β-lactamases (bla TEM, bla SHV, bla CTXM-1, bla VEB, bla OXA-1 ) and class C β-lactamases gene frequency in Pseudomonas aeruginosa isolated from various clinical specimens in Khartoum State, Sudan: a cross sectional study

Background: Pseudomonas aeruginosa is a pathogenic bacterium, causing nosocomial infections with  intrinsic and acquired resistance mechanisms to a large group of antibiotics, including β-lactams. This study aimed to determine the susceptibility pattern to selected antibiotics and to index the first reported β-lactamases genes frequency in Ps. aeruginosa in Khartoum State, Sudan. Methods: 121 Ps. aeruginosa clinical isolates from various clinical specimens were used in this cross sectional study conducted in Khartoum State. Eighty isolates were confirmed as Ps. aeruginosa through conventional identification methods and species specific primers. The susceptibility pattern of the confirmed isolates to selected antibiotics was done following the Kirby Bauer disk diffusion method. Multiplex PCR was used for detection of seven β-lactamase genes ( blaTEM, blaSHV, blaCTXM-1, blaVEB, blaOXA-1, blaAmpC and blaDHA). Results: Of the 80 confirmed Ps. aeruginosa isolates, 8 (10%) were resistant to Imipenem while all isolates were resistant to Amoxicillin and Amoxyclav (100%). A total of 43 (54%) Ps. aeruginosa isolates were positive for blaTEM, blaSHV, blaCTXM-1, blaVEB and blaOXA-1 genes, while 27 (34%) were positive for class C β- Lactamases, and 20 (25%) were positive for both classes. Frequency of beta-lactamases genes was as follows: blaTEM, 19 (44.2%); blaSHV, 16 (37.2%); bla CTX-M1, 10 (23.3%); blaVEB, 14 (32.6%); blaOXA-1, 7 (16.3%). blaAmpC 22 (81.5%) and bla DHA 8 (29.6%).  In total, 3 (11.1%) isolates were positive for both bla AmpC and blaDHA genes. Conclusion: Ps. aeruginosa isolates showed a high rate of β- lactamases production, with co-resistance to other antibiotic classes. The lowest resistance rate of Ps. aeruginosa was to Imipenem followed by Gentamicin and Ciprofloxacin. No statistically significant relationship between production of β-lactamases in Ps. aeruginosa and resistance to third generation cephalosporins was found.

β-lactamases (bla TEM, bla SHV, bla CTXM-1, bla VEB, bla OXA-1 ) and class C β-lactamases gene frequency in Pseudomonas aeruginosa isolated from various clinical specimens in Khartoum State, Sudan: a cross sectional study

Background:Pseudomonas aeruginosa is a pathogenic bacterium, causing nosocomial infections with  intrinsic and acquired resistance mechanisms to a large group of antibiotics, including β-lactams. This study aimed to determine the susceptibility pattern to selected antibiotics and to index the first reported β-lactamases genes frequency in Ps. aeruginosa in Khartoum State, Sudan. Methods: 121 Ps. aeruginosa clinical isolates from various clinical specimens were used in this cross sectional study conducted in Khartoum State. Eighty isolates were confirmed as Ps.aeruginosa through conventional identification methods and species specific primers. The susceptibility pattern of the confirmed isolates to selected antibiotics was done following the Kirby Bauer disk diffusion method. Multiplex PCR was used for detection of seven β-lactamase genes ( blaTEM, blaSHV, blaCTXM-1, blaVEB, blaOXA-1, blaAmpC and blaDHA). Results: Of the 80 confirmed Ps. aeruginosa isolates, 8 (10%) were resistant to Imipenem while all isolates were resistant to Amoxicillin and Amoxyclav (100%). A total of 43 (54%) Ps. aeruginosa isolates were positive for blaTEM, blaSHV, blaCTXM-1, blaVEB and blaOXA-1 genes, while 27 (34%) were positive for class C β- Lactamases, and 20 (25%) were positive for both classes. Frequency of beta-lactamases genes was as follows: blaTEM, 19 (44.2%); blaSHV, 16 (37.2%); bla CTX-M1, 10 (23.3%); blaVEB, 14 (32.6%); blaOXA-1, 7 (16.3%). blaAmpC 22 (81.5%) and bla DHA 8 (29.6%).  In total, 3 (11.1%) isolates were positive for both bla AmpC and blaDHA genes. Conclusion:Ps. aeruginosa isolates showed a high rate of β- lactamases production, with co-resistance to other antibiotic classes. The lowest resistance rate of Ps. aeruginosa was to Imipenem followed by Gentamicin and Ciprofloxacin. No statistically significant relationship between production of β-lactamases in Ps. aeruginosa and resistance to third generation cephalosporins was found.

In vitro and in vivo Inhibitory Activity of NADPH Against the AmpC BER Class C β-Lactamase

β-Lactamase-mediated resistance to β-lactam antibiotics has been significantly threatening the efficacy of these clinically important antibacterial drugs. Although some β-lactamase inhibitors are prescribed in combination with β-lactam antibiotics to overcome this resistance, the emergence of enzymes resistant to current inhibitors necessitates the development of novel β-lactamase inhibitors. In this study, we evaluated the inhibitory effect of dinucleotides on an extended-spectrum class C β-lactamase, AmpC BER. Of the dinucleotides tested, NADPH, a cellular metabolite, decreased the nitrocefin-hydrolyzing activity of the enzyme with a K _i value of 103 μM in a non-covalent competitive manner. In addition, the dissociation constant (K _D) between AmpC BER and NADPH was measured to be 40 μM. According to our in vitro susceptibility study based on growth curves, NADPH restored the antibacterial activity of ceftazidime against a ceftazidime-resistant Escherichia coli BER strain producing AmpC BER. Remarkably, a single dose of combinatory treatment with NADPH and ceftazidime conferred marked therapeutic efficacy (100% survival rate) in a mouse model infected by the E. coli BER strain although NADPH or ceftazidime alone failed to prevent the lethal bacterial infection. These results may offer the potential of the dinucleotide scaffold for the development of novel β-lactamase inhibitors.

Modified Penicillin Molecule with Carbapenem-Like Stereochemistry Specifically Inhibits Class C β-Lactamases

Bacterial β-lactamases readily inactivate most penicillins and cephalosporins by hydrolyzing and "opening" their signature β-lactam ring. In contrast, carbapenems resist hydrolysis by many serine-based class A, C, and D β-lactamases due to their unique stereochemical features. To improve the resistance profile of penicillins, we synthesized a modified penicillin molecule, MPC-1, by "grafting" carbapenem-like stereochemistry onto the penicillin core. Chemical modifications include the trans conformation of hydrogen atoms at C-5 and C-6 instead of cis, and a 6-α hydroxyethyl moiety to replace the original 6-β aminoacyl group. MPC-1 selectively inhibits class C β-lactamases, such as P99, by forming a nonhydrolyzable acyl adduct, and its inhibitory potency is ∼2 to 5 times higher than that for clinically used β-lactamase inhibitors clavulanate and sulbactam. The crystal structure of MPC-1 forming the acyl adduct with P99 reveals a novel binding mode for MPC-1 that resembles carbapenem bound in the active site of class A β-lactamases. Furthermore, in this novel binding mode, the carboxyl group of MPC-1 blocks the deacylation reaction by occluding the critical catalytic water molecule and renders the acyl adduct nonhydrolyzable. Our results suggest that by incorporating carbapenem-like stereochemistry, the current collection of over 100 penicillins and cephalosporins can be modified into candidate compounds for development of novel β-lactamase inhibitors.