Displaying publications 41 - 60 of 63 in total

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  1. Naidu AJ, Yadav M
    J Med Microbiol, 1997 Oct;46(10):833-8.
    PMID: 9364139
    Aeromonas hydrophila strains obtained from diarrhoeal samples of human patients (19 isolates) and freshwater ponds (11 isolates) were analysed for siderophore production. Both clinical and environmental isolates showed significantly increased siderophore production under iron-limiting conditions both at 28 degrees C and at 37 degrees C. Clinical isolates consistently produced higher levels of siderophores than did the environmental isolates. The role of plasmids in moderating siderophore production was studied after curing with acridine orange. Treatment with acridine orange for 24 h removed the larger plasmids but the smaller plasmids (< 5 MDa), more common in the environmental isolates, were resistant to curing. As found in the untreated isolates, the cured clinical isolates produced higher mean levels of siderophores than the cured environmental isolates. Siderophore production in A. hydrophila was significantly influenced by iron-limiting cultural conditions and the source of isolates, but plasmid content and growth temperature at 28 degrees C or 37 degrees C had little effect on production. The basis for the greater production of siderophores in clinical isolates than in environmental isolates needs further study.
  2. Khosravi Y, Tay ST, Vadivelu J
    J Med Microbiol, 2011 Jul;60(Pt 7):988-994.
    PMID: 21436370 DOI: 10.1099/jmm.0.029868-0
    In this study, 90 non-replicate imipenem-resistant Pseudomonas aeruginosa (IRPA) Malaysian isolates collected between October 2005 and March 2008 were subjected to a screening test for detection of the integron and the gene cassette. Class 1 integrons were detected in 54 IRPA clinical isolates, whilst three isolates contained class 2 integrons. Analysis of the gene cassettes associated with the class 1 integrons showed the detection of accC1 in isolates carrying bla(IMP-7) and aacA7 in isolates carrying bla(VIM-2). aadA6 was detected in two isolates carrying bla(IMP-4). Using random amplification of polymorphic DNA analysis, 14 PCR fingerprint patterns were generated from the 32 isolates carrying metallo-β-lactamase (MBL) genes (35.5 %), whilst 20 patterns were generated from the 58 non-MBL gene isolates (64.4 %). Based on the differences in the fingerprinting patterns, two clusters (A and B) were identified among the MBL-producing isolates. Cluster A comprised 18 isolates (56 %) carrying the bla(VIM) gene, whereas cluster B comprised 14 (44 %) isolates carrying the bla(IMP) gene. The non-MBL isolates were divided into clusters C and D. Cluster C comprised 22 non-MBL isolates harbouring class 1 integrons, whilst cluster D consisted of three isolates carrying class 2 integrons. These findings suggest that the class 1 integron is widespread among P. aeruginosa isolated in Malaysia and that characterization of cassette arrays of integrons will be a useful epidemiological tool to study the evolution of multidrug resistance and the dissemination of antibiotic resistance genes.
  3. Chua AL, Elina HT, Lim BH, Yean CY, Ravichandran M, Lalitha P
    J Med Microbiol, 2011 Apr;60(Pt 4):481-485.
