Letter: Resistant pseudomonads in a neurosurgical unit

Pathogenesis and therapy of Pseudomonas aeruginosa keratitis

Considerable progress has been made recently in understanding the pathogenesis of pseudomonas keratitis including its adhesion, invasion and the role of the glycocalyx. Adhesion to epithelial cells has been shown in vitro to depend on pili but their relationship to the glycocalyx biofilm has yet to be explored. The actions of its toxins and proteases have been established by studying the effects of deletion mutants. However, in animal models pseudomonads have been unable to cause an invasive infection in the presence of an intact corneal epithelium and have required associated trauma. Why early necrosis of the cornea can occur in an immunocompetent individual is still not clear but may reflect the delayed access of polymorphonuclear cells (PMNs) in an avascular tissue. Whether the corneal necrosis that later occurs is then due to the PMNs or pseudomonas toxins is not established. Topical fortified gentamicin therapy remains the treatment of choice for early infection. The use of medical and surgical adjunctive therapy is often needed to cope with the complications of advanced disease and has been reviewed.

Amikacin, gentamicin and tobramycin resistant Pseudomonas aeruginosa in a leukaemic ward. Epidemiology and genetic studies

Four patients in a leukaemic ward were infected with multi-resistant Pseudomonas aeruginosa. Similar organisms were found in the environment and it appeared that lapses in aseptic routine contributed to the outbreak. Serological, bacteriophage and pyocin-typing revealed that a fifth patient was infected with a distinct strain, but agarose gel electrophoresis indicated that all patient and environmental strains carried the same plasmid. The plasmid had a molecular weight of 47 (s.d. +/- 2) X 10(6) dal and was transfer deficient. It conferred resistance to carbenicillin, gentamicin, kanamycin, streptomycin, sulphonamide, tetracycline and tobramycin and determined an aminoglycoside adenylyltransferase active against amikacin in-vitro and not in-vivo. Spread of this non-transferable plasmid to a different Ps. aeruginosa strain and dissemination of multi-resistant organisms led to serious infections.

Characteristics of Pseudomonas aeruginosa in relation to laboratory-induced resistance to gentamicin

Pseudomonas aeruginosa strain C2 was habituated to gentamicin by serial passage in broth containing increasing concentrations of the antibiotic and up to 250 microgram/ml. The resistant progenies differed from the parent strain in antibiotic susceptibility to two other aminoglycosides, colonial morphology, lytic phage patterns, phage adsorption, and agglutination with the seven Fisher's antisera. All the progenies failed to grow at 42 degrees C and oxidised glucose in O/F tubes after incubation at 37 degrees C for three days but were catalase- and oxidase-positive. Reversion to the original properties of the parent strain was demonstrated in all cases after 10 serial subcultures in antibiotic-free broth.