Molecular Typing and Antimicrobial Susceptibility Profiles of Streptococcus uberis Isolated from Sheep Milk

Intramammary infections are a major problem for dairy sheep farms, and Streptococcus uberis is one of the main etiological agents of ovine mastitis. Surveys on antimicrobial resistance are still limited in sheep and characterization of isolates is important for acquiring information on resistance and for optimizing therapy. In this study, a sampling of 124 S. uberis isolates collected in Sardinia (Italy) from sheep milk was analyzed by multilocus-sequence typing (MLST) and pulsed field gel electrophoresis (PFGE) for genetic relatedness. All isolates were also subjected to antimicrobial susceptibility analysis by the disk diffusion test using a panel of 14 antimicrobials. Resistance genes were detected by PCR assays. MLST analysis revealed that the isolates were grouped into 86 sequence types (STs), of which 73 were new genotypes, indicating a highly diverse population of S. uberis. The most frequently detected lineage was the clonal complex (CC)143, although representing only 13.7% of all characterized isolates. A high level of heterogeneity was also observed among the SmaI PFGE profiles, with 121 unique patterns. Almost all (96.8%) isolates were resistant to at least one antimicrobial, while all exhibited phenotypic susceptibility to oxacillin, amoxicillin-clavulanic acid and ceftiofur. Of the antimicrobials tested, the highest resistance rate was found against streptomycin (93.5%), kanamycin (79.8%) and gentamicin (64.5%), followed by novobiocin (25%) and tetracycline-TE (19.3%). Seventy-four (59.7%) isolates were simultaneously resistant to all aminoglycosides tested. Seventeen isolates (13.7%) exhibited multidrug resistance. All aminoglycosides-resistant isolates were PCR negative for aad-6 and aphA-3′ genes. Among the TE-resistant isolates, the tetM gene was predominant, indicating that the resistance mechanism is mainly mediated by the protection of ribosomes and not through the efflux pump. Three isolates were resistant to erythromycin, and two of them harbored the ermB gene. This is the first study reporting a detailed characterization of the S. uberis strains circulating in Sardinian sheep. Further investigations will be needed to understand the relationships between S. uberis genotypes, mastitis severity, and intra-mammary infection dynamics in the flock, as well as to monitor the evolution of antimicrobial resistance.

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Molecular Typing and Antimicrobial Susceptibility Profiles of Streptococcus uberis Isolated From Sheep Milk

10.20944/preprints202111.0140.v1 ◽

2021 ◽

Author(s):

Nives Maria Rosa ◽

Ilaria Dupre ◽

Elisa Azara ◽

Carla Maria Longheu ◽

Sebastiana Tola

Keyword(s):

Antimicrobial Resistance ◽

Antimicrobial Susceptibility ◽

Genetic Relatedness ◽

Efflux Pump ◽

Resistance Mechanism ◽

Resistance Rate ◽

Disk Diffusion Test ◽

Sheep Milk ◽

Streptococcus Uberis

Intrammary infections are a major problem for dairy sheep farms, and Streptococcus uberis is one of the main etiological agents of ovine mastitis. Surveys on antimicrobial resistance are still limited in sheep and characterization of isolates is important for acquiring information on resistance and for optimizing therapy. In this study, a sampling of 124 S. uberis isolates collected in Sardinia (Italy) from sheep milk was analysed by multilocus-sequence typing (MLST) and pulsed field gel electrophoresis (PFGE) for genetic relatedness. All isolates were also subjected to antimicrobial susceptibility analysis by the disk diffusion test using a panel of 14 antimicrobials. Resistance genes were detected by PCR assays. MLST analysis revealed that the isolates were grouped into 86 sequence types (STs), of which 73 were new genotypes, indicating a highly diverse population of S. uberis. The most frequently detected lineage was the clonal complex (CC)143, although representing only 13.7% of all characterized isolates. A high level of heterogeneity was also observed among the SmaI PFGE profiles, with 121 unique patterns. Almost all (96.8%) isolates were resistant to at least one antimicrobial, while all exhibited phenotypic susceptibility to oxacillin, amoxicillin-clavulanic acid and ceftiofur. Of the antimicrobials tested, the highest resistance rate was found against streptomycin (93.5%), kanamycin (79.8%) and gentamicin (64.5%), followed by novobiocin (25%) and tetracycline-TE (19.3%). Seventy-four (59.7%) isolates were simultaneously resistant to all aminoglycosides tested. Seventeen isolates (13.7%) exhibited multidrug resistance. All aminoglycosides-resistant isolates were PCR negative for aad-6 and aphA-3’ genes. Among the TE-resistant isolates, the tetM gene was predominant, indicating that the resistance mechanism is mainly mediated by the protection of ribosomes and not through the efflux pump. Three isolates were resistant to erythromycin, and two of them harboured the ermB gene. This is the first study reporting a detailed characterization of the S. uberis strains circulating in Sardinian sheep. Further investigations will be needed to understand the relationships between S. uberis genotypes, mastitis severity, and intra-mammary infection dynamics in the flock, as well as to monitor the evolution of antimicrobial resistance.

