Frequency and Characterization of Antibiotic Resistance among Gram Negative Bacilli

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Mohammed, Musa Abdalla Ali
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university of Khartoum
Background Antimicrobial resistance among pathogenic bacteria is a world-wide concern. The antimicrobial susceptibility pattern of common pathogenic bacteria is essential to guide pathogen-specific therapy, particularly extended spectrum beta-lactamases (ESBLs) producing strains being a major problem in hospitalized as well as community based patients. Infections due to ESBLs-producers range from uncomplicated urinary tract infection to life threatening sepsis. This study is aimed to evaluate the epidemiological data concerning the frequency of clinically significant Gram negative bacilli and determine the resistance patterns against commonly used antibiotics. In addition to determine the extended-spectrum β-lactamases (ESBLs) among Escherichia coli and Klebsiella species and to identify some genes, namely: CTX-M, SHV, and TEM, responsible for extended-spectrum beta-lactamase (ESBL) phenomenon among isolates from two different hospitals in Khartoum State, Sudan. Methods: This descriptive study was conducted at the Department of Microbiology, Faculty of Medical Laboratory Sciences, University of Khartoum. Three hundred and eighty four isolates of Gram-negative rods were obtained from various clinical specimens. Identification of the isolates was based on cultural characteristics and reactions in standard biochemical tests. All the isolates were tested for the following antibiotics; amikacin, aztreonam, cefotaxime, ceftazidime, ceftriaxone, ciprofloxacin, ertapenem, gentamicin, imipenem, mezlocillin, piperacillin, piperacillin/tazobactam, ticarcillin, ticarcillin/clavulanic acid and tobramycin by the disk diffusion technique according to the Clinical Laboratory Standards Institute (CLSI) guidelines. The detection of ESBL production was done phenotypically by screening and confirmatory test using Modified double disk synergy test (MDDST). ESBLs producing strains were tested for the presence of ESBL encoding genes using PCR with specific primers for the detection of CTX-M, SHV and TEM genes. Results: Out of 384 isolates, the highest percentage of resistance 76.0% (n= 292) was found in ticarcillin, followed by mezlocillin 73.4% (n = 282), piperacillin 70.6% (n = 271) and ticarcillin/ clavulanic acid 48.2% (n= 185). In addition, 270 (70.3%) of these strains were resistant to cefotaxime, 265 (69.0%) to ceftriaxone, 232 (60.4%) to aztreonam, 208 (54.2%) to ceftazidime, 212 (55.2%) to tobramycin, 194 (50.5%) to gentamicin, 29 (7.6%) to amikacin, 187 (48.7%) to ciprofloxacin and 51 (13.3%) to ertapenem. Imipenem was the most effective antibiotic tested, with low resistance rate 4.7% (n= 18). Out of 218 Escherichia coli and Klebsiella species, ESBL was demonstrated in 106 (48.6%) of the isolates that phenotypically positive. The most common source of ESBL producers was wound swabs. All isolates showed high susceptibility rate to imipenem and amikacin. The presence of CTX-M, SHV and TEM genes was confirmed in 91 (85.8%) of phenotypically positive isolates. The ESBL genes were detected in 42 Klebsiella species and in 49 of Escherichia coli isolates. The commonest frequent ESBL gene was TEM which was 65.9% and observed in 51.6% and 64.3% of Escherichia coli and Klebsiella species, respectively. The frequency of CTX-M gene was 58 and was observed in 26 of Escherichia coli, and 32 of Klebsiella species isolates. The frequency of SHV gene was 56 and was observed in 16 and 40 of Escherichia coli and Klebsiella species respectively. Conclusions The study revealed that antibiotics resistance has become a significant problem and will continue as bacteria continue to develop resistance under the selective pressure of antibiotics. Antimicrobial resistance can be controlled with continued surveillance, infection control procedures and improved antibiotic usage. Judicious use of antibiotics is an important step in preventing emergence of antibiotic resistance.
Frequency and Characterization of Antibiotic Resistance among Gram Negative Bacilli