Fluoroquinolone resistance in clinical and environmental isolates of Escherichia coli in Mexico City

Aims:  To assess the different phenotypes and mechanisms of fluoroquinolone (FQ) resistance in clinical and environmental isolates of Escherichia coli .
Methods and Results:  We compared FQ-resistant E. coli isolates, measuring minimal inhibitory concentrations (MIC) of ciprofloxacin, along with susceptibility to other antibiotics. We also searched for the presence of efflux pumps, using efflux inhibitors, and for plasmid-borne FQ-resistance by PCR. We found that, aside from the higher FQ-resistance prevalence among clinical strains, environmental ones resist much lower concentrations of ciprofloxacin. Efflux pumps mediate fluoroquinolone resistance as frequently among environmental isolates than in clinical strains. Plasmid-borne qnrA genes were not detected in any resistant strain.
Conclusions:  Environmental FQ-resistant strains may have a nonclinical origin and/or a selective pressure different from the clinical use of FQs.
Significance and Impact of the Study:  The identification of the source of low-level FQ-resistant strains (ciprofloxacin MIC c . 8 μg ml⁻¹) in the environment could be important to curb the rapid emergence and spread of FQ-resistance in clinical settings, as these strains can easily become fully resistant to FQ concentrations achievable in fluids and tissues during therapy.     

156例尿路感染大肠埃希菌耐药性分析

目的探讨大肠埃希菌尿路感染的临床发病特点及对抗生素的耐药情况。方法对2001年1月至2005年12月尿路感染患者尿培养分离出的156株大肠埃希菌进行耐药性分析,用纸片扩散法表型确证试验检测ESBLs。结果大肠埃希菌耐药率最低的抗菌药物是亚胺培南、美罗培南、头孢哌酮/舒巴坦、氧哌嗪青霉素/他唑巴坦,分别为1.28%、1.92%、3.21%、5.13%;对氨苄西林、氟喹诺酮类、庆大霉素、复方新诺明耐药率均>70%。产ESBLs的大肠埃希菌对亚胺培南、美罗培南、头孢哌酮/舒巴坦、氧哌嗪青霉素/他唑巴坦的耐药性均<10%,对氨苄西林、头孢菌素类、氟喹诺酮类均表现出很强的耐药性。结论治疗大肠埃希菌感染时,需根据药敏结果选用碳青霉烯类、β-内酰胺类/β-内酰胺酶抑制剂等。     

Detection of extended-spectrum beta-lactamase-producing Escherichia coli isolates in faecal samples of Iberian lynx

Aims: To characterize the diversity of extended‐spectrum beta‐lactamase (ESBL)‐producing Escherichia coli isolates recovered within the faecal microbiota of Iberian lynx. The identification of other associated resistance genes and the analysis of clonal relationship were also focused in this study. Methods and Results: From 2008 to 2010, 128 faecal samples of Iberian lynx (wild and captive animals) were collected. Eleven tested samples contained cefotaxime‐resistant E. coli isolates (all belonging to captive animals) and 10 ESBL‐producing isolates were showed. CTX‐M‐14 and SHV‐12 ESBL‐types were detected and seven different patterns were identified by pulsed‐field gel electrophoresis analysis. Conclusions: The occurrence of unrelated multiresistant E. coli in faecal flora of captive specimens of Iberian lynx, including the presence of ESBLs, resistant genes in integrons and virulence determinants was showed in this study. Significance and Impact of the Study: The results obtained in this study highlight the environmental problem as future reintroductions of Iberian lynx could lead to a spread of resistant bacteria. Additionally, ESBL‐producing bacteria can represent a health problem for this endangered species.     

Detection of carbohydrases as a possible method of differentiating faecal and non-faecal Escherichia coli

Abstract Escherichia coli isolated from faeces, urine, wounds and pus were examined for the production of carbohydrases, i.e., maltase, lactase and invertase. Two of the carbohydrases, lactase and maltase, have been detected in E. coli of faecal origin (100 strains) whereas these enzymes were not detected in non-faecal E. coli (146 strains). These inductive enzymes were produced optimally in synthetic medium, pH 7.2, at 37°C for 10 h.
The presence of maltase and lactase in the faecal E. coli may be used as a complementary test for differentiating faecal E. coli from non-faecal E. coli .     