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Molecular Characterization of Antimicrobial Resistance and Virulence Genes of Bacterial Pathogens from Bovine and Caprine Mastitis in Northern Lebanon

Microorganisms ◽

10.3390/microorganisms9061148 ◽

2021 ◽

Vol 9 (6) ◽

pp. 1148

Author(s):

Zahie Abboud ◽

Lucia Galuppo ◽

Marco Tolone ◽

Maria Vitale ◽

Roberto Puleio ◽

...

Keyword(s):

Antimicrobial Resistance ◽

Molecular Characterization ◽

Antimicrobial Susceptibility ◽

Meca Gene ◽

Toxin Gene ◽

Pcr Screening ◽

E Coli ◽

Presenting Symptoms ◽

Flight Mass Spectrometry ◽

Streptococcus Uberis

Mastitis is an infectious disease encountered in dairy animals worldwide that is currently a growing concern in Lebanon. This study aimed at investigating the etiology of the main mastitis-causing pathogens in Northern Lebanon, determining their antimicrobial susceptibility profiles, and identifying their antimicrobial resistance (AMR) genes. A total of 101 quarter milk samples were collected from 77 cows and 11 goats presenting symptoms of mastitis on 45 dairy farms. Bacterial identification was carried out through matrix-assisted laser desorption/ionization-time of flight mass spectrometry. Antimicrobial susceptibility was tested by disc diffusion and broth microdilution methods. Molecular characterization included polymerase chain reaction (PCR) screening for genes encoding extended-spectrum beta-lactamases (ESBLs) and plasmid-mediated AmpC among Enterobacterales isolates, and virulence factors among Staphylococcus isolates. Escherichia coli isolates were subjected to phylogenetic typing by a quadruplex PCR method. The most frequently identified species were Streptococcus uberis (19.2%), Streptococcus agalactiae (15.1%), E. coli (12.3%), and Staphylococcus aureus (10.96%). Gram-positive bacteria were resistant to macrolides and tetracycline, whereas gram-negative bacteria displayed resistance to ampicillin and tetracycline. Two ESBL genes, blaTEM (83.3%) and blaOXA (16.7%), and one AmpC beta-lactamase gene, blaCMY-II (16.7%), were detected among six E. coli isolates, which mainly belonged to phylogenetic group B1. Among Staphylococcus spp., the mecA gene was present in three isolates. Furthermore, four isolates contained at least one toxin gene, and all S. aureus isolates carried the ica operon. These findings revealed the alarming risk of AMR in the Lebanese dairy chain and the importance of monitoring antimicrobial usage.

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Serotype distribution, antimicrobial susceptibility, antimicrobial resistance genes and virulence genes of Salmonella isolated from a pig slaughterhouse in Yangzhou, China

AMB Express ◽

10.1186/s13568-019-0936-9 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 2

Author(s):

Quan Li ◽

Jian Yin ◽

Zheng Li ◽

Zewei Li ◽

Yuanzhao Du ◽

...

Keyword(s):

