Detection of pneumolysin and autolysin genes among antibiotic resistant Streptococcus pneumoniae in invasive infections

Purpose: To detect the presence of autolysin and pneumolysin genes among Streptococcus pneumoniae strains isolated from different disease entities among Indian patients. The study also attempted to determine antimicrobial susceptibility of the isolates. Materials and Methods: A total of 24 S. pneumoniae isolates were checked for the presence of lytA gene coding for autolysin and ply gene coding for pneumolysin using polymerase chain reaction (PCR). All the isolates were subjected to susceptibility testing by disc diffusion method for 10 different therapeutically relevant antibiotics. Minimum inhibition concentration (MIC) was determined using broth dilution method for ampicillin, penicillin and ciprofloxacin. Results: Eleven isolates from ocular infections and 13 isolates from different invasive diseases showed susceptibility to most of the antibiotics tested except chloramphenicol and ciprofloxacin. Fifty percentage of the isolates showed resistance to chloramphenicol and ciprofloxacin. A moderate level of resistance of 18% was noted for cefepime and ceftriaxone. Only 6% of resistance was observed for amoxicillin and ceftazidime. MIC levels ranged from 0.015 to 1 μg/mL for ampicillin and only one isolate had an MIC of 1 μg/mL. The MIC levels for penicillin ranged from 0.062 to 4 μg/mL, wherein nine isolates showed high levels of MICs ranging from 2 to 4 μg/mL. Six isolates had a very high resistance levels for ciprofloxacin with MIC ranging from 32-128 μg/mL. The presence of lytA was observed in 23 out of 24 isolates tested whereas only 17 isolates were positive for pneumolysin. Four ocular isolates and one isolate from ear infection were negative for pneumolysin. Conclusion: Emerging resistance observed for cefepime and ceftriaxone might be due their increased and frequent usage nowadays. Presence of pneumolysin appears to be more critical for pathogenesis of invasive infections than the ocular infections. However, presence of lytA gene in all the isolates signifies that irrespective of site of isolation, kind of infection caused, autolysin is an obligate necessity for this organism