1
|
Chen J, Wang L, Li W, Zheng X, Li X. Genomic Insights Into Cadmium Resistance of a Newly Isolated, Plasmid-Free Cellulomonas sp. Strain Y8. Front Microbiol 2022; 12:784575. [PMID: 35154027 PMCID: PMC8832061 DOI: 10.3389/fmicb.2021.784575] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2021] [Accepted: 12/17/2021] [Indexed: 11/13/2022] Open
Abstract
Our current knowledge on bacterial cadmium (Cd) resistance is mainly based on the functional exploration of specific Cd-resistance genes. In this study, we carried out a genomic study on Cd resistance of a newly isolated Cellulomonas strain with a MIC of 5 mM Cd. Full genome of the strain, with a genome size of 4.47 M bp and GC-content of 75.35%, was obtained through high-quality sequencing. Genome-wide annotations identified 54 heavy metal-related genes. Four potential Cd-resistance genes, namely zntAY8, copAY8, HMTY8, and czcDY8, were subjected to functional exploration. Quantitative PCR determination of in vivo expression showed that zntAY8, copAY8, and HMTY8 were strongly Cd-inducible. Expression of the three inducible genes against time and Cd concentrations were further quantified. It is found that zntAY8 responded more strongly to higher Cd concentrations, while expression of copAY8 and HMTY8 increased over time at lower Cd concentrations. Heterologous expression of the four genes in Cd-sensitive Escherichia coli led to different impacts on hosts’ Cd sorption, with an 87% reduction by zntAY8 and a 3.7-fold increase by HMTY8. In conclusion, a Cd-resistant Cellulomonas sp. strain was isolated, whose genome harbors a diverse panel of metal-resistance genes. Cd resistance in the strain is not controlled by a dedicated gene alone, but by several gene systems collectively whose roles are probably time- and dose-dependent. The plasmid-free, high-GC strain Y8 may provide a platform for exploring heavy metal genomics of the Cellulomonas genus.
Collapse
Affiliation(s)
- Jinghao Chen
- Hebei Key Laboratory of Soil Ecology, Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Shijiazhuang, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Likun Wang
- Hebei Key Laboratory of Soil Ecology, Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Shijiazhuang, China
| | - Wenjun Li
- Hebei Key Laboratory of Soil Ecology, Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Shijiazhuang, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Xin Zheng
- Hebei Key Laboratory of Soil Ecology, Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Shijiazhuang, China
| | - Xiaofang Li
- Hebei Key Laboratory of Soil Ecology, Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Shijiazhuang, China
- *Correspondence: Xiaofang Li,
| |
Collapse
|
2
|
Cohen S, Sweeney HM. Transduction of Methicillin Resistance in Staphylococcus aureus Dependent on an Unusual Specificity of the Recipient Strain. J Bacteriol 2010; 104:1158-67. [PMID: 16559089 PMCID: PMC248273 DOI: 10.1128/jb.104.3.1158-1167.1970] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Resistance to methicillin was transduced by phage 80 or 53 from two naturally occurring methicillin-resistant strains of Staphylococcus aureus to methicillin-susceptible recipient strains at frequencies of 10(-7) to 10(-9). Ultraviolet irradiation of transducing phage and posttransductional incubation at 30 C were essential for useful frequencies of transduction. Effectiveness as a recipient for this transduction was highly specific. Strain NCTC 8325 (PS47) in its native state was an ineffective recipient but became effective after it had received by transduction one of several penicillinase plasmids. This acquired effectiveness was retained in most cases after elimination of the plasmid by ethidium bromide treatment. Like the donor strain, the progeny were heterogeneous in the degree of their resistance to methicillin, which was expressed by a higher proportion of cells as the temperature of incubation was lowered from 37 to 30 C. Separate transductants varied widely in the degree of resistance acquired by transduction. Methicillin resistance was stable in the donor and transductant strains. We favored the interpretation that methicillin resistance in our strains was determined by a single chromosomal gene, although the possibility that it was determined by two or more closely linked genes could not be excluded.