    PMID: 21183596 DOI: 10.1099/jmm.0.027433-0
    Vibrio cholerae has caused severe outbreaks of cholera worldwide with thousands of recorded deaths annually. Molecular diagnosis for cholera has become increasingly important for rapid detection of cholera as the conventional methods are time-consuming and labour intensive. However, traditional PCR tests still require cold-chain transportation and storage as well as trained personnel to perform, which makes them user-unfriendly. The aim of this study was to develop a thermostabilized triplex PCR test for cholera which is in a ready-to-use form and requires no cold chain. The PCR test specifically detects both toxigenic and non-toxigenic strains of V. cholerae based on the cholera toxin A (ctxA) and outer-membrane lipoprotein (lolB) genes. The thermostabilized triplex PCR also incorporates an internal amplification control that helps to check for PCR inhibitors in samples. PCR reagents and the specific primers were lyophilized into a pellet form in the presence of trehalose, which acts as an enzyme stabilizer. The triplex PCR was validated with 174 bacteria-spiked stool specimens and was found to be 100 % sensitive and specific. The stability of the thermostabilized PCR was evaluated using the Q10 method and it was found to be stable for approximately 7 months at 24 °C. The limit of detection of the thermostabilized triplex PCR assay was 2×10(4) c.f.u. at the bacterial cell level and 100 pg DNA at the genomic DNA level, comparable to conventional PCR methods. In conclusion, a rapid thermostabilized triplex PCR assay was developed for detecting toxigenic and non-toxigenic V. cholerae which requires minimal pipetting steps and is cold chain-free.
  4. Ahmad N, Nawi S, Rajasekaran G, Maning N, Aziz MN, Husin A, et al.
    J Med Microbiol, 2010 Dec;59(Pt 12):1530-1532.
    PMID: 20724515 DOI: 10.1099/jmm.0.022079-0
  5. Ahmad N, Ruzan IN, Abd Ghani MK, Hussin A, Nawi S, Aziz MN, et al.
    J Med Microbiol, 2009 Sep;58(Pt 9):1213-1218.
    PMID: 19528158 DOI: 10.1099/jmm.0.011353-0
    Community-acquired meticillin-resistant Staphylococcus aureus (CA-MRSA) occurring among hospital isolates in Malaysia has not been reported previously. As CA-MRSA reported worldwide has been shown to carry SCCmec types IV and V, the aim of this study was to determine the SCCmec types of MRSA strains collected in Malaysia from November 2006 to June 2008. From a total of 628 MRSA isolates, 20 were SCCmec type IV, whilst the rest were type III. Further characterization of SCCmec type IV strains revealed 11 sequence types (STs), including ST22, with the majority being ST30/Panton-Valentine leukocidin positive. Eight out of nine CA-MRSA were ST30, one was ST80, and all were sensitive to co-trimoxazole and gentamicin. Five new STs designated ST1284, ST1285, ST1286, ST1287 and ST1288 were discovered, suggesting the emergence of novel clones of MRSA circulating in Malaysian hospitals. The discovery of the ST22 strain is a cause for concern because of its ability to replace existing predominant clones in certain geographical regions.
  6. Tay ST, Na SL, Chong J
    J Med Microbiol, 2009 Feb;58(Pt 2):185-191.
    PMID: 19141735 DOI: 10.1099/jmm.0.004242-0
    The genetic heterogeneity and antifungal susceptibility patterns of Candida parapsilosis isolated from blood cultures of patients were investigated in this study. Randomly amplified polymorphic DNA (RAPD) analysis generated 5 unique profiles from 42 isolates. Based on the major DNA fragments of the RAPD profiles, the isolates were identified as RAPD type P1 (29 isolates), P2 (6 isolates), P3 (4 isolates), P4 (2 isolates) and P5 (1 isolate). Sequence analysis of the internal transcribed spacer (ITS) gene of the isolates identified RAPD type P1 as C. parapsilosis, P2 and P3 as Candida orthopsilosis, P4 as Candida metapsilosis, and P5 as Lodderomyces elongisporus. Nucleotide variations in ITS gene sequences of C. orthopsilosis and C. metapsilosis were detected. Antifungal susceptibility testing using Etests showed that all isolates tested in this study were susceptible to amphotericin B, fluconazole, ketoconazole, itraconazole and voriconazole. C. parapsilosis isolates exhibited higher MIC(50) values than those of C. orthopsilosis for all of the drugs tested in this study; however, no significant difference in the MICs for these two Candida species was observed. The fact that C. orthopsilosis and C. metapsilosis were responsible for 23.8 and 4.8 % of the cases attributed to C. parapsilosis bloodstream infections, respectively, indicates the clinical relevance of these newly described yeasts. Further investigations of the ecological niche, mode of transmission and virulence of these species are thus essential.