Public Health ◽

Antimicrobial Resistance ◽

Resistance Genes ◽

Antimicrobial Susceptibility ◽

Virulence Genes ◽

Multidrug Resistant ◽

Resistance Rate ◽

Economic Losses ◽

Production Chain ◽

Antimicrobial Resistance Genes

AbstractSalmonella is an important food-borne pathogen associated with public health and high economic losses. To investigate the prevalence and the characteristics of Salmonella in a pig slaughterhouse in Yangzhou, a total of 80 Salmonella isolates were isolated from 459 (17.43%) samples in 2016–2017. S. Derby (35/80, 43.75%) was the most prevalent, followed by S. Rissen (16/80, 20.00%) and S. Newlands (11/80, 13.75%). The highest rates of susceptibility were observed to cefoxitin (80/80, 100.0%) and amikacin (80/80, 100.0%), followed by aztreonam (79/80, 98.75%) and nitrofurantoin (79/80, 98.75%). The highest resistance rate was detected for tetracycline (65/80, 81.25%), followed by ampicillin (60/80, 75.00%), bactrim (55/80, 68.75%), and sulfisoxazole (54/80, 67.50%). Overall, 91.25% (73/80) of the isolates were resistant to at least one antibiotic, while 71.25% (57/80) of the isolate strains were multidrug resistant in the antimicrobial susceptibility tested. In addition, 86.36% (19/22) of the 22 antimicrobial resistance genes in the isolates were identified. Our data indicated that the resistance to certain antimicrobials was significantly associated, in part, with antimicrobial resistance genes. Furthermore, 81.25% (65/80) isolates harbored the virulence gene of mogA, of which 2 Salmonella Typhimurium isolates carried the mogA, spvB and spvC virulence genes at the same time. The results showed that swine products in the slaughterhouse were contaminated with multidrug resistant Salmonella commonly, especially some isolates carry the spv virulence genes. The virulence genes might facilitate the dissemination of the resistance genes to consumers along the production chain, suggesting the importance of controlling Salmonella during slaughter for public health.

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Characterization of resistance mechanisms of Enterobacter cloacae Complex co-resistant to carbapenem and colistin

BMC Microbiology ◽

10.1186/s12866-021-02250-x ◽

2021 ◽

Vol 21 (1) ◽

Author(s):

Shixing Liu ◽

Renchi Fang ◽

Ying Zhang ◽

Lijiang Chen ◽

Na Huang ◽

...

Keyword(s):

Lipid A ◽

Efflux Pump ◽

Resistance Mechanism ◽

Carbapenem Resistance ◽

Enterobacter Cloacae ◽

Resistance Mechanisms ◽

Colistin Resistance ◽

Carbapenem Resistant ◽

Horizontal Spread

Abstract Background The emergence of carbapenem-resistant and colistin-resistant ECC pose a huge challenge to infection control. The purpose of this study was to clarify the mechanism of the carbapenems and colistin co-resistance in Enterobacter cloacae Complex (ECC) strains. Results This study showed that the mechanisms of carbapenem resistance in this study are: 1. Generating carbapenemase (7 of 19); 2. The production of AmpC or ESBLs combined with decreased expression of out membrane protein (12 of 19). hsp60 sequence analysis suggested 10 of 19 the strains belong to colistin hetero-resistant clusters and the mechanism of colistin resistance is increasing expression of acrA in the efflux pump AcrAB-TolC alone (18 of 19) or accompanied by a decrease of affinity between colistin and outer membrane caused by the modification of lipid A (14 of 19). Moreover, an ECC strain co-harboring plasmid-mediated mcr-4.3 and blaNDM-1 has been found. Conclusions This study suggested that there is no overlap between the resistance mechanism of co-resistant ECC strains to carbapenem and colistin. However, the emergence of strain co-harboring plasmid-mediated resistance genes indicated that ECC is a potential carrier for the horizontal spread of carbapenems and colistin resistance.

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Prevalence and antimicrobial resistance of Listeria species and molecular characterization of Listeria monocytogenes isolated from retail ready-to-eat foods

FEMS Microbiology Letters ◽

10.1093/femsle/fnaa006 ◽

2020 ◽

Vol 367 (4) ◽

Author(s):

Seza Arslan ◽

Fatma Özdemir

Keyword(s):