Collapse
Affiliation(s)
- S Cohen
- Department of Microbiology, Michael Reese Hospital and Medical Center, Chicago, Illinois 60616
| | | |
Collapse
|
3
|
Udo EE, Grubb WB. New Staphylococcus aureus incompatibility group 1 plasmids encoding penicillinase production and resistance to different antibacterial agents. J Chemother 2001; 13:34-42. [PMID: 11233798 DOI: 10.1179/joc.2001.13.1.34] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022]
Abstract
Eleven Staphylococcus aureus plasmids encoding penicillinase production and resistance to different antibacterial agents were transferred to laboratory recipient strains in mixed-culture transfer and transduction experiments and characterized by restriction endonuclease analysis and incompatibility. The plasmids were differentiated into four types (types A-D) on the basis of their resistance phenotypes and restriction endonuclease patterns. One type encoded resistance to cadmium and arsenate. The second type encoded resistance to cadmium, mercuric compounds and nucleic acid-binding compounds. The third type encoded resistance to cadmium, kanamycin, neomycin and streptomycin while the fourth type encoded resistance to kanamycin, neomycin and ethidium bromide. Plasmids within the same class were structurally related or similar and were different from those in the other classes. Three plasmids, pWBG626, pWBG628, and pWBG663, representing three of the four plasmid types, belonged to incompatibility group 1. These new plasmids add to the number of known incompatibility group 1 plasmids and have resistance phenotypes which should be useful for studying incompatibility of new S. aureus plasmids.
Collapse
Affiliation(s)
- E E Udo
- Department of Microbiology, Faculty of Medicine, Kuwait University.
| | | |
Collapse
|
4
|
Yazdankhah SP, Sørum H, Oppegaard H. Comparison of genes involved in penicillin resistance in staphylococci of bovine origin. Microb Drug Resist 2000; 6:29-36. [PMID: 10868805 DOI: 10.1089/mdr.2000.6.29] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Ten penicillin-resistant and -susceptible staphylococci, isolated from bovine mastitis milk, were studied for the presence of genes that are, or may be, involved in resistance against penicillin. The repressor (blaI), antirepressor (blaR1), and structural (blaZ) genes of the beta-lactamase-operon were found to be closely linked in all penicillin-resistant strains. The beta-lactamase gene cluster was more commonly located on chromosomal rather than plasmid DNA in the strains studied. The transposase (p480) gene, which has been identified in the Staphylococcus aureus beta-lactamase transposon Tn552, was found in only one single penicillin-resistant S. aureus strain. The other penicillin-resistant S. aureus isolates contained IS1181 in close location with the beta-lactamase gene cluster. In only one S. haemolyticus isolate was the beta-lactamase gene cluster found in close association with IS257. Penicillin-resistant S. aureus strains, which were additionally resistant to tetracycline, contained IS257 in close association with the tetracycline resistance gene (tetK). Sequence analysis of blaI, blaR1, and blaZ in two penicillin-resistant S. aureus strains revealed 94-96% sequence homology with bla in staphylococci of human origin. The results indicate a predominance of class I bla transposons rather than Tn3 family class II transposons in the isolates used in this study.
Collapse
Affiliation(s)
- S P Yazdankhah
- Department of Pharmacology, Microbiology and Food Hygiene, Norwegian School of Veterinary Science, Oslo.
| | | | | |
Collapse
|
5
|
Maranan MC, Moreira B, Boyle-Vavra S, Daum RS. Antimicrobial resistance in staphylococci. Epidemiology, molecular mechanisms, and clinical relevance. Infect Dis Clin North Am 1997; 11:813-49. [PMID: 9421702 DOI: 10.1016/s0891-5520(05)70392-5] [Citation(s) in RCA: 108] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Staphylococcal infections continue to pose important clinical problems in children and adults. Antibiotic resistance among the staphylococci has rendered therapy of these infections a therapeutic challenge. Despite early, uniform susceptibility to penicillin, staphylococci acquired a gene elaborating beta-lactamase that rendered penicillin inactive and that is borne by nearly all clinical isolates. "Penicillinase-resistant beta-lactams," such as methicillin, were introduced in the early 1960s, but resistance to them has become an increasing concern. The mechanism of the so-called "methicillin resistance" is complex. Moreover, once confined to the ecology of hospitals and other institutions, a recent increase in community-acquired methicillin-resistant S. aureus infections has been observed. Glycopeptides, until now the only uniformly reliable therapeutic modality, have been increasingly used for therapy of staphylococcal infections. The recent recognition of clinical isolates with reduced susceptibility to glycopeptides is of concern.
