A 1-year prospective study was carried out in two large urban centers of São Paulo State, Brazil, to determine the prevalences and roles of the different Escherichia coli pathotypes in children less than 5 years of age with diarrhea presenting to the emergency rooms of public hospitals or visiting private pediatricians' offices. Of the pathotypes sought, typical enteroaggregative and atypical enteropathogenic types of E. coli were isolated for 8.9% and 5.4% of 774 diarrhea cases, respectively, and were found to be dominant and significantly associated with diarrhea.

Bacterial resistance to antibiotics in community-acquired respiratory tract infections is a serious problem and is increasing in prevalence world-wide at an alarming rate. Streptococcus pneumoniae, one of the main organisms implicated in respiratory tract infections, has developed multiple resistance mechanisms to combat the effects of most commonly used classes of antibiotics, particularly the beta-lactams (penicillin, aminopenicillins and cephalosporins) and macrolides. Furthermore, multidrug-resistant strains of S. pneumoniae have spread to all regions of the world, often via resistant genetic clones. A similar spread of resistance has been reported for other major respiratory tract pathogens, including Haemophilus influenzae, Moraxella catarrhalis and Streptococcus pyogenes. To develop and support resistance control strategies it is imperative to obtain accurate data on the prevalence, geographic distribution and antibiotic susceptibility of respiratory tract pathogens and how this relates to antibiotic prescribing patterns. In recent years, significant progress has been made in developing longitudinal national and international surveillance programs to monitor antibiotic resistance, such that the prevalence of resistance and underlying trends over time are now well documented for most parts of Europe, and many parts of Asia and the Americas. However, resistance surveillance data from parts of the developing world (regions of Central America, Africa, Asia and Central/Eastern Europe) remain poor. The quantity and quality of surveillance data is very heterogeneous; thus there is a clear need to standardize or validate the data collection, analysis and interpretative criteria used across studies. If disseminated effectively these data can be used to guide empiric antibiotic therapy, and to support-and monitor the impact of-interventions on antibiotic resistance.

During investigation of susceptibility testing methods for polymyxins, 24 multidrug-resistant clinical isolates of Pseudomonas aeruginosa were observed to have a distinct, reproducible phenotype in which skipped wells were observed during broth microdilution testing for polymyxin B. Possible mechanisms underlying this phenotype were investigated. The effects of various concentrations of polymyxin B on growth, the expression of resistance genes, and outer-membrane permeability were observed. Real-time PCR was performed to compare the expression, in response to selected concentrations of polymyxin B, of genes related to the PhoP-PhoQ and PmrA-PmrB two-component regulatory systems in polymyxin B-susceptible isolate PAO1, polymyxin B-resistant isolate 9BR, and two isolates (19BR and 213BR) exhibiting the skipped-well phenotype. 19BR and 213BR appeared to have similar basal levels of expression compared to that of PAO1 for phoQ, arnB, and PA4773 (from the pmrAB operon), and in contrast, 9BR had 52-and 280-fold higher expression of arnB and PA4773, respectively. The expression of arnB and PA4773 increased in response to polymyxin B in a concentrationdependent manner for 9BR but not for 19BR and 213BR. For these isolates, expression was significantly increased for arnB and PA4773, as well as phoQ, only upon exposure to 2 g/ml polymyxin B but not at a lower concentration of 0.125 g/ml. The sequencing of the pmrAB and phoPQ operons for all three isolates revealed a number of unique mutations compared to that for PAO1. 1-N-phenylnaphthylamine (NPN) was used to study the effect of preincubation with polymyxin B on the self-promoted uptake of polymyxin B across the outer membrane. The preincubation of cells with 2 g/ml polymyxin B affected baseline membrane permeability in 19BR and 213BR and also resulted in a reduced rate of NPN uptake in these isolates and in PAO1 but not in 9BR. The results presented here suggest that the skipped-well isolates have the ability to adapt to specific concentrations of polymyxin B, inducing known polymyxin B resistance genes involved in generating alterations in the outer membrane.The emergence of multidrug-resistant gram-negative organisms and the simultaneous lack of new clinically available antimicrobial agents have led to a resurgence of older compounds such as the polymyxins (6). These agents, including polymyxin B and colistin, have highly potent activity against gramnegative organisms, including Pseudomonas aeruginosa, but were previously abandoned due to a reported high incidence of nephrotoxicity and neurotoxicity (12).Resistance to polymyxin B is predominantly associated with decreased uptake into the bacterial cell resulting from a reduced capacity for initial binding (23). Polymyxin B and other polycationic compounds enter the cell via a process known as self-promoted uptake (10, 11). Polymyxin B binds to outer-membrane lipopolysaccharide (LPS) displacing Mg 2ϩ and disrupting the Mg 2ϩ cross bridges between anionic LPS molecules in the outer membrane, thus leading to membrane des...

