Susceptibility of Coagulase-negative Staphylococci to Lysostaphin and Other Antibiotics

In general, coagulase-negative staphylococci were found to be relatively less susceptible to the lytic action of lysostaphin than coagulase-positive staphylococci. To achieve, arbitrarily, a lysis greater than 75%, it was necessary to use an increased concentration of enzyme or a longer incubation period than that usually required with coagulase-positive strains. For the most part, the cultures studied were sensitive to oxacillin, cloxacillin, dicloxacillin, nafcillin, ancillin, cephalothin, cephaloridine, fusidic acid, lincomycin, novobiocin, and neomycin [median minimal inhibitory concentrations (MIC) of 1.56 mug/ml or less]. Some degree of resistance (median MIC values of 12.5 mug/ml or greater) to benzylpenicillin, ampicillin, methicillin, tetracycline, chloretetracycline, erythromycin, ristocetin, and lysostaphin was found. Ten methicillin-resistant, coagulase-negative staphylococal strains were found to be cross-resistant to all nine of the penicillins tested, but much less resistant to the two cephalosporin analogues. In several instances, some of these strains seemed to be more sensitive to benzylpenicillin and to certain of the semisynthetic penicillins than to methicillin. Of the 18 antibiotics tested with the viable plate count method, the methicillin-resistant strains were found to be the most sensitive to lincomycin and novobiocin.     

Comparative Inhibition of Methicillin-resistant Strains of Staphylococcus aureus by Lysostaphin and Otner Antibiotics

Sixteen methicillin-resistant strains of Staphylococcus aureus obtained from Europe were found to be sensitive to the lytic activity of lysotaphin. With only minor exceptions, the strains were found to be sensitive to novobiocin, erythromycin, fusidic acid, and lincomycin, and slightly less sensitive to vancomycin and chloramphenicol. All strains were resistant to tetracycline, penicillinase-sensitive penicillins (benzylpenicillin, ampicillin, and propicillin), penicillinase-resistant penicillins (methicillin, nafcillin, ancillin, oxacillin, cloxacillin, and dicloxacillin), and two cephalosporin antibiotics (cephalothin and cephaloridine).     

Antimicrobial Resistance of Escherichia coli O157 Isolated from Humans, Cattle, Swine, and Food

A total of 361 Escherichia coli O157 isolates, recovered from humans, cattle, swine, and food during the years 1985 to 2000, were examined to better understand the prevalence of antimicrobial resistance among these organisms. Based on broth microdilution results, 220 (61%) of the isolates were susceptible to all 13 antimicrobials tested. Ninety-nine (27%) of the isolates, however, were resistant to tetracycline, 93 (26%) were resistant to sulfamethoxazole, 61 (17%) were resistant to cephalothin, and 48 (13%) were resistant to ampicillin. Highest frequencies of resistance occurred among swine isolates (n = 70), where 52 (74%) were resistant to sulfamethoxazole, 50 (71%) were resistant to tetracycline, 38 (54%) were resistant to cephalothin, and 17 (24%) were resistant to ampicillin. Based on the presence of Shiga toxin genes as determined by PCR, 210 (58%) of the isolates were identified as Shiga toxin-producing E. coli (STEC). Among these, resistance was generally low, yet 21 (10%) were resistant to sulfamethoxazole and 19 (9%) were resistant to tetracycline. Based on latex agglutination, 189 (52%) of the isolates were identified as E. coli O157:H7, among which 19 (10%) were resistant to sulfamethoxazole and 16 (8%) were resistant to tetracycline. The data suggest that selection pressure imposed by the use of tetracycline derivatives, sulfa drugs, cephalosporins, and penicillins, whether therapeutically in human and veterinary medicine or as prophylaxis in the animal production environment, is a key driving force in the selection of antimicrobial resistance in STEC and non-STEC O157.     