Effect of temperature and htpR on the biosynthesis of superoxide dismutase in Escherichia coli

The synthesis of Mn- and FeSODs in response to temperature changes was examined in strains of Escherichia coli with different mutations in sod and htpR genes. Growth at or shift to elevated temperatures induced FeSOD but not MnSOD. The induction of FeSOD by heat was inhibited by chloramphenicol and was independent of the heat shock (htpR-controlled) regulon. FeSOD was more stable at 42 degrees C than was MnSOD.     

Detection and distribution of probiotic Escherichia coli Nissle 1917 clones in swine herds in Germany

AIMS: To verify the presence of Escherichia coli Nissle 1917 as a natural isolate in swine and to characterize in vitro probiotic properties as well as in vivo persistence in a feeding experiment. METHODS AND RESULTS: During studies on the intestinal microflora of pigs, we isolated E. coli Nissle 1917 sporadically from a pig population over a period of 1 year. The identity of the isolates as E. coli Nissle 1917 was verified by serotyping, Nissle-specific PCR, macrorestriction analysis (pulsed field gel electrophoresis) and the determination of in vitro probiotic properties in invasion and adhesion assays using a porcine intestinal epithelial cell line. Both the E. coli isolates and the E. coli Nissle 1917 strain showed strong reductions in adhesion of porcine enteropathogenic E. coli and invasion of Salmonella typhimurium with epithelial cells in vitro, with a probiotic effect. Screening of five epidemiologically unlinked swine farms and two wild boar groups showed one farm positive for E. coli Nissle 1917. A feeding experiment with four piglets showed viable E. coli Nissle 1917 in the intestine of three animals. CONCLUSIONS: The results of this study suggest that the E. coli Nissle 1917 strain is already partially established in swine herds, but the colonization of individual animals is variable. SIGNIFICANCE AND IMPACT OF THE STUDY: We report natural, long-term colonization and transmission of the probiotic E. coli Nissle 1917 strain in a swine herd, characterized individual persistence and colonization properties in swine and established an in vitro porcine intestinal epithelial cell model of probiotic action. The results of this study would have implications in the use of this strain as a probiotic in swine and contribute to a better understanding of the individual nature of intestinal bacterial persistence and establishment.     

The effects of dietary additives on faecal levels of Lactobacillus spp., coliforms,and Escherichia coli,and faecal prevalence of Salmonella spp. and Campylobacter spp. in US production nursery swine1

Aims: In the United States, carbadox and copper sulfate are growth promoters commonly used in combination in nursery swine diets. Our aim was to determine how selected dietary additives affect selected bacterial populations and pathogens in nursery swine, and compare to larch extract, which contains potential antibacterial activities. Methods and Results: Piglets were weaned and sorted into one of the four treatments: (i) basal diet without antimicrobials; (ii) basal diet with carbadox + copper sulfate; (iii) basal diet + 1000 ppm larch extract; or (iv) basal diet + 2000 ppm larch extract. Diets were fed for a 4‐week period after weaning. In both trials, the carbadox + copper sulfate group consumed more feed over the 4‐week period relative to the other three diet groups (P < 0·05), but did not gain significantly more weight. Faecal shedding of Salmonella spp. was not affected by dietary supplement in either trial, but faecal shedding of Campylobacter spp. was the lowest for the carbadox + copper sulfate diet. In faecal samples collected at the end of each trial, Lactobacillus spp. cell counts for the basal and larch extract diets were nearly 1·0 log₁₀ g^?1 faeces greater (P < 0·05) than the carbadox + copper sulfate group, whereas the coliforms and Escherichia coli were nearly 1·0 log₁₀ g^?1 faeces lower (P < 0·05). Conclusions: Compared to basal fed animals, supplementation with carbadox + copper sulfate significantly altered faecal E. coli, coliform bacteria and Lactobacillus spp. Larch extract has no benefit up to 0·2% of diet in regard to pathogen shedding, whereas carbadox + copper sulfate decreased faecal shedding of Campylobacter spp. Significance and Impact of the Study: Current swine management practices in the United States may be beneficial to managing Campylobacter spp. shedding in nursery swine, but also result in significant changes in the resident gastrointestinal microflora.     

Enhanced survival of plasmid-containing Escherichia coli in aquatic microcosms

The survival of Escherichia coli K-12 J62-1 containing the antibiotic-resistance plasmid R1 and an isogenic plasmid-free strain were studied in pond water microcosms. The number of plasmid-containing cells recovered from the microcosms remained constant over a sampling period of 31 days whereas plasmid-free cell numbers declined.     

