In Staphylococcus aureus, in addition to mutations in the grl and gyr gene loci, multidrug efflux pumps like NorA contribute to decreased fluoroquinolone susceptibility. Efflux pumps can be inhibited by the plant alkaloid reserpine, which, at 20 mg/L, reduced sparfloxacin, moxifloxacin and ciprofloxacin IC50s and MICs by up to four-fold in 11, 21 and 48 of the 102 unrelated clinical isolates tested, respectively. The effect was less pronounced with the hydrophobic drugs sparfloxacin and moxifloxacin than with the hydrophilic drug ciprofloxacin and was stable in all 25 clonally related isolates tested.
The topical agent mupirocin plays a crucial role in strategies designed to control outbreaks of methicillin-resistant Staphylococcus aureus. The extent of high- or low-level mupirocin resistance amongst S. aureus from European hospitals is not known. Six hundred and ninety-nine S. aureus and 249 coagulase-negative staphylococci (CNS) derived from blood, hospital-acquired pneumonia or skin and soft tissue infections from 19 European hospitals were tested for susceptibility to mupirocin and oxacillin. Methicillin sensitivity was found in 72% and 32% of S. aureus and CNS, respectively. High-level mupirocin resistance was detected in 1.6% of S. aureus and 5.6% of CNS isolates, while low-level mupirocin resistance was detected in 2.3% of S. aureus and 7.2% of CNS isolates. Amongst S. aureus, methicillin-resistant isolates were twice as likely to have high- or low-level mupirocin resistance. This difference was less pronounced in CNS. No relationship was found between the site of infection and prevalence of mupirocin resistance. High- and low-level mupirocin resistance was detected amongst staphylococci from 10 and 16 of the hospitals studied, respectively. To maintain the relatively low prevalence of mupirocin resistance in Europe amongst both S. aureus and CNS, the prudent use of mupirocin restricted to defined infection control strategies should be emphasized.
One hundred sixteen unrelated clinical isolates ofStaphylococcus aureus (70 ciprofloxacin resistant and 46 ciprofloxacin susceptible) from eight countries were studied for the presence of mutations in the grlA, grlB,gyrA, and gyrB gene loci. Two mutations withingrlA (located at codons 80 and 84) and two mutations withingyrA (located at codons 84 and 88) were clearly associated with ciprofloxacin resistance, although other mutations detected within the four genes studied may also contribute to decreased susceptibility.
The use of DNA amplification techniques such as the polymerase chain reaction (PCR) in modern diagnostic microbiology not only allows the sensitive and specific identification of micro-organisms but also the detection of specific antibiotic resistance genes. This study describes a multiplex PCR on bacterial colonies picked directly from agar plates without preceding DNA preparation. Eubacteria and staphylococci were identified by 16s rRNA specific PCR products. In parallel, specific primers were used for the detection of staphylococcal coa and mecA genes. This 4-h multiplex PCR, consisting of four sets of primers, was evaluated for rapid and specific differential diagnosis of methicillin-resistant and methicillin-susceptible strains of Staphylococcus aureus and coagulase-negative staphylococci. To analyse specificity of the amplification products, 100 non-staphylococcal, eubacterial isolates and 20 Candida albicans strains were tested. In a first step, specificity of all four single sets of primers was evaluated before the coamplification within the multiplex PCR procedure was performed. The results were compared with those of conventional susceptibility and typing methods. The specific 16s rRNA PCR product for eubacterial isolates (n = 786) and staphylococci (686) was found in all strains tested. The coa gene was detected only in S. aureus (488) strains with a specificity of loo%, and was not detected in any of the coagulase-negative staphylococci (198). The mecA gene was detected in 98% of methicillin-resistant staphylococci (393) and in 2% of all methicillin-susceptible staphylococci (293). The multiplex PCR with coamplification of different determinants provides rapid reliable information on staphylococcal identification and methicillin susceptibility supporting the diagnosis, treatment and control of staphylococcal infections.
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