Collapse
Affiliation(s)
- M C Maranan
- Department of Pediatrics, University of Chicago, Illinois, USA
| | | | | | | |
Collapse
|
6
|
Abstract
Staphylococci have developed a variety of strategies for dealing with the presence of antibiotics encountered in clinical environments. Resistance to beta-lactams and other antimicrobial agents has been accomplished by a diverse array of molecular mechanisms. Options available to treat infections caused by staphylococci resistant to methicillin are limited, and the next generation of antibiotics to be introduced, should glycopeptide resistance become an important clinical problem, is not yet on the horizon.
Collapse
Affiliation(s)
- B M Moreira
- Department of Pediatrics, University of Chicago, Illinois, USA
| | | |
Collapse
|
7
|
Hackbarth CJ, Chambers HF. blaI and blaR1 regulate beta-lactamase and PBP 2a production in methicillin-resistant Staphylococcus aureus. Antimicrob Agents Chemother 1993; 37:1144-9. [PMID: 8517704 PMCID: PMC187918 DOI: 10.1128/aac.37.5.1144] [Citation(s) in RCA: 124] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
For Staphylococcus aureus, it is hypothesized that two genes located upstream of the beta-lactamase gene, blaZ, are required for the inducible expression of beta-lactamase. blaR1 is predicted to encode a signal-transducing membrane protein, and blaI is predicted to encode a repressor protein. These same two genes may also regulate the production of penicillin-binding protein 2a (PBP 2a), a protein essential for expression of methicillin resistance. To confirm that these two genes encode products that can control both beta-lactamase and PBP 2a production, blaI, blaR1, and blaZ with a 150-nucleotide deletion at the 3' end were subcloned from a 30-kb staphylococcal beta-lactamase plasmid and three beta-lactamase-negative strains of methicillin-resistant S. aureus were transformed with the recombinant plasmid containing that insert. The production of PBP 2a and a nonfunctional beta-lactamase was detected by fluorography and by immunoblots with polyclonal antisera directed against each of the proteins. Whereas the parent strains did not produce beta-lactamase and constitutively produced PBP 2a, PBP 2a and a truncated beta-lactamase were now inducible in the transformants. Therefore, two plasmid-derived genes regulate the production of both PBP 2a and beta-lactamase.
Collapse
|
8
|
Wang PZ, Projan SJ, Novick RP. Nucleotide sequence of beta-lactamase regulatory genes from staphylococcal plasmid pI258. Nucleic Acids Res 1991; 19:4000. [PMID: 1861992 PMCID: PMC328499 DOI: 10.1093/nar/19.14.4000] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Affiliation(s)
- P Z Wang
- Department of Plasmid Biology, Public Health Research Institute, City of New York, Inc., NY 10016
| | | | | |
Collapse
|
9
|
al-Masaudi SB, Day MJ, Russell AD. Antimicrobial resistance and gene transfer in Staphylococcus aureus. THE JOURNAL OF APPLIED BACTERIOLOGY 1991; 70:279-90. [PMID: 2055789 DOI: 10.1111/j.1365-2672.1991.tb02937.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- S B al-Masaudi
- School of Pure and Applied Biology, University of Wales College of Cardiff, UK
| | | | | |
Collapse
|
10
|
|
11
|
Minato K, Abiko Y. Beta-lactam antibiotics resistant Rothia dentocariosa from infected postoperative maxillary cyst: studies on R-plasmid and beta-lactamase. GENERAL PHARMACOLOGY 1984; 15:287-92. [PMID: 6333373 DOI: 10.1016/0306-3623(84)90003-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
A cephalexin and penicillin G resistant strain of Rothia dentocariosa was clinically isolated from pus of infected postoperative maxillary cyst. The strain contained multiple plasmids. Plasmid curing tests with rifampicin eliminated cephalexin and penicillin G resistant phenotypic functions and 47 megadalton plasmids from the strain. Beta-Lactamase isolated from the strain hydrolyzed cephalosporin more efficiently than penicillin.
