无乳链球菌致病性研究进展

doi:10.16431/j.cnki.1671-7236.2024.03.040

摘要/Abstract

摘要： 无乳链球菌(Streptococcus agalactiae)是一种分布广泛的人兽共患性致病菌,通过形成生物膜可在奶牛乳腺中黏附、定植并长期存活,同时增强对宿主免疫防御的抵抗,引起奶牛乳腺感染而发生亚临床型乳腺炎,是全球范围内引起奶牛乳腺炎的最常见病原体之一,给奶牛养殖业和奶业造成巨大的经济损失。此外,其还可感染骆驼与罗非鱼等多种动物,造成严重的动物福利恶化,且存在人与动物间接传播的可能。无乳链球菌是一种革兰阳性机会致病菌,可在健康成年人的胃肠道及泌尿生殖道中无症状定植,感染新生儿可导致危及生命的败血症及脑膜炎的发生,并常伴有严重的神经系统后遗症。近年来,成人无乳链球菌感染的发病率呈上升趋势,尤其是对孕妇、老年人及免疫力低下的人群具有更高的易感率,可引起皮肤和软组织感染以及更为严重的败血症、脑膜炎和心内膜炎等疾病的发生。尽管使用抗生素治疗可部分缓解症状,但耐药菌株的出现和传播使得抗生素的治疗效果逐步下降,对无乳链球菌感染的控制愈发困难。笔者就无乳链球菌对多种动物及不同人群的致病性进行综述,以期为无乳链球菌的综合防控提供参考。

关键词: 无乳链球菌; 感染; 致病性

Abstract: Streptococcus agalactiae (S. agalactiae) is a widely distributed zoonotic pathogen.It can survive indefinitely in mammary glands of cows,by forming a biofilm that allows them to adhere and persist in the mammary gland,concomitantly enhancing resistance to host immune defense.S. agalactiae causes sub-clinical mastitis,which is one of the most common pathogens leading to mastitis in dairy herds worldwide,which causes huge economic losses to dairy industry.In addition,S. agalactiae can also infect various animals such as Camelus and Oreochromis niloticus,causing serious deterioration in animal welfare,and there is a possibility of indirect transmission between humans and animals. S. agalactiae is a Gram positive opportunistic pathogen that can asymptotically colonize the gastrointestinal and urogenital tracts of healthy adults.Infection of newborns can lead to life-threatening sepsis and meningitis,often accompanied by severe neurological sequelae.In recent years,the incidence rate of adult S. agalactiae infection is on the rise,especially for pregnant women,the elderly and people with low immunity.It can cause skin and soft tissue infections and more serious septicemia,meningitis,endocarditis and other diseases.Although the symptoms can be partially alleviated by treatment with antibiotics,the emergence and spread of drug-resistant strains have gradually reduced the effectiveness of treatment,and the control of S. agalactiae infection becomes more and more difficult.In this paper,the author summarized the pathogenicity of S. agalactiae to humans and different animals,in order to provide reference for the prevention and control of S. agalactiae.

Key words: Streptococcus agalactiae; infection; pathogenicity

中图分类号:

S852.61

陈晶, 马骏, 范钊玮, 刘慧婷, 崔玉东. 无乳链球菌致病性研究进展[J]. 中国畜牧兽医, 2024, 51(3): 1277-1285.

CHEN Jing, MA Jun, FAN Zhaowei, LIU Huiting, CUI Yudong. Research Progress on Pathogenicity of Streptococcus agalactiae[J]. China Animal Husbandry and Veterinary Medicine, 2024, 51(3): 1277-1285.

