scholarly journals Antimicrobial Susceptibility of 260Clostridium botulinumType A, B, Ba, and Bf Strains and a NeurotoxigenicClostridium baratiiType F Strain Isolated from California Infant Botulism Patients

2018 ◽  
Vol 62 (12) ◽  
Author(s):  
Jason R. Barash ◽  
Joe B. Castles ◽  
Stephen S. Arnon
Keyword(s):  
Antimicrobial Susceptibility ◽  
Large Bowel ◽  
Botulinum Neurotoxin ◽  
Antimicrobial Agents ◽  
Infectious Complications ◽  
Suspected Sepsis ◽  
Content Type ◽  
Infant Botulism ◽  
Susceptibility Study ◽  
Almost All

ABSTRACTInfant botulism is an infectious intestinal toxemia that results from colonization of the infant large bowel byClostridium botulinum(or rarely, by neurotoxigenicClostridium baratiiorClostridium butyricum), with subsequent intraintestinal production and absorption of botulinum neurotoxin that then produces flaccid paralysis. The disease is often initially misdiagnosed as suspected sepsis or meningitis, diagnoses that require prompt empirical antimicrobial therapy. Antibiotics may also be needed to treat infectious complications of infant botulism, such as pneumonia or urinary tract infection. Clinical evidence suggests (see case report below) that broad-spectrum antibiotics that are eliminated by biliary excretion may cause progression of the patient’s paralysis by lysingC. botulinumvegetative cells in the large bowel lumen, thereby increasing the amount of botulinum neurotoxin available for absorption. The purpose of this antimicrobial susceptibility study was to identify an antimicrobial agent with little or no activity againstC. botulinumthat could be used to treat infant botulism patients initially diagnosed with suspected sepsis or meningitis, or who acquired secondary infections, without lysingC. botulinum. Testing of 12 antimicrobial agents indicated that almost all California infant botulism patient isolates are susceptible to most clinically utilized antibiotics and are also susceptible to newer antibiotics not previously tested against large numbers ofC. botulinumpatient isolates. No antibiotic with little or no activity againstC. botulinumwas identified. These findings reinforce the importance of promptly treating infant botulism patients with human botulism immune globulin (BIG-IV [BabyBIG]).

scholarly journals Antimicrobial Susceptibility to Azithromycin among Salmonella enterica Isolates from the United States

2011 ◽  
Vol 55 (9) ◽  
pp. 3985-3989 ◽  
Author(s):  
Maria Sjölund-Karlsson ◽  
Kevin Joyce ◽  
Karen Blickenstaff ◽  
Takiyah Ball ◽  
Jovita Haro ◽  
...  
Keyword(s):  
United States ◽  
Antimicrobial Susceptibility ◽  
Salmonella Enterica ◽  
Antimicrobial Agents ◽  
The United States ◽  
Outcome Data ◽  
Content Type ◽  
Susceptibility Data ◽  
Retail Meat ◽  
Clinical Breakpoints

ABSTRACTDue to emerging resistance to traditional antimicrobial agents, such as ampicillin, trimethoprim-sulfamethoxazole, and chloramphenicol, azithromycin is increasingly used for the treatment of invasiveSalmonellainfections. In the present study, 696 isolates of non-TyphiSalmonellacollected from humans, food animals, and retail meats in the United States were investigated for antimicrobial susceptibility to azithromycin. Seventy-twoSalmonella entericaserotype Typhi isolates from humans were also tested. For each isolate, MICs of azithromycin and 15 other antimicrobial agents were determined by broth microdilution. Among the non-TyphiSalmonellaisolates, azithromycin MICs among human isolates ranged from 1 to 32 μg/ml, whereas the MICs among the animal and retail meat isolates ranged from 2 to 16 μg/ml and 4 to 16 μg/ml, respectively. AmongSalmonellaserotype Typhi isolates, the azithromycin MICs ranged from 4 to 16 μg/ml. The highest MIC observed in the present study was 32 μg/ml, and it was detected in three human isolates belonging to serotypes Kentucky, Montevideo, and Paratyphi A. Based on our findings, we propose an epidemiological cutoff value (ECOFF) for wild-typeSalmonellaof ≤16 μg/ml of azithromycin. The susceptibility data provided could be used in combination with clinical outcome data to determine tentative clinical breakpoints for azithromycin andSalmonella enterica.

