Chloramphenicol resistance in Pseudomonas cepacia because of decreased permeability

Abstract

The mechanism of chloramphenicol resistance was examined in a high-level-resistant isolate of Pseudomonas cepacia from a patient with cystic fibrosis. We investigated potential resistance mechanisms, including production of chloramphenicol acetyltransferase, ribosomal resistance, and decreased permeability. This strain (MIC, 200 ,ug/ml) had no detectable chloramphenicol acetyltransferase activity. In in vitro translation experiments in which we compared the resistant isolate with a susceptible strain of P. cepacia, inhibition of amino acid incorporation was equivalent even in organisms that were preincubated with sub-MICs of chloramphenicol. A 21.9-kilobase (kb) fragment of DNA was cloned which coded for chloramphenicol resistance; this fragment was expressed in P. cepacia but not in Escherichia coli. Quantitation of chloramphenicol uptake in the isogenic pair of susceptible and resistant organisms revealed a nearly 10-fold decrease of drug entry into the resistant strain. Comparison of isolated outer membrane proteins and lipopolysaccharide patterns identified no significant differences between the isogenic pair of organisms. We concluded that the mechanism of chloramphenicol resistance in this strain is decreased permeability.Pseudomonas cepacia is an important nosocomial pathogen and an organism that can cause severe pulmonary infections in children and young adults with cystic fibrosis (CF). Originally recognized as a plant pathogen in 1950 (5), the role of P. cepacia in hospital-acquired infections of the urine, lungs, and bloodstream was first reported in the early 1970s (12,19,22,28,35). Colonization with P. cepacia occurs late in the course of pulmonary disease in patients with CF, and in several CF centers, outbreaks of virulent strains have resulted in severe and overwhelming pneumonia in a subpopulation of patients (21, 37).The major problem in the treatment of infections caused by P. cepacia is multiple antibiotic resistance. Isolates from patients with CF, in particular, are often highly resistant to the P-lactam agents and aminoglycosides that are used to treat Pseudomonas aeruginosa (4, 9, 15). Antibiotics with clinical efficacy against P. cepacia include chloramphenicol, trimethoprim, and the quinolones (12,21,28). However, more than half of clinical isolates may be resistant to these agents as well. Investigations of chloramphenicol resistance in P. cepacia strains from patients with CF consistently report that 45 to 50% of isolates are resistant (MIC,.10 ,ug/ml).In this report we describe the characterization of chloramphenicol resistance in P. cepacia. We used an isolate of P. cepacia from a patient with CF; this isolate was resistant to chloramphenicol, trimethoprim, and ciprofloxacin, as well as all P-lactams and aminoglycosides tested, and was selected to characterize the resistance mechanism. We cloned a 21.9-kilobase (kb) DNA fragment that encoded resistance to chloramphenicol in P. cepacia but that was not expressed in Escherichia coli. Potential mechanisms of resistance, including enzy...

Susceptibility-resistance profile of micro-organisms isolated from herbal medicine products sold in Nigeria

“…Inducible -lactam activity is a general property of Pseudomonas cepacia (Prince et al, 1988). Resistance to chloramphenicol was similar to those of clinical strains in the study of Burns et al (1989).…”

“…The importance of surveying resistant environmental strains is that under favourable situations, they may transfer their resistance plasmids to pathogens. The problem is especially serious in hospitals where the environment can be a factor in the selection of multiresistant strains (O'Brien andAcar, 1987, Prince et al, 1988;Bryan, 1989;Burns et al, 1989). If such organisms are present in medicaments, they could behave as opportunist pathogens and initiate an infection, particularly in immuno-compromised patients.…”

Salicylate induces an antibiotic efflux pump in Burkholderia cepacia complex genomovar III (B. cenocepacia)

“…Upstream of the four structural genes and oriented in the opposite direction is a sequence encoding a putative LTTR (ceoR). Transfer of a cosmid clone containing all five components of the ceo gene cluster into an antibioticsusceptible B. multivorans laboratory strain also transferred resistance to chloramphenicol, trimethoprim, and ciprofloxacin, but not resistance to the aminoglycosides or β-lactam antibiotics (16).…”

“…The first of these investigated the regulation of ceoR. The putative ceoR promoter region was fused upstream of the promoterless lacZ in the broad host range vector pDN19lacΩ (16), and the construct was introduced into strain PC121. PC121 is a B. cenocepacia clinical isolate that demonstrates salicylate production and antibiotic resistance induced by low iron concentrations, rather than constitutively, as seen in the wild-type strain K61-3.…”

Characterization of the nonenzymatic chloramphenicol resistance (cmlA) gene of the In4 integron of Tn1696: similarity of the product to transmembrane transport proteins

“…Another less prevalent mechanism of chloramphenicol resistance, which does not involve modification of the compound, but rather its entry into the bacterial cell, has been appropriately termed nonenzymatic and has been observed principally in gram-negative bacteria. The genetic determinants of this mechanism are usually plasmid encoded, such as in Pseudomonas aeruginosa and in members of the family Enterobacteriaceae (6, 10-12, 16,23,26,35,46); resistance determinants of chromosomal origin were also reported in Haemophilus influenzae (5), Pseudomonas cepacia (4), and Salmonella typhi (60). In most instances, it was demonstrated that nonenzymatic chloramphenicol resistance involves a membrane permeability barrier and that porins appear to be deficient in some of these strains.…”