参考文献

[1] KONG F, GOWAN S, MARTIN D, et al.Serotype identification of group B streptococci by PCR and sequencing[J].Journal of Clinical Microbiology, 2002, 40(1):216-226.
[2] KONG F, MA L, GILBERT G L.Simultaneous detection and serotype identification of Streptococcus agalactiae using multiplex PCR and reverse line blot hybridization[J].Journal of Medical Microbiology, 2005, 54(12):1133-1138.
[3] SLOTVED H C, KONG F, LAMBERTSEN L, et al.Serotype Ⅸ, a proposed new Streptococcus agalactiae serotype[J].Journal of Clinical Microbiology, 2007, 45(9):2929-2936.
[4] CARVALHO-CASTRO G A, SILVA J R, PAIVA L V, et al.Molecular epidemiology of Streptococcus agalactiae isolated from mastitis in Brazilian dairy herds[J].Brazilian Journal of Microbiology, 2017, 48(3):551-559.
[5] PANG M, SUN L, HE T, et al.Molecular and virulence characterization of highly prevalent Streptococcus agalactiae circulated in bovine dairy herds[J].Veterinary Research, 2017, 48(1):65.
[6] MORALES-UBALDO A L, RIVERO-PEREZ N, VALLADARES-CARRANZA B, et al.Bovine mastitis, a worldwide impact disease:Prevalence, antimicrobial resistance, and viable alternative approaches[J].Veterinary and Animal Science, 2023, 21:100306.
[7] TAVARES T, PINHO L, BONIFACIO A E.Group B streptococcal neonatal meningitis[J].Clinical Microbiology Reviews, 2022, 35(2):e7921.
[8] DONG Y, BASMACI R, TITOMANLIO L, et al.Neonatal sepsis:Within and beyond China[J].Chinese Medical Journal, 2020, 133(18):2219-2228.
[9] DAVIES H G, CARRERAS-ABAD C, LE DOARE K, et al.Group B Streptococcus:Trials and tribulations[J].Pediatric Infectious Disease Journal, 2019, 38(6S Suppl 1):S72-S76.
[10] FRANCOIS WATKINS L K, MCGEE L, SCHRAG S J, et al.Epidemiology of invasive group B streptococcal infections among nonpregnant adults in the United States, 2008-2016[J].JAMA Internal Medicine, 2019, 179(4):479-488.
[11] PITTS S I, MARUTHUR N M, LANGLEY G E, et al.Obesity, diabetes, and the risk of invasive group B streptococcal disease in nonpregnant adults in the United States[J].Open Forum Infectious Diseases, 2018, 5(6):y30.
[12] SEALE A C, BIANCHI-JASSIR F, RUSSELL N J, et al.Estimates of the burden of group B streptococcal disease worldwide for pregnant women, stillbirths, and children[J].Clinical Infectious Diseases, 2017, 65(Suppl 2):S200-S219.
[13] LI C, SAPUGAHAWATTE D N, YANG Y, et al.Multidrug-resistant Streptococcus agalactiae strains found in human and fish with high penicillin and cefotaxime non-susceptibilities[J].Microorganisms, 2020, 8(7):1055.
[14] 范雪,邵伟,赵艳坤,等.无乳链球菌毒力基因与耐药性的相关性研究进展[J].中国畜牧兽医, 2021, 48(1):375-384. FAN X, SHAO W, ZHAO Y K, et al.Research progress on the correlation between virulence genes and drug resistance of Streptococcus agalactiae[J].China Animal Husbandry&Veterinary Medicine, 2021, 48(1):375-384.(in Chinese)
[15] NOCARD E, MOLLAREAU A.Sur une mammite contagieuse des vaches laitières[J].Annales de l'Institut Pasteur, 1887, 1:109-126.
[16] ROSINI R, MARGARIT I.Biofilm formation by Streptococcus agalactiae:Influence of environmental conditions and implicated virulence factors[J].Frontiers in Cellular and Infection Microbiology, 2015, 5:6.
[17] KABELITZ T, AUBRY E, VAN VORST K, et al.The role of Streptococcus spp.in bovine mastitis[J].Microorganisms, 2021, 9(7):1497.
[18] CHENG W N, HAN S G.Bovine mastitis:Risk factors, therapeutic strategies, and alternative treatments-A review[J].Asian-Australasian Journal of Animal Sciences, 2020, 33(11):1699-1713.
[19] MWEU M M, NIELSEN S S, HALASA T, et al.Annual incidence, prevalence and transmission characteristics of Streptococcus agalactiae in Danish dairy herds[J].Preventive Veterinary Medicine, 2012, 106(3-4):244-250.
