Sensitivity of Brucella spp to tetracycline and its analogues.

Abstract

SYNOPSIS The sensitivity to eight tetracyclines of 100 strains of brucellae, comprising strains of Brucella abortus, Br. melitensis, and Br. suis, was determined. Demethylchlortetracycline was the most effective against all the groups of brucellae, whereas oxytetracycline and chlortetracycline were the least effective. The mean MIC value for demethylchlortetracycline, doxycycline, lymecycline, and tetracycline was < 1 ,ug/ml. Strains of Br. abortus biotype 2 and Br. suis were the most sensitive strains examined.Tetracyclines are the most effective of the chemotherapeutic agents in the treatment of brucellosis (Spink, 1964;Rizzo-Naudi et al, 1967). Robertson et al (1973) have shown that strains of Brucella abortus are almost uniformly sensitive to tetracycline, and the minimum inhibitory concentiation (MIC) values are between four and eight times less than the peak plasma levels. Steigbigel et al (1968), in an extensive study, found significant differences in the in-vitro antimicrobial activity of tetracycline and its various chemical analogues.In this investigation the sensitivity of strains of Br. abortus, Br. melitensis, and Br. suis were determined to tetracycline and seven of its analogues. The ditch plate method, described by Robertson et al (1973) as a suitable method for determining the MIC of various antibiotics to brucellae, was used after further preliminary investigation. Material and methods BRUCELLA STRAINSThe 100 strains of brucellae used in this study were isolated from human and animal sources. They were classified according to the criteria of Alton and Jones (1967) into 67 strains of Br. abortus, 23 strains of Br. melitensis, and 10 strains of Br. suis, and divided into their biotypes. The strains of Br. abortus were either isolated from cow's milk or cultured from the blood of patients with brucellosis in north-west Lancashire, the strains of Br. melitensis were isolated from patients infected abroad, and the strains of Br. suis were isolated from animal sources abroad. Received for publication 5 May 1976The strains were grown on serum-dextrose (SD) agar, prepared from blood agar base No. 2 (Oxoid) incorporating 5% horse serum and 1 % dextrose. All plates were incubated in air containing 10% CO2 at 37°C for three days. TETRACYCLINE SOLUTIONStock solutions of the following eight tetracyclines were prepared in 10% dimethylformamide (DMF): chlortetracycline, demethylchlortetracycline, doxycline, lymecycline, methacycline, minocycline, oxytetracycline, and tetracycline. They were obtained as powders of known potency from Mast Laboratories, Liverpool.The solutions were prepared as required and sterilized by membrane filtration. MINIMUM INHIBITORY CONCENTRATION OF THE CONTROL STRAINThe WHO prototype Br. abortus biotype 2 was used as the control strain and the MIC of each tetracycline was determined as follows:A series of two-fold dilutions of each of the tetracyclines was prepared in SD agar plates ranging from 4 ,tg/ml to 0-1 ,ug/ml. Control plates were prepared containing the highest proportion o...

In vitro susceptibility of Brucella melitensis to antibiotics

“…The MIC of streptomycin remained essentially unchanged from that observed by many investigators for the past half century (3,12). Rifampin MIC90s in previous studies were reported to range from 0.02 to 0.10 ,ug/ml, values confirmed again by our findings (8,10,12). In vitro susceptibility to co-trimoxazole was also found to be in the range described previously.…”

“…Minocycline demonstrated the lowest MIC in our study, a finding that has been repeatedly demonstrated for the various tetracycline compounds (8,10,11). The low MIC, however, was not accompanied by a rapid kill.…”

“…Tubes were incubated in the conditions mentioned above. Aliquots were obtained at the following times: 0 min, 30 min, 2 h, 8 h, 12 accurately detectable number of CFU per milliliter was 10. This number was determined in previous tests by using various bacterial dilutions in this broth following the incubation conditions mentioned above.…”

In Vitro Activity of Eight Fluoroquinolones Against Clinical Isolates of Brucella Melitensis

“…to be susceptible to some of the fluoroquinolones [4,[13][14][15]; this investigation was extended to test 8 different fluoroquinolones which are either commercially available or in the various stages of development. The relapse rate with conventional drugs used against B. melitensis has been reported to range between 5-70% [10][11][12]. Compared to these figures, the fluoroquinolones were found to be extremely effective agents against B. melitensis.…”

Functional Characterization of Brucella melitensis NorMI, an Efflux Pump Belonging to the Multidrug and Toxic Compound Extrusion Family

“…Therefore, to be effective, the treatment of acute brucellosis requires drugs that penetrate macrophages. With conventional drugs such as tetracycline, aminoglycosides, or sulfonamides, high relapse rates have been reported (8,13,23). More recently, increasing resistance of Brucella spp.…”