Acid Resistance Rates Research Articles

Antimicrobial Resistance in Escherichia coli Isolates from Healthy Food Animals in South Korea, 2010-2020.

Antimicrobial-resistant bacteria in food animals pose a major public health threat worldwide. In this study, we aimed to assess the antimicrobial resistance profiles and resistance trends of commensal Escherichia coli isolated from the feces of healthy cattle, pigs, and chickens in South Korea during 2010 and 2020. A total of 7237 E. coli isolates (2733 cattle, 2542 pig, and 1962 chicken isolates) were tested for susceptibility towards 12 antimicrobials. About 48%, 90%, and 97% of cattle, pig, and chicken isolates, respectively, were resistant to one or more antimicrobial agents. Cattle isolates presented low resistance (<15%) to most of the tested antimicrobials. In contrast, chicken and pig isolates demonstrated a relatively high (>45%) resistance rate to ampicillin, chloramphenicol, streptomycin, and tetracycline. We observed high ciprofloxacin and nalidixic acid resistance rates in chicken (76.1% and 88.6%, respectively), isolates in pig (12.7% and 26.7%, respectively) and cattle (2.7% and 8.2%, respectively) isolates. Notably, a very small proportion of isolates (<5%) from cattle, chickens, and pigs demonstrated resistance to amoxicillin/clavulanic acid, cefoxitin, and colistin. We identified ceftiofur resistance in a small proportion of chicken (8.8%), pig (3.7%), and cattle (0.7%) isolates. We noted an increasing but fluctuating trend of ampicillin, amoxicillin/clavulanic acid, ceftiofur, cefoxitin, chloramphenicol, ciprofloxacin, and streptomycin resistance in pig isolates. Similarly, the ampicillin, ceftiofur, and chloramphenicol resistance rates were increased but fluctuated through time in chicken isolates. Overall, 56% of the isolates showed multidrug-resistant (MDR). The proportion of MDR isolates was low in cattle (17.1%); however, this proportion was high in chickens (87.1%) and pigs (73.7%). Most of the resistance patterns included streptomycin and tetracycline in pigs and cattle, and ciprofloxacin and nalidixic acid in chickens. In conclusion, this study showed high resistance of commensal E. coli isolated from major food animals in Korea to commonly used antimicrobials including critically important antimicrobials. These bacteria could not only be a resistance reservoir but also could have potential to spread this resistance through gene transfer to pathogenic bacteria. Thus, the high prevalence of antimicrobial resistance in food animals highlights the urgent need for measures to restrict and ensure the prudent use of antimicrobials in Korea.

The evaluation of second line drug susceptibilities and molecular epidemiological profiles of multidrug resistance Mycobacterium tuberculosis isolates isoleted from different region of Turkey

Introduction: This study was planned to determine the second line drug resistance and molecular epidemiological profiles of multidrug resistant Mycobacterium tuberculosis isolates isolated from different geographical regions of Turkey.&#x0D; Material and Method: In our study, 63 MDR M. tuberculosis isolates were evaluated for the drug susceptibility sent from different tuberculosis laboratories of Turkey. Secondary antituberculosis drugs resistance was evaluated by indirect proportion method. Epidemiological origins were evaluated by using IS6110-RFLP and spoligotyping methods. &#x0D; Results: Cycloserine, ethionamide, capreomycin, thiacetozone, ofloxacin, kanamsin and paraaminosalicylic acid resistance rates were 15.87%, 19.04%, 7.93%, 6.34%, 11.11%, 12.69% and 6.34.%, respectively. According to spoligotyping results, 11 different patterns were obtained, including 52 isolates consisting of 5 clusters and 11 patterns consisting of a single isolate. When we compared our results with the spoligotype database in the world; 42 of 52 isolates forming 5 clusters were identified as predefined spoligotypes (LAM7-TUR, LAM9, T clade). 10 isolates showed the characteristics of the U spoligotype family. Of the 11 isolates that produced 11 different patterns, 8 were Haarlem and T spoligotypes. It was found that 2 isolates had the characteristics of Orphan and 1 isolate had the characteristics of BOV family. &#x0D; Conclusion: In our study, LAM7-TUR, LAM9, T clade spoligotype families are common in our country and in the world were determined.