[20] RAMIREZ N F, KEEFE G, DOHOO I, et al.Herd-and cow-level risk factors associated with subclinical mastitis in dairy farms from the high plains of the northern Antioquia, Colombia[J].Journal of Dairy Science, 2014, 97(7):4141-4150.
[21] EDELSTEIN R M, PEGRAM R G.Contagious skin necrosis of Somali camels associated with Streptococcus agalactiae[J].Tropical Animal Health and Production, 1974, 6(4):255-256.
[22] YOUNAN M, ALI Z, BORNSTEIN S, et al.Application of the California mastitis test in intramammary Streptococcus agalactiae and Staphylococcus aureus infections of camels (Camelus dromedarius) in Kenya[J].Preventive Veterinary Medicine, 2001, 51(3-4):307-316.
[23] YOUNAN M, BORNSTEIN S.Lancefield group B and C streptococci in East African camels (Camelus dromedarius)[J].Veterinary Record, 2007, 160(10):330-335.
[24] TAVELLA A, BETTINI A, COCCHI M, et al.Isolation of Streptococcus agalactiae in a female llama (Lama glama) in South Tyrol (Italy)[J].BMC Veterinary Research, 2018, 14(1):343.
[25] SELIGSOHN D, CRESTANI C, GITAHI N, et al.Investigation of extramammary sources of group B Streptococcus reveals its unusual ecology and epidemiology in camels[J].PLoS One, 2021, 16(12):e252973.
[26] KORNBLATT A N, ADAMS R L, BARTHOLD S W, et al.Canine neonatal deaths associated with group B streptococcal septicemia[J].Javma-Journal of the American Veterinary Medical Association, 1983, 183(6):700-701.
[27] MESSIER S, DAMINET S, LEMARCHAND T.Streptococcus agalactiae endocarditis with embolization in a dog[J].Canadian Veterinary Journal-Revue Veterinaire Canadienne, 1995, 36(11):703-704.
[28] FORTIN M, HIGGINS R.Mixed infection associated with a group B Streptococcus in a dog[J].Canadian Veterinary Journal-Revue Veterinaire Canadienne, 2001, 42(9):730.
[29] YILDIRIM A O, LAMMLER C, WEISS R, et al.Pheno-and genotypic properties of streptococci of serological group B of canine and feline origin[J].FEMS Microbiology Letters, 2002, 212(2):187-192.
[30] KEET D F, GROBLER D G, RAATH J P, et al.Ulcerative pododermatitis in free-ranging African elephant (Loxodonta africana) in the Kruger National Park[J].Onderstepoort Journal of Veterinary Research, 1997, 64(1):25-32.
[31] ZAPPULLI V, MAZZARIOL S, CAVICCHIOLI L, et al.Fatal necrotizing fasciitis and myositis in a captive common bottlenose dolphin (Tursiops truncatus) associated with Streptococcus agalactiae[J].Journal of Veterinary Diagnostic Investigation, 2005, 17(6):617-622.
[32] EVANS J J, PASNIK D J, KLESIUS P H, et al.First report of Streptococcus agalactiae and Lactococcus garvieae from a wild bottlenose dolphin (Tursiops truncatus)[J].Journal of Wildlife Diseases, 2006, 42(3):561-569.
[33] DELANNOY C M, CRUMLISH M, FONTAINE M C, et al.Human Streptococcus agalactiae strains in aquatic mammals and fish[J].BMC Microbiology, 2013, 13:41.
[34] HETZEL U, KONIG A, YILDIRIM A O, et al.Septicaemia in emerald monitors (Varanus prasinus Schlegel 1839) caused by Streptococcus agalactiae acquired from mice[J].Veterinary Microbiology, 2003, 95(4):283-293.
[35] BISHOP E J, SHILTON C, BENEDICT S, et al.Necrotizing fasciitis in captive juvenile Crocodylus porosus caused by Streptococcus agalactiae:An outbreak and review of the animal and human literature[J].Epidemiology and Infection, 2007, 135(8):1248-1255.
[36] AMBORSKI R L, SNIDER T R, THUNE R L, et al.A non-hemolytic, group B Streptococcus infection of cultured bullfrogs, Rana catesbeiana, in Brazil[J].Journal of Wildlife Diseases, 1983, 19(3):180-184.
