Comparison of bacterial diversity in wheat bran and in the gut of larvae and newly emerged adult of Musca domestica (Diptera: Muscidae) by use of ethidium monoazide reveals bacterial colonization

The objective of the current study is to investigate the bacterial colonization within the gut of the house fly, Musca domestica L. (Diptera: Muscidae), at the larval stage and the bacterial community of the gut of the house fly at the newly emerged adult stage. After using ethidium monoazide to inhibit recovery of nucleic acids from dead bacteria, three polymerase chain reaction (PCR)-amplified 16S rDNA libraries from wheat bran, larvae, and newly emerged adults was constructed, analyzed, and compared. In total, 24, 11, and four phylotypes in the 16S rDNA libraries of wheat bran and the gut of larvae and adults, respectively, were found and assigned to three phylogenetic phyla of the domain Bacteria: Firmicutes, Proteobacteria, and Bacteroidetes. In the wheat bran library, 76% of the total number of sequences were affiliated to the genera Pseudomonas, Halomonas, Providencia, and Ignatzschineria. The three genera Morganella (79.05%), Providencia (8.78%), and Ignatzschineria (9.46%) dominated the library of the larval gut. Compared with the wheat bran library, the relative abundance of Morganella morganii (Winslow) was significantly higher (79.05 versus 0.8%), whereas that of Ignatzschineria larvae and of Providencia spp. was similar. These results demonstrate that M. morganii, Providencia spp., and I. larvae colonized the gut of the house fly larvae. Live bacteria of M. morganii, Providencia spp., and Proteus spp. were found in the gut of newly emerged adults. Therefore, the bacteria M. morganii and Providencia spp. colonized the larval gut could survive in the gut from larval metamorphosis to adult eclosion of the house fly.     

Microbiology of the oil fly, Helaeomyia petrolei

Helaeomyia petrolei larvae isolated from the asphalt seeps of Rancho La Brea in Los Angeles, Calif., were examined for microbial gut contents. Standard counts on Luria-Bertani, MacConkey, and blood agar plates indicated ca. 2 x 10(5) heterotrophic bacteria per larva. The culturable bacteria represented 15 to 20% of the total population as determined by acridine orange staining. The gut itself contained large amounts of the oil, had no observable ceca, and maintained a slightly acidic pH of 6.3 to 6.5. Despite the ingestion of large amounts of potentially toxic asphalt by the larvae, their guts sustained the growth of 100 to 1,000 times more bacteria than did free oil. All of the bacteria isolated were nonsporeformers and gram negative. Fourteen isolates were chosen based on representative colony morphologies and were identified by using the Enterotube II and API 20E systems and fatty acid analysis. Of the 14 isolates, 9 were identified as Providencia rettgeri and 3 were likely Acinetobacter isolates. No evidence was found that the isolates grew on or derived nutrients from the asphalt itself or that they played an essential role in insect development. Regardless, any bacteria found in the oil fly larval gut are likely to exhibit pronounced solvent tolerance and may be a future source of industrially useful, solvent-tolerant enzymes.     

The increased sensitivity of rifamycin-resistant mutants of Methylobacterium AM1 to a variety of antimicrobial agents

Rifamycin-resistant strains of Methylobacterium AM1 are more sensitive to β-lactam antibiotics, chloramphenicol, tetracycline, spectinomycin, puromycin, nalidixic acid, benzalkonium chloride and p -fluorophenylalanine than are rifamycin-sensitive strains. This suggests that mutation to rifamycin resistance is associated with a general increase in membrane permeability and may have a bearing on the use of rifamycin-resistant mutants in genetic and biochemical studies of this organism.     

Microbiology of the Oil Fly, Helaeomyia petrolei

Helaeomyia petrolei larvae isolated from the asphalt seeps of Rancho La Brea in Los Angeles, Calif., were examined for microbial gut contents. Standard counts on Luria-Bertani, MacConkey, and blood agar plates indicated ca. 2 × 10⁵ heterotrophic bacteria per larva. The culturable bacteria represented 15 to 20% of the total population as determined by acridine orange staining. The gut itself contained large amounts of the oil, had no observable ceca, and maintained a slightly acidic pH of 6.3 to 6.5. Despite the ingestion of large amounts of potentially toxic asphalt by the larvae, their guts sustained the growth of 100 to 1,000 times more bacteria than did free oil. All of the bacteria isolated were nonsporeformers and gram negative. Fourteen isolates were chosen based on representative colony morphologies and were identified by using the Enterotube II and API 20E systems and fatty acid analysis. Of the 14 isolates, 9 were identified as Providencia rettgeri and 3 were likely Acinetobacter isolates. No evidence was found that the isolates grew on or derived nutrients from the asphalt itself or that they played an essential role in insect development. Regardless, any bacteria found in the oil fly larval gut are likely to exhibit pronounced solvent tolerance and may be a future source of industrially useful, solvent-tolerant enzymes.     

