An outbreak of catalase-negative methicillin-resistant Staphylococcus aureus.

The wide dissemination of a major epidemic methicillin-resistant Staphylococcus aureus (MRSA) clone in Brazilian hospitals (Brazilian clone) limits the value of molecular typing techniques such as pulsed-field gel electrophoresis (PFGE) for outbreak investigation. We report the first outbreak of a catalase-negative strain of MRSA, which was initially detected by the unusual result of this phenotypical test. The outbreak occurred in the Hospital Sanatorinhos de Carapicuíba, a 237-bed secondary hospital located in São Paulo, Brazil. From May to August 2002, a total of 11 MRSA isolates were recovered from four patients in the intensive care unit. All the isolates were catalase negative and susceptible only to vancomycin and linezolid. Three of the four patients eventually died. Molecular typing demonstrated an indistinguishable PFGE pattern among the 11 isolates, with similarities to the Brazilian clone and the hospital's usual MRSA strain. This report emphasizes the importance of an uncommon phenotypical result as a marker for initiating an outbreak investigation and should encourage clinical laboratories to recognize and report such isolates.

Antimicrobial susceptibility of coagulase-negative staphylococci and characterization of isolates with reduced susceptibility to glycopeptides.

The antimicrobial susceptibility of 239 coagulase-negative staphylococci (CNS) isolates consecutively collected from blood culture in patients admitted in a 600-bed teaching hospital was evaluated. The isolates were identified to the species level by conventional methods and the MicroScan Positive Combo Panel type 6 system, and their susceptibility to vancomycin, teicoplanin, and oxacillin were tested by agar dilution, disk diffusion, and MicroScan-WalkAway system. The species distribution was as follows: Staphylococcus epidermidis 120 (50.2%), S. hominis 29 (12.1%), S. haemolyticus 24 (10.0%), S. cohnii 14 (5.9%), and isolates from other CNS species 52 (21.8%). The percentage of resistance to oxacillin was 74.5% by agar dilution. The highest percentages of oxacillin resistance were found among S. haemolyticus (95.8%) and S. epidermidis (80.8%). Teicoplanin resistance (MIC > or = 32 micrograms/mL) was detected in five S. haemolyticus isolates, whereas intermediate resistance (MIC = 16 micrograms/mL) was detected in nine strains. These isolates with reduced susceptibility to teicoplanin were resistant to oxacillin, but remained susceptible to vancomycin (MIC < or = 4 micrograms/mL). Two isolates, one S. haemolyticus and one S. epidermidis, showed a vancomycin MIC of 8 micrograms/mL, and both MicroScan and disk diffusion methods classified these isolates as susceptible. Our results showed that glycopeptide resistance is emerging among CNS isolates in our institution and the disk diffusion method may not detect isolates with decreased susceptibility to these antimicrobial agents.

Comparative In Vitro Activities of Moxifloxacin (Bay 12-8039) and Other Antimicrobial Agents Against Respiratory Tract Pathogens in Brazil.

Clinical isolates of respiratory tract pathogens were susceptibility tested against six different antimicrobial agents. The in vitro activity of moxifloxacin was compared with that of levofloxacin, cefaclor, amoxicillin-clavulanate acid, azithromycin and trimethoprim-sulfamethoxazole against 111 isolates, including Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis and other species isolated from respiratory tract infections. All isolates were susceptible to moxifloxacin, except for two isolates of Pseudomonas aeruginosa which showed intermediate-resistance (MIC=6µg/mL), and one isolate of Escherichia coli which showed resistance (MIC>32µg/mL). Only moxifloxacin and amoxicillin-clavulanic acid were active against 100% of S. pneumoniae isolates at the suceptible breakpoint (MIC90, 0.25 µg/mL and 0.064 µg/mL respectively). The rank order of the activity among this group of drugs against S. pneumoniae was as follows (% of susceptibility): moxifloxacin = amoxicillin-clavulanic acid (100%) > levofloxacin (97%) > cefaclor (71%) > trimethoprim-sulfamethoxazole (54%) > azithromycin (53%). Except for trimethoprim-sulfamethoxazole, all antimicrobial agents were 100% active against H. influenzae and M. catarrhalis. The fluoroquinolones, moxifloxacin and levofloxacin, were the most potent compounds against these pathogens (MIC(90) 0.032 0.19 µg/mL). These in vitro susceptibility testing data of moxifloxacin support the view that this fluoroquinolone will have an important therapeutic role in the treatment of respiratory tract diseases.