High level of quinolone resistance in <Emphasis Type="Italic">Escherichia coli</Emphasis> from healthy chicken broilers

The development of resistance to quinolones (nalidixic acid, ciprofloxacin and enrofloxacin) in 2006–2008 was evaluated in 317 strains of Escherichia coli isolated from healthy chicken broilers from various farms. The isolates (2006/2007/2008) showed a high resistance to nalidixic acid (87/85/67 %), ciprofloxacin (CIP) (49/54/29 %) and enrofloxacin (ENR) (52/42/22 %). Nalidixic acid-resistant isolates with low level of MIC for CIP and ENR represented a single mutation; intermediary MIC for CIP and ENR were related to two mutations and high level resistance MIC for CIP (≥4 mg/L) and ENR (≥16 mg/L) represented three mutations (two in gyrA and one in parC). There was a correlation between the phenotype reading of high-level resistance and mutations in gyrA (Ser83Leu, Asp87Tyr or Asp87Asn) and parC (Ser80Ile) gene. Plasmid-mediated quinolone-resistance qnrS gene was detected in one Escherichia coli strain with a high level of ciprofloxacin resistance. Our results demonstrate the increase in occurrence of multiresistant E. coli strains with a high level of chromosomal and plasmid resistance to fluoroquinolones.     

Decolorization of Acid Orange 7 by bacteria of different tinctorial type: a comparative study

The abilities of two bacterial strains of opposite tinctorial type, the Gram-negative Alcaligenes faecalis and the Gram-positive Rhodococcus erythropolis, to decolorize reaction medium containing initially 10, 50, 100, 200 and 500 mg l⁻¹ of the monoazo dye Acid Orange 7 are discussed. The dye-binding properties of the strains and the starting rate of the decolorization reaction in dependence on the initial dye concentration are compared. An assumption is made that the higher dye-binding ability of A. faecalis is due to the existence of an outer membrane. The experimental data revealed relative independence of the decolorization dynamics on the dye-binding properties of the cell, which could be regarded as an indirect confirmation of the known extracellular redox-mediator-dependent mechanism of azo group reduction.     

Role of interspecies interactions in dual-species biofilms developed in vitro by uropathogens isolated from polymicrobial urinary catheter-associated bacteriuria

Most catheter-associated urinary tract infections are polymicrobial. Here, uropathogen interactions in dual-species biofilms were studied. The dual-species associations selected based on their prevalence in clinical settings were Klebsiella pneumoniae–Escherichia coli, E. coli–Enterococcus faecalis, K. pneumoniae–E. faecalis, and K. pneumoniae–Proteus mirabilis. All species developed single-species biofilms in artificial urine. The ability of K. pneumoniae to form biofilms was not affected by E. coli or E. faecalis co-inoculation, but was impaired by P. mirabilis. Conversely, P. mirabilis established a biofilm when co-inoculated with K. pneumoniae. Additionally, E. coli persistence in biofilms was hampered by K. pneumoniae but not by E. faecalis. Interestingly, E. coli, but not K. pneumoniae, partially inhibited E. faecalis attachment to the surface and retarded biofilm development. The findings reveal bacterial interactions between uropathogens in dual-species biofilms ranged from affecting initial adhesion to outcompeting one bacterial species, depending on the identity of the partners involved.     

Isolation of new 6-methylnicotinic-acid-degrading bacteria, one of which catalyses the regioselective hydroxylation of nicotinic acid at position C2

2-Hydroxynicotinic acid is an important building block for herbicides and pharmaceuticals. Enrichment strategies to increase the chances of finding microorganisms capable of hydroxylating at the C2 position and to avoid the degradation of nicotinic acid via the usual intermediate, 6-hydroxynicotinic acid, were used. Three bacterial strains (Mena 23/3–3c, Mena 25/4–1, and Mena 25/ 4–3) were isolated from enrichment cultures with 6-methylnicotinic acid as the sole source of carbon and energy. Partial characterization of these strains indicated that they represent new bacterial species. All three strains completely degraded 6-methylnicotinic acid, and evidence is presented that the first step in the degradation pathway of strain Mena 23/3–3c is hydroxylation at the C2 position. Resting cells of this strain grown on 6-methylnicotinic acid also hydroxylated nicotinic acid at the C2 position, but did not further degrade the product. Strain Mena 23/ 3–3c showed the highest degree of 16S rRNA sequence similarity to members of the genera Ralstonia and Burkholderia. Received: 4 April 1997 / Accepted: 10 June 1997     

