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Susceptibility of three groups of Staphylococcus aureus to newer antimicrobial agents
Abstract:
Because of the need for non-beta-lactam antimicrobics with antistaphylococcal activity, 14 antimicrobics (3 penicillinase-resistant penicillins, 7 aminocyclitols [5 new], 2 macrolides [1 new], clindamycin, and a new polysaccharide, everninomicin) were tested in vitro for activity against 22 penicillin-susceptible, 51 penicillin-resistant, and 47 methicillin-resistant strains of Staphylococcus aureus. Gentamicin, tobramycin, sisomicin, and verdamicin inhibited almost all strains at concentrations less than 1 mug/ml. The methicillin-resistant strains were as susceptible as other strains to the aminocyclitols and everninomicin. In contrast, many of the methicillin-resistant strains were also resistant to erythromycin, rosamicin, and clindamycin at attainable serum concentrations. The use of the bacterial synthetic amino acid medium, in comparison with Mueller-Hinton broth, resulted in an increase in the observed resistance of methicillin-resistant strains to the penicillinase-resistant semisynthetic penicillins.
Insights
New non-beta-lactam antimicrobics, including novel aminocyclitols and everninomicin, show potent activity against Staphylococcus aureus. Methicillin-resistant strains remain susceptible to these agents, unlike some macrolides and clindamycin.
Area of Science:
- Microbiology
- Pharmacology
- Infectious Diseases
Background:
- The rise of antibiotic resistance in Staphylococcus aureus necessitates the development of novel non-beta-lactam antimicrobics.
- Methicillin-resistant Staphylococcus aureus (MRSA) poses a significant clinical challenge due to its resistance to common antibiotics.
Purpose of the Study:
- To evaluate the in vitro antistaphylococcal activity of various non-beta-lactam antimicrobics against diverse strains of Staphylococcus aureus.
- To compare the efficacy of new agents, including novel aminocyclitols and everninomicin, against susceptible, penicillin-resistant, and methicillin-resistant strains.
Main Methods:
- In vitro susceptibility testing of 14 antimicrobics against 120 Staphylococcus aureus strains (penicillin-susceptible, penicillin-resistant, and methicillin-resistant).
- Agents tested included penicillinase-resistant penicillins, novel and existing aminocyclitols, macrolides, clindamycin, and everninomicin.
- Antimicrobial activity was assessed using minimum inhibitory concentrations (MICs).
Main Results:
- Aminocyclitols (gentamicin, tobramycin, sisomicin, verdamicin) and everninomicin demonstrated potent activity, inhibiting most strains at concentrations below 1 µg/ml.
- Methicillin-resistant strains showed similar susceptibility to aminocyclitols and everninomicin as other strains.
- Conversely, many methicillin-resistant strains exhibited resistance to erythromycin, rosamicin, and clindamycin at achievable serum concentrations.
Conclusions:
- Novel aminocyclitols and everninomicin represent promising non-beta-lactam alternatives with broad antistaphylococcal activity, including against MRSA.
- The emergence of resistance to macrolides and clindamycin in MRSA highlights the need for alternative therapeutic options.
- Culture medium composition can influence observed resistance patterns, particularly for penicillinase-resistant penicillins against MRSA.