Genetic diversity of Lactobacillus spp. isolates from oral cavity and their probiotic and antimicrobial properties

The kind of used food is effective on diversity of Lactobacillus biota in the oral cavity. Dairy products are major sources of probiotics including lactobacillus. Probably, these lactobacillus species have probiotics properties and they could benefit human health. In this study, consumers of domestic dairy products were selected and Lactobacillus spp. from their oral cavity were isolated and probiotic potential of these bacteria were investigated. Saliva samples were collected from one hundred people and cultured on MRS agar. Samples were incubated in anaerobic condition. Thirty predominant species from 100 persons were isolated and selected for probiotics properties assay by growth at gastric and gastrointestinal conditions (acid pH 3 and bile 0.3 w/v conditions respectively). Antibiotic susceptibility profile and antimicrobial activity of the isolates were defined. Predominant species were L. gasseri (53%) followed by L. fermentum and L. salivarius. All isolates were susceptible to Tigecycline, Penicillin, Tetracyclin and Ticaracillin. In addition, all isolates were resistance to Co-trimoxazole and Tobramycin. Acid resistance rate was higher than bile resistance. In addition, 26% of the isolates were resistant to acid and bile salt, which indicates good probiotic potential. Eight isolates had inhibitory activity against bacterial growth including L. gasseri, L. salivarius, L. crispatus and L. curvatus. The higher antimicrobial activity was showed by L. gasseri (five isolates) against Bacillus cereus. Therefore, some of these Lactobacillus species like of L. gasseri can be good candidate to inhibit of B. cereus growth in foods.

Effect of particle size of fly ash on the properties of lightweight insulation materials

The paper reports the effects of fly ash particle size on the properties of the lightweight insulation materials. The microstructure and mechanical properties of lightweight insulation materials are separately investigated by SEM (scanning electron micrograph) and tabulate thermal conductivity apparatus methods. In addition, the effects of particle size distribution of fly ash on the properties of lightweight insulation materials is studied by grey incidence analysis. The results show that when the ball milling time increases, the particle size of fly ash decreases and the distribution becomes narrow. At the same time, the polymerization state of fly ash would be depolymerize from high poly structure to low polymeric structure. Moreover, the linear shrinkage, bulk density, compressive strength, acid resistance and thermal conductivity of lightweight insulation materials have also increased, but the apparent porosity decreases. And the studies highlight that when the content of fine fly ash particles increases, the nucleation and growth of mullite is accelerated and the sintering driving force is improved at high temperature, which have a positive effect on improving the physicochemical properties of materials. The particles ranging from 20 to 30μm has a great influence on the linear shrinkage, bulk density, compressive strength, acid resistance rate and thermal conductivity of lightweight insulation materials.

Change in Antimicrobial Susceptibility of Skin-Colonizing Staphylococcus aureus in Korean Patients with Atopic Dermatitis during Ten-Year Period.

BackgroundA small subset of adolescents atopic dermatitis (AD) tends to persist. This also leads to get more antibiotics exposure with advancing years. Antibiotic resistance has been regarded as a serious problem during Staphylococcus aureus treatment, especially methicillin-resistant S. aureus (MRSA).ObjectiveIt was investigated the S. aureus colonization frequency in the skin lesions and anterior nares of adolescent AD patients and evaluated the changes in S. aureus antimicrobial susceptibility for years.MethodsPatients who visited our clinic from September 2003 to August 2005 were classified into group A, and patients who visited from August 2010 to March 2012 were classified into group B. To investigate the differences with regard to patients' age and disease duration, the patients were subdivided into groups according to age. Lesional and nasal specimens were examined.ResultsAmong the 295 AD patients, the total S. aureus colonization rate in skin lesions was 66.9% (95/142) for group A and 78.4% (120/153) for group B. No significant changes in the systemic antimicrobial susceptibilities of S. aureus strains isolated from adolescent AD patients were observed during about 10-year period. The increased trend of MRSA isolation in recent adolescent AD outpatients suggest that the community including school could be the source of S. aureus antibiotic resistance and higher fusidic acid resistance rates provides evidence of imprudent topical use.ConclusionRelatively high MRSA isolation and fusidic acid resistance rates in recent AD patients suggest that the community harbors antibiotic-resistant S. aureus.

Bactibilia and Antibiotic Resistance in Elective Cholecysctectomy: An Updated Ecologic Survey.

