Drug resistance profiles of Gram-negative bacilli isolated from clinical samples in Cross River State, Nigeria
Authors: Ulom Udey Ifop , Ibeneme Emmanuel Onyekachukwu , Eyo Aniekan-Augusta Okon , Asuquo Anne Ebri , Utsalo Simon James 
Published: November 2022

Objectives:
Resistance of Gram-negative bacilli (GNB) to antimicrobial agents is increasing worldwide. This is fast becoming a serious public health concern as these bacteria display multiple antibiotic resistance mechanisms. This study was aimed at evaluating antibiotic resistance profiles of GNB from clinical samples in Cross River State, Nigeria.

Material and Methods:
Urine and stool samples of 600 randomly selected participants were analyzed. Samples were inoculated onto CLED agar and selenite-F broth, respectively, and enriched bacterial growth in selenite-F broth was subcultured on deoxycholate citrate agar. Gram stain procedure was used to determine the Gram reaction of isolates and identification was carried out using the Microbact 24E GNB identification kit. Antibiotic susceptibility testing was performed using the Kirby–Bauer disk diffusion method. Multiple antibiotic resistance indices (MARIs) for each isolate were calculated. Data analysis was carried out using Microsoft Excel Package 2016 and GraphPad Prism version 6.

Results:
A total of 129 non-repetitive GNB were isolated and categorized by their ability to ferment sugars. The lactose-fermenting Enterobacteriaceae (LFE) were the most predominant isolates (32 Klebsiella pneumoniae and 25 Escherichia coli). There were 50 non-sugar-fermenting Gram-negative bacilli (NSF-GNB) comprising Pseudomonas spp. (28), Acinetobacter spp. (15), Burkholderia cepacia (3), and one isolate each of Tatumella ptyseos, Alcaligenes faecalis, Aeromonas hydrophila, and Stenotrophomonas maltophilia. Non-lactose-fermenting Enterobacteriaceae comprised Proteus spp. (14), Providencia stuartii (4), and Serratia rubidaea (4). Antimicrobial susceptibility test results showed that tetracycline was the least effective with 71.3% of isolates showing resistance. About 65% of LFE and 95.5% of non-lactose-fermenting Enterobacteriaceae (NLFE) showed resistance to tetracycline. Resistance of all isolates to tigecycline, a member of a new class of antibiotics, was 31% (40/129); however, all isolates of E. coli, S. rubidaea, and Acinetobacter spp. were susceptible to tigecycline. Resistance profiles of LFE to tested antibiotics showed comparable resistance levels for ceftriaxone and tetracycline between K. pneumoniae and E. coli. However, the resistance of K. pneumoniae to ceftazidime, ciprofloxacin, and tigecycline was 50%, 44%, and 13% compared with E. coli – 32%, 32%, and 0%, respectively. E. coli showed, on average, higher resistance levels to carbapenems compared with K. pneumoniae. Among NLFE, Proteus spp. was more resistant than P. stuartii to cephalosporins, quinolones, and tigecycline. In contrast, P. stuartii isolates were twice as resistant to the carbapenems as Proteus spp. Except for ciprofloxacin, tetracycline, and gentamicin, S. rubidaea was susceptible to all other antibiotics. Among NSF-GNB, Acinetobacter spp. was the most resistant to all other carbapenems, except ertapenem. Pseudomonas spp. were the most resistant to fluoroquinolones. The mean of the total MARI was 0.45 ± 0.26, with 54.3% (70/129) of isolates having MARI above the total mean. About 73% (95/129) of the total GNB had MARI above 0.2. Multidrug resistance in Enterobacteriaceae, Pseudomonas aeruginosa, and Acinetobacter species was 53.2%, 100%, and 93.3%, respectively.

Conclusion:
The high level of antibiotic resistance of GNB, especially by NLFE and NSF-GNB, portends great danger for the health sector as these organisms are opportunistic pathogens and pose serious health risks as nosocomial pathogens and community-acquired pathogens in immunosuppressed individuals.