The objective of the study was to evaluate the association between mutations in oprD gene and carbapenem resistance. Eight carbapenem-resistant Pseudomonas aeruginosa, evaluated in this study, were isolated from pediatric ventilated patients. Drug pattern of imipenem and meropenem was determined according to the Clinical and Laboratory Standards Institute (CLSI) criteria. The oprD gene was amplified by PCR using specific primers, and sequencing was performed. The amino acid alterations in the oprD gene of carbapenem-resistant isolates were compared with the corresponding sequence of P. aeruginosa PAO1. OprD gene of all eight carbapenem-resistant isolates of P. aeruginosa was found having defective chromosomal mutations. Different classes of mutations were found. In this study, distinct base substitution was the commonest aberration in oprD gene, causing premature termination. Other frequent mechanisms of oprD inactivation resulted from 1-bp insertions or deletions or point mutation, leading to premature stop codon. In these isolates, amino acid variations among oprD groups were observed mainly at the external loops. Different classes of mutations of P. aeruginosa oprD gene were associated with carbapenem-resistant isolates from endotracheal aspirates of pediatric ventilated patients.

Pseudomonas aeruginosa, an increasingly prevalent opportunistic human pathogen, is the most common gram-negative bacterium found in nosocomial infections. Antimicrobial resistance in P. aeruginosa is a problem of growing concern and limits our therapeutic alternatives and therefore associated with a significant morbidity and mortality. Carbapenem antibiotics, such as imipenem and meropenem, represented a viable therapeutic option for treatment of serious infections caused by P. aeruginosa. Carbapenem enters into the pseudomonal membrane through a specific porin, oprD (Trias and Nikaido, 1990). It is a specific channel which also allows the permeation of basic amino acids and small peptides containing these residues (Trias and Nikaido, 1990; and Huang and Hancock, 1993). However, resistance to the carbapenems may develop in clinical isolates of P. aeruginosa after exposure and usually occurs through a loss of oprD (Quinn et al., 1986; and Margaret et al., 1989).

P. aeruginosa strains are generally less susceptible to a number of antibiotics than other gram-negative bacteria. The primary reason is its high natural resistance to variety of antibiotics. This organism has an outer membrane with a low level of permeability and thereby intrinsically resistant to a wide variety of generally used antibiotics (Yoneyama and Nakae, 1993; and Masuda et al., 1995). Mutational impermeability is important in resistance to several antibiotics, including  -lactams and fluoroquinolones. Yoneyama and Nakae (1993) published that elimination of OprD from most imipenem-resistant P. aeruginosa isolates is due to efficient selection of oprD deletion mutants. In this paper, we report the result of sequencing of oprD gene from carbapenem-resistant P. aeruginosa isolates, collected from endotracheal aspirates of pediatric patients in order to assess the chromosomal mutations.

Genetics & Evolution Journal, CEL-I Endonuclease, Heterozygous Mutants, Homozygous Mutants, Biological Processes, Plant Mutants, Solanum Lycopersicon, Microcentrifuge Tubes, Homozygous Plants, Plant Genes, Cross Pollination, Heteroduplex Formation.