The emergence of resistance to antimicrobial agents is a global public health problem. The discovery of potent antimicrobial agents was one of the greatest contributions to medicine in the 20th century. Unfortunately, the emergence of antimicrobial-resistant pathogens now threatens these advances. Antimicrobial resistance has resulted in increased morbidity and mortality as well as higher health-care costs. Many commensal and pathogenic organisms have developed resistance to well established and newer antibiotics.
Although a number of factors can be identified which contribute to the problem, clearly the antibiotic as a selective agent and the resistance gene as the vehicle of resistance are the two most import factors. Antibiotic use has encouraged growth of the resistant strains, leading to an imbalance in prior relationships between susceptible and resistant bacteria. In Pakistan, like the other developing countries, there is a general increase in the antibiotic resistance as the availability and use of antibiotics are poorly controlled, which results in a high rate of resistance, particularly to the older antibiotics.
The study was carried out for the period of four years from January 2000 to September 2003, in order to evaluate the prevalence and development of resistance in clinically significant gram-negative bacilli and gram-positive cocci against cephalosporins. Bacterial growth was identified up to genus and species level. A total of 3,641 samples were received by the pathology laboratory of Ayub Medical complex, Abbottabad, Pakistan, which comprised of 1,862 urine, 902 pus and 877 miscellaneous samples. Miscellaneous group represented samples which comprised of few specimens and included blood, sputum, stool, different body fluids, high vaginal swabs, ear/throat/nasal swabs, tracheal secretions and wounds. All samples were evaluated and studied for four years.
E. coli was found to be the most prevalent gram-negative bacilli and S. aureus as gram-positive cocci in four years. Gender-wise prevalence, revealed a trend of high infection rate in males. In pus samples 56.8% male patients were infected with E. coli while in case of S. aureus 69.1 % and 30.9% patients infected were males and females respectively. Similar trend of higher infection rate in males was also observed in other gram-negative bacilli. An identical pattern of high number of infected males among gram-negative bacilli was also noticed in urine samples. In urine sample 51.7% were males and 48.3% were females patients infected by E. coli. Whereas 59.7% female patients were infected with S. aureus in urine samples showing higher trend of female infection.
The data of month-wise prevalence for pus samples did not showed any definite trend, occurrence of various gram-negative bacilli and gram-positive cocci were scattered all over the year from 2000 to 2003. The isolates were subjected to culture sensitivity test using Bauer and Kirby disc diffusion method. Overall 35 antimicrobial discs were used during the study period from January 2000 to September 2003 out of which 14 were cephalosporins.
In case of E. coli high resistance was observed for cefixime (71 %), K. pneumoniae also showed highest resistance against cefixime (100%), whereas, P. aeruginosa exhibited maximum resistance to cefuroxime (100%). In case of P.mirabilis high resistance was observed for cefazolin (89%). Among most commonly used antibiotics, ceftazidime and cefoperazone were proved to be most effective against P. aeruginosa with resistance rate of 35% and 25% respectively. In this study, among most frequently used antibiotics discs, S. aureus exhibited highest resistance to cefixime (66%). Ceclor and cefazolin was found to be most effective, with the resistance rate of only (9%) and (23%) respectively. The study also demonstrated that E. coli, was found to be highly susceptible to ceftriaxone and ceftazidime. While analyzing percentage usage of cephalosporin antibiotics discs for susceptibility testing, the highest percentage usage was noticed in cephradine, followed by ceftazidime and ceftriaxone respectively.
Minimum inhibitory concentration (MIC) values of E. coli (n = 136), K. pneumoniae (n = 20), P. aeruginosa (n = 20), P. mirabilis (n = 20) and S. aureus (n = 44) were determined using agar dilution method for all the 240 isolates of these species of gram-negative bacilli and gram-positive cocci randomly selected from clinical samples. MIC values were determined against cephalosporin antibiotics including first, second and third generations respectively. For each generation antibiotic active pharmaceutical ingredient (API), were used for MIC determination.
MIC50 and MIC90 values for E. coli, K. pneumoniae, P. aeruginosa, P. mirabilis and S. aureus against first, second and third generations cephalosporin (APIs), were also determined and subjected to Student â€˜tâ€™-test, Correlation and Single Factor Analysis of Variance (ANOVA).
When MIC50 and MIC90 values of E. coli, K. pneumoniae, P. aeruginosa, P. mirabilis and S. aureus against first, second and third generation cephalosporin (APIs) were compared by ANOVA, the p-value was found to be significant (p<0.05) in the case of E. coli, P. aeruginosa and P. mirabilis, indicating that significant difference existed among MIC50 and MIC90 values of first, second and third generations (APIs) whereas in the case of K. pneumoniae a non significant p-value (p<0.05) was found indicating a non significant difference between MIC50 and MIC90 values of first, second and third generation (APIs). For S. aureus a non significant p-value (p<0.05) was found with reference to MIC50 values for first, second and third generations (APIs) and significant p-value (p<0.05) existed among first, second and third generation (APIs) with reference to MIC90.
Minimum bactericidal concentrations (MBC) using broth macrodilution method were determined for isolates of E. coli, K. pneumoniae, P. aeruginosa, P. mirabilis and S. aureus. The overall MBCs of first, second and third generation cephalosporins against E. coli, K. pneumoniae, P. aeruginosa, P. mirabilis and S .aureus ranged from 1 to 2 two-fold dilutions more than their MICs.
Isolates of E. coli (n = 136) and K. pneumoniae (n = 20) from clinical samples were screened using double disc diffusion method to determine the prevalence of ESBL-producer. Among E. coli 14 (10.29%) while in case of K. pneumoniae 7 (35%) were found to be ESBL-producers. ESBL-producing strains were resistant to most of the Î²-lactam and non Î²-lactams, but a majority of them were still susceptible to imipenem.
The study revealed that antibiotic resistance has become a significant problem and will continue as bacteria continue to evolve under the selective pressure of antibiotics. The development of resistance is almost certainly an inevitable consequence of the clinical use of antimicrobial drugs. The variety of mechanisms by which bacteria acquire resistance to antimicrobial drugs is surprising. More research is urgently needed to define mechanisms of resistance, to look for new targets for antimicrobial drugs, to discover more effective ways of using our existing drugs, to minimize the development of resistance, to ascertain the most useful therapy for infections due to multi drug resistant organisms, and to learn how to prevent these infections.
It can be controlled with continued surveillance, infection control procedures and improved antibiotic usage, which are critical in preventing the re-emergence of infectious diseases as a major cause of morbidity and mortality. Strict control on the use of antibiotics and appropriate measures against over the counter availability and self-medication is recommended.