The role of bactibilia as a risk factor for an unfavorable outcome during biliary disease or surgical procedures remains obscure. Our aim was to identify possible risk factors for bactibilia and their possible relations to complications after elective cholecystectomy. As secondary aims, composition and antibiotic resistance patterns were studied. Bile and gallbladder mucosa samples from 358 elective cholecystectomies were collected prospectively between June 2009 and June 2012. Ordinary microbiologic cultures and antibiograms were performed. All pre-operative factors associated with bactibilia were studied by stepwise logistic regression multivariable analysis. The bacteria isolated most frequently from 103 positive cultures were Escherichia coli (21.3%), Enterococcus spp. (14.7%), and Enterobacter spp. (14.7%) with a global amoxicillin-clavulanic acid resistance rate of 53.7%. Age >65 y, male gender, previous instrumentation or disease of the biliary tract, and high American Society of Anesthesiologists score were independent risk factors. No correlation was found between bactibilia and surgical complications. Although the influence of bactibilia in developing surgical complications is limited, its composition and the high rate of resistance can be influential enough to modify antibiotic treatment in biliary tract infections, especially in high-risk patients.

Emergent and evolving antimicrobial resistance cassettes in community-associated fusidic acid and meticillin-resistant Staphylococcus aureus

Fusidic acid is a topical and systemic antimicrobial used for the treatment of staphylococcal infections in hospitals and the community. Sales of fusidic acid and resistance rates among meticillin-resistant Staphylococcus aureus (MRSA) doubled between 1990 and 2001. For the following decade, fusidic acid resistance rates among isolates from Addenbrooke's Hospital (Cambridge, UK) were compared with national resistance rates from MRSA bacteraemia surveillance data and with antimicrobial sales data. Sales of fusidic acid remained relatively constant between 2002 and 2012, whilst fusidic acid resistance increased two- and four-fold in MRSA bacteraemias nationally and in MRSA isolates from Cambridge, respectively. A subgroup of MRSA resistant only to fusidic acid increased after 2006 by 5-fold amongst bacteraemias nationally and 17-fold (to 7.7% in 2012) amongst Cambridge MRSA isolates. All of the available local isolates from 2011 to 2012 (n=23) were acquired in the community, were not related epidemiologically and belonged to multilocus sequence typing (MLST) groups ST1, 5, 8, 45 or 149 as revealed from analysis of whole-genome sequence data. All harboured the fusC gene on one of six distinct staphylococcal cassette chromosome (SCC) elements, four of which were dual-resistance chimeras that encoded β-lactam and fusidic acid resistance. In summary, fusidic acid-resistant MRSA increased in prevalence during the 2000s with notable rises after 2006. The development of chimeric cassettes that confer dual resistance to β-lactams and fusidic acid demonstrates that the genetics underpinning resistance in community-associated MRSA are evolving.

LONG-TERM RESULTS OF CORONARY STENTING IN PATIENTS WITH IHD AND CONCOMITANT TYPE 2 DIABETES MELLITUS: VIEW THROUGH THE EFFICIENCY PRISM OF DOUBLE DISAGGREGANT THERAPY

Aim. To assess the state of vascular-thrombocytic hemostasis and estimate the influence of disaggregant therapy on long-term results of coronary stenting in patients with ischemic heart disease (IHD) and concomitant type 2 diabetes mellitus (DM). Materials and methods. Retrospective analysis of influence of concomitant type 2 diabetes mellitus (DM) on the long-term results of IHD intervention treatment using the technique of coronary stenting as well as efficiency of double disaggregant therapy is presented in the paper. 165 patients were examined: group 1 - 96 patients with IHD and concomitant type 2 DM, group 2 - 69 IHD patients without carbohydrate metabolism disorders. Results. No significant differences between the groups in the average number of installed stents were revealed; type 2 DM patients more often underwent implantation of stents longer than 20 mm (χ 2=4,01, p=0,0454). According to ADP test data, no differences between the groups in the absence rate of effective clopidogrel-induced disaggregation in 48 hours after the beginning of double disaggregant therapy (19 (28,8 %) patients of the main group and 22 (27,5 %) -comparison group, p=0,05) were detected. According to the data of ASPI-test with arachidonic acid, ASA resistance statistically significantly predominated in patients of the main group - 13 (19,7 %) patients. Dynamic analysis of aggregatograms of patients from each group resulted in no statistically significant differences according to all the studied tests by the day 30 of double antiplatelet therapy in the main group, whereas in IHD patients without carbohydrate metabolism disorders growth of disaggregation conditioned by both clopidogrel and ASA was observed. Correlation analysis showed in patients with concomitant type 2 DM dependence of fatal outcome on absence of sufficient disaggregation effect of both clopidogrel and ASK. Conclusions. Combination of IHD with type 2 DM is accompanied by lesser efficiency and greater acetylsalicylic acid resistance rate in patients who underwent coronary stenting that can serve as a basis for necessity of platelet aggregation control with individualization of therapy and active use of new disaggregants in this group of patients.