[37] MORICK D, DAVIDOVICH N, BIGAL E, et al.Fatal infection in a wild sandbar shark (Carcharhinus plumbeus), caused by Streptococcus agalactiae, type Ⅰa-ST7[J].Animals, 2020, 10(2):284.
[38] 姚学良,徐晓丽,李贺密,等.红尾皇冠鱼(Aequidens rivulatus)病原无乳链球菌的分离、鉴定与特性分析[J].渔业科学进展, 2015, 36(2):106-112. YAO X L, XU X L, LI H M, et al.Biological characteristics of pathogenic Streptococcus agalactiae isolated from Aequidens rivulatus[J].Progress in Fishery Sciences, 2015, 36(2):106-112.(in Chinese)
[39] ELDAR A, BEJERANO Y, LIVOFF A, et al.Experimental streptococcal meningo-encephalitis in cultured fish[J].Veterinary Microbiology, 1995, 43(1):33-40.
[40] 陈怀君,郭长明,朱善元,等.海南罗非鱼源无乳链球菌的分离鉴定及生物学特性研究[J].中国畜牧兽医, 2021, 48(8):3058-3068. CHEN H J, GUO C M, ZHU S Y, et al.Isolation, identification and biological characteristics of Streptococcus agalactiae from tilapia in Hainan[J]. China Animal Husbandry&Veterinary Medicine, 2021, 48(8):3058-3068.(in Chinese)
[41] 袁橙,陈怀君,袁圣,等.福建省漳州市罗非鱼无乳链球菌分离鉴定及毒力基因和耐药性研究[J].中国畜牧兽医, 2022, 49(9):3655-3664. YUAN C, CHEN H J, YUAN S, et al.Isolation, identification and study on virulence gene and drug resistance of Streptococcus agalactiae from tilapia in Zhangzhou city, Fujian province[J]. China Animal Husbandry&Veterinary Medicine, 2022, 49(9):3655-3664.(in Chinese)
[42] LAITH A A, AMBAK M A, HASSAN M, et al.Molecular identification and histopathological study of natural Streptococcus agalactiae infection in hybrid tilapia (Oreochromis niloticus)[J].Veterinary World, 2017, 10(1):101-111.
[43] CHEN S L.Genomic insights into the distribution and evolution of group B Streptococcus[J].Frontiers in Microbiology, 2019, 10:1447.
[44] MANNING S D, SPRINGMAN A C, MILLION A D, et al.Association of group B Streptococcus colonization and bovine exposure:A prospective cross-sectional cohort study[J].PLoS One, 2010, 5(1):e8795.
[45] CHEN M, WANG R, LUO F G, et al.Streptococcus agalactiae isolates of serotypesⅠa, Ⅲ and Ⅴ from human and cow are able to infect tilapia[J].Veterinary Microbiology, 2015, 180(1-2):129-135.
[46] BARKHAM T, ZADOKS R N, AZMAI M, et al.One hypervirulent clone, sequence type 283, accounts for a large proportion of invasive Streptococcus agalactiae isolated from humans and diseased tilapia in Southeast Asia[J].PLoS Neglected Tropical Diseases, 2019, 13(6):e7421.
[47] LANCEFIELD R C, HARE R.The serological differentiation of pathogenic and non-pathogenic strains of hemolytic streptococci from parturient women[J].Journal of Experimental Medicine, 1935, 61(3):335-349.
[48] FRY R M.Prevention and control of puerperal sepsis:Bacteriological aspects[J].British Medical Journal, 1938, 2(4049):340-342.
[49] DEUTSCHER M, LEWIS M, ZELL E R, et al.Incidence and severity of invasive Streptococcus pneumoniae, group A Streptococcus, and group B Streptococcus infections among pregnant and postpartum women[J].Clinical Infectious Diseases, 2011, 53(2):114-123.
[50] KESSOUS R, WEINTRAUB A Y, SERGIENKO R, et al.Bacteruria with group-B Streptococcus:Is it a risk factor for adverse pregnancy outcomes?[J].Journal of Maternal-Fetal&Neonatal Medicine, 2012, 25(10):1983-1986.
[51] NAN C, DANGOR Z, CUTLAND C L, et al.Maternal group B Streptococcus-related stillbirth:A systematic review[J].BJOG-An International Journal of Obstetrics and Gynaecology, 2015, 122(11):1437-1445.
[52] SEALE A C, BLENCOWE H, BIANCHI-JASSIR F, et al.Stillbirth with group B Streptococcus disease worldwide:Systematic review and Meta-analyses[J].Clinical Infectious Diseases, 2017, 65(Suppl 2):S125-S132.
