warranted to elucidate transmission dynamics.