Organic Acid Resistance and Toxin Gene Profiles of B. cereus Isolated from Red Pepper Powder

AbstractThe objectives of the study were to determine the diversity of organic acid resistance as well as the toxin gene profiles of Bacillus cereus isolated from red pepper powder and to analyze the inhibition kinetics of unstressed type culture and resistant food isolates against organic acids.Among 68 B. cereus isolated from red pepper and processing environmental samples (n = 180), 1.4–16.7% of the cells could survive at 0.5% of acetic, malic and tartaric acid. Parameter α of the Weibull model for type strain were up to threefold lower than for resistant food isolate at 0.2% or lower concentration of organic acid treatment. All the B. cereus isolates were positive for three genes in the nonhemolytic enterotoxin complex (nheA, nheB and nheC), entFM and bceT genes. The ces gene‐encoding emetic toxin was detected in nine (13.2%) of the 68 isolates tested.Practical ApplicationsBacillus cereus is an etiological agent of foodborne illness in Korea. The food products under risk for B. cereus food poisoning are pasteurized (dairy foods or cooked chilled foods) and dry foods. When B. cereus has been exposed to sublethal acid treatment conditions, adapted or resistant strains have developed. Acid resistance of the strain cause a food safety problem because it may result in enhanced protection for cells which are subsequently exposed to lethal heat or hydrogen peroxide stress. The rate of acid resistance and the kinetic parameters of wild type food isolates against organic acid treatment can be used to develop intervention strategies and in risk assessment to assure food safety. A diversity of toxin gene profiles which include diarrheal and emetic toxins also provide useful information in risk assessment of food poisoning caused by B. cereus.

The Prevalence, Genotype and Antimicrobial Susceptibility of High- and Low-Level Mupirocin Resistant Methicillin-ResistantStaphylococcus aureus

BackgroundMupirocin has been used for the treatment of skin infections and eradication of nasal carriage of methicillin-resistant Staphylococcus aureus (MRSA). The increased use of this antibiotic has been accompanied by outbreaks of MRSA that are resistant to mupirocin.ObjectiveThis study aims to determine the prevalence, genotype and antimicrobial susceptibility of mupirocin-resistant MRSA from 4 Korean hospitals.MethodsA total 193 MRSA clinical isolates were collected from four university hospitals. Antimicrobial susceptibility tests, including mupirocin, and pulsed-field gel electrophoresis (PFGE) pattern analysis were performed.ResultsOverall, 27 of the 193 (14.1%) MRSA isolates were resistant to mupirocin. All of the (A) hospital isolates showed high-level (HL) mupirocin resistance and the low-level (LL) mupirocin resistant strains were from three other hospitals. The PFGE patterns of 16 mupirocin-resistant isolates were divided into 5 clusters (1-5), and the nine HL mupirocin-resistant isolates belonged to cluster 1. Both the HL and LL mupirocin-resistant MRSA isolates were susceptible to vancomycin and rifampin, but they were resistant to ciprofloxacin, clindamycin and tetracycline. The erythromycin and fusidic acid resistance rates were different between the HL and LL resistant isolates.ConclusionHL mupirocin-resistant isolates that could transfer this resistance to other bacteria were detected and these isolates were clonally related. The emergence of mupirocin resistant isolates emphasizes the importance of using antibiotics judiciously and carefully monitoring the prevalence of mupirocin resistance.

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.