Cephalothin—Its In Vitro Antibacterial Spectrum as Studied in a Diagnostic Laboratory

Of 655 bacterial strains isolated in a routine clinical diagnostic laboratory, 564 (86 per cent) were found sensitive to cephalothin by disk sensitivity test. However, the fraction of sensitive Gram-negative bacilli and enterococci declined sharply at concentrations approximating those obtained in serum after the usual recommended dosages. Gram-positive bacteria remained sensitive throughout the entire range of testing concentrations.Unless very high dosages are used, cephalothin cannot be considered a broad-spectrum antibacterial agent for use while cultures are pending. Even with very high dosages all strains of Pseudomonas spp. and significant fractions of other Gram-negative bacillary species remain resistant to cephalothin.If used alone, the high potency cephalothin disk may yield inadequate information and should be supplemented by a lower potency disk, standardized measurements of zone diameters, or a screening plate.     

Moderate Prevalence of Antimicrobial Resistance in Escherichia coli Isolates from Lettuce,Irrigation Water,and Soil

Fresh produce is known to carry nonpathogenic epiphytic microorganisms. During agricultural production and harvesting, leafy greens can become contaminated with antibiotic-resistant pathogens or commensals from animal and human sources. As lettuce does not undergo any inactivation or preservation treatment during processing, consumers may be exposed directly to all of the (resistant) bacteria present. In this study, we investigated whether lettuce or its production environment (irrigation water, soil) is able to act as a vector or reservoir of antimicrobial-resistant Escherichia coli. Over a 1-year period, eight lettuce farms were visited multiple times and 738 samples, including lettuce seedlings (leaves and soil), soil, irrigation water, and lettuce leaves were collected. From these samples, 473 isolates of Escherichia coli were obtained and tested for resistance to 14 antimicrobials. Fifty-four isolates (11.4%) were resistant to one or more antimicrobials. The highest resistance rate was observed for ampicillin (7%), followed by cephalothin, amoxicillin-clavulanic acid, tetracycline, trimethoprim, and streptomycin, with resistance rates between 4.4 and 3.6%. No resistance to amikacin, ciprofloxacin, gentamicin, or kanamycin was observed. One isolate was resistant to cefotaxime. Among the multiresistant isolates (n = 37), ampicillin and cephalothin showed the highest resistance rates, at 76 and 52%, respectively. E. coli isolates from lettuce showed higher resistance rates than E. coli isolates obtained from soil or irrigation water samples. When the presence of resistance in E. coli isolates from lettuce production sites and their resistance patterns were compared with the profiles of animal-derived E. coli strains, they were found to be the most comparable with what is found in the cattle reservoir. This may suggest that cattle are a potential reservoir of antimicrobial-resistant E. coli strains in plant primary production.     

Susceptibility to and resistance determinants of fusidic acid in Staphylococcus aureus isolated from Chinese children with skin and soft tissue infections

This study aims to determine the resistance rates and determinants of fusidic acid among Staphylococcus aureus isolates collected from Chinese pediatric patients with skin and soft tissue infections (SSTIs). Between 2008 and 2009, a total of 186 clinical S. aureus isolates were collected from the pediatric patients with SSTIs, abscess (44.6%) was the most common SSTI in children 0-16 years old. Four clinical isolates (4/186, 2.2%) were resistant to fusidic acid. Two of these isolates were methicillin-resistant S. aureus (MRSA) that carry the fusC gene. The other two isolates were methicillin-sensitive S. aureus (MSSA) that carry the fusB gene. In the two fusB-positive clinical isolates, the fusB gene was located in a transposon-like element that has 99% identity with a pUB101 fragment from S. aureus. The four fusidic acid-resistant clinical isolates were ST1-MRSA-SCCmecV-t127, ST93-MRSA-SCCmecIII-t202, ST680-MSSA-t5415, and ST680-MSSA-t377. The fusidic acid resistance rate of S. aureus isolated from Chinese pediatric patients with SSTIs was low, and the genes fusB and fusC were the main resistance determinants. The transposon-like element that contains the fusB gene might participate in the transmission of fusidic acid resistance genes. This is the first report regarding the emergence of fusidic acid-resistant clinical S. aureus isolates in mainland China.     

Fusidic-acid-resistant staphylococci

Penicillin-resistant staphylococci were examined to determine the spontaneous mutation frequency of resistance to antistaphylococcal antibiotics including fusidic acid, cephalothin and lincomycin. Fusidic-acid-resistant mutants were obtained about twenty times more frequently than cephalothin-resistant mutants and about one hundred times more frequently than lincomycin-resistant mutants. Among the fusidic-acid-resistant mutants, ninety-seven per cent were resistant to 20 g/ml and thirty percent to 100 g/ml of the drug. The fusidic-acid-resistant mutants had prolonged generation times not related to the level of drug resistance. Cross-resistance between fusidic acid and cephalothin and between lincomycin and erythromycin was detected. Preliminary evidence was presented indicating that fusidic-acid-resistant mutants inactivate fusidic acid to a greater extent than sensitive cells.     