Biological treatment of the components of solid oligomeric waste from a nylon-6 production plant

On partial analysis of the solid oligomeric waste of a nylon-6 production plant, it was found to contain ε-caprolactam, 6-aminocaproic acid (6-ACA) and its linear and cyclic oligomers. Out of four bacterial isolates capable of utilizing caprolactam as the sole growth substrate, Alcaligenes faecalis was found to be the most potent and utilized 90% of caprolactam in 24 h. In shake flask experiments, when the solid waste after solubilization was treated with a consortium of bacteria of four different genera, except the cyclic oligomers, all the other constituents were found to be degraded. A reduction of the chemical oxygen demand (COD) of the solid waste to the level of 63–66% was obtained when it was treated with either a consortium of the bacterial isolates or only a single isolate, A. faecalis. Alcaligenes faecalis could bring about a decrease of 95% in the caprolactam content of the solid waste, while 6-ACA and its linear oligomers were almost completely degraded. Alcaligenes faecalis cells adapted on solid waste could degrade the linear oligomers at a faster rate as compared to cells adapted on caprolactam. However, cyclic oligomers could not be degraded in either case. When solid waste, partially hydrolysed with acid to yield 6-ACA as the major constituent, was treated with the consortium of bacterial isolates, a 95% reduction in the COD was achieved. This revised version was published online in November 2006 with corrections to the Cover Date.     

Evolutionary relationships among photosynthetic bacteria

To understand the evolution of photosynthetic bacteria it is necessary to understand how the main groups within Bacteria have evolved from a common ancestor, a critical issue that has not been resolved in the past. Recent analysis of shared conserved inserts or deletions (indels) in protein sequences has provided a powerful means to resolve this long-standing problem in microbiology. Based on a set of 25 indels in highly conserved and widely distributed proteins, all main groups within bacteria can now be defined in clear molecular terms and their relative branching orders logically deduced. For the 82 presently completed bacterial genomes, the presence or absence of these signatures in various proteins was found to be almost exactly as predicted by the indel model, with only 11 exceptions observed in 1842 observations. The branching order of different bacterial groups as deduced using this approach is as follows: low G+C Gram-positive (Heliobacterium chlorum) ↔ high G+C Gram-positive ↔ Clostridium–Fusobacterium–Thermotoga ↔ Deinococcus–Thermus ↔ green nonsulfur bacteria (Chloroflexus aurantiacus) ↔ Cyanobacteria ↔ Spirochetes ↔ Chlamydia–Cytophaga–Flavobacteria–green sulfur bacteria (Chlorobium tepidum) ↔ Aquifex ↔ Proteobacteria (δ and ∈) ↔ Proteobacteria (α) ↔ Proteobacteria (β) and ↔ Proteobacteria (γ). The Heliobacterium species, which contain an Fe–S type of reaction center (RC 1) and represent the sole photosynthetic phylum from the Gram-positive or monoderm bacteria (i.e., bounded by only a single membrane), is indicated to be the most ancestral of the photosynthetic lineages. Among the Gram-negative or diderm bacteria (containing both inner and outer cell membranes) the green nonsulfur bacteria, which contain a pheophytin-quinone type of reaction center (RC 2), are indicated to have evolved first. The later emerging photosynthetic groups which contain either one or both of these reaction centers could have acquired such genes from the earlier branching lineages by either direct descent or by means of lateral gene transfer. This revised version was published online in August 2006 with corrections to the Cover Date.     

Cultivable Bacterial Diversity of Alkaline Lonar Lake, India

Aerobic, alkaliphilic bacteria were isolated and characterized from water and sediment samples collected in the winter season, January 2002 from alkaline Lonar lake, India, having pH 10.5. The total number of microorganisms in the sediment and water samples was found to be 10²–10⁶ cfu g⁻¹ and 10²–10⁴ cfu ml⁻¹, respectively. One hundred and ninety-six strains were isolated using different enrichment media. To study the bacterial diversity of Lonar lake and to select the bacterial strains for further characterization, screening was done on the basis of pH and salt tolerance of the isolates. Sixty-four isolates were subjected to phenotypic, biochemical characterization and 16S rRNA sequencing. Out of 64, 31 bacterial isolates were selected on the basis of their enzyme profile and further subjected to phylogenetic analysis. Phylogenetic analysis indicated that most of the Lonar lake isolates were related to the phylum Firmicutes, containing Low G+C, Gram-positive bacteria, with different genera: Bacillus, Paenibacillus, Alkalibacillus, Exiguobacterium, Planococcus, Enterococcus and Vagococcus. Seven strains constituted a Gram-negative bacterial group, with different genera: Halomonas, Stenotrophomonas and Providencia affiliated to γ-Proteobacteria, Alcaligenes to β-Proteobacteria and Paracoccus to α-Proteobacteria. Only five isolates were High G+C, Gram-positive bacteria associated with phylum Actinobacteria, with various genera: Cellulosimicrobium, Dietzia, Arthrobacter and Micrococcus. Despite the alkaline pH of the Lonar lake, most of the strains were alkalitolerant and only two strains were obligate alkaliphilic. Most of the isolates produced biotechnologically important enzymes at alkaline pH, while only two isolates (ARI 351 and ARI 341) showed the presence of polyhydroxyalkcanoate (PHA) and exopolysaccharide (EPS), respectively.     