scholarly journals Analysis of Whole-Genome Sequences for the Prediction of Penicillin Resistance and β-Lactamase Activity inBacillus anthracis

mSystems ◽  
2018 ◽  
Vol 3 (6) ◽  
Author(s):  
A. S. Gargis ◽  
H. P. McLaughlin ◽  
A. B. Conley ◽  
C. Lascols ◽  
P. A. Michel ◽  
...  
Keyword(s):  
Sequence Analysis ◽  
Antimicrobial Susceptibility ◽  
Sigma Factor ◽  
Antimicrobial Agents ◽  
Susceptibility Testing ◽  
Antimicrobial Susceptibility Testing ◽  
Penicillin Resistance ◽  
Whole Genome ◽  
Activity Levels ◽  
Content Type

ABSTRACTPenicillin (PEN) is a low-cost option for anthrax treatment, but naturally occurring resistance has been reported. β-Lactamase expression (bla1,bla2) inBacillus anthracisis regulated by a sigma factor (SigP) and its cognate anti-sigma factor (RsiP). Mutations leading to truncation of RsiP were previously described as a basis for PEN resistance. Here, we analyze whole-genome sequencing (WGS) data and compare the chromosomalsigP-bla1regions from 374B. anthracisstrains to determine the frequency of mutations, identify mutations associated with PEN resistance, and evaluate the usefulness of WGS for predicting PEN resistance. Few (3.5%) strains contained at least 1 of 11 different mutations insigP,rsiP, orbla1.Nine of these mutations have not been previously associated with PEN resistance. Four strains showed PEN resistance (PEN-R) by conventional broth microdilution, including 1 strain with a novel frameshift inrsiP. One strain that carries the samersiPframeshift mutation as that found previously in a PEN-R strain showed a PEN-susceptible (PEN-S) phenotype and exhibited decreasedbla1andbla2transcription. An unexpectedly small colony size, a reduced growth rate, and undetectable β-lactamase activity levels (culture supernatant and cell lysate) were observed in this PEN-S strain. Sequence analysis revealed mutations in genes associated with growth defects that may contribute to this phenotype. WhileB. anthracisrsiPmutations cannot be exclusively used to predict resistance, four of the five strains withrsiPmutations were PEN-R. Therefore, theB. anthracissigP-bla1region is a useful locus for WGS-based PEN resistance prediction, but phenotypic testing remains essential.IMPORTANCEDetermination of antimicrobial susceptibility ofB. anthracisis essential for the appropriate distribution of antimicrobial agents for postexposure prophylaxis (PEP) and treatment of anthrax. Analysis of WGS data allows for the rapid detection of mutations in antimicrobial resistance (AMR) genes in an isolate, but the presence of a mutation in an AMR gene does not always accurately predict resistance. As mutations in the anti-sigma factor RsiP have been previously associated with high-level penicillin resistance in a limited number of strains, we investigated WGS assemblies from 374 strains to determine the frequency of mutations and performed functional antimicrobial susceptibility testing. Of the five strains that contained mutations inrsiP, only four were PEN-R by functional antimicrobial susceptibility testing. We conclude that while sequence analysis of this region is useful for AMR prediction inB. anthracis, genetic analysis should not be used exclusively and phenotypic susceptibility testing remains essential.

scholarly journals Antimicrobial Susceptibility and Clonality of Clinical Ureaplasma Isolates in the United States

