Comamonas (Pseudomonas) testosteroni endocarditis

Bacteria of Zoonotic Interest Identified on Edible Freshwater Fish Imported to Australia

Previous research has shown that freshwater edible fish imported into Australia are not compliant with Australian importation guidelines and as a result may be high risk for bacterial contamination. In the present study, the outer surface of imported freshwater fish were swabbed, cultured, confirmatory tests performed and antimicrobial patterns investigated. Channidae fish (Sp. A/n = 66) were contaminated with zoonotic Salmonella sp./Staphylococcus aureus (n = 1/66) and other bacteria implicated in cases of opportunistic human infection, these being Pseudomonas sp. (including P. mendocina and P. pseudoalcaligenes (n = 34/66)); Micrococcus sp. (n = 32/66); Comamonas testosteroni (n = 27/66) and Rhizobium radiobacter (n = 3/66). Pangasiidae fish (Species B/n = 47) were contaminated with zoonotic Vibrio fluvialis (n = 10/47); Salmonella sp. (n = 6/47) and environmental bacteria Micrococcus sp. (n = 3/47). One sample was resistant to all antimicrobials tested and is considered to be Methicillin Resistant S. aureus. Mud, natural diet, or vegetation identified in Sp. A fish/or packaging were significantly associated with the presence of Pseudomonas spp. The study also showed that visibly clean fish (Sp. B) may harbour zoonotic bacteria and that certain types of bacteria are common to fish groups, preparations, and contaminants. Further investigations are required to support the development of appropriate food safety recommendations in Australia.

An investigation of clinical characteristics and antimicrobial agent susceptibility patterns in clinical Comamonas testosteroni isolates: An increasingly prevalent nosocomial pathogen

BACKGROUND

Comamonas testosteroni is a gram-negative bacillus, known before 1987 as Pseudomonas testosteroni. Although considered as a rare pathogen, its frequency has been increasing. Data regarding its antibiotic susceptibility are insufficient. To date, forty-four cases have been reported in the literature. In this study, we identified the C. testosteroni infections observed in our hospital and evaluated their antimicrobial agent susceptibility patterns compared with cases reported in the literature.

METHODS

For the purposes of the present study, patients admitted to hospital between November 2019 and December 2020 were screened. Those with clinical and laboratory signs of infection with positive C. testosteroni growth in culture were enrolled. Clinical isolates obtained from the samples processed in accordance with standard microbiological examination procedures in our laboratory were defined by MALDI-TOF mass spectrometry with 99.9% probability as C. testosteroni.

RESULTS

C testosteroni infection was detected between November 2019 and December 2020 in eight patients in our hospital. Six of them had a bloodstream infection (BSI), one had pneumonia, and one had urinary tract infection due to C. testosteroni. Coexistence of COVID-19 was detected in four patients. Six out of the eight cases with BSI had hospital-acquired infection and all of the infections were healthcare-associated. When antimicrobial agent susceptibility results reported in the literature were evaluated in combination with the current results, ceftazidime and meropenem were found to be the most susceptible agents (96.1% and 80%, respectively).

CONCLUSIONS

The frequency of nosocomial C. testosteroni infections and resistance to antimicrobial agents are gradually increasing. While resistance to carbapenems is on the upswing, third-generation cephalosporins are still seen as suitable treatment options.

The Emergence of the Genus Comamonas as Important Opportunistic Pathogens

Comamonas spp. are non-fermenting Gram-negative bacilli. They were first discovered in 1894, and since then, twenty-four species have been characterized. The natural habitat of these bacteria is soil, wastewater/sludge, fresh water such as ponds and rivers, and the animal intestinal microbiome. They were also isolated from industrial settings, such as activated sludge and polluted soil, and from the hospital environment and clinical samples, such as urine, pus, blood, feces, and kidney. Comamonas spp. are associated with environmental bioremediation and are considered an important environmental bacterium rather than a human pathogen. However, in the 1980s, they became a concern when several human infections associated with these species were reported. Here, the Comamonas genus was examined in terms of its members, identification techniques, and pathogenicity. Seventy-seven infection cases associated with these microorganisms that have been discussed in the literature were identified and investigated in this project. All relevant information regarding year of infection, country of origin, patient information such as age, sex, underlying medical conditions if any, type of infection caused by the Comamonas species, antibiotic susceptibility testing, treatment, and outcomes for the patient were extracted from case reports. The findings suggest that even though Comamonas spp. are thought of as being of low virulence, they have caused harmful health conditions in many healthy individuals and even death in patients with underlying conditions. Antimicrobial treatment of infections associated with these species, in general, was not very difficult; however, it can become an issue in the future because some strains are already resistant to different classes of antibiotics. Therefore, these pathogens should be considered of such importance that they should be included in the hospital screening programs.

