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The Microbiology Laboratory
Published in Keith Struthers, Clinical Microbiology, 2017
The β-haemolytic streptococci are further subdivided on the basis of their cell wall polysaccharide. This ‘Lancefield grouping’ relies on the extraction of the polysaccharide by enzyme or acid. The procedure used is outlined in Figure 5.20. The soluble extract is mixed with latex beads coated with group-specific antibodies; an agglutination reaction identifies the group the isolate belongs to. There are six major groups of β-haemolytic streptococci, termed A, B, C, D, F and G, and within these there are a number of important pathogens, including group A streptococcus, Streptococcus pyogenes, group B streptococcus, Streptococcus agalactiae and group C streptococcus, Streptococcus dysgalactiae.
Streptococcus
Published in Dongyou Liu, Laboratory Models for Foodborne Infections, 2017
Another classification scheme proposed by Sherman in 1937 incorporating Lancefield grouping and other criteria divides streptococci into four groups: pyogenic, viridans, lactic, and enterococci. The pyogenic division comprises β-hemolytic strains of Lancefield groups A, B, C, E, F, and G. The viridans division consists of non-β-hemolytic streptococci that are not tolerant to high-pH growth conditions and salt and do not grow at 10°C. The lactic division includes strains of dairy origin, which are nonhuman pathogenic. This group differs from the pyogenic group by being non-β-hemolytic, growing at 10°C but not at 45°C, and failure to grow in broth with 6.5% NaCl. The lactic division was reclassified as the Lactococcus genus in the mid-1980s. The enterococci division includes Lancefield group D strains, which are now known as the genus Enterococcus. Members of this genus have the capacity to grow in broths at high pH (9.6), high salt concentrations (6.5% NaCl), and a wide temperature range (10°C–45°C), with some enterococci demonstrating β-hemolytic property (see Chapter 10) [3].
Screening for group B Streptococcus (GBS) at labour onset using PCR: accuracy and potential impact – a pilot study
Published in Journal of Obstetrics and Gynaecology, 2018
Sandhya Ramesh Babu, Rachel McDermott, Irum Farooq, David Le Blanc, Wendy Ferguson, Naomi McCallion, Richard Drew, Maeve Eogan
A convenience sample of 160 patients was recruited into the study. Sequential low vaginal and rectal swabs were taken using the Cepheid Coban Sample Collection Device, which are recto-vaginal two pronged swabs and sent to the laboratory for processing. Samples were stored in the fridge until the next working day and then processed. For the GeneXpert PCR test, the manufacturer’s guidance was followed. Briefly, the GBS cartridge was removed from the package and one of the swabs was inserted into the GeneXpert GBS cartridge chamber S, by snapping the shaft at the score mark. The cartridge was then inserted into the analyser and the results were recorded from the attached computer screen. The second prong of the swab was inoculated into a Todd Hewitt Broth and incubated overnight in air at 35 ± 2 °C. The next day an aliquot of broth was subbed on to a GBS chromogenic agar plate and streaked so as to have individual colonies. This plate was then incubated in air for 18–24 h and examined the following day. Suspect colonies are pink and were identified by Lancefield grouping. Those colonies that agglutinated with the B reagent were considered as GBS isolates and their identification was confirmed on the Vitek-2 system (BioMerieux, Marcy l'Etoile, France). Scientists processing the PCR swabs were not blinded to the culture results and vice versa. These swabs were analysed with a study number only, and the results were not released to attending clinicians and were not linked with any other laboratory tests the patient may have undergone during labour, delivery or postpartum period.
Incidence of invasive Group B Streptococcus (iGBS) infections and the factors associated with iGBS mortality in adults during 2013–2017: a retrospective study at Thailand’s largest national tertiary referral center
Published in Annals of Medicine, 2021
Pakpoom Phoompoung, Nantaporn Pirogard, Amornrut Leelaporn, Nasikarn Angkasekwinai
Demographic data, clinical manifestations, and outcomes were retrieved from medical records. Invasive GBS infection was defined as isolation of GBS from a normally sterile site, such as blood, cerebrospinal fluid, synovial fluid, vitreous fluid, or operative samples of pus or tissue obtained from a site of focal suppuration, accompanied by symptoms and signs of clinical disease. Patients with skin and soft tissue infection (SSTI), such as non-necrotizing bacterial cellulitis, necrotizing fasciitis, pyomyositis, and diabetic foot ulcers caused by GBS, were also included. Diagnosis of SSTI was based on the presence of local or systemic signs and symptoms of inflammation. Diagnosis of osteomyelitis was made when imaging showed characteristic features, including loss of bone cortex with bony erosion or demineralization, focal loss of trabecular pattern or marrow radiolucency, periosteal reaction or bone sclerosis, and/or presence of sinus tract formation and/or sequestrum [14]. Community-acquired infection was defined as GBS infections occurring within 48 h after hospital admission. Bacteraemia was defined as isolation of GBS from one or more blood cultures. Primary bacteraemia was defined as bacteraemia of unidentified origin with no associated clinical disease at other organs. Secondary bacteraemia was defined as bacteraemia accompanied by positive culture from other sites or associated clinical disease at other organs. Blood samples were processed using the BACTEC or BacT/Alert system (bioMérieux SA, Marcy l’Etoile, France). Positive blood samples were then further subcultured on blood agar. The presence of beta-hemolysis of bacterial colonies on blood agar heightened the suspicion of GBS. GBS was then identified by Gram staining showing Gram-positive cocci in the chain, with negative PYR, positive CAMP test, and negative bile-esculin test. Lancefield grouping (serogroup B) was used to confirm the diagnosis. Islam’s Medium, which is a selective GBS medium, was also used as described in the literature [15]. In patients from whom multiple or repeated specimens were obtained for culture, we included only one in our analysis.