Technical aspects of the use of 3′,6′-diacetyl fluorescein for vital fluorescent staining of bacteria

Viable bacteria of several species have the capability to incorporate 3′,6′-diacetyl fluorescein (FDA) and rapidly hydrolyze it to fluorescein, which is stored intracellularly. However, several strains of viableEscherichia coli andAlcaligenes faecalis do not evolve and accumulate significant amounts of fluorescein when incubated on glass slides in the presence of FDA. In the present study, 10⁵–10⁷ E. coli orA. faecalis bacteria (viability more than 95%) were accumulated in separate experiments on 0.45-μm membrane filters and then stained for 5–10 min with FDA diluted immediately before use in phosphate-buffered saline, freshly prepared nutrient broth, or nutrient broth preconditioned by overnight growth of the respective bacteria. It was shown that in all cases about 20% of the bacteria did evolve significant amounts of fluorescein, thus enabling a visual observation of these cells in the fluorescence microscope.Bacillus cereus bacteria—that evolved and accumulated fluorescein on glass slides—were shown to be fluorescent on membrane filters after FDA staining. 100%, 40%, or 70% of the bacteria were stained if the FDA solution used had been prepared in nutrient broth preconditioned by overnight growth of the same bacteria, fresh nutrient broth, or phosphate-buffered saline, respectively. This preliminary study indicates the necessity of determining the technical conditions required for FDA staining for each bacterial species under study.     

Antibacterial activity of the leaf essential oil of <Emphasis Type="Italic">Blumea mollis</Emphasis> (D. Don) Merr.

The antibacterial activity of the leaf essential oil of Blumea mollis was assayed against 14 clinically isolated bacterial strains on Muller–Hinton Agar medium and Muller–Hinton Agar medium with 5% sheep blood. The essential oil had promising antibacterial activity against all the bacterial strains tested. The highest mean zone of inhibition and lowest values of minimum inhibitory concentration were recorded against methicillin-resistant Staphylococcus aureus followed by beta hemolytic Streptococcus pyogenes. The Gram-positive bacteria were more sensitive than Gram-negative bacteria. Among the bacterial strains tested, Psudomonas aeruginosa was resistant to the essential oil. The results of the present study suggest that the essential oil of B. mollis is one of the new medicinal resources as an antibacterial agent against the bacterial strains tested.     

Pumilicin 4, A Novel Bacteriocin with Anti-MRSA and Anti-VRE Activity Produced by Newly Isolated Bacteria <Emphasis Type="Italic">Bacillus pumilus</Emphasis> Strain WAPB4

A total of 34 bacterial strains with anti-methicillin-resistant Staphylococcus aureus (MRSA) activity were isolated from 69 soil and water samples collected from four areas of Thailand. One strain, WAPB4 identified as Bacillus pumilus, showed remarkable antibacterial activity against MRSA, vancomycin-resistant Enterococcus faecalis (VRE), and several Gram-positive test bacteria. Bacteriocin produced by WAPB4 was designated as pumilicin 4. It was heat stable up to 121°C, 15 min and active within the pH range of 3–9. Its activity disappeared when treated with pronase E, chymotrypsin, and trypsin, demonstrating its proteinaceous nature. At high dosage (80 AU mL⁻¹), the effect of pumilicin 4 was bactericidal to both MRSA and VRE. Bacteriostasis was observed for a low dose of bacteriocin (20 AU mL⁻¹). Purification of pumilicin 4 was performed by a three-step procedure, i.e., solvent extraction, solid phase extraction, and reversed-phase chromatography. The molecular mass of purified pumilicin 4 as determined by mass spectrometry was 1994.62 Dalton. This present study is the first report of a novel bacteriocin, pumilicin 4, produced by B. pumilus that has potential for use as an alternative antibacterial agent for the treatment of infection with MRSA and VRE.     