  7. Fadzilah MN, Faizatul LJ, Hasibah MS, Sam IC, Bador MK, Gan GG, et al.
    J Med Microbiol, 2009 Jan;58(Pt 1):142-143.
    PMID: 19074667 DOI: 10.1099/jmm.0.004622-0
    A 17-year-old man with acute lymphoblastic leukaemia had fever and diarrhoea during a febrile neutropenic episode. A spiral-shaped, Gram-negative anaerobic bacterium was isolated from blood, and confirmed as Anaerobiospirillum succiniciproducens by 16S rRNA sequencing. The patient responded to imipenem.
  8. Nami Y, Abdullah N, Haghshenas B, Radiah D, Rosli R, Khosroushahi AY
    J Med Microbiol, 2014 Aug;63(Pt 8):1044-1051.
    PMID: 24913559 DOI: 10.1099/jmm.0.074161-0
    Forty-five lactic acid bacteria (LAB) were isolated from the vaginal specimens of healthy fertile women, and the identities of the bacteria were confirmed by sequencing of their 16S rDNA genes. Among these bacteria, only four isolates were able to resist and survive in low pH, bile salts and simulated in vitro digestion conditions. Lactococcus lactis 2HL, Enterococcus durans 6HL, Lactobacillus acidophilus 36YL and Lactobacillus plantarum 5BL showed the best resistance to these conditions. These strains were evaluated further to assess their ability to adhere to human intestinal Caco-2 cells. Lactococcus lactis 2HL and E. durans 6HL were the most adherent strains. In vitro tests under neutralized pH proved the antimicrobial activity of both strains. Results revealed that the growth of Escherichia coli O26, Staphylococcus aureus and Shigella flexneri was suppressed by both LAB strains. The antibiotic susceptibility tests showed that these strains were sensitive to all nine antibiotics: vancomycin, tetracycline, ampicillin, penicillin, gentamicin, erythromycin, clindamycin, sulfamethoxazole and chloramphenicol. These data suggest that E. durans 6HL and Lactococcus lactis 2HL could be examined further for their useful properties and could be developed as new probiotics.
  9. Alfizah H, Norazah A, Hamizah R, Ramelah M
    J Med Microbiol, 2014 May;63(Pt 5):703-709.
    PMID: 24757218 DOI: 10.1099/jmm.0.069781-0
    Antibiotic resistance is increasing worldwide, and it has been regarded as the main factor reducing the efficacy of Helicobacter pylori therapy. The aim of this study was to determine the phenotype and genotype of antibiotic-resistant strains of H. pylori in the Malaysian population and to evaluate the impact of antibiotic resistance to eradication outcome. One hundred and sixty-one H. pylori isolates were analysed in this study. Metronidazole, clarithromycin, fluoroquinolone, amoxicillin and tetracycline susceptibilities were determined by Etest. PCR followed by DNA sequencing was carried out to determine mutations. The medical records of the patients infected with resistant strains were reviewed to determine the eradication outcome. Metronidazole resistance was encountered in 36.6 % of H. pylori isolates, whereas clarithromycin and fluoroquinolone resistance was observed in 1.2  and 1.9 % of isolates, respectively. All strains tested were susceptible to amoxicillin and tetracycline. Frameshift and nonsense mutations in rdxA and frxA genes resulting in stop codons contributed to metronidazole resistance, which leads to reduced eradication efficacy. A2142G and A2143G mutations of 23S rRNA were identified as causing failure of the eradication therapy. Mutation at either codon 87 or 91 of the gyrA gene was identified in fluoroquinolone-resistant strains. However, the effect of resistance could not be assessed. This study showed that frameshift and nonsense mutations in rdxA or frxA genes and point mutations in the 23S rRNA affected the efficacy of H. pylori eradication therapy.
