Multilocus sequence typing of Staphylococcus aureus isolates recovered from cows with mastitis in Brazilian dairy herds.

Staphylococcus aureus is a major pathogen associated with bovine mastitis, one of the most important infectious diseases occurring in dairy cattle herds worldwide. In the present study, S. aureus isolates recovered from cows with mastitis in dairy herds located in the south-east of Brazil were genotyped by PFGE and multilocus sequence typing (MLST). PFGE identified 60 pulsotypes (PTs), which were found to be distributed among six clonal complexes (CCs) by MLST. All PTs with similarity percentages greater than 65 % belonged to the same CC. Most of the PTs belonged to CC126 (n=28) and CC97 (n=19), which were represented by 91 % of the isolates. These CCs have also been recovered from cows with mastitis in countries located in different continents, but they have rarely been isolated from human specimens. Few isolates were represented by PTs belonging to CCs that are frequently isolated from human specimens (CC1, CC5 and CC30). These data reinforce the hypothesis that a limited number of S. aureus CCs are responsible for most bovine mastitis cases internationally. Specific features of the specialized clones should be studied for use as future targets of mastitis control measures.

Occurrence and Characteristics of Erythromycin-Resistant Streptococcus pneumoniae Strains Isolated in Three Major Brazilian States.

We investigated the occurrence and phenotypic and genotypic characteristics of erythromycin-resistant Streptococcus pneumoniae strains isolated in three major states in Brazil, from 1990 to 1999. Of the 931 pneumococcal strains evaluated, 40 (4.3%) were erythromycin-resistant (Ery-R). Among the 40 Ery-R strains, 90.0%, 80.0%, 27.5%, 5.0%, and 2.5% were resistant to tetracycline, trimethoprim-sulfamethoxazole, penicillin, chloramphenicol, and rifampin, respectively. None of the strains were resistant to ofloxacin or to vancomycin. Most [37 (92.5%)] of the 40 Ery-R isolates presented the MLS(B) phenotype and 3 (7.5%) strains showed the M phenotype. PCR testing indicated that all MLS(B) phenotype isolates harbored the erm(B) gene only, whereas the mef(A/E) gene was present in all isolates presenting the M phenotype. The tet(M) gene was the most frequent (86.1%) among Ery-R isolates that were also resistant to tetracycline. Pulsed-field gel electrophoresis (PFGE) analysis after SmaI digestion revealed the occurrence of clonal relationships within groups of strains belonging to serotypes 14, 19A, and 23F. All Ery-R isolates belonging to serotype 14 were susceptible to penicillin and were included in a single clonal group (named Ery(14)-A) related to the England(14-)9 internationally spread clone.

Phenotypic and genotypic characterization of clinical and intestinal enterococci isolated from inpatients and outpatients in two Brazilian hospitals.

The phenotypic and genotypic characteristics of clinical and intestinal enterococcal isolates recovered from inpatients and outpatients of two Brazilian hospitals, located in Niterói city, Rio de Janeiro, Brazil, were compared. A total of 601 strains were studied, including 253 isolated from different clinical sources and 348 intestinal strains (205 isolated from inpatients and 143 from outpatients) recovered from fecal specimens. Isolates were identified by using conventional physiological tests and evaluated for high-level resistance to aminoglycosides (HLR-A) and resistance to vancomycin and ampicillin by the agar screening technique. Susceptibility to several antimicrobial agents was evaluated by the disk diffusion method. The genetic diversity of Enterococcus faecalis strains presenting HLR-A was assessed by pulsed-field gel electrophoresis of chromosomal DNA after SmaI digestion. E. faecalis was the most frequent species among clinical isolates (90.1%) and intestinal strains from inpatients (53.6%). E. casseliflavus was the prevalent species among intestinal isolates from outpatients (35.0%). Clinical isolates were shown to be resistant to erythromycin (53.0%), tetracycline (52.2%), ciprofloxacin (36.4%), gentamicin (36.4%), streptomycin (30.4%), chloramphenicol (34.4%), norfloxacin (32.0%), imipenem (3.2%), and ampicillin (2.8%). Vancomycin resistance was only detected in intrinsic vancomycin-resistant enterococcal species. The overall prevalence of HLR-A was 52.2% among clinical isolates and 40.5% among intestinal strains. However, HLR-A was significantly more frequent among intestinal strains obtained from inpatients (56.6%) than among strains from outpatients (17.5%). Three major clonal groups were found among E. faecalis strains exhibiting HLR-GE or HLR-GE/ST (clonal groups GE-A and GE-B), and strains exhibiting HLR-ST (clonal group ST-A). HLR-A, particularly HLR-GE, was most frequently associated with enterococcal strains of nosocomial origin. Isolates included in the major clonal groups were recovered from clinical and intestinal sources from patients in both hospitals, indicating both intrahospital and interhospital spread of strains.