Antimicrobial resistance of Escherichia coli O157 isolated from humans, cattle, swine, and food

A total of 361 Escherichia coli O157 isolates, recovered from humans, cattle, swine, and food during the years 1985 to 2000, were examined to better understand the prevalence of antimicrobial resistance among these organisms. Based on broth microdilution results, 220 (61%) of the isolates were susceptible to all 13 antimicrobials tested. Ninety-nine (27%) of the isolates, however, were resistant to tetracycline, 93 (26%) were resistant to sulfamethoxazole, 61 (17%) were resistant to cephalothin, and 48 (13%) were resistant to ampicillin. Highest frequencies of resistance occurred among swine isolates (n = 70), where 52 (74%) were resistant to sulfamethoxazole, 50 (71%) were resistant to tetracycline, 38 (54%) were resistant to cephalothin, and 17 (24%) were resistant to ampicillin. Based on the presence of Shiga toxin genes as determined by PCR, 210 (58%) of the isolates were identified as Shiga toxin-producing E. coli (STEC). Among these, resistance was generally low, yet 21 (10%) were resistant to sulfamethoxazole and 19 (9%) were resistant to tetracycline. Based on latex agglutination, 189 (52%) of the isolates were identified as E. coli O157:H7, among which 19 (10%) were resistant to sulfamethoxazole and 16 (8%) were resistant to tetracycline. The data suggest that selection pressure imposed by the use of tetracycline derivatives, sulfa drugs, cephalosporins, and penicillins, whether therapeutically in human and veterinary medicine or as prophylaxis in the animal production environment, is a key driving force in the selection of antimicrobial resistance in STEC and non-STEC O157.     

Antibiotic susceptibility of potentially probiotic Bifidobacterium isolates from the human gastrointestinal tract

Sixteen Bifidobacterium isolates from the human gastrointestinal tract were assayed for susceptibility to 44 antibiotics by soft agar overlay disc diffusion on TPY agar. Five isolates (3/7 B. bifidum and 2/3 B. breve ) exhibited atypical antibiotic susceptibility profiles. Poor growth in the agar overlay accounted for susceptibility of B. bifidum but not B. breve isolates. All other isolates were resistant to cefoxitin (30 μg), aztreonam (30 μg), vancomycin (30 μg), amikacin (30 μg), gentamicin (10 μg), kanamycin (30 μg), streptomycin (10 μg), fusidic acid (10 μg), trimethoprim (5 μg), norfloxacin (10 μg), nalidixic acid (30 μg), metronidazole (5 μg), polymyxin B (300 μg) and colistin sulphate (10 μg), and they were susceptible to the six penicillins studied, cephalothin (30 μg), cefuroxime (30 μg), cefaclor (30 μg), ceftizoxime (30 μg), cefotaxime (30 μg), bacitracin (10 μg), chloramphenicol (30 μg), erythromycin (15 μg), clindamycin (2 μg), rifampicin (5 μg) and nitrofurantoin (300 μg). In addition, they varied in their susceptibility to cephradine (30 μg), cephazolin (30 μg), cefoperazone (75 μg), ceftriaxone (30 μg), ofloxacin (5 μg) and furazolidone (15 μg). They were resistant, or only marginally moderately susceptible, to ceftazidime (30 μg), netilmicin (10 μg), sulphamethoxazole (100 μg), cotrimoxazole (25 μg) and ciprofloxacin (5 μg), and susceptible or marginally moderately susceptible to tetracycline (30 μg). All B. bifidum isolates were susceptible to cefixime (5 μg). Four micro-organism-drug combinations were evaluated for β-lactamase activity but its absence suggested that cell wall impermeability was responsible for cephalosporin resistance among bifidobacteria. The antibiotic susceptibility of B. animalis 25527T was similar to that of the human isolates.     

