Log10 Reduction In Viable Counts Research Articles

Design, synthesis and biological evaluation of (Quinazoline 4-yloxy)acetamide and (4-oxoquinazoline-3(4H)-yl)acetamide derivatives as inhibitors of Mycobacterium tuberculosis bd oxidase

New chemical scaffolds with novel mechanism of action are urgently needed for the treatment of drug resistant tuberculosis. The oxidative phosphorylation pathway of Mycobacterium tuberculosis consists of multiple clinically validated drug targets. This pathway can function through any one of the two terminal oxidases-the proton pumping cytochrome bc1-aa3 supercomplex, or the less energy efficient but high affinity cytochrome bd oxidase. Inhibiting the bc1 complex alone has been found bacteriostatic and not bactericidal. On the other hand, inhibition of both these oxidases turns lethal to the pathogen. In the present study, we used a bc1 complex mutant of M. tuberculosis to screen (Quinazoline 4-yloxy)acetamide and (4-oxoquinazoline-3(4H)-yl)acetamide derivatives against the alternate oxidase, i.e., cytochrome bd oxidase. Two molecules, S-021-0601 and S-021-0607 were found to inhibit the mutant with MICs 8 and 16 μM respectively, compared to MICs of 128 and 256 μM against the wild type M. tuberculosis. In the wild type, one of the compounds showed synergism with Q203, an inhibitor of bc1 complex, in inhibiting growth under aerobic conditions. Both compounds showed synergism with Q203 in depleting bacterial ATP and inhibiting oxygen consumption. Both the compounds at 32 μM (one-fourth or one-eighth of their MICs for wild type) were bactericidal to wild type bacteria under hypoxic condition, causing ∼1.9 log10 reduction in viable counts which increased to ∼4-log10 when combined with Q203.

101 Time to recurrence and antimicrobial susceptibility of first-time detected Achromobacter xylosoxidans in respiratory tract specimens from patients with cystic fibrosis

Introduction: Fosfomycin and tobramycin in a 4:1 (w/w) ratio (F:T) has been developed for treatment of bacterial respiratory infections. The aim of this study was to investigate whether this combination was synergistic against respiratory pathogens under aerobic and anaerobic conditions. Methods: Clinical P. aeruginosa (PA, n = 15) isolates were grouped according to their F:T MIC: i. 10mg/L; ii. >1020mg/L and iii. >20mg/L. Five PA isolates from each group and a further 5 MRSA isolates were selected for time-kill studies using F:T at a concentration of 2x aerobic MIC and both antibiotics alone at the concentration used in the combination. Synergy was defined as a 2 log10 reduction in viable count at 24 h with the combination compared to the most active agent alone. Results: The F:T combination was found to be synergistic against 20% and 45% of isolates under aerobic and anaerobic conditions, respectively (Table). Some PA isolates had re-grown at 24 h when tested against fosfomycin and tobramycin alone under both conditions; however, F:T remained bactericidal at 24 h. F:T showed no antagonism when tested against any of the isolates under either growth condition. Conclusion: This study demonstrates by time-kill that F:T is synergistic against clinical PA and MRSA isolates with synergistic activity more pronounced under anaerobic conditions. F:T may therefore be a viable treatment option for anaerobic and aerobic infections caused by these bacterial respiratory pathogens.

English

Crude extracts of four actinomycetes species belonging to Actinoplane [NB 034],Streptomyces [TR 007] and Actinopolyspora [NB 069 and TR 008] genera were screened for antibacterial activities against a wide range of bacterial strains. The extracts showed antibacterial activities against both Gram-negative and Gram-positive test bacteria with zones of inhibition ranging between 2 and 27 mm (NB 034); 9 and 15 mm (TR 007); 8 and13 (NB 069) and 2 and 12 mm (NB 069). The minimum inhibitory concentration (MIC) of the extracts against the test bacteria ranged from 0.039 - 5 mg/ml, while the minimum bactericidal concentrations (MBC) ranged from 5 to >10 mg/ml. The extracts exhibited concentration-time dependent killing of Staphylococcus aureus OKOH2A and Staphylococcus scuiri OKOH2B with a 0.73log10 and 0.88log10reduction in viable counts respectively, while a re-growth phenomenon was exhibited byKlebsiella pneumonia ATCC 4352 and Escherichia coli ATCC 25922 at MIC, 2 × MIC and 4 × MIC of Streptomyces (TR 007) Actinopolyspora (TR 008) extracts. All the active extracts exhibited bacteriostatic activities.   Key words: Actinoplane, Streptomyces, Actinopolyspora, antibiotic production.

In vitro activity of tea-tree oil against clinical skin isolates of meticillin-resistant and -sensitive Staphylococcus aureus and coagulase-negative staphylococci growing planktonically and as biofilms

The susceptibility of Staphylococcus aureus [meticillin-resistant (MRSA) and meticillin-sensitive (MSSA)] and coagulase-negative staphylococci (CoNS), which respectively form part of the transient and commensal skin flora, to tea-tree oil (TTO) was compared using broth microdilution and quantitative in vitro time-kill test methods. MRSA and MSSA isolates were significantly less susceptible than CoNS isolates, as measured by both MIC and minimum bactericidal concentration. A significant decrease in the mean viable count of all isolates in comparison with the control was seen at each time interval in time-kill assays. However, the only significant difference in the overall mean log10 reduction in viable count between the groups of isolates was between CoNS and MSSA at 3 h, with CoNS isolates demonstrating a significantly lower mean reduction. To provide a better simulation of in vivo conditions on the skin, where bacteria are reported to grow as microcolonies encased in glycocalyx, the bactericidal activity of TTO against isolates grown as biofilms was also compared. Biofilms formed by MSSA and MRSA isolates were completely eradicated following exposure to 5 % TTO for 1 h. In contrast, of the biofilms formed by the nine CoNS isolates tested, only five were completely killed, although a reduction in viable count was apparent for the other four isolates. These results suggest that TTO exerts a greater bactericidal activity against biofilm-grown MRSA and MSSA isolates than against some biofilm-grown CoNS isolates.