High biodiversity and distinct assembly patterns of microbial communities in groundwater compared with surface water

The differences in bacterial community assembly mechanism between surface water and groundwater, as well as the driving factors of environmental factors, are still unknown. Here we aimed to answer these questions by analyzing microbial community samples from surface water and groundwater. We observed a strong connection between microbial communities in surface water and groundwater and several human pathogens are shared between surface water and groundwater; however, the richness and diversity of groundwater microbial communities were greater than those of surface water, regardless of the season. Additionally, bacterial community compositions of surface water and groundwater differed significantly between seasons. Most importantly, the groundwater community exhibited a highly deterministic assembly process (56% contributed by deterministic process, with neutral community model R² = 0.277) compared with surface water (51% contributed by deterministic process, with R² = 0.526). This study provides a deep understanding of the effects of environmental factors on surface water and groundwater microbial communities, to better protect water resources.

Genomic Analysis of Carbapenem-Resistant Comamonas in Water Matrices: Implications for Public Health and Wastewater Treatments

Comamonas spp. are Gram-negative bacteria that catabolize a wide range of organic and inorganic substrates. Comamonas spp. are abundant in aquatic and soil environments, including wastewater, and can cause opportunistic infections in humans. Because of their potential in wastewater bioaugmentation and bioremediation strategies, the identification of Comamonas species harboring genes encoding carbapenemases and other clinically important antibiotic resistance genes warrant further investigation. Here, we present an analysis of 39 whole-genome sequences comprising three Comamonas species from aquatic environments in South Australia that were recovered on media supplemented with carbapenems. The analysis includes a detailed description of 33 Comamonas denitrificans isolates, some of which carried chromosomally acquired bla_GES-5, bla_OXA, and aminoglycoside resistance (aadA) genes located on putative genomic islands (GIs). All bla_GES-5- and bla_OXA-containing GIs appear to be unique to this Australian collection of C. denitrificans. Notably, most open reading frames (ORFs) within the GIs, including all antimicrobial resistance (AMR) genes, had adjacent attC sites, indicating that these ORFs are mobile gene cassettes. One C. denitrificans isolate carried an IncP-1 plasmid with genes involved in xenobiotic degradation and response to oxidative stress. Our assessment of the sequences highlights the very distant nature of C. denitrificans to the other Comamonas species and its apparent disposition to acquire antimicrobial resistance genes on putative genomic islands. IMPORTANCE Antimicrobial resistance (AMR) poses a global public health threat, and the increase in resistance to "last-resort drugs," such as carbapenems, is alarming. Wastewater has been flagged as a hot spot for AMR evolution. Comamonas spp. are among the most common bacteria in wastewater and play a role in its bioaugmentation. While the ability of Comamonas species to catabolize a wide range of organic and inorganic substrates is well documented, some species are also opportunistic pathogens. However, data regarding AMR in Comamonas spp. are limited. Here, through the genomic analyses of 39 carbapenem-resistant Comamonas isolates, we make several key observations, including the identification of a subset of C. denitrificans isolates that harbored genomic islands encoding carbapenemase bla_GES-5 or extended-spectrum β-lactamase bla_OXA alleles. Given the importance of Comamonas species in potential wastewater bioaugmentation and bioremediation strategies, as well as their status as emerging pathogens, the acquisition of critically important antibiotic resistance genes on genomic islands warrants future monitoring.

Comamonas testosteroni bacteremia: A rare unusual pathogen detected in a burned patient: Case report and literature review

Introduction and importance

Comamonas testosteroni is a rare human pathogen that is not part of the human microbiome. There are only 51 cases reported worldwide with 7 cases resulted in death.

Case presentation

We report a case of a 16-year-old boy with an extended burn complicated by catheter-related bloodstream C. testosteroni infection.

Clinical discussion

Comamonas species are usually community-acquired pathogens that are susceptible to a wide variety of antibiotics including aminoglycosides, fluoroquinolones, carbapenems, piperacillin-tazobactam, trimethoprim-sulfamethoxazole, and cephalosporins. However, in our case, we reported a nosocomial multidrug-resistant infection by C. testosteroni that responded only to colistin.