Staphylococcus aureus Response to Lysostaphin in Some Fermented Foods

The addition of lysostaphin to starting materials for cheese and fermented sausage that were artificially contaminated with Staphylococcus aureus resulted in an initial decrease in the staphylococcal flora. In a simulated cheese process, lysostaphin remained with the curd after separation of the whey. In both cheese and fermented sausage samples that were produced experimentally in the laboratory, a significant S. aureus population ultimately developed, even in the presence of lysostaphin. Staphylococcal isolates from these treated products were not more resistant to the lytic enzyme than was the parent strain.     

Multiple-Antibiotic Resistance of Enterococcus spp. Isolated from Commercial Poultry Production Environments

The potential impact of food animals in the production environment on the bacterial population as a result of antimicrobial drug use for growth enhancement continues to be a cause for concern. Enterococci from 82 farms within a poultry production region on the eastern seaboard were isolated to establish a baseline of susceptibility profiles for a number of antimicrobials used in production as well as clinical environments. Of the 541 isolates recovered, Enterococcus faecalis (53%) and E. faecium (31%) were the predominant species, while multiresistant antimicrobial phenotypes were observed among all species. The prevalence of resistance among isolates of E. faecalis was comparatively higher among lincosamide, macrolide, and tetracycline antimicrobials, while isolates of E. faecium were observed to be more frequently resistant to fluoroquinolones and penicillins. Notably, 63% of the E. faecium isolates were resistant to the streptogramin quinupristin-dalfopristin, while high-level gentamicin resistance was observed only among the E. faecalis population, of which 7% of the isolates were resistant. The primary observations are that enterococci can be frequently isolated from the poultry production environment and can be multiresistant to antimicrobials used in human medicine. The high frequency with which resistant enterococci are isolated from this environment suggests that these organisms might be useful as sentinels to monitor the development of resistance resulting from the usage of antimicrobial agents in animal production.     

Decreased efficacy of antimicrobial agents in a polymicrobial environment

The airways of people with cystic fibrosis (CF) often harbour diverse polymicrobial communities. These airway infections can be impossible to resolve through antibiotic intervention, even though isolates of the individual species present are susceptible to the treatment when tested in vitro. In this work, we investigate how polymicrobial cultures comprised of key CF-associated pathogens respond to challenge with species-specific antimicrobial agents; colistin (targets Pseudomonas aeruginosa), fusidic acid (targets Staphylococcus aureus), and fluconazole (targets Candida albicans). We found that growth in a polymicrobial environment protects the target microorganism (sometimes by several orders of magnitude) from the effect(s) of the antimicrobial agent. This decreased antimicrobial efficacy was found to have both non-heritable (physiological) and heritable (genetic) components. Whole-genome sequencing of the colistin-resistant P. aeruginosa isolates revealed single nucleotide polymorphisms and indels in genes encoding lipopolysaccharide (LPS) biosynthesis and/or pilus biogenesis, indicating that a previously undescribed colistin resistance mechanism was in operation. This was subsequently confirmed through further genetic analyses. Our findings indicate that the polymicrobial nature of the CF airways is likely to have a significant impact on the clinical response to antimicrobial therapy.Subject terms: Clinical microbiology, Antibiotics     

Patterns of Antimicrobial Resistance Observed in Escherichia coli Isolates Obtained from Domestic- and Wild-Animal Fecal Samples, Human Septage, and Surface Water

A repeated cross-sectional study was conducted to determine the patterns of antimicrobial resistance in 1,286 Escherichia coli strains isolated from human septage, wildlife, domestic animals, farm environments, and surface water in the Red Cedar watershed in Michigan. Isolation and identification of E. coli were done by using enrichment media, selective media, and biochemical tests. Antimicrobial susceptibility testing by the disk diffusion method was conducted for neomycin, gentamicin, streptomycin, chloramphenicol, ofloxacin, trimethoprim-sulfamethoxazole, tetracycline, ampicillin, nalidixic acid, nitrofurantoin, cephalothin, and sulfisoxazole. Resistance to at least one antimicrobial agent was demonstrated in isolates from livestock, companion animals, human septage, wildlife, and surface water. In general, E. coli isolates from domestic species showed resistance to the largest number of antimicrobial agents compared to isolates from human septage, wildlife, and surface water. The agents to which resistance was demonstrated most frequently were tetracycline, cephalothin, sulfisoxazole, and streptomycin. There were similarities in the patterns of resistance in fecal samples and farm environment samples by animal, and the levels of cephalothin-resistant isolates were higher in farm environment samples than in fecal samples. Multidrug resistance was seen in a variety of sources, and the highest levels of multidrug-resistant E. coli were observed for swine fecal samples. The fact that water sample isolates were resistant only to cephalothin may suggest that the resistance patterns for farm environment samples may be more representative of the risk of contamination of surface waters with antimicrobial agent-resistant bacteria.     