Antimicrobial Resistance ◽

Genetic Relatedness ◽

Fragment Length Polymorphism ◽

Food Samples ◽

Diffusion Method ◽

Consumer Health ◽

Disk Diffusion Method ◽

Listeria Species ◽

Virulence Markers

ABSTRACT A wide variety of foods can be contaminated with Listeria species, especially L. monocytogenes. Ready-to-eat (RTE) foods are predominantly associated with human listeriosis caused by L. monocytogenes. Therefore, this study aimed to assess the presence of Listeria species in RTE foods and to characterize L. monocytogenes isolates by means of detection of virulence markers, serotypes and genetic relatedness. Of the 300 RTE food samples, 59 (19.7%) were positive for Listeria species: L. innocua (13.3%), L. monocytogenes (5%), L. welshimerii (2.3%), L. grayi subsp. murrayi (1.3%), L. grayi (1%), L. ivanovii (1%) and L. ivanovi subsp. londoniensis (0.3%). All L. monocytogenes isolates identified were positive for the actA, iap, inlA, inlB, inlC, inlJ, plcA and prfA virulence genes and biofilm. The isolates were serotyped as 1/2c (33.3%), 4b (26.7%), 1/2a (26.7%), 1/2b (6.7%) and 3c (6.7%) by the multiplex-PCR and agglutination methods. PCR-restriction fragment length polymorphism with AluI and MluCI resulted in three and two profiles, respectively. Pulsed-field gel electrophoresis differentiated the L. monocytogenes isolates into 15 ApaI and 12 AscI patterns. Antimicrobial resistance of all Listeria isolates was determined by the disk diffusion method. Most L. monocytogenes isolates were sensitive to antimicrobials used in the treatment of listeriosis. This study shows the presence of potential pathogenic and antimicrobial-resistant L. monocytogenes in RTE foods that may lead to consumer health risks.

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Virulence genotyping and antimicrobial resistance profiles of Yersinia enterocolitica isolated from meat and meat products in Egypt

Brazilian Journal of Biology ◽

10.1590/1519-6984.229998 ◽

2020 ◽

Author(s):

G. A. Younis ◽

R. M. Elkenany ◽

H. A. Dowidar

Keyword(s):

Antimicrobial Resistance ◽

Yersinia Enterocolitica ◽

Genetic Relatedness ◽

Meat Product ◽

Meat Products ◽

High Sensitivity ◽

Resistance Rate ◽

Chicken Meat ◽

Nucleotide Sequence Analysis ◽

Rrna Gene

Abstract Pathogenic Yersinia enterocolitica (Y. enterocolitica) is one of the food-borne entero-pathogen responsible for yersiniosis in humans. The purpose of this research was to survey the prevalence, virulence-associated genes, and antimicrobial resistance of Y. enterocolitica isolated from meat and meat product samples in Egypt. Forty-one (5.9%) out of 700- samples of chicken meat, beef, ground beef, and sausage were positive Y. enterocolitica with a high prevalence in chicken meat (12%). Five virulence genes (ail, inv, ystA, ystB, and yadA) were characterized among 41 Y. enterocolitica isolates with variable frequencies. Among the strains tested, the ystB gene was detected with a high percentage (78.1%), followed by inv gene (70.7%), ail gene (14.6%), ystA gene (12.2%), and yadA gene (2.4%). A high resistance rate was estimated to amoxicillin-clavulanic acid (100%), followed by cefazolin (95%), ampicillin (65.9%), and doxycycline (51.2%), whilst a high sensitivity rate was observed to gentamicin and ciprofloxacin (97.6% each). Interestingly, the multidrug resistance was specified in the 70.7% of strains and showing 13 resistance patterns. Based on nucleotide sequence analysis of the 16s rRNA gene, the phylogenetic tree showed the genetic relatedness amongst Y. enterocolitica isolates. These findings highlighted the emergence of virulent and multidrug-resistant pathogenic Y. entrocolitica in retailed meat and meat products in Egypt.

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Cultivation of bacterial pathogens and antimicrobial resistance in canine periapical tooth abscesses

Veterinary Integrative Sciences ◽

10.12982/vis.2021.040 ◽

2021 ◽

Vol 19 (3) ◽

pp. 513-524

Author(s):

Natcha Chawnan ◽

◽

Kannika Na Lampang ◽

Raktham Mektrirat ◽

Nattakarn Awaiwanont ◽

...

Keyword(s):

