Effects of Amoxicillin, Gentamicin, and Moxifloxacin on the Hemolytic Activity of Staphylococcus aureus In Vitro and In Vivo

Abstract

In Staphylococcus aureus infection hemolysis caused by the extracellular protein ␣-toxin encoded by hla is thought to contribute significantly to its multifactorial virulence. In vitro, subinhibitory concentrations of ␤-lactam antibiotics and fluoroquinolones increase the levels of hla and ␣-toxin expression, whereas aminoglycosides decrease the levels of hla and ␣-toxin expression. In the present study we investigated the effects of subinhibitory concentrations of amoxicillin, gentamicin, and moxifloxacin on hla and ␣-toxin expression and total hemolysis of S. aureus strain 8325-4, a high-level ␣-toxin producer, and its ␣-toxin-negative mutant, DU 1090, in vitro and in a rat model of chronic S. aureus infection. The levels of expression of hla and ␣-toxin and total hemolysis did not differ significantly when amoxicillin, gentamicin, or moxifloxacin was added to cultures of S. aureus strain 8325-4. In vivo, strain 8325-4 induced a significantly increased level of hemolysis in infected pouches compared to that in uninfected control pouches, but the hemolysis was reduced to control levels by treatment with doses of amoxicillin, gentamicin, or moxifloxacin that reduced bacterial numbers by 2 orders of magnitude. Additionally, the effects of subinhibitory concentrations of the three antibiotics on total hemolysis of four methicillin-resistant S. aureus and three methicillin-sensitive S. aureus (MSSA) clinical isolates were assessed in vitro. A significant increase in total hemolysis was observed for only one MSSA strain when it was treated with amoxicillin but not when it was treated with moxifloxacin or gentamicin. When purified ␣-toxin was incubated with purified human neutrophil elastase, ␣-toxin was cleaved nearly completely. The results suggest that the penicillin-induced increases in S. aureus ␣-toxin expression are strain dependent, that reduction of bacterial numbers in vivo counteracts this phenomenon effectively, and finally, that in localized S. aureus infections ␣-toxin activity is controlled by neutrophil elastase.Staphylococcus aureus causes a broad range of life-threatening diseases in humans (19). Its virulence is multifactorial (1, 4), including the extracellularly released 33.2-kDa polypeptide ␣-toxin (␣-hemolysin) (3, 31). ␣-Toxin is thought to be a major virulence factor of S. aureus since ␣-toxin-negative mutants of the wild-type strain 8325-4, such as DU 1090, were revealed to have significantly reduced levels of toxicity in animal models of human S. aureus infection (5,25,27,28). In vitro data suggest that antibiotics modify the expression of ␣-toxin. For example, macrolides (21, 26), aminoglycosides (26), and clindamycin (26) reduced the level of ␣-toxin production, whereas ␤-lactam antibiotics strongly increased (18, 26) and fluoroquinolones slightly increased (26) its level of production. Sterile culture supernatants of S. aureus strains treated with nafcillin in vitro were significantly more toxic for rats than untreated culture supernatants (18).On the basis of these results, it was hypot...

Moxifloxacin Efficacy and Vitreous Penetration in a Rabbit Model ofStaphylococcus aureusEndophthalmitis and Effect on Gene Expression of Leucotoxins and Virulence Regulator Factors

“…No significant expression of leukotoxins or regulatory factors was detected in the vitreous 1 h after the administration of the 20-mg/kg dose, either because of the low bacterial density or because of a potential reduction of the expression. Worlitzsch et al (46) reported a decrease of total hemolytic activity by S. aureus in infected rat pouches treated with MXF.…”

Reduced Aeration Affects the Expression of the NorB Efflux Pump of Staphylococcus aureus by Posttranslational Modification of MgrA

“…Under reduced-aeration conditions, our data suggest that the posttranslational modification that blocks MgrA dimerization, combined with an increase in protease expression, contributed to norB derepression. Abscesses and the cystic fibrosis airway are environments that are both acidic and low in oxygen (pH is 5.5 in abscesses) (28,29), conditions that may result in additive effects on MgrA regulation and the expression of NorB and other effector proteins, the levels of which are under its control. Thus, understanding the mechanisms behind bacterial adaptation to stresses such as acidity or oxygen level may identify targets for interfering with bacterial fitness and resistance to antibiotics at sites of infection.…”

Amphibian antimicrobial peptide fallaxin analogue FL9 affects virulence gene expression and DNA replication in Staphylococcus aureus

“…It has been shown previously that the expression of virulence genes in S. aureus is affected by subinhibitory concentrations of different antibiotics (Ohlsen et al, 1998;Worlitzsch et al, 2001;Nielsen et al, 2012). Knowledge of how pathogenic bacteria react in the presence of a subinhibitory concentration of AMPs is important information that to date has not been thoroughly investigated when evaluating the potential of peptides as drugs used in the inhibition of pathogenic bacteria.…”