Antimicrobial susceptibility, β-lactamase and enterotoxin production in <Emphasis Type="Italic">Bacillus cereus</Emphasis> isolates from clinical and food samples

The antimicrobial susceptibility of 30 clinical and 30 food Bacillus cereus isolates was determined. All isolates were susceptible to streptomycin, ciprofloxacin and gentamicin, 90 % of them to clindamycin and vancomycin, and 67 % to erythromycin. All isolates were resistant to amoxicillin with clavulanic acid, ampicillin, cefotaxime, ciprofloxacin, cloxacillin, cefotaxime with clavulanic acid and penicillin. The MIC values (determined by E-tests) were 48–256 mg/L for ampicillin, 0.19–1.5 mg/L for gentamicin, 0.125–1.0 mg/L for clindamycin, 0.047–4.0 mg/L for erythromycin and 1.5–16 mg/L for vancomycin. The MICs 4.6–18.75 g/L were observed for penicillin using the microdilution method. The presence of metallo-β-lactamases was detected by E-test for 100 % of strains. Nonhemolytic diarrheal enterotoxin (NHE) was produced by 98.3 % of strains, while 31.7 % of them produced hemolytic diarrheal enterotoxin (HBL). Clinical isolates produced 10 % more HBL than food isolates. The psychrotrophic strains isolated from food samples produced NHE at 6.5 °C in 73 % of cases.     

ClinicalPseudomonas aeruginosa: Potential factors of pathogenicity and resistance to antimicrobials

Resistance to 17 antimicrobials, surface hydrophobicity, motility, biofilm, production ofN-acylhomoserine lactone signal molecules (N-butyrylhomoserine lactone andN-3-oxolauroylhomoserine lactone) and response to oxidative stress were analyzed in 47 clinicalPseudomonas aeruginosa strains. In addition to natural resistance, the strains demonstrated the greatest level of resistance to cefotaxime (91.5 %). Isolates in the range of 44.7–57.4 % were resistant to aminoglycosides and ciprofloxacin, of 25.5–36.2 % to cephalosporins. On the other hand, 97.9 % remained susceptible to meropenem, 93.6 % to piperacillin + tazobactam and 87.2% to piperacillin. The majority of the strains (72.3 %) manifested their hydrophilic character. Higher zones of motility showed 12 isolates (in average 54.8 mm) as compared to the others (30.2 mm). Approximately 1/3 of the strains (29.8 %) produced a higher amount of biofilm quantified by measuring the absorbance of solubilized crystal violet (0.20–0.46) than the rest of isolates (0–0.19). All but two strains producedN-3-oxolauroylhomoserine lactone and in 48.9 % of samplesN-butyrylhomoserine lactone were detected. Only four isolates with higher biofilm production showed both types of homoserine lactone. Majority of the strains (70.2 %) manifested higher resistance to H₂O₂ than the rest of the strains. The group of strains resistant to aminoglycosides and ciprofloxacin revealed a significantly higher number of hydrophobic strains (compared with the sensitive ones). In contrast, higher number of strains sensitive to aminoglycosides and ciprofloxacin or only to ciprofloxacin producedN-butyrylhomoserine lactone and biofilm (compared to the resistant ones). Such association was not found among the rest of the tested parameters. The results indicate that the resistance to antimicrobials inP. aeruginosa isolates was not generally associated with changes in the production of the pathogenicity factors.     

Class 1 integron in staphylococci

As a major concern in public health, methicillin-resistant staphylococci (MRS) still remains one of the most prevalent pathogens that cause nosocomial infections throughout the world and has been recently labeled as a “super bug” in antibiotic resistance. Thus, surveillance and investigation on antibiotic resistance mechanisms involved in clinical MRS strains may raise urgent necessity and utmost significance. As a novel antibiotic resistance mechanism, class 1 integron has been identified as a primary source of antimicrobial resistance genes in Gram-negative organisms. However, most available studies on integrons had been limited within Gram-negative microbes, little is known for clinical Gram-positive bacteria. Based on series studies of systematic integrons investigation in hundreds of staphylococci strains during 2001–2006, this review concentrated on the latest development of class 1 integron in MRS isolates, including summary of prevalence and occurrence of class 1 integron, analysis of correlation between integron and antibiotic resistance, further demonstration of the role integrons play as antibiotic determinants, as well as origin and evolution of integron-associated gene cassettes during this study period.     