Conclusion

Reporting unusual cases of nosocomial sepsis due to rare multidrug-resistant pathogens is detrimental. As it sheds light on how virulent nosocomial infections are becoming, and can be very alarming to other practitioners and clinical microbiologists, in order to achieve a better awareness of the importance of controlled antibiotics use.

-

Comamonas testosteroni is a rare human pathogen that is not part of the human microbiome, and is rarely recognized as a human pathogen.

-

The majority of C.testosteroni infections are community-acquired rather than nosocomial. Most of the previously reported patients were immunodeficient (burn patient in our case).

-

Till now, there are 51 cases reported (52 if our case is published) which most of these are due to intra-abdominal source.

-

Comamonas species are usually susceptible to a wide spectrum of antibiotics. However, we report a nosocomial infection by C. testosterone which was sensitive only to colistin.

Bacteremia caused by Comamonas testosteroni an unusual pathogen

Comamonas species are rare isolates in microbiology laboratories and have been infrequently reported as an infectious agent in routine clinical practice. They have a wide range of natural habitats including water, soil, and plants as well as from some hospital devices, such as intravenous lines and the reservoir water in the humidifiers of respiratory therapy equipment. Comamonas testosteroni is rarely recognized as a human pathogen. In spite of its uncommon human pathogenesis, there are few reports where it was reported as an aggressive opportunistic pathogen, and that was mostly related to Testosterone species. Herewith, we are reporting this pathogen from the blood of an immunocompetent female. The aim of this case report is to alert clinicians and laboratory physicians for the potential diagnosis and clinical approach of bloodstream infections caused by such unusual pathogens. This is the first documented case of bacteremia caused by C. testosteroni from India.

The characterization of a short chain dehydrogenase/reductase (SDRx) in Comamonas testosteroni

C. testosteroni is a research topic that can degrade steroid hormones into water and carbon dioxide through a series of enzymes in the body. Short-chain dehydrogenase (SDR) are a class of NAD (P) H-dependent oxidoreductases in C. testosteroni. Its main function is catalyzing the redox of the hydroxyl/ketone group of the hormone. In this paper, a SDR gene(SDRx) is cloned from C. testosteroni ATCC11996 and expressed. The polyclonal antibody was prepared and the SDRx gene knocked out by homologous recombination. Wild type and mutant C. testosteroni induced by testosterone, estradiol, estrone and estriol. The growth curves of the bacteria were measured by spectrophotometer. ELISA established the expression of SDRx protein, and high-performance liquid chromatography(HPLC) detected the contents of various hormones. The results show that the growth of wild type was faster than mutant type induced by testosterone. The concentration of SDRx is 0.318 mg/ml under testosterone induction. It has a great change in steroid hormones residue in culture medium measured by HPLC: Testosterone residue in the mutant type group was 42.4 % more than the wild type in culture medium. The same thing happens with induced by estrone. In summary, this SDRx gene involved in the degradation of testosterone and estradiol, and effects the growth of C. testosteroni.

Moderation effects of food intake on the relationship between urinary microbiota and urinary interleukin-8 in female type 2 diabetic patients

Background

Our previous study demonstrated that the composition of the urinary microbiota in female patients with type 2 diabetes mellitus (T2DM) was correlated with the concentration of urinary interleukin (IL)-8. As the composition of urine is mainly determined by diet, diet might mediate the correlation.

Methods

Seventy female T2DM patients and 70 healthy controls (HCs) were recruited. Midstream urine was used for the urine specimens. Urinary IL-8 was determined by enzyme-linked immunosorbent assay. A Chinese Food Frequency Questionnaire was used to collect food intake data. The independent variables in the hierarchical regression analysis were the relative abundances of the bacterial genera and species that were significantly different between the T2DM and HCs and between the T2DM patients with and without detectable urinary IL-8, and the bacterial genera associated with IL-8 concentration in the multiple regression model reported in our previous research. IL-8 concentration was the dependent variable, and nutrient intakes were moderator variables.

Results

Fiber and vitamin B3 and E intake exerted enhancing effects, and water intake exerted a buffering effect, on the positive relationship between the relative abundance of Ruminococcus and IL-8 concentration (p < 0.05). Cholesterol and magnesium intake exerted enhancing effects on the positive relationship between the relative abundance of Comamonas and IL-8 concentration (p < 0.05).

Conclusion

Modulating T2DM patients’ dietary patterns may prevent bladder inflammation.

