title: An investigation into the stability and sterility of citric acid solutions used for cough reflex testing.
abstract: Citric acid is used in cough reflex testing in clinical and research settings to assess reflexive cough in patients at risk of swallowing disorders. To address a lack of knowledge in this area, this study investigated the stability and sterility of citric acid solutions. Triplicate solutions of citric acid (0.8 M) in isotonic saline were stored at 4 ± 2 °C for up to 28 days and analysed by high-performance liquid chromatography. Microbiological sterility of freshly prepared samples and bulk samples previously used for 2 weeks within the hospital was determined using a pour plate technique. Microbial survival in citric acid was determined by inoculating Staphylococcus aureus, Escherichia coli, or Candida albicans into citric acid solution and monitoring the number of colony-forming units/mL over 40 min. Citric acid solutions remained stable at 4 °C for 28 days (98.4 ± 1.8 % remained). The freshly prepared and clinical samples tested were sterile. However, viability studies revealed that citric acid solution allows for the survival of C. albicans but not for S. aureus or E. coli. The microbial survival study showed that citric acid kills S. aureus and E. coli but has no marked effect on C. albicans after 40 min. Citric acid samples at 0.8 M remained stable over the 4-week testing period, with viable microbial cells absent from samples tested. However, C. albicans has the ability to survive in citric acid solution if inadvertently introduced in practice. For this reason, in clinical and research practice it is suggested to use single-use aliquots prepared aseptically which can be stored for up to 28 days at 4 °C.
authors.affiliation: School of Pharmacy, Faculty of Medical and Health Sciences, University of Auckland, Private Bag, Auckland, 92019, New Zealand.
authors.forename: James R
authors.initials: JR
authors.lastname: Falconer
authors.forename: Zimei
authors.initials: Z
authors.lastname: Wu
authors.forename: Hugo
authors.initials: H
authors.lastname: Lau
authors.forename: Joanna
authors.initials: J
authors.lastname: Suen
authors.forename: Lucy
authors.initials: L
authors.lastname: Wang
authors.forename: Sarah
authors.initials: S
authors.lastname: Pottinger
authors.forename: Elaine
authors.initials: E
authors.lastname: Lee
authors.forename: Nawar
authors.initials: N
authors.lastname: Alazawi
authors.forename: Molly
authors.initials: M
authors.lastname: Kallesen
authors.forename: Derryn A
authors.initials: DA
authors.lastname: Gargiulo
authors.forename: Simon
authors.initials: S
authors.lastname: Swift
authors.forename: Darren
authors.initials: D
authors.lastname: Svirskis
mesh_terms: D058491:Bacterial Load; D002176:Candida albicans / Q000254:growth & development; D002851:Chromatography, High Pressure Liquid; D019343:Citric Acid / Q000592:standards*; D003080:Cold Temperature; D015169:Colony Count, Microbial; D003371:Cough / Q000503:physiopathology*; D003680:Deglutition Disorders / Q000503:physiopathology; D004340:Drug Contamination; D004355:Drug Stability; D004926:Escherichia coli / Q000254:growth & development; D006801:Humans; D007552:Isotonic Solutions; D050296:Microbial Viability; D012018:Reflex / Q000502:physiology; D019141:Respiratory System Agents / Q000592:standards*; D012965:Sodium Chloride; D013211:Staphylococcus aureus / Q000254:growth & development; D013997:Time Factors
chemical_list: D007552:Isotonic Solutions; D019141:Respiratory System Agents; D019343:Citric Acid; D012965:Sodium Chloride