Bacteriologic and plasmid analysis of etiologic agents of conjunctivitis in Lagos, Nigeria

Abstract

Background: Conjunctivitis, an inflammation of the conjunctiva, is one of the most common eye problems affecting all age groups in Nigeria. A better understanding of its epidemiology and the antibiotic susceptibility of etiologic bacterial agents is crucial for the initiation of preventive and therapeutic measures. This study determined the distribution and patterns of bacterial infections in Nigerian patients with conjunctivitis. Antibiotic resistance patterns and the plasmid profiles of these pathogens were also investigated.

Methodology: A total of 83 consecutive and non-duplicate conjunctival specimens were collected from patients attending eye clinics at three different hospitals in Lagos, Nigeria, between February and September 2010. Specimens were cultured on standard bacteriologic media and the recovered isolates speciated using standard techniques. Susceptibility of pathogens to antibiotics and plasmid DNA extraction were carried out by disk diffusion and alkaline lysis methods. Conjugation experiment was done with rifampicin-resistant Escherichia coli DH5α as the recipient cell. Data were analyzed using the chi-square test.

Results: All the specimens were culture-positive, yielding a total of 155 bacterial isolates. Gram-positive cocci comprising Staphylococcus aureus (27.7%) and coagulase-negative Staphylococcus sp. (22.6%) accounted for 50.3% (78 of 155) of conjunctivitis cases, followed by Gram-positive bacilli (22.6%), Gram-negative bacilli (21.3%), and Gram-negative cocci (4.5%). Corynebacterium spp. were the most commonly isolated Gram-positive bacilli accounting for 16.1% of conjunctivitis cases. Pseudomonas aeruginosa topped with 9.7% as the most commonly isolated Gram-negative bacilli. Other Gram-negative bacilli in order of their isolations were E. coli (6.5%), Proteus sp. (3.2%), Klebsiella sp. (1.9%), and Enterobacter aerogenes (1.9%). Moraxella spp. were the only Gram-negative cocci isolated, and they accounted for 4.5% of the total conjunctival infections. Further analysis of the complexity of infections showed that 25 specimens elicited mono-infections, while cases of polymicrobial infections caused by two pathogens and three or more pathogens constituted 51.8% and 18.1% of conjunctivitis specimens screened, respectively. The disparity in the percentage contribution of three infection patterns was significant (P < 0.05). Antibiotic susceptibility testing revealed chloramphenicol and ofloxacin as the least and most active antibiotics tested as 99 (63.9%) and 149 (96.1%) of the 155 recovered isolates were sensitive to them. On the whole, the least susceptible pathogen was P. aeruginosa with sensitivities ranging from 20% to 80%, while Moraxella sp. represented the most sensitive pathogen with sensitivities ranging from 71.4% to 100%. Other bacterial isolates also elicited antibiotic sensitivities in the range of 33.3-100%. A total of 101 isolates were screened for plasmids, of which 45 harbored plasmids, yielding a plasmid frequency of 44.6%. Conjugal transfer of resistance to chloramphenicol, ampicillin, and streptomycin was detected in the transconjugants after the mating experiment. The antibiotic resistances were transferred either singly or in combination from six of the seven selected donor strains. The antibiotic resistance pattern transferred by these donor strains was partial and was associated with the transfer of R plasmids of sizes 21.3, 15.2, and 5.0 kb from three of the six transferable strains. The frequencies of transfer of antibiotype or R plasmids to the transconjugants ranged from 1.8 × 10(-7) to 1.4 × 10(-5) transconjugants per donor strain.

Conclusion: Conjunctivitis as an eye problem in Lagos is polymicrobial with infections associated with transferable R plasmids for chloramphenicol, ampicillin, and streptomycin. Continuous surveillance of conjunctivitis in relation to etiology, drug susceptibility, and plasmid transferability in the study area is therefore recommended.

Fig. 1

Agarose gel electrophoresis of ocular pathogens recovered as mono-infections. Lane 1 HindIII λ DNA markers; Lane 2 E. coli; Lanes 3–5 P. aeruginosa; Lane 6 E. aerogenes; Lane 7 K. pneumoniae; Lane 8 Moraxella sp.

Fig. 2

Agarose gel electrophoresis of ocular pathogens recovered as polymicrobial infections. Lane 1 10-kb DNA marker; Lanes 2 and 3 S. aureus; Lane 4 Bacillus sp.; Lane 5 Corynebacterium sp.; Lane 6 Bacillus sp.; Lane 7 Moraxella sp.; Lane 8 P. aeruginosa; Lane 9 Klebsiella sp.; Lane 10 negative control (sterile water); Lanes 11–13 Coagulase-negative Staphylococcus sp.