Comamonas testosteroni-associated peritonitis in a pediatric peritoneal dialysis patient

Comamonas testosteroni (C. testosteroni) has been rarely observed as an infectious agent in clinical practice. Few reports described its potential pathogenicity in bloodstream and abdominal infections. Here, we report our experience in the treatment of a C. testosteroni-associated peritonitis in a four-year-old girl receiving chronic peritoneal dialysis (PD). The organism was shown to be highly susceptible to appropriate antibiotic therapy. Infection responded promptly and the patient was managed conservatively without withdrawal from PD.

High correlation between genotypes and phenotypes of environmental bacteria Comamonas testosteroni strains

BACKGROUND

Members of Comamonas testosteroni are environmental microorganisms that are usually found in polluted environment samples. They utilize steroids and aromatic compounds but rarely sugars, and show resistance to multiple heavy metals and multiple drugs. However, comprehensive genomic analysis among the C. testosteroni strains is lacked.

RESULTS

To understand the genome bases of the features of C. testosteroni, we sequenced 10 strains of this species and analyzed them together with other related published genome sequences. The results revealed that: 1) the strains of C. testosteroni have genome sizes ranging from 5.1 to 6.0 Mb and G + C contents ranging from 61.1% to 61.8%. The pan-genome contained 10,165 gene families and the core genome contained 3,599 gene families. Heap's law analysis indicated that the pan-genome of C. testosteroni may be open (α = 0.639); 2) by analyzing 31 phenotypes of 11 available C. testosteroni strains, 99.4% of the genotypes (putative genes) were found to be correlated to the phenotypes, indicating a high correlation between phenotypes and genotypes; 3) gene clusters for nitrate reduction, steroids degradation and metal and multi-drug resistance were found and were highly conserved among all the genomes of this species; 4) the genome similarity of C. testosteroni may be related to the geographical distances.

CONCLUSIONS

This work provided an overview on the genomes of C. testosteroni and new genome resources that would accelerate the further investigations of this species. Importantly, this work focused on the analysis of potential genetic determinants for the typical characters and found high correlation between the phenotypes and their corresponding genotypes.

Polymicrobial Bacteremia Involving Comamonas testosteroni

Comamonas spp. are uncommon isolates in microbiology laboratories and have been rarely observed as an infectious agent in clinical practice. They have widespread environmental distribution and have been isolated from water, soil, and plants as well as from some hospital devices such as intravenous catheters and water contained in humidifier reservoirs used in respiratory treatment. The genus Comamonas originally contained the following species: acidovorans, testosteroni, kerstersii, terrigena, denitrificans, and nitrativorans. It now contains 17 species, while acidovorans spp. have been reclassified as Delftia acidovorans. In spite of its uncommon human pathogenesis, there are few reports on the aggressive manner of it as an opportunistic pathogen, mostly related to testosteroni spp. We present a case of polymicrobial bacteremia involving Comamonas testosteroni. The aim of this case report is to alert clinicians to the potential diagnosis of bloodstream infections caused by uncommon pathogens.

Bacteremia caused by Comamonas kerstersii in a patient with diverticulosis

We report for the first time a case of bacteremia caused by Comamonas kerstersii in a 65-year-old patient with sign of diverticulosis. In addition, we review the isolation of Comamonas sp. and related organisms in our hospital over 25 years.

Intra-abdominal infections due to Comamonas kerstersii

Herein, we report four cases of Comamonas kerstersii intra-abdominal infections representing the first report of human infections caused by this Comamonas species. In addition, our work demonstrates the association of C. kerstersii with peritonitis secondary to appendix rupture.

Description of Acidovorax wautersii sp. nov. to accommodate clinical isolates and an environmental isolate, most closely related to Acidovorax avenae

Three Gram-negative strains, NF 1078(T), NF 1598 and NF 1715, were isolated from clinical (two) and environmental (one) samples, respectively. Sequence analysis of the 16S rRNA genes revealed similarity of 100% among the three strains and next highest similarity to the type strain of Acidovorax avenae (98.16%). The three strains were able to acidify lactose and rhamnose on low peptone phenol red agar and to alkalinize citrate on Simmons' agar and were negative for nitrate reduction. The DNA G+C content of strain NF 1078(T) was 67.1 mol%. The level of DNA-DNA relatedness between this strain and the type strains of A. avenae (ATCC 19860(T), LMG 2117(T)) was 29%. Based on these phylogenetic, phenotypic and genotypic analyses, the three strains could be distinguished clearly from all other recognized Acidovorax species and should be classified as representatives of a novel species of the genus Acidovorax, for which the name Acidovorax wautersii sp. nov. is proposed. The type strain is NF 1078(T) (=LMG 26971(T)=CCUG 62584(T)).

