RESUMO
The statistical methods and parameters commonly used to define bacterial susceptibility to antibiotics in vitro such as MIC(50), linear regression or others, usually lead to a considerable loss of information: they do not take into account the heterogeneity of the bacterial population. In contrast, multivariate data analyses are more adapted to the description of biological systems. In this way, a population of a given bacterial species can be separated into homogenous classes corresponding to the different sensitivity and resistance phenotypes. The applications of this mathematical approach include: (i) a new model for more relevant interpretation of antimicrobial susceptibility test results; (ii) numerical estimation of breakpoints having a known risk; (iii) calibration of a technique relative to a reference technique; (iv) detection of strains with new phenotypes; (v) in vitro evaluation of the activity of new compounds.
Assuntos
Antibacterianos/farmacologia , Farmacorresistência Bacteriana , Testes de Sensibilidade Microbiana/métodos , Modelos Teóricos , Automação , Bactérias/classificação , Bactérias/efeitos dos fármacos , Bactérias/isolamento & purificação , Infecções Bacterianas/tratamento farmacológico , Calibragem , Heterogeneidade Genética/efeitos dos fármacos , Bactérias Gram-Negativas/efeitos dos fármacos , Bactérias Gram-Negativas/isolamento & purificação , Fenótipo , Fatores de RiscoRESUMO
Salmonella enterica serotype Typhi clinical isolates (n = 91) resistant to nalidixic acid (Nal(r)) were collected from sporadic cases and minor outbreaks throughout Vietnam between 1996 and 2004. These isolates were typed and compared by four methods: Vi phage typing, PstI ribotyping, XbaI and SpeI pulsed-field gel electrophoresis (PFGE), and single-nucleotide polymorphism (SNP) analysis. The results indicated that 65% of the isolates were not typeable by Vi phage typing. In contrast, the ribotyping and, with more accuracy, the SNP analysis methods indicated that all Nal(r) isolates belonged to a single clone (ribotype 3a, haplotype H58) that was found previously and that largely consisted of plasmid-encoded multidrug-resistant serotype Typhi isolates. PFGE demonstrated the occurrence of microevolution within this clone. We identified two major combined PFGE profiles: X1-S1 and X3-S6. X3-S6 predominated between 1996 and 2002 but was replaced by X1-S1 after 2002. Nevertheless, PFGE, with a Simpson's index of 0.78, was not considered an optimal discriminatory method for investigating typhoid fever outbreaks in Vietnam. The rate of quinolone resistance increased and the rate of multidrug resistance decreased during the study period. From 2002 to 2004, 80.6% of the isolates from South Vietnam were resistant only to Nal. The mechanism of Nal resistance in most of the isolates (94%) was a mutation in the quinolone resistance-determining chromosomal region of gyrA that led to the amino acid substitution Ser83Phe. No plasmid-located qnrA, qnrB, or qnrS was detected.
Assuntos
Quinolonas/farmacologia , Salmonella typhi/classificação , Tipagem de Bacteriófagos , Farmacorresistência Bacteriana Múltipla , Eletroforese em Gel de Campo Pulsado , Evolução Molecular , Testes de Sensibilidade Microbiana , Polimorfismo de Nucleotídeo Único , Ribotipagem , Salmonella typhi/efeitos dos fármacos , Salmonella typhi/genética , Fatores de Tempo , VietnãRESUMO
Salmonella enterica serovar Typhi strains resistant to ampicillin, chloramphenicol, tetracyclines, streptomycin, and cotrimoxazole, isolated from sporadic cases and minor outbreaks in Vietnam between 1995 and 2002, were typed and compared. Plasmid fingerprinting, Vi bacteriophage typing, XbaI pulsed-field gel electrophoresis, and PstI ribotyping showed that endemic, epidemic multidrug-resistant typhoid fever was due, for at least 74.1% of the isolates, to one or two clones of serovar Typhi harboring a single resistance plasmid. PstI ribotyping was used as a basic technique to ensure that a serovar Typhi expansion was clonal.