2016 ◽  
Vol 60 (8) ◽  
pp. 4793-4798 ◽  
Author(s):  
Javier Fernández ◽  
Melissa J. Karau ◽  
Scott A. Cunningham ◽  
Kerryl E. Greenwood-Quaintance ◽  
Robin Patel
Keyword(s):  
United States ◽  
Antimicrobial Susceptibility ◽  
Antimicrobial Agents ◽  
Ureaplasma Urealyticum ◽  
Resistance Mechanism ◽  
The United States ◽  
Resistance Mechanisms ◽  
Resistant Isolate ◽  
Limited Information ◽  
Content Type

ABSTRACTUreaplasma urealyticumandUreaplasma parvumare pathogens involved in urogenital tract and intrauterine infections and also in systemic diseases in newborns and immunosuppressed patients. There is limited information on the antimicrobial susceptibility and clonality of these species. In this study, we report the susceptibility of 250 contemporary isolates ofUreaplasma(202U. parvumand 48U. urealyticumisolates) recovered at Mayo Clinic, Rochester, MN. MICs of doxycycline, azithromycin, ciprofloxacin, tetracycline, erythromycin, and levofloxacin were determined by broth microdilution, with MICS of the last three interpreted according to CLSI guidelines. Levofloxacin resistance was found in 6.4% and 5.2% ofU. parvumandU. urealyticumisolates, respectively, while 27.2% and 68.8% of isolates, respectively, showed ciprofloxacin MICs of ≥4 μg/ml. The resistance mechanism of levofloxacin-resistant isolates was due to mutations inparC, with the Ser83Leu substitution being most frequent, followed by Glu87Lys. No macrolide resistance was found among the 250 isolates studied; a singleU. parvumisolate was tetracycline resistant.tet(M) was found in 10U. parvumisolates, including the single tetracycline-resistant isolate, as well as in 9 isolates which had low tetracycline and doxycycline MICs. Multilocus sequence typing (MLST) performed on a selection of 46 isolates showed high diversity within the clinicalUreaplasmaisolates studied, regardless of antimicrobial susceptibility. The present work extends previous knowledge regarding susceptibility to antimicrobial agents, resistance mechanisms, and clonality ofUreaplasmaspecies in the United States.

scholarly journals In VitroAntimicrobial Susceptibility to Isepamicin of 6,296 Enterobacteriaceae Clinical Isolates Collected at a Tertiary Care University Hospital in Greece

2012 ◽  
Vol 56 (6) ◽  
pp. 3067-3073 ◽  
Author(s):  
Sofia Maraki ◽  
George Samonis ◽  
Drosos E. Karageorgopoulos ◽  
Michael N. Mavros ◽  
Diamantis Kofteridis ◽  
...  
Keyword(s):  
Antimicrobial Susceptibility ◽  
Therapeutic Option ◽  
Tertiary Care ◽  
University Hospital ◽  
Cross Resistance ◽  
Intrinsic Resistance ◽  
Content Type ◽  
Microbiological Laboratory ◽  
Almost All