  10. Tay ST, Tan HW, Na SL, Lim SL
    J Med Microbiol, 2011 Nov;60(Pt 11):1591-1597.
    PMID: 21700741 DOI: 10.1099/jmm.0.032854-0
    In this study, six clinical isolates (two from blood, two from urine and one each from a bronchoalveolar lavage and a vaginal swab) were identified as Candida rugosa based on carbohydrate assimilation profiles using API 20C AUX and ID32 C kits (bioMérieux). Sequence analysis of the D1/D2 domain of the yeasts differentiated the isolates into two subgroups, A and B (three isolates per subgroup), which were closely related (99.1-99.6 % nucleotide similarity) to C. rugosa strain ATCC 10571. Compared with the C. rugosa type strain, the intergenic transcribed spacer (ITS) nucleotide similarity for subgroup A was only 89.2 % (29 mismatches and one deletion) and for subgroup B was 93.7 % (20 mismatches). All isolates grew green colonies on Oxoid Chromogenic Candida Agar, with darker pigmentation observed for subgroup A. All isolates were able to grow at 25-42 °C but not at 45 °C. The isolates had identical enzymic profiles, as determined by API ZYM (bioMérieux) analysis, and produced proteinase. High amphotericin MICs (≥1 µg ml(-1)) were noted for two isolates from each subgroup. Dose-dependent susceptibility to fluconazole (MIC 32 µg ml(-1)) was noted in a blood isolate. The biofilms of the isolates demonstrated increased resistance to amphotericin and fluconazole. The greater ITS sequence variability of subgroup A isolates is in support of this yeast being recognized as a distinct species; however, further verification using more sophisticated molecular approaches is required. A sequence comparison study suggested the association of subgroup A with environmental sources and subgroup B with clinical sources. Accurate identification and antifungal susceptibility testing of C. rugosa are important in view of its decreased susceptibility to amphotericin and fluconazole. The ITS region has been shown to be a valuable region for differentiation of closely related subgroups of C. rugosa.
  11. Amran F, Aziz MN, Ibrahim HM, Atiqah NH, Parameswari S, Hafiza MR, et al.
    J Med Microbiol, 2011 Sep;60(Pt 9):1312-1316.
    PMID: 21459913 DOI: 10.1099/jmm.0.027631-0
    The in vitro antifungal susceptibilities of 159 clinical isolates of Candida species from patients with invasive candidiasis in Kuala Lumpur Hospital, Malaysia, were determined against amphotericin B, fluconazole, voriconazole, itraconazole and caspofungin. The most common species were Candida albicans (71 isolates), Candida parapsilosis (42 isolates), Candida tropicalis (27 isolates) and Candida glabrata (12 isolates). The susceptibility tests were carried out using an E-test. The MIC breakpoints were based on Clinical Laboratory Standards Institute criteria. Amphotericin B and voriconazole showed the best activities against all the isolates tested, with MIC(90) values of ≤1 µg ml(-1) for all major species. Only one Candida lusitaniae isolate was resistant to amphotericin B, and all the isolates were susceptible to voriconazole. In total, six isolates were resistant to fluconazole, comprising two isolates of C. albicans, two of C. parapsilosis, one C. tropicalis and one C. glabrata, and all of these isolates showed cross-resistance to itraconazole. The MIC(90) of itraconazole was highest for C. glabrata and C. parapsilosis. Caspofungin was active against most of the isolates except for five isolates of C. parapsilosis. The MIC(90) of caspofungin against C. parapsilosis was 3 µg ml(-1). In conclusion, amphotericin B remains the most active antifungal agent against most Candida species except for C. lusitaniae. Voriconazole is the best alternative for fluconazole- or itraconizole-resistant isolates. Although five of the C. parapsilosis isolates showed in vitro resistance to caspofungin, more clinical correlation studies need to be carried out to confirm the significance of these findings. Currently, despite the increase in usage of antifungals in our hospitals, especially in the management of febrile neutropenia patients, the antifungal-resistance problem among clinically important Candida isolates in Kuala Lumpur Hospital is not yet worrying. However, continued antifungal-susceptibility surveillance needs to be conducted to monitor the antifungal-susceptibility trends of Candida species and other opportunistic fungal pathogens.