黑水虻幼虫及预蛹抗逆性的初步研究

本文初步研究了老熟和预蛹阶段的黑水虻Hermetiaillucens对于酒精毒性、氧胁迫和高渗透压条件下的耐受特性,结果显示黑水虻幼虫和预蛹在三种胁迫因子处于20%～60%(浓度)的较低水平时,其平均死亡率低于20%,表现出良好的抗逆性。高浓度的酒精、矿物油和氯化钠溶液对于黑水虻的生存都会产生负面影响,但是幼虫与预蛹由于其生理形态上的变化,致使其在抗逆性方面表现出显著差异,预蛹阶段的黑水虻对矿物油较为敏感,而幼虫则对高盐环境的耐受性表现较弱。     

R—Factors of Escherichia coli from Dressed Beef and Humans

One hundred eighty Escherichia coli strains isolated from raw and cooked dressed beef and from healthy humans were screened for resistance to each of nine antibiotics: chlortetracycline, ampicillin, chloramphenicol, kanamycin, neomycin, nalidixic acid, dihydrostreptomycin, oxytetracycline, and tetracycline. Nearly 80% of the 98 beef isolates and 54% of the 82 human isolates were resistant to one or more of the antibiotics tested. Ampicillin resistance was most frequent among beef isolates, and dihydrostreptomycin resistance was most frequent among isolates of human origin. About 74% of the multiply resistant beef strains and 85% of the multiply resistant human strains transferred all or part of their resistance to E. coli K-12 recipients.     

Effect of quinolone treatment on selection and persistence of quinolone-resistant Escherichia coli in swine faecal flora

AIMS: To study the effect of oral administration of a quinolone on emergence of resistance in an indicator bacterial species from faecal flora. METHODS AND RESULTS: Quinolone resistance was studied in Escherichia coli obtained from the faecal contents of pigs housed in nine commercial farrow-to-finish herds in France after administration of flumequine to sows. The percentage of quinolone-resistant E. coli increased in the faeces of sows after administration of flumequine (mean 21.78% at day 7 vs 6.42% before treatment for nalidixic acid) and then decreased (mean 12.6 and 10.4 at days 30 and 60, respectively for nalidixic acid), being not significantly different from initial values 1 month post-treatment. In young pigs, the proportion of resistant strains was lower and decreased over rearing period. Moreover, changes over time of both total E. coli and the proportion of resistant bacteria exhibited great inter-individual variability. CONCLUSIONS: Restoration of susceptible faecal flora occurred within 2 months after flumequine treatment. SIGNIFICANCE AND IMPACT OF THE STUDY: Effect of flumequine treatment of sows on the quinolone resistance of faecal E. coli of both sows and their progeny is noticeable but transitory.     

Antibiotic resistance and molecular characterization of poultry isolates of Salmonella by RAPD-PCR

The antibiotic resistance profile of 17 poultry isolates of Salmonella was studied against 24 different antibiotics. 69–88% of the Salmonella isolates displayed a high level of resistance, particularly against penicillin, rifampicin, erythromycin, clarithromycin, clindamycin, sulphamethoxazole and vancomycin. In contrast, a relatively low or moderate level of resistance was observed against furazolidone, spectinomycin, ciprofloxacin, chloramphenicol, cefepime, carbenicillin, nalidixic acid, streptomycin, oxacillin and cephalothin (11–59%). Moreover, resistance to multiple antibiotics (2–5) was also observed among the Salmonella strains, and none of the isolates was found susceptible to all the antibiotics used. Similarity coefficient among Salmonella strains by RAPD-PCR analysis varied from 0.60 to 0.86, and all the salmonellae could be classified into seven groups on the basis of dendrogram analysis. Generally, a very high level of concordance between RAPD-PCR profile and antibiotic profile was not observed, which indicates that genes for antibiotic resistance may not always be present on genomic DNA rather may be plasmid-borne.     