Evaluation of resistance to fusidic acid in Staphylococci isolates

Objectives: Staphylococci were most prominent factors that responsible for skin, soft tissue and foreign body infections. Gaining resistance to methicillin and various antibiotics in these microorganisms over the years increased morbidity and mortality, especially in hospitalized patients. In such situations number of preferred antibiotics was limited. The aim of this study was to investigate in-vitro susceptibility of fusidic acid to clinic isolates of Staphylococci. Materials and methods: The seventy-seven coagulase negative staphylococci (CNS) and 37 Staphylococcus aureus strains isolated from various clinical specimens were included in this study. Staphylococci were identified with gram stain, catalase and coagulase tests. According to “Clinical and Laboratory Stan dards Institute (CLSI)” criteria, antimicrobial susceptibility testing was performed by Kirby-Bauer disc diffusion method. Results: The seventy-four percent of the isolated CNS were defined as methicillin sensitive-CNS (MS-CNS), 26% of the isolated CNS were defined as methicillin resistant (MR-CNS). While 40% of MR-CNS was resistant to fusidic acid, fusidic acid resistance was found to be 24% in MS-CNS. In methicilline-sensitive S.aureus strains fusidic acid resistance rate were detected as 13%; and in methicillin-resistant S.aureus strains the rate were 14%. Conclusion: Susceptibility of fusidic acid in Staphylococcus aureus strains were found higher than coagulase-negative staphylococci. Fusidic acid remains as an alternative in the treatment of infections due to staphylococci. J Microbiol Infect Dis 2011;1(1):22-25.

Fusidic Acid Resistance Rates and Prevalence of Resistance Mechanisms among Staphylococcus spp. Isolated in North America and Australia, 2007-2008

Among 4,167 Staphylococcus aureus and 790 coagulase-negative Staphylococcus (CoNS; not S. saprophyticus) isolates collected consecutively from North American and Australian hospitals, only 87 (1.7% overall) isolates displayed a fusidic acid (FA; also known as CEM-102) MIC of > or = 2 microg/ml (FA resistance). These strains were further evaluated with a multiplex PCR to amplify the acquired resistance genes fusB, fusC, and fusD. Mutations in fusA and fusE were evaluated in all isolates showing an absence of acquired resistance genes and/or showing FA MIC values of > or = 64 microg/ml. S. aureus resistance rates were very low in the United States (0.3%) and were higher in Canada and Australia (7.0% for both countries). Among CoNS isolates, FA resistance rates were significantly more elevated than that for S. aureus (7.2 to 20.0%; the highest rates were in Canada). All 52 (41 CoNS) FA-resistant isolates from the United States showed FA MIC results of < or = 64 microg/ml, and 7 of 11 S. aureus isolates carried fusC. CoNS strains from the United States carried fusB or fusC. In Canada, fusB and fusC occurrences were similar among S. aureus and CoNS isolates, and modestly elevated FA MIC values were observed (all MIC results were < or = 32 microg/ml). Isolates from Australia showed MIC values ranging from 2 to 32 microg/ml, and S. aureus isolates were predominantly fusC positive. fusA mutations were detected in only three S. aureus isolates, conferring FA MIC values of 2 to 8 microg/ml. Target mutations have been considered the primary FA resistance mechanism among Staphylococcus spp.; however, acquired resistance genes appear to have a dominant role in resistance against this older antimicrobial agent. In summary, this study shows that acquired genes are highly prevalent among FA-resistant strains (>90%) in three nations with distinct or absence (United States) of fusidic acid clinical use.

Occurrence and molecular characterization of fusidic acid resistance mechanisms among Staphylococcus spp. from European countries (2008)

To determine fusidic acid resistance rates (MICs of > or = 2 mg/L) and the prevalence of fusidic acid resistance mechanisms among Staphylococcus spp. collected from European countries (2008). Staphylococcal isolates (3134) collected from Europe were tested by CLSI broth microdilution. Isolates displaying a fusidic acid MIC of > or = 2 mg/L (non-susceptible; European Committee on Antimicrobial Susceptibility Testing breakpoint) were tested for fusB, fusC and fusD. The fusidic acid target sites fusA and fusE were then sequenced, and a method for the detection of the fusA mutation L461K was developed. Selected isolates were typed by PFGE. Fusidic acid resistance rates were higher among coagulase-negative staphylococci (CoNS) compared with Staphylococcus aureus. Acquired fusidic acid resistance genes were detected in 64.9% of the samples; fusB and fusC were detected among 10.1% and 16.9% of the fusidic acid-resistant S. aureus and among 26.5% and 11.3% of the CoNS, respectively. Ireland and Greece showed the highest S. aureus fusidic acid resistance levels, with low rates of acquired fusidic acid resistance genes. Isolates from these countries displayed MIC values of > or = 512 mg/L, the presence of the elongation factor G L461K alteration and clonal occurrences. Low S. aureus fusidic acid resistance rates (1%-3%) were observed in Germany, Israel, Italy, Poland, Spain and Sweden. Isolates with MIC values < or = 64 mg/L showed a great diversity of acquired fusidic acid resistance mechanisms. Acquired fusidic acid resistance genes were detected in the majority of fusidic acid-resistant isolates from Belgium, France, Switzerland, Sweden, Italy and the UK (72.2%-92.9%), and were slightly less frequent in Germany, Spain and Israel (61.3%-66.7%). This contemporary study showed that acquired fusidic acid resistance genes were prevalent among fusidic acid-non-susceptible European staphylococcal isolates.