[53] RUSSELL N J, SEALE A C, O'DRISCOLL M, et al.Maternal colonization with group B Streptococcus and serotype distribution worldwide:Systematic review and Meta-analyses[J].Clinical Infectious Diseases, 2017, 65(Suppl 2):S100-S111.
[54] HUANG J, LIN X Z, ZHU Y, et al.Epidemiology of group B streptococcal infection in pregnant women and diseased infants in mainland China[J].Pediatrics and Neonatology, 2019, 60(5):487-495.
[55] LE DOARE K, HEATH P T.An overview of global GBS epidemiology[J].Vaccine, 2013, 31(Suppl 4):S7-S12.
[56] CUTLAND C L, MADHI S A, ZELL E R, et al.Chlorhexidine maternal-vaginal and neonate body wipes in sepsis and vertical transmission of pathogenic bacteria in South Africa:A randomised, controlled trial[J].Lancet, 2009, 374(9705):1909-1916.
[57] MADRID L, SEALE A C, KOHLI-LYNCH M, et al.Infant group B streptococcal disease incidence and serotypes worldwide:Systematic review and Meta-analyses[J].Clinical Infectious Diseases, 2017, 65(S2):160-172.
[58] O'SULLIVAN C P, LAMAGNI T, PATEL D, et al.Group B streptococcal disease in UK and Irish infants younger than 90 days, 2014-15:A prospective surveillance study[J].Lancet Infectious Diseases, 2019, 19(1):83-90.
[59] LAWN J E, BIANCHI-JASSIR F, RUSSELL N J, et al.Group B streptococcal disease worldwide for pregnant women, stillbirths, and children:Why, what, and how to undertake estimates?[J].Clinical Infectious Diseases, 2017, 65(Suppl 2):S89-S99.
[60] ZIMMERMANN P, GWEE A, CURTIS N.The controversial role of breast milk in GBS late-onset disease[J].Journal of Infection, 2017, 74(Suppl 1):S34-S40.
[61] BERARDI A, ROSSI C, LUGLI L, et al.Group B Streptococcus late-onset disease:2003-2010[J].Pediatrics, 2013, 131(2):e361-e368.
[62] KOHLI-LYNCH M, RUSSELL N J, SEALE A C, et al.Neurodevelopmental impairment in children after group B streptococcal disease worldwide:Systematic review and Meta-analyses[J].Clinical Infectious Diseases, 2017, 65(Suppl 2):S190-S199.
[63] SENDI P, JOHANSSON L, NORRBY-TEGLUND A.Invasive group B streptococcal disease in non-pregnant adults:A review with emphasis on skin and soft-tissue infections[J].Infection, 2008, 36(2):100-111.
[64] FARLEY M M.Group B streptococcal disease in nonpregnant adults[J].Clinical Infectious Diseases, 2001, 33(4):556-561.
[65] EDWARDS M S, BAKER C J.Group B streptococcal infections in elderly adults[J].Clinical Infectious Diseases, 2005, 41(6):839-847.
[66] BALLARD M S, SCHONHEYDER H C, KNUDSEN J D, et al.The changing epidemiology of group B Streptococcus bloodstream infection:A multi-national population-based assessment[J].Infectious Diseases, 2016, 48(5):386-391.
[67] SKOFF T H, FARLEY M M, PETIT S, et al.Increasing burden of invasive group B streptococcal disease in nonpregnant adults, 1990-2007[J].Clinical Infectious Diseases, 2009, 49(1):85-92.
[68] RATO M G, BEXIGA R, FLORINDO C, et al.Antimicrobial resistance and molecular epidemiology of streptococci from bovine mastitis[J].Veterinary Microbiology, 2013, 161(3-4):286-294.
[69] REYES J, CHAFFER M, SANCHEZ J, et al.Evaluation of the efficacy of intramuscular versus intramammary treatment of subclinical Streptococcus agalactiae mastitis in dairy cows in Colombia[J].Journal of Dairy Science, 2015, 98(8):5294-5303.
[70] HERNANDEZ L, BOTTINI E, CADONA J, et al.Multidrug resistance and molecular characterization of Streptococcus agalactiae isolates from dairy cattle with mastitis[J].Frontiers in Cellular and Infection Microbiology, 2021, 11:647324.
[71] KEEFE G P.Streptococcus agalactiae mastitis:A review[J].Canadian Veterinary Journal-Revue Veterinaire Canadienne, 1997, 38(7):429-437.
