Antimicrobial Resistant Streptococcus pneumoniae

Introduction: Pneumococcal infections are important cause of morbidity and mortality. Knowledge of antimicrobial susceptibility patterns plays important role in the selection of appropriate therapy. Present study was undertaken to analyze the susceptibility patterns of pneumococcal isolates against commonly used antimicrobials with special reference to determination of minimum inhibitory concentration (MIC) of penicillin in a tertiary care hospital in eastern Nepal.


INTRODUCTION
2][3] In our part of the world, empirical treatment still depends upon penicillin and other beta lactam antibiotics.However, with the rapid emergence of resistance, this is no longer a safe assumption. 4Trends indicate that pneumococci resistant to antibiotics are increasing worldwide.Therefore it may be expected that penicillin resistance may emerge sooner or later.
To determine the exact concentration of antibiotics required to inhibit the organism, determination of susceptibility by minimum inhibitory concentration (MIC) is preferred.This will also help to confi rm the intermediate/ relative resistant which may indicate the development of impending resistance among local isolates.Present study was undertaken to analyze the susceptibility pattern of pneumococcal isolates with special reference to determination of MIC of penicillin.

METHODS
Cross-sectional study conducted at Microbiology unit of BP Koirala Institute of Health Sciences, Dharan, during April 2005 to April 2006, after obtaining approval from the research committee.S. pneumoniae isolates obtained from different clinical specimens submitted for culture sensitivity were included, duplicate sample from same patient were excluded.Gram stain of all samples except blood was done and cultured onto blood agar, chocolate agar and MacConkey agar medium.Pneumococci were identifi ed by standard methods based on colony morphology, susceptibility to optochin (5μg) and bile solubility.5 Antimicrobial susceptibility test (AST) was performed according to the Clinical and Laboratory Standards Institute (CLSI) recommendations.6Oxacillin (1μg) disc was used to screen for penicillin resistance.Cefotaxime (30μg), ciprofl oxacin (5μg), chloramphenicol (30μg), cotrimoxazole (1.25/23.75μg),erythromycin (15μg) and vancomycin 5μg) discs were used to perform the AST.MIC was determined by broth dilution method for penicillin according to the CLSI recommendations. 7ata were recorded in Ms Offi ce EXCEL and percentage was calculated.

RESULTS
A total of 30 isolates of S. pneumoniae were obtained from the clinical specimen of 26 patients.These were from the cases of pneumonia (8), meningitis (9), septicemia (2) and infective keratitis (7).In two patients with meningitis pneumococcus was isolated simultaneously from blood and CSF.In other two patients with pneumonia two separate blood culture specimens yielded pneumococci (Table 1).
It was observed that the type of infection varied in different age groups.50% of the patients with septicemia and meningitis were below fi ve years whereas keratitis was common among adults and older age groups.
The youngest patient affected from septicemia and meningitis were 10 days and 60 days respectively.Age of patients with pneumonia ranged from 20-61 years.Sputum culture of the pneumonia patients did not yield the causative agents.Out of eight patients with pneumonia, pneumococci were recovered from blood in fi ve and pleural fl uid three.
Disc diffusion susceptibility testing showed that the isolates from normally sterile body sites were susceptible to antimicrobials other than cotrimoxazole.A total of six (23.1%) strains were resistant to cotrimoxazole which included two isolates each from CSF and blood and one each from pleural fl uid and corneal scraping.One isolate from the pleural fl uid was also resistant to ciprofl oxacin.No resistance to penicillin was observed by disc diffusion testing.Similarly all the isolates were susceptible to chloramphenicol, cefotaxime, erythromycin and vancomycin (Table 2).
Results of MIC determination showed that overall fi ve (17%) of the isolates had relative resistance to penicillin (Table 3).Of the invasive infections three (9.5%) had