Hydroxysteroid dehydrogenases (HSDs) in bacteria: a bioinformatic perspective

Steroidal compounds including cholesterol, bile acids and steroid hormones play a central role in various physiological processes such as cell signaling, growth, reproduction, and energy homeostasis. Hydroxysteroid dehydrogenases (HSDs), which belong to the superfamily of short-chain dehydrogenases/reductases (SDR) or aldo-keto reductases (AKR), are important enzymes involved in the steroid hormone metabolism. HSDs function as an enzymatic switch that controls the access of receptor-active steroids to nuclear hormone receptors and thereby mediate a fine-tuning of the steroid response. The aim of this study was the identification of classified functional HSDs and the bioinformatic annotation of these proteins in all complete sequenced bacterial genomes followed by a phylogenetic analysis. For the bioinformatic annotation we constructed specific hidden Markov models in an iterative approach to provide a reliable identification for the specific catalytic groups of HSDs. Here, we show a detailed phylogenetic analysis of 3α-, 7α-, 12α-HSDs and two further functional related enzymes (3-ketosteroid-Δ(1)-dehydrogenase, 3-ketosteroid-Δ(4)(5α)-dehydrogenase) from the superfamily of SDRs. For some bacteria that have been previously reported to posses a specific HSD activity, we could annotate the corresponding HSD protein. The dominating phyla that were identified to express HSDs were that of Actinobacteria, Proteobacteria, and Firmicutes. Moreover, some evolutionarily more ancient microorganisms (e.g., Cyanobacteria and Euryachaeota) were found as well. A large number of HSD-expressing bacteria constitute the normal human gastro-intestinal flora. Another group of bacteria were originally isolated from natural habitats like seawater, soil, marine and permafrost sediments. These bacteria include polycyclic aromatic hydrocarbons-degrading species such as Pseudomonas, Burkholderia and Rhodococcus. In conclusion, HSDs are found in a wide variety of microorganisms including bacteria and archaea, suggesting that steroid metabolism is an evolutionarily conserved mechanism that might serve different functions such as nutrient supply and signaling. Article from a special issue on steroids and microorganisms.

Nasopharyngeal microbiota in infants with acute otitis media

Background. Interspecies interactions of the nasopharyngeal microbiota are likely to be involved in the pathogenesis of acute otitis media (AOM). Capturing the breadth of microbial interactions requires a detailed description of the microbiota during health and AOM.

Methods. The nasopharyngeal microbiota of 163 infants with (n = 153) or without (n = 10) AOM was characterized using nasopharyngeal swabs and multiplexed pyrosequencing of 16S rRNA. Nasopharyngeal swab specimens were collected during 4 winter seasons from 2004 through 2010 for infants with AOM and during 2010 for controls.

Results. Fifty-eight bacterial families were identified, of which Moraxellaceae, Streptococcaceae, and Pasteurellaceae were the most frequent. Commensal families were less prevalent in infants with AOM than in controls. In infants with AOM, prior exposure to antimicrobials and administration of the heptavalent conjugated pneumococcal polysaccharide vaccine (PCV7) were also associated with reduced prevalence of distinct commensal families (Streptococcaceae and Corynebacteriaceae). In addition, antimicrobial exposure increased the prevalence of Enterobacteriaceae and the abundance of Pasteurellaceae. Other factors, such as age, sex, day care, and a history of recurrent AOM, did not influence the microbiota.

Conclusions. Infants’ nasopharyngeal microbiota undergoes significant changes during AOM and after exposure to antimicrobials and PCV7, which is mainly attributable to reduced prevalence of commensal bacterial families.

Comamonas testosteroni infection in Taiwan: Reported two cases and literature review

Comamonas testosteroni is a widely distributed aerobic gram-negative bacillus. Infection by C testosteroni is infrequent, and no such cases have been reported in Taiwan. Here, we would like to present a 54-year-old alcoholic patient from Taiwan, and his left leg was injured during a fishing trip, resulting in left leg cellulitis and C testosteroni bacteremia. The patient's fever subsided after initial treatment with extended-spectrum cephalosporin, whereas his erythematous swelling did not resolve until switched to ciprofloxacin. The second patient is a 73-year-old Taiwanese male with chronic hepatitis B infection, liver cirrhosis, and hepatocellular carcinoma. Comamonas testosteroni bacteremia was found after transarterial embolization. Further studies are necessary to determine the best antibiotic(s) for patients infected with C testosteroni.