Occurrence of ceftriaxone-resistant commensal bacteria on a dairy farm and a poultry farm

Approximately 40 samples of animal feces, drinking water, feed, bedding, pine wood shavings, compost, and manure slurry were collected from two animal research farms (one dairy and one poultry) and analyzed for ceftriaxone-resistant bacteria. Our study revealed that the total percentage of aerobic bacteria with reduced susceptibility to ceftriaxone (minimal inhibitory concentration (MIC) > or = 16 micro g/mL) ranged from 0.9% to 10.8% in dairy feces and from 0.05% to 3.93% in chicken feces. The percentages of ceftriaxone-resistant bacteria (MIC > or = 64 micro g/mL) were in the range of 0.01% - 2.3% in dairy feces and 0.01% - 0.79% in chicken feces. Environmental samples contained a wide range of ceftriaxone-resistant bacterial populations. Among those environmental samples, fresh pine wood shavings used as chicken bedding contained the highest percentages (41.5%) of ceftriaxone-resistant bacteria, as determined by a plating method. A total of 105 ceftriaxone-resistant (MIC > or = 128 micro g/mL) bacterial isolates were isolated from the above samples and tested for resistance to nine antibiotics: ampicillin, ceftriaxone, streptomycin, kanamycin, gentamicin, chloramphenicol, tetracycline, ciprofloxacin, and nalidixic acid. The most prevalent resistance pattern (34.3%) among isolates included resistance to all nine antibiotics. Results from this study suggest that ceftriaxone-resistant bacteria exist in farm environments, and the ceftriaxone resistance was frequently associated with resistance to multiple antibiotics. Environmental sources such as pine wood shavings used as bedding can be a potential reservoir for transmitting the multidrug-resistant bacteria.     

Antimicrobial resistance in bacteria isolated from aquaculture sources in Australia

AIMS: To carry out a preliminary assessment of the occurrence of resistance to antimicrobials in bacteria that has been isolated from a variety of aquaculture species and environments in Australia. METHOD AND RESULTS: A total of 100 Gram-negative (Vibrio spp. and Aeromonas spp. predominantly) and four Gram-positive bacteria isolated from farmed fish, crustaceans and water from crab larval rearing tanks were obtained from diagnostic laboratories from different parts of Australia. All the isolates were tested for sensitivity to 19 antibiotics and Minimal Inhibitory Concentrations were determined by the agar dilution method. Plasmid DNA was isolated by the alkali lysis method. Resistance to ampicillin, amoxycillin, cephalexin and erythromycin was widespread; resistance to oxytetracycline, tetracycline, nalidixic acid and sulfonamides was common but resistance to chloramphenicol, florfenicol, ceftiofur, cephalothin, cefoperazone, oxolinic acid, gentamicin, kanamycin and trimethoprim was less common. All strains were susceptible to ciprofloxacin. Multiple resistance was also observed and 74.4% of resistant isolates had between one and ten plasmids with sizes ranging 2-51 kbp. CONCLUSIONS: No antibiotics are registered for use in aquaculture in Australia but these results suggest that there has been significant off-label use. SIGNIFICANCE AND IMPACT OF STUDY: Transfer of antibiotic resistant bacteria to humans via the food chain is a significant health concern. In comparison with studies on terrestrial food producing animals, there are fewer studies on antibiotic resistance in bacteria from aquaculture enterprises and this study provides further support to the view that there is the risk of transfer of resistant bacteria to humans from consumption of aquaculture products. From the Australian perspective, although there are no products registered for use in aquaculture, antimicrobial resistance is present in isolates from aquaculture and aquaculture environments.     