DISCUSSION
S. pneumoniae infections continue to impose a signifi cant burden on human globally.With the introduction of polysaccharide pneumococcal vaccine, infections associated with this organism in the west are on the decline.However developing countries continue to bear the brunt of pneumococcal infections.enicillin has been the standard drug to treat pneumococcal infections for more than half a century.However, following the fi rst report of penicillin resistance in 1967, there has been steady increase of resistant pneumococci.Rate of resistance varies geographically and largely refl ect differing patterns of antimicrobial use.Worldwide, rate of penicillin resistance among pneumococci has been changing.According to a study by Asian network on surveillance of resistant pathogen (ANSORP), the frequencies of nonsusceptible pneumococcal strains to penicillin was as high as 79.7% in Korea and as low as 3.8% in India. 11Cleveland clinic reported the steady development of resistance to penicillin among invasive isolates of pneumococci over a span of 25 years. 12Penicillin resistance was detected in 64% isolates obtained from pediatric age group in a study in China. 13In a small study conducted at our centre in 2001, 4% of the total isolates were found to be penicillin resistant but all the invasive isolates were susceptible to penicillin.
8][9] Prevalence of pneumococcal strains with intermediate/relative resistance MIC 0.1-1.0mg/L has increased at an alarmingly rate worldwide in the past decade.According to a recent surveillance data, the worldwide prevalence of S. pneumoniae with reduced susceptibility to penicillin is 18.2%. 14A study from north India too revealed the presence of 18.3% of clinical isolates and 16% of nasopharyngeal isolates possessing reduced susceptibility to penicillin. 15In the present study, 17% of the total isolates had relative resistance to penicillin, which included two (7.6%) strains from invasive infections.Our fi nding is similar to that of others though the number of isolates were less. 14,15gh level penicillin resistant pneumococci with MIC 2mg/L have also emerged and are becoming more common in certain geographical area.These strains are also observed to be multidrug resistant, thus posing potential threats in the treatment of pneumococcal diseases. 9,14Pneumococci with high level penicillin resistance were not encountered in the present study.However, one strain was multidrug resistant, exhibiting resistance to cotrimoxazole, ciprofl oxacin, and relative resistance to penicillin.Its prevalence among the invasive isolates is similar to fi ndings from other reports from Indian subcontinent. 10,15,16In the present study, prevalence of resistance to cotrimoxazole (23.1%) was low as compared to prevalence reported in other studies including one conducted in Nepal. 15,16 could be due to infrequent use of cotrimoxazole in this part.High level resistance to penicillin was not observed in the present study.Relative resistance to penicillin was also not detected in the routinely performed disc susceptibility testing.It underscores the importance of determination of MIC.MIC testing is important not only for the effective management of this potentially life threatening infection but also for continuous monitoring and early detection of resistance.MIC determination technique performed in the present study is economical but cumbersome.Considering the serious nature of the infection and importance of prompt report, the methods for the rapid detection of MIC (eg.E-test) is desirable for the timely optimization of the therapy.
Since the fi rst documentation of resistance strains of pneumococcus, there has been rapid increase and spread of resistance all over.Because pneumococci are part of the normal commensal fl ora they are constantly under pressure and are likely to acquire resistance to antibiotics given for various other infections.Considering the relative resistance among pneumococci in the present study, refraining from the use of antibiotics in

CONCLUSIONS
Pneumococci, being a commensal fl ora are constantly under pressure and are likely to acquire resistance to antibiotics given for various other infections.Penicillin resistant pneumococci prevail in our setup though invasive infections are still caused by the susceptible kind.Considering the relative resistance among pneumococci as observed in the present study, judicious use of antibiotics in upper respiratory tract infections is important to limit the development and spread of high level resistance to penicillin among clinical isolates of pneumococci.Moreover, as routinely performed disc susceptibility testing was not able to detect the relative resistance to penicillin, our study underscores importance of determination of MIC in laboratory.As the present study reveals the laboratory based results, further study on pneumococcal infections, its antimicrobial resistance profi le and correlation with clinical and epidemiological features including serotype /serogroup prevalence is recommended in future.

Table 1 . Pattern of Pneumococcal infections in different age groups in BPKIHS hospital
Khanal et al.Antimicrobial Resistant Streptococcus pneumoniae in a Tertiary Care Hospital in Eastern Nepal

Table 3 . MIC of Penicillin in S. pneumoniae isolates
Khanal et al.Antimicrobial Resistant Streptococcus pneumoniae in a Tertiary Care Hospital in Eastern Nepal