[72] KEEFE G.Update on control of Staphylococcus aureus and Streptococcus agalactiae for management of mastitis[J].Veterinary Clinics of North America-Food Animal Practice, 2012, 28(2):203-216.
[73] COBO-ANGEL C, JARAMILLO-JARAMILLO A S, LASSO-ROJAS L M, et al.Streptococcus agalactiae is not always an obligate intramammary pathogen:Molecular epidemiology of GBS from milk, feces and environment in Colombian dairy herds[J].PLoS One, 2018, 13(12):e208990.
[74] JORGENSEN H J, NORDSTOGA A B, SVILAND S, et al.Streptococcus agalactiae in the environment of bovine dairy herds--Rewriting the textbooks?[J].Veterinary Microbiology, 2016, 184:64-72.
[75] 彭周杰,包蕾.产时抗菌药物预防治疗B族链球菌感染对早发型新生儿败血症发生率及病原菌分布的影响[J].中国当代儿科杂志, 2022, 24(1):49-53. PENG Z J, BAO L.Effect of intrapartum antibiotic prophylaxis of group B Streptococcus infection on the incidence and bacteriological profile of early-onset neonatal sepsis[J].Chinese Journal of Contemporary Pediatrics, 2022, 24(1):49-53.(in Chinese)
[76] CORVAGLIA L, TONTI G, MARTINI S, et al.Influence of intrapartum antibiotic prophylaxis for group B Streptococcus on gut microbiota in the first month of life[J].Journal of Pediatric Gastroenterology and Nutrition, 2016, 62(2):304-308.
[77] SEEDAT F, STINTON C, PATTERSON J, et al.Adverse events in women and children who have received intrapartum antibiotic prophylaxis treatment:A systematic review[J].BMC Pregnancy and Childbirth, 2017, 17(1):247.
[78] SEKI T, KIMURA K, REID M E, et al.High isolation rate of MDR group B streptococci with reduced penicillin susceptibility in Japan[J].Journal of Antimicrobial Chemotherapy, 2015, 70(10):2725-2728.
[79] CAMPO C H, MARTINEZ M F, OTERO J C, et al.Vagino-rectal colonization prevalence by Streptococcus agalactiae and its susceptibility profile in pregnant women attending a third-level hospital[J].Biomedica, 2019, 39(4):689-698.
[80] GHAMARI M, JABALAMELI F, EMANEINI M, et al.Multiple-locus variable-number tandem repeat analysis for genotyping of erythromycin-resistant group B streptococci in Iran[J].New Microbes and New Infections, 2022, 45:100957.
[81] CHENG Z, QU P, KE P, et al.Antibiotic resistance and molecular epidemiological characteristics of Streptococcus agalactiae isolated from pregnant women in Guangzhou, South China[J].Canadian Journal of Infectious Diseases&Medical Microbiology, 2020, 2020:1368942.
[82] GUO Y, DENG X, LIANG Y, et al.The draft genomes and investigation of serotype distribution, antimicrobial resistance of group B Streptococcus strains isolated from urine in Suzhou, China[J].Annals of Clinical Microbiology and Antimicrobials, 2018, 17(1):28.
[83] HAYS C, LOUIS M, PLAINVERT C, et al.Changing epidemiology of group B Streptococcus susceptibility to fluoroquinolones and aminoglycosides in France[J].Antimicrobial Agents and Chemotherapy, 2016, 60(12):7424-7430.
[84] ZHENG J X, CHEN Z, XU Z C, et al. In vitro evaluation of the antibacterial activities of radezolid and linezolid for Streptococcus agalactiae[J].Microbial Pathogenesis, 2019, 139:103866.
[85] GUO H, FU M, PENG Q, et al.Antimicrobial resistance and molecular characterization of Streptococcus agalactiae from pregnant women in Southern China[J].Journal of Infection in Developing Countries, 2019, 13(9):802-809.
[86] WANG P, TONG J J, MA X H, et al.Serotypes, antibiotic susceptibilities, and multi-locus sequence type profiles of Streptococcus agalactiae isolates circulating in Beijing, China[J].PLoS One, 2015, 10(3):e120035.
[87] PICCINELLI G, GARGIULO F, CORBELLINI S, et al.Emergence of the first levofloxacin-resistant strains of Streptococcus agalactiae isolated in Italy[J].Antimicrobial Agents and Chemotherapy, 2015, 59(4):2466-2469.