Effect of Ciprofloxacin on S. aureus and E. coli Growth in Presence of Vitamin C Using Cup Cut Diffusion Method

Ciprofloxacin is a second-generation of fluoroquinolone, broad-spectrum antibiotic with bactericidal activity against Gram-positive and Gram-negative organisms. It is one of the most widely used antibiotics, because of its efficacy, safety, and relatively low cost. Ascorbic acid (vitamin C) is water-soluble monosaccharide antioxidant; it is essentially required by the body for its various biochemical and physiological processes. S. aureus is Gram-positive cocci; widely distributed in the environment, it is a member of the normal flora of the body. S. aureus is not always pathogenic; it is a common cause of skin infections including abscesses, respiratory infections such as sinusitis, and food poisoning. E. coli is Gram-negative bacteria, found in the environment, foods, and intestines. Most E. coli strains are harmless; it is part of the normal microbiota of the gut. However, some serotypes of E. coli cause serious food poisoning in their hosts; it can cause diarrhea, while others cause urinary tract infections, respiratory illness and pneumonia, and other illnesses. Method: Cup cut diffusion method was applied. Experiment I: is carried out to choose the concentration of vitamin C to be used in experiment II. The negative control is normal saline, added in cup in each plate, vitamin C (100 mg/mL, 200 mg/mL, 400 mg/mL) was added, the volume in each cup was 100 μL. Experiment II: Eight groups of treatments were applied. The first is the negative control (1% normal saline), the second group is the positive control of vitamin C (200 mg/mL). The third, fourth and fifth groups are ciprofloxacin with different concentrations (10 mg/mL, 20 mg/mL, 40 mg/mL); the sixth, seventh and eighth are the combination of vitamin C with each concentration of ciprofloxacin (10 mg/mL, 20 mg/mL, 40 mg/mL). Each group includes six petri dishes. Bacterial plates were incubated at 37 oC for 24 h and 48 h. Zone of inhibition is measured in mm. Results and conclusion: Ciprofloxacin produces dose dependent increase in zone of inhibition of S. aureus and E. coli growth, after 24 and 48 hours incubation. While vitamin C in the concentration used produced inhibitory effect on the growth of S. aureus and E. coli, after 24 hours incubation, vitamin C effect was not changed after 48 hours incubation. After 24 hours incubation, vitamin C potentiated the effect of ciprofloxacin at low concentration (10 mg/mL); while vitamin C antagonized the effect of ciprofloxacin at higher concentrations (20 and 40 mg/mL) on S. aureus growth. In the same time, ciprofloxacin antagonized the inhibitory effect of vitamin C on S. aureus growth. After 48 hours incubation, S. aureus produced resistance against ciprofloxacin alone, and that combined with vitamin C compared to zone of inhibition after 24 hours. Ciprofloxacin produced dose dependent inhibition of E. coli growth after incubation for 24 and 48 hours. Vitamin C potentiated the inhibitory effect induced by ciprofloxacin (additive effect). The inhibitory effect of ciprofloxacin, vitamin C and the combination was not changed after 48 hours compared to 24 hours.