Objective:We assessed the antimicrobial resistance patterns of pathogens responsible for urinary tract infections (UTI) in outpatients in São Paulo, Brazil, as well as the Escherichia coli antimicrobial resistance trend. Materials and Methods: Outpatients urine cultures were collected from January 2000 to December 2003. Statistical analysis considered positive results for one bacterial species with colony count ≥ 100,000 CFU/mL. Stratification was done on age group and gender. Statistical tests used included chi-square and the chi-square test for trend to evaluate differences between susceptibility rates among age groups and ordering in the E. coli resistance rates per year, respectively. Results: There were 37,261 positive results with Enterobacteriaceae isolated in 32,530 (87.3%) and Gram-positive cocci in 2,570 (6.9%) cultures. E. coli had the highest prevalence (71.6%). Susceptibility tests were performed in 31,716 cultures. E. coli had elevated resistance rates (> 30%) to ampicillin, trimethoprim-sulfamethoxazole, and tetracycline. Significant differences between age groups and ordering among years were observed. Conclusions: The use of trimethoprim-sulfamethoxazole is precluded in the population studied due to elevated resistance rates (> 30%) among most prevalent pathogens. Significant resistance rate differences among age groups and years were observed, particularly for fluoroquinolones. Fluoroquinolones should be used with caution. Nitrofurantoin should be used as empirical therapy for primary, non-complicated urinary tract infections.

Establish the susceptibility pattern of Gram-negative bacteria causing infections in ICU patients, MYSTIC Program Brazil 2003. Gram-negative bacteria (n = 1,550) causing nosocomial infections were collected at 20 Brazilian centers. The central laboratory confirmed the identification and performed the susceptibility tests by Etest methodology (AB Biodisk, Solna, Sweden) for meropenem, imipenem, ciprofloxacin, ceftazidime, cefepime, cefotaxime, piperacillin/tazobactam, gentamicin, and tobramycin. Interpretation criteria used were according to National Committee for Clinical Laboratory Standards (NCCLS). Pseudomonas aeruginosa (30.3%) was the most frequent isolate, followed by E. coli (18.6%), Klebsiella pneumoniae (16.9%), Acitenobacter baumannii (8.8%), and Enterobacter cloacae (7.1%). Pseudomonas aeruginosa (n=470) isolates presented susceptibility rates of 64% to meropenem, 63.8% to piperacillin/tazobactam, 63.4% to amikacin, 58.7% to imipenem. Acitenobacter baumannii presented susceptibility rates to meropenem of 97.1%, and 73% to tobramycin. E. coli and K. pneumoniae were highly susceptible to both carbapenems. Carbapenem resistance among the Enterobacteriaceae is still rare in the region. Acitenobacter baumannii and P. aeruginosa presented elevated resistance rates to all antimicrobials. Since they play an important role in nosocomial infections in this environment, the use of empirical combination therapy to treat these pathogens may be justified.

Pharmacodynamic exposures, measured as the ratio of steady-state total drug area under the curve to MIC (AUC/MIC), were modelled using a 5000-patient Monte-Carlo simulation against 119 non-duplicate clinical isolates of Staphylococcus aureus and 82 coagulase-negative staphylococci (CNS) collected from hospitals in Brazil between 2003 and 2005. Pharmacodynamic targets included an AUC/MIC >82.9 for linezolid and >345 for teicoplanin and vancomycin, as well as a free drug AUC/MIC >180 for vancomycin. The cumulative fractions of response (CFRs) against all S. aureus isolates were 96.0%, 30.1%, 71.6%, 48.0% and 65.1% for linezolid 600 mg every 12 h, teicoplanin 400 mg every 24 h and 800 mg every 24 h, and vancomycin 1000 mg every 12 h and every 8 h, respectively. Using a free drug target for vancomycin improved the CFR to 94.6% for the high-dose regimen, but did not substantially alter results for the lower dose. CFRs against all CNS isolates were 97.8%, 13.4%, 34.6%, 10.9% and 31.3%, respectively, for the same antibiotic regimens. The CFR was reduced for all compounds among the methicillin-resistant isolates, except for linezolid against methicillin-resistant CNS. Sensitivity analyses did not alter the final order of pharmacodynamic potency against these isolates. Although higher doses of vancomycin and teicoplanin increased the CFR, the likelihood of achieving bactericidal targets was still lower than with linezolid. The results for the high-dose vancomycin regimen were highly dependent on the pharmacodynamic target utilised. These data suggest that linezolid has a greater probability of attaining its requisite pharmacodynamic target than teicoplanin and vancomycin against these staphylococci.

A case-control (46 cases, 23 controls) study was done to determine risk factors for an outbreak of a multiresistant Acinetobacter baumanii (only susceptible to colistin) in a university hospital. The use of antecedent antibacterials and intubation were independent risk factors. No common source was found. With control measures, the outbreak resolved gradually.

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