  12. Nami Y, Haghshenas B, Abdullah N, Barzegari A, Radiah D, Rosli R, et al.
    J Med Microbiol, 2015 Feb;64(Pt 2):137-46.
    PMID: 25525206 DOI: 10.1099/jmm.0.078923-0
    Genetic and environmental factors can affect the intestinal microbiome and microbial metabolome. Among these environmental factors, the consumption of antibiotics can significantly change the intestinal microbiome of individuals and consequently affect the corresponding metagenome. The term 'probiotics' is related to preventive medicine rather than therapeutic procedures and is, thus, considered the opposite of antibiotics. This review discusses the challenges between these opposing treatments in terms of the following points: (i) antibiotic resistance, the relationship between antibiotic consumption and microbiome diversity reduction, antibiotic effect on the metagenome, and disease associated with antibiotics; and (ii) probiotics as living drugs, probiotic effect on epigenetic alterations, and gut microbiome relevance to hygiene indulgence. The intestinal microbiome is more specific for individuals and may be affected by environmental alterations and the occurrence of diseases.
  13. Biglari S, Alfizah H, Ramliza R, Rahman MM
    J Med Microbiol, 2015 Jan;64(Pt 1):53-8.
    PMID: 25381148 DOI: 10.1099/jmm.0.082263-0
    Antimicrobial resistance in Acinetobacter baumannii is a growing public health concern and an important pathogen in nosocomial infections. We investigated the genes involved in resistance to carbapenems and cephalosporins in clinical A. baumannii isolates from a tertiary medical centre in Malaysia. A. baumannii was isolated from 167 clinical specimens and identified by sequencing of the 16S rRNA and rpoB genes. The MIC for imipenem, meropenem, ceftazidime and cefepime were determined by the E-test method. The presence of carbapenemase and cephalosporinase genes was investigated by PCR. The isolates were predominantly nonsusceptible to carbapenems and cephalosporins (>70 %) with high MIC values. ISAba1 was detected in all carbapenem-nonsusceptible A. baumannii harbouring the blaOXA-23-like gene. The presence of blaOXA-51-like and ISAba1 upstream of blaOXA-51 was not associated with nonsusceptibility to carbapenems. A. baumannii isolates harbouring ISAba1-blaADC (85.8 %) were significantly associated with nonsusceptibility to cephalosporins (P<0.0001). However, ISAba1-blaADC was not detected in a minority (<10 %) of the isolates which were nonsusceptible to cephalosporins. The acquired OXA-23 enzymes were responsible for nonsusceptibility to carbapenems in our clinical A. baumannii isolates and warrant continuous surveillance to prevent further dissemination of this antibiotic resistance gene. The presence of ISAba1 upstream of the blaADC was a determinant for cephalosporin resistance. However, the absence of this ISAba1-blaADC in some of the isolates may suggest other resistance mechanisms and need further investigation.
  14. Issa R, Abdul H, Hashim SH, Seradja VH, Shaili N', Hassan NAM
    J Med Microbiol, 2014 Oct;63(Pt 10):1284-1287.