Antibiotic Resistance in Bacteria Isolated from the Deep Terrestrial Subsurface

Various natural environments have been examined for the presence of antibiotic-resistant bacteria and/or novel resistance mechanisms, but little is known about resistance in the terrestrial deep subsurface. This study examined two deep environments that differ in their known period of isolation from surface environments and the bacteria therein. One hundred fifty-four strains of bacteria were isolated from sediments located 170–259 m below land surface at the US Department of Energy Savannah River Site (SRS) in South Carolina and Hanford Site (HS) in Washington. Analyses of 16S rRNA gene sequences showed that both sets of strains were phylogenetically diverse and could be assigned to several genera in three to four phyla. All of the strains were screened for resistance to 13 antibiotics by plating on selective media and 90% were resistant to at least one antibiotic. Eighty-six percent of the SRS and 62% of the HS strains were resistant to more than one antibiotic. Resistance to nalidixic acid, mupirocin, or ampicillin was noted most frequently. The results indicate that antibiotic resistance is common among subsurface bacteria. The somewhat higher frequencies of resistance and multiple resistance at the SRS may, in part, be due to recent surface influence, such as exposure to antibiotics used in agriculture. However, the HS strains have never been exposed to anthropogenic antibiotics but still had a reasonably high frequency of resistance. Given their long period of isolation from surface influences, it is possible that they possess some novel antibiotic resistance genes and/or resistance mechanisms. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A Treatment Plant Receiving Waste Water from Multiple Bulk Drug Manufacturers Is a Reservoir for Highly Multi-Drug Resistant Integron-Bearing Bacteria

The arenas and detailed mechanisms for transfer of antibiotic resistance genes between environmental bacteria and pathogens are largely unclear. Selection pressures from antibiotics in situations where environmental bacteria and human pathogens meet are expected to increase the risks for such gene transfer events. We hypothesize that waste-water treatment plants (WWTPs) serving antibiotic manufacturing industries may provide such spawning grounds, given the high bacterial densities present there together with exceptionally strong and persistent selection pressures from the antibiotic-contaminated waste. Previous analyses of effluent from an Indian industrial WWTP that processes waste from bulk drug production revealed the presence of a range of drugs, including broad spectrum antibiotics at extremely high concentrations (mg/L range). In this study, we have characterized the antibiotic resistance profiles of 93 bacterial strains sampled at different stages of the treatment process from the WWTP against 39 antibiotics belonging to 12 different classes. A large majority (86%) of the strains were resistant to 20 or more antibiotics. Although there were no classically-recognized human pathogens among the 93 isolated strains, opportunistic pathogens such as Ochrobactrum intermedium, Providencia rettgeri, vancomycin resistant Enterococci (VRE), Aerococcus sp. and Citrobacter freundii were found to be highly resistant. One of the O. intermedium strains (ER1) was resistant to 36 antibiotics, while P. rettgeri (OSR3) was resistant to 35 antibiotics. Class 1 and 2 integrons were detected in 74/93 (80%) strains each, and 88/93 (95%) strains harbored at least one type of integron. The qPCR analysis of community DNA also showed an unprecedented high prevalence of integrons, suggesting that the bacteria living under such high selective pressure have an appreciable potential for genetic exchange of resistance genes via mobile gene cassettes. The present study provides insight into the mechanisms behind and the extent of multi-drug resistance among bacteria living under an extreme antibiotic selection pressure.     

Differentially Expressed Outer Membrane Proteins of Vibrio alginolyticus in Response to Six Types of Antibiotics

Vibrio alginolyticus is an opportunistic pathogen that occasionally causes life-threatening infections in individuals and results in great losses in marine aquacultures of crustaceans and fish. Recently, antibiotic-resistant strains of the bacterium from clinical and environmental sources have been reported with increasing frequency. However, few reports were involved in the antibiotic resistance of this bacterium at molecular levels. In the present study, Western blotting was utilized to investigate altered OM proteins of V. alginolyticus in response to six types of antibiotics: erythromycin, kanamycin, tetracycline, streptomycin, nalidixic acid, and chloromycetin. Seventeen OM proteins have been reported here for the first time to be related to antibiotic resistance. They were porins OmpU, OmpN, putative OmpU and LamB; transport proteins VA0802, VA2212 (FadL) and VPA0860; TolC family TolC and VA1631; lipoprotein VA0449; OmpA family VPA1186 and VA0764; iron-regulated proteins OmpV, VPA1435, and VA2602; and receptor protein OmpK; hypothetical protein VA1475. Importantly, VA2212 was up-regulated in response to the five antibiotics except nalidixic acid, and VPA1186 was down-regulated in response to the six antibiotics in antibiotic-stressed bacteria. They might be potentially universal targets for designing the new drugs that inhibit multi-resistant bacteria. These findings suggested that parallel investigations into a bacterium responding to several types of antibiotics would be helpful not only for the further understanding of antibiotic-resistant mechanisms but also for the screening of valuable targets of new drugs controlling antibiotic-resistant bacteria.     