ABSTRACTThe reevaluation of “forgotten” antibiotics can identify new therapeutic options against extensively drug-resistant Gram-negative pathogens. We sought to investigate isepamicin in this regard. We retrospectively evaluated the antimicrobial susceptibility to isepamicin ofEnterobacteriaceaesp. isolates from unique patients, collected at the microbiological laboratory of the University Hospital of Heraklion, Crete, Greece, from 2004 to 2009. Susceptibility testing was done with the automated Vitek 2 system. The breakpoints for susceptibility to isepamicin, tigecycline, and other antibiotics were those proposed by the Comité de l'Antibiogramme de la Société Française de Microbiologie (CA-SFM), the FDA, and the CLSI, respectively. A total of 6,296 isolates were studied, including primarily 3,401 (54.0%)Escherichia coli, 1,040 (16.5%)Klebsiella pneumoniae, 590 (9.4%)Proteus mirabilis, and 460 (7.3%)Enterobactersp. isolates. Excluding the species with intrinsic resistance to each antibiotic, antimicrobial susceptibility was highest for colistin (5,275/5,441 isolates [96.9%]) and isepamicin (6,103/6,296 [96.9%]), followed by meropenem (5,890/6,296 [93.6%]), imipenem (5,874/6,296 [93.3%]), and amikacin (5,492/6,296 [87.2%]). The antimicrobial susceptibility of the 1,040K. pneumoniaeisolates was highest for isepamicin (95.3%), followed by colistin (89.3%) and meropenem (63.0%). Regarding resistantK. pneumoniaeisolates, susceptibility to isepamicin was observed for 91.1% of the 392, 87.7% of the 375, and 85.6% of the 111 isolates that were nonsusceptible to the carbapenems, all other aminoglycosides, and colistin, respectively. Isepamicin exhibited highin vitroactivity against almost all of theEnterobacteriaceaespecies. It could particularly serve as a last-resort therapeutic option for carbapenem-resistantK. pneumoniaein our region, where it is endemic, as it does not show considerable cross-resistance with other aminoglycosides.

scholarly journals Global Assessment of Antimicrobial Susceptibility among Gram-Negative Organisms Collected from Pediatric Patients between 2004 and 2012: Results from the Tigecycline Evaluation and Surveillance Trial

2015 ◽  
Vol 53 (4) ◽  
pp. 1286-1293 ◽  
Author(s):  
Sue C. Kehl ◽  
Michael J. Dowzicky
Keyword(s):  
North America ◽  
Antimicrobial Susceptibility ◽  
Antimicrobial Agents ◽  
Pediatric Patients ◽  
Age Groups ◽  
Active Agent ◽  
Asia Pacific ◽  
Gram Negative ◽  
Content Type

The Tigecycline Evaluation and Surveillance Trial (TEST) was designed to monitor susceptibility to commonly used antimicrobial agents among important pathogens. We report here on susceptibility among Gram-negative pathogens collected globally from pediatric patients between 2004 and 2012. Antimicrobial susceptibility was determined using guidelines published by the Clinical and Laboratory Standards Institute (CLSI). MostEnterobacteriaceaeshowed high rates of susceptibility (>95%) to amikacin, tigecycline, and the carbapenems (imipenem and meropenem); 90.8% ofAcinetobacter baumanniiisolates were susceptible to minocycline, and susceptibility rates were highest in North America, Europe, and Asia/Pacific Rim. Amikacin was the most active agent againstPseudomonas aeruginosa(90.4% susceptibility), with susceptibility rates being highest in North America. Extended-spectrum β-lactamases (ESBLs) were reported for 11.0% ofEscherichia coliisolates and 24.2% ofKlebsiella pneumoniaeisolates globally, with rates reaching as high as 25.7% in the Middle East and >43% in Africa and Latin America, respectively. Statistically significant (P< 0.01) differences in susceptibility rates were noted between pediatric age groups (1 to 5 years, 6 to 12 years, or 13 to 17 years of age), globally and in some regions, for all pathogens exceptHaemophilus influenzae. Significant (P< 0.01) differences were reported for all pathogens globally and in most regions, considerably more frequently, when pediatric and adult susceptibility results were compared. Amikacin, tigecycline, and the carbapenems were activein vitroagainst most Gram-negative pathogens collected from pediatric patients;A. baumanniiandP. aeruginosawere susceptible to fewer antimicrobial agents. Susceptibility rates among isolates from pediatric patients were frequently different from those among isolates collected from adults.

scholarly journals Clinical and Microbiological Aspects of β-Lactam Resistance in Staphylococcus lugdunensis

