Magnitude of Extended-Spectrum Beta-Lactamase-Producing Gram-Negative and Beta-Lactamase-Producing Gram-Positive Pathogens Isolated from Patients in Dar es Salaam, Tanzania: A Cross-Sectional Study

Background The worldwide emergence of antibiotic-resistant bacteria threatens to overshadow the dramatic advances in medical sciences since the discovery of antibiotics. Antibiotic resistance has rendered some antibiotics obsolete, creating a reliance on synthetic drugs. In some instances, bacteria can be resistant to all antibiotics. The problem of antibiotic resistance is eminent in resource-limited countries like Tanzania, where systematic surveillance and routine susceptibility tests are rarely conducted. Therefore, this study aimed to investigate the magnitude of beta-lactamase-producing Gram-positive pathogens and Enterobacteriaceae with extended-spectrum beta-lactamase (ESBL) in Dar es Salaam, Tanzania. Methodology This multi-site cross-sectional study involved three private hospitals in Dar es Salaam, Tanzania. The study was conducted between July and September 2008. Bacterial isolates were collected, identified, and subjected to antibiotic-sensitivity testing against cephalosporins, including ceftriaxone, cefuroxime and cefotaxime, and clavulanic acid, which are antibiotics readily available on the Tanzanian market at the time of the study. The microdilution method was employed to determine beta-lactamase and ESBL production per the Clinical Laboratory and Standards Institute (CLSI) protocol. Cephalosporins, including ceftriaxone, cefuroxime and cefotaxime, the beta-lactamase inhibitor, and clavulanic acid, were serially diluted with concentrations ranging from 0.011 mg/ml to 200 mg/ml. Each of these antibiotics was subjected to sensitivity tests by determining the minimum inhibitory concentrations (MIC) of the clinical isolates of bacteria using a 96-well microdilution plate. Five microliters of bacterial suspension were inoculated into each well-containing 120µl of sterile Mueller-Hinton broth before incubation overnight. Results A total of 111 bacterial isolates were tested. Of the 111 tested bacterial isolates, 85 (76.6%) and 26 (23.4%) were Gram-negative and Gram-positive bacteria, respectively. Fifty-six clinical isolates (50.4%) were Escherichia coli, and 13 Salmonella species (11.7%) were among the Gram-negative isolates. On the other hand, 15 (13.5%) and 11 (9.9%) Gram-positive bacteria were Staphylococcus aureus and Streptococcus species, respectively, of all isolates. The majority of these clinical isolates, 71 (64.0%), were obtained from mid-stream urine, while the remaining were from stool, vaginal secretions, blood, pus, catheter sip, and urethra. A high proportion of tested Gram-negative bacteria, 58 (68.2%), were identified as ESBL producers, and 16 (61.5%) of the Gram-positive bacteria were identified as beta-lactamase producers. Cefuroxime was the least effective, exhibiting the largest MIC (18.47 ± 22.6 mg/ml) compared to clavulanic acid alone (5.28 ± 8.0 mg/ml) and clavulanic acid-cefuroxime (5.0± 12.32 mg/ml). Of all isolates, 78.2% were sensitive to chloramphenicol. Only five isolates had MIC larger than 32.23 mg/ml as opposed to cefotaxime and ampicillin, which had more isolates in that similar MIC range. Conclusion There is a high proportion of beta-lactamase, particularly ESBL-producing pathogens, in Dar es Salaam, Tanzania. Therefore, regular detection of beta-lactamase and ESBL production may help detect resistance to beta-lactam antibiotics.