Sains Malaysiana 42(3)(2013): 301–306

Divalent Cations (Mg²⁺, Ca²⁺) Protect Bacterial Outer Membrane Damage by Polymyxin B

(Kation Divalen  (Mg2+, Ca2+) Melindungi Membran Luar Bakteria daripada Kemusnahan

oleh Polymyxin B)

Ahmad Zorin Sahalan*, Abdul Hamid Abd. Aziz, Hing Hiang Lian & Mohamed Kamel Abd. Ghani

Department of Biomedical Science, Faculty of Health Sciences, Universiti Kebangsaan Malaysia

Jln Raja Muda Abd Aziz, 50300 Kuala Lumpur, Malaysia

Received: 19 October 2011/Accepted: 2 October 2012

ABSTRACT

Polymyxin B interacts with divalent cations by displacing cations from their binding sites in the lipopolysaccharide (LPS) molecules. It leads to the disorganization of the outer membrane component of the Gram negative bacteria, which releases LPS component from bacterial surface causing severe membrane leakage and finally cell death. In this paper, the reversible activity of PMB was investigated in the presence of access divalent cations such as Mg²⁺ or Ca²⁺. Membrane damage and cell disruption were monitored by detecting leakage of the outer membrane and cytoplasmic enzyme marker (β-lactamase and β-galactosidase), release of LPS component (KDO) from bacterial cells and bacterial survival. With the presence of divalent cations, leakage of enzyme markers and LPS released was significantly reduced when bacteria were exposed to PMB. The survival curve also significantly increased. The inhibitory of damage caused by PMB also depended on the type of divalent cation present. Ca²⁺ has been shown to be more effective in protecting the bacteria cells than Mg²⁺. This is because Ca²⁺ appears more frequently as a constituent of the structural components of the bacteria. In conclusion, the presence of higher concentration of divalent cation particularly with Ca²⁺ inhibits PMB activity and maintained bacterial survival.

Keywords: Calcium; divalent cation; E.coli; magnesium; polymyxin B

ABSTRAK

Polymixin B (PMB) bertindak pada dinding sel bakteria dengan mengeluarkan kation divalen daripada tapak ikatannya di lipopolisakarida (LPS). Keadaan ini akan mengakibatkan komponen dinding bacteria gram negatif terganggu kestabilannya serta menyebabkan komponen dinding sel khasnya LPS terkeluar dari permukaan sel bakteria, seterusnya mengakibatkan kebocoran pada dinding sel dan akhirnya bakteria akan mati. Dalam penyelidikan ini proses berbalik daripada kesan di atas telah dikaji. Perencatan aktiviti PMB telah diuji dengan kehadiran kation seperti Mg²⁺ atau Ca²⁺yang berlebihan dalam persekitaran bakteria. Kerosakan pada dinding dan kemusnahan sel dipantau dengan menggunakan penanda enzim sitoplasma seperti β-laktamase dan β-galaktosidase serta pembebasan LPS yang diuji daripada komponennya seperti (KDO) dan kemandirian bakteria. Dengan kepekatan kation divalen ditingkatkan, didapati berlakunya penurunan kerosakan daripada dinding sel bakteria akibat daripada tindakan PMB. Lengkuk kemandirian bakteria juga didapati telah meningkat. Kesan perencatan kerosakan pada bakteria oleh PMB juga banyak bergantung kepada jenis kation divalen. Ca²⁺ telah menunjukan kesan yang baik dalam melindungi bakteria daripada PMB berbanding dengan Mg²⁺. Ini adalah kerana Ca²⁺ merupakan bahan penting di dalam komponen struktur dinding sel bakteria. Kesimpulannya, kehadiran kepekatan kation yang tinggi khasnya Ca²⁺ boleh menyebabkan aktiviti PMB terencat seterusnya mengekalkan kemandirian bakteria.

Kata kunci: E.coli; kalsium; kation divalen; magnesium; polymyxin B

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*Corresponding author; email: ahmadzorinsahalan@yahoo.com