title: Biofilm formation and dispersal of Staphylococcus aureus under the influence of oxacillin.
abstract: 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.
authors.affiliation: Pakistan Council of Scientific and Industrial Research Laboratories Complex, Karachi, Pakistan. Electronic address: mirani_mrsa@yahoo.com.
authors.forename: Zulfiqar Ali
authors.initials: ZA
authors.lastname: Mirani
authors.forename: Mubashir
authors.initials: M
authors.lastname: Aziz
authors.forename: Mohammad Naseem
authors.initials: MN
authors.lastname: Khan
authors.forename: Irfan
authors.initials: I
authors.lastname: Lal
authors.forename: Najam Ul
authors.initials: NU
authors.lastname: Hassan
authors.forename: Seema Ismat
authors.initials: SI
authors.lastname: Khan
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D018441:Biofilms / Q000187:drug effects / Q000254:growth & development*; D006801:Humans; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D008826:Microbial Sensitivity Tests; D010068:Oxacillin / Q000494:pharmacology*; D013203:Staphylococcal Infections / Q000382:microbiology; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism
chemical_list: C095698:Agr protein, Staphylococcus aureus; D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D015534:Trans-Activators; D010068:Oxacillin
keywords: Biofilm dispersal; MRSA; Oxacillin; Staphylococcus aureus; icaA