Antibiotic resistance of Salmonella strains isolated from fish and crustaceans

A total of 240 Salmonella strains, 158 from 730 fish samples and 82 from 276 crustacean samples, obtained during a 2 year period, were examined for resistance to 10 antibiotics. More than 90% of the strains were resistant to bacitracin, penicillin and novobiocin. The least resistance was observed to chloramphenicol (6·7%) and nalidixic acid (12%). Multiple antibiotic resistance indexing of the strains showed that more than 95% originated from high risk sources of contamination such as poultry, swine, cattle and human environments where antibiotics are often used.     

Phenotypic and genetic characterization of multidrug-resistant <Emphasis Type="Italic">Salmonella</Emphasis> Infantis strains isolated from broiler chicken meats in Turkey

Twenty Salmonella Infantis strains resistant against kanamycin, tetracycline, neomycin, spectinomycin, sulphonamide, nalidixic acid and trimethoprim were selected for this study out of 103 Salmonella strains isolated from broiler samples collected from several markets in the Bolu and Ankara regions of Turkey. The resistance genes aadA1, aphA1, sul1, tet(A), dfrA5/dfrA14 and gyrA were determined for these multidrug-resistant S. Infantis strains. S. Infantis strains contained a mega plasmid with the molecular size of 206 kb. The strains were divided into three groups according to the pulsed field gel electrophoresis patterns of XbaI digested chromosomal DNA. A Ser83→Tyr83 point mutation was found in the gyrA gene of all quinolone-resistant isolates. Filter mating experiments showed that 206 kb plasmid transferred nalidixic acid resistance associated with class I integrons.     

Impact of an urban effluent on antibiotic resistance of riverine Enterobacteriaceae and Aeromonas spp

In order to evaluate the impact of an urban effluent on antibiotic resistance of freshwater bacterial populations, water samples were collected from the Arga river (Spain), upstream and downstream from the wastewater discharge of the city of Pamplona. Strains of Enterobacteriaceae (representative of the human and animal commensal flora) (110 isolates) and Aeromonas (typically waterborne bacteria) (118 isolates) were selected for antibiotic susceptibility testing. Most of the Aeromonas strains (72%) and many of the Enterobacteriaceae (20%) were resistant to nalidixic acid. Singly nalidixic acid-resistant strains were frequent regardless of the sampling site for Aeromonas, whereas they were more common upstream from the discharge for enterobacteria. The most common resistances to antibiotics other than quinolones were to tetracycline (24.3%) and beta-lactams (20.5%) for Enterobacteriaceae and to tetracycline (27.5%) and co-trimoxazole (26.6%) for Aeromonas. The rates of these antibiotic resistances increased downstream from the discharge at similar degrees for the two bacterial groups; it remained at high levels for enterobacteria but decreased along the 30-km study zone for Aeromonas. Genetic analysis of representative strains demonstrated that these resistances were mostly (enterobacteria) or exclusively (Aeromonas) chromosomally mediated. Moreover, a reference strain of Aeromonas caviae (CIP 7616) could not be transformed with conjugative R plasmids of enterobacteria. Thus, the urban effluent resulted in an increase of the rates of resistance to antibiotics other than quinolones in the riverine bacterial populations, despite limited genetic exchanges between enterobacteria and Aeromonas. Quinolone resistance probably was selected by heavy antibiotic discharges of unknown origin upstream from the urban effluent.     

Dynamics of drug resistance of Vibrio cholerae isolated from surface water reservoirs in Siberia and the Soviet Far East in 1976-1990]

In the study on antibiotic resistance 1383 strains of El Tor Vibrio cholerae isolated from surface water reservoirs in 12 administrative territories of the Siberia and Far East within a period of 15 years were tested. The following antibiotics were used: ampicillin, streptomycin, monomycin, polymyxin, tetracycline, chloramphenicol, rifampicin and nalidixic acid. The resistance was unstable and its pattern was wave-like according to annual changes in the biological cycle. It was especially evident in regard to ampicillin, streptomycin, monomycin and polymyxin. The highest numbers of the strains were resistant to polymyxin, ampicillin and streptomycin (up to 100 per cent in some years). The lowest numbers of the strains were resistant to chloramphenicol (0.4 per cent) and tetracycline (1.9 per cent). No strains resistant to rifampicin and nalidixic acid were isolated. In some cases the antibiotic resistance level depended on the geographical zone where the strain was isolated. A direct quantitative dependence of the resistance level on the MIC was observed: the lower the MIC of the drug was, the lower the number of the strains resistant to it was. Within the 15-year period there was no general tendency to increase the resistance in V. cholerae to the antibiotics used.     