In vitro activity against anaerobes of retapamulin, a new topical antibiotic for treatment of skin infections

Retapamulin is the first agent of the pleuromutilin class formulated as a topical antibacterial for treating skin infections. The aim of this study was to determine the antimicrobial activity of retapamulin by determining the minimal inhibitory concentration (MIC) values of this new drug and comparators against a wide range of anaerobic bacteria of human origin. The in vitro activity of retapamulin and six comparators (amoxicillin, amoxicillin/clavulanic acid, ceftriaxone, imipenem, clindamycin and metronidazole) was evaluated against 232 anaerobic clinical isolates. MICs were determined by the CLSI reference agar dilution method (M11-A6). Ceftriaxone, clindamycin and amoxicillin/clavulanic acid resistance rates were 54%, 42% and 9.6%, respectively, within the Bacteroides fragilis group. Despite high resistance rates to various antibiotics, retapamulin inhibited 37/52 (71%) strains of the B. fragilis group and 85/87 (98%) of the other Gram-negative bacilli at a concentration of 2 mg/L or less. All the investigated strains of Clostridium perfringens were inhibited by 1 mg/L retapamulin. Three strains of C. difficile and one strain of C. clostridioforme demonstrated decreased susceptibility to retapamulin. Based on inhibitory concentrations, retapamulin was more active than clindamycin, metronidazole and ceftriaxone against Propionibacterium acnes and anaerobic Gram-positive cocci, as all isolates were inhibited by <or=2 mg/L. At <or=2 mg/L, retapamulin inhibited 90% of all 232 anaerobes tested, whereas overall resistance rates for the comparators were as follows: co-amoxiclav, 2%; metronidazole, 12%; clindamycin, 15% and ceftriaxone, 20%. The broad anaerobic spectrum demonstrated by retapamulin in vitro is attractive. Pending further clinical investigation, retapamulin may offer an alternative treatment for anaerobic skin infections in this era of increasing resistance.

Increasing incidence of quinolone resistance in human non-typhoid Salmonella enterica isolates in Korea and mechanisms involved in quinolone resistance

We investigated the trends of nalidixic acid resistance in human non-typhoid Salmonella enterica in a Korean population, and examined some possible mechanisms involved in this resistance. A total of 261 clinical strains were tested. For all strains, the MICs of nalidixic acid were determined. Nalidixic acid-resistant strains underwent further analysis, including determination of MICs of other antibiotics, mutation analysis within the topoisomerase genes, organic solvent tolerance test, western blotting for AcrA, marOR mutation analysis, ciprofloxacin accumulation test, and PCR for the qnr gene. The clonal relationships of Salmonella strains were examined by random amplified polymorphic DNA analysis. The incidence of nalidixic acid resistance increased from 1.8% in 1995-96 to 21.8% in 2000-02. The resistance rate was higher in S. enterica serotype Enteritidis (21.6%) than in serotype Typhimurium (12.1%). The nalidixic acid resistance rates in Salmonella Enteritidis varied according to the phage type (PT) and Salmonella Enteritidis PT 1 was most commonly associated with resistance to nalidixic acid. Several cases of clonal spread, especially by Salmonella Enteritidis PT 1, were identified. Of the 46 nalidixic acid-resistant strains, 43 had single mutations in the gyrA gene. Four strains were organic solvent-tolerant and were associated with decreased ciprofloxacin accumulation; three of these showed increased expression of AcrA and had novel mutations in marOR (84L). The qnr gene was not identified. Recently, the rate of nalidixic acid resistance in Korean clinical Salmonella strains markedly increased and it was partly due to the clonal spread of Salmonella Enteritidis, especially PT 1. The main mechanism of nalidixic acid resistance was a mutation in the gyrA region.