    PMID: 25038139 DOI: 10.1099/jmm.0.072611-0
    A quantitative real-time PCR (qPCR) followed by high resolution melting (HRM) analysis was developed for the differentiation of Mycobacterium species. Rapid differentiation of Mycobacterium species is necessary for the effective diagnosis and management of tuberculosis. In this study, the 16S rRNA gene was tested as the target since this has been identified as a suitable target for the identification of mycobacteria species. During the temperature gradient and primer optimization process, the melting peak (Tm) analysis was determined at a concentration of 50 ng DNA template and 0.3, 0.4 and 0.5 µM primer. The qPCR assay for the detection of other mycobacterial species was done at the Tm and primer concentration of 62 °C and 0.4 µM, respectively. The HRM analysis generated cluster patterns that were specific and sensitive to distinguished small sequence differences of the Mycobacterium species. This study suggests that the 16S rRNA-based real-time PCR followed by HRM analysis produced unique cluster patterns for species of Mycobacterium and could differentiate the closely related mycobacteria species.
  15. Benacer D, Mohd Zain SN, Ahmed AA, Mohd Khalid MKN, Hartskeerl RA, Thong KL
    J Med Microbiol, 2016 Jun;65(6):574-577.
    PMID: 27058766 DOI: 10.1099/jmm.0.000262
  16. Underwood AP, Kaakoush NO, Sodhi N, Merif J, Seah Lee W, Riordan SM, et al.
    J Med Microbiol, 2016 Mar;65(3):219-226.
    PMID: 26698172 DOI: 10.1099/jmm.0.000216
    Given that Campylobacter jejuni is recognized as the most common cause of bacterial gastroenteritis worldwide, recent findings showing comparable levels of Campylobacter concisus in patients with gastroenteritis would suggest that this bacterium is clinically important. The prevalence and abundance of Campylobacter concisus in stool samples collected from patients with acute gastroenteritis was examined using quantitative real-time PCR. The associated virulence determinants exotoxin 9 and zonula occludens toxin DNA were detected for Campylobacter concisus-infected samples using real-time PCR. Campylobacter concisus was detected at high prevalence in patients with gastroenteritis (49.7 %), higher than that observed for Campylobacter jejuni (∼5 %). The levels of Campylobacter concisus were putatively classified into clinically relevant and potentially transient subgroups based on a threshold developed using Campylobacter jejuni levels, as the highly sensitive real-time PCR probably detected transient passage of the bacterium from the oral cavity. A total of 18 % of patients were found to have clinically relevant levels of Campylobacter concisus, a significant number of which also had high levels of one of the virulence determinants. Of these patients, 78 % were found to have no other gastrointestinal pathogen identified in the stool, which strongly suggests a role for Campylobacter concisus in the aetiology of gastroenteritis in these patients. These results emphasize the need for diagnostic laboratories to employ identification protocols for emerging Campylobacter species. Clinical follow-up in patients presenting with high levels of Campylobacter concisus in the intestinal tract is needed, given that it has been associated with more chronic sequelae.
  17. Peremalo T, Madhavan P, Hamzah S, Than L, Wong EH, Nasir MDM, et al.
    J Med Microbiol, 2019 Mar;68(3):346-354.
    PMID: 30724730 DOI: 10.1099/jmm.0.000940
    PURPOSE: Non-albicansCandida species have emerged as fungal pathogens that cause invasive infections, with many of these species displaying resistance to commonly used antifungal agents. This study was confined to studying the characteristics of clinical isolates of the C. rugosa complex and C. pararugosa species.

    METHODOLOGY: Seven isolates of the C. rugosa complex and one isolate of C. pararugosa were obtained from two tertiary referral hospitals in Malaysia. Their antifungal susceptibilities, biofilm, proteinase, phospholipase, esterase and haemolysin activities were characterized. Biofilms were quantified using crystal violet (CV) and tetrazolium (XTT) reduction assays at 1.5, 6, 18, 24, 48 and 72 h.Results/Key findings. The E-test antifungal tests showed that both species have elevated MICs compared to C. albicans and C. tropicalis. The highest biomass was observed in one of the C. rugosa isolates (0.237), followed by C. pararugosa (0.206) at 18 h of incubation. However, the highest bioactivity was observed in the C. rugosa ATCC 10571 strain at 24 h (0.075), followed by C. pararugosa at 48 h (0.048) and the same C. rugosa strain at 24 h (0.046), with P<0.05. All isolates exhibited high proteinase activity (+++) whereas six isolates showed very strong esterase activity (++++). All the isolates were alpha haemolytic producers. None of the isolates exhibited phospholipase activity.