2016 ◽  
Vol 55 (2) ◽  
pp. 585-595 ◽  
Author(s):  
Ian H. McHardy ◽  
Jennifer Veltman ◽  
Janet Hindler ◽  
Katia Bruxvoort ◽  
Marissa M. Carvalho ◽  
...  
Keyword(s):  
Antimicrobial Susceptibility ◽  
Antimicrobial Agents ◽  
Medical Center ◽  
Tertiary Care ◽  
Disk Diffusion ◽  
Staphylococcus Lugdunensis ◽  
Disk Diffusion Test ◽  
Content Type ◽  
Tertiary Care Medical Center ◽  
Zone Edge

ABSTRACTAntimicrobial susceptibility results from broth microdilution MIC testing of 993Staphylococcus lugdunensisisolates recovered from patients at a tertiary care medical center from 2008 to 2015 were reviewed. Ninety-two oxacillin-susceptible isolates were selected to assess the accuracy of penicillin MIC testing, the penicillin disk diffusion test, and three β-lactamase tests, including the cefoxitin-induced nitrocefin test, penicillin cloverleaf assay, and penicillin disk zone edge test. The results of all phenotypic tests were compared to the results ofblaZPCR. The medical records of 62 patients from whomS. lugdunensiswas isolated, including 31 penicillin-susceptible and 31 penicillin-resistant strains, were retrospectively reviewed to evaluate the clinical significance ofS. lugdunensisisolation, the antimicrobial agents prescribed, if any, and the clinical outcome. MIC testing revealed that 517/993 (52.1%) isolates were susceptible to penicillin and 946/993 (95.3%) were susceptible to oxacillin. The induced nitrocefin test was 100% sensitive and specific for the detection of β-lactamase compared to theblaZPCR results, whereas the penicillin disk zone edge and cloverleaf tests showed sensitivities of 100% but specificities of only 9.1% and 89.1%, respectively. The penicillin MIC test had 100% categorical agreement withblaZPCR, while penicillin disk diffusion yielded one major error. Only 3/31 patients with penicillin-susceptible isolates were treated with a penicillin family antimicrobial. The majority of cases were treated with other β-lactams, trimethoprim-sulfamethoxazole, or vancomycin. These data indicate that nearly all isolates ofS. lugdunensisare susceptible to narrow-spectrum antimicrobial agents. Clinical laboratories in areas with resistance levels similar to those described here can help promote the use of these agents versus vancomycin by effectively designing their antimicrobial susceptibility reports to convey this message.

scholarly journals Antimicrobial susceptibility testing of Bordetella pertussis in Taiwan prompted by a case of pertussis in a paediatric patient

2008 ◽  
Vol 57 (12) ◽  
pp. 1577-1580 ◽  
Author(s):  
Shu-Man Yao ◽  
Gwo-Jen Liaw ◽  
Ying-Yan Chen ◽  
Meng-Hsiu Yen ◽  
Ya-Hui Chen ◽  
...  
Keyword(s):  
Bordetella Pertussis ◽  
Antimicrobial Susceptibility ◽  
Antimicrobial Agents ◽  
Susceptibility Testing ◽  
Antimicrobial Susceptibility Testing ◽  
Resistant Isolate ◽  
Notifiable Disease ◽  
Low Incidence ◽  
Almost All

In Taiwan, pertussis is a notifiable disease with a low incidence in recent years, and antimicrobial susceptibility testing for the causative agent, Bordetella pertussis, has not been reported to date. In May 2007, the Centers for Disease Control, Taiwan, was informed of a 1-month-old pertussis patient who did not respond to erythromycin treatment. In this study, we report the result of antimicrobial susceptibility testing performed for the suspected erythromycin-resistant isolate, as well as for an additional 27 B. pertussis clinical isolates that represented almost all epidemiologically unrelated isolates obtained throughout Taiwan between 2003 and 2007. All isolates were fully susceptible to azithromycin, erythromycin, clarithromycin and trimethoprim/sulfamethoxazole (MIC ≤0.047 μg ml−1). This result demonstrates the general susceptibility of B. pertussis to antimicrobial agents in vitro in Taiwan.