Inhibition of uropathogens by lactic acid bacteria isolated from dairy foods and cow’s intestine in western Nigeria

A total of 96 lactic acid bacteria (LAB) were isolated from African indigenous fermented products and cow’s intestines to study their inhibitory capability against multi-drug-resistant uropathogens. Escherichia coli accounted for approximately 45% of isolated uropathogens, followed by Staphylococcus spp. (20%). The Gram negative uropathogens were highly resistant to quinolones, co-trimoxazole, teicoplanin and some β-lactams, while the Staphylococcus spp. showed high resistance to aminoglycosides, β-lactams and macrolides. Twenty-four LAB isolates were selected based on their antimicrobial activity against two uropathogenic Staphylococcus aureus strains and bacteriocin production. LAB strains showing antimicrobial activity were grouped into smaller groups through amplified ribosomal DNA restriction analysis (ARDRA). Representative strains were identified as Weissella spp., Enterococcus faecium, Lactococcus lactis and Lactobacillus brevis through sequencing of 16S rDNA. The Weissella spp. and L. brevis strains demonstrated remarkable inhibitory activity against seven strains of Gram negative uropathogens. Two strains of L. lactis produced a bacteriocin-like inhibitory substance active against Lactobacillus sakei. In this study, an unusual high rate of co-trimoxazole, quinolones and macrolides resistance among uropathogens from south west Nigeria was discovered. Based on their sensitivity to Weissella spp., there is a potential for using these LAB as a natural approach for the protection against the uropathogens assayed.     

Molecular Diagnosis of Urinary Tract Infections by Semi-Quantitative Detection of Uropathogens in a Routine Clinical Hospital Setting

Background

The objective of our study was the development of a semi-quantitative real-time PCR to detect uropathogens. Two multiplex PCR reactions were designed to detect Escherichia coli, Klebsiella spp., Enterobacter spp., Citrobacter spp., Proteus mirabilis, Enterococcus faecalis, and Pseudomonas aeruginosa. 16S based PCR was performed in parallel to detect Gram-positive and Gram-negative bacteria. Firstly to identify non-targeted agents of infection in the same urine specimen, and secondly to quantify background flora. The method was evaluated in comparison with standard bacterial culture, and a commercial PCR kit for detection of uropathogens.

Findings

Analysis with a known panel of 116 clinical isolates yielded a PCR specificity of 100%. Analysis of urine specimens from 211 patients revealed a high correlation of PCR Cq values with both culture positivity and quantity. Concordance between PCR and culture was 98% when both methods yielded results. PCR was found to be more sensitive than culture. With a cut-off Cq value of 33, the negative predictive value of PCR was 94%. The 16S PCR confirmed most results. One specimen was positive by 16S PCR suggesting another cause of infection not detected by the specific PCR assays.

Conclusion

We conclude that it is feasible to detect and identify uropathogens by multiplex real-time PCR assay.     

Enterococcus seriolicida Is a Junior Synonym of Lactococcus garvieae,a Causative Agent of Septicemia and Meningoencephalitis in Fish

The reference strains of Enterococcus seriolicida (ATCC 49156^T) (T = type strain) and of Lactococcus garvieae (ATCC 43921^T) and 30 field strains of Gram-positive cocci isolated from diseased rainbow trout in Italy were found to be phenotypically (API 20 STREPT and API 50 CH) and genetically (DNA-DNA hybridization) similar. The high DNA-DNA homologies (70–100%) and the low ΔT_m(e) (less than 1.1°C) among these strains showed that Enterococcus seriolicida and Lactococcus garvieae are synonyms, describing a single bacterial species. E. seriolicida strains should be classified as L. garvieae, which must be considered as a major pathogen of freshwater and salt water fish with a world-wide distribution.     

Temporal variation in juvenile fish communities of Kaunas reservoir littoral zone,Lithuania

The aim of this study was to assess juvenile fish communities in terms of species composition, fish diversity and density in the littoral zone of the Kaunas reservoir before (in 1989–1990, period I) and after (in 1999–2000, period II, and in 2006–2007, period III) launching the Kruonis hydroelectric pumped plant (Kruonis HPP). During the whole research period, 20 fish species were caught. According to the frequency of occurrence, the three-spined stickleback Gasterosteus aculeatus, European perch Perca fluviatilis and roach Rutilus rutilus were regarded as constant species in all investigated periods. Significant differences were established in juvenile fish community density between period I and periods II and III, whereas species richness (S) and species diversity indices (H′, J′) did not change significantly. The density of the shoreline community in period III was more than two times lower than in period I, probably due to higher fluctuations in water level of the reservoir, resulting from the Kruonis HPP operation.     

