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

An important role of a "probable ATP-binding component of ABC transporter" during the process of Pseudomonas aeruginosa resistance to fluoroquinolone

In order to find new drug target to eliminate the fluoroquinolone resistance, the in vitro progress of Pseudomonas aeruginosa fluoroquinolone resistance was mimicked, and then proteomic analysis was applied to comparing different protein profiles during the resistant process. The results show that the expression of a "probable ATP-binding component of ATP binding cassette (ABC) transporter" existed in ciprofloxacin-intermediate and -resistant strains, but not in sensitive strain. In addition, the ciprofloxacin concentrations in P. aeruginosa strains, which were obtained from the progress of P. aeruginosa fluoroquinolone resistance, were determined by means of HPLC; the results show that the decrease of the intracellular concentration of drug and the expression of this new protein nearly take place simultaneously. The changes of mRNA levels of the probable ATP-binding component of ABC transporter were detected by virtue of RT-PCR and showed that this protein did not express in the sensitive strains but expressed increasingly in the intermediate and resistant strains. In order to determine the relationships between the development of antibiotic resistance and this protein further, a DNAzyme was designed to aim at the mRNA of the probable ATP-binding component of ABC transporter directly; the ciprofloxacin resistance of P. aeruginosa was partially reduced in vivo by inhibiting the expression of this protein. This DNAzyme has no effect on sensitive strain. And the comparison of drug intracellular concentrations between DNAzyme-treated strains and its control strains shows that this protein may be included in the course of active drug efflux.

Adaptive resistance to benzalkonium chloride, amikacin and tobramycin: the effect on susceptibility to other antimicrobials

AIMS

To produce strains of antimicrobial-resistant Pseudomonas aeruginosa via adaptation to benzalkonium chloride, amikacin and tobramycin and to then examine the incidence, or otherwise, of cross-resistance between antibiotics and between antibiotics and benzalkonium chloride.

METHODS AND RESULTS

Adaptation was obtained by progressive subculturing in subinhibitory concentrations of the antimicrobials. Pseudomonas aeruginosa NCIMB 10421 adapted to grow in high concentrations of benzalkonium chloride (BC) had lower MIC to antibiotics than the wild type, whereas Ps. aeruginosa adapted to grow in antibiotics had greater MIC to benzalkonium by a small degree.

CONCLUSIONS

Adaptive resistance to BC of Ps. aeruginosa generally produced cultures with a decrease in resistance to several antibiotics. Adaptive resistance to the aminoglycosides Ak and Tm produced a low-level increase in tolerance to BC. The adaptive mechanisms of resistance appear to be different for the different types of antimicrobials used.

SIGNIFICANCE AND IMPACT OF THE STUDY

The relationships between biocide and antibiotic resistance are complex. It appears, from this study, that an organism resistant to a common biocide can become sensitive to antibiotics, but the converse was not true. Could this observation be used in a strategy to alleviate antibiotic resistance?

Phenotypic factors correlated with the absence of virulence among gentamicin-resistant Pseudomonas aeruginosa strains

Previous reports have suggested that clinical strains of gentamicin-resistant Pseudomonas aeruginosa (GRPA) generally produce only superficial infections (wounds, urinary tract infections) in contrast to their more invasive gentamicin-susceptible counterparts (GSPA). In view of this finding, a comparative study of a number of phenotypic properties of 20 GRPA and GSPA strains (10 isolates) was assessed to determine how closely related these two populations are and how their phenotypic properties might reflect virulence. GRPA isolates were found to be more adherent to buccal cells than their susceptible counterparts (P = 0.0001). Motility, however, was generally restricted in the GRPA population when compared with GSPA isolates (P = 0.02), although on the basis of zone diameters, some strains overlapped into the other group. Enzymatically, GSPA isolates produced significantly more lipase activity against C-14 lipids than GRPA strains (P = 0.04). No differences were recorded between the two populations in dye sensitivity or in their ability to grow on minimal media at 37 and 42 degrees C. Only 35% of the GRPA isolates agglutinated in 1 of the 17 monospecific antisera reactive for P. aeruginosa. The results of this study suggest that in vivo-generated GRPA strains possess phenotypic properties intermediate between those described for in vitro-derived GRPA isolates and their progenitor GSPA strains. The increased adherence of clinical GRPA isolates to buccal cells may explain their predilection to produce wound and urinary tract infections, whereas their lack of systemic dissemination may be partially due to decreased motility and to reduced lipase production.

Gentamicin-resistantPseudomonas aeruginosa: Concepts regarding their evolution and attenuated virulence

Pseudomonas aeruginosa, a free-living bacterial species, is a major nosocomial pathogen, especially of compromised patients within medical facilities. Numerous factors contribute to the ecological selection of this bacterial species within the hospital environment, among which the expression of newly acquired or quiescent enzymatic capability seems par-amount. The emergence of pathogenic strains ofP. aeruginosa appears to be gradual, embodying a transition of strains from their natural aquatic environment, to establishing inanimate (hospital) and animate (human) reservoirs. In this stepwise transition, subsets ofP. aeruginosa may evolve which express a survival trait, for example, gentamicin resistance, but concomitantly suffer a loss of invasive potential. In this study,P. aeruginosa strains from natural [22], hospital [11], and stool [17] sources were evaluated for their physiological and exoenzymatic activity and compared with gentamicin-resistantP. aeruginosa (GRPA) strains [49] of clinical origin. As a whole, environmental and hospital isolates showed reduced enzymatic potential, for example, frequency of production of elastase, lipase, deoxyribonuclease, and pyocyanin production. Human fecal isolates most closely resembled the prototype of human invasiveP. aeruginosa in their gentamicin susceptibility (95%) and increased frequencies of exoenzymes, including elastase production. On the other hand, GRPA were frequently apyocyanogenic (9/49), lacked extracellular enzymes correlated with pathogenicity, and were rarely isolated from systemic sites. When encountered, these strains appeared to represent colonization of a body site rather than incitants of overt infection. As a "subset" ofP. aeruginosa, gentamicin resistance was seen predominantly among serotype 11 strains, and encountered most frequently from patients with localized urinary tract infections.