Comparative in vitro exoenzyme-suppressing activities of azithromycin and other macrolide antibiotics against Pseudomonas aeruginosa

Abstract

The inhibitory effects of azithromycin (AZM), a new 15-membered macrolide antibiotic, on the production of exotoxin A, total protease, elastase, and phospholipase C by Pseudomonas aeruginosa were determined, and the virulence-suppressing effects of AZM were compared with those of erythromycin (EM), roxithromycin (RXM), and rokitamycin (RKM). The elfect of exposure ofP. aeruginosa PA103 or B16 in cultures to sub-MICs of these macrolide antibiotics on the production of exoenzymes was determined. AZM suppressed the in vitro production of extracellular and intracellular exotoxin A by P. aeruginosa PA103 more than did EM, even at a concentration of only 2 ,ug/ml. At concentrations of between 4 and 32 ,ug/ml, AZM also inhibited total protease, elastase, and phospholipase C production by P. aeruginosa B16 more than did EM, RXM, and RKM. AZM was effective in suppressing exotoxin A and total protease production through 24 h of incubation in the presence of drug at sub-MICs, but it had no significant effect on either the growth of P. aeruginosa or its total protein production. Moreover, at a concentration of 4 ,ug/ml, AZM suppressed exoenzyme production by other strains of P. aeruginosa more than did EM. These findings indicate that AZM, EM, RXM, and RKM each has an inhibitory effect on exoenzyme production separate from the antimicrobial effect and that, of these macrolides, AZM has the strongest virulence-suppressing effect.Pseudomonas aeruginosa is an opportunistic pathogen which frequently causes severe septicemia in immunocompromised hosts (4, 5). It is also the principal pulmonary pathogen in patients with cystic fibrosis (24, 33) and diffuse panbronchiolitis (16). P. aeruginosa exoenzymes, including exotoxin A, alkaline protease, elastase, and phospholipase C, are known to be virulence factors of importance in the various types of P. aeruginosa infections (26). The findings of our previous studies have suggested that P. aeruginosa isolates from blood cultures produce large quantities of exotoxin A and total protease (10) and that the production of exotoxin A plays an important role in the pathogenesis of endogenous P. aeruginosa septicemia in mice (13).It has recently been reported that treatment with erythromycin (EM) improves the clinical symptoms and prognosis of patients with chronic pulmonary infections (18). Kita et al. (18) have shown that erythromycin stearate (EMS) suppresses the production of protease and leukocidin by P. aeruginosa without affecting cell growth and speculated that EMS may affect the virulence factors of this organism (18) and host defense mechanisms (7, 9, 17). More recently, we have shown that erythromycin lactobionate (EML) suppresses the in vitro pro-

Effects of macrolides on pneumolysin of macrolide-resistantStreptococcus pneumoniae

“…Previous studies suggested that sub-inhibitory levels of macrolides could inhibit bacterial virulence factors in vitro [11,12]. LAGROU et al [19] also reported that sub-MIC of erythromycin reduced the haemolytic activity of PLY by MRSP.…”

“…Some recent reports have shown the effects of sub-minimum inhibitory concentrations (sub-MIC) of macrolides on bacterial virulence factors [11]. For example, sub-MIC of azithromycin (AZM) inhibited exotoxin A, total protease, elastase and phospholipase C production by Pseudomonas aeruginosa without affecting the growth of P. aeruginosa [12].…”

Exploiting Quorum Sensing To Confuse Bacterial Pathogens

“…This was an unexpected finding, considering the high levels of resistance that P. aeruginosa shows toward these drugs, and general anti-inflammatory effects associated with macrolides were suggested to account for the positive results (312). However, in vitro testing with subinhibitory concentrations of macrolides indicated an additional effect of their application on reduction of P. aeruginosa virulence factor expression, including decreased production of exotoxin A, proteases, elastase, DNase, leukocidin, and phospholipase C (313)(314)(315). Positive outcomes from sub-MIC AZM treatments against P. aeruginosa in a murine pneumonia model provided further laboratory evidence that macrolides could affect the physiology of the bacteria without inhibiting their growth in vivo (316).…”

Protective effect of granulocyte colony-stimulating factor (G-CSF) in a granulocytopenic mouse model of Pseudomonas aeruginosa lung infection through enhanced phagocytosis and killing by alveolar macrophages through priming tumour necrosis factor-alpha (TNF-α) production

“…The strain was isolated clinically from a blood sample at Nagasaki University Hospital (Nagasaki, Japan) [7,8]. Lipopolysaccharide (LPS) extracted from P. aeruginosa serotype 10 was obtained from Sigma Chemical Co. (St Louis, MO).…”