Department of Microbiology, Dr ALM Post Graduate Institute of Basic Medical Sciences, University of Madras, Taramani, Chennai 600 113, Tamil Nadu, India.
Central Research Laboratory, Sri Manakula Vinayagar Medical College and Hospital, Madagadipet, Pondicherry 605 107, India.
J Med Microbiol. 2014 Jul;63(Pt 7):962-967. doi: 10.1099/jmm.0.068486-0. Epub 2014 May 27.
Enteric fever is a major public health problem in developing countries. Due to the problem of resistance to first-line drugs and fluoroquinolone, cephalosporins are currently used for treatment of enteric fever. Cephalosporin resistance in Salmonella spp. is mainly due to production of extended-spectrum β-lactamases (ESBLs). The majority of ESBLs in Salmonella are derivatives of the TEM and SHV β-lactamase families. The objectives of this study were to detect antibiotic susceptibility patterns, ESBL production and TEM-, SHV- and CTX-M-encoding genes (blaTEM, blaSHV and blaCTX-M) among clinical isolates of Salmonella spp. A total of 134 Salmonella isolates [Salmonella Typhi (n = 101), Salmonella Paratyphi A (n = 31), Salmonella Paratyphi B (n = 1) and Salmonella Typhimurium (n = 1)] were included in this study. Multidrug resistance was seen in 5/134 (3.73%) isolates, all of which belonged to serotype S. Typhi. A better susceptibility profile was observed for first-line drugs (ampicillin, chloramphenicol, co-trimoxazole and tetracycline) and cephalosporins (cefotaxime, ceftazidime, ceftriaxone, cefixime and cefepime). However, 131 (97.76%) of the 134 isolates were resistant to nalidixic acid and one (0.75%) was resistant to ciprofloxacin. TEM-1-type β-lactamase (blaTEM-1) was detected in six (4.47%) of the 134 isolates, which belonged to the serotype S. Typhi. All six TEM-positive isolates were negative for the blaSHV gene and none of the isolates was positive for the blaCTX-M gene. The presence of the blaTEM gene encoding TEM-1 β-lactamase is believed to confer resistance only to penicillins and early cephalosporins; however, the resistance spectrum of TEM-1 descendants may extend to second-, third- and fourth-generation cephalosporins. The ESBLs derived from TEM-1 differ from their progenitors by as few as 1 aa, and have the ability to hydrolyse third-generation cephalosporins. Therefore, appropriate selection and rotation of antibiotics as well as continuous monitoring of antibiotic susceptibility profiles could help to control the emergence and spread of resistant strains.
肠热病是发展中国家的一个主要公共卫生问题。由于一线药物和氟喹诺酮类药物的耐药问题，目前头孢菌素类药物被用于治疗肠热病。沙门氏菌属中产超广谱β-内酰胺酶（ESBLs）是导致头孢菌素类药物耐药的主要原因。沙门氏菌属中的大多数 ESBL 是 TEM 和 SHVβ-内酰胺酶家族的衍生物。本研究的目的是检测临床分离的沙门氏菌属的抗生素敏感性模式、ESBL 产生以及 TEM、SHV 和 CTX-M 编码基因（blaTEM、blaSHV 和 blaCTX-M）。本研究共纳入 134 株沙门氏菌分离株[伤寒沙门氏菌（n=101）、甲型副伤寒沙门氏菌（n=31）、乙型副伤寒沙门氏菌（n=1）和鼠伤寒沙门氏菌（n=1）]。5/134（3.73%）株分离物表现出多药耐药性，均属于血清型 S. Typhi。一线药物（氨苄西林、氯霉素、复方磺胺甲噁唑和四环素）和头孢菌素类药物（头孢噻肟、头孢他啶、头孢曲松、头孢克肟和头孢吡肟）的药敏谱较好。然而，134 株分离物中有 131 株（97.76%）对萘啶酸耐药，1 株（0.75%）对环丙沙星耐药。在 134 株分离物中检测到 6 株（4.47%） TEM-1 型β-内酰胺酶（blaTEM-1），均属于血清型 S. Typhi。6 株 TEM 阳性分离株均未检测到 blaSHV 基因，且无分离株 blaCTX-M 基因阳性。编码 TEM-1β-内酰胺酶的 blaTEM 基因的存在仅被认为对抗生素青霉素和早期头孢菌素类药物具有耐药性；然而，TEM-1 衍生物的耐药谱可能扩展至第二代、第三代和第四代头孢菌素类药物。TEM-1 衍生的 ESBLs 与其前体仅相差 1 个 aa，具有水解第三代头孢菌素类药物的能力。因此，适当选择和轮换抗生素以及持续监测抗生素敏感性谱有助于控制耐药菌株的出现和传播。