Expression and secretion of functional miniantibodies McPC603scFvDhlx in cell-wall-less L-form strains of Proteus mirabilis and Escherichia coli : A comparison of the synthesis capacities of L-form strains with an E. coli producer strain

The paper describes the synthesis of the phosphorylcholine-binding miniantibody McPC603scFvDhl x in cell-wall-less L-form strains of Escherichia coli and Proteus mirabilis. Cells of these strains were transformed with the plasmid pACK02scKan, carrying the miniantibody (miniAb) coding sequence under the control of the lac promoter. L-form transformants of both species were able to synthesize the functional miniAb as an extracellular soluble product. The highest quantities were obtained by P. mirabilis L-form strains after induction with 5 mM isopropyl β-d-thiogalactopyranoside (IPTG). Yields of 45–75 mg/l total antibody protein and of 10–18 mg/l functional miniAb were estimated in the growth medium of shaking cultures 40–80 h after induction with IPTG. About 10% of the active miniAb remained cell-bound. The yields of functional miniAb could be optimized by lowering the growth temperature from 37 °C to 26–32 °C and by supplementation of the medium with 80 mM sodium fumarate. A comparison of the specific activities revealed that the P. mirabilis L-form strains have a similar synthesis capacity (2–4 mg functional miniAb/g cell dry weight) to that of the producer strain E. coli RV308. The results show that the processes of correct folding and assembling of the miniAb molecules are possible without the periplasmic compartment. Received: 14 April 1997 / Received revision: 17 July 1997 / Accepted: 25 August 1997     

The novel function of the Saccharomyces cerevisiaeCBP2 gene as a splicing factor essential to excision of the Saccharomyces douglasiiLSU intron in vivo

In the yeast Saccharomyces cerevisiae, the product of the nuclear gene CBP2 is required exclusively for the splicing of the terminal intron of the mitochondrial cytochrome b gene. The homologous gene from the related yeast, Saccharomyces douglasii, has been shown to be essential for respiratory growth in the presence of a wild-type S. douglasii mitochondrial genome and dispensable in the presence of an intronless mitochondrial genome. The two CBP2 genes are functionally interchangeable although the target intron of the S. cerevisiaeCBP2 gene is absent from the S. douglasii mitochondrial genome. To determine the function of the CBP2 gene in S. douglasii mitochondrial pre-RNA processing we have constructed and analyzed interspecific hybrid strains between the nuclear genome of S. cerevisiae carrying an inactive CBP2 gene and S. douglasii mitochondrial genomes with different intron contents. We have demonstrated that inactivation of the S. cerevisiaeCBP2 gene affects the maturation of the S. douglasii LSU pre-RNA, leading to a respiratory-deficient phenotype in the hybrid strains. We have shown that the CBP2 gene is essential for excision of the S. douglasii LSU intron in vivo and that the gene is dispensable when this intron is deleted or replaced by the S. cerevisiae LSU intron. Received: 1 October 1997 / Accepted: 18 November 1997     

Temperature effect on bacterial azo bond reduction kinetics: an Arrhenius plot analysis

Studied was the effect of temperature in the range 12–46 °C on the rate of bacterial decolorization of the mono-azo dye Acid Orange 7 by Alcaligenes faecalis 6132 and Rhodococcus erythropolis 24. With both strains the raise of temperature led to a corresponding raise of decolorization rate better manifested by R. erythropolis. The analysis of the Arrhenius plot revealed a break near the middle of the temperature range. The regression analysis showed practically complete identity of the observed break point temperatures (T _BP): 20.7 °C for Alc. faecalis and 20.8 °C for R. erythropolis. The values of the activation energy of the decolorization reaction (E _a) were found to depend on both the organism and the temperature range. In the range below T _BP the estimated values of E _a were 138 ± 7 kJ mol⁻¹ for Alc. faecalis and 160 ± 8 kJ mol⁻¹ for R. erythropolis. In the range above T _BP they were 54.2 ± 1.8 kJ mol⁻¹ for Alc. faecalis and 37.6 ± 4.1 kJ mol⁻¹ for R. erythropolis. Discussed are the possible reasons for the observed abrupt change of the activation energy.