Skin Commensal Staphylococci May Act as Reservoir for Fusidic Acid Resistance Genes

We analyzed the occurrence and mechanisms of fusidic acid resistance present in staphylococci isolated from 59 healthy volunteers. The fingers of the volunteers were screened for the presence of staphylococci, and the collected isolates were tested for resistance to fusidic acid. A total of 34 fusidic acid resistant staphylococcal strains (all were coagulase-negative) were isolated from 22 individuals (22/59, 37.3%). Examination of the resistance genes revealed that acquired fusB or fusC was present in Staphylococcus epidermidis, Staphylococcus capitis subsp. urealyticus, Staphylococcus hominis subsp. hominis, Staphylococcus warneri and Staphylococcus haemolyticus. Resistance islands (RIs) carrying fusB were found in S. epidermidis and S. capitis subsp. urealyticus, while staphylococcal chromosome cassette (SCC)-related structures harboring fusC were found in S. hominis subsp. hominis. Genotypic analysis of S. epidermidis and S. hominis subsp. hominis indicated that the fus elements were disseminated in diverse genetic strain backgrounds. The fusC elements in S. hominis subsp. hominis strains were highly homologous to SCCfusC in the epidemic sequence type (ST) 239/SCCmecIII methicillin-resistant S. aureus (MRSA) or the pseudo SCCmec in ST779 MRSA. The presence of acquired fusidic acid resistance genes and their genetic environment in commensal staphylococci suggested that the skin commensal staphylococci may act as reservoir for fusidic acid resistance genes.     

Development of a modified DNA extraction method for pulsed-field gel electrophoresis analysis of Staphylococcus aureus and enterococci without using lysostaphin

A modified pulsed-field gel electrophoresis (PFGE) protocol was developed and applied to clinical isolates of Staphylococcus aureus and enterococci to reduce the cost of using lysostaphin. This protocol reduces the expenses of PFGE typing of S. aureus and enterococci as it removes the use of lysostaphin during the spheroplast formation from these bacteria.     

379株血培养病原菌的临床分布及耐药性分析

目的了解血培养病原菌种类、临床分布及耐药情况。方法对2008年6月至2009年6月的379株血培养病原菌及其药敏情况用WHONET5.4软件进行统计分析。结果 379株病原菌中,分离率从高到低依次是凝固酶阴性葡萄球菌(133/35.1%)、大肠埃希菌(44/11.6%)、肺炎克雷伯菌(32/8.4%)、鲍曼不动杆菌(30/7.9%)、铜绿假单胞菌(25/6.6%)、金黄色葡萄球菌(18/4.7%)、肠球菌(13/3.4%)和其他(75/22.2%)。这些菌株主要分布在ICU和普外科。药敏结果分析显示:革兰阳性球菌中,未发现利奈唑胺和万古霉素耐药株。金黄色葡萄球菌和凝固酶阴性葡萄球菌对苯唑西林的耐药率分别为61.1%和89.5%;屎肠球菌对多数抗生素耐药率超过80%,粪肠球菌对青霉素类抗生素敏感性较高。革兰阴性杆菌中,大肠埃希菌和肺炎克雷伯菌中产ESBLs菌株比例分别为36.4%和31.3%,且发现2株耐亚胺培南的肺炎克雷伯菌;鲍曼不动杆菌除对卡那霉素保持敏感外,对其他抗生素的耐药率为50%~100%;铜绿假单胞菌对头孢曲松的耐药率为100%,对其他β-内酰胺类抗生素、氨基糖苷类和喹诺酮类抗生素的耐药率相对较低。结论临床上应规范血培养标本留取方法以减少污染,加强细菌耐药监测、严格抗生素使用,以延缓细菌耐药情况的发生和发展。     

Staphylococcus aureus bacteraemia: 400 episodes in St Thomas's Hospital.

