Antibacterial effects of antibiotics and cell-free preparations of probiotics against Staphylococcus aureus and Staphylococcus epidermidis associated with conjunctivitis

Conjunctivitis, caused by bacterial infections, represents health concern and diagnosis of the disease is pivotal for the proper selection of the treatment. The main causes of bacterial conjunctivitis vary in different countries. The current study investigated the common bacterial causes of bacterial conjunctivitis from eye clinics' attendants and evaluated the effectiveness of different therapeutic approaches. Eye swabs from patients, diagnosed with conjunctivitis, were assessed microbiologically and the isolated bacteria were identified using the standard biochemical identification and sequencing of the 16S rRNA gene. Antibiotics' susceptibility of the conjunctivitis-associated bacterial pathogens was evaluated against nineteen broad-spectrum antibiotics. In the meanwhile, cell-free preparations from probiotic Lactobacillus and Bifidobacterium strains were used to evaluate their antagonistic activities. Findings from this study showed that out of 52 specimen, 17 eye swabs from patients with conjunctivitis were bacterial culture-positive. The identity of the bacterial species, using the biochemical identification system, was Staphylococcus aureus (4 isolates) and S. epidermidis (13 isolates). Staphylococcus spp. showed susceptibility to linezolid, vancomycin, novobiocin, and fluoroquinolones (norfloxacin, ofloxacin, ciprofloxacin and levofloxacin). However, isolates from the two Staphylococcus spp. expressed resistance to penicillin G, oxacillin, and cephalexin. As alternatives to antibiotics, the growth of Staphylococcus spp., including isolates with antibiotic resistance, was inhibited by cell-free preparations of the 4 probiotic Lactobacillus and the 2 Bifidobacterium strains. These findings provide evidence that topical antibiotics such as fluoroquinolones are still effective antimicrobial agents against staphylococci associated with conjunctivitis whereas probiotic preparations could be promising for further research to pave the way for their therapeutic applications against ophthalmic diseases.