Antimicrobial Resistance ◽

Antimicrobial Susceptibility ◽

Bacterial Pathogens ◽

Bacterial Species ◽

Resistance Rate ◽

Chiang Mai ◽

Diagnostic Laboratory ◽

Dental Surgery ◽

E Coli ◽

Amoxicillin Clavulanate

This research aimed to assess the occurrence of bacterial pathogens and their antimicrobial resistance in dogs presenting with canine periapical tooth abscesses. Sample swabs were performed on 45 dogs who had undergone dental surgery between January 2019 and August 2020 at the Veterinary Teaching Hospital, Chiang Mai University. Samples were analyzed within 24 hours at Veterinary Diagnostic Laboratory, Chiang Mai University to identify any bacterial species and to investigate their potential antimicrobial susceptibility according to CLSI guidelines. A high proportion of gram-negative and facultative species were identified. Out of the 17 species obtained, Pseudomonas aeruginosa (34.6 %) was determined to be the predominant species followed by Escherichia coli (15.4%) and Klebsiella pneumoniae (11.5%), respectively. P. aeruginosa was highly resistant (100.0%) to ampicillin and clindamycin, while E. coli and K. pneumoniae were found to be highly resistant (100.0%) to clindamycin in terms of antimicrobial susceptibility. However, E. coli was more resistant to enrofloxacin, gentamicin, and norfloxacin than K. pneumoniae. When focusing on the resistance rates of all species, clindamycin exhibited the highest degree of resistance, followed by ampicillin and amoxicillin, respectively. Amoxicillin-clavulanate is an empirical antibiotic in our area that has exhibited a resistance rate of 48.7%. The outcomes of our study have suggested that fluoroquinolone and aminoglycoside could be used to treat canine periapical tooth abscesses. However, the renal effect of these drugs must be considered. Importantly, antibiotic selection must depend upon the results of bacterial culture and antimicrobial susceptibility tests in order to reduce any potential antimicrobial resistance issues.

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The Expression of Efflux Pump Genes in Methicillin-Resistant Staphylococcus aureus (MRSA) Strains Isolated from Blood Cultures in Iran

Archives of Clinical Infectious Diseases ◽

10.5812/archcid.99804 ◽

2020 ◽

Vol 15 (5) ◽

Author(s):

Arezoo Bostanmaneshrad ◽

Jamileh Norouzi ◽

Gita Eslami ◽

Ali Hashemi

Keyword(s):

Staphylococcus Aureus ◽

Efflux Pump ◽

Resistance Mechanism ◽

Expression Level ◽

Resistance Pattern ◽

Dilution Method ◽

University Hospitals ◽

Efflux Pump Inhibitor ◽

Disk Diffusion Test ◽

Methicillin Resistant

Background: Efflux pump is a significant resistance mechanism in Staphylococcus aureus. A total of 100 patients with bacteremia from Shahid Beheshti University Hospitals of Tehran in Iran were tested for the expression of efflux pump genes, contributing to S. aureus antimicrobial resistance. Objectives: this study was conducted to identify resistance pattern, and to evaluate the inhibitory effect of efflux pump, MIC of ciprofloxacin, and expression levels of norA, norB, and norC efflux pump genes in the presence of an efflux pump inhibitor against MDR S. aureus. Methods: A total of 100 MRSA isolates were investigated in different hospitals of Shahid Beheshti University of Medical Sciences from April 2017-2018. Owing to new consensus guidelines from the Clinical and Laboratory Standards Institute (CLSI), both the Kirby-Bauer disk diffusion test and micro-dilution method were used to evaluate antimicrobial susceptibility. Efflux pump activity using carbonyl cyanide 3-chlorophenylhydrazone (CCCP) was identified as a chemical efflux pump inhibitor. E-test was used to determine Vancomycin-resistant antibiotic. Broth micro-dilution method for S. aureus isolates resistant to ciprofloxacin has been developed for minimum inhibitory concentration (MIC) of ciprofloxacin and CCCP and their composition. Quantitative Real-time Polymerase Chain Reaction (qRT-PCR) was used to investigate the expression level of norA, norB, and norC efflux pump genes. Results: A total of 38 of 45 MRSA isolates (84.4%) showed resistance to ciprofloxacin. Moreover, 100% of isolates had the norA and norB genes. Further, 95% of S. aureus isolates had the norC gene. According to this study, ciprofloxacin MIC has decreased by CCCP compared to ciprofloxacin. There was an increase in the expression level of norA, norB, and norC efflux pump genes in methicillin-resistant and ciprofloxacin-resistant S. aureus strains based on RT- PCR. In this study, four different spA types were obtained as the most prevalent type of spA by t037and t790 (23.3%) and t030 (14.1%) and t044 (12.2%). Conclusions: This study indicates that the prevalence of ciprofloxacin-resistant S. aureus strains has a rising trend among MRSA clinical isolates. The ability of S. aureus isolates to be converted into drug-resistant strains using efflux pump mechanism has become a widespread concern.