Impact of microbial diversity on rapid detection of enterohemorrhagic Escherichia coli in surface waters

Enterohemorrhagic Escherichia coli (EHEC) are a physiologically, immunologically and genetically diverse collection of strains that pose a serious water-borne threat to human health. Consequently, immunological and PCR assays have been developed for the rapid, sensitive detection of presumptive EHEC. However, the ability of these assays to consistently detect presumptive EHEC while excluding closely related non-EHEC strains has not been documented. We conducted a 30-month monitoring study of a major metropolitan watershed. Surface water samples were analyzed using an immunological assay for E. coli O157 (the predominant strain worldwide) and a multiplex PCR assay for the virulence genes stx(1), stx(2) and eae. The mean frequency of water samples positive for the presence of E. coli O157, stx(1) or stx(2) genes, or the eae gene was 50%, 26% and 96%, respectively. Quantitative analysis of selected enriched water samples indicated that even in samples positive for E. coli O157 cells, stx(1)/stx(2) genes, and the eae gene, the concentrations were rarely comparable. Seventeen E. coli O157 strains were isolated, however, none were EHEC. These data indicate the presence of multiple strains similar to EHEC but less pathogenic. These findings have important ramifications for the rapid detection of presumptive EHEC; namely, that current immunological or PCR assays cannot reliably identify water-borne EHEC strains.     

Water potential changes in faecal matter and Escherichia coli survival

Aims: This study investigated the influence of a range of evaporation rates (2·0, 5·3 and 7·4 mm day⁻¹) on degradation of E. coli (ATCC Strain 25922) inoculated in canine faeces. Methods and Results: Experiments were carried out in an environmental chamber and a first order exponential decay function (Chick’s Law) was used to estimate degradation rates. We estimated die-off coefficients using linear regression. Die-off rates were −0·07, −0·22 and −0·23 h⁻¹, respectively, for evaporation rates of 2·0, 5·3 and 7·4 mm day⁻¹ (P = 0·000+, for each model). Nearly complete die-off was found within 15–60 h (7·4–2·0 mm day⁻¹ evaporation rates), which corresponds with a water potential of approximately −22·4 MPa. Conclusions: This study indicates that canine faeces need not be desiccated to achieve complete loss of indicator organisms. Water potential, which is a combination of osmotic and matric potential, is a key stress that increases as evaporation removes water from the faecal matrix and increases concentration of the remaining faecal solution. Evaporation may remove populations of indicator organisms in faeces relatively quickly, even though faeces are not completely dehydrated. Significance and Impact of the Study: This research may be used as the foundation for studies more closely resembling real-world evaporation conditions including diurnal fluctuations, rewetting and freezing.     

Aerobactin production and plasmid distribution in Escherichia coli clinical isolates

The distribution of plasmids as a function of aerobactin production, antibiotic resistance and antimicrobial agents production was studied in 139 Escherichia coli strains obtained from clinical sources. Ninety eight per cent of the strains analyzed presented plasmids with a median value of 2.97 plasmids per cell. Differences in the number of plasmids were observed for aerobactin production (3.52 for aerobactin producing strains, 2.56 (for non-producing ones) and antibiotic resistance (3.19 for antibiotic resistant strains and 2.58 for the sensitive ones). But this was not the case for antibacterial agent production (2.96 for the producing strains, 2.98 for the non-producing ones. Ecological implications of these results are discussed.     

Quinolone action in Escherichia coli cells carrying gyrA and gyrB mutations

Abstract We have isolated spontaneous mutant strains of Escherichia coli KL16 showing different levels of nalidixic acid (NAL) resistance. From 40 independent mutants, 36 had gyrA and four had gyrB mutations. Most of the gyrA mutations (30/36) conferred high level NAL resistance. In contrast, the only gyrB mutation that conferred a relatively high level of NAL resistance also determined enhanced susceptibility to quinolones with a piperazinyl substituent at C7 position of the quinolone ring (amphoteric quinolones). This gyrB mutation (denoted gyrB1604 ), jointly with a gyrA mutation (denoted gyrA972 ) which confers a high level of quinolone resistance, were used to construct strain IC2476, carrying the two gyr mutant alleles. The susceptibility of this strain to amphoteric quinolones (pipemidic acid, norfloxacin and ciprofloxacin) was similar to that of the gyrA972 single mutant. This result indicates that the change in GyrA subunit which determines a high level of quinolone-resistance has the capacity to mask the hypersusceptibility to amphoteric quinolones promoted by the GyrB1604 mutant subunit. This capacity was further confirmed by studying the effects of ciprofloxacin (CFX) on gyrase inhibition in the gyrA972 gyrB1604 strain.     