Catheter-related bacteremia caused by Comamonas testosteroni in a hemodialysis patient

Comamonas testosteroni has rarely been implicated as a human pathogen. In general, the outcome of C. testosteroni infections is favorable. We report a case of fatal bacteremia caused by C. testosteroni in a 64-year-old woman on hemodialysis.

The Comamonas testosteroni steroid biosensor system (COSS)--reflection on other methods

Natural and synthetic steroid hormones are released uncontrolled into the environment and are considered as pollutants with regard to their endocrine activity and negative influence on all kind of organisms. Due to their widespread presence, endocrine activity even at low concentrations, and their potential adverse effects in both the environment and human health, there is an increasing need for the development of rapid, sensitive and quantitative techniques for measuring trace levels of these steroids. In addition to classical analytical methods like GC-MS, LC-MS and others, several techniques have been established that are based on human nuclear steroid receptors as reporter systems. However, many of these systems require human or yeast cell culture and are therefore time consuming and expensive, while others suffer from too low sensitivity or cover only one specific steroid compound. These are some of the main reasons that limit current techniques for environmental application. The remarkable ability of certain microorganisms to transform and degrade the steroid nucleus and to respond with the induced expression of steroid regulated genes lead us to explore, whether the steroid signalling machinery of Comamonas testosteroni could be used to construct a steroid sensoring system that is sensitive, rapid, easy to perform, and which could also be applied to detect environmental steroid mixtures at low concentrations. Both whole C. testosteroni mutant cells as well as the cytosol thereof were used as new and sensitive fluorescence based biosensor systems for the successful determination and quantification of a variety of different steroids. We could show that our COSS (Comamonas testosteroniSteroid Sensor) is able to detect testosterone, estradiol and cholesterol in concentrations of 29pg/mL, 0.027pg/mL, and 9.7pg/mL, respectively. The sensitivity of the COSS together with the fact that it is very fast, reproducible and can be used for high-throughput screening in a microplate format makes it suitable for the detection of single steroid hormones or steroid hormone mixtures in environmental samples at low costs. In summary, the COSS is able to detect steroid hormone effects at the molecular level through activation of bacterial steroid-sensing systems. In the future, it may be further developed as a useful tool for the integrative assessment of ecotoxicological potentials caused by hormonally active agents and endocrine-disrupting compounds.

Implanted-port-catheter-related sepsis caused by Acidovorax avenae and methicillin-sensitive Staphylococcus aureus

Acidovorax avenae is a gram-negative rod in the family Comamonadaceae and a phytopathogen found in the environment. Human infections caused by members of the Comamonadaceae are extremely rare. We report a case of implanted-port-catheter-related sepsis caused by Acidovorax avenae and methicillin (meticillin)-sensitive Staphylococcus aureus (MSSA).

Post-operative endophthalmitis due to an unusual pathogen, Comamonas testosteroni

Here, we describe the first report of post-operative endophthalmitis due to Comamonas testosteroni in an elderly diabetic patient after complicated cataract surgery. The isolate was identified by using Mini API strips. The patient was successfully treated with intravitreal ceftazidime and oral ciprofloxacin.

Carbonyl Reductases and Pluripotent Hydroxysteroid Dehydrogenases of the Short-chain Dehydrogenase/reductase Superfamily

Carbonyl reduction of aldehydes, ketones, and quinones to their corresponding hydroxy derivatives plays an important role in the phase I metabolism of many endogenous (biogenic aldehydes, steroids, prostaglandins, reactive lipid peroxidation products) and xenobiotic (pharmacologic drugs, carcinogens, toxicants) compounds. Carbonyl-reducing enzymes are grouped into two large protein superfamilies: the aldo-keto reductases (AKR) and the short-chain dehydrogenases/reductases (SDR). Whereas aldehyde reductase and aldose reductase are AKRs, several forms of carbonyl reductase belong to the SDRs. In addition, there exist a variety of pluripotent hydroxysteroid dehydrogenases (HSDs) of both superfamilies that specifically catalyze the oxidoreduction at different positions of the steroid nucleus and also catalyze, rather nonspecifically, the reductive metabolism of a great number of nonsteroidal carbonyl compounds. The present review summarizes recent findings on carbonyl reductases and pluripotent HSDs of the SDR protein superfamily.