Bactericidal activity of micromolar N-chlorotaurine: evidence for its antimicrobial function in the human defense system.

N-Chlorotaurine, the main representative of long-lived oxidants found in the supernatant of stimulated granulocytes, has been investigated systematically with regard to its antibacterial activity at different physiological concentrations for the first time. N-Chlorotaurine (12.5 to 50 microM) demonstrated a bactericidal effect i.e., a 2 to 4 log(10) reduction in viable counts, after incubation at 37 degrees C for 6 to 9 h at pH 7.0, which effect was significantly enhanced in an acidic milieu (at pH 5. 0), with a 3 to 4 log(10) reduction after 2 to 3 h. Moreover, bacteria were attenuated after being incubated in N-chlorotaurine for a sublethal time, as demonstrated with the mouse peritonitis model. The supernatant of stimulated granulocytes exhibited similar activity. Transmission electron microscopy revealed changes in the bacterial cell membrane and cytoplasmic disintegration with both reacting systems, even in the case of a mere attenuation. The results of this study suggest a significant bactericidal function of N-chlorotaurine and other chloramines during inflammation.

Response of single species biofilms and microcosm dental plaques to pulsing with chlorhexidine.

The aim of this study was to determine the effect of pulsing chlorhexidine gluconate, at concentrations commonly used in mouthwashes, on Streptococcus sanguis biofilms and microcosm dental plaques in vitro. Biofilms were grown on bovine enamel and nutrients were supplied in the form of artificial saliva. Pulsing experiments were carried out on steady-state biofilms using 0.05 or 0.2% chlorhexidine solutions delivered twice daily for 1 min. In a separate study, the enamel discs on which the biofilms were formed were pre-treated with chlorhexidine and pulsed directly after inoculation and then at regular intervals. With both concentrations of chlorhexidine used, a c.2 log10 reduction in the viable counts of S. sanguis was achieved with the initial pulse, but as pulsing continued, the bacterial population recovered, albeit not to the previous level. A c.1 log10 reduction in the total viable counts of the microcosm plaques was seen after the first pulse with 0.2% chlorhexidine. The total count then recovered rapidly and, after the fifth pulse, the total viable counts were not significantly different from those before pulsing. The total counts then remained at a similar level throughout the course of the experimental runs. Pre-treatment of the enamel discs with 0.2% chlorhexidine before inoculation produced viable counts of c.10(5) cfu/mm2, a 1 log10 reduction compared with untreated discs. After pulsing with 0.2% chlorhexidine at 8 h, a 3 log10 reduction was seen in the total aerobic and anaerobic counts, but again the viable counts subsequently increased despite twice-daily chlorhexidine pulsing. Regardless of the nature of the biofilm, pulsing initially achieved substantial kills, but the viability of the biofilms subsequently increased despite continued pulsing. Chlorhexidine was effective at reducing the viability of microcosm plaques when it was applied to the substratum before exposure to bacteria and subsequently pulsed on to the biofilms.

Heat tolerance of vancomycin resistant Enterococcus faecium.

The heat tolerance of 27 Enterococcus faecium isolates in water was studied. Stationary phase cultures including vancomycin resistant and sensitive clinical and food isolates were exposed to heat at 60 degrees, 65 degrees, 71 degrees, and 80 degrees C for one, three, 10, and 30 minutes and the log10 reductions in bacterial counts were determined. Exposure at 71 degrees and 80 degrees C resulted in > 6 log10 reduction in viable counts for all isolates. Seven (24%) isolates survived (< 5 log10 reduction) heat at 65 degrees C for 10 minutes. The E faecium isolates were more resistant to heat than the two E faecalis reference strains. No differences in heat tolerance were observed between vancomycin sensitive and resistant strains or between isolates of human or food origin.

Sensitization of Escherichia coli to nisin by maltol and ethyl maltol

When used separately, 20 mmol l-1 maltol or 1600 AU ml-1 nisin resulted in a 0-0.6 log10 reduction in viable counts of Escherichia coli in a buffer system. However, when added in combination they yielded a 1.8-5.5-log-cycle reduction in viable counts of E. coli at pH 5.0 and 6.8 respectively. It is postulated that maltol (and ethyl maltol) destabilizes the cell outer membrane by chelation of Mg2+ and/or Ca2+, thus permeabilizing the E. coli cell to nisin.

Further studies on post‐antibiotic effect and synergism in two strains of Streptococcus faecalis

The differences in the synergistic potential for either killing effect or increase in duration of post-antibiotic effect (PAE) seen with various beta-lactam-aminoglycoside combinations in two strains of Streptococcus faecalis were further studied to examine this relationship in more detail. It was seen that a strain which produced a synergistic increase in recovery period (PAE greater than or equal to 0.5 h), comparing the beta-lactam antibiotics alone and when combined with streptomycin, showed increased sensitivity (greater than or equal to 1 log10 reduction in viable counts) to a subinhibitory concentration of streptomycin added to a culture recovering from the PAE; this was not demonstrated with a strain showing no increase in PAE when briefly exposed to a combination therapy, although its corresponding killing curve was clearly synergistic. Moreover, it was seen that the differences in the synergistic prolongation of recovery period when combining various aminoglycosides at 1/4 x MIC with ampicillin were consistent with the different duration of PAE with the particular aminoglycoside alone at the MIC.