Collapse
|
12
|
|
13
|
Lacey RW. Antibiotic resistance plasmids of Staphylococcus aureus and their clinical importance. BACTERIOLOGICAL REVIEWS 1975; 39:1-32. [PMID: 1091256 PMCID: PMC413879 DOI: 10.1128/br.39.1.1-32.1975] [Citation(s) in RCA: 87] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
|
14
|
Stiffler PW, Sweeney HM, Cohen S. Co-transduction of plasmids mediating resistance to tetracycline and chloramphenicol in Staphylococcus aureus. J Bacteriol 1974; 120:934-4. [PMID: 4455688 PMCID: PMC245860 DOI: 10.1128/jb.120.2.934-944.1974] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Independent plasmids mediating resistance either to tetracycline (Tc) or chloramphenicol (Cm) were transduced successively into Staphylococcus aureus strain 8325. From this doubly resistant donor strain, Tc was co-transduced with a frequency of 40 to 50% when Cm was selected. Co-transduction of Cm was 5 to 10% with Tc selection. Plasmid elimination was infrequent and restricted to the Cm plasmid. A variant, doubly resistant strain gave 100% co-transduction of Tc and Cm and a high rate of joint elimination of both plasmid markers. Co-transduction of the plasmids from recombination-deficient donor strains was much reduced if the plasmids had been introduced separately into the donor strain, but occurred at the normal high rate if they had been introduced jointly. The plasmids were co-transformed at relatively low rates with closed circular deoxyribonucleic acid (DNA) from doubly resistant donors, but not with DNA from a mixed lysate of singly resistant strains. Our evidence favored a hypothesis of recombination-dependent, reversible linkage between the two plasmids as the basis for their co-transduction. Examination of plasmid DNA from the doubly resistant strains by ultracentrifugal and electron microscopic methods did not disclose any physical differences between singly and doubly resistant strains that might account for the observed co-transduction.
Collapse
|
15
|
Shraer DP, Blagoveshchenskii VA. Elimination of the penicillinase inducibility gene of Staphylococcus aureus by acridine orange. Bull Exp Biol Med 1974; 77:570-2. [PMID: 4441690 DOI: 10.1007/bf00797426] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
|
16
|
Lacey RW. Genetic basis, epidemiology, and future significance of antibiotic resistance in Staphylococcus aureus: a review. J Clin Pathol 1973; 26:899-913. [PMID: 4593862 PMCID: PMC477927 DOI: 10.1136/jcp.26.12.899] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
|
17
|
Novick RP, Bouanchaud D. The problems of drug-resistant pathogenic bacteria. Extrachromosomal nature of drug resistance in Staphylococcus aureus. Ann N Y Acad Sci 1971; 182:279-94. [PMID: 5285292 DOI: 10.1111/j.1749-6632.1971.tb30664.x] [Citation(s) in RCA: 179] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
|
18
|
Shaw WV. Biochemical mechanisms of transferable drug resistance. ADVANCES IN PHARMACOLOGY AND CHEMOTHERAPY 1971; 9:131-72. [PMID: 4949129 DOI: 10.1016/s1054-3589(08)60446-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
|
19
|
Dulaney EL. Activity of selected compounds against penicillinase producing Staphylococcus aureus. TRANSACTIONS OF THE NEW YORK ACADEMY OF SCIENCES 1970; 32:843-57. [PMID: 5279955 DOI: 10.1111/j.2164-0947.1970.tb02760.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
|
20
|
Vernon EG, Sweeney HM, Cohen S. Evidence for genetic interaction between plasmid and chromosomal penicillinase linkage groups in Staphylococcus aureus. J Bacteriol 1970; 103:826-9. [PMID: 5474889 PMCID: PMC248163 DOI: 10.1128/jb.103.3.826-829.1970] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Spontaneous reciprocal recombination was detected between the regulator genes of penicillinase plasmids and chromosomal penicillinase linkage groups of Staphylococcus aureus. The frequency of recombination varied with different penicillinase linkage groups.