    CONCLUSION: Elevated MICs were shown for the C. rugosa complex and C. pararugosa for commonly used antifungal drugs. Further studies to identify virulence genes involved in the pathogenesis and genes that confer reduced drug susceptibility in these species are proposed.

  18. Hishamshah M, Ahmad N, Mohd Ibrahim H, Nur Halim NA, Nawi S, Amran F
    J Med Microbiol, 2018 Jun;67(6):806-813.
    PMID: 29724267 DOI: 10.1099/jmm.0.000750
    Purpose. In this study, we aim to describe and compare the demographical, clinical and laboratory features of leptospirosis and dengue co-infections (LDCI) against single leptospirosis infections in Malaysia.Methodology. Data of patients admitted to various hospitals in Malaysia from 2011 to 2015 diagnosed with leptospirosis in our laboratory were obtained from their admission records. Co-infection with dengue was determined by collecting dengue serology results. Multivariate analysis and multiple logistic regression were used to differentiate features between single leptospirosis infection and confirmed LDCI.Results/Key findings. Only 602 (29.11 %) out of 2068 leptospira-positive patients were concurrently tested for dengue during their admission in which 44 (7.31 %) patients had positive non-structural protein 1 (confirmed LDCI) while 140 (23.26 %) were positive for dengue IgM (probable LDCI) with the highest number of cases recorded in high-density suburban districts. Myalgia and arthralgia were the only significant distinguishing clinical feature of LDCI while significant laboratory features were thrombocytopenia and high levels of alanine and aspartate transaminases. Only thrombocytopenia displayed a predictive value for LDCI from analysis of multiple logistic regression. Death occurred in 19 (3.16 %) patients in this dataset studied but only three (0.50 %) were attributed to LDCI.Conclusion. There is a considerable prevalence of LDCI in this country of which overlapping demographic, clinical and laboratory presentations pose diagnostic and therapeutic challenges. Efforts to raise awareness regarding LDCI, better access to diagnostic services and further prospective studies are warranted.
  19. Ng JML, Ngeow YF, Saw SH, Ng HF, Zin T
    J Med Microbiol, 2022 Dec;71(12).
    PMID: 36748567 DOI: 10.1099/jmm.0.001618
    Introduction Listeriosis, a foodborne infection caused by Listeria monocytogenes, could lead to febrile listerial gastroenteritis and a more invasive form which is often associated with a high mortality and hospitalisation rate. Gentamicin, used as an adjunct therapy with ampicillin, remains the treatment of choice for this life-threatening and invasive infection.Gap statement Nevertheless, there is little data on gentamicin resistance determinants in L. monocytogenes.Aim In this study, we selected and characterised B2b, a gentamicin-resistant mutant derived from L. monocytogenes ATCC 19115 to determine the target(s) of resistance in L. monocytogenes after exposure to gentamicin.Methodology Whole-genome sequencing was carried out to identify the mutation site(s) and possible mechanism(s) of resistance. The mutant was characterised using antimicrobial susceptibility testing and PCR. For biological verifications, complementation and allelic exchange mutagenesis were carried out.Results We found that the gentamicin resistance in B2b was caused by a 10 bp deletion in atpG2 which encodes a gamma subunit of the ATP synthase in L. monocytogenes. Using atpG2 PCR, various other mutations were identified in other gentamicin resistant mutants derived from ATCC 19115. In addition, the mutation from B2b, when introduced into L. ivanovii, also caused gentamicin resistance in this Listeria species.Conclusion Hence, atpG2 mutations appear to be important determinants of gentamicin resistance not only in L. monocytogenes but possibly also in other Listeria species.
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