Four hundred episodes of Staphylococcus aureus bacteraemia occurred in St Thomas''s Hospital from 1969 to 1983, accounting for 17.5% of all episodes of bacteraemia. The mortality was 24%, half attributable to underlying disease, and was highest in patients over 50. Almost 60% of the bacteraemias were acquired in hospital, and the source of the organism was generally obvious, with vascular access sites the most common (37%). Bone and joint infections accounted for 11.5% of episodes and endocarditis for 7%. Most staphylococci were resistant to penicillin only; three isolates were resistant to methicillin and five to fusidic acid. Microbiologists seldom influenced directly the choice of initial antibiotic treatment (though this usually conformed to the hospital''s antibiotic prescribing policy) but had considerable influence over definitive treatment, usually cloxacillin or flucloxacillin alone or in combination with fusidic acid. S aureus bacteraemia is easy to identify and treat, though underlying disease may influence the outcome. Efforts should be made to prevent the largely iatrogenic disease.     

Isolation and characterization of methicillin-resistantStaphylococcus aureus from livestock and poultry meat

Meat samples from sheep, bovine, camel and poultry were collected from Amman area and were processed and tested for the presence of methicillin (oxacillin) resistantStaphylococcus aureus (MRSA). Identity ofS. aureus was ensured by Gram-staining and a battery of biochemical tests. From 1260 meat samples, 157S. aureus positive isolates were identified. Of the 157 isolates, 30 were resistant to methicillin levels greater than 2 μg/ml and only 15 weremecA-positive MRSA originating mainly from sheep and chicken. Subjecting themecA-positive MRSA to antibiotic susceptibility testing revealed that all isolates were resistant to β-lactam antibiotics (ampicillin, penicillin, and oxacillin) and were sensitive to vancomycin, trimethoprim, chloramphenicol and cephalothin. Randomamplified polymorphic DNA (RAPD) analysis ofmecA-positive animal isolates generated six different patterns. Comparing these results with results of isolates of human origin of our laboratory there is some molecular epidemiological relatedness between both and could be a possible source of infections through consuming contaminated meat products, direct contact or meat processing.     

Identification of virulence factors in Vibrio cholerae isolated from Iraq during the 2007-2009 outbreak

Thousands of people were infected with Vibrio cholerae during the outbreak in Iraq in 2007-2009. Vibrio cholerae was shown to be variable in its content of virulence determinants and in its antibiotic sensitivity. This study was designed to isolate and characterize clinical and environmental V.?cholerae isolates and to determine antibiotic sensitivity, enzyme and toxin production, and the presence of virulence genes. Eighty clinical and five environmental bacterial isolates were collected and diagnosed by subjecting them to microscopic, biochemical, serological, and molecular analysis. The results revealed that 55% of clinical isolates belonged to the Inaba serotype, 32.5% to the Ogawa serotypes, and 12.5% to the Non-O1 serotype. All environmental V.?cholerae isolates belonged to the Non-O1 serotype. All environmental isolates were sensitive to all examined antimicrobial agents, while all clinical isolates showed a high sensitivity (100%) to ampicillin, gentamicin, cephalothin, tetracycline, erythromycin, and ciprofloxacin, and a high resistance (97.5%) to co-trimoxazole, nalidixic acid, and chloramphenicol. It was found that all V.?cholerae (O1) isolates were resistant to the Vibrio static O129 and all Non-O1 V.?cholerae isolates were sensitive to the Vibrio static O129. All clinical and environmental isolates produced hemolysin (100%) and lecithinase (100%), while they showed various production rates of protease (90% of clinical and 60% of environmental) and lipase (50% of clinical and 20% of environmental). The ompW gene was amplified in all the clinical and environmental V.?cholerae isolates, but not in other related and nonrelated bacteria. Multiplex PCR analysis showed that the toxR gene was amplified in all clinical and environmental isolates, while ctxA, ctxB, tcpA genes were amplified only in clinical (O1) isolates. This study indicates the differences in the production of some enzymes and toxins and in the content of virulence genes between clinical and environmental isolates in Iraq during the outbreak (2007-2009).