scholarly journals In VitroActivities of Antibiotics and Antimicrobial Cationic Peptides Alone and in Combination against Methicillin-Resistant Staphylococcus aureus Biofilms

2012 ◽  
Vol 56 (12) ◽  
pp. 6366-6371 ◽  
Author(s):  
Emel Mataraci ◽  
Sibel Dosler
Keyword(s):  
Staphylococcus Aureus ◽  
Antimicrobial Agents ◽  
Antibiofilm Activity ◽  
Cationic Peptides ◽  
Planktonic Cells ◽  
Methicillin Resistant ◽  
Content Type ◽  
Mrsa Strains ◽  
Almost All

ABSTRACTMethicillin-resistantStaphylococcus aureus(MRSA) strains are most often found as hospital- and community-acquired infections. The danger of MRSA infections results from not only the emergence of multidrug resistance but also the occurrence of bacteria that form strong biofilms. We investigated thein vitroactivities of antibiotics (daptomycin, linezolid, teichoplanine, azithromycin, and ciprofloxacin) and antimicrobial cationic peptides {AMPs; indolicidin, CAMA [cecropin (1-7)–melittin A (2-9) amide], and nisin} alone or in combination against MRSA ATCC 43300 biofilms. The MICs and minimum biofilm eradication concentrations (MBECs) were determined by the broth microdilution technique. Antibiotic and AMP combinations were assessed using the checkerboard technique. For MRSA planktonic cells, MICs of antibiotics and AMPs ranged between 0.125 and 512 and 8 and 16 mg/liter, respectively, and the MBEC values were between 512 and 5,120 and 640 mg/liter, respectively. With a fractional inhibitory concentration of ≤0.5 as the borderline, synergistic interactions against MRSA biofilms were frequent with almost all antibiotic-antibiotic and antibiotic-AMP combinations. Against planktonic cells, they generally had an additive effect. No antagonism was observed. All of the antibiotics, AMPs, and their combinations were able to inhibit the attachment of bacteria at 1/10 MIC and biofilm formation at 1× MIC. Biofilm-associated MRSA was not affected by therapeutically achievable concentrations of antimicrobial agents. Use of a combination of antimicrobial agents can provide a synergistic effect, which rapidly enhances antibiofilm activity and may help prevent or delay the emergence of resistance. AMPs seem to be good candidates for further investigations in the treatment of MRSA biofilms, alone or in combination with antibiotics.

scholarly journals Optical Screening for Rapid Antimicrobial Susceptibility Testing and for Observation of Phenotypic Diversity among Strains of the Genetically Clonal Species Bacillus anthracis

2017 ◽  
Vol 55 (3) ◽  
pp. 959-970 ◽  
Author(s):  
Heather P. McLaughlin ◽  
Amy S. Gargis ◽  
Pierre Michel ◽  
David Sue ◽  
Linda M. Weigel
Keyword(s):  
Antimicrobial Resistance ◽  
Bacillus Anthracis ◽  
Antimicrobial Susceptibility ◽  
Antimicrobial Agents ◽  
Phenotypic Diversity ◽  
New Technology ◽  
Time Lapse ◽  
Growth Characteristics ◽  
Content Type ◽  
Broth Microdilution Method