Collapse
|
21
|
Cohen S, Vernon EG, Sweeney HM. Differential depression of staphylococcal plasmid and chromosomal penicillinase genes by a class of unlinked chromosomal mutations (R2-). J Bacteriol 1970; 103:616-21. [PMID: 5474880 PMCID: PMC248135 DOI: 10.1128/jb.103.3.616-621.1970] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
We described previously a class of mutations (phenotypic designation R2(-)) in Staphylococcus aureus that were unlinked to penicillinase genes but nevertheless imposed constitutive synthesis of this enzyme upon wild-type plasmids. The plasmids affected by these mutations have been found to possess the same maintenance-compatibility type (I) and to form penicillinase of serotype A. Three plasmids that had a different maintenance-compatibility type (II) and formed penicillinase of serotype C were only slightly derepressed in R2(-) mutants. Three chromosomal penicillinase genes were variably derepressed, the range extending from negligible to nearly complete derepression. The differences in degree of derepression among the three types of penicillinase linkage groups were tentatively ascribed to position effects.
Collapse
|
22
|
Asheshov EH, Woods JM, Dyke KG. Penicillinase synthesis in Staphylococcus aureus: the effect of inducer and of the cellular location of the genetic determinants on the amount of enzyme formed. Genet Res (Camb) 1970; 16:95-9. [PMID: 5488988 DOI: 10.1017/s0016672300002305] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
SUMMARYA comparison was made of the amount of penicillinase produced by strains ofStaphylococcus aureuscarrying chromosomal penicillinase genes, plasmid penicillinase genes and strains carrying both chromosomal and plasmid genes. Plasmid genes were found to produce at least twice as much enzyme as homologous chromosomal genes. The results suggest that there are, on average, two plasmids per chromosome in exponentially growing cells.Two inducers were used in these experiments—methicillin and 2-(2′-carboxyphenyl)-benzoyl-6-aminopenicillanicacid (CBAP). The latter proved a more efficient inducer than methicillin and this difference was most apparent when more than onei+gene was present, which suggests that the efficiency of induction reflects the ability of the inducer to react with represser.
Collapse
|
23
|
Peyru G, Wexler LF, Novick RP. Naturally occurring penicillinase plasmids in Staphylococcus aureus. J Bacteriol 1969; 98:215-21. [PMID: 5781577 PMCID: PMC249925 DOI: 10.1128/jb.98.1.215-221.1969] [Citation(s) in RCA: 66] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
A series of plasmids harbored by naturally occurring penicillin-resistant strains of Staphylococcus aureus were surveyed with a view toward exploring the variability in plasmid-linked marker patterns. Plasmids were transduced from their natural hosts to either of two plasmid-negative laboratory strains by selection for cadmium resistance, and the transductants were tested for all other markers previously found to be plasmid-linked. All of the strains that were able to serve as genetic donors to one of the two stock strains could donate cadmium and lead resistance as linked, plasmid-borne markers. Among the other plasmid markers, a wide variety of patterns was found, including four plasmids that did not carry the penicillinase determinant. Each of the 26 plasmids studied, including the latter 4, was found to belong to one of the two incompatibility sets of penicillinase plasmids previously identified. With the exception of the penicillinase-negative plasmids, which were found in both sets, all the plasmids of incompatibility set I directed the production of penicillinase type A; those belonging to set II directed either type A or type C. Those of set II without exception increased the sensitivity of their host strains to bismuth ion; those of set I carried determinants of bismuth resistance or did not affect the sensitivity of their host to this ion. No other perfect correlations between markers were encountered; in particular, there was no correlation between penicillinase serotype and the excretion of the enzyme. This finding allows the prediction that there is, in addition to all of the markers thus far identified, a plasmid-linked determinant of penicillinase excretion.
Collapse
|