The effect of subminimal inhibitory concentrations of penicillin on growth rate and haemolysin activity of group G Streptococcus

The influence of the subminimal inhibitory concentrations (1/3 and 1/4 of the MIC) of penicillin on growth rate and on haemolysin production of a strain of group G Streptococcus was studied. It was shown that 1/3 of the MIC almost completely inhibited the bacterial growth, but it was not able to inhibit haemolysin activity in the culture supernate. The generation time of bacteria grown in 1/4 of the MIC was approximately twice longer than that of the control culture. In all cultures, the haemolysin, after being produced (or liberated), reached a peak and decreased to low levels, which could suggest that group G Streptococcus produces some end products of metabolism that are able to inhibit haemolysin activity

Enzymatic activity of a group C Streptococcus in a penicillin-medium

Dye-binding assays were employed to study the effects of penicillin on the production of hyaluronidase and deoxyribonuclease by a group C streptococcal strain. Enzymatic activities were measured in supernates of bacterial cultures that had been exposed to low concentrations of the drug during growth. The addition of antibiotic resulted in an increase in the production of hyaluronidase and in a decrease in that of deoxyribonuclease. These alterations in the elaboration of extracellular substances and their release into the frowth environment could be of importance as the Streptococcus is affected in vivo during treatment with penicillin.

Precisäo da alça calibrada em contagem de bactérias viáveis (Shigella sonnei) / Accuracy of calibrated loop in available bacterial count (Shigella sonnei)

A variância entre os volumes tomados com alça calibrada, de uma soluçäo de ácido hialurônico, foi comparada com a variância dos volumes da mesma soluçäo, retirados com micropipeta automática. A primeira foi bem maior. Esta comparaçäo foi também realizada com uma suspensäo de Shigella sonnei: näo se observou diferença significativa

Efeito de concentraçöes subinibitórias de penicilina sobre antígenos de estreptococos do grupo G / Effect of subinhibitory concentrations of penicillin on antigens of group G streptococci

O efeito de concentraçöes subinibitórias de penicilina sobre a produçäo do antígeno grupo-específico e da hialuronidase extracelular foi avaliado em uma amostra de estreptococo pertencente ao grupo G de Lancefield. Em todas as concentraçöes uma maior quantidade de antígeno grupo-específico foi extraída das células e a atividade específica de hialuronidase se mostrou aumentada em até 1400% nos sobrenadantes das culturas. O maior aumento na expressäo de ambos os antígenos foi observado em 1/2 da CMI

Efeito de concentraçöes subinibitórias de penicilina sobre a morfologia de estreptococos do Grupo G / Effect of subinhibitory concentrations of penicillin on the morphology of Group G streptococci

O efeito de concentraçöes subnibitórias de penicilina, sobre a morfologia celular e colonial, foi avaliado em uma amostra de estreptococo pertencente ao grupo G de Lancefield. Este efeito foi mais evidente quando os microrganismos foram cultivados em 1/2 da CMI. Uma análise estatística permitiu a verificaçäo de que o número de cocos por cadeia se mostrou diminuído (1/2p < 0,01) em cultura cultivada em meio líquido acrescido de 1/2 da CMI, em relaçäo à cultura controle. Quando o antibiótico estava presente em concentraçöes de 1/4, 1/8 e 1/16 da CMI seus efeitos apresentaram-se menos evidentes. Mas o número de cocos por cadeia se mostrou aumentado (1/2p < 0,01). Foi possível, através da transformaçäo das constantes das exponenciais em "probits", demonstrar estatisticamente, que a concentraçäo de penicilina que possibilitaria a formaçäo de maiores cadeias é aquela de aproximadamente 1/7 da CMI