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Genetic determinants of multi-drug resistance in Acinetobacter baumannii at an academic hospital in Pretoria, South Africa

10.1101/809129 ◽

2019 ◽

Author(s):

Noel-David Nogbou ◽

Dikwata Thabiso Phofa ◽

Maphoshane Nchabeleng ◽

Andrew Munyalo Musyoki

Keyword(s):

South Africa ◽

Antimicrobial Resistance ◽

Genetic Relatedness ◽

Efflux Pump ◽

Multi Drug Resistance ◽

Drug Resistant ◽

Genetic Determinants ◽

Pump System ◽

Active Efflux ◽

Almost All

AbstractAntimicrobial resistance is now globally recognised as the greatest threat to human health. Acinetobacter baumanniis’ (A. baumannii) clinical significance has been driven by its ability to obtain and transmit antimicrobial resistance factors. In South Africa, A. baumannii is a leading cause of healthcare associated infections (HAI). In this study, we investigated the genetic determinants of multi-drug resistant A. baumannii (MDRAB) at a teaching hospital in Pretoria, South Africa.One hundred non repetitive isolates of A. baumannii were collected for the study at Dr George Mukhari Tertiary Laboratory (DGMTL). Antimicrobial susceptibility testing was performed using the VITEK2 system (bioMerieux, France). The prevalence of common resistance associated genes and AdeABC efflux pump system associated genes were investigated using conventional PCR. Genetic relatedness of isolates was then determined using rep-PCR.Seventy (70) of 100 isolates collected were confirmed to be multi-drug resistant and were blaOXA51 positive. Phenotypically, the isolates where resistant to almost all tested antibiotics. However, one isolate showed intermediate susceptibility to tigecycline while all were susceptible to colistin. Oxacillinase encoding gene blaOXA-23 was the most detected at 99% and only 1% was positive for blaOXA-40. The PCR results for metallo-betalactamase (MBL) encoding genes showed that MBL blaVIM was the most frequently detected at 86% and blaSIM-1 at 3% was the least detected. Out of 70 isolates, 56 isolates had the required gene combination for an active efflux pump. The most prevalent clone was clone A at 69% of the isolates. Regarding treatment; colistin and tigecycline are the most effective against strains encountered at DGMTL as all tested carbapenems seem to have lost their effectiveness.The major genotypic determinants for drug resistances are oxacillinases: blaOXA-51 (100%) and blaOXA-23 (99%). The study reports for the first time, blaOXA-40 and blaSIM-1 detection in A. baumannii in South Africa.

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The Asp20-to-Asn Substitution in the Response Regulator AdeR Leads to Enhanced Efflux Activity of AdeB in Acinetobacter baumannii

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.02413-15 ◽

2015 ◽

Vol 60 (2) ◽

pp. 1085-1090 ◽

Cited By ~ 12

Author(s):

Jennifer Nowak ◽

Thamarai Schneiders ◽

Harald Seifert ◽

Paul G. Higgins

Keyword(s):

Acinetobacter Baumannii ◽

Antimicrobial Susceptibility ◽

Efflux Pump ◽

Response Regulator ◽

Two Component System ◽

Content Type ◽

Susceptibility Data ◽

Genes Encoding ◽

Induced Changes

ABSTRACTOverexpression of the resistance-nodulation-cell division-type efflux pump AdeABC is often associated with multidrug resistance inAcinetobacter baumanniiand has been linked to mutations in the genes encoding the AdeRS two-component system. In a previous study, we reported that the Asp20→Asn amino acid substitution in the response regulator AdeR is associated withadeBoverexpression and reduced susceptibility to the antimicrobials levofloxacin, tigecycline, and trimethoprim-sulfamethoxazole. To further characterize the effect of the Asp20→Asn substitution on antimicrobial susceptibility, the expression of the efflux genesadeB,adeJ, andadeG, and substrate accumulation, four plasmid constructs [containingadeR(Asp20)S,adeR(Asn20)S,adeR(Asp20)SABC, andadeR(Asn20)SABC] were introduced into theadeRSABC-deficientA. baumanniiisolate NIPH 60. NeitheradeRSconstruct induced changes in antimicrobial susceptibility or substrate accumulation from that for the vector-only control. TheadeR(Asp20)SABCtransformant showed reduced susceptibility to 6 antimicrobials and accumulated 12% less ethidium than the control, whereas the Asn20 variant showed reduced susceptibility to 6 of 8 antimicrobial classes tested, and its ethidium accumulation was only 72% of that observed for the vector-only construct.adeBexpression was 7-fold higher in theadeR(Asn20)SABCtransformant than in its Asp20 variant. No changes inadeGoradeJexpression or in acriflavine or rhodamine 6G accumulation were detected. The antimicrobial susceptibility data suggest that AdeRS does not regulate any resistance determinants other than AdeABC. Furthermore, the characterization of the Asp20→Asn20 substitution proves that the reduced antimicrobial susceptibility previously associated with this substitution was indeed caused by enhanced efflux activity of AdeB.

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