Shiga toxin-producing Escherichia coli and enteropathogenic Escherichia coli in healthy goats in India: occurrence and virulence properties

AIMS: To describe the occurrence and virulence gene pattern of shiga toxin-producing Escherichia coli (STEC) and enteropathogenic E. coli (EPEC) in healthy goats of Jammu and Kashmir, India. METHODS AND RESULTS: A total of 220 E. coli strains belonging to 60 different 'O' serogroups was isolated from 206 local (nonmigratory) and 69 migratory goats. All the 220 strains were screened for the presence of stx(1), stx(2), eaeA and hlyA genes. Twenty-eight E. coli (75.6%) strains from local and nine (24.3%) strains from migratory goats belonging to 18 different serogroups showed at least presence of one virulence gene studied. Twenty-eight strains (16.47%) (belonging to 13 different serogroups) from local goats carried stx(1) gene alone or in combination with stx(2) gene, while as only one strain (2%) from migratory goats possessed stx(2) gene alone. Interestingly in the present study none of the STEC strains carried eaeA gene. Similarly, none of the strains from local goats possessed eaeA and none of the migratory goats possessed stx(1) gene. Eight strains (16%) (belonging to four different serogroups) from migratory goats carried eaeA gene. Twenty-five (14.7%) and seven (14%) strains from local and migratory goats harboured hlyA gene respectively. CONCLUSIONS: Healthy goats of Jammu and Kashmir state serve as a reservoir of STEC and EPEC. Further studies in this direction are needed to work out whether or not they are transmitted to humans in this part of world. SIGNIFICANCE AND IMPACT OF THE STUDY: This study is the first report of isolation of STEC and EPEC strains from healthy goats in Jammu and Kashmir State of India, which could be a source of infection to humans.     

Distribution and characterization of integrons in Escherichia coli strains of animal and human origin

One hundred and twenty clinical and commensal Escherichia coli strains isolated in Switzerland from humans and from companion and farm animals were analysed for the prevalence of integrons of classes 1, 2, and 3 and for the characterization of their gene cassettes. The relationships between integron carriage and host category, and between integron carriage and phylogenetic E. coli lineage were also analysed. Integrons were detected in 48 (40%) of the isolates and were thus widely disseminated in the human and animal E. coli strains considered. Moreover, the association between integron carriage and certain animal categories (farm animals) suggests that animals that are raised for economic purposes might be exposed to a major antibiotic pressure. Finally, our data confirm that E. coli commensal strains represent a significant source of antibiotic-resistant determinants.     

猪源大肠杆菌耐药质粒图谱及耐药性分析

目的:探讨猪大肠杆菌的耐药质粒图谱、耐药性及耐药基因之间的关系。方法:从湖南省株洲、益阳的四个猪场分离出9株大肠杆菌,进行质粒电泳图谱分析、用PCR法检测耐喹诺酮类耐药基因Gyr A、Par C和耐四环素类耐药基因Tet A、Tet B,并采用Kirby-bauer法对这9株大肠杆菌进行药敏(18种抗生素)试验。结果:其中9株大肠杆菌含有三条或者三条以上的质粒条带,且其质粒谱型均不相同;9株大肠杆菌均检测出4种耐药基因Gyr A、Par C、Tet A和Tet B;9株大肠杆菌对所选用的抗生素存在不同程度的耐药性,其中7株大肠杆菌对10种或10种以上的抗生素耐药,最高对13种抗生素耐药,氨苄西林、青霉素、阿莫西林、红霉素的耐药率达100%,对四环素、多西环素的耐药率达到88.9%,而多粘菌素B、阿奇霉素、大观霉素耐药率较低。结论:耐药性与质粒条带数、耐药基因之间并无明显的相关性;猪大肠杆菌呈多重耐药之势,在治疗大肠杆菌病时最好根据药敏实验结果选用合适的抗生素。