ABSTRACTDuring high-impact events involvingBacillus anthracis, such as the Amerithrax incident of 2001 or the anthrax outbreaks in Russia and Sweden in 2016, critical decisions to reduce morbidity and mortality include rapid selection and distribution of effective antimicrobial agents for treatment and postexposure prophylaxis. Detection of antimicrobial resistance currently relies on a conventional broth microdilution method that requires a 16- to 20-h incubation time forB. anthracis. Advances in high-resolution optical screening offer a new technology to more rapidly evaluate antimicrobial susceptibility and to simultaneously assess the growth characteristics of an isolate. Herein, we describe a new method developed and evaluated as a rapid antimicrobial susceptibility test forB. anthracis. This method is based on automated digital time-lapse microscopy to observe the growth and morphological effects of relevant antibiotics with an optical screening instrument, the oCelloScope.B. anthracisstrains were monitored over time in the presence or absence of penicillin, ciprofloxacin, or doxycycline. Susceptibility to each antibiotic was determined in ≤4 h, 75 to 80% less than the time required for conventional methods. Time-lapse video imaging compiled from the optical screening images revealed unexpected differences in growth characteristics among strains ofB. anthracis, which is considered to be a clonal organism. This technology provides a new approach for rapidly detecting phenotypic antimicrobial resistance and for documenting growth attributes that may be beneficial in the further characterization of individual strains.

scholarly journals Relationship between Antimicrobial Susceptibility and Multilocus Sequence Type of Mycoplasma bovis Isolates and Development of a Method for Rapid Detection of Point Mutations Involved in Decreased Susceptibility to Macrolides, Lincosamides, Tetracyclines, and Spectinomycin

2019 ◽  
Vol 85 (13) ◽  
Author(s):  
Eiji Hata ◽  
Takehiro Harada ◽  
Megumi Itoh
Keyword(s):  
Antimicrobial Susceptibility ◽  
Antimicrobial Agents ◽  
Point Mutations ◽  
Melting Curve ◽  
Sequence Type ◽  
23S Rrna ◽  
Mycoplasma Bovis ◽  
Rrna Gene ◽  
Content Type ◽  
Transition Mutation

ABSTRACT Mycoplasma bovis isolates belonging to the sequence type 5 (ST5) group, the dominant group in Japan since 1999, were low susceptible to 16-membered macrolides and tetracyclines and were confirmed to have a guanine-to-adenine transition mutation at position 748 in the 23S rRNA gene (rrl) and adenine-to-thymine transversion mutations at positions 965 and 967 in the 16S rRNA gene (rrs) (Escherichia coli numbering). Moreover, isolates of ST93 and ST155, members of the ST5 group, were low susceptible to lincosamides and azithromycin and showed an adenine-to-guanine transition mutation at position 2059 of rrl. Isolates of ST93 were additionally low susceptible to spectinomycin and showed a cytosine-to-adenine transversion mutation at position 1192 of rrs. Strains of the ST5 group seem to spread to Japan and Europe from North America with imported cows, while strains of ST93 and ST155 originated in Japan. Melting curve analysis using hybridization probes revealed the existence of point mutations involved in decreased susceptibility to macrolides, lincosamides, and spectinomycin, as demonstrated by changes in the melting curve shape and/or decreases in the melting peak temperature, so the susceptibility to these antimicrobials can be assessed on the same day. For decreased susceptibility to fluoroquinolones to exist, nonsynonymous mutations in the DNA gyrase gene (gyrA) and topoisomerase IV gene (parC) had to coexist. The combination of amino acid substitutions of serine at position 83 in gyrA and serine at position 80 in parC resulted in particularly low susceptibility to fluoroquinolones. IMPORTANCE Mycoplasma bovis is the main causal species of bovine mycoplasmal disease and leads to significant economic losses because of its severe symptoms, strong infectivity, and refractoriness. As for mastitis, culling cows with intramammary infections is a general countermeasure to prevent spreading. The conventional antimicrobial susceptibility test for mycoplasma is time-consuming and troublesome, but no quick and easy method for grasping the antimicrobial susceptibility of the causal strain exists at present. Treatment without antimicrobial susceptibility information may be one reason why M. bovis infection is refractory. Detecting a mutation involved in decreased susceptibility to antimicrobial agents of the causal strain makes it possible to easily select suitable antimicrobials for treatment, and this technique will help improve the cure rate and prevent the overuse of ineffective antimicrobial agents. In this study, we developed a technique to quickly and easily assess antimicrobial susceptibility based on the genetic characteristics of M. bovis strains in Japan.

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