Unusual association of a plasmid with nalidixic acid resistance in an epidemic strain of Shigella dysenteriae type 1 from Asia

The association of a 20-MDa plasmid with nalidixic acid resistant (Nalr) strains of Shigella dysenteriae 1 has been examined. The plasmid, which is readily transferable, does not itself code for nalidixic acid resistance but offers a survival advantage to its host under nalidixic acid stress. The plasmid-containing cultures of S. dynsenteriae 1 produced Nalr mutants in vitro at a frequency 1000-fold higher than their plasmidless parent strains, after two exposures to nalidixic acid. Using a similar procedure, mutants resistant to other antibiotics such as chloramphenicol, tetracycline, or ciprofloxacin could not be isolated. The genome of S. dysenteriae 1 appears to carry a heavy load of the insertion sequence IS1. The propensity of the plasmid-containing strains to readily mutate to nalidixic acid resistance and its possible relevance to the observed association of the plasmid with Nalr clinical isolates is discussed.     

Susceptibility of Arcobacter butzleri isolates to 23 antimicrobial agents

AIMS: The objective of this study was to determine the susceptibility of Arcobacter butzleri isolates to various antimicrobial agents used in the treatment of infectious diseases in humans and animals. METHODS AND RESULTS: Thirty-nine A. butzleri strains isolated from broiler chickens were tested for their susceptibility to 23 antimicrobial agents using a disc diffusion method. All isolates were resistant to aztreonam, cefuroxime sodium, cephalothin, orbenin, oxacillin, penicillin G and trimethoprim/sulphamethoxazol. Of the 39 isolates tested, 26 were also found resistant to amoxycillin, amoxycillin/clavulanic acid and ampicillin. One isolate was resistant to, and four showed intermediate level of resistance to, erythromycin. All isolates were susceptible to amikacin, chloramphenicol, danofloxacin, enrofloxacin, nitrofurantoin, nalidixic acid, tetracyclines and tobramycin. CONCLUSIONS: The majority of the isolates were found resistant to antibiotics commonly used for the treatment of infectious bacterial diseases in humans and animals. SIGNIFICANCE AND IMPACT OF THE STUDY: This study shows that A. butzleri strains vary in their resistance to certain kinds of antibiotics and caution should be taken when choosing a suitable antibiotic for the treatment of disease(s) caused by this organism.     

斑节对虾(非洲群体)肠道细菌抗生素耐药性及耐药基因分布特征

【目的】解析斑节对虾(Penaeus monodon)(非洲群体)(俗称“金刚虾”,以下同)携带耐药菌及耐药基因现状。【方法】本研究从山东滨州北海新区采集了金刚虾,对其肠道细菌常用抗生素的耐药菌性质及数量、占比及种类进行检测,通过荧光定量PCR技术分析肠道内容物样品中的4类抗生素的4种耐药性基因分布特征。【结果】肠道中可培养细菌总数约1.45×10⁵–2.13×10⁶ CFU/g,有四环素、萘啶酸、氟苯尼考、庆大霉素4种抗生素耐药菌的检出,其中喹诺酮类萘啶酸耐药菌占比最高,达到35.00%,氨基糖苷类庆大霉素占比最少。10种抗生素药敏性质分析表明,肠道可培养细菌对庆大霉素、氟苯尼考等6种抗生素高度敏感,对四环素、卡那霉素中度敏感,对萘啶酸、青霉素、阿莫西林耐药。从分离的耐药菌鉴定结果可以得出,可培养的抗生素耐药菌主要集中在弧菌属,基于属水平的不同抗生素耐药菌统计显示,不同抗生素耐药菌种类存在明显差异,且同一菌属有耐多种抗生素的情况。荧光定量PCR检测分析,4种耐药基因的丰度不同,tet A基因相对拷贝